The thawing and freezing of ice within asteroids causes fractures to form inside these space rocks, allowing water to spread through them. This helps them carry key molecules that could have provided ingredients for the formation of life on Earth.
at Imperial College London and his colleagues analysed a small portion of the 5.4 grams of material brought back from asteroid Ryugu in 2020 by Japan鈥檚 Hayabusa 2 spacecraft. Samples have previously been shown to include chemicals that are important for living organisms, lending credence to the idea that the ingredients for life were brought to Earth by space rocks.
Now, Genge and his team have discovered using 聽X-ray computed tomography that the samples showed signs of fracture, and that the cracks were filled with clay and sulfide minerals, which are formed in conjunction with water 鈥� suggesting that water played a key role in creating these vital organic ingredients. Genge says this organic matter, which contained some of the building blocks of life, would have been delivered to early Earth.
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鈥淚t鈥檚 like taking your initial ingredients and then marinating them for a while inside the asteroid before adding them to Earth,鈥� says Genge. 鈥淲ho knows if adding just the raw materials would have been enough [to create life on Earth alone] or not. We don鈥檛 actually know how life began yet.鈥�
Such cracks have been observed in meteorites 鈥� asteroids that have landed on Earth 鈥� but these were thought to be a result of the high-temperature journey through the atmosphere or impact with the ground.
Genge says ice in the interior of Ryugu and asteroids like it would have been melted by the decay of short-lived radioisotopes. The fluid would then have risen towards the surface and frozen once more. More warm, liquid water behind it would have created interior forces, pushing up towards the surface in a cycle of thawing and freezing that fractured the rock.
As well as fracturing Ryugu, the cyclic pattern would have allowed water to escape through cracks as geysers that erupt from the asteroid鈥檚 surface, says Genge.
鈥淭he one thing we do know is that by 4 billion years ago, the first living thing had already appeared on Earth,鈥� says Genge. 鈥淭hat鈥檚 life being in a hurry to get started. And that, to me, is the main evidence that habitable planets like Earth need these very water-rich and organic-rich asteroids.鈥�
Nature Astronomy
