Back in the fall of 2008, an asteroid now known as 2008 TC3 impacted Earth in Sudan’s Nubian Desert, bringing with it fragments from the mantle of another planetary body. Researchers studying one of the hundreds of meteorite fragments discovered evidence of volcanic activity. According to their study, published in Proceedings of the National Academy of Sciences this week, the fragment originated from an early solar system protoplanet that had active volcanic processes like we have on Earth.
Volcanism is a fundamental geological process that contributed the growth of planetary bodies in the days of the early solar system, billions of years ago. These small planetary embryos were only tens to hundreds of kilometers in size. Numerous rocks with basaltic composition have already been found on the moon, Mars, asteroids, and of course Earth. On our planet, however, there’s another type of volcanism that generates “trachyandesite lavas.” Until now, there’s been no evidence of this process elsewhere.
Using microscopy and spectroscopy, a team led by Addi Bischoff from Universität Münster examined one of the 600 fragments strewn across the desert -- collectively known as the “Almahata Sitta” meteorites. Their original parent body (or bodies) were likely destroyed in collisions with other asteroids.
The team’s focus was on the 24.2-gram sample labeled ALM-A (Almahata Sitta trachyandesitic meteorite), which was covered with a greenish, shiny fusion crust. They found that the ALM-A sample was rich in volatiles and silicon -- the result of trachyandesitic, alkali-, and silica-rich volcanism. “We found rocks were being produced by volcanism on small asteroids just six-and-a-half million years after the formation of the first solid material in the solar system,” Bischoff explains to Australia’s ABC News.
Their findings suggest that the volcanic processes that produce these kinds of rock compositions on Earth may have been active in early solar system bodies from around 4.56 billion years ago. "I would have thought that these kinds of rocks could only have formed much later, on larger bodies like Earth,” Bischoff adds. “But to have this happening on asteroids so early is fantastic.”
Pictured above, you can see the greenish hue of the specimen (A), as well as a view of a thin section of ALM-A with polarized light (B). The presence of glass (C,D) indicates very rapid cooling, which helped confirmed a lava origin.