Skywatch

  • November 24, 2005

    Episode 11: Ceres May Have Water Ice

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    So what does it take to be a planet? Astronomers using the Hubble Space Telescope have noticed that Ceres, the largest of the asteroids circling the Sun, may contain large amounts of water ice frozen beneath its surface. Ceres is already odd because it's round like a planet, not potato-shaped like most asteroids. Its roundness suggests that its interior likely has a rocky inner core with dense materials, and a thin, dusty and lighter outer crust. Rocky planets like Earth and Mars have a similar structure. So Ceres could be an embryonic planet. It might have formed into a larger sphere if gravity from nearby Jupiter hadn't prevented more material from falling onto Ceres billions of years ago. A new NASA mission called Dawn will launch in 2006 to orbit Ceres and take the first close-up look at the asteroid. Dawn will also visit Vesta, the solar system's second largest asteroid.