The first spacecraft ever to orbit Mercury is about to become the first spacecraft to smash into the planet. NASA says the Messenger probe will conclude its hugely successful mission when it crashes at 8,750mph into the side of the planet facing the sun today at 3:26pm EDT. The probe has been in orbit around Mercury for four years—or more than 16 Mercury years—and NASA says a final maneuver exhausted the last of its helium gas, leaving it incapable of "fighting the downward push of the sun's gravity." It will serve NASA until the end: The spacecraft has been taking low-altitude photos in its final days, sending back images of craters much like the one its crash will create today, Ars Technica reports.
"Messenger has been an amazing mission. The only previous Mercury mission, Mariner 10, flew past the planet three times in 1974 and 1975, giving us only an incomplete view," a professor of planetary sciences tells the Guardian. "Messenger revealed the whole globe in detail." The trove of information Messenger has sent back, which includes signs of recent volcanic eruptions and of possible ice at the poles, shows that Mercury is a "misfit planet that seems not to belong where we now find it," the professor says. "Biggest mystery to be solved next time," the spacecraft's Twitter feed said last week. "Questions would probably be best answered by a lander. What is that dark material at the poles?"