It’s a mission that’s been more than ten years in the making, but later tonight, at approximately 11:35pm PST, the European Space Agency’s Rosetta space probe will reach the end of its four-billion-mile journey and attempt to land on a comet. If it succeeds, it will be the first spacecraft in history to do so.

Back in early August, the probe arrived at the orbit of the comet 67P/Churyumov-Gerasimenko, and has been studying it for the past couple months as it prepares to land. The ESA estimates that the rock is roughly 20 trillion pounds, and 2.5 miles wide at its broadest point. In terms of shape, observers have likened 67P to a misshapen dumbbell or rubber duck. Up until recently, the ESA couldn’t get a clear enough view of the oddly-shaped rock to figure out where to land, but now that Rosetta is up close and personal, they’ve scoped out a good spot.

Just before midnight tonight, Rosetta will release a 220-pound lander craft called Philae, which will begin a slow, 13-mile descent to a relatively flat section located near the “duck’s” head. Once it reaches the comet’s surface, Philae will blast a harpoon into the rock, anchoring itself and preventing the craft from drifting away. After it’s secured to the rock, the craft will deploy a small drill to collect samples and analyze the chemical composition of the comet’s surface.

All the data Philae collects during this process will be relayed back to Rosetta via radio signals, which will then be bounced back to Earth, taking about 6 hours to reach us even at the speed of light. The lander craft will continue to gather data until March, when the comet gets so close to the sun that the ESA predicts Philae’s instruments will stop working. It could happen sooner, too. Dust might accumulate on Philae’s solar panels, and choke out its power supply.

But that’s not likely to happen for a few more months — assuming the landing goes as planned. In the meantime, you can check out the ESA’s livestream of the Rosetta mission up above.

Images: ESA