Members of Space Studies Board (SSB) committees of the National Academies of Sciences, Engineering, and Medicine may be invited to testify before committees of the U.S. House of Representatives or the U.S. Senate about the findings and recommendations of their reports. During 2017, four hearings were held where members of the SSB family testified to Congress.
THE INTERNATIONAL SPACE STATION AFTER 2024: OPTIONS AND IMPACTS
On March 22, 2017, the U.S. House of Representatives Subcommittee on Space (Committee on Science, Space and Technology) held a hearing titled “The International Space Station after 2024: Options and Impacts.” Robert J. Ferl, co-chair of the Committee on Biological and Physical Sciences in Space (CBPSS), provided testimony on behalf of the National Academies’ Division on Engineering and Physical Sciences, the Aeronautics and Space Engineering Board, and the SSB. More information and the full testimony is available at https://science.house.gov/legislation/hearings/space-subcommittee-hearing-iss-after-2024-options-and-impacts and is reprinted, unedited, below.
Mr. Chairman, Ranking Member, and Members of the Subcommittee:
Good morning. Thank you for the opportunity to submit testimony and participate in the discussion surrounding the options for and impacts of microgravity space science after 2024. This is a very important subject and the discussion is timely, due to the rapid evolution and diversification of spaceflight capabilities available to our nation, as well as the functional maturation of the International Space Station.
I speak to you today as a scientist with more than 25 years of spaceflight related research, largely funded by grants from NASA and having made use of many spaceflight and spaceflight-related platforms. My research is dedicated to the intertwined goals of 1) understanding the impacts spaceflight has upon terrestrial life to better develop safer deep space capabilities for human exploration, and 2) expanding what we know about the limits of terrestrial biology as we consider both human expansion in the solar system and by extension our place in the universe.
My comments today are informed not only by the research I have carried out but also by consultative roles I have played associated with NASA program development for many years. I was a member of a writing committee for National Research Council1 decadal survey recommendations contained in “Recapturing a Future for Space Exploration: Life and Physical Sciences Research for a New Era,” published by the National Academies in 20112 (referred to hereafter as the Decadal or Decadal Survey). This Decadal Survey lays out a comprehensive portfolio of life and physical sciences research that is enabled by spaceflight and that enables further spaceflight exploration. I am currently the Co-Chair (with
1 Now more commonly referred to as The National Academies of Sciences, Engineering and Medicine.
Dr. Elizabeth Cantwell of Arizona State University) of the National Academies’ Standing Committee on Biological and Physical Sciences in Space (CBPSS). In addition, I am Co-Chair (with Mr. Daniel Dumbacher of Purdue University and formerly of NASA) the National Academies’ Committee on A Midterm Assessment of Implementation of the Decadal Survey on Life and Physical Sciences Research at NASA,3 which will be completed by the end of 2017. I am a recent past President of the American Society for Gravitational and Space Research (ASGSR), the society of research scientists most closely aligned with the science portfolio under discussion today.
It should be noted that I speak to you today in my capacity as an academic scientist. While my comments are informed by and deeply influenced by my experience and association with the committees of the National Academies and by my association with the ASGSR, I speak solely from my personal perspective—and I should add that nothing I say today should be construed as previewing any findings of the Academies midterm assessment study.
My comments are guided by overarching questions which are stated here then expanded in the narrative to follow. The answers to these questions emphasize space life and physical sciences as they enable exploration, as moving into deep space is a major part of the discussion at this hearing. Yet the microgravity research that benefits Earth is an equally important part of this area of science.
- What is the status of space life and physical sciences research and how is this status affected by NASA deep space exploration goals and timetables?
- Is the ISS uniquely required for space life and physical sciences research?
- How would privatized low earth orbit systems influence space life and physicalscience?
- What are the opportunities and challenges that Congress should consider as it decides whether or not to extend ISS beyond 2024?
I will be sharing a positive view regarding the current status and activities on the ISS, a view richly informed by very recent experiments conducted on the ISS. These experiments draw directly upon the ISS as a critical, unique and extraordinarily capable research platform. These experiments also emanate from NASA programs that have been designed to further the science of the Decadal Survey. My comments are also informed by past experiments on the ISS and Space Shuttle, as well as experiments on spaceflight analog platforms, and ground-based experiments in extreme terrestrial environments as planetary exploration analogs. Most of my direct experience and expertise is in the life sciences.
However the operations and practical discussions, as well as the community status, are applicable to the physical sciences. The challenges that need to be met to move us towards deep space exploration are complex and multidisciplinary. The integration of life and physical sciences in ISS research is part of what my community believes will be necessary to solve the issues of deep space exploration.
- What is the status of critical ISS research in space life and physical sciences that is needed to enable deep space exploration and produce fundamental research that is enabled by microgravity? Can sufficient progress be expected to be made by 2024 on the enabling research, or is additional time on the ISS needed? What will be required to complete the enabling research by2024?
For the purposes of today’s discussion, I offer the following observations. The Space Life and Physical Sciences Research and Applications Division (SLPSRA) within NASA was formed only six years ago, in 2011, in alignment with Decadal Survey. It should be noted that space life and physical sciences has always been a program within NASA, though over the years it has been its own enterprise directorate or in the science directorate, and is now a division within the Human Exploration and Mission Operations Directorate. SLPSRA initially sought to revive and invigorate NASA’s microgravity space life and physical sciences portfolio and reestablish the community of science needed to conduct these areas of research described in the Decadal Survey. It has been very successful in this regard. There again exists a vibrant science community that is engaged in SLPSRA research projects and programs, and is ready for more growth. SLPSRA is closely associated with the Human Research Program and SLPSRA integrates science activities across many disciplines in support of microgravity research, making progress in a wide range of science that supports NASA’s needs while creating STEM excitement and recruiting new scientists. The ISS maturation as a laboratory has moved beyond facility management to include a strong effort to track its science impacts. A simple perusal of the ISS science website,4 for example, reveals a regular outpouring of science happenings in space, and results and scientific publications are noted and measured as major output metrics, similar to the metrics used by other national research agencies. SLPSRA has also engaged with the National Academies to monitor progress of Decadal recommended science. SLPSRA has activated its programs, fueled the community and is now producing major science discoveries,
all in what is essentially a few short years. It is my personal assessment that the status of the overall Decadal portfolio is in a healthy state of growth and accomplishment, and becoming more so as the access to ISS increases.
Space life and physical sciences contribute effectively to NASA research and technology needs. While the time between now and 2024 will see tremendous progress in science in support of exploration, NASA’s need for exploration-related science will neither cease nor be fully met. NASA works to enhance and enable exploration by undertaking research to improve our understanding of and reduce the risk associated with putting humans in extreme extraterrestrial environments. Meeting this challenge is not a simple matter of identifying risks and establishing tolerance thresholds for future astronauts. It is a matter of continual evaluation and discovery of principles that enhance the overall exploration endeavor. The resulting portfolio of science activity is built upon the dual notions of research enabling space exploration and research that is enabled by space exploration—in a manner that actually breaks down the traditional notions of fundamental research versus applied research. Exploration life and physical sciences research is a body of work that is a continuum, and critical advances can and do arise from across the entire continuum. Exploration research recognizes there is seldom a direct connection between experiment intent and practical outcome. The future development of the most important exploration-related research therefore transcends the ISS question, and the need for the kinds of research supported by SLPSRA will continue throughout the evolution of spaceflight exploration, well beyond LEO and ISS.
As space exploration and utilization expands, research ahead of that exploration will be needed. As in all major technology endeavors, such as terrestrial transportation and aviation, continual research improves safety and enhances efficiency. One particularly relevant spaceflight example involves our increasing understanding of radiation effects on biology. Although we have accumulated data on the effects of radiation on biological tissues for more than 70 years, only in the past 15 have we had the ability to explore how this information translates to the spaceflight environment, and even more recently have we been able to observe the effects on the cardiovascular system and brain, and how these systems might be affected by more chronic exposure. In this and in many other areas we will continue to learn how spaceflight effects create unanticipated interactions between risks, and develop more effective solutions that mitigate those risks.
- Is the ISS uniquely required for space life and physical sciences research or could other space-based platforms be suitable for carrying out such research? What other types of platforms could be used?
The short answer to whether the ISS is uniquely required for space life and physical sciences research, is yes. The ISS is currently the only space-based platform that provides extended access to the spaceflight environment, and as such, provides the only means to assess the long-term effects of this environment on terrestrial organisms, on physical systems, and on how physics and engineering principles can be utilized to mitigate the long term effects of spaceflight on biological organisms, structures and physical processes. To reiterate, the key word phrases are extended access and long-term. Extended and long- term data are crucial to inform more fully the preparations for and the future execution of successful deep space exploration activities such as crewed transit missions to the moon or Mars, as well as for private-sector endeavors such as asteroid mining, and any missions that would involve crewed vehicles and stations.
While other platforms, such as suborbital vehicles and sortie missions in orbital vehicles, can fulfill important research niches (such as the evaluation of biological and physical responses to the initial transition from unit gravity to microgravity) none, at present, can maintain the sustained spaceflight environment over long periods of time such as is required to fully support an exploration initiative. It is, however, possible that these other platforms could be employed to lower the pressure on ISS resources. These possibilities and their challenges are discussed below.
It is also important to note that the ISS is now a fully functioning laboratory. It has a well-trained crew that appreciates science. It has well equipped science bays. NASA has processes and procedures for getting samples up, sample processing on orbit, and bringing samples down. It has increasingly sophisticated onboard analytic capabilities, such as the recently demonstrated DNA sequencing. The ISS is equipped with many unique science facilities, launched at great expense but providing considerable payback. Keeping them on orbit lets those facilities serve multiple investigations over many years. But relaunching those facilities for sortie flights or to other platforms would reiterate the costs. So while it is possible to argue that other platforms may provide microgravity research capabilities, the costs would need to be compared to the current model of simply launching samples to existing facilities that are maintained on orbit on the ISS.
The current model relies heavily on international partnerships and the US commercial launch sector for access to and from the ISS. Some of these partnerships are only a few years old and have not had the time to be a well measured part of the discussion. Yet it is likely these partnerships need to continue, and perhaps be enhanced in order for research science to fully exploit the capabilities of the ISS.
Moreover, successful science in space is more than just a well-appointed platform. A trained and trainable crew is required. A steady cadence of launch opportunities that keeps pace with science advancement is critical, a cadence that enables and supports the cycle wherein hypotheses are tested and answered, leading to new insights and the next cycle of question and answer. In addition, strong, regular, grant program management at the agency level is necessary to keep the science community vibrant and engaged. Currently the ISS, with some notable exceptions listed below, together with SLPSRA, does this. Any transition to other platforms would have to keep these points in clear focus.
- What would be the impact on research if NASA were to turn low Earth orbit over to the private sector?
The potential transition of LEO to the private sector is a compelling notion. However the notion is complex and nuanced when considering the spectrum of microgravity science under discussion. Without careful consideration of this notion, we risk assurance that the nation’s exploration goals could be met.
Could a private space laboratory serve the needs of space life and physical sciences? Fundamentally, yes. Essentially it does not matter to the science community who the operator of the laboratory is, whether private or government. What matters on the practical level is the cost and reliability of research access. Government laboratory facilities are dedicated to providing access at reasonable costs to all research. Private sector laboratory facilities seek a more immediate return on investment, which affects costs and priority of access. What matters on a strategic level is continued stewardship of the space life and physical sciences portfolio by the United States in general and by NASA in particular. Similar to the Decadal Studies that guide the science in the Science Mission Directorate of NASA, the “Recapturing a Future for Space Exploration“ Decadal Survey guides SLPSRA as the primary steward of space life and physical sciences. Our exploration of space will constantly pull innovation from this area of science and NASA stewardship of space life and physical sciences must, I believe, be maintained. The goals of the private sector are driven by fundamentally different outcomes than those which service the exploration needs of NASA. In order for a private or commercial LEO operation to serve the microgravity life and physical sciences, agreements would have to be in place that ensure that NASA’s needs receive the priority and access necessary to ensure science success. This is especially true for “long-range studies of the potential benefits to be gained from, the Opportunities for, and the problems involved in the utilization of aeronautical and space activities for peaceful and scientific purposes.”5 Transition to a private-sector, commercial platform provider would therefore require care and attention to assure that the space life and physical sciences research necessary to meet NASA exploration initiatives remain as clear priorities.
Could private research supplant NASA stewardship of the portfolio of science covered by the Decadal? Not likely. While the goals of the private sector may overlap with exploration science on occasion, the time-scales and risks of research are not typically embraced by the private sector. It is likely that there would be a tendency toward prioritizing profit-directed investigations, as is entirely appropriate for the shareholders of a company, but which would be inconsistent with the needs of NASA. Similarly, it seems unlikely that expansion of the northwestern United States enabled by the Lewis and Clark expedition would have been so remarkably successful without government sponsorship.
Is commercial research a part of the research portfolio covered by the Decadal Survey on space life and physical sciences? Yes, most likely. In point of fact, that type of collaboration is already occurring today. The research enterprise consists of science carried out by industry researchers, federal researchers, and academic researchers. Any of these scientists that comprise the community as a whole may conduct science in support of NASA goals. And certainly we have seen an increase in the research scientists of private companies doing microgravity research, suggesting that scientist participation across the range of government and private activities can contribute to and compete to provide research in support of SLPSRA and NASA’s exploration research goals.
Therefore a shift to private-sector platform providers as part of an increasingly privatized LEO ecosystem could be part of a successful microgravity sciences program. However, I am convinced NASA will need to maintain stewardship of space life and physical sciences, in order to ensure that our national scientific enterprise continues to meet NASA needs, priorities and timeframes - regardless of the academic, industrial or governmental location of the scientists conducting the work.
- What, in your view, are the opportunities and challenges for the future of space life and physical sciences, and what issues should Congress consider regarding those opportunities and challenge as it decides whether or not to extend ISS beyond 2024?
The strategic science challenges and opportunities for the space life and physical sciences largely remain as articulated in the Decadal Survey. While tremendous progress has been made in some areas over these last six years, there is plenty of work that remains undone, particularly in the physical sciences and larger-scale biological systems such as mammalian studies. Generally stated, the biological and physical systems work on the ISS is just reaching an acceptable rate of progress. The physics and chemistry of the manufacturing revolution that is underway are just beginning to be explored for adaptation to space.
The integration of biological and physical systems that feed forward to exploration scenarios is in its infancy. The high fidelity evaluations of the molecular, genetic, and epigenetic responses of biological organisms and systems to long-term spaceflight (primarily humans, human pathogens, and plants) is just now close to fully underway.
5 National Aeronautics and Space Act of 1958, Pub. L. No. 85-568, 72 Stat. 426-438 (Jul. 29, 1958).
The primary questions regarding the movement toward those strategic science goals can, in my opinion, be reduced to several essential tactical and operational issues. Any serious projections of science accomplishments and science remaining by 2024 must come to grips with these issues.
The first issue is crew time. At present, crew time available to science is often cited as the single biggest limitation to the conduct of science on the ISS. This is the one area where the ISS itself has yet to reach its envisioned science potential. All too often, space life and physical science waits near the bottom of a queue for crew time. Some experiments that are highly important to the pursuit of Decadal- recommended science need crew time beyond what the SLPSRA program is allotted. The result is that some funded science can be situated such that it never makes it out of the queue, and may be dropped altogether. So, I believe the first issue that Congress may wish to consider is the mechanisms for getting more crew on the ISS. The importance of this cannot be overstated – in my opinion the amount of crew time available for space life and physical science is the single biggest factor in evaluating the possibility of accomplishing the science needed before heading to deep space.
A closely related issue is competing program priorities in the allocation of ISS resources. Additional crew on the ISS would create the potential for more space life and physical sciences, but only if science priorities are kept in balance with other programs. The establishment of the ISS National Laboratory effectively brings non-NASA science to the ISS, which greatly increases the reach of microgravity science toward Earth-directed goals and extends the value of the ISS investments. Yet the National Lab, too, draws upon the limited ISS resources. It is my personal view that Congress should examine the prioritization of resources across the spectrum of ISS users when considering the prospects of getting enough science accomplished out of the space life and physical sciences to effectively reach for deep space by 2024.
The “Recapturing a Future for Space Exploration” Decadal Survey provides a comprehensive set of research priorities for the space life and physical sciences. While an entire chapter (Chapter 11) is dedicated to the capabilities of the ISS, it should be noted that the Decadal recognizes that ground- based experiments are necessary in some areas. In addition, some microgravity and spaceflight related studies are well suited for platforms other than the ISS. A robust consideration of ground studies and all available microgravity platforms would ensure that the entire portfolio moves forward, targeting to ISS those experiments that actually require its unique capabilities. Congress should examine and be mindful of the full range of platforms, analogs and ground based facilities currently and potentially available to Decadal research and should seek to enhance access to those platforms and facilities especially when such access meets the dual goals of supporting exploration research while relieving throughput stress on the ISS itself.
Lastly I also believe that Congress may wish to consider all current limitations on travel of materials and crew to and from the ISS. While additional crew members would greatly accelerate the progress of the Decadal science portfolio, other factors affects science as well. Greater access to up-mass and down- mass, especially in environmentally conditioned compartments, would clearly accelerate science.
Repeatability, quicker access to space, accessible laboratory equipment that parallels ground laboratory equipment, the ability to get samples back to Earth and to the research team, all improve science on the ISS and increase our readiness for deep space science and exploration.
Dealing with each of these tactical issues, together with providing a level of strategic funding for the space life and physical sciences, has the potential to demonstrate a possibly dramatic impact on any evaluation of the amount of science to be accomplished on the ISS by 2024.
Summary and conclusions:
We are approaching a very appropriate time to consider space life and physical sciences within the context of the operational life of the International Space Station. The increasing success of ISS research is now well documented and available for evaluation, while the SLPSRA Division has years of productivity to be measured and evaluated. Over the course of this calendar year the National Academies will conduct and release its Mid Term Assessment of the Decadal Survey. This Assessment should provide deep insights that inform the questions raised in this testimony.
From a personal perspective I believe that there are key unknowns that potentially have a dramatic impact on these considerations:
- The trajectory of crew time available for research on the ISS could significantly influence any evaluation of science attainable by 2024.
- The development of commercial spaceflight outside of NASA sponsorship remains an intangible but important factor in considering the pace of microgravity science in support of deep space exploration.
And the largest unknown is the unknowable discovery that will inevitably occur as this body of space life and physical science progresses. The unique qualities of spaceflight must be deeply understood and continually explored across the spectrum of space life and physical science to extract the innovation required to best enable and enhance deep space exploration, and to return benefits to the Earth.
ADVANCES IN THE SEARCH FOR LIFE
On April 26, 2017, the U.S. House of Representatives Committee on Science, Space and Technology held a hearing titled “Advances in the Search for Life.” Dr. James Kasting, chair of the planning committee for the Workshop on the Search for Life Across Space and Time, provided testimony on behalf of the National Academies’ Division on Engineering and Physical Sciences, and the SSB. More information and the full testimony is available at https://science.house.gov/legislation/hearings/full-committee-hearing-advances-search-life and reprinted, unedited, below.
Chairman Smith, Ranking Member Johnson, and Members of the House Committee on Science, Space, and Technology, thank you for allowing me to testify at this important committee hearing. I was selected for this spot because I chaired the planning committee for a recent National Academies’workshop entitled “Searching for Life Across Space and Time” held on Dec. 5-6, 2016, in Irvine, CA. Henceforth, I will refer to this as the ‘Biosignatures Workshop’. As you will recognize, an Academies’ workshop is a venue for discussion and debate—an essential effort in allowing the scientific process to unfold. Published proceedings chronicle the presentations and discussions that take place at these types of Academies’ activities, and the proceedings from the December event will be published later this Spring. My testimony today will attempt to summarize my personal perspective on key points made by various participants at that workshop. However, I will update this story with four important discoveries, three of which were announced after the workshop was held. And I will attempt to show how the present search for life relates to the ongoing search for intelligent life, which was not discussed at the workshop. I should emphasize that I am speaking in my personal capacity as an active researcher and am not speaking on behalf of the National Academies of Sciences, Engineering, and Medicine.
Relation of the search for life to SETI
Interest in the search for life off the Earth has been growing continuously over the last four decades. Many of us are ultimately motivated by the Search for Extraterrestrial Intelligence (SETI), which has been going on for that amount of time, or longer. We would like to know whether there is someone else to talk to out there in the galaxy, or in the larger Universe. The late Carl Sagan helped pioneer this search and inspired millions of people worldwide, including me, to share his aspirations.
In a logical world, however, SETI would have been preceded by a search for less complex forms of life. If life does originate in places other than Earth, then simple life forms are probably more abundant than complex or intelligent life forms, according to the Drake equation that Carl Sagan helped formulate (along with Frank Drake). We started looking for intelligent life first because the technology for building radio telescopes matured well before that needed to look for life itself. Looking for simple life is difficult. Within the solar system, we can do this most effectively by sending spacecraft to other planets and observing them either from orbit or from landers/rovers, like the Curiosity rover that is exploring Mars right now. Outside of the solar system, astronomers have identified numerous exoplanets from the ground using the radial velocity, or Doppler, method. More recently our knowledge of exoplanets has exploded as a result of NASA’s successful Kepler Space Telescope mission. Kepler found planets by detecting their transits in front of their parent stars. Thanks to Kepler, we now know the addresses of thousands of exoplanets, and we also know that most stars are accompanied by two or more planets. But we know virtually nothing about whether any of these planets are habitable or inhabited. Figuring this out is our biggest goal for the future.
Subdividing the search for life
At the recent Biosignatures Workshop, we divided the search for extraterrestrial life into four quadrants, as shown in Fig. 1. The two vertical columns represent in-situ life detection (which we can do in the solar system) and remote life detection (which is all that we can hope to do for exoplanets, given present technology). The two horizontal rows represent life ‘as we know it’ and life ‘as we don’t know it’. We don’t really know how different alien life would be from us, and this affects where we think to look for it, as well as the techniques we might use to identify it.
In situ detection of life as we know it
Life as we know it here on Earth shares many common characteristics. At its most basic level: 1) Life is carbon-based, 2) it requires the presence of liquid water at least some of the time, and 3) it utilizes the molecules DNA and RNA to store and transfer genetic information. Mars is one planet within the solar system where we might search for
this type of life. Indeed, various researchers have proposed that life could have been transferred from Mars to Earth, or vice versa, by meteorites. So, it might not actually be surprising to find DNA-based life on Mars. One workshop participant, Gary Ruvkin from Harvard Medical School, suggested sending a modern, mobile DNA sequencer to Mars. Such machines can detect and analyze extraordinarily small samples of DNA, and would likely be able to find Earth-like life if it was there. But if martian organisms don’t rely on DNA, then such a search would be fruitless even if Mars was teeming with life.
Big strides in Mars’ exploration have been taken over the last few years by the Mars Exploration Rovers, which began their mission in 2003, and by the Curiosity rover, which has operated since 2014. John Grotzinger from Caltech, who has been involved in both missions, gave an overview of Curiosity results, highlighting the evidence for long-lived lakes. Jennifer Eigenbrode from NASA’s Goddard Space Flight Center talked about detection of organic compounds. Organic compounds have indeed been found, but that is to be expected because of continual meteorite bombardment. Bottom line: Curiosity has found additional evidence of habitability—i.e., an environment with conditions appropriate to the support of life at some time in the past—but nothing that would definitely indicate present or past life. Curiosity has also reported seeing methane, in agreement with ground-based observations, but that finding remains controversial. (Some researchers have argued that Curiosity brought the methane with it from Florida.) The ESA-Russian ExoMars Trace Gas Orbiter mission, which is at Mars now and will achieve its science orbit early next year, will hopefully answer this question.
Mars exploration is proceeding at a good rate, with missions launched at nearly every 2- year opportunity. The big debate is whether to concentrate on additional orbiters and rovers, sample return, or human exploration. I will not attempt to weigh in on this question. This will be one of the issues discussed by the 2022 planetary science decadal survey, organized by the National Academies of Sciences, Engineering, and Medicine.
Jupiter’s moon, Europa, and Saturn’s moon, Enceladus, both harbor subsurface oceans and could also conceivably be home to life as we know it. But they differ from Mars in the sense that transfer of life between the outer solar system and Earth is considered unlikely. So, if we were to find life on one of these moons, it would likely indicate that life
originated more than once—a point made by JPL’s Kevin Hand at the workshop. This in itself would be a discovery of enormous importance, as we still do not know whether the origin of life is a chance event, or whether it happens whenever the circumstances are right. Possible life forms on these moons could still be carbon-based and require liquid water, but whether they would utilize DNA and RNA is an open question that biologists would love to answer.
Update #1: The most exciting news in this field is the recent announcement (made well after the workshop) that molecular hydrogen, H2, has been identified in the plume emanating from Enceladus’ south polar region (J.H. Waite et al., Science, 2017). The Cassini spacecraft has flown through the plume multiple times and had previously identified CH4 (methane) and CO2 (carbon dioxide), in addition to the major constituent H2O. Finding H2, and measuring its concentration relative to H2O, allowed researchers to estimate the thermodynamic free energy available from the reaction: CO2 + 4 H2 → CH4 + 2 H2O. This is one of the reactions used by methanogenic bacteria here on Earth to power their metabolism. The Cassini researchers calculated that the available free energy in Enceladus’ subsurface ocean was an enormous 80±20 kJ/mole. To put this in perspective, methanogens on Earth can typically draw H2 down until they are only getting about 10-15 kJ/mole. Synthesizing ATP (adenosine tri-phosphate) from ADP (adenosine di-phosphate) requires 35.6 kJ/mole. ATP is the standard unit of energy ‘currency’ for terrestrial organisms. If the new analysis is correct, there is plenty of free energy available to sustain life in Enceladus’ ocean. But we are left to ponder why, if methanogens are there, have they not drawn H2 down to lower concentrations, as they do here on Earth. Could it perhaps be because they are limited by other factors, e.g., nutrient supply? Given the uncertainties, it would clearly be wrong to conclude at this time that Enceladus is inhabited. But there is lots of incentive to study this object further.
Progress in learning about ocean worlds has been greatly accelerated by the approval of funds for NASA’s Europa Clipper mission. Clipper will make multiple passes by Europa and may be able to sample plumes that have been reported based on observations from the Hubble Space Telescope. Clipper should also be able to determine the thickness of Europa’s icy crust and take spectra of the brownish material that is thought to ooze up through the cracks. A Europa lander mission, which has been extensively studied but not yet been approved, could take this search even further. It is considered to be technically difficult, though, because of the intense charged particle radiation environment on and around Europa.
In situ detection of life as we don’t know it
Some biologists (and chemists) who like to think ‘out of the box’ have suggested that life may be a more general phenomenon than what we encounter here on Earth. A formal report issued by the National Academies in 2007, entitled The Limits of Organic Life in Planetary Systems, examined this hypothesis in some detail. Informally, this document is sometimes referred to as the ‘Weird Life’ report. NASA and NSF co-organized a recent ‘Ideas Lab’ to follow up on this report. Life on Saturn’s moon Titan, if it exists, would fall into this category. Titan, which has been explored over the past 15 years by the NASA-ESA Cassini mission and the accompanying Huygens probe, sports lakes of liquid methane. The mean surface temperature is a frigid 93 K, compared to 288 K here on Earth. Whether or not life could originate or survive on Titan is unknown. Earth-like life obviously could not, but perhaps there is some kind of life that could. Finding life on Titan would be even more profound than finding life on Enceladus or Europa because it would suggest that life is an extremely general phenomenon. Some astrobiologists, including me, are skeptical about this idea; however, it is a testable hypothesis that deserves consideration. Indeed, Ellen Stofan proposed a Discovery-class space mission to drop a boat into Titan’s methane seas and sample them. Stofan’s mission was turned down, not because it lacked scientific merit, but because no one thought it could fit under the Discovery cost cap. It will likely be done someday, not necessarily to find life, but just to see what is there.
Remote detection of life as we know it
The search for life as we know it extends to exoplanets, as well. None of the other planets in the solar system are truly Earth-like; they differ greatly in their masses, and of course they are all at different distances from the Sun. But rocky exoplanets within the liquid water ‘habitable zones’ around their parent stars could conceivably be Earth-like. We will not be able to explore them directly, however, at least for the foreseeable future, and so we will have to rely on remote life detection techniques. Life that is present at the surface of a planet can modify the planet’s atmosphere in a way that is remotely detectable, using spectroscopy. This falls within my own area of expertise, and so I can report on developments in this area with some degree of confidence.
It was recognized many years ago (Joshua Lederberg, Nature, 1964) that Earth’s atmosphere is well out of thermodynamic equilibrium and that this is largely due to the presence of life. But thermodynamic disequilibrium, by itself, is not necessarily a sign of life. I have just argued above that the high availability of free energy in Enceladus’ ocean—a sign of thermodynamic disequilibrium—could actually indicate that methanogenic life is not present. Earth’s atmosphere is in extreme disequilibrium for a specific reason: Photosynthetic organisms living on its surface produce O2 as a byproduct of using H2O to reduce CO2 to organic matter. Most of the very large amount of O2 in Earth’s atmosphere, 21 percent by volume, was produced in this way. At the same time, there are anaerobic (O2-free) regions on Earth where methanogens can produce CH4. Other anaerobic organisms (denitrifying bacteria) produce nitrous oxide, N2O, which is also a reduced gas that can react with O2. Thus, the simultaneous presence of significant quantities of O2 and a reduced gas such as CH4 or N2O remains the best remote biosignature that we know of. This realization has not changed substantially for the last 50 years.
Progress has been made, however, in identifying other, somewhat more ambiguous, biosignatures. Some researchers prefer to call these ‘biohints’. Our own research group makes computer models of Earth’s atmosphere during the Archean Eon, which lasted from 3.8 to 2.5 billion years ago. O2 was not yet abundant during this period, but life was most certainly present during most or all of this time. Our models suggest that CH4 should have been abundant during this time period, perhaps accompanied by organic haze. So, early Earth could have looked a little bit like Titan. We would be able to distinguish an ‘Earth’ from a ‘Titan’, however, because the ‘Earth’ would be much warmer and its atmosphere would contain H2O and CO2, as well. Both of these gases are completely frozen out of Titan’s atmosphere.
Significant attention has also been paid to the question of whether O2 by itself could be considered a biosignature. This question is motivated by the fact that O2 would be much easier to spot in Earth’s atmosphere than would CH4 or N2O, because of its much higher concentration.
So, if other Earth-like planets do exist, but not around the very nearest stars, we may well encounter this situation. Consequently, theoreticians like myself have spent considerable time and energy studying the possibility of false positives for life, i.e., planets that might accumulate high levels of atmospheric O2 without life being present. I will mention just one of these false positives here, because it is the easiest to understand: Suppose that you had a planet like early Venus that was initially endowed with lots of water, but that lost that water because it was too close to its star, and so it experienced a runaway greenhouse. The H2O would be photodissociated by stellar ultraviolet radiation, the hydrogen would escape to space, and O2 would be left behind. Fortunately, this particular false positive would be easy to identify, because the water would be gone. (Unless, of course, we caught the planet right in the act of losing its water. But we would be suspicious of such a planet, anyway, because it would lie within the inner edge of its star’s habitable zone.)
I will not bore you with a lengthy discussion of all of the possible false positives, or the ways we might have of ruling them in or out. As I said, there is a growing literature on this topic, which is available on request. I should say that much of this research has been funded by NASA’s R&A programs, particularly Exobiology, Habitable Worlds, Emerging Worlds, and the NASA Astrobiology Institute. NASA has been forward-looking in funding these programs, which are helping to lay the groundwork for the interpretation of future exoplanet spectra. As a result, there is now a community of researchers, many of them young (unlike myself), who are poised to take advantage of such data when they become available.
Planets around M stars
Planets orbiting M stars (dim red-dwarf stars) deserve special mention because they are the ones that are most likely to be observed over the next 10-15 years. An Earth-like planet is, by definition, roughly Earth-sized, whereas M stars are significantly smaller than the Sun. Thus, M- star planets create a deeper dip in the star’s light when they transit (go in front of) the star. The habitable zone of an M star is also much closer to the star (because the star is so dim), and hence the probability of a transit is higher. When the planet transits the star, a small amount of the star’s light passes through the planet’s atmosphere, and this can be examined spectroscopically. Consequently, M-star planets can be studied with existing and planned space telescopes. Existing telescopes (Hubble and Spitzer) have only been able to characterize gas or ice giant planets (hot Jupiters and warm Neptunes). But the James Webb Space Telescope (JWST), which launches next year, may be able to obtain spectra of a few rocky, habitable-zone planets. This, of course, is an extremely exciting prospect.
Update #2: Another major discovery that was announced after the December Biosignatures workshop was the existence of 7 planets orbiting the M star TRAPPIST-1. I will not say much about this discovery, as Adam Burgasser (who was on the TRAPPIST team) will presumably cover this topic in his testimony. At least three of these planets are within their star’s habitable zone, and so characterizing these planets spectroscopically has already become a major science goal for JWST. This discovery, like the two that follow, was made using ground-based telescopes.
Update #3: A new transiting, habitable-zone planet was announced just last week orbiting the M star LHS1140 (J.A. Dittmann et al., Nature, 2017). This planet was found by the MEarth survey, headed by David Charbonneau of Harvard University. The star is roughly twice as massive as TRAPPIST-1, weighing in at ~0.15 times the mass of our Sun. This will be another likely target for JWST.
Update #4: There is a rocky planet orbiting within the habitable zone of the nearest star, Proxima Centauri. This should actually be update #1, as it was announced at the end of last summer, well before the workshop. It caused quite a buzz at the workshop, and we had a talk by one of the co- discoverers, Matteo Broge. Broge works at the European Southern Observatory (ESO) in Chile and is a member of the HARPS team. HARPS is a high-resolution spectrograph used for making radial-velocity measurements on stars. This discovery is quite unlike the TRAPPIST-1 and LHS1140 discoveries, because Proxima Centauri b, as the planet is called, does not transit. It therefore cannot be observed by JWST in the same way that the TRAPPIST-1 planets can.
Instead, if we wish to characterize this planet spectroscopically, we will have to do direct imaging: separating the light reflected by the planet from that emitted by the star. This can be done either by placing a coronagraph within the telescope or, if the telescope is in space, by placing a starshade at some distance in front of the telescope to block the light from the star. Because Proxima Centauri is an M star, it may be possible to directly image its planet from the ground. Broge and his colleagues are designing instruments for one of the 8-m ESO telescopes in the hopes of doing this. Whether they will succeed is uncertain, according to him. Within the next 10-12 years, however, the astronomers in the US, Europe, and elsewhere hope to build 30- 40 m ground-based telescopes with state-of-the-art coronagraphs, and Broge was optimistic that Proxima Centauri b can be studied in this way.
Direct imaging of Earth-like planets around Sun-like stars
The ultimate goal in the astronomical search for life is to look for Earth-like planets orbiting Sun-like (F-G-K) stars. Such planets are difficult to study in transit because i) the probability of a transit is small, and ii) the planet is small compared to the star. Think of it this way: an observer looking at the Sun from a great distance would have only a 0.5 percent chance of seeing the Earth transit. That means that we would need to look at ~200 Sun-like stars to find one that had a transiting Earth-like planet, even if every one of them had such a planet going around it. Or, to say this another way, most of the nearby stars probably do have planets (based on Kepler), but they remain invisible to us because the plane of their orbit is not within our line of sight. We can only observe such planets by using direct imaging. And, for an Earth-like planet around a Sun-like star, the contrast ratio (relative brightness) between the star and the planet is 1010, i.e., the star is 10 billion times brighter. We don’t think that we can do this level of coronagraphy from the ground; rather, we need a big, direct imaging telescope up in space.
The good news is that NASA is once again studying such telescopes. (I was involved in such a study 12 years ago for TPF-C, Terrestrial Planet Finder-Coronagraph, but the project was cancelled after only 6 months.) At the Biosignatures Workshop, Shawn Domagal-Goldman from NASA’s Goddard Space Flight Center talked about two possible designs for such a telescope. The Habitable Planets Explorer (HabEx) would be a 4-to-6 m diameter telescope designed specifically for planet-finding. The Large UltraViolet-Optical-InfraRed space telescope (LUVOIR) would be a 9-to-15 m diameter general purpose telescope that could also do exoplanets. Both telescopes would be positioned at the Earth-Sun L2 Lagrange point, where JWST is slated to operate. It is my great hope to have a telescope fly while I am still around to see it.
Remote detection of life as we don’t know it
For completeness, I will briefly mention the fourth quadrant of the search for extraterrestrial life: searching remotely for life as we don’t know it. This quadrant is filled in with a ‘?’ in Fig. 1, because it is not particularly well-defined. Sara Seager at MIT and her colleague William Bains have speculated in the literature about rocky planets with H2-rich atmospheres in which ammonia, NH3, is a byproduct of photosynthesis. They have termed such planets “Haber-worlds”. Whether or not such planets might exist is unknown. We invited Bains to give a talk at the Biosignatures workshop, though, simply because we did not want to be exclusionary. I personally would not optimize a space telescope to look for such planets.
However, if we had a telescope like HabEx or LUVOIR and were using it to make observations, I would agree that one should not ignore the possibility of such planets. With a good direct- imaging telescope, we will simply look at all the nearby planetary systems and see what is there. With luck, we may even find evidence for life. But, in any case, we will learn whether Earth is a special place in the galaxy, or whether Earth-like planets abound. Sara Seager, whom I just defamed earlier in this paragraph, is quite eloquent when she speaks of this search. She calls it ‘the second
Copernican revolution’. I agree with her perspective. It is within our power, at this time, to make some of the greatest astronomical discoveries ever. I hope that we can find the scientific and political will to make it happen.
With that, I conclude my testimony and I would be happy to address any questions you may have. Thank you, Chairman Smith and Committee Members, for your attention.
PLANETARY FLAGSHIP MISSIONS: MARS ROVER 2020 AND EUROPA CLIPPER
On July 18, 2017, the U.S. House of Representatives Subcommittee on Space (Committee on Science, Space and Technology) held a hearing titled “Planetary Flagship Missions: Mars Rover 2020 and Europa Clipper.” Dr. William B. McKinnon, co-chair of the Committee on Astrobiology and Planetary Science (CAPS), provided testimony on behalf of the National Academies’ Division on Engineering and Physical Sciences, and the SSB. More information and the full testimony is available at https://science.house.gov/legislation/hearings/space-subcommittee-hearing-planetary-flagship-missions-mars-rover-2020-and and reprinted, unedited, below.
Chairman Babin, Ranking Member Bera, and Members of the House Committee on Science, Space, and Technology, Subcommittee on Space:
Thank you for the opportunity to appear before you today at this important hearing. I speak to you today as a scientist with more than 40 years of spaceflight related research, largely funded by grants from NASA’s planetary science division. I also have the honor to serve as Co-Chair of the Committee on Astrobiology and Planetary Sciences (CAPS) of the National Academies of Sciences, Engineering and Medicine. However, I want to note that my testimony today is my own and should not be taken as reflecting any consensus views or advice from CAPS or the National Academies. The views I express today are based on my personal assessment of information and presentations made available to CAPS as it has been monitoring the implementation of the planetary science decadal survey. CAPS is one of five subcommittees of the Academies’ Space Studies Board—each of which is charged to assist the federal government in integrating and planning programs in space sciences by providing advice on the implementation of decadal survey recommendations. I have the honor of co-chairing CAPS along with Dr. Christopher House of The Pennsylvania State University. We are particularly honored to chair this important committee at a time when it embarks on its work with a new charter from the Academies that will enable our committee to issue short, topical reports thatwill provide guidance to federal agencies that support astrobiology and planetary science research.
The scope of CAPS spans space-based and supporting ground-based planetary research within our own planetary system, including, for example, geosciences, atmospheres, particles and fields of planets, moons, rings, and small bodies, as well as astrobiology, sample analysis, planetary astronomy, and planetary protection. The CAPS’s scope also includes appropriate cross- disciplinary areas and consideration of budget and programmatic aspects of the implementation of the decadal survey.
Chairman Babin, I would like to thank you and the committee for giving me the opportunity to present to you today some personal perspectives on the implementation of the most recent 2011 decadal survey in planetary sciences—“Vision and Voyages for Planetary Sciences in the Decade 2013-2022.” Because others this morning will give the committee comprehensive reports on the status of the Mars 2020 and Europa Clipper missions, my testimony will focus on some of the driving principles that underpinned the decadal survey’s recommendations for these missions and other elements of the planetary science program at NASA.
It is also worth noting that as we meet today, an ad hoc committee (not CAPS) has been established by the Academies on the request of NASA to review the response of NASA’s Planetary Science program to the 2011 decadal survey. That committee’s work is well underway and it is charged to recommend any actions that could be taken to optimize the science value of the planetary science program including how to take into account emergent discoveries since the publication of the decadal survey in the context of current and forecasted resources available to NASA. The midterm review committee is also being asked to provide guidance about implementation of the decadal’s recommended mission portfolio and decision rules for the remaining years of the current decadal survey, but it is specifically charged to not “revisit or redefine the scientific priorities or mission recommendations from [Vision and Voyages].” The midterm study is also undertaking the review of the Mars exploration architecture called for by the Congress in the most recent NASA authorization legislation. I am also pleased to report that NASA and the Academies have also acted expeditiously to initiate the other two studies called for in that legislation on science strategies for exoplanet discovery and characterization and for astrobiology and the search for life. All three of these studies will provide critical inputs into the upcoming decadal surveys in astronomy and astrophysics and in planetary sciences that are expected to get underway in December 2018 and the Spring of 2020, respectively.
Mr. Chairman, I would like first to remind us all what a National Academies decadal survey in space science is supposed to be. Decadal surveys are carried out with a cadence of approximately 10 years for each space science discipline.
The National Academies have conducted decadal surveys for more than 50 years, since astronomers first developed a strategic plan for ground-based astronomy in the 1964 report “Ground-Based Astronomy: A Ten-Year Program.” The committees and supporting panels that carry out the decadal surveys are drawn from the broad community associated with the discipline in review, and these volunteers comprise some of the nation’s leading scientists and engineers. The Academies’ decadal surveys are notable in their ability to sample thoroughly the research interests, aspirations, and needs of a scientific community. Through a rigorous process lasting about 2 years, a primary survey committee and “thematic” supporting panels of community members construct a prioritized program of science goals and objectives and define an executable strategy for achieving them.
Decadal survey reports to agencies and other government entities play a critical role in defining the nation’s agenda in that science area for the following 10 years, and often beyond. Eleven decadal surveys have now been completed and in 2015 the Academies released a so-called “survey of surveys” report—“The Space Science Decadal Surveys: Lessons Learned and Best Practices”. Mr Chairman, I would recommend to you and the members of the committee that report’s accounting of lessons learned on the decadal process. You will see therein a reflection of what I believe is the widely-held belief of the space science research community that the decadal surveys have been a model in the world of science for how community consensus can be achieved—on science goals and on a program of activities to achieve them.
Mr. Chairman, I would like to return for a moment to the science of astrobiology and in particular the search for life. CAPS has collaborated with the Academies’ Committee on Astronomy and Astrophysics to assemble a committee drawn from the planetary and astronomy research communities under the leadership of Dr. James Kasting, also a CAPS member, to organize a workshop held in December 2016 on facilitating an expert dialogue on the current status of extraterrestrial life detection and related issues. That workshop considered important questions such as:
- What is our current understanding of the limits of life and life’s interactions with the environments of planets and moons?
- Are we today positioned to design, build and conduct experiments or observations capable of life detection remotely or in situ in our own solar system and from afar on extrasolar worlds?
- How could targeted research help advance the state of the art for life detection, including instrumentation and precursor research, to successfully address these challenges?
A proceedings report that will document the workshop, including summaries of individual presentations and ensuing discussions will be published by the National Academies very shortly and will provide invaluable input into the exoplanet and astrobiology studies now getting underway and which are of such interest to this committee. More information on the workshop and the current state of the challenge of the science of the search for life can be found in Dr. Kasting’s testimony to the Committee on Science, Space and Technology on April 26, 2017.
Mr. Chairman it is also worth noting that astrobiology is increasingly at the heart of our exploration of the solar system. CAPS has heard about these exciting science opportunities through NASA, opportunities such as: the scientific program of the Opportunity and Curiosity rovers that are roaming the martian surface and the 2020 rover that is under development; the Psyche and Lucy missions that will provide context to our understanding of the origin of habitable worlds and the formation of organic-rich planetary bodies, respectively; the development of the Europa Clipper mission and the planning for a potential future landing on the surface of Europa; and of course the inclusion of Ocean Worlds in New Frontiers 4.
Indeed in the Vision and Voyages decadal survey, astrobiology was at the heart of the scientific rationale for two of the top large flagship mission recommendations. The compelling science that drove the survey to recommend the concepts “MarsAstrobiology Explorer-Cacher Descope”—now being implemented as Mars 2020—and “Jupiter Europa Orbiter Descope”— now being implemented as Europa Clipper— were:
- Perform in situ science on Mars samples to look for evidence of ancient life or prebiotic chemistry; and collect, document, and package samples for future collection and return to Earth; and
- Explore Europa to investigate its habitability.
Since the release of the decadal survey report in 2011, CAPS has been receiving frequent reports on the implementation of these priorities by NASA. Since then the committee co-chairs have reported to the Space Studies Board at its semi-annual meetings and repeatedly at the most recent SSB meetings. I, Chris House and our predecessor co-chairs have reported to the board our personal assessment that the Planetary Science Division is in a good state and the decadal’s priorities are being pursued. In particular we have noted that the Mars 2020 astrobiology/sample-caching rover mission continues its development toward a 2020 launch; the Europa Clipper mission to explore Europa and investigate its habitability is in Phase B (design phase); two Discovery-class missions have been selected (Psyche, M-[or metal]-type asteroid orbiter and Lucy, multi-Trojan asteroid flyby), and another one is in extended Phase A
(NEOCam) development; and finally the next New Frontiers class mission proposals were submitted April 28th of this year and are currently being assessed.
Mr. Chairman, one of the most exciting possibilities in space science today is the opportunity we have to find evidence for extant, or extinct, extraterrestrial life in the solar system. In that regard, our current suite of astrobiology missions is key to the future of planetary science. The opportunity to explore Europa in detail is therefore all the more exciting. With this in mind, I am sure CAPS—and indeed the planetary midterm review committee—will continue to consider the impacts of the evolution of NASA’s plans to explore Europa. The multiple flyby Europa Clipper mission is, I believe, highly responsive to the decadal survey in science and cost. Indeed it is my personal view, and one that I have expressed in other forums (such as when I was chair of the Outer Planets Assessment Group—a group supported by NASA to provide community input to Dr. Green and the Planetary Science Division), that the Europa Clipper mission is in many ways superior to the original Jupiter Europa orbiter mission considered by the decadal. The Clipper design solves many thorny engineering problems, which I can discuss if you wish. Important from a CAPS perspective, the evolution of the Jupiter Europa orbiter to the Europa Clipper is in my view just the sort of outcome we would hope for as the result of decadal recommendations.
I would now like to address the possibility of a Europa lander. No mission to land on Europa was proposed to the survey committee and panels as the decadal was being conducted. It is, however, worth noting that two Europa lander concepts were briefly discussed, but not prioritized, in the 2003 decadal survey for planetary science, “New Frontiers in the Solar System: An Integrated Exploration Strategy.” Today we all know that NASA has been directed to add a lander to the overall Europa exploration program and to launch the Europa Clipper on a Space Launch System (SLS) vehicle. Mr. Chairman, I am sure you will recognize that a key concern for the decadal survey panels and steering committee was to understand the risks associated with cost and affordability, as well as risks associated with complexity and the state of technology development. There is, in addition, the programmatic challenge posed to the overall planetary science program by the development of another large, strategic mission so close in time with Mars 2020 and Europa Clipper. That said, there is also the scientific opportunity afforded by landing on Europa, the opportunity to address one of the greatest scientific questions—is there life, extant life, beyond the Earth? These are all issues that I expect CAPS will continue to consider and on which we may issue future reports as we consider our task to provide advice on the implementation of the decadal survey. I also expect the midterm review committee’s report that will be published in the Spring of 2018 will also consider these opportunities and challenges. Understanding these issues is key to pursing another key goal of the Vision and Voyages decadal survey—maintaining a balance across the whole planetary sciences program at NASA.
As noted in the decadal, the statement of task for the survey called for the creation of a prioritized list of flight investigations for the decade 2013-2022. A prioritized list implies that the elements of the list have been judged and ordered with respect to a set of appropriate criteria.
Four criteria were used by the decadal steering committee as it made the difficult choices among a suite of very compelling science opportunities across the breadth of solar system exploration. The first and most important was science return per dollar. Science return was judged with respect to the key science themes, namely:
- Building new worlds—understanding solar system beginnings,
- Planetary habitats—searching for the requirements for life, and
- Workings of solar systems—revealing planetary processes through time.
The second criterion was programmatic balance—striving to achieve an appropriate balance among mission targets across the solar system and an appropriate mix of small (e.g., Discovery class), medium (e.g., New Frontiers class), and large (flagship) missions. The other two criteria were technological readiness and availability of trajectory opportunities within the 2013-2022- time period. Costs and technical risks were estimated via the independent Cost and Technical Evaluation (CATE) process developed by the Aerospace Corporation for the National Academies. In addition, the decadal recommendations were placed into a context of likely resources available, that is, the Planetary Science Division’s budget for the decade in question. A nominal projected budget, as well as both an enhanced and a more cost-constrained budget for the decade were considered.
The decadal survey went on to recommend that NASA’s suite of planetary missions for the decade 2013-2022 should consist of a balanced mix of Discovery, New Frontiers, and large missions, enabling both a steady stream of new discoveries and the capability to address larger challenges such as sample return missions and outer planet exploration. The program recommended in the decadal was designed to achieve such a balance. To prevent the balance among mission classes from becoming skewed, the decadal noted that it is crucial that all missions, particularly the most-costly ones, be initiated with a good understanding of their probable costs. The CATE process was designed specifically to address this issue by taking a realistic approach to cost estimation—albeit of early proof-of-concept designs. It is also important that there be an appropriate balance among the many potential targets in the solar system. Achieving this balance was one of the key factors informing the recommendations for medium and large missions presented in the decadal. These
considerations also led to the decadal recommending among its flagship class of missions, investigations of Uranus and Neptune— targets that represent a wholly distinct class of planet, the so-called ice giants. The ice giants are one of the great remaining unknowns in the solar system, the only class of planet that has never been explored in detail, and one tied directly to the plethora of exoplanet discoveries. The decadal recommended that the third-highest-priority flagship mission was the Uranus Orbiter and Probe mission and that, if the budget allowed, it should be initiated the exploration of the ice giants in the decade 2013-2022 even if both of what are now Mars 2020 and Europa Clipper take place. I note here that NASA takes such recommendations seriously. An ice giant mission study, put together by a science definition team, has recently been released by NASA. Similarly, a Europa lander mission study, put together by its own science definition team, has also been released. Both of these reports are, in my view, beautiful and visionary documents which fully capture the scientific promise and excitement of NASA’s exploration of the solar system. And such reports can also be regarded as “pre-next-decadal,” in the sense that they can feed forward to the deliberations of the next planetary science decadal survey.
Regarding decadal recommendations, issues of balance across the solar system and balance among mission sizes are related. For example, it is difficult to investigate targets in the outer solar system with small or in some cases even medium-class missions. Though I note here the successful reconnaissance of the Pluto system by New Horizons and ongoing, focused studies of Jupiter by the Juno orbiter, which just flew over the Great Red Spot (pictures of which you may have seen). These two missions are part of NASA’s medium-class, New Frontiers portfolio. Nevertheless, some targets are ideally suited to small missions. The decadal’s recommendations reflect this fact and implicitly assume that Discovery missions will address important questions whose exploration does not require the capability provided by medium or large missions.
A scientifically appropriate balance of solar system exploration activities must be found by selecting the set of missions that best addresses the highest priorities among the overarching science questions associated with the three crosscutting science themes identified by the comprehensive community-consensus-building process that the decadal survey represents. As we in CAPS consider the implementation of the decadal survey’s recommendations, we will do so in accordance with this principle.
Mr. Chairman, as a second grader I watched the liftoff of John Glenn and Friendship 7 and as a teenager I watched Neil Armstrong walk on the Moon. Over these past three score years NASA’s exploration of the solar system from Mercury out to Pluto and beyond has revolutionized our conception of ourselves and our planet. But I believe, given our ongoing discoveries and characterization of planets around other stars and the very real possibility of detecting extant life in an ocean world in the outer solar system, that we are approaching an even greater revolution in our understanding of our place in the Universe. Without doubt, NASA’s planetary science program has the real and present potential of leading to a true paradigm shift in human knowledge and awareness as we continue to explore the origins of our solar system and the life it sustains.
In conclusion, I thank you for giving me the opportunity to testify today and welcome any questions you may have.
On December 6, 2017, the U.S. House of Representatives Subcommittee on Space (Committee on Science, Space and Technology) held a hearing titled “NASA’s Next Four Large Telescopes.” Dr. Christopher F. McKee, member of the National Academy of Science and the Committee on Astronomy and Astrophysics (CAA), provided testimony on behalf of the National Academies’ Division on Engineering and Physical Sciences, and the SSB. More information and the full testimony is available at https://science.house.gov/legislation/hearings/subcommittee-space-hearing-nasa-s-next-four-large-telescopes and reprinted, unedited, below.
Chairman Babin, Ranking Member Bera, and members of the committee:
Thank you for the opportunity to appear before you today in my capacity as a member of the Committee on Astronomy and Astrophysics (CAA) of the National Academies of Sciences, Engineering and Medicine. CAA is one of five subcommittees of the Academies’ Space Studies Board that span the science disciplines supported by NASA. In the case of the CAA, the committee is also a subcommittee of the Academies’ Board on Physics and Astronomy, so that the one committee can cover all of astronomy and astrophysics, including programs supported by the National Science Foundation and the Department of Energy. Each of the five subcommittees is charged to assist the federal government in integrating and planning programs in space sciences by providing advice on the implementation of decadal survey recommendations. As you know, the National Academies’ decadal surveys—mandated by law—provide NASA with consensus advice from the scientific community on proposed science priorities for the decade ahead.
I have the honor of serving on the CAA and, as you mentioned in your introductory remarks, I was one of the co-chairs of the 2001 decadal in astronomy and astrophysics. The highest recommendation in our report, Astronomy and Astrophysics in the New Millennium, was the James Webb Space Telescope (JWST), a truly remarkable feat of engineering that is expected to deliver groundbreaking scientific capability beyond that envisioned when we
recommended it. I am also honored to be a member of the CAA when, under a new charter from the Academies, it is able to issue fast-turn-around reports that will provide guidance to federal agencies that support astronomy and astrophysics research.
Chairman Babin, I would like to thank you and the committee for giving me the opportunity to present to you today some perspectives on the status of NASA’s program in astrophysics—drawing in particular on the Academies’ 2016 report New Worlds, New Horizons: A Midterm Assessment which came to some very important conclusions on the status of the implementation of the 2010 decadal and looked forward to the next decadal. I’d like to start by reading a quote from that report:
New Worlds, New Horizons in Astronomy and Astrophysics (NWNH), the report of the 2010 decadal survey of astronomy and astrophysics, put forward a vision for a decade of transformative exploration at the frontiers of astrophysics. This vision included mapping the first stars and galaxies as they emerge from the collapse of dark matter and cold clumps of hydrogen, finding new worlds in a startlingly diverse population of extrasolar planets, and exploiting the vastness and extreme conditions of the universe to reveal new information about the fundamental laws of nature. NWNH outlined a compelling program for understanding the cosmic order and for opening new fields of inquiry through the discovery areas of gravitational waves, time-domain astronomy, and habitable planets. . . . Already in the first half of the decade, scientists and teams of scientists working with these cutting-edge instruments and with new capabilities in data collection and analysis have made spectacular discoveries that advance the NWNH vision.
Mr. Chairman, while the discoveries are remarkable, the fact that they have occurred is not: The Congress, the Executive and the research community have relied on the independent and non- advocacy convening power of the National Academies to develop a national consensus on which scientific space missions NASA should pursue across the programs in the Science Mission Directorate. This process, over a period of nearly 60 years, has led to the United States developing clear leadership across all the fields of space science, which is why the Congress has repeatedly instructed NASA and the Executive to use the decadals as the foundation of the agency’s strategic planning in space science. Every prioritization process produces winners and losers, but there is broad support in the scientific community for the consensus-building process that has given us winners such as Hubble, Cassini, and Curiosity.
Mr. Chairman, members of the committee, as you well know the decadal process involves a broad cross section of the community. In the case of the 2010 decadal survey in astronomy and astrophysics, the Academies appointed nearly 200 astronomers to the survey committee, supporting panels and working groups. They received input from hundreds of astronomers, who submitted over 700 white papers describing opportunities for the current decade. The committee identified 20 key science questions that provided a framework for evaluating a compelling program of high-priority research activities. The science goals for the decade were focused into three science objectives, labeled “Cosmic Dawn,” “New Worlds,” and “Physics of the Universe.” The committee then undertook the hard and painful task, necessitated by the relatively severe financial constraints under which the agencies were expected to have to operate, of prioritizing the many exciting and realizable activities presented to it. The resulting program is described in the 2010 decadal report.
Mr. Chairman, today NASA is implementing the decadal survey. The Wide-Field Infrared Survey Telescope (WFIRST) was the 2010 decadal’s highest-ranked large space observatory with science goals that drew on and combined a set of mission concepts proposed by the community into a unified science program that, as the decadal report said, is “designed to settle essential questions in both exoplanet and dark energy research, and will advance topics ranging from galaxy evolution to the study of objects within our own galaxy.” The midterm report underscored the continuing scientific case for the pursuit of this mission and its planned implementation with a larger mirror than envisioned at the time of the decadal’s prioritization, saying that the 2.4-meter telescope, larger infrared detectors, and addition of a coronagraph make the 2016 design of WFIRST an ambitious and powerful facility. However, because the risk of cost growth in WFIRST could distort the NASA program balance and limit options for the next decadal survey, the midterm report called for an independent technical, management, and cost assessment of WFIRST. The report recommended that, if the mission cost estimate were high enough to compromise the scientific priorities and the balanced astrophysics program recommended by the decadal, then NASA should descope the mission. At our last CAA meeting in October, we heard the results of that assessment and the resulting efforts requested by NASA from the mission team to reduce the planned cost of the mission. The committee will no doubt hear at its March meeting the outcome of those efforts, and we may be asked to comment in a CAA report.
Meanwhile Mr. Chairman, it is also worth noting that the midterm report endorsed NASA’s plans for executing the second priority recommendation of the 2010 decadal, the enhancement of the Explorer program, and that NASA should execute at least four Explorer Announcements of Opportunity during the 2012-2021 decade, each
with a Mission of Opportunity call, and each followed by mission selection. The Explorer program is currently supporting the development of the Transiting Exoplanet Survey Satellite (TESS), scheduled for launch in March 2018. This satellite will use similar techniques to the highly-successful Kepler telescope, but it will observe bright, relatively nearby stars over the whole sky, thus identifying exoplanet targets that are ideal for follow up by the James Webb Space Telescope and other facilities.
NASA is also implementing the third and fourth high-priority recommendations in partnership with our European colleagues at ESA through participation in the Athena x-ray telescope and in the ambitious and exciting opportunity that will be provided by the LISA gravitational wave observatory. LISA will open a new window on the cosmos by measuring the ripples in space-time produced by the merger of black holes much more massive than can be detected by the NSF-supported LIGO facility, which has confirmed Einstein’s theory of gravity and solved the mystery of the source of many of the elements in the periodic table beyond iron—such as gold and uranium.
There are many other exciting aspects to NASA’s execution of decadal survey recommendations that I could address, but I have concentrated on the highest priorities of the recent decadal survey since they set the context for the next decadal that is expected to start in about a year’s time.
At the CAA we have heard in presentations, made over the last 2-3 years, how NASA is supporting teams of astronomers and engineers to develop mission concepts for the large strategic class of missions—sometimes called flagship missions—and for moderate-scale missions. The scientific cases being developed for each telescope are compelling and ambitious. This methodical approach to preparing the community for the decadal is, in my personal opinion, vitally important. The CAA is at the same time preparing to release the first call for white paper inputs from the community in advance of the survey so that when the chair is appointed, she or he will have fresh community input on the science when designing the plan to execute what is nominally called Astro2020.
It would, Mr. Chairman, be remiss of me to provide any comparisons among the missions that will be proposed to the decadal survey as I have complete confidence in the ability of the survey process to assess the science cases for each, the technical challenges each bring, and the likely affordability of the missions. This is what my community has been doing now for nearly 60 years, and each time the result has been a flexible and impactful program that pursues large strategic-class missions that can take over a decade to develop and launch and that produce major scientific results unmatched by any other nation, as well as pursuing smaller, rapid response missions like the TESS exoplanet mission I discussed earlier.
Mr. Chairman and members of the committee, the bottom line result of the decadal survey process in astronomy and astrophysics—and in the other scientific fields supported by NASA—is that the United States has reaped the benefits of this community-based process which the Academies conduct on behalf of the nation under its unique charter from the Congress. I am here today to reiterate why this process works as well as it does, and to answer any questions you may have.