February 21, 2013
Magma Ocean In Mercury’s Past May Have Led To Two Different Rock Types
Lee Rannals for redOrbit.com - Your Universe Online
An MIT team of scientists say that Mercury may have had a large ocean of magma very early in its history, shortly after its formation about 4.5 billion years ago.
A group of scientists analyzed X-ray fluorescence data from MESSENGER collected back in 2011. They were able to identify two distinct compositions of rocks on the planet's surface. Afterwards, they were left wondering what geological processes could have given rise to this distinct surface composition.
The team used the compositional data to recreate the two rocks in the lab, and subjected each synthetic rock to high temperatures and pressures to simulate various geological processes.
After the experiments, the scientists found only one phenomenon could explain the two compositions, which was that a vast magma ocean created two different layers of crystals, then eventually remelted into magma and erupted onto Mercury's surface.
“The thing that´s really amazing on Mercury is, this didn´t happen yesterday,” said Timothy Grove, a professor of geology at MIT. “The crust is probably more than 4 billion years old, so this magma ocean is a really ancient feature.”
The team set out to find an explanation for the differences in rock composition, and in order to do this they translated the chemical element ratios into the corresponding building blocks that make up rocks. Afterwards they consulted finely powdered chemicals to recreate the rocks in the lab.
“We just mix these together in the right proportions and we´ve got a synthetic copy of what´s on the surface of Mercury,” Grove said in a recent statement.
They melted the samples of synthetic rock in a furnace, cranking the heat up and down to simulate geological processes that would cause crystals to form in the melt. Once they cooled the samples, they picked out tiny crystals and melted them for analysis. Grove found that two compositions were too different to have originated from the same region, and found that they may have come from two separate regions within the planet.
“You can tell what would happen as the melt cools and crystals form and change the chemical composition of the remaining melted rock,” Grove said. “The leftover melt changes composition.”
The easiest explanation, according to Grove, is that a large magma ocean eventually formed different compositions of crystals as it solidified. This ocean eventually remelted, spewing lava onto the surface of the planet in a massive volcanic eruption.
He believes this magma ocean existed very early in Mercury's history, and may have been created from violent processes that formed the planet.
“The acquisition of data by spacecraft must be combined with laboratory experiments,” Bernard Charlier, another researcher on the project, said. “Although these data are valuable by themselves, experimental studies on these compositions enable scientists to reach the next level in the interpretation of planetary evolution.”
Scientists just recently released a high-resolution map of Mercury, including different color filters to enhance the actual variations in color. Over 88,000 images were collected by MESSENGER to create the high-resolution photo, which was revealed during the annual meeting of the American Academy for the Advancement of Science (AAAS).
Results of the new study are published in the journal Earth and Planetary Science Letters.