[Intro]

Back in 2019, the New Horizons spacecraft reached the Kuiper belt, an icy ring of rocks out beyond the planets that's left over from the early solar system.  Its goal was to shed some light on the earliest moments of the solar system, and its images have already given us a better picture of our origins.

But we don't always have to travel over six billion kilometers to peer back into our past. There are lots of clues much closer to home. For instance, certain meteorites contain small spherical grains of rock
called chondrules. They're less than a few millimeters in diameter and scientists think they formed as liquid droplets, cooled and  hardened.

Later, they accreted onto larger rocks which occasionally land on Earth as meteorites. What's incredible and also useful about chondrules is that they all date back to the first three million years of our solar system's existence. So they offer us a window into the past and by studying them we can figure out things like the temperature and composition of the disk they formed out of.

In 2014, researchers even used chondrules from a meteorite found in India to paint a picture of the Sun's early magnetic field. From  what they can, tell the planets seemed to have formed much faster than they should have, if only gravity were at play. And some  hypotheses have suggested that magnetic fields could have played a role in that somehow.

But for a long time scientists didn't have any evidence to test those ideas. Then in 2014 they got their chance. This meteorite called Semarkona was full of chondrules and they were perfectly intact. A lot of times chondrules get altered by heat or chemical reactions, so their internal magnets get realigned to all point in the same direction.

But the magnetic grains in Semarkona were all pointing in random directions, just like you would expect if they accreted randomly after
cooling. So they still reflected the magnetic field that was around when they formed. Scientists were able to measure the strength of the magnetic field in the individual chondrules, and they found
that when these grains formed, the young Sun's magnetic field was a hundred thousand times stronger than the one in interstellar space today.

Models suggest that a magnetic field this strong would have pushed gas and dust inward, encouraging more collisions and faster accretion, which could explain how our planets form so quickly. And we know this all thanks to a few grains the size of sand.

Now meteorites without chondrites can tell us a lot about the early solar system too, for example igneous meteorites are made of cooled lava, and like igneous rocks on Earth their composition can tell us a lot about what was going on inside the worlds they came
from.

Like in 2018, scientists found incredible history in a meteorite that
landed in the Sahara. They could tell by its composition that it originally came from some objects crust because it was full of silica, which is a lightweight mineral that melts at low temperatures and rises toward the surface. That alone told them that the rock had to have come from a body that was well developed since it's light and heavy minerals had time to separate into layers.

That's not so unusual, but there was something really weird about it,
it was old. It was the oldest igneous meteorite anyone had ever found and it was also older than any of the planets in the solar system today. So this meteorite must have come from a proto planet that's long gone, one that got destroyed, or kicked out as the inner solar system came together.

So we have a piece of a planet that doesn't exist anymore, and so it's pretty incredible that we know anything about it at all. But aside from showing us that Earth has a long-lost sibling, it also tells us
that proto planets were around long enough and grew large enough to form layers.

Before that, scientists didn't know these protoplanets had been so
evolved, so this one rock changed the way we imagine and model the inner solar system of the past. Finally, another group of rocks could hold secrets about the gas giants in the outer solar system.

The Trojan asteroids are a population of asteroids locked in stable orbits ahead of and behind Jupiter. Scientists believe that they are remnants of the disc the planets formed out of and that Jupiter captured them as it grew. Since Jupiter was the first planet to form, these asteroids could be some of the most primitive in the entire solar system.

So they could potentially hold a lot of clues about the formation of the outer solar system. But they could also help scientists get to the bottom of another question, how much did Jupiter wander around before it settled into its current orbit. And that's a big question because Jupiter is so massive that wherever it was, it was definitely shaping the solar system as we know it. And the Trojans offer an interesting clue about how.

See there are about 50 percent more asteroids in the group ahead of Jupiter than there are in the group behind. Computer simulations
show that if Jupiter had formed in place and stayed where it was, the Trojan asteroids would be divided evenly. On the other hand, if Jupiter migrated inward while the solar system was forming, it  would have had a stronger influence on objects in front of it, so it would have locked more asteroids in ahead of it, than behind.

This suggests that Jupiter drifted toward the Sun and back again at
some point, which may have brought icy objects to the asteroid belt and stunted Mars' growth. And the Trojan asteroids give us a way to explore that. It's kind of incredible that we have so many ways to look back four-and-a-half billion years into the past, and it will be
exciting to see what else we learn from New Horizons as it sails through the Kuiper Belt. But in the meantime, there are plenty of clues to look out for right in our backyard. 

Thanks for watching this episode of Scishow Space. If you liked it you might like our video about why the solar system is surprisingly weird. You can watch that one next.

[Outro]
 
 
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