National Academies Press: OpenBook

New Frontiers in Solar System Exploration (2003)

Chapter: Near-Earth Objects

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Suggested Citation:"Near-Earth Objects." National Research Council. 2003. New Frontiers in Solar System Exploration. Washington, DC: The National Academies Press. doi: 10.17226/10898.
Page 22
Suggested Citation:"Near-Earth Objects." National Research Council. 2003. New Frontiers in Solar System Exploration. Washington, DC: The National Academies Press. doi: 10.17226/10898.
Page 23
Suggested Citation:"Near-Earth Objects." National Research Council. 2003. New Frontiers in Solar System Exploration. Washington, DC: The National Academies Press. doi: 10.17226/10898.
Page 24

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Near-Earth Objects magine yourself lying in an open lunar craters, the scars of such will be struck by an object large I field on a warm summer evening, watching the sky as it darkens. Suddenly, a streak of light traces across impacts are still evident on Earth’s surface (see page 14). Scientifically, the history of impacts on Earth is enough (greater than 300 meters in diameter) to cause significant damage. Current telescopic surveys have the sky. As you continue to watch vital for understanding how the plan- identified an estimated 50 percent of you see another, and then another. et evolved and how life arose. For near-Earth objects (NEOs; asteroids Over the course of the evening, you example, it has been suggested that and comets whose orbits cross that of lose count of the number of streaks. most of the water on this planet was Earth) that have a diameter of 1 kilo- The meteor shower you are watching delivered by comet impacts (see the meter or greater, and approximately offers evidence that the solar system is Kuiper Belt Objects section, pages 12- 10 to 15 percent of objects between replete with small pieces of cosmic 13). A better-known example of the 0.5 and 1 km. NASA’s current goal is debris. Most of this material is too role of impacts is the Cretaceous- to finish cataloging the objects larger small to detect—too small, that is, Tertiary event 65 million years ago than 1 km by 2008, but the agency until it collides with Earth’s atmos- that led to global mass extinctions, has no formal plans to extend the phere and provides the celestial light including that of the dinosaurs. search to smaller objects. show you are witnessing. Impacts are not now as numerous as Searching for NEOs demands an Meteor showers are only one type they were in the first billion years of exacting observational strategy. To of evidence of these bits of wandering the solar system’s history, but the locate NEOs as small as 300 meters rock. While you are counting the potential for a major impact is still requires a survey down to 24th magni- meteor trails, the Moon rises into the there. A close examination of Earth’s tude (sensitive enough to detect sky. Studying it with binoculars, you history shows that there is a 1 percent objects 16 million times fainter than pick out some of the craters that cover chance in the next century that Earth the feeblest stars that are visible to the the lunar surface—craters caused by meteoroids hitting a surface without a protective atmosphere like Earth’s. It rarely happens, but sometimes these objects do descend through Earth’s atmosphere, impact the surface, and form craters like those seen on the Moon. Though not as numerous as The 19-km-long asteroid 951 Gaspra (above) and the 33-km-long 433 Eros (right) as seen, respectively, by Galileo from a distance of 5,300 km while en route to Jupiter and by the NEAR Shoemaker orbiter from a distance of about 200 km. 22 New Frontiers in Solar System Exploration

Large Synoptic Survey Telescope Guiding Themes Addressed Important Planetary Science Questions Addressed The Origin What hazards do solar system objects present to Earth’s and Evolution biosphere? of Habitable What kinds of objects are in the solar system, and how many are there? Worlds Processes What does the solar system tell us about the development How Planetary and evolution of extrasolar planetary systems, and vice versa? Systems Work several hundred NEOs per night and far deeper than any previous survey, obtain astrometric (positional) meas- but also—and just as importantly—it urements on the much larger (and will add the dimension of time and growing) number of NEOs already cat- thereby open up a new realm of dis- alogued. Precise astrometry is needed covery. By surveying the sky each to determine the orbits of the NEOs month for over a decade, LSST would and to assign a hazard assessment to revolutionize our understanding of each object. Astrometry at monthly various topics in astronomy concern- intervals would ensure against losing ing objects whose brightnesses vary track of these fast-moving objects in on time scales of days to years. A simulation of a design for the Large the months and years after discovery. NEOs, which drift across a largely Synoptic Survey Telescope. This ground- In its most recent decadal survey unchanging sky, are easily identified. based telescope will survey the visible (Astronomy and Astrophysics in the New The LSST could locate 90 percent of all sky once each week. Millennium, National Academy Press, near-Earth objects down to 300 m in Washington, D.C., 2001), the astrono- size, enable computations of their my and astrophysics community sin- orbits, and permit assessment of their Profile gled out the proposed Large Synoptic threat to Earth. In addition, this facili- Survey Telescope (LSST) as one of its ty could be used to discover and track Large Synoptic Survey Telescope highest-priority ground-based instru- objects in the Kuiper Belt, the largely ments. The SSE Survey echoed this unexplored, primordial component of Mission Type: Ground-based Facility finding and named the LSST as the our solar system. Beyond the solar sys- Cost Class: Small solar system exploration community’s tem, it would discover and monitor a top-ranked ground-based facility. wide variety of variable objects, such Priority Measurements: Instruments like the Hubble Space as the optical afterglows of cosmic • Survey the Kuiper Belt. Telescope and the Keck telescopes in gamma-ray bursts. In addition, it • Survey the population of near-Earth Hawaii are designed to study selected, would find approximately 100,000 objects down to 300 km in diameter. localized regions of the sky with very supernovae per year and be useful for high sensitivity. Another type of tele- many other cosmological observations. scope is needed to survey the entire At this time, NASA has no system- naked eye). Images have to be taken sky relatively quickly, so that periodic atic survey capability to discover the every 10 seconds to allow complete maps can be constructed that display population distribution of solar system coverage of the sky in a reasonable how objects change in position and/or bodies. The LSST would enable the amount of time, a necessary capability appearance from week to week. compilation of a systematic inventory that is almost 100 times greater than The LSST is a 6.5-m-effective-diam- of near-Earth objects that is crucial to that of existing survey telescopes. eter, very wide field (~3 degrees) tele- an improved understanding of Earth’s Furthermore, NEOs spend only a frac- scope that will produce a digital map cosmic environment, especially to the tion of each orbit in Earth’s neighbor- of the visible sky every week. For this prediction of future hazards posed to hood where they are most easily seen. type of survey observation, the LSST our species. Many of the targets are as Repeated observations over a decade will be a hundred times more capable yet undiscovered, and construction of would be required to explore the full than the Keck telescopes, the world’s the LSST provides a necessary first step volume of space populated by these largest at present. Not only will LSST toward a rational spacecraft explo- objects. Such a survey would identify carry out an optical survey of the sky ration program for these bodies. 23

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New Frontiers in Solar System Exploration Get This Book
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Over the last four decades, robotic spacecraft have visited nearly every planet, from torrid Mercury to frigid Neptune. The data returned by these Pioneers, Mariners, Vikings, and Voyagers have revolutionized our understanding of the solar system. These achievements rank among the greatest accomplishments of the 20th century. Now, at the opening of the 21st, it is appropriate to ask, where do we go from here?

In 2001, NASA asked the National Academies to study the current state of solar system exploration in the United States and devise a set of scientific priorities for missions in the upcoming decade (2003-2013). After soliciting input from hundreds of scientists around the nation and abroad, the Solar System Exploration Survey produced the discipline's first long-range, community-generated strategy and set of mission priorities: New Frontiers in the Solar System: An Integrated Exploration Strategy. The key mission recommendations made in the report, and the scientific goals from which the recommendations flow, are summarized in this booklet.

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