London, March 14 : A pair of mysterious meteorites discovered in Antarctica in 2006, may be remnants of a dwarf planet that was smashed apart early in the solar system's history.
In the solar system's first few tens of millions of years, collisions between rocky objects and the decay of radioactive isotopes melted the interiors of large objects.
Magma oceans - perhaps hundreds of kilometres deep - lapped over the Moon, the Earth, and other large bodies, allowing dense material to settle towards their centres in a process called differentiation.
According to a report in New Scientist, the meteorites, dubbed GRA 06128 and GRA 06129, after the Graves Nunataks area of Antarctica where they were found together in 2006, show evidence of such differentiation - which suggests they came from a massive body.
That's because the two objects are made mostly of a mineral called feldspar, which constitutes about 75 to 90% of their volume.
Feldspar is even more abundant in some lunar rocks. That is thought to be the result of crystals of feldspar solidifying from the early magma ocean on the Moon.
According to Allan Treiman of the Lunar and Planetary Institute in Houston, Texas, US, who led a study of one of the fragments, the amount of feldspar in the two meteorite fragments suggests that they are remnants of a very large body that differentiated in a similar way.
Other studies of the meteorite agree that the parent body must have been massive enough to have separated into layers.
"The feldspar concentrations suggest that body was probably smaller than the 3500-kilometre-wide Moon, but larger than Vesta, the third largest asteroid in the solar system at 578 kilometres across," said Treiman.
By measuring the radioactive decay of elements in the meteorite, scientists have shown that the rock must have formed around 4.5 billion years ago, when Earth and the other planets were coalescing.
"Studying these fragments of a now-vanished object from that era provides a rare window into the early solar system," said Treiman.
At that time, a lot of dwarf-planet size objects were flying around the solar system. Some would have been flung out of the solar system through gravitational interactions with other objects, while others collided to help build the planets present in the solar system today.
"This is a piece of a dwarf-planet size body that apparently no longer exists," Treiman told New Scientist. "We have here a sample of a strange new world, a sample we've never seen before," he added.