Ice found hiding right next to the Sun

Mercury is generally thought of as a small, hot chunk of rock noted only for being the first planet in our solar system. But data from the MESSENGER satellite has been proving that we haven’t been looking closely enough, as the planet’s surface shows evidence of a variety of activity.

First, the hidden ice. It hasn’t been hidden from MESSENGER, flying low over the planet’s surface since 2011, as much as it’s been hidden from the Sun. The ice has been seen in the craters near the poles, which never see direct sunlight, keeping conditions considerably colder than the equator’s peak temperatures of 800 °F. What’s more, the ice may be home to organic materials, although nobody has gone so far as suggesting we’ll ever find something alive there.

Other parts of the surface are looking more lively than the well-preserved ice. Formations called “hollows” are being found in multiple locations, and may be the result of recent sublimation events just below the surface. When the volatile material suddenly sublimates, the ground it was under sinks down, creating the flat-bottomed hollow. We know these are recent, and possibly contemporary, because they’re being found inside craters known to be at least 10 million years old. (Remember, “recent” means something different when you’re speaking geology!)

The final new feature turning up on Mercury’s surface may also be due to activity underground. As the core of the planet cools, the planet has contracted, which causes wrinkles and buckling on the surface (think of a deflating balloon losing it’s smooth shape as it deflates). Based on these new wrinkles, or scarps, scientists think Mercury has shrunk up to 10 kilometers since it’s creation 4.5 billion years ago.

The stream of new data is soon going to dry up though. MESSENGER is expected to run out of fuel at the end of the month, and then crash into the planet. In the mean time, NASA is getting all they can out of the mission by having MESSENGER flying lower and lower for closer high-resolution photography to better document Mecury’s surface.

Source: Small, Shrinking Mercury Is a Planetary Space Oddity by Nadia Drake, No Place Like Home