Mercury has been hiding a secret. During the fiery birth of the Solar System around 4.6 billion years ago, the four rocky inner worlds began to take shape, but the geology of the planet closest to the Sun – based on measurements taken by the MESSENGER space probe – looks very different from that of the other three.
Now, after a series of ingenious experiments – those designed to physically reproduce Mercury’s volcanic activity – a team from the Massachusetts Institute of Technology (MIT) think that they now know what this distant planet is made of: enstatite chondrite, an incredibly rare meteorite type that makes up no more than 2 percent of all meteorite samples found on Earth.
This team’s experiments also suggest that Mercury lost a huge amount of its internal heat within just half a billion years. Specifically, its temperature dropped by 240°C (432°F) between 4.2 and 3.7 billion years. The only way to achieve this rapid cooling was if Mercury once experienced incredibly violent, speedy volcanism shortly after its fiery birth.
“This is the first place where we actually have an estimate of how fast the interior cooled during an early part of a planet’s history,” Timothy Grove, the Ida Green Professor of Geology at MIT and one of the authors of the Earth and Planetary Science Letters study, said in a statement.
A sample of an enstatite chondrite found on Earth. Captmondo/Wikimedia Commons; CC BY SA 3.0