Could you land on a comet? Normally, the force of gravity holds a lander to the surface of a larger body, like a planet or a moon. The less mass an object has, the less gravity pulls you toward it. Comets are small. Gravity won’t do you a lot of good, so you would need to hang on tight.
That’s what Philae is doing. The European Space Agency (ESA) sent a spacecraft named Rosetta to Comet 67P/Churyumov–Gerasimenko, and Rosetta carried a dishwasher-sized probe called Philae, which was to land on the comet. The comet is about the size of a mountain, which may seem big, but think how small a mountain is in comparison to a planet! The Philae lander had to come equipped with screws in its feet and harpoons to grasp the surface.
Philae detached from Rosetta early this morning (09:03 GMT, 02:03 Arizona time) and began its descent. Curiosity had seven minutes of terror landing on Mars, but Philae took seven hours from separation to landing. At 16:03 GMT, ESA heard from the little lander. Philae had successfully touched down! But remember those harpoons? They didn’t work. Philae is clinging on by the screws in its feet, but it’s there.
Philae’s view of the comet. Courtesy ESA.
Philae will photograph and analyze the comet for the next two and a half days. If it gets enough sunlight for power, it can keep going for an “extended phase” lasting until March 2015—four whole months of comet science! After that, the comet will be closer to the sun and Philae will probably be too hot to work. Comet 67P/Churyumov-Gerasimenko will also heat up as it gets closer to the sun, so we might be able to see it active, with ices sublimating (turning from solid to gas) and creating the tails of gas and dust comets are famous for. Maybe the most exciting reasons to study a comet up close are that we get to see way, way back in history, and we get to learn about the far, far off outer solar system. Here’s wishing Philae just the right amount of sun.
Is landing on a comet even possible? Yes, but it’s tricky. Hang on tight, Philae!
Rosetta main website
Timeline, instruments, and and landing details from Emily Lakdawalla
Bad Astronomy’s coverage, part one and part two