Summer/Fall 2002 Vol. 2 No. 2
One might expect a place that is dark, frigid, and dauntingly remote to have a tough time attracting visitors. And so far that's been Pluto's fate: It is the only planet in the solar system that has never been visited by a robotic probe. Now a new National Research Council report says Pluto and its neighborhood are too scientifically compelling for NASA to wait any longer to send a mission there.
It's not just the lure of being the last unexplored planet in the solar system that makes Pluto so intriguing to scientists. Perhaps most interesting about the distant planet is that it's the largest known member of the Kuiper Belt, a field of icy, rocky objects that are thought to have changed little since they first condensed some 4.6 billion years ago.
"Data collected on the Kuiper Belt over the last decade suggest that it's made up of innumerable objects, and that they have a bizarre variety of properties," said Michael Belton, president, Belton Space Exploration Initiatives, Tucson, Ariz., and chair of the committee that wrote the report. "A mission would let us study some of those properties more closely." This examination may help scientists understand how the solar system began, because the giant planets are believed to have been created from objects like those in the Kuiper Belt. A mission might also provide clues to the origin of life on Earth, the report says, which may have started with organic material delivered by a comet from the region billions of years ago.
A mission to Pluto and the Kuiper Belt has been on and off NASA's agenda for several years. The Bush administration eliminated funding for the mission in NASA's 2003 budget, citing the high cost involved. But the report says that a trip to the Kuiper Belt could gather enough data -- possibly paradigm-shifting information -- to justify its price tag, which is midsize by space-exploration standards.
Another reason not to delay the mission is that the time window for studying Pluto is closing. The planet is beginning the leg of its 248-year solar orbit that is farthest from the sun; more of the surface will be shadowed and the atmosphere will freeze, making study impossible. A thaw -- and another chance to survey the brightest object in the murky Kuiper Belt -- won't happen again for more than a century.
The report makes several recommendations for NASA's space exploration agenda over the next decade, prioritizing missions within different size classes -- including large missions, which NASA has shied away from in recent years. But giving up larger missions would be a mistake, the committee believes. "For the scientific health of the space program you need a major mission from time to time," said Belton. "They're costly, but they can help us achieve a breadth of knowledge that smaller missions can't."
The next large mission should be sent to Jupiter's moon Europa, the report says. The satellite is thought to have an ocean under its icy crust -- which makes it, with Mars, the best place beyond Earth to search for life. The mission would confirm the presence of the ocean, study its qualities, and try to determine whether it does in fact harbor living organisms.
Important research can be done from the ground as well, the report notes, urging NASA to partner with the National Science Foundation to build a large-aperture survey telescope, which could survey the faintest objects in the entire northern sky every week. In addition to aiding the study of distant Kuiper Belt objects, the telescope would offer a very concrete benefit: the ability to better detect and assess the risk posed by small asteroids and comets that most frequently collide with Earth. --Sara Frueh
New Frontiers in the Solar System: An Integrated Exploration Strategy. Solar System Exploration Survey Steering Committee, Space Studies Board, Division on Engineering and Physical Sciences (2002, approx. 457 pp.; ISBN 0-309-08495-4; available from National Academies Press, tel. 1-800-624-6242; $44.95 plus $4.50 shipping for single copies).
The panel was chaired by Michael S. Belton, president, Belton Space Exploration Initiatives. The study was funded by NASA.