Comments on: The Ringed Planet’s Ringed Moon

By: StevoR

StevoR — Wed, 12 Mar 2008 07:31:04 +0000

Thanks for that John Weiss.

Didn’t know Enceladus’ atmosphere was only at the south pole … Figured it would’ve spread all around the planet although I knew it was thin. Cool! Leran something new every day ..

By: John Weiss

John Weiss — Fri, 07 Mar 2008 17:37:41 +0000

AR: Yeah, you could tell with sufficiently precise measurements. The Moon doesn’t orbit the Sun, it orbits Earth. It’s distance from the Sun varies with each month (which is different from the annual variation). In principle this could be measured (the effect is ~0.3%), but would probably be pretty rough to actually do. Using a heliostat to measure the apparent diameter of the Sun throughout a year might permit this.

zandperl: There are no solar wind protons at Rhea, Saturn’s magnetosphere keeps them out. There are protons in the magnetosphere, but they have such large gyroradii that detecting something like a ring around Rhea is probably right out.

StevoR: Right all around (Hyperion and Janus and Epimetheus). The co-orbital will swap again in 2009 sometime.

And Enceladus only has an atmosphere at the south pole, as far as I know. In that location, it’s due to the jets in that region (like Io’s patchy atmosphere due to its volcanoes). If you shut off the source, you’d lose the atmosphere fairly quickly I’m pretty sure.

changcho: It depends somewhat on the impact angle. A large, glancing blow could kick debris into orbit. This is, after all, how we think we got our Moon. I’m not sure that that’s any less probable than capturing ring material with no obvious way to dissipate energy. (Apart from three-body captures, of course.)

By: PsyberDave

PsyberDave — Fri, 07 Mar 2008 17:11:31 +0000

Colonists on Uranus?

Nice.

I bet they will be Klingons.

By: StevoR

StevoR — Fri, 07 Mar 2008 11:17:54 +0000

Spoketh # Lugosion 06 Mar 2008 at 8:45 pm

“There’s rings around Uranus!?!? Sounds like someone needs to work on their personal hygiene.”

No more asinine joke sabout Ouranos please .. I’ve heard ‘em all – & pity the poor colonist who’ll one day (perhaps, if humans are .. well not lucky but rather smart & brave) live in that Uranian system!

By: StevoR

StevoR — Fri, 07 Mar 2008 10:34:10 +0000

Oh & Saturn’s also got the moons that switch orbits (Janus & Epimetheus?) too right ..?

Plus the odd spongecake texture surface, oddly rotating natural satellite Hyperion correct?

(Off top of head could look it up but …nah!)

By: StevoR

StevoR — Fri, 07 Mar 2008 10:31:08 +0000

Interesting to note that the NASA press release stated Rhea lacks an atmosphere yet Enceladus has one – but Rhea is larger (second only to Titan of Saturn’s many moons) and I’d presume more massive too ..

Why is that – anyone?

Cool discovery though I’m keen to see more findings on this.
If asteroids can have moons – and some (eg. Ida and Sylvia) do then why not a moon with rings although I would’ve thought the primary planets gravity would intervene & prevent it?

Thanks Phil Plait, Dr Bad Astronomer sir, well done as ever!

BTW. Your name ( & webblog) was mentioned and book shown on the big lecture screen at a talk on astronomical hoaxes by Steve Roberts of the Victorian Astronomical Society & Australian Skeptics at the March meeting of the South Australian Astronomical Society the other night. Thought you’d like to know! The video is even available if folks want .. Good talk too.

By: AR

AR — Fri, 07 Mar 2008 07:07:28 +0000

Speaking of moon’s, I’ve been wondering about something you might be able to answer: If there were an observer on the far side of Earth’s moon with knowledge of modern physics but ignorant about the structure of our own solar system, could they, without leaving their home or launching spacecraft, deduce the existence of Earth? Because it seems to me like the Moon would be indistinguishable from a planet with a 2,551,000 second long day from that point, but I know that astronomers can be very clever when necessary, so I can’t be sure.