Signs of recent tectonic activity found on cooling Mercury

Thought-to-be-lifeless hell-ball actually has a rich inner life

NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) craft has found evidence that Sol's innermost planet is tectonically active.

That's kind of a big deal because until now only Earth was known to be tectonically active. And because tectonic activity brings lovely stuff up from a planet's innards, and that lovely stuff is very useful for cooking chemicals that have the potential to eventually form cells, knowing that there's at least one other tectonically active world out there is encouraging.

MESSENGER found evidence of tectonic activity after lowering its altitude to snap more detailed pictures of Mercury. Doing so revealed what NASA is calling “previously undetected small fault scarps— cliff-like landforms that resemble stair steps.”

Fault scarps can appear after events like earthquakes, which can themselves be caused by a planet cooling and contracting. We've seen big scarps on Mercury before, hinting at cooling in aeons past.

But the cooling hypothesis is now heating up, thanks to a Nature Geoscience letter penned by a group of planetary scientists who've been able to peer at recent MESSENGER data.

“These small scarps have tens of metres of relief, are only kilometres in length and are comparable in scale to small young scarps on the Moon,” the authors write. Their small-scale, pristine appearance, crosscutting of impact craters and association with small graben all indicate an age of less than 50 Myr.” If they were older, the letter argues, they'd have been smoothed out to nothingness by collisions with incoming debris

“We propose that these scarps are the smallest members of a continuum in scale of thrust fault scarps on Mercury,” the letter says. The young age of the small scarps, along with evidence for recent activity on large-scale scarps, suggests that Mercury is tectonically active today and implies a prolonged slow cooling of the planet’s interior.”

The hypothesis is more evidence that our Solar System is full of vivacious worlds and moons, to add to this week's news of water jets of Europa and revelations of Dwarf planet Ceres' ice volcano the warm, wobbling liquid thought to reside on Saturnian moon Enceladus and unexpected volcanic activity on Pluto.

If nothing else, these discoveries show that Earth is not atypical. And seeing as Earth produced life, life, gorgeous life capable of producing wonders like presidential debates it's great to know the chances of it appearing elsewhere look just a little bit higher now that we've seen Mercury is still impressively shaky. ®

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