Carolyn Porco just tweeted about a beautiful image from Cassini, showing the icy moon Tethys hanging in space:
How forbidding and lovely!
Tethys is big, about 1100 km (660 miles) across (about 1/3 the diameter as our own Moon). Its density is actually a bit less than that of water, so it’s most likely predominantly composed of water ice. The surface is bombarded with craters, including the big one at the bottom called Melanthius. It’s 250 km across (150 miles!) and sports a massive central peak, common in larger craters. The crater itself is from a gigantic impact on the moon, and the central mountain forms when material is first displaced by the impact, then flows back. Under those titanic stresses, solid material can actually flow as the impact shock wave passes through, so these peaks are seen on lots of big objects in the solar system.
Cassini was 670,000 km (415,000 miles) from Tethys when it took this shot, which is nearly twice the Earth-Moon distance. The Sun is shining on Tethys from the left (the angle between the Sun, Tethys, and Cassini was about 41°, for those keeping track at home). You can see just how beaten Tethys is by looking at the terminator, the day/night dividing line, where shadows highlight the cratering. Even so, sandblasting by particles in Saturn’s rings has smoothed the moon’s surface, making it highly reflective — it’s shiny!
If there ever comes a day when I tire of seeing pictures like this, write my obituary. I’ll be done.
Image credit: NASA/JPL/Space Science Institute
July 14th, 2010 at 3:15 pm
Its belly button is an outie!
July 14th, 2010 at 3:22 pm
I´m done.
Seeing the well known rocks of our Solar System at ever more varieng angles and backgrounds is just getting old.
Sorry, but I want us to actually Go There. And beyond.
July 14th, 2010 at 3:23 pm
That’s no moon.
July 14th, 2010 at 3:29 pm
Can a surface be bombarded with craters?
July 14th, 2010 at 3:34 pm
It is. Yet another rock, possibly with a bunch of ice. And no amount of exclamation points will that anymore exciting than that. Until we go there.
July 14th, 2010 at 4:20 pm
@Craig #3
Your right “That’s no moon” … It’s a navel orange!
How exciting it would be to see images from a space craft in orbit of this!!!
Lets go! I packed already!
July 14th, 2010 at 4:34 pm
Though I wonder, what other popular 1980′s icon will appear next in a press release about Tethys.
Still, it really is an awesome shot.
July 14th, 2010 at 4:38 pm
Wow… that’s…
I remember growing up in the seventies, seeing the first Viking pictures, the first Voyager shots…I can’t believe this has become old hat to anyone.
Come on, people. We built an eye out of metal, put it on top of one of the largest explosions in human history, and threw it out into space so precisely it went exactly where we wanted it. Go there? WE ARE THERE! This is a dream.
Is that what growing up is like? I’m still stunned by tiny chunks of rock floating in space, but then I’m still amazed by every blade of grass. You can’t get tired of this stuff. This is everything.
July 14th, 2010 at 4:57 pm
Am I the only one who gets the Imperial Stormtrooper March playing through his head when he sees pictures of moons that look like this (Mimas particularly)?
DUN DUN DUN … DUN daDUN… DUN daDUN!!
July 14th, 2010 at 5:03 pm
Jens…Craig was making a Star Wars reference based on the resemblance of Tethys to the Death Star.
The quote is a pretty famous one for those of us who still get off on this kind of stuff.
July 14th, 2010 at 5:29 pm
Hey, what about moving it into Earth LEO or GEO–all that water ice!
Or, impact Mars–re-flood it after 3 by!
July 14th, 2010 at 6:45 pm
Somewhat OT but how cool is this?
http://io9.com/5586578/breathtaking-slr-photos-show-everyday-life-aboard-the-iss/gallery/
Yeah, its IO9. Sorry.
July 14th, 2010 at 7:52 pm
How often do you think Carolyn Porco changes her wallpaper?
July 14th, 2010 at 9:08 pm
Hi. Off topic question. It’s eleven pm eastern time in Maine and I just saw a shooting star moving wnw across the sky. It was incredibly bright with a thick white plume trailing it. Is there any meteor showers expected in my area or was it just a random one?
July 14th, 2010 at 9:24 pm
it looks like a boob
sorry for being like that everybody.
July 14th, 2010 at 9:32 pm
@Jens: I’d rather not go there to be honest. I’d rather send a robot there, does not look like a fun place to go.
@Chet: Do you want to be responsible for a the gravitational changes cause by moving a planetoid around the solar system?
July 14th, 2010 at 9:58 pm
Great, Saturn has *two* Death Stars. We are so hosed…
July 14th, 2010 at 10:07 pm
Hm, thought this was Mimas at first because of the big Death Star-esque crater… Nice picture!
July 14th, 2010 at 10:24 pm
Great image – Cassini never fails to deliver stunning images & neither does Carolyn Porco and I, for one, just love that! To them I say a big “thankyou.”
@6. Russell Says:
A gargantuan scoop of vanilla ice cream.
That’s what it looks like to me.
@17. KSK Says:
July 14th, 2010 at 10:52 pm
@ 14. John Page Says:
I’d recomend checking out the Meteor showers online website here :
http://meteorshowersonline.com/index.html
its got a lot of good info and resources that may be handy for you in answering that.
A quick glance through my 2010 Sky At Night astronomy calendar that lists the main meteor showers for the northern hemisphere+ reveals no likely candidate ones – the closest being the Southern Delta Aquarids which peak on July 28th. So it is most likely a sporadic meteor but I could be wrong.
You’re lucky – and observant. There is certainly something awe-inspiring, magnificently beautiful and so incredibly satisfying about seeing a bright “shooting star.” They are nature’s firework’s (along with lightning) set off at random and surprising us with spectacle. I love watching them myself.
************************************
+ I’m a Southern Hemispherean myself but I do get the english magazines & esp. Patrick Moore’s one!
July 14th, 2010 at 11:18 pm
I love the smaller, almost duplicate crater just north of the main gun…
July 14th, 2010 at 11:41 pm
Thanks Messier. It was a gorgeous sight.
July 14th, 2010 at 11:44 pm
ouu, what a cute planet :p
July 15th, 2010 at 3:07 am
Ooooh . . . Shiny!
July 15th, 2010 at 7:21 am
Predominantly composed of water? Like Europa, but colder, so the surface is not completely smooth? Notwithstanding, the surface looks less cratered than you might expect – compare the Moon, or Mercury. Has anyone estimated how long ago Melanthius might have been created?
Melanthius is about 245 km across, roughly a quarter of the diameter of Tethys. Tethys has an other large crater, Odysseus (not visible in this image), which is getting on for twice as large – 445 km across.
July 15th, 2010 at 7:51 am
Disappointed, I thought Phil was going to give us an estimate of the height of that central peak. I’ll have to try it myself. Tethys scales at 1100km = 102 mm on my screen. The mountain scales at least 2 mm high (big margin of error here), which works out to 22 km. Olympus Mons on Mars is about 27 km high, so I think this peak needs to be measured to see if O.M. retains its title. And it needs a name.
July 15th, 2010 at 9:34 am
@ ^ Mapnut : Thanks for that.
As for a name – Melanthius Mons?
July 15th, 2010 at 12:08 pm
I don’t care if people here are jaded. I find it amazing. I want to go to “beyond” too but I’m still just amazed that we even get pictures like this. If you want to go there, then go there. I find sophisticated cynicism boorish.
July 15th, 2010 at 3:33 pm
looks like an egg to me. An gargantuan egg. Wonder what is inside, and what hatches from it when the time comes
July 15th, 2010 at 4:18 pm
Anyone for mountian cilming? should be easy if this moons gravity is low .
July 15th, 2010 at 8:01 pm
@ ^ mike burkhart :
Yes the gravity certainly would be low!
As the BA noted in the Opening Post here :
A quick look at a couple of relative sizes posters (from Scientific American magazine years ago) shows that Tethys is smaller than Pluto and even the Ouranosian moon Ariel. Among Saturn’s major moons Tethys is smaller than Titan, Rhea and Iapetus about the same size as Dione and looks about twice as big as Enceladus and the slightly smaller again Mimas – which is the original “death star” moon!
Mountain climbing on the central peak of Melanthius crater? I’d love to see – or better yet *do* that!
@ 28. Nerdista : I agree!
July 15th, 2010 at 8:52 pm
@Nerdista: I’m not jaded, I’m more of a realist. It’s much more realistic to send a robot than a human for these kinds of missions. Unless we’re trying to build a colony of some sort, I feel that sending humans to the location is daunting and inefficient.
July 15th, 2010 at 11:14 pm
All we need to do now is to make a giant glass of scotch for this ice sphere!
July 16th, 2010 at 7:50 am
It looks so cool. Hahaha Cool, get it?
…
…
…
Fine, be that way, don’t laugh.
July 16th, 2010 at 12:05 pm
“[Tethys's] density is actually a bit less than that of water…”
How do we know that?
July 16th, 2010 at 9:35 pm
Aaron,
I think we can calculate its mass, first, from how it orbits Saturn. Knowing its mass and then measuring its size yields its density.
July 17th, 2010 at 1:15 am
26. Mapnut Says:
July 15th, 2010 at 7:51 am
Disappointed, I thought Phil was going to give us an estimate of the height of that central peak. I’ll have to try it myself. Tethys scales at 1100km = 102 mm on my screen. The mountain scales at least 2 mm high (big margin of error here), which works out to 22 km. Olympus Mons on Mars is about 27 km high, so I think this peak needs to be measured to see if O.M. retains its title. And it needs a name.
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I googled another photo of Tethys which showed the moon from almost directly above the Melanthius crater. The first photo shows Mount Melanthius (for want of another name for the impact peak in the center of the crater) edge on; the second photo reveals Mount Melanthius to be a ridge approximately 18 miles in length. Assuming my scale estimate is correct, the Melanthius peak appears in the second photo to be casting a shadow about four miles in length. Estimating that the Sun as seen from the Melanthius crater floor was appearing 20 degrees above the Tethys horizon, we can use simple Trig to calculate that Mount Melanthius rises around 7,000 to 7,400 feet above the crater’s floor. Standing at its base, Mount Melanthius would be an impressive sight.
July 18th, 2010 at 9:05 am
@ ^ Alabama_Al : Thanks for calculating that – an impressive mountain indeed. Wonder how it does compare with Olympus Mons more precisely and other volcanoes on the Martian Tharsis bulge and Elysium plateau plus on the weird fractured Ouranosian moon Miranda too?
July 19th, 2010 at 10:44 am
the crater is close in size to the chixulub impact site on the yucatan. the hit must of raised the mother of all snow falls.
July 19th, 2010 at 4:34 pm
Truly awesome photo, but about that on/off switch at the bottom…