Meteorite offers clues to asteroid Vesta’s inner life

Researchers find first evidence surface of body was once covered in an ocean of molten rock

Chinese scientists said a meteorite found in Algeria showed that an ancient magma ocean once existed on Vesta, one of the largest asteroids in our solar system.

The researchers said that while Vesta was much smaller than the moon and other planets, the “planetary embryo” had a similar evolutionary history to the moon.

Vesta, which is about 530km wide, has a structure of core, mantle and crust – much like the moon and Earth. The moon has a diameter of nearly 3,500km while Earth’s is almost 13,000km.

Vesta emerged in the first 1 to 2 million years after the solar system formed and is now the second largest body in the asteroid belt, which sits between Mars and Jupiter.

Space scientists view Vesta and other asteroids as protoplanets and have been looking for clues about how they evolved.

The Chinese researchers, from institutes in Guiyang, Hefei, Changsha, Nanjing and Xian, said: “Its structure and chemical features provide critical insights into the origin and formation history of parent planetary bodies in the early solar system.”

Soon after the moon’s formation its outer surface melted, forming an ocean of magma on the surface.

The latest study, published in peer-reviewed journal Nature Astronomy yesterday, looks at a 230-gram meteorite found in Algeria in 2021 and sold to a Chinese buyer the following year.

The Chinese researchers later confirmed its Vestan origin by comparing it with previous samples traced to the asteroid.

Lead author Li Shijie, a researcher at the Chinese Academy of Sciences’ Centre for Lunar and Planetary Sciences in Guiyang, said the analysis showed that more than 90 per cent of the meteorite was composed of a mineral called anorthite, a key indicator of a magma ocean.

Anorthosites are formed when magma oceans solidify and the only ones that have previously been found have come from the Earth or the moon.

Previous meteorites from Vesta have shown no signs of the mineral, but Li said the new discovery suggested there was an ancient magma ocean on the asteroid.

He said their calculations suggested that anorthite formed at a depth of 30km in the magma ocean and may have floated to the surface of Vesta, a process that could happen in as little as 200 years or as long as 20,000 years.

The team said remote sensing may struggle to detect an anorthositic crust on Vesta’s surface today. Nasa’s Dawn spacecraft, a probe launched in 2007 and sent to explore Vesta and Ceres, the largest asteroid, found no traces.

Li said it was possible the evidence for the magma lake had been removed when the asteroid collided with other objects as the solar system was taking shape.

“In the early days of the solar system, intensive collisional bombardment events were common … Large amounts of crust – just like eggshells – may have been eroded,” Li said.