According to new research published in the journal Geophysical Research Letters, the main phase of volcanism on Mercury ended by 3.5 billion years ago, with only small-scale volcanism enduring beyond that time.
This colorful view of Mercury was produced by using images from the color base map imaging campaign during MESSENGER’s primary mission. These colors are not what Mercury would look like to the human eye, but rather the colors enhance the chemical, mineralogical, and physical differences between the rocks that make up the planet’s surface. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington.
There are two types of volcanic activity: effusive and explosive.
Explosive volcanism is often a violent event that results in large ash and debris eruptions.
Effusive volcanism refers to widespread lava flows that slowly pour out over the landscape — believed to be a key process by which planets form their crusts.
Determining the ages of effusive volcanic deposits can give planetary scientists a handle on a planet’s geological history. For example, effusive volcanism was active a few hundred million years ago on Venus, a few million years ago on Mars, and it still takes place on our planet today.
Until now, the duration of effusive volcanic activity on Mercury, made of the same materials as these other planets, had not been known.
A team of scientists led by North Carolina State University’s Paul Byrne determined when the bulk of Mercury’s crust-forming volcanism ended by using images from NASA’s MESSENGER mission.
Because there are no physical samples from the planet that could be used for radiometric dating, the team used crater size-frequency analysis, in which the number and size of craters on the planet’s surface are placed into established mathematical models, to calculate absolute ages for effusive volcanic deposits on Mercury.
According to Dr. Byrne and co-authors, major volcanism on Mercury stopped at 3.5 billion years ago, in stark contrast to the volcanic ages found for Venus, Mars and Earth.
“There is a huge geological difference between Mercury and Earth, Mars or Venus,” Dr. Byrne said.
“Mercury has a much smaller mantle, where radioactive decay produces heat, than those other planets, and so it lost its heat much earlier.”
“As a result, Mercury began to contract, and the crust essentially sealed off any conduits by which magma could reach the surface.”
“These new results validate forty-year-old predictions about global cooling and contraction shutting off volcanism,” Dr. Byrne added.
“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.”
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Paul K. Byrne et al. Widespread effusive volcanism on Mercury likely ended by about 3.5 Ga. Geophysical Research Letters, published online July 21, 2016; doi: 10.1002/2016GL069412
