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Session 4: Understanding the Solar System: How Did It Begin and How Is It Evolving? Moderator: Charles Woodward, University of Minnesota; Space Studies Board Member Speakers: Heidi B. Hammel, Space Science Institute, Boulder, Colorado Edward C. Stone, California Institute of Technology, and Former Director, Jet Propulsion Laboratory Panelists: Andrew Lawler, Science Journalist Dietram A. Scheufele, Professor and Chair of Science Communication, University of Wisconsin, Madison INTRODUCTION Charles Woodward, professor of astronomy at the University of Minnesota, opened the session by talking about how scientists are trying to unlock the diary of the origins of planetary systems, and one way to communicate that is through visual imagery in near real time. The public can watch the rovers moving across Mars, for example. He then showed a 40-second video of how scientists currently think planetary systems form. HEIDI B. HAMMEL Heidi B. Hammel, senior research scientist and co-director of the Space Science Institute in Boulder, Colorado, joked that she was going to talk about the history of the solar system that preceded the “two seconds” of human evolution that Roger-Maurice Bonnet of the International Space Science Institute talked about in Session 1. Using the Orion nebula as an example of galaxy formation, she showed many images to explain how galaxies evolve and planets form from protoplanetary disks, or proplyds, which are nascent solar systems. The question is, How do you get from a proplyd to a solar system like ours? Focusing in on our solar system, she recounted how much our knowledge has changed since she defended her dissertation in 1988 and had to explain the evolution of the solar system. At that time, it was believed that the gases of the inner rocky planets were blown off by the Sun into the outer system where they settled onto the rocky cores of the outer planets that therefore are gaseous. Pluto was a problem in this structure, but scientists at the time said “oh, it’s a comet.” But in 1992, the first Kuiper belt object (KBO) was found. That was the first push of what she calls the “Humpty Dumpty” effect. The theory of the Kuiper belt dated back to the 1950s, but the first KBO was found only in 1992 after which the number of objects identified in the Kuiper belt exploded. That was the beginning of the end of Pluto’s designation as a planet. Today, scientists understand that the solar system is not an “empty place that has eight or maybe nine planets” but is very dynamic. The “second shove” of “Humpty Dumpty off the wall” came in the mid-1990s when “people starting talking about planetary migration” following the realization that orbits of KBOs—and Pluto—are not necessarily circular. Some of their orbits are eccentric, and many have tilts to the plane of the ecliptic 29
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10,000 mi 16,100 km 3.4” FIGURE 8 Comparison of the size of a collision on Jupiter to size of Earth. SOURCE: Heidi Hamel, presentation to the workshop on Sharing the Adventure with the Public⎯The Value and Excitement of “Grand Questions” of Space Science and Exploration, November 9, 2010. Jupiter: Courtesy NASA, ESA, H. Hammel (Space Science Institute), and the Jupiter Impact Team. Earth: Courtesy of NASA. in which the planets orbit the Sun. Some KBOs are in columns and clusters in resonant orbits with Neptune: “For every two times Neptune goes around, the Kuiper belt goes around three times. They are locked in a dance,” Hammel explained. Pluto is one of these objects, and there are more than 300 objects just like it. That structure developed when the giant planets migrated, sweeping up the tiny objects and locking them into orbital resonances. The discovery of exoplanets beginning in 1995 is “what sent Humpty Dumpty over the edge,” with 490 exoplanets discovered to date. Everything she learned in graduate school about planetary formation, she said, is “out the window.” So the question is how to put Humpty Dumpty back together again. Hammel showed a series of seven slides that explained the current theory of how solar systems form, starting with a collapsing cloud of gas and dust that forms a star, leading to clumps of dust grains sticking together and getting angular momentum that turn them into disks that grow into planestismals that stick together and become protoplanets that collide with one another to form planets and then gas attaches to the larger ones. Finally, the planets get redistributed. “It’s complex and it’s messy. Lots of whooshing and crashing,” Hammel exclaimed, adding that all of this knowledge has developed during her career. “In 5 or 10 years, they’ll tell you a completely different story. That’s just the nature of science,” she added. Our solar system itself is still a “work in progress” with massive impacts on Jupiter, for example. She provided a number of examples, including a series of images of a recent collision between Jupiter and a comet or asteroid that she took using the Hubble Space Telescope. “I try to people-ize this,” she said, by showing what the impact site would have been like on Earth (Figure 8). It would be a “biosphere- 30
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FIGURE 9 The Earth-Moon system as viewed from the vicinity of Saturn by the Cassini spacecraft. SOURCE: Courtesy of NASA/Jet Propulsion Laboratory/Space Science Institute. changing” event, noting that was probably what happened to the dinosaurs. Scientists are learning that these impacts happen all the time, but we only now have the technology to see them. Comets crashing into other bodies move water around in the solar system, Hammel continued, and there is water on several solar system bodies. NASA’s Phoenix lander exposed ice on Mars, there is water on the Moon, scientists believe there is a liquid water ocean under the icy crust of Jupiter’s moon Europa, and Saturn’s moon Enceladus has water “spewing out of . . . stripes in its southern hemisphere.” She stressed that the point she was trying to make was that there are no “static” planets, they are all changing all the time, including Earth. During her talk, Hammel noted that Facebook and Twitter have become tools for scientists to share information with each other about events like the Jupiter collision, and that amateur astronomers are an important part of the science community looking for these events. Showing an image taken by the Cassini spacecraft of Saturn backlit by the Sun (Figure 9), she pointed out that Earth is seen as a tiny dot, and even the Moon can be seen in Earth’s orbit. She said that is why she studies planets, because it helps us understand Earth. 31
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EDWARD C. STONE Edward C. Stone, the David Morrisroe Professor of Physics and vice provost for special projects at the California Institute of Technology and former director of the Jet Propulsion Laboratory (JPL), began by talking broadly about the value of exploration. He started by explaining what he calls the five frontiers of space: • Physical—going somewhere, sending things to places we’ve never been before; • Knowledge—science, understanding what it is that’s out there; • Technical—developing the capability to actually do things in space; • Human—how humans can perform and be effective in space; and • Applications—using space to better life on Earth. “Exploration is a journey that expands these frontiers, and the value and excitement comes from those journeys,” he explained. For planetary exploration, the three that are particularly germane are physical, knowledge, and technical. Stone referenced a new book by Stephen J. Pyne1 about the Voyager missions2 in which he tries to put this new era of exploration in a context of the tradition of exploration in the Renaissance, the Enlightenment, and even the mythological journeys. This drive for exploration dates back millennia, Stone said. Frontiers need the unknown, so the value and excitement of space exploration is discovery, and often we find it is different than we expected, as Hammel just described, Stone continued. Another value of exploration is that it is outward looking, an optimistic human activity—”a hopeful expression of humanity.” These “frontiers are immense” and there is much work for the next generation to do, too. These five frontiers of space will not be exhausted soon. He went on to say that robots are our surrogates, they see what we would see, and they become part of our experience. Other values of exploration are the fascination with the ingenuity required to do this, and the images, which are beautiful and inspirational. All of these are reasons that exploration has value beyond the science. In terms of engaging the public with exploration, Stone recounted how in 1973 he was at a press conference at NASA’s Ames Research Center about the Pioneer 10 mission, and reporters were very interested in what was being learned. So when he was working on the Voyager mission, he decided JPL should help reporters tell the story as the spacecraft reached Jupiter in 1979. For 10 days, they had a press conference every morning—at that time it was the only way to engage with the public—and that forced them to sort out their ideas and challenge each other so they could reasonably tell the press each day “what we knew and what we didn’t know.” Ten years later, in 1989, when Voyager reached Neptune, technology had advanced to where the public could see the images at the same time as JPL, and planetariums around the country stayed open at night and people lined up to see the first images. Today, Mars images are on the Web, and people can see them on their desktops, Stone said. “Now we have the social networks; that’s a whole new capability,” and there is a need to “find out how to do this in a way that is manageable for the science teams,” he said. Especially when there are long-term missions like the Mars Exploration Rovers, rather than a spacecraft like Voyager that makes a one-time pass by a planet, he added. His concern is how, in this new environment where the data are easily available to everyone, scientists can help the public understand what all the data mean—who are the 1 S.J. Pyne, Voyager: Seeking Newer Worlds in the Third Great Age of Discovery, Viking, New York, 2010. 2 In addition to his other duties over the decades, Stone has been the chief scientist for the Voyager 1 and Voyager 2 probes since 1972. The primary mission for the Voyager spacecraft was studying Jupiter, Saturn, Neptune and Uranus. The probes are now on their way out of the solar system sending back data about the heliosphere, and Stone remains involved in the missions. 32
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guides? That used to be done through the press conferences and the interaction between the scientists and the reporters. The Voyager “adventure” continues, he said. Voyager 1 is 10 billion miles away in the outermost layer of the heliosphere, and in another 4 or 5 years will be in interstellar space for the first time. PANEL DISCUSSION Andrew Lawler, a science writer, and Dietram A. Scheufele, a professor and chair of science communication at the University of Wisconsin, Madison, joined Woodward, Hammel, and Stone on the panel. Woodward asked how Facebook and the Internet can be used to guide the public in understanding the idea of exploration and its return on investment. Lawler replied that people connect to a story through narratives and commended Hammel, in particular, for her skill at telling the story of the solar system as though it was a “living creature.” He said solar system exploration missions are particularly well suited to narrative because they have a natural beginning, middle, and end and convey science to the public in a way that is easy for people to absorb. Scheufele said that engaging with the interested public is easy, but the question is how to reach the people who are not inclined, for example, to go to science museums. Fifty percent of highly educated Americans go to museums at least once a year, which means that the other 50 percent do not go at all, he pointed out. For people who only went to high school, attendance is less than 10 percent. The “tricky part” is how to reach audiences who are not inclined to go to museums. Science is not an issue the public cares about, he asserted. He also noted that half of the U.S. public does not know how long it takes for Earth to move around the Sun. A discussion ensued about the value of images in connecting the public with solar system exploration. Hammel said that the new social media tools like Facebook allow scientists to push out images from spacecraft like the Hubble Space Telescope, which allows the public to explore along with the scientists “so scientists have to be out there in those media.” Woodward noted that the public was very interested in the decision to recategorize Pluto so that it no longer is a planet and wondered if scientists provided the public with the information needed to understand why. Hammel said astronomers “failed miserably.” She insisted that it was an easy story to tell, and it only takes her 15 minutes to explain it, but astronomers did not think they had to tell it. Lawler agreed, saying that astronomers did not understand that there is “a real emotional tie that people have with planets,” going back to astrology. They are mythical figures, and “when you mess with [them] people get upset.” He said that the public felt Pluto was being “knocked off its throne,” and they needed a new story, not just for their old story to be destroyed. Hammel tells that new story, he said. AUDIENCE INTERACTION Woodward asked the members of audience their views about whether robotic exploration is an investment, or if human spaceflight exploration is a complement to robotic exploration, or “should we send the astronauts.” An audience member proposed that a long-term goal such as an independent colony off of Earth in space should be established and then intermediate human spaceflight goals could be established. Scheufele responded that he does not believe the public agrees that there is an intrinsic value to science, but rather that it is driven by global competitiveness. Citing the Apollo era as a period when the U.S. public was strongly supportive of science because of the competition with the Soviet Union, he argued that the same approach needs to be taken to generate excitement again. If China does something spectacular in space, the United States will want to spend more on space to compete with them, he said. 33
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Lawler strongly disagreed, arguing that Apollo is a model, and the problem is that the science community is still “hooked” on that model, but everything has changed, and the model does not work anymore. It is a psychological problem in the space community that is being overcome quietly by using Twitter and other social media to reach the public, adding “I don’t think we will see a single massive program.” China and India may take that approach because they have not done it yet, “but we will not repeat it,” he insisted. From the audience, Sara Seager, Massachusetts Institute of Technology, asked what the motivation is for planetary exploration. Her issue appeared to be the extent to which solar system exploration is designed to search for life because one would have a different program if that is the primary motivation. Efforts would be focused on studying methane on Mars and not exploring the rest of the solar system. Hammel repeated what she had said earlier, that the motivation is to understand planetary processes so we can better understand Earth. Seager disagreed and asked Stone for his comments. Stone said that Mars is not the only possible location for life in the solar system, and that Enceladus, Europa, and Titan are other possibilities. More missions are needed, but “we can’t do everything, you have to make choices,” and that is the task of the ongoing National Research Council Planetary Science Decadal Survey. An audience member asked about how to take the public “along for the ride.” Woodward replied that most people who buy a ticket for a ride want a destination and to answer a question on the journey. In this context, he asked the panelists whether the search for life is the right motivating question that can engage not only the scientists, but the public who need to support it. Scheufele said the interest of scientists on one hand and the public and politicians on the other do not have to be at odds. The key is to find a hook to draw the public in, and often it turns out to be some “weird side story” that attracts attention. Lawler added that there are scientific questions and then there are questions about how to get the public and politicians to fund them. He cited the Mars meteorite ALH 84001 as an example—public interest translated into money to explore Mars, even though many scientists were skeptical of the claims. 34