on Ceres

It’s going to be a big year for Solar System research. Not only is there good news about a future mission to Europa, this summer the New Horizons space probe will shoot past Pluto, and the Dawn spacecraft is now approaching Ceres.

1 Ceres is an interesting object. It’s the largest asteroid – almost 500 kilometers in diameter – in the asteroid belt. And now that the Dawn spacecraft has visited 4 Vesta and shown it’s not in hydrostatic equilibrium (i.e. not round) Ceres is the only one that qualifies as a dwarf planet. It may have an atmosphere, it may have a substantial amount of ice…

Since my last post on the subject of planets, I’ve run into some rather spirited planetary scientists who informed me that the geophysical definition of a “planet” is “anything in hydrostatic equilibrium”. In that sense, Ceres IS a planet (as it was originally thought to be back in the 1800s when it was first discovered), as is the Earth, the Moon, Europa, Enceladus, Titan, Triton, Miranda, Titania, Oberon, Pluto, Charon, Eris, Haumea, Makemake, and dozens of others. I’m not sure I like diluting the term “planet” to things that are not the most prominent objects in a star system, but I can at least agree that Ceres is a fascinating little world.

Prior to the Dawn flyby, the best image we had of Ceres was this, taken by the Hubble Space Telescope in 2003:
1 Ceres, as seen by the Hubble Space Telescope in 2003.
Since Dawn began its approach in January, our view of Ceres has gone from that, to this:
1 Ceres, January 25th
to this:
1 Ceres, as imaged on February 19th
And what a world. It looks like a tiny moon. It’s like someone lifted a bunch of craters and wrapped them around a small ball.

And no one knows what those bright dots are. I’m sure we will soon. The bright spots may have been visible since those HST pictures. The suggestions are that Ceres may have volcanoes, or ice, or something shiny… Not being a planetary scientist, all I can do is sit back and watch.

Sometimes the best questions in science are “what the hell is that?”


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