Jimmy Westlake: Dawn arrives at Ceres this week
Steamboat Springs — 2015 might well be called “The Year of the Dwarf Planets.” Not one but two of the five dwarf planets in our solar system will be visited for the first time by robotic spacecraft this year, starting with dwarf planet and largest member of the asteroid belt, Ceres.
Ceres was discovered telescopically Jan. 1, 1801, by Italian astronomer Giuseppe Piazzi and immediately was announced as a new planet in our solar system, orbiting in the huge gulf between Mars and Jupiter. After many other small objects were found orbiting in the same vicinity as Ceres, it eventually was demoted from planet-hood and awarded the consolation prize of being the biggest of the asteroids.
Astronomers of that time wondered if these many small pieces might be the remains of a disrupted planet. Because they essentially looked like little stars through the telescope rather than spherical orbs like the known planets, they were given the name “star-like planets,” or asteroids.
Ceres’ classification changed yet again in 2006 when the International Astronomical Union invented a new class of objects called dwarf planets. As a result, Ceres was promoted from asteroid to dwarf planet. The IAU has not yet officially addressed Ceres’ dual classification as the smallest dwarf planet and the largest asteroid.
Ceres is about 595 miles in diameter — about the size of the state of Texas. From Earth, it appears as little more than a tiny ball with indistinct light and dark patches on its surface, even using the Hubble Space Telescope.
Ceres formed beyond the “frost line” in our nascent solar system, 4.6 billion years ago, so astronomers believe that it might contain a large amount of ice or maybe even liquid water inside. It likely has a small rocky/metallic core, then an icy layer, topped off with a dusty/icy crust.
After an eight-year journey, NASA’s Dawn spacecraft, launched in September 2007, is poised to arrive at Ceres and be captured into orbit around it Friday, March 6.
Dawn will then settle into a one-year scientific mission to map and explore the surface of what could be described as the smallest terrestrial planet. We know virtually nothing about this Texas-sized asteroid/dwarf planet thing, so Dawn will open our eyes to it for the first time. Expect surprises.
Already, images taken by Dawn as it approaches Ceres have far exceeded Hubble’s best shots. We now can see craters large and small pocking Ceres’ surface.
Of particular interest are several extremely bright, reflective patches inside of some craters. The images are not yet clear enough to determine the nature of Ceres’ bright spots, but speculation is running high that they might represent the surfaces of reflective frozen lakes or maybe even ice volcanoes.
We won’t know more until Dawn loops back closer to Ceres in about six weeks or so.
For the latest images and information on Dawn’s discoveries at Ceres, visit the Dawn homepage on the Internet at dawn.jpl.nasa.gov.
We only get to see a dwarf planet for the very first time once. This is our one chance to see Ceres for the first time. Enjoy this mission of discovery, brought to you by Giuseppe Piazzi and NASA’s Dawn spacecraft.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Check out Jimmy’s astrophotography website at http://www.jwestlake.com.
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