Ceres may be an invader from the outer solar system

I'm starting to wonder what normal is in the solar system.

Take Ceres. It was the first object to be found between Mars and Jupiter. Over a million main belt asteroids are now known, but Ceres is the largest. planetary scientists don't call it an asteroid because it's so big. An object that was well on its way to becoming a planet, but ran out of material before it could, is a Protoplanet.

It's over 900 kilometers across, and the Dawn spacecraft which went into space around the dwarf planet in March of 2015 revealed a rich, diverse, and spectacularly bizarre geography, with a crater with lots of bright spots that turned out to be salt.

There was a bigger surprise than the presence of ammonia. It's rare in the main asteroid belt, because it's at temperatures typical there. The presence of Ammonia mixed in with other compounds on the dwarf planet suggests it formed farther out in the solar system than previously thought. If that is the case, it must have moved between Mars and Jupiter.

We know that planets can move inward and outward, but could it also be true of Ceres?

A team of planetary scientists has published their research looking into this, and found that it is definitely possible.

This idea has been studied by many scientists. One way to do this is to use numerical simulations that use the mathematics of gravity and planetary interactions to see how multi-body systems would behave. The new thing here is that they start with a population of small objects out past Saturn, and then begin the simulations at a time when Jupiter and Saturn formed.

It is likely that a lot of big planets, 5 or so times the mass of the Earth, formed in the outer solar system and migrated inward, but couldn't get past Jupiter and Saturn. Two or three giant planets formed past Saturn, including Uranus and Neptune; a third may have formed and been ejected by interactions with Jupiter.

The new work starts with the fact that there may have been as many as 3,600 icy/rocky bodies past Saturn. There was still a disk of gas around the Sun at that time, and the Ceresoids, which were called by the paper they call them, are unlikely to become a thing. The bodies drag through the gas, but they also leave a wake behind them, and that wake causes the Ceresoids to fall. They would be helped by all of this.

Scientists found that most of the objects are lost after running the sims. Depending on where the body started out in the solar system, a small fraction survives. We're starting with 3,600 objects, so that's a tiny percentage. 70% of the objects that wound up in the asteroid belt had sizes similar to that of Ceres, and a third of them had a low tilt, according to the simulations.

After the gas giants formed, the giant planets started moving around. This wreaked havoc on the main asteroid belt, and probably cleared most of the objects in the main belt. When they account for that and all the other objects lost, their simulations show that about one Ceres-like object would remain.

That's convenient. That's how many we have. The next largest rock is Vesta, but it is only half the size of Ceres. The simulations seem to get an answer that's about right.

I caution that getting the right answer doesn't mean a simulation is right. Other factors could be important that the sims don't include. I wrote that about one of them is left. Some runs would have more. This result is statistical. That does match reality, so that means they appear to be doing this right. They note that any simulation is a simplified and idealized version of reality, and list where their work is limited. It is important to note where things could be improved in the future.

We used to think that the solar system formed where we see it today. We now know that it's not true. The outer planets are just one example of this. The movement is complex and subtle. Even though the planets are not engraved in space, they will change over billions of years. We can use our understanding of gravity to see where things were when the solar system was young.

As we run the virtual clock of our solar system backwards, I wonder what other surprises await us. It is possible that the first world that started off very different than it is now is Ceres.

I started questioning that a long time ago.