Astro Bob A look at celestial happenings in the Northland and beyond Bob King View my profile Click here to view previous posts or additional resources

Eenie, meenie, miney Mimas

Sunlight glints off a plate of ice floating in a raft of broken ice on Lake Superior recently. Favorable winds pushed lake ice into shore where it broke into sheets that piled one atop the other. Photo: Bob King

NASA's Cassini spacecraft orbiting Saturn has just returned the closest picture ever of the "Death Star" moon Mimas (MY-muss). The craft swooped only 9,000 miles from the 250-mile diameter moon this weekend and took this photo from 43,000 miles away on its way inbound. Mimas' composition resembles what's currently floating on Lake Superior -- it's almost all ice mixed with a small amount of rock.

Bodies like moons and planets are spherical because their self gravity literally molds them into spheres. Smaller moons and most asteroids and comets are irregular in shape because their gravity is too weak to do the job. At 250 miles across, Mimas is thought to be about the smallest an object can be and still crunch itself into a near-spherical shape. 

Saturn's moon Mimas. The large crater at left is Herschel. In the background are the cloudtops of Saturn. Hi-res photo HERE. Credit: NASA/JPL/Space Science Institute

Look at all those craters! In the deep chill that reigns at Saturn's distance, this little guy still preserves the battering it received during the early years of the solar system when meteorites and asteroids were more plentiful than they are today. The most amazing feature on the crater-pocked moon is the 80-mile-diameter crater Herschel, named after William Herschel who discovered Mimas in his telescope on September 17, 1789. Herschel crater is a third the size of the moon. An equivalent-sized crater on Earth would be nearly as large as the contiguous United States!

The fictional Death Star from the Star Wars movie series bears an uncanny resemblance to Saturn's moon Mimas. The moon-sized ship is said to house a more than a million people and has a superlaser capable of destroying planets. Credit and copyright: Lucasfilm Ltd. & TM. All Rights Reserved.

This week's highlights include a close conjunction tonight (Tues.) of Jupiter and Venus just above the west-southwest horizon directly below the crescent moon. Look about 15-20 minutes after sunset and use binoculars. The asteroid Vesta will be easy to pinpoint immediately west (right) of the star Gamma Leonis tonight as well. For a Vesta locator map, scroll three blog entries down. Clear skies are forecast for the Upper Midwest this evening so put on your hat and step into the cosmos.

Posted by: rking@duluthnews.com on 2/16/2010 at 8:36 AM | Comments (0) | Permalink | Edit

Tags: lake superior, death star, planet updater, astro bob, life, mimas, saturn, cassini