Death Star moon Mimas meets its twin in Tethys

Saturn’s two “Death Star” moons – Tethys (right) with its 276-mile diameter Odysseus crater and smaller Mimas with its 86-mile wide crater Herschel. Credit: NASA

I originally planned a book review on a new asteroid book today but decided to hold off a couple days because of little time and other plans. Don’t worry, it’ll arrive in this space shortly. For fun I thought I’d share a recently released photo taken by the Cassini space probe of Saturn’s moon Tethys (TEE-this). This 660-mile wide ice ball orbits the planet every 1.9 days. In 6-inch and larger telescopes it’s a faint point of light hovering near the planet like a moth around a candle flame. Mimas is even closer to the great ringed one, zipping around it in just under a day.

George Lucas Death Star from the Star Wars movie series.

Both it and another Saturnian moon, Mimas (MEE-muss) have large craters that size and appearance-wise are a good match for the concave disks of the superlasers in the infamous Death Stars, the moon-sized battle stations built by the evil Galactic Empire in the Star Wars movies. Mimas earned the nickname Death Star moon years ago, but Cassini proves that seen from the right angle, Tethys is just as capable of going over to the dark side.

Both moons have densities indicating they’re composed mostly of water ice. That tells us something about how bitterly cold (about 325 below F surface temp) it must be at Saturn’s distance from the sun for craters blasted from ice to remain sharp and clear 4 billion years after their origin.

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About astrobob

My name is Bob King and I work at the Duluth News Tribune in Duluth, Minn. as a photographer and photo editor. I'm also an amateur astronomer and have been keen on the sky since age 11. My modest credentials include membership in the American Association of Variable Star Observers (AAVSO) where I'm a regular contributor, International Meteorite Collectors Assn. and Arrowhead Astronomical Society. I also teach community education astronomy classes at our local planetarium.

7 thoughts on “Death Star moon Mimas meets its twin in Tethys

  1. Aloha astrobob!

    I fully realize that all previous “space probes” have given humankind almost all the knowledge of “space” we know and that were it not for them, Cassini wouldn’t have been possible. That said, for me personally, this one “space probe” has given me more delight in the absolutely breathtaking photographs of Saturn and its moons that it has found so far. In fact, I use one of the photos it took as a “wallpaper” picture on my computer due to what I think is the sheer beauty of this planet.

    It was taken with Saturn actually BETWEEN the Sun and Cassini so there is this fascinating “backlighting” of the planet and its “rings”. The rings don’t have much color to them and seem to be shades of ‘green and grey’. But the very fact that we were able to get a photo that is so crisp and clear of this planet from so very far away…well, it still leaves me almost speechless. Most people seem to think that these photos aren’t “real” and NASA has simply made “digital” pictures for release. Of course NASA may have “touched up” these photos, but for the most part, they are the real deal sent back to us from Cassini. Those that refuse to believe these pics are real may also be the ones who believe the moon landing was staged in Hollywood/some desert.

    For a great selection of these photographs, all anyone has to do is a search on MSN using ‘bing’ for “cassini photos of Saturn” and click on the 1st ‘result’ that comes up. Or, click on/use this link:

    http://www.bing.com/images/search?q=cassini+photos+of+saturn&qpvt=cassini+photos+of+saturn&FORM=IGRE

    I realize that the “feeling” of seeing the planets through a telescope gives us an awesome and mind-boggling experience, but our accomplishments of sending spacecraft that we’ve built way, way “out there” and successfully do what we wanted them to is one of the greatest achievements in humankinds short history and will never cease to amaze and ‘shock’ me. It’s a real shame that this equipments “reward” should be ‘self destruction’. Too bad we don’t reserve enough fuel and program them to make a soft enough landing so if and when the time comes that we have “colonies” on the moon and perhaps other planets, we could find them and preserve them in some sort of “historical science museum”. Or even for “parts” that may be recyclable!

    It just seems to be one of our “legacies” to leave “trash/garbage” wherever humankind goes. There has to be a better way if all we want to do is dispose of these spacecraft (send them hurtling toward the Sun?). Don’t you think, or don’t you?

    • Wayne,
      I agree with you on the wonderful images sent back by Cassini and their capacity for inspiration but must take exception with your description that they’re real “for the most part”. I’m afraid this might imply to some readers that some of the images are faked. I don’t believe you intended that but wanted to call it out. While false colors are used to enhance contrast or show differences in composition, heat content, etc., NASA clearly states why those colors are added. They also point out in captions when something’s a true photo vs. an artist rendition.

      As for crashing the two probes, I think you’re sweating the small stuff. NASA eked science out of the mountain hits by studying the impacts. They also used the crash to determine whether fuel tank readings were accurate. To launch them from low lunar orbit into the sun would require a great deal more fuel, increasing the cost of the project and making it less likely to be funded in the first place. While I’m fastidious about not littering, wherever we might explore we necessarily have to leave parachutes, backshells, landers and equipment. Like you, I think we should keep it to a minimum, but at least for the foreseeable future these are tiny bits of “garbage” in a vast empty landscape. More concerning to me is the enormous amount of junk we’ve sent into orbit around Earth. There’s so much litter up there, collisions – and the creation of more litter – are inevitable.

  2. Bob, have you heard anything recently about the three sunspots in a group and one of them is splitting, and another similar active region only a few days away and another coronal hole, as it says this could be bad for us even though I don’t know why as I’m sure throughout earths life we have had plenty of these that cause no damage, but it say’s that this could knock the electrical grids out etc, but usually you tell us about any for possible auroras, but this is all made out to be bad. Thanks if you can help :-)

    • Lynn,
      Nothing unusual about any of this. There’s a slight chance for moderate flares in the coming few days but nothing out of the ordinary. Coronal holes are extremely common; none are aimed toward Earth currently.

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