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Dawn Mission Readies for Asteroid Belt

If you want to follow the Dawn mission to Ceres and Vesta in detail, you’ll want to know about Dawn’s Early Light, the newsletter being published online to keep scientists up to date about its progress. With a launch window opening in late June, Dawn will be worth following on many fronts, not the least of which are its targets: Ceres and Vesta. These tiny protoplanets seem to be at opposite ends of the planetary formation spectrum. Ceres shows signs of water-bearing minerals and an extremely tenuous atmosphere, while Vesta is dry and significantly cratered.

The asteroid and protoplanet Ceres

In fact, the large impact crater that covers much of Vesta’s southern hemisphere is thought to be the source of material we can study here on Earth. Howardite, eucrite, and diogenite (HED) meteorites are now thought to have been ejected less than a billion years ago by the crater-forming impact, which flung debris that fell millions of years later onto our planet. Can we really identify meteorites conclusively as coming from Vesta? The delivery mechanism seems sound and experimental work suggests Vesta as the ultimate source (click here for more on this work from Michael Drake at the University of Arizona’s Lunar and Planetary Laboratory).

Image: Ceres as viewed by the Keck Observatory (Mauna Kea, HI). What was once thought to be a flat surface now seems rich in features. Does Ceres contain water from the days of the Solar System’s formation? Credit: NASA, ESA, J. Parker (Southwest Research Institute).

As to Ceres, its surface shows no signs of water ice but studies with the Hubble Space Telescope have looked at its shape and spin rate, both of which imply a rocky core covered by a layer of ice that could be anywhere from 60 to 120 kilometers thick. Dawn should be able to tell us something about the internal structure of these protoplanets, both of which have remained intact since their formation. And that helps us understand the conditions under which these objects formed, as well as deepening our understanding about the basic building blocks of larger planet formation.

In mid-June, the spacecraft goes from the processing facility at Titusville FL to the launch pad preparatory to beginning its eight-year journey to the asteroid belt. From a propulsion standpoint, Dawn’s ion engines offer another chance to shake down a useful outer-planet technology. We’re talking tiny levels of acceleration here — about the weight of a piece of paper in your hand — but over long acceleration times, ion engines make it possible to fly missions that would be far heavier (and pricier) if performed with chemical rockets. Factors like that helped to keep the Dawn mission alive despite NASA’s current budgetary woes.

Comments on this entry are closed.

  • Chris Wren April 16, 2007, 10:58

    I’m just old enough that when I was in Kindergarten, the books in the school library about planets were, with the exception of the moon, illustrated entirely with paintings, because there were no photographs of any objects in the solar system, beyond unhelpful fuzzy disks.

    I remember the section on the asteroid belt had an arresting image of an earth-type planet exploding violently. Yes, in 1967 that was still a plausible enough theory of asteroid formation to warrant inclusion in school books! Anyway, I’ve always been fascinated by asteroids since, and I can’t wait to see some decent images of Ceres, especially.

  • Paul Dietz April 16, 2007, 16:12

    Yes, in 1967 that was still a plausible enough theory of asteroid formation to warrant inclusion in school books!

    When did oxygen isotope results on meteorites (that showed they must have come from many parent bodies) come out?

  • Chris Wren April 16, 2007, 19:13

    Those results could well have come out in the early to mid sixties, or even sooner, but the trickle down effect wouldn’t have reached the Canadian elementary school system, I’m sorry to say.

  • Adam April 17, 2007, 1:25

    Dawn will be a very cool mission, but we’ll be getting detailed data on Ceres roughly the same time as the Pluto probe has its close encounter. At least Dawn has a stop at Vesta in the mean time.

  • Robin Goodfellow April 17, 2007, 2:26

    It’s not entirely clear in the summary so I think it’s worthwhile to point out that Dawn is a very different type of mission than the sort we’re used to. It has two targets but it is not a combination flyby / rendezvous mission, rather it is a multi-rendezvous mission. Dawn will travel to Vesta, orbit Vesta and study it in depth for half a year, then leave Vesta orbit, head to Ceres, and enter into orbit around Ceres for the remainder of its mission. These are two separate, robust, surveys of asteroids. It’s a kind of mission that is only possible with high-efficiency propulsion such as ion engines. It’ll be interesting to see how it turns out. This one mission will increase our knowledge of asteroids as much as the Voyagers and Pioneers increased our knowledge of the outer Solar System.

    As a side note, CONTOUR would have made an excellent complement to Dawn had it not met such an unfortunate fate early in its mission.

  • ljk April 17, 2007, 9:57

    D A W N ‘ S E A R L Y L I G H T Dawn Science Symposium

    The Dawn Science Team issponsoring a Science Symposium on
    June 28, 29 and 30 in Cocoa Beach Florida. The scientific sessions
    will cover the origin and evolution of planetary systems, the
    mineralogy and geochemistry of Vesta, the geology and
    geophysics of Vesta, what we know about Ceres and a review
    of Dawn objectives, mission payload and op erations.

    For those who register early enough there will be an opportunity
    to tour the Cape Canaveral Air Force Base and to view the launch
    from inside the Kennedy Space Center. The symposium will
    consist of invited and contributed papers , oral and poster sessions.
    All contributions on the above topics are welcome.

    If you are interested in attending this meeting and wish to
    be included on the distribution list for registration and
    accommodation information, please contact:


  • Darnell Clayton April 18, 2007, 22:59

    This is really cool to hear!

    We need more satellites to research these asteroids, as it has been noted recently that Ceres may contain a lot of water underneath its surface.

    In my honest opinion, asteroids represent not only future mining colonies for humanity (can you say ching, ching!) but also as stepping stones towards the gas giants.