Mercury's Dramatic Lava Flows Came From Extremely Rare Meteorites

A false color image of Mercury, highlighting the different surface compositions. NASA
Robin Andrews 28 Jun 2016, 14:32

NASA’s MESSENGER spacecraft orbited Mercury between 2011 and 2015, and revealed that thick lava flows covered parts of its surface. Using an X-ray spectrometer instrument, the composition of over 5,800 lava flows were determined, and Grove’s team used this data to delve into the evolution of Mercury. After all, this lava was once magma deep inside the planet, which means that the lava flows contain the geological history of the pockmarked planet.

Speaking of which, Mercury is covered in craters, and the more craters there are on these ancient lava flows, the older the lava flows must be. Based on this, the youngest lava flows were 3.7 billion years old, whereas the oldest were around 4.2 billion years of age.

Using the chemical compositions determined by MESSENGER, the two types of lava flows were physically recreated in a laboratory, with the help of a powerful pressurized furnace. The older lava flows had a melting point of around 1,650°C (3,002°F) at pressures present at a depth of 360 kilometers (224 miles), whereas the younger ones were only molten at temperatures of 1,410°C (2,570°F) at pressures present at 160 kilometers (99 miles) depth.

Mercury's surface is covered in craters. NASA

This meant that, within 500 million years, the lava erupting at the surface came from a magma source that had cooled at least 240°C (432°F) – rapid by any measure. This suggests that volcanism, often the primary cooling mechanism of any rocky world, must have been quite rapid and dramatic back then.

Looking at the crystals that formed in their synthetic lava, the team were also able to determine the composition of much of the interior of Mercury. The closest geochemical match was to an enstatite chondrite, a stony meteorite rich in magnesium, and one that’s very distinct from the geologies of Earth, Venus, and Mars.

So Mercury not only had unique volcanism, but it also has truly novel geology. Now all we need is a sample from the surface to confirm all this.

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