Your Guide to the Year in Science: 2008

Other Worlds Revealed

This year of planetary exploration will start hot. This month, after a 3.5-year journey, NASA's Messengerspacecraft will make the first of three flybys of Mercury, the closest planet to the sun and the least-explored rocky planet in the solar system. After the third pass, Messengerwill settle in orbit around the planet in 2011. The feat requires a huge amount of energy, careful trajectory planning, and strong radiation and temperature shielding. And once Messengerarrives, scientists will have much to explore. One critical puzzle: Why is diminutive Mercury made of the densest material in the solar system? The answer should shed light on how the rest of the solar system formed and evolved.

Speaking of "planet" and "evolved," another really big question about the solar system comes to mind-was there, or is there now, life on Mars? The Phoenix lander, set to touch down in the ice-rich Martian arctic this May, could provide clues. Phoenix will use its robotic arm to dig into the topsoil and ice and collect ground samples for onboard analysis. Scientists hope it can resolve a years-old controversy about the presence (or absence) of Martian life. In the late 1970s, the two Viking landers failed to detect any signs of life on Mars. But when, a quarter century later, scientists used duplicates of the Viking's detectors to search for life in the dry valleys of Antarctica and Chile's Atacama Desert-regions on Earth where we know life exists-the detectors failed to find it. Were the Viking landers blind to the presence of life on Mars? Phoenix could find out.

The search is also on for far-flung Earth-like planets. This year, scientists anticipate that the French space agency's Corot satellite-the first space telescope dedicated to planet-hunting-will turn up many of the 250 planets they're hoping to find, including dozens of Earth-like worlds. In addition, the Canary Islands' Gran Telescopio Canarias will begin studying the disks of dust swirling around distant stars for evidence of new planetary systems.-Melinda Wenner

Turn the page to find out just how many of yesterday's predictions have come true.