Photos suggest Mercury is actively shrinking

Surface of Mercury

NASA/JHUAPL/Carnegie Institution of Washington/USGS/Arizona State University
A topographic map showing the surface of Mercury. Blues and purples are lower elevations, greens and browns are higher elevations.

Mercury can't get a break. Not only is it the smallest officially recognized planet in our Solar System, but it's also shrinking.

In a study published in Nature Geoscience, new analysis of photos taken by NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft show distinct landforms that indicate the planet is still contracting as it slowly cools down from its molten early years at the start of the Solar System.

Researchers found thin step-like cliffs in photos taken by MESSENGER, much smaller than the narrow ones that had been discovered back in the 1970s. These smaller features, called fault scarps, managed to survive intact after the planet was slammed with meteorites, meaning that they probably formed recently.


NASA/JHUAPL/Carnegie Institution of Washington/Smithsonian Institution
Fault scarps (steep cliff-like geographic features) spotted by MESSENGER.

The discovery is exciting to researchers because it shows that Mercury's slow shrink wasn't something that happened in the distant past, but might still be going on, bringing Mercury into the very small circle of tectonically active planets (planets whose interior has not fully solidified, like Earth).

"This is why we explore," NASA Planetary Science Director Jim Green said. "For years, scientists believed that Mercury's tectonic activity was in the distant past. It's exciting to consider that this small planet – not much larger than Earth's moon – is active even today."

Unfortunately we're going to have to wait to get another, closer look at the fault scarps. MESSENGER purposefully crashed into Mercury last year after years of observing the planet. But researchers are already drawing up their wish lists for future missions.

Stay cool, Mercury.

Related: Look back at Mercury's solar transit earlier this year:

Transit of Mercury 2016
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Transit of Mercury 2016
ADDS DETAILSThe 2016 Mercury planetary transit is seen in a NASA conceptual image, made of many images captured by the Solar and Heliospheric Observatory (SOHO) during the last Mercury transit in 2006. Mercury will pass between Earth and the sun in the rare astronomical event between about 7:12 a.m. and 2:42 p.m. EDT (11:12 - 18:42 GMT) on May 9, 2016. NASA/Handout via Reuters ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. EDITORIAL USE ONLY
People look at planet Mercury transiting across the sun with solar filters at a public viewing in Kolkata, India May 9, 2016. REUTERS/Rupak De Chowdhuri TPX IMAGES OF THE DAY

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