steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
A fifth moon of Pluto has been discovered.

Here is a Hubble Space Telescope press release.

And here is an article from Sky and Telescope.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Tiny, Gentle Pluto May In Fact Be A Killer

A bit of an overdramatic headline, but the article's got interesting stuff in it. The core idea is that the New Horizons spacecraft is on the way to the Pluto system, scheduled to arrive in 2015; when the project was first designed, Pluto was only known to have one moon, the rather large Charon, but since then, 3 smaller moons have been discovered - two that were first suspected in 2005 and confirmed in 2006, and one that was discovered in 2011. And there are suspicions that there may be more small moons; partly this is a matter of "well, if there were three hiding until recently, maybe there are more that are still hiding", but there's a more concrete aspect: there were actually two specific satellite candidates that were found, but more observation is needed in order to figure out if they're actually satellites or not. In addition, there's a possibility that impacts onto these moons may create rings around Pluto. The more moons and rings there are around Pluto, the more risk there is that New Horizons will smash into something and be damaged or destroyed when it gets to the Pluto system.

I'd heard before about the concerns for New Horizons about Pluto having more moons and rings. What was new to me in this article, and particularly interesting, was that there are specific identified candidates for further moons, not just a general sense that there could be more moons.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Mike Brown on the sizes of Eris and Pluto, and why the discovery that Eris is almost exactly the same diameter as Pluto actually tells us that Eris is more different from Pluto than expected.

Basically: We know Eris is a bit more massive than Pluto, so if it also had a bit bigger diameter than Pluto, it could have the same density, and therefore be made more or less of the same stuff. But since it's the same diameter, it must be denser, and therefore made of different stuff.
steorra: Part of Saturn in the shade of its rings (Default)
[personal profile] steorra
Vesta
So, a few days ago, Dawn entered orbit around Vesta, and is now slowly spiralling in towards its intended science orbit. Already it has sent back some pictures that show interesting amounts of detail: this one from July 17 (press release for the image) and this one from July 18 (press release for the image).

Both pictures largely show the south polar terrain, where a large impact is believed to have taken quite a chunk off of Vesta; in the middle of the south polar terrain is a large peak.

What catches my attention is the texture of the south polar terrain. There are a lot of grooves and ridges that I suppose were probably formed in some way by the impact. There are craters on it, but it's not thoroughly cratered, which ought to indicate that it's not very very old. (It would be nice to see how cratered the rest of Vesta appears, for comparison, but the pictures we have so far don't show that very well; you can see a bit of the non-south-polar terrain in the July 17 picture.)

Pluto's moons
On Wednesday, the discovery of a fourth moon orbiting Pluto was announced! It was discovered with the Hubble Space Telescope.

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