Looking Up: Big Little Ceres

May 21, 2018

The Earth, moon, and Ceres in comparison
Credit Gregory H. Revera, NASA/JPL-Caltech/UCLA/MPS/DLR/IDA / wikimedia commons

This week on Looking Up we check in on one of our solar system neighbors... Ceres.

Can we talk Ceres for a minute? Or, more precisely, 90 seconds? You see, Ceres, the largest asteroid in the Solar System, is particularly well positioned to observe this week, and you should take a look – Ceres-ously!

The asteroid belt lies between Mars and Jupiter and has lots and lots of hunks of rock floating around out there. Some astronomers think that, were it not for the gravity of Jupiter keeping the rocks all messed up, that these rocks would have coalesced to form a planet at the dawn of the Solar System. But, because Jupiter is a bully, we have lots of rocks, and as I said, the biggest is Ceres.

Ceres was discovered in 1800, when a group of astronomers went looking in the place they thought a planet should be. And they found Ceres. Now size-wise, Ceres is big for an asteroid, but isn’t really planet-sized. But at roughly the size of Texas, it’s a big hunk of rock, big enough that for about 50 years or so, Ceres was called the “9th planet” of the Solar System. It was dethroned from the planetary perch in the mid-1800s, but as the largest of the asteroids, and the only one big enough to be pulled into a sphere by its own gravity, Ceres is now classified as a dwarf planet, the same as Pluto. But unlike Pluto, Ceres may have a liquid ocean of water under its surface! 

Credit NASA, ESA, and A. Feild (STScI) / wikimedia commons

Ceres in in Leo these days, as it moved around the Sun in its 4.5 year orbit. So take a look at this damp dwarf planet and shake a fist at the bully Jupiter for keeping Ceres down.  

This image was taken by NASA's Dawn spacecraft of dwarf planet Ceres on Feb. 19 from a distance of nearly 29,000 miles (46,000 kilometers). It shows that the brightest spot on Ceres has a dimmer companion, which apparently lies in the same basin.
Credit NASA/JPL-Caltech/UCLA/MPS/DLR/IDA / nasa.gov

If you’d like to take a closer look at Ceres or any of the other wonderful and amazing things in the sky, please visit csastro.org for a link to information on our monthly meetings and our free public star parties.