Danny Boyle’s science fiction movie Sunshine features a spaceship design I found particularly iconic; designed to fly straight at our star and get as close in as possible, the Icarus (oh, come on…) is shaped like an enormous heat-shield mushroom. The stem, which contains everything we might say defines a “ship,” lives in the shadow of the front-facing shield section — a design feature ripped straight from real NASA mission profiles. NASA has yet to make a ship for flying an explosive into the heart of the sun, however, so the heat shield silhouette isn’t quite so exaggerated. The Messenger probe, which was launched in 2011 to orbit and study Mercury, is just such an example, but its heat shield can only protect it from a single side.
NASA will work to wring the last drops of science out of the little orbiter, but soon enough it will fall close enough to the surface that the heat reflected back will melt the solder holding it together. The heat shield is designed to deal with temperatures of up to 350°C, but the ship itself can withstand less than 200°C. As the satellite dips below 26 kilometers altitude, it will be subject to more and more heat on the unshielded side and eventually break apart. In the image above, you can see the heat shield on the right, oriented between the probe and the sun. All that sticks out beyond its cover are the solar panels.
The problem really comes from Messenger’s success, as the probe was not still supposed to be operating at this point. (You’d think NASA would be used to expanded lifetimes for space tech at this point, though the optics of extended missions are good enough NASA would be foolish to start making more realistic lifetime estimates.) On January 21, the probe’s last gasp at life will see it actually eject any remaining pressurant in the fuel system for a final burst of energy. With the extra juice, Messenger will have enough velocity to stay in orbit for a further two months.
Those months will give NASA an up-close look at the surface of our solar system’s fire world, letting astronomers look inside craters and get a better sense of the planet’s chemical makeup. Among its other achievements, Messenger has studied the planet’s surface topology, its magnetic field, and even found water ice at the northern pole (yes, on a planet that melts satellites). Unfortunately, when Messenger does eventually crash it will likely do so on the far side of the planet, and thus won’t come back into view until 2024. The planet’s gravitational field is notoriously unevenly shaped, and NASA can’t even properly predict where it will touch down. Studying the exact shape and, perhaps, origin of this wacky gravity well is one of Messenger’s many goals.
Until January 15, NASA is holding a contest to name features of Mercury’s surface. You can suggest the name of any artist (writer, painter, musician) who’s been famous for more than 50 years and dead for more than 3 — a somewhat cynical but undeniably smart rule to have. In a post-4chan Internet, it’s always good to put a “no dumb ones” clause into your online contests and surveys.
Messenger has already been successful by any measure but, as has become standard NASA procedure at this point, it will be resurrected to achieve even more. Mercury’s distance and temperature will probably keep us from heading there with a manned mission any time soon, but that doesn’t mean astronomers are done exploring its many and sun-charred secrets.