A spacecraft photographs itself approaching a comet in deep space

The European Space Agency's Rosetta spacecraft approaches its cometary quarry in this composite image captured on October 7, 2014. Credit: ESA/Rosetta/Philae/CIVA

From humanity's first, flawed foray to the surface of a comet to the celebrated discovery of (and less celebrated skepticism about) primordial gravitational waves, 2014 has brought some historic successes and failures in space science and physics. Here are my selections for the top ten stories from this year, with a look forward at what might happen next.

1. Philae lands on a comet

The biggest story beyond Earth's atmosphere was unquestionably the spectacular November climax to the European Space Agency's decade-long Rosetta mission, when the Philae lander touched down on comet 67P/Churyumov-Gerasimenko. Alas, Philae didn't stick its landing — instead, it bounced into a shadowy crevice where, starved of sunlight, its solar-powered batteries ran out of juice. But before it went into hibernation, the lander managed to pull off some impressive science. With a bit of luck and ingenuity, mission scientists may coax Philae back to life next year, as the comet swings closer to the sun.

2. Curiosity finds methane on Mars

NASA's Curiosity rover, tasked with searching for signs of past habitability and life on the Red Planet, may instead have found something far more interesting: evidence for present, extant life. The rover has periodically detected mysterious spikes of methane, also known as natural gas, wafting through the thin Martian air, scientists announced in December. The gas can be produced abiotically, but on Earth at least, methane is mostly made by life – specifically a class of bacteria appropriately called “methanogens” — which suggests that Mars may host methane-belching microbes. It’s too soon to say for sure, but Curiosity and future robotic explorers, such as Europe’s ExoMars mission and NASA’s Mars 2020 rover, will work on solving the mystery.

3. Cosmologists glimpse gravitational waves from the big bang – or just some galactic dust

In March, researchers from the BICEP2 experiment said they had seen signs of gravitational waves in the oldest light in the universe, the cosmic microwave background (CMB). The announcement set people to speculating about future Nobel Prizes, because the observations would provide crucial evidence for the cosmological theory of “inflation,” which posits that the universe experienced a huge increase in its expansion rate shortly after the big bang. Early inflation of the universe, if true, would have created gravitational waves that imprinted curlicue polarization patterns on the CMB — the very patterns that the BICEP2 team saw. Subsequent analyses, however, were somewhat deflating: they suggested that BICEP2’s observed polarization patterns might only be due to the cosmic microwave background scattering off clumps of simple interstellar dust. The story is far from over: next-generation instruments may deliver more data for or against the BICEP2 result as soon as next year.

4. National Ignition Facility achieves a milestone in fusion power

The quest for practical, utility-scale power from thermonuclear fusion received a modest boost in early 2014, when scientists using the National Ignition Facility (NIF) in California announced they had successfully released slightly more energy from a fusing fuel pellet than the pellet had absorbed from laser pulses used to initiate the reaction. Though this was an impressive world first, the achievement still falls short of NIF’s primary purpose of achieving “ignition,” in which a fusion reaction releases much greater amounts of energy and can become self-sustaining. In February 2009, when the $3.5 billion facility’s array of 192 lasers was first powered up, ignition was slated for October 2012, but slipped deadlines and budget cuts in years since have cast uncertainty over when or if NIF will achieve its primary goal.

5. NASA's Orion spacecraft flies high

The first test flight of Orion, NASA’s versatile spacecraft meant to take astronauts to the Moon, asteroids, and eventually to Mars, was a big success. Launched in December on a mighty Delta IV Heavy rocket, the Orion capsule orbited the Earth twice, reaching a peak altitude of 5,800 kilometers — the highest any human-rated spacecraft has ventured since the end of the Apollo missions in the early 1970s. Such heights were necessary to test the mettle of Orion’s electronics against the radiation found in the Earth-circling Van Allen belts, and to prove the resilience of Orion’s heat shield, which must withstand the extreme temperatures of reentering the Earth’s atmosphere when returning from deep-space destinations.

6. Kepler doubles number of known exoplanets in a single day

NASA’s planet-hunting space telescope, Kepler, ended its primary mission in May 2013, but discoveries keep flooding in. On February 26, researchers announced they had found 715 new exoplanets by combing the archives of data from Kepler’s first two years of observations, almost doubling the total number of confirmed worlds beyond our solar system. Most of the new planets are smaller than Neptune, and four are less than 2.5 times the size of Earth, which suggests astronomers are on the cusp of finding Earth-sized worlds in abundance. Kepler’s extended mission, dubbed K2, recently found its first planet, and several new space telescopes, including NASA’s Transiting Exoplanet Survey Satellite and the European Space Agency’s PLATO mission, will continue the search in coming years.

7. Disaster strikes private spaceflight companies

Two major accidents within the span of a single week cast a shadow over the “New Space” industry, a collection of private companies hoping to reinvigorate spaceflight through innovation and lower costs. In late October, an Antares rocket operated with no crew by Orbital Sciences Corp., exploded seconds after lifting off on a resupply mission to the International Space Station. Days later, Virgin Galactic’s SpaceShipTwo rocket plane broke apart in midair during a test flight, killing one pilot and severely injuring another. Investigations of both accidents are ongoing. Although both companies seem likely to eventually recover, the accidents underscore how risky space travel still is.

8. The search for dark matter heats up

In 2014, three of the world’s largest, most ambitious dark-matter detection experiments moved forward with plans for major upgrades, raising the possibility that at long last we might soon learn what exactly the elusive stuff actually is. For the moment, researchers can’t say much more than that dark matter constitutes most matter in the universe and makes its presence known almost solely through the force of gravity. Once in a while, scientists might be able to observe dark matter particles colliding with particles of normal matter, or witness a pair of dark matter particles interacting with and annihilating each other. With funding from the U.S. Department of Energy and the National Science Foundation, the Super Cryogenic Dark Matter Search-SNOLAB (SuperCDMS) and LZ Dark Matter Experiment (LZ) will each search for dark matter candidates called weakly interacting massive particles (WIMPs). Another experiment, the Axion Dark Matter eXperiment (ADMX-Gen2), looks for axions — dark-matter candidates that are even more weakly interacting than WIMPs. The Alpha Magnetic Spectrometer on the International Space Station, and other experiments, are also pushing forward with further observations. It could be that, as with all past generations of dark-matter detectors, these latest projects find nothing at all. Even so, those null results would still bring us closer to deciphering dark matter’s cosmological mystery.

9. Cassini deepens our view of Saturn's eerily Earth-like moon, Titan

Since arriving in Saturn’s orbit in 2004, the Cassini spacecraft has spent much of its time investigating Saturn’s largest moon, Titan, a familiar, yet alien, world. Like Earth, Titan has land, seas and rivers beneath a thick nitrogen-rich atmosphere. But Titan is far colder than Earth — so cold that ice there behaves more like rock. Titan’s seas and rivers are filled with liquid hydrocarbons, substances such as methane that are gaseous at Earth temperatures. Like Earth, Titan has a cycle of seasons, though Titan’s cycle lasts more than seven Earth years. The moon’s northern hemisphere began warming in 2009 as it tilted toward the sun. Titan’s weather has been slowly and steadily changing with the seasonal shift, heating up its northerly hydrocarbon seas and causing waves, which researchers have spied periodically through 2014 using Cassini’s radar. This year, Cassini’s radar also revealed some of those seas to be as deep as 200 meters and composed mostly of methane, rather than ethane as had previously been thought. At the moon’s south pole, Cassini has studied a giant high-altitude cloud of hydrogen cyanide, linking its formation to the rapid cooling caused by the changing seasons. Again and again, each new Cassini finding shows Titan to be a dynamic, complex place, despite its cryogenic climate – potentially dynamic and complex enough to support some form of alien life. Cassini’s studies will cease in 2017, when it plunges into Saturn’s atmosphere in a deliberate effort to avoid contaminating any potential Titanian biosphere.

10. ALMA snaps a baby photo of an infant planetary system

From its perch high in the arid mountains of northern Chile, the Atacama Large Millimeter/submillimeter Array (ALMA) is poised to unveil new wonders from across the cosmos with its high-resolution radio eyes. In November, astronomers released a new ALMA image demonstrating its unprecedented capabilities, a jaw-dropping view of the disk around the young Sun-like star, HL Tau, some 450 light-years distant. The high-resolution image, equivalent to a penny from 100 kilometers, reveals gaps and rings in the gas and dust surrounding the star, features produced by planets sweeping up material as they form. Future ALMA observations could boost resolutions even higher, potentially revealing the planets themselves around this and other young stars.