Mercury is the last of the classical planets, the planets known to the astronomers of Egypt and Greece and Rome and the Far East. It’s an object that has captivated the imagination and the attention of astronomers for millennia.

Mercury has always been a bit of an oddball as the only planet in the Solar System that does not follow a basically circular orbit.

Until recently, Mercury was not believed to contain the volatile elements required for making violent volcanic explosions.

New data from the MESSENGER spacecraft has shown that this was not always the case.

Not only was Mercury rife with volcanic activity early in the planet’s history, but it lasted much longer than anyone would have expected. The research comes from lead author Timothy Goudge from Brown University and was published in the Journal of Geophysical Research: Planets.

Earth is filled with chemicals like water and carbon dioxide which have relatively low boiling points and facilitate volcanic explosions. As they get cycled through with lava and get closer to the surface, they change from liquid to gas and expand, building up pressure. Eventually, the pressure just becomes too great, and the gasses and lava explode into an eruption. Mercury, on the other hand, has not been thought to be as geologically exciting.

Images returned from NASA’s MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft reveal about 3,600 cubic miles (15,000 cubic kilometers) of solidified lava inside a single crater on Mercury’s western hemisphere.

That’s enough lava to fill the entire Baltimore-Washington metropolitan area to a height 12 times that of the Washington Monument, according to Maria Zuber of the Massachusetts Institute of Technology, who is a co-investigator for the mission.

“That’s an awful lot of volcanic material in one place for such a little planet,” Zuber told reporters during a Wednesday briefing. Scientists think this volcanism may have happened 3.8 billion to 4 billion years ago, Zuber said, adding that a more precise date would require studies of rock samples.

In order to come to this conclusion, the team measured the sizes and numbers of craters on the most heavily cratered terrains using images obtained by the MESSENGER spacecraft.

The researchers then extrapolated to Mercury a model originally developed for comparing the Moon’s crater distribution to a chronology based on the ages of rock samples gathered during the Apollo missions.

“By comparing the measured craters to the number and spatial distribution of large impact basins on Mercury, we found that they started to accumulate at about the same time, suggesting that the resetting of Mercury’s surface was global and likely due to volcanism,” Marchi, who has a joint appointment between two of NASA’s Lunar Science Institutes – one at the SwRI in Boulder and another at the Lunar and Planetary Institute in Houston – said in a press release.

Those results set the age boundary for the oldest terrains on Mercury back to the same point in time as the Late Heavy Bombardment (LHB) period, an age of intense cosmic bumper cars recorded in lunar and asteroidal rocks and by the numerous craters on the Moon, Earth and Mars in addition to Mercury.

Meanwhile, the researchers found that the youngest and broadest volcanic provinces dated back roughly 3.6 billion to 3.8 billion years, just after the end of the LHB, leading the researchers to hypothesize that these large projectiles puncturing the planet’s thin surface may have caused increased volcanism that ultimately led, according to Chapman, to a “global resurfacing.”

The work was funded by the NASA Discovery Program.

Source: https://goo.gl/3RLqGf