NASA

Sometimes, you just can't make it to Friday.

Around 3:30 p.m. EDT this afternoon, NASA's Messenger spacecraft, a $446 million probe that was launched in 2004 to study Mercury's geology and atmosphere, is expected to crash into the planet, ending a successful four-year orbit.

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"Following this last maneuver, we will finally declare the spacecraft out of propellant, as this maneuver will deplete nearly all of our remaining helium gas,” Daniel O’Shaughnessy, a mission systems engineer, said in a NASA press release. “At that point, the spacecraft will no longer be capable of fighting the downward push of the sun's gravity.”

Messenger (which stands for "MErcury Surface, Space ENvironment, GEochemistry, and Ranging") was launched in 2004 and began orbiting Mercury in 2011. It has since circled the planet more than 4,000 times, and sent back more than 270,000 photos and 10 terabytes of data about Mercury's surface, magnetic fields, and atmospheric composition. The probe weighs about 1,000 pounds, and is expected to leave a 50-foot-wide crater when it crash-lands near Mercury's North Pole after running out of fuel.

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Not much was known about Mercury in 2004, when Messenger was launched. Since then, it has discovered lots of important facts about the planet, including the existence of enormous patches of subterranean ice in Mercury's polar regions that could help tell us how water and other organic compounds made it from the outer solar system to Earth. The probe's camera has also produced iconic images like this:

NASA scientists, for their part, seem to be keeping it together emotionally. "While spacecraft operations will end, we are celebrating MESSENGER as more than a successful mission," said John Grunsfeld, associate administrator for the Science Mission Directorate at NASA. “It’s the beginning of a longer journey to analyze the data that reveals all the scientific mysteries of Mercury.”

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If spacecraft snuff film is your thing, you can watch a webcast of the crash at SLOOH. And if not, the Messenger's Twitter account will be capturing the bittersweet action: