
Did you know there’s a strange little “dwarf planet” named Ceres that hangs out inside the asteroid belt between Jupiter and Mars?
Astronomers are interested in the little planetoid, and they’re using data from a long-ago mission by the NASA Dawn spacecraft to get closer to figuring out where Ceres came from. The conventional wisdom has been that Ceres was formed in and from the asteroid field where it currently orbits, but some researchers think it may have come from a bit farther away.
Ceres has some qualities that set it apart from the other rocks in the asteroid belt which is why scientists are questioning the conventional wisdom about its origins. Compared to an asteroid, Ceres is huge, but it’s tiny when stacked up next to the moon; the orbiting body is only 596 miles wide. For comparison, the diameter of Earth, the distance from our planet’s center to the surface, is just less than 8,000 miles.
What sets Ceres apart from its asteroid neighbors? First, it’s size; Ceres is by far the largest rock on that particular space block. It also seems to be composed of different material from its orbiting neighbors. For example, there is frozen ammonia on Ceres (this was new information sent back to earth by the Dawn craft between 2015 and 2018).
Because scientists believe ammonia is only stable in the outer solar system far away from the sun, some think this may indicate that Ceres was formed on the edge of our solar system. Perhaps it made its way closer to the sun and was captured by the gravitational pull in the asteroid belt region between Mars and Jupiter.
But the plot has a twist. Even newer data is tugging some scientists back into the “born among the asteroids” camp. A 450 million-year-old impact crater on Ceres measuring 40 miles across allows researchers to see into the planetary body’s past and examine the chemicals that make it up.
You see, Ceres is what is called a “cryovolcanic” object. That is, it has volcanoes that emit icy sludge instead of hot lava. The impact crater scientists are studying appears to have evidence of a liquid brine that has bubbled up over billions of years, and this brine may have produced ammonium, which is very close to ammonia except that it has an extra ion. This might explain how ammonia could form on an object much closer to the sun.