Holding an extraterrestrial tale in our hands
This image obtained by the framing camera on NASA's Dawn spacecraft shows the south pole of the giant asteroid Vesta. Image: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Recently, scientists at Curtin University analysed samples from the second-largest asteroid in our solar system, Vesta. We had a hand, quite literally, in preparing samples for this analysis at the John De Laeter Centre. But even more exciting than handling extraterrestrial samples are the researchers’ findings about Vesta’s early life.
Prof Fred Jourdan said Vesta is of tremendous interest to scientists trying to understand more about what planets are made of, and how they evolved:
“Vesta is the only largely intact asteroid which shows complete differentiation with a metallic core, a silicate mantle and a thin basaltic crust, and it’s also very small, with a diameter of only about 525 km.
In a sense it’s like a baby planet, and therefore it is easier for scientists to understand it than say, a fully developed, large, rocky planet.”
Vesta was named after the virgin goddess of home and hearth from Roman mythology. To give you an idea of its size, you could squeeze at least three Vesta-size asteroids side by side in the state of New South Wales, Australia.
Vesta was visited by the NASA Dawn spacecraft in 2011. As a result of this mission it was observed that the asteroid had a more complex geological history than previously thought. With the aim of hoping to understand more about the asteroid, the Curtin research team analysed well-preserved samples of volcanic meteorites found in Antarctica that were identified as having fallen to Earth from Vesta.
Crushed sample of meteorite showing volcanic minerals. Image: Prof Fred Jourdan
Prof Jourdan explains his team’s research using these samples:
“Using an argon-argon dating technique, we obtained a series of very precise ages for the meteorites, which gave us four very important pieces of new information about timelines on Vesta.
Firstly, the data showed that Vesta was volcanically active for at least 30 million years after its original formation, which happened 4,565 million years ago. While this may seem short, it is in fact significantly longer than what most other numerical models predicted, and was unexpected for such a small asteroid.
Our research suggests pockets of magmas must have survived on Vesta, and were potentially related to a slow-cooling partial magma ocean located inside the asteroid’s crust.”
Co-researcher Dr Trudi Kennedy, also from Curtin’s School of Earth and Planetary Sciences, said the research identified the timeframes when very large impacts from asteroids striking Vesta carved out craters of ten or more kilometres deep into the asteroid’s volcanically active crust:
“To put this into perspective, imagine a large asteroid smashing into the main volcanic island of Hawaii and excavating a crater 15 kilometres deep – that gives you an idea of what tumultuous activity was happening on Vesta in the early days of our Solar System.”
Scientists further explored the data and were able to understand what was happening deeper in the asteroid by calculating how long it took for Vesta’s thick crustal layer to cool down. Some of these sample rocks were located far beneath the crust and as a result were not affected by the asteroid impacts, but, being relatively close to the mantle, they were strongly affected by the natural heat gradient of the protoplanet and were metamorphosed as a result.
Dr Kennedy explains what makes this interesting:
“Our data further confirms the suggestion that the first flows of erupted lava on Vesta were buried, deep into its crust, by more recent lava flows, essentially layering them on top of each other. They were then ‘cooked’ by the heat of the protoplanet’s mantle, modifying the rocks.”
The team also concluded that the meteorites they analysed were excavated from Vesta during a large impact, possibly 3.5 billion years ago. The fragments agglomerated into a rubble pile asteroid, which protected them from any subsequent impacts. A rubble pile asteroid is formed when a group of ejected rocks assemble under their own gravity, creating an asteroid that is essentially a pile of rocks clumped together.
Dr Kennedy concludes:
“This is very exciting for us because our new data brings lots of new information about the first 50 million years or so of Vesta’s early history, which any future models will now have to take in to account,”
It also raises the point that if volcanism could last longer than previously thought on the protoplanet, then maybe volcanism on the early Earth itself might have been more energetic than we currently think.”