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 typesof volcanism – explosive and effusive. When asked to picture volcanicactivity, the average person would most likely think of the former,conjuring up images of a cataclysmic eruption that sends vastquantities of lava and ash up into the sky.
The second form of volcanic activity, which is just as dramatic in its own way, ischaracterized by enormous lava flows traveling up from the interiorof a planet to cover vast swathes of the surface. It is thought thateffusive volcanism is an important part of how planets suchas our own form their outer crust.
By studying the outer layer of otherplanets, we can establish when the last crust-forming bouts oflarge-scale volcanism took place, and from this we can learn a lotabout the evolutionary path taken by that celestial body.
It is estimated that major terrainforming volcanic activity ceased on Mars a few million years ago, andthat it is still actively taking place on Earth today. However, priorto a recent study carried out by scientists from North Carolina StateUniversity, when this process ceased on theplanet Mercury was an unknown.
It is not possible to directly examinea sample of a lava flow, and establish its age via radiometric dating,as would be the case for terrain on Earth, as nospacecraft has ever descended to the surface of the tortured planet.However, since the most recent effusive volcanism events would havehardened to formed the outermost layer of Mercury's surface, the teamfrom NC State University was able to examine crater impacts in orderto estimate the cut off point for the planet's volcanic activity.
The researchers used images collectedby NASA's MESSENGER spacecraft in order todetermine crater size anddistribution on Mercury's surface. This data was then combined withestablished mathematical models used to calculate the age of asurface region based on these factors.
Thestudy suggests it is likely that Mercury has not experiencedsignificant levels of crust forming volcanism for roughly 3.5 billionyears. This timescale lends credence to the theory that the conduitsused to transport the magma from the interior of the planet weresealed off as Mercury began to cool, which in turn caused the planetto contract.
"These new results validate40-year-old predictions about global cooling and contraction shuttingoff volcanism," states Paul Byrne, assistant professor andplanetary geologist at NC State. "Now that we can account forobservations of the volcanic and tectonic properties of Mercury, wehave a consistent story for its geological formation and evolution,as well as new insight into what happens when planetary bodies cooland contract."
The study has been published online inthe journal Geophysical Research Letters.
