It’s small, it’s hot, and it’s shrinking. Surprising new NASA-funded research suggests that Mercury is contracting even today, joining Earth as a tectonically active planet.

(NASA/JHUAPL/Carnegie Institution of Washington/USGS/Arizona State University)

At a Glance

NASA researchers discovered that Mercury is tectonically active and shrinking.The scientists discovered scarps small enough that they believe they are still geologically young, meaning Mercury is still contracting.

Mercury already holds the title as the smallest planet in our solar system, but a new study reveals the planet is undergoing "Mercuryquakes"and shrinking even further. Researchers believe it is the second tectonically active planet in our solar system.

Images from NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft mission show , according to a release from the agency.

The study, recently published in Nature Geoscience, said the mission " of tectonic history have been dominated by contraction expressed by lobate fault scarps that are hundreds of kilometers long."

The scientists discoveredscarps small enough that it's believed they're still geologically young, meaning the Swift Planet is still contracting.

“The young age of the small scarps means that Mercury joins Earth as a tectonically active planet, with new faults likely forming today as Mercury’s interior continues to cool and the planet contracts,” lead author Tom Watters said in the release.

Small graben, or narrow linear troughs, have been found associated with small fault scarps (lower white arrows) on Mercury, and on Earth’s moon. The small troughs, only tens of meters wide (inset box and upper white arrows), likely resulted from the bending of the crust as it was uplifted, and must be very young to survive continuous meteoroid bombardment.

(NASA/JHUAPL/Carnegie Institution of Washington/Smithsonian Institution)

Large fault scarps were first discovered on Mercury during flybys of the Marine 10 spacecraft in the mid-1970s, according to the release. MESSENGER confirmed the faults and found that the planet is actually shrinking. The large scarps were formed as Mercury’s interior cooled, which caused the planet to contract and the crust to break and jut upward along faults. This created cliffs up to hundreds of miles long, with some rising more than a mile high.

In the final 18 months of MESSENGER’s mission, the altitude was lowered, showing Mercury’s surface at a much higher resolution. This revealed the small fault scarps, which had to be very young to withstand the steady bombardment of meteoroids and comets, NASA also reported.

" this small, indicating that they must have formed relatively recently," study co-author Maria Banks told Phys.org. "They are comparable in size to very young fault scarps identified on the lunar surface attributed to shrinking of the moon."

The active faulting on the planet is consistent with recent findings that Mercury’s global magnetic field has existed for billions of years and with the planet’s slow cooling of its still-hot outer core, according to NASA. It’s likely that Mercury also experiences quakes of its own, but that will have to be confirmed by seismometers.

"This is why we explore," NASA Planetary Science Director Jim Green said in the release. "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."