The Year in Science: Space Exploration

NASA's latest manned rocket, Saturn's moons, comet smashing, and more.


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NASA's New Post-Shuttle Rocket Looks Like a Blast From the Past

The July 26 launch of the space shuttle Discovery carried a clear message about the future of NASA—just not the message the agency intended. In the two-and-a-half years since a piece of foam had broken free from the external fuel tank of the shuttle Columbia, NASA had redesigned the tank, reviewed its safety procedures, and developed new ways to apply foam. The Discovery launch demonstrated the intractability of the problem: Despite the fixes, the tank once again shed chunks of foam. Although the shuttle landed unharmed, the agency again grounded its fleet, making clear the need for a better way to get astronauts into space.

Two months later, NASA administrator Michael Griffin unveiled the agency's Crew Exploration Vehicle, which he described as "Apollo on steroids." It will take over soon after the shuttle is retired in 2010, and it will transport humans back to the moon by 2018 and later to Mars. The crew will travel in a capsule placed at the leading edge of a rocket, as with the Apollo missions, rather than strapped to the rocket's side, as with the shuttle. "Apollo had debris galore coming off on launch," says NASA spokesman Allard Beutel. "But nobody worried because the crew was on top." Although the new rocket will use engines derived from the shuttle, the capsule will be a fresh design three times the size of the Apollo capsule—large enough to put four astronauts on the moon.

After showing the designs for the Crew Exploration Vehicle, Griffin admitted that, in retrospect, the shuttle program "was not the right path" for NASA. Nevertheless, the shuttle can do some things that its replacement cannot. In particular, the new vehicle is not designed to carry heavy equipment, such as laboratory modules, to the International Space Station. NASA hopes to resume shuttle flights by May and to keep them going long enough to finish building the space station, using no more than 18 launches. Griffin is contemplating a 19th launch to service the Hubble Space Telescope. Without that mission, the Hubble's batteries could fail as early as 2007 or 2008. —David Epstein

Yeah, the Rings Are Great, but It's Saturn's Moons That Stand Out

Saturn's bizarre satellites proved to be the surprise highlight of the $3 billion Cassini mission this year.

Scientists have lavished the most attention on Saturn's largest moon, Titan, a 3,200-mile-wide world covered with a thick, hazy atmosphere. Huygens, a companion probe to Cassini, landed there last January, snapping astonishing photos of riverbeds and shorelines on the way down. "What we found is that sometime in the past or present there was liquid flowing on the surface," says Carolyn Porco, head of Cassini's imaging team at the Space Science Institute in Boulder. Not liquid water—Titan is far too cold—but liquid methane, which is similar to the natural gas found in wells on Earth. "Methane is to Titan what water is to Earth," Porco says. Subsequent images and radar maps from Cassini uncovered wind-blown features, tectonic faults, and perhaps methane-spewing volcanoes.

More startling, Cassini found that Enceladus, just one-tenth the size of Titan, is also active, venting water vapor and a spray of fine icy particles from cracks at its south pole. For unknown reasons, parts of the south pole, at –200 degrees Fahrenheit, are 125 degrees warmer than the rest of the moon. Enceladus's venting hints at the presence of warmer regions deep inside—an environment that could support the chemistry of life, Porco says: "It's another place in the solar system that's warm and wet." 

Other Cassini images show an improbable 12-mile-high ridge cutting across Iapetus, Saturn's third-largest moon. Tiny Hyperion, about 100 miles wide, looks like a giant sponge, with much of its insides consisting of empty space; crater-scarred Phoebe seems to be an interloper from the outer solar system. More is yet to come: Cassini is scheduled to make 55 more loops around the planet over the next two and a half years.  —Elise Kleeman

Deep Impact Exposes Comet Secrets

In July NASA's Deep Impact spacecraft smashed an 800-pound probe into comet Tempel 1, blasting a house-size hole and creating a spectacular shower of cosmic debris. Almost immediately, data produced by the mission cast doubt on the widespread belief that comets are solid balls of ice and rock. It also forced scientists to rethink their ideas about how comets transported water and organic material around the newborn solar system 4.6 billion years ago.

More than 60 telescopes on Earth and in space watched the event, many of them also monitoring the comet in the weeks before and after the impact. "No comet has ever been studied quite as intensively as Tempel 1," says Deep Impact's lead scientist, astronomer Mike A'Hearn of the University of Maryland. The observations showed that the comet is not hard and icy but soft and weakly held together, "comparable to the best powder snow you can imagine for skiing." Its surface shattered to a talcum powder–like dust at the impact site, and debris from deep within contained more organic material than expected. Planetary scientists believe that the early Earth was bombarded with comets; the vast quantities of carbon-rich compounds released by those impacts could have influenced the origin of life.

Deep Impact's detailed pictures of the comet's surface also confounded expectations. Some areas were speckled with craters, but large regions looked inexplicably flat and smooth. Meanwhile, other researchers have continued to watch Tempel 1 in the following months as it returned to its normal state. They found that jets of gas and dust erupt from the surface frequently, about once a week. "This was something of a surprise," A'Hearn says. "Probably all comets do it. We just had never realized how often they do it, because nobody had ever looked hard enough."  —Elise Kleeman

NASA Probe Discovers Rolling Rocks, Gullies, Shifting Sands on Mars

Sightings of shifting sand dunes, rolling boulders, and a dwindling polar ice cap in the past year demonstrate that the Red Planet is a far more dynamic world than scientists suspected.

NASA's orbiting Mars Global Surveyor revealed fresh gullies as long as three football fields on a dune west of the Hellas Basin. The same slope was smooth and unblemished in 2002. Scientists suspect that carbon dioxide trapped beneath the surface during winter vaporized when temperatures rose, releasing gas and causing sand to pour down the dune's face. The probe also snapped photos of boulders that had tumbled down a five-mile-wide crater, gouging shallow troughs not seen a year before. Possible causes include wind and seismic activity, although Mars's atmosphere is one-hundredth as dense as Earth's, and researchers have not yet found reliable evidence of Marsquakes. Meanwhile, carbon dioxide ice at the south pole has dwindled for three consecutive summers, suggesting long-term climate change is under way.

None of these sightings would be possible if not for the extraordinary durability of the Mars Global Surveyor, which has been orbiting the planet since 1997. Meanwhile, the Opportunity and Spirit rovers, which landed in January 2004, have kept rolling long past their predicted shelf life of 90 days. In September Spirit completed a 14-month climb up Husband Hill in Gusev Crater and sent back a panorama of weathered rocks containing details of past Mars environments. "Everyone is amazed at the longevity, excited about the results, and perhaps a little tired," says Michael Meyer, chief scientist of NASA's Mars Exploration Program.

Next up: The Mars Reconnaissance Orbiter, launched last August 12, enters Mars orbit in March. Its radar sounder will seek buried water, while its camera will map features as small as a coffee table, aiding the search for potential habitats of past or present life. "Stay tuned," says Meyer. —Jack Kelley

Voyagers Survive Bean Counters and Head Toward the Stars

Eric Christian, a space scientist at NASA's headquarters in Washington, D.C., began studying data from the twin Voyager probes while working on his Ph.D. thesis nearly 20 years ago. When he heard that NASA might shut down mission support for the two spacecraft in October because of budget cuts, his heart sank. Fortunately, he was not alone: Outcry from scientists and the media helped restore the roughly $4.5 million per year needed to continue the Voyagers' unique explorations of the outer fringe of the solar system.

Voyager 1 and Voyager 2 were launched in 1977 to take a grand tour of the outer planets—Jupiter, Saturn, Uranus, and Neptune. In 1990 the probes took on a new duty: moving beyond the planets and into interstellar space. In September scientists confirmed that Voyager 1 is succeeding. Instrument readings indicate that it has crossed the termination shock, the region where the solar wind—particles blowing outward from the sun—plows into the extremely thin material between the stars. Voyager 1 is now about 9 billion miles from the sun, making it the most distant man-made object in the universe.

Data readings seem to show that the solar wind moves more slowly than expected at the edge of the solar system. Voyager 1 also found a peculiar deficit of high-energy particles known as anomalous cosmic rays. The finding challenges the widely accepted idea that cosmic rays are interstellar particles that receive an energetic kick at the termination shock, says Matthew Hill, a physicist now at Johns Hopkins University. "The interstellar composition is not what we thought it was."

The two probes could continue to function until at least 2020, by which time Voyager 1 should be completely beyond our solar system and Voyager 2's healthier solar-wind instrument will make better measurements of the speed of the distant solar wind. Ed Stone of Caltech, chief scientist for the Voyager project, is thrilled that the spacecraft will be allowed to continue blazing a trail to the stars: "Every time the Voyagers get somewhere new, we find something unexpected." —David Epstein

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