Mercury's volcanoes have been (mostly) snoozing for billions of years

The tan colored region in the upper section of this color map of Mercury represents a region that experienced effusive volcanism in the ancient past(Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

Researchers have estimated that around 3.5 billion years ago, Mercury underwent its final major burst of volcanic activity. The results of the study will help scientists understand how Mercury evolved into the scorched planet we know today.

There are broadly speaking, two types of volcanism – explosive and effusive. When asked to picture volcanic activity, the average person would most likely think of the former, conjuring up images of a cataclysmic eruption that sends vast quantities of lava and ash up into the sky.

The second form of volcanic activity, which is just as dramatic in its own way, is characterized by enormous lava flows traveling up from the interior of a planet to cover vast swathes of the surface. It is thought that effusive volcanism is an important part of how planets such as our own form their outer crust.

By studying the outer layer of other planets, we can establish when the last crust-forming bouts of large-scale volcanism took place, and from this we can learn a lot about the evolutionary path taken by that celestial body.

It is estimated that major terrain forming volcanic activity ceased on Mars a few million years ago, and that it is still actively taking place on Earth today. However, prior to a recent study carried out by scientists from North Carolina State University, when this process ceased on the planet Mercury was an unknown.

It is not possible to directly examine a sample of a lava flow, and establish its age via radiometric dating, as would be the case for terrain on Earth, as no spacecraft has ever descended to the surface of the tortured planet. However, since the most recent effusive volcanism events would have hardened to formed the outermost layer of Mercury's surface, the team from NC State University was able to examine crater impacts in order to estimate the cut off point for the planet's volcanic activity.

The researchers used images collected by NASA's MESSENGER spacecraft in order to determine crater size and distribution on Mercury's surface. This data was then combined with established mathematical models used to calculate the age of a surface region based on these factors.

The study suggests it is likely that Mercury has not experienced significant levels of crust forming volcanism for roughly 3.5 billion years. This timescale lends credence to the theory that the conduits used to transport the magma from the interior of the planet were sealed off as Mercury began to cool, which in turn caused the planet to contract.

"These new results validate 40-year-old predictions about global cooling and contraction shutting off volcanism," states Paul Byrne, assistant professor and planetary geologist at NC State. "Now that we can account for observations of the volcanic and tectonic properties of Mercury, we have a consistent story for its geological formation and evolution, as well as new insight into what happens when planetary bodies cool and contract."

The study has been published online in the journal Geophysical Research Letters.

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