Before the solar system was packed with the eight planets we know today – or nine if you still include Pluto – it was full of planetesimals. Planetesimals were essentially small planets, ranging from a few metres to a few hundred miles wide. They were made out of the dust which originally surrounded the Sun, which either melted completely or simply turned into “rubble piles” as the bigger planets came to be.
However, “strange” meteorites found across Earth show that one planetesimal went against the trends.
New research has found that a series of meteorites across Earth come from the same celestial body.
What has left scientists stumped though is that the family of meteorites come from a body that was both melted, and turned into rubble – something which scientists did not think was possible.
The study, from the Massachusetts Institute of Technology, has revolutionised the way experts classify meteorites.
The researchers believe they likely outcome was the planetesimal was made of several layers, including a liquid core which produced a powerful magnetic field.
As a result, the solid outer layers, along with the ‘meted interior’, both eventually collided with Earth billions of years down the line, allowing both melted (chondritic) and unmelted (achondritic) meteorites.
Lead author Clara Maurel, a graduate student in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS), said: “This is one example of a planetesimal that must have had melted and unmelted layers. It encourages searches for more evidence of composite planetary structures.
“Understanding the full spectrum of structures, from nonmelted to fully melted, is key to deciphering how planetesimals formed in the early solar system.”
The team showed that it was possible for a body with a liquid core to collide with another object, and for that impact to dislodge material from the core.
That material would then migrate to pockets close to the surface where the meteorites originated.
What the study also shows is, because the planetesimal had a liquid core, it must have formed over millions of years, whereas before experts believed they formed instantaneously.
Now, the researchers will look to the asteroid belt to better understand if the planetesimal in question was unique.
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EAPS Professor Benjamin Weiss said: “Most bodies in the asteroid belt appear unmelted on their surface.
“If we’re eventually able to see inside asteroids, we might test this idea.
“Maybe some asteroids are melted inside, and bodies like this planetesimal are actually common.”
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