Volcanic activity on Mercury ended 3.5 billion years ago: study

Major volcanic activity on Mercury planet most likely ended about 3.5 billion years ago, according to a new study which shed light into its geological evolution. 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, researchers from North Carolina State (NC State) University in the US said.

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

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, 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.

"There is a huge geological difference between Mercury and Earth, Mars or Venus," said Paul Byrne from North Carolina State University. "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," said Byrne.

The results validate 40-year-old predictions about global cooling and contraction shutting off volcanism, he said. "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," said Byrne. According to researchers, major volcanic activity on the planet Mercury most likely ended about 3.5 billion years ago. 

The findings were published in the journal Geophysical Research Letters.