You can see Ceres, a salty asteroid

Ceres - but what is it?

I've mentioned the dwarf planet Ceres in my posts before, but only in passing. it's a little hard to introduce Ceres, due to confusion over nomenclature. It used to be considered the largest asteroid, but with all the debate over asteroids and dwarf planets, I really have no idea what I'm meant to call it.

It's certainly the largest object found in the so-called "asteroid belt", but also the only defined "dwarf planet" found this side of Neptune. Apart from that, well, frankly you can call it what you want in this post-modern world.


We've known about Ceres since the start of the 19th Century. Astronomers had been looking for planets in the zone between Mars and Jupiter. Kepler had noticed this gap was large enough to contain a planet, but didn't seen to have one. Following a search, astronomers discovered a number of objects. They called this group "asteroids", meaning things that are "almost, but not quite, entirely unlike stars".

I'm not saying it's aliens, but...

In modern times, the thing that's most interesting about Ceres is its white dots. The Hubble Space Telescope got a few photos of odd bright patches on Ceres back in 2004.

Clearly - aliens.

It's not aliens

In 2015, NASA's Dawn probe entered orbit around Ceres (after having previously visited Vesta). This is a photo it took on approach. The white dots are clearly visible.

After a lot of observations, scientists concluded that that these patches are made up of bright salt, mostly sodium carbonate. These had probably formed when salty water bubbled up from Ceres' "muddy" interior, the water then sublimating off into space.

Judging from the amount of mixing the surface gets from being bombarded by meteorites, the percolation of brine to the surface is still happening, meaning Ceres is still volcanically active.

You can see Ceres

It's a bit of a challenge, though. Ceres is magnitude 7.7, so you're going to need a medium sized telescope, a tracking mount and a camera. Currently, Ceres is between Aquarius and Sculptor, not far from the Helix Nebula. It rises after 6pm (Melbourne time) and sets at about 9am, and transits slightly to the north of the equator, nearly directly overhead. In short, it's perfectly placed for observers in the Southern Hemisphere. If you've got a go-to mount, find a star called SAO 191585.

How to photograph it - and then how to tell tell you've got it

To see Ceres, the technique is pretty much any dim solar system object. Take an exposure of about 30 seconds while your mount is tracking. Then about an hour or more, come back and take another one, or better still, keep taking images continuously for a couple of hours.

To check you've got it, while you're in the field, compare images taken an hour or so apart. Ceres will be the dot that moves slowly across the face of the other stars. Make sure you're not foxed by a satellite, which would appear as a line rather than a dot. If you can't see it, don't despair, it may show up in processing.

My rig's field of view is about 1.8° wide, and Ceres takes about ten days to cross this. It doesn't move quickly.

Good luck!

...and apologies to Douglas Adams