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After more than four years orbiting Mercury, the Messenger spacecraft has made a hero’s exit. At 3:26 pm Eastern Time on April 30, the refrigerator-sized space probe finished its final dive to the surface of the planet, creating a new crater on Mercury’s already pockmarked surface.
Under ordinary circumstances, Messenger should’ve crashed weeks ago, but NASA’s scientists found a way to squeeze extra mission time out of the nearly exhausted probe by venting helium out of the craft’s fuel tanks. That allowed Messenger to vault a bit higher in its degrading orbit, adding a little more data to the mountain of information that Messenger has sent, including more than 270,000 images of the surface.
The craft has turned up some surprising finds on our sun’s nearest neighbor. Not least of which was the discovery that, despite the planet reaching temperatures of up to 800 degrees Fahrenheit, Mercury harbors ice in shaded craters. The craft also found traces of Mercury’s past volcanic activity; revealed strange bright, bluish craters called “hallows”; and found traces of volatile chemicals including potassium, sulfur, chlorine, and sodium—probably brought by asteroids and comets—on its surface.
Messenger hit Mercury’s surface at around 8,750 miles per hour and created a crater about 50 feet wide, according to one of NASA’s initial reports.
Messenger is hardly the first space probe to take a swan dive. The Jupiter orbiter Galileo plunged to its death in 2003, crushed by the force of the Jovian atmosphere. Galileo was sent on a collision course with Jupiter so it wouldn’t potentially contaminate the moon Europa, which seems to have a vast layer of water beneath its icy crust. But before it was squished, Galileo’s final dive “allowed us to get much closer to Jupiter with our science instruments than we had before,” NASA scientist Torrence Johnson told CNN at the time.
In 2012, Ebb and Flow, twin space probes that were measuring the moon’s gravity field, were sent on a deliberate crash course near the end of their mission to be sure they wouldn’t strike any important historical landmarks on the moon, like the Apollo landing sites. And in 2014, the LADEE (Lunar Atmosphere and Dust Environment Explorer) was similarly guided to a spectacular end on the dark side of the moon, far away from Neil Armstrong’s footprints.
Not all impacts are Viking funerals; some crashes are explicitly part of the mission from the get-go. The Deep Impact probe sent a piece of itself—an impactor that was mostly made up of a 220-pound lump of copper—smashing into the comet Tempel 1. The rest of the spacecraft kept flying, its instruments trained on the comet. The crash made a crater thought to be more than 300 feet wide and nearly 100 feet deep. One of the interesting results from the crash was that scientists figured out that Tempel 1 was spongier in structure than expected, with no dense icy core at its center.
Similarly, when Messenger bites the dust, it might unveil some interesting tidbits about what lies just beneath Mercury’s surface. But even if we learn nothing from its end, Messenger’s life of discovery was one any space probe’s team could be proud of.
Image: NASA
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