Cassini Flies by Tethys

September 26, 2005 8:04 PM

Cassini Flies by Tethys and Hyperion, and the photos so far have been awesome and weird. I especially want to point out this fascinating view, which, if you look at it closely, reveals what appears to be a string of small impact craters, in a straight line over older terrain. What kind of meteor impact could have produced such an excellent formation of craters? Hyperion photos are coming. (Kokogiak's got backup in case the JRUNS strike.)
posted by brownpau (29 comments total)

first person to notice the strongbad reference! woohoo!

but seriously, that's rad as hell. the weirdest thing about those photos, to my mind, is that they seem to be inverted. rather than looking at a craterous moon from the outside, it feels like we're looking at the moon from the inside (like a balloon) and seeing the craters appear like bumps all along the inside of the moon.

that's the problem with photos taken close enough to remove all context, I suppose.

really really great. thanks.
posted by shmegegge at 8:08 PM on September 26, 2005

a string of small impact craters, in a straight line over older terrain

Looks like a line of divots in the sand under an eave on the summer cottage
posted by CynicalKnight at 8:16 PM on September 26, 2005

I was going to say that it must be a pattern-recognition thing, like the Man in the Moon, because I didn't see the line you were talking about. Then I looked at the 'closely' link and zoomed in (Firefox scaled it by default) and FINALLY saw what you were posting about.

I'm amazed you saw it in the first place. Good eye for detail there.
posted by Malor at 8:17 PM on September 26, 2005

Tethys has the worst skin, ever.

But seriously folks, I went out once to see a flyby of Neptune at a local observatory. I was in awe of the low light strangeness out there on the back 6 of our solar system. Tethys looks like such foment, yet still and metallic, a potential. The Cassini adventure has been so beautiful and haunting.
posted by Oyéah at 8:18 PM on September 26, 2005

I'm looking at Tethys, but I can't seem to find the farcasters.
posted by Sangermaine at 8:28 PM on September 26, 2005

but seriously, that's rad as hell. the weirdest thing about those photos, to my mind, is that they seem to be inverted.

I get the same thing, with a lot of photos of planet surfaces (Mars as well, for instance) and it really annoys me - I wish I could see the craters as craters, instead of as bumps. Is there any trick to making my brain turn them inside-out?
posted by Jimbob at 8:33 PM on September 26, 2005

Save the pictures and turn them upside down.
posted by longsleeves at 8:40 PM on September 26, 2005

I see it! How strange.
posted by wsg at 8:41 PM on September 26, 2005

Or try inverting the colors (negative view)
posted by longsleeves at 8:44 PM on September 26, 2005

Hyperion looks like a potato made of coral. Thanks for the site, brownpau.
posted by Cranberry at 8:58 PM on September 26, 2005

Beautiful/Confounding/Enlightening/Amazing
Thank you very much!
posted by numlok at 9:00 PM on September 26, 2005

Now I'm no astronomer, but I seem to remember when Shoemaker-Levy hit Jupiter, the tidal forces on it had fractured it into a series of subcomets. Actually, here's a website. So perhaps this is a similar phenomena, on a smaller scale.
posted by freedryk at 9:18 PM on September 26, 2005

Thanks for this.
posted by interrobang at 9:26 PM on September 26, 2005

Yeah, that crater/bump illusion is wild. I looked at this one as it loaded and saw the craters plain as day. Then I looked away for a second and looked back and all I could see was BUMPS. Now I can't get the craters back.

As to the line of small craters, that is fascinating. The only thing that I can think of is an object that comes in at a flat tragectory and skips (like a stone on water) to a stop. Notice how the craters at the bottom are bigger and farther apart, and then smaller and closer together? (Object moving from 7:00 to 1:00 in direction.)
posted by spock at 10:23 PM on September 26, 2005

I agree with freedryk that a series of smaller bits in a line impacted with it while the terrain rotated out from under it.
posted by devetron at 10:33 PM on September 26, 2005

freedryk, devetron, my thought too. Comet-or-whatever gets pulled apart by tides into a line of fragments, fragments hit Tethys.

Try as I might, though, I can't make myself see those craters right-side-out. Usually I can do it by tilting my head or staring long enough. It's the Mystery of Tethys!
posted by hattifattener at 11:11 PM on September 26, 2005

The bit with the craters looking like bumps might be related to an optical illusion that occurs if your light source is on the floor. Because the overwhelming majority of animal and human development took place with the sun as the only souce of light, when the light comes from below rather than above convex and concave deformations on a smooth surface are visually inverted for most people.

Is it possible the weird lighting/camera angles at work here may be producing the same effect?
posted by Ryvar at 11:22 PM on September 26, 2005

Is it possible the weird lighting/camera angles at work here may be producing the same effect?

I think so. It appears to me that, as Sunlight is coming from the bottom left (sort of south-west, looking at it like a map), it creates a shadow on the south-western western edge of each of the craters (the sun is low in the sky to the left and down, so if you were at the bottom of the crater up against that wall, you couldn't see the Sun).

Then, as you get to the eastern edge, the sudden change in the angle at the top of the crater between the normal to the surface and the line of sight to the sun decreases the flux of sunlight through the solid angle towards the camera. So you end up with a crater that has a dark outline all the way around, very similar to what you'd see if looking at a hill from above at noon: like a bump. Were the sun light roughly in line with the camera, I belive that everything would appear more naturally.
posted by dsword at 12:07 AM on September 27, 2005

I'm looking at Tethys, but I can't seem to find the farcasters.

Ha, you got to it first, and probably in a funnier way than I would have. Cheers :)
posted by mikeweeney at 4:07 AM on September 27, 2005

My first theory on the line of bumps was a bouncy graze by a passing rock on extra-soft terrain, but yeah, freedryk's sequential-pieces-of-a-tidal-torn-meteor is most sensible. Also, Tethys is composed mostly of water ice, is very tenuous in structure because of its huge "death star" crater, and it orbits within the E Ring, so it must be pretty steadily bombarded by all sorts of matter.
posted by brownpau at 4:20 AM on September 27, 2005

Update! Check out the raw images for incoming photos of Hyperion.
posted by brownpau at 4:22 AM on September 27, 2005

Excellent post. I like the Hyperion pictures even better.
posted by OmieWise at 5:22 AM on September 27, 2005

In Mike Collins' book Carrying the Fire, about the Apollo 11 mission, there is a similar photograph of a line of craters on the Moon. I'm sure the photo is somewhere on-line in the NASA archives. It was even more impressive than these photos.

Excellent shots. This sort of thing gives me wood. Plus, it's kind of neat knowing that somewhere, millions of miles away, a little object of ours is floating around somewhere.
posted by bondcliff at 6:09 AM on September 27, 2005

Looks like we might have had our own multiple strike here on earth (pdf).
posted by leebree at 6:51 AM on September 27, 2005

Cranberry's right: Hyperion has this bizarre, beautiful "coral" look to it. Great links.
posted by selfnoise at 8:21 AM on September 27, 2005

A chain of craters is called a catena. There are a number of them on the Moon; one of the best known is Davy. Volcanic activity has been proposed as one possibility (a known phenomenon on Earth; see the Hawaiian islands), but the most likely source of cratering, as opposed to convex formations, is a tidally-broken orbiting object. The Moon has (or had) magma, which produced the "seas" when released by a meteor strike, but no drifting continents.


Uh, the thing on the right is part of the spacecraft.

More on crater chains.
posted by dhartung at 10:13 AM on September 27, 2005

RE the crater/bump visual conundrum: look at the dark area of a crater and imagine dropping something down the slope. Try and picture it rolling and disappearing from view - when I do that all the bumps "jump" back into being craters...
posted by jalexei at 11:11 AM on September 27, 2005

Jalexei, that is so cool! Thanks!
posted by longsleeves at 4:19 PM on September 27, 2005

Hyperion looks just like my old bathtub sponge!

I have to go take a bath now, and reminisce.
posted by jfwlucy at 5:35 PM on September 27, 2005