NASA

The shuttle Endeavour is silhouetted against the light of an orbital sunset in this picture, taken from the International Space Station before a Feb. 9 docking. Click to see a slideshow of 2010's best space images.

Earthlike worlds, otherworldly life on Earth, the fading of the shuttle fleet and the rise of the shuttle's successors made headlines in 2010. So what will 2011 bring?

The past year has been marked by uncertainty over the direction of America's space effort, and the questions will continue into the next year. When 2010 began, NASA expected to be retiring the space shuttle fleet by now. When 2010 ends, the space agency will still have as many as three shuttle flights to go.

The longer term is even fuzzier: Will NASA target a mission to a near-Earth asteroid? To the moons of Mars? Heck, the space agency doesn't yet know with certainty what its spending plan will be for the rest of the current fiscal year — and it's not clear how the political change-over in the House will affect the revised vision for the space effort.

The space effort is more than NASA, however. Some of the year's highlights came from other quarters. For example, there was the extended test of the Pentagon's secret X-37B space plane. There was the first free flight of SpaceShipTwo, which could usher in a long-awaited era of commercial space tourism. There were the maiden flights of SpaceX's Falcon 9 launch vehicle and its Dragon capsule, which could resupply the International Space Station once the shuttles truly retire. There were space successes by other countries, such as China (with its Chang'e 2 moon mission) and Japan (with the return of its Hayabusa asteroid probe and the deployment of its Ikaros solar sail.)

There were also setbacks and strange twists: Japan's Venus probe missed its mark just this month. NASA's Spirit rover fell mute on Mars. And what kind of year would it be without a few rounds of UFO reports, such as the spate of sightings in China, the release of decades-old "X-Files" in Britain and the testimony of military men about strange missile-base incidents?

Every year since 1997, we've reviewed the top space stories of the previous 12 months and looked ahead to the trends to watch in the 12 months to come. It's up to you to choose which story from 2010 and which trend for 2011 should lead the list. To refresh your memory, last year's top story was the LCROSS moon-crashing mission — which, by the way, continued to make news this year. You projected that the top trend would be the impact of newly developed rockets such as SpaceX's Falcon 9 on future spaceflight.

Here's this year's roundup. Please vote for your top story and top trend using the polls included on this page, or cast a write-in vote with your comments below. For a visual recap of the year, including some jaw-dropping imagery from Hubble's 20th year, check out our "Year in Space" slideshow — and please vote for your favorite space picture of 2010 at the end of the slideshow. On Dec. 30, we'll recap the winning choices for top story of 2010, top picture of 2010 and top trend of 2011.

NASA's shifting course: President Barack Obama announces his plan to cancel the Constellation "back-to-the-moon" program and retool the space agency for a longer-term vision that would send astronauts to a near-Earth asteroid by 2025 and perhaps to the moons of Mars by the 2030s. Members of Congress bristle at some elements of Obama's plan, and prominent critics complain that America would be turning back from the final frontier. By the end of the year, policymakers jury-rig a compromise.

Sunrise for private rockets: SpaceX notches two successful flights of its Falcon 9 rocket, and NASA doles out millions of dollars for the development of other private-sector spaceships that could take the shuttle's place. Scaled Composites and Virgin Galactic make headway on their suborbital space venture: SpaceShipTwo flies free at last during unpowered test glides.

Earth-sized worlds on the horizon: Scientists sift through data about distant planets, including a "super-Earth" that could conceivably sustain life as we know it, just 20 light-years away. The readings are so delicate that it's difficult to confirm whether that particular super-Earth actually exists. Nevertheless, preliminary findings from NASA's Kepler planet-hunting probe suggest that there could be millions of planets roughly the size of Earth in the Milky Way galaxy. Such reports buoy hopes that Earthlike environments and even alien life may someday be found.

Alien life, or false dawn? Speaking of alien life, a controversial study suggests that the chemistry of life could be different from what we assume has to be the case. Could atoms of arsenic take the place of phosphorus in the DNA and proteins of exotic bacteria harvested from a salty lake in California? The controversy is still raging as the year draws to a close, but the debate demonstrates that astrobiology is finally coming down to Earth.

UFOs take the spotlight: Investigative journalist Leslie Kean makes a splash with her book "UFOs: Generals, Pilots and Government Officials Go on the Record." Skeptics question the book's assumptions, but Kean holds her ground. The media spotlight follows UFO reports from China as well as from New York and Texas. Meanwhile, a U.N. space official stirs up a discussion over the procedure for dealing with potential revelations about extraterrestrial life.

Cast a write-in vote: You have lots of alternatives to choose from, including the aforementioned X-37B mission, China's space effort and Japan's successes and failures in space. You could also go with the buzz over this year's total solar eclipse, the latest news about Saturn and its moons, or the stunning flyby of Comet Hartley 2. Feel free to let me know what I'm missing in your comments below.

Now for the top trends of 2011:

Farewell to the shuttle fleet: The likeliest schedule calls for Atlantis to take on the final space shuttle flight in late June, bringing the 30-year program to an end. But will NASA be able to stick to that schedule? Will SpaceX and other private-sector providers stick to their schedule as well for developing the spacecraft for resupplying the space station? By the end of the year, will museums really be making plans to exhibit the most complicated flying machines ever built?

All aboard for suborbital rides: Virgin Galactic's billionaire founder, Richard Branson, said last month that commercial space tours would be flown on SpaceShipTwo (a.k.a. the VSS Enterprise) in "about 12 months." I'm doubtful about that timetable, but I'd love to be proven wrong. In any case, the schedule calls for the professional pilots to put new suborbital rocket planes to the test next year — not only SpaceShipTwo, but XCOR's Lynx Mark I as well.

Sunset, sunrise for Mars missions: Will the Spirit rover's seven-year-long mission on Mars officially draw to a close in 2011? Will its twin rover Opportunity make it to the giant Endurance Crater? Will NASA's Curiosity rover be ready for launch as scheduled in the fall? What giant leaps will NASA consider for future missions to the Red Planet?

Rendezvous with an asteroid: The Dawn spacecraft is due to go into orbit around the asteroid Vesta in July and spend a year studying the second-largest body in the asteroid belt. Some astronomers wonder whether Vesta should be considered a dwarf planet, like Ceres (which is Dawn's eventual destination) or Pluto. It really doesn't matter which planetary pigeonhole Vesta is put into — either way, the Dawn mission should be a real eye-opener. 

Exoplanet quest pays off: The next big release of data from the Kepler planet-hunting mission is due in February, and astronomers are already gearing up for big revelations. The findings could confirm earlier suggestions that super-Earths account for a significant proportion of the planets detected in Kepler's survey. Some scientists suggest that super-Earths could be even more hospitable to life than our own planet. What new light will next year's exoplanetary studies shed on the big questions we have about life, the universe and everything? Stay tuned. ...

Cast a write-in vote: I'd love to hear about other out-of-this-world developments that could be on the horizon in 2011. Feel free to speculate — or tell me what I've missed — in your comments below.

More of the year in review:

• The year in science
• The worst tech of 2010
• Top 10 YouTube videos of 2010
• Complete coverage of the year in review

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