Although small and very hot, we have found out that Mercury has something in common with our planet and no other object in the Solar System. They are both tectonically active.
During the final 18 months of NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, the spacecraft was lowered close enough to the surface to spot several cliff-like structures on the planet.
These small fault scarps, which are only a few kilometers in length, are the latest piece of evidence of recent geological activity on Mercury.
According to the paper, published in Nature Geoscience, the small faults are estimated to have formed in the last 50 million years, and they are a further indication that the planet is shrinking.
“Steady meteoroid bombardment quickly degrades and destroys structures this small, indicating that they must have formed relatively recently,” said study co-author Maria Banks from the Planetary Science Institute in a statement. “They are comparable in size to very young fault scarps identified on the lunar surface attributed to shrinking of the Moon.”
The small fault scarps seen by MESSENGER. NASA/JHUAPL/Carnegie Institution of Washington/Smithsonian Institution
The shrinking of Mercury was first put forward in 1974 when another NASA probe, Mariner 10, discovered large scarps on its surface. As the interior cools, the surface breaks and moves upward, forming these features. The large faults formed over billions of years, unlike the smaller faults that are caused by more recent activity.
“The young age of the small scarps means that Mercury joins Earth as a tectonically active planet in our Solar System, with new faults likely forming today as Mercury’s interior continues to cool,” said lead author Thomas Watters, a Smithsonian senior scientist at the National Air and Space Museum in Washington, in a statement.
Internal activity is also suggested by the fact that Mercury has a relatively strong magnetic field. It is only 1 percent of Earth’s own, but it's stable enough to be consistent with a still hot outer core. Researchers consider it likely that Mercury experiences quakes, and maybe in the future we could land a seismographer and confirm this hypothesis.
There are several active worlds in the Solar System. Io has volcanos, and Europa and Enceladus have active geysers. But to be tectonically active, a planet needs to have a cracked surface that is being pushed around by internal forces. Only Mercury and Earth have that.