80. from Vermin to Destination: a Mission to an Asteroid
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© 2012, Astronomical Society of the Pacific No. 80 • Spring 2012 • www.astrosociety.org/uitc 390 Ashton Avenue, San Francisco, CA 94112 From Vermin to Destination: A Mission to an Asteroid by Anna Spitz (Lunar and Planetary Laboratory at the University of Arizona, Tucson, Arizona) Why go to an Asteroid? What’s in an Acronym? Long ago astronomers used to call asteroids “ver- It Reveals the Scientific Goals of the Mission! min of the skies.” These small rocky bodies “got in the way” of “important” objects of study. But now O – Origins study earliest materi- asteroids are one of the hottest topics of interest for als to learn about researchers, students, and policy makers. They are origins of the Solar destinations, remnants of earliest materials, sources System and of life for precious minerals, possible threats, and even targets for human colonization. No longer simply S I – Spectral compare to telescope thought of as fragments or pieces of a failed planet, Interpretation observations and they are fascinating objects in their own right and meteorite analyses can hold the clues to our past as well as our future. R I – Resource identify useful metals The next big step in understanding asteroids is Identification and materials NASA’s, OSIRIS-REx mission, which will explore one of these primitive objects and return a sample S – Security more fully charac- to Earth. terize the orbit to Scientists study asteroids through telescopic understand behavior observations and by analyzing meteorites, rocks and trajectory from space. Observations through telescopes and laboratory analyses reveal much information, but The OSIRIS-REx spacecraft will launch in 2016, spend 505 days at R – Regolith examine surface rock traveling to an asteroid and returning a sample to 1999 RQ36 and return a sample of the asteroid to Earth In 2023. Ex – Explorer composition and Earth will furnish scientists with opportunities to distribution on the analyze an unaltered sample and directly link the their (gloved) hands some of the oldest material asteroid source with the sample. Researchers will hold in in the Solar System. In fact, when the OSIRIS-REx Universe in the Classroom No. 80 • Spring 2012 Page 1 asteroid sample return mission is complete (launch Now they reside not only in distinct areas such as in 2016 and sample return in 2023) future scientists the main asteroid belt (between Mars and Jupiter), will use instruments and techniques not yet devel- the Kuiper Belt (beyond the orbit of Neptune) oped to unlock secrets about the truly fundamental and the Oort Cloud (at about ¼ of the distance to building blocks of our Solar System and provide the nearest star), but travel in other orbits, some clues to origins of life on our planet. of which cross Earth’s path. The Solar System is a Visiting an asteroid that crosses the Earth’s orbit much messier place that we imagined even just a will also give researchers a chance to learn more few years ago. about the orbits of potentially hazardous objects. Asteroids come in many varieties: some have The OSIRIS-REx mission’s rendezvous with an as- remained relatively untouched since they coalesced, teroid having a relatively high potential for an Earth some have melted or been disrupted. Scientists have impact late in the 22nd century will help scientists defined their characteristics using telescopic obser- better understand the factors affecting asteroid vations and analyzing meteorites. Most asteroids orbits and help predict their future trajectories. are small and irregularly shaped — think “potato.” Robotic missions such as the OSIRIS-REx asteroid sample return mission are the precursor News from Telescopic Observations to human missions to asteroids. The journey, the Using telescopes, ground-based observers concen- information obtained during rendezvous, and the trate on finding asteroids, examining light curves, Ground-based radar observations in 1999 and 2005 revealed the shape and rotation state of 1999 RQ36. Credit: Arecibo Observatory materials returned to Earth will all provide data to and taking spectra. Several large surveys of small and Goldstone Planetary Radar System. evaluate asteroids as stepping stones to even more bodies, most notably the Catalina Sky Survey and distant destinations or as “filling stations” with pre- LINEAR, have discovered over 500,000 asteroids cious materials such as water and metals. in the main belt and over 8,000 near-Earth ob- jects (NEOs). [To see a remarkable video by Scott What Do We Know About Asteroids? Manley that shows the accelerating pace of discov- Asteroids are the most direct remnants of the origi- ery between 1980–2010, go to http://www.youtube. nal building blocks that formed the planets of our com/watch?v=S_d-gs0WoUw.] Solar System and are relatively pristine samples of Scientists use a variety of observations to study the initial conditions in the solar nebula 4.6 billion asteroids: years ago. They are fundamental to our understand- • Optical observations can estimate the shape, ing of planet formation and may provide important rotation period, orientation of the rotation clues about the origin of life here on the Earth. axis, and whether the object is solid or a rub- The early Solar System was a chaotic place. ble pile (a collection of smaller rocks loosely Planets and planetesimals — small rocky fragments held together by gravity). — may have collided and shifted positions creating • Observers use radio observations to infer reservoirs of small bodies, asteroids and comets. composition. Radio waves react differently Three asteroids (433 Eros, 21 Lutetia and 25143 Itokawa) visited by The collisions and gravitational interactions over spacecraft demonstrate the variety of appearance in asteroids. to different materials: rock does not look like 4.6 billion years moved these small bodies around. Credit: NASA, ESA, and ISAS/JAXA. metal. Astronomers on Earth can also bounce Universe in the Classroom No. 80 • Spring 2012 Page 2 a radio signal off of an asteroid to get shape the Solar System and life: information and to refine the orbit. • How did the Solar System form? • Astronomers using both orbiting and ground- • What kinds of materials exist in the Solar based telescopes employ infrared spectroscopy System? to tease out the compositions of asteroids. • What was the source of organic materials that led to the origin of life? News from Meteorites • Where did Earth’s water come from? The rocks that fall to Earth from space, meteor- • Are asteroids bringers of life or death — or ites, provide abundant examples of the variety of both? materials in our Solar System. Scientists classify In the last decade several robotic spacecraft have meteorites based on composition, mineralogy, and visited asteroids, including NASA’s Near Earth age. They conclude that these rocks represent parts Asteroid Rendezvous (NEAR)-Shoemaker mission of asteroids originally from the area between Mars to Eros, NASA’s Dawn mission to Vesta and Ceres, and Jupiter but through orbital perturbations and and Japan’s Hayabusa mission to 25143 Itokawa, an collisions were fragmented and thrown into orbits S-type (stony) asteroid Hayabusa collected about which intersect with Earth. Scientists can make connections when they A comparison of reflectance spectra of asteroid and meteorite Completed Missions to Small Bodies match meteorite spectra to asteroid spectra: they types. After: “Classifying and Modeling NEO Material Properties and infer compositional similarity based on similar Interactions”, John L. Remo, in Hazards due to Comets & Asteroids Cassini-Huygens: mission to Saturnian sys- (1994, T. Gehrels, ed., The University of Arizona Press, 1300 p.), p. 561. features exhibited in the spectra. But unless they tem with fly-by of asteroid 2685 Masursky observe an object prior to its fall or go to an object Dawn: mission to asteroids 4 Vesta and 1 and return a sample, making an unambiguous con- Ceres nection is hard. more about NEOs. In 2011, asteroid 2055 YU55 The only time that people observed an NEO passed within the Moon’s orbit, just 324,900 kilo- Deep Space 1: mission to asteroid 9969 in orbit, watched it fall to Earth, and collected its meters (201,900 miles) from Earth. Radar and opti- Braille fragments was in October 2008. Richard Kowalski cal observations, revealed puzzling surface features. Galileo: mission to Jovian system with fly-by of the Catalina Sky Survey discovered 2008 TC3. Scientists measured the albedo (reflectivity) of this of asteroids 951 Gaspra and 243 Ida Calculations quickly revealed that it would enter C-type (carbonaceous or carbon-rich) asteroid and Hayabusa: asteroid sample return from the Earth’s atmosphere just 19 hours later. The assessed the composition. The OSIRIS-REx mission 25143 Itokawa bolide exploded above Sudan’s desert and a few scientists were quite excited to use these data to NEAR-Shoemaker: near-Earth asteroid ren- months later, searchers recovered over 10 kilograms inform their modeling and planning for what they dezvous mission to 433 Eros (23 pounds) of the object, now a meteorite called might find when they reach their target asteroid. Rosetta: mission to comet 67P/Churyumov– Almahata Sitta. Gerasimenko with fly-by of asteroid 21 Lutetia With 8,000 known NEOs, and tens of thou- What Can a Mission to an Asteroid Tell Us? sands still undiscovered, it isn’t difficult to see why Traveling to an asteroid and bringing back a sample Stardust: mission to 5535 Anne Frank and astronomers observe close fly-bys fairly frequently. gives us material to inspect and understand so collect samples from comet Wild 2 Earth fly-bys can offer terrific opportunities to learn scientists can examine fundamental questions about Universe in the Classroom No. 80 • Spring 2012 Page 3 1,500 microscopic grains (mostly 10–100 microm- of the original components of the terrestrial planets. eters) and returned them to Earth. Dawn is orbiting Scientists link them with carbonaceous chondrites, Vesta now and will depart for Ceres in July 2012.