Volcanic activity on Mercury stopped 3.5 bn years ago

Shedding new insight into the geological evolution of Mercury, researchers have found that major volcanic activity on the planet Mercury most likely ended about 3.5 billion years ago.

"These new results validate 40-year-old predictions about global cooling and contraction shutting off volcanism," Paul Byrne, Assistant Professor at the North Carolina State University.

"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," Byrne noted.

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, such as the Mount Saint Helens eruption in 1980.

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 researchers 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 Earth today.

Until now, the duration of effusive volcanic activity on Mercury, made of the same materials as these other planets, had not been known.

In this study, published in the journal Geophysical Research Letters, the researchers determined when the bulk of Mercury's crust-forming volcanism ended by using photographs of the surface imaged by NASA's MESSENGER mission.

Because there are no physical samples from the planet that could be used for radiometric dating, the researchers 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 their results, major volcanism on Mercury stopped at around 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," Byrne said.

--IANS

gb/vm