Hubble Delivers Photos of Ceres and Vesta

[Fraser]

On July 7, 2007 NASA will launch its next explorer into the Solar System. This spacecraft's destinations are the asteroids Ceres and Vesta, where it will help answer many unknowns about the formation and structure of these minor planets. ...

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[eachus]

<i>This will make it the first spacecraft to ever orbit two different objects in the Solar System.</i>

Several lunar missions orbited Earth before moving to lunar orbit, including, of course, eight* Apollo missions. If you don't count the Moon as a Solar System object, several other planetary missions first orbited the Earth before leaving for other planets. And Voyager 2 used gravitational slingshot maneuvers to visit Jupiter, Saturn, Uranus, and Neptune.

Dawn will however, be the first (human-built) spacecraft to orbit two asteroids or minor planets.

*Or nine, depending on how you count Apollo 13. It was on a free return orbit, but did pass behind the Moon, and did a burn there to get back to Earth faster. When it did the burn it was technically in a lunar orbit. The criteria I am using is whether the orbit approximates an ellipse or a hyperbola with respect to the planet.

Um, I obviously don't agree with the new definition of planet. By that definition, Earth is not a planet. Even if you ignore the Moon, which is hard, almost all Aten asteroids cross Earth's orbit. What to call the Moon though is a real problem if you think that way. It does not orbit the Earth, it's orbit around the Sun is always convex. And, as I said above, the Moon is hard to ignore. I think of the Earth and the Moon as a twin planet, but you may prefer to think of the Moon as a minor planet. In any case, when doing accurate multi-body orbit predictions for the solar system, it is a lot easier to ignore Jupiter's moons, and Pluto, than the Moon.

[EDG]

Oh, I've been looking forward to this mission for a LONG time...

[OneHotJupiter]

A tantalizing taste of what's to come! Great photos!

Cannot wait for DAWN!

[Disinfo Agent]

Great pictures. I had no idea that asteriods could be so colorful. They look a bit like Mars.

[Blondin]

Ceres & Vesta may not be big enough to qualify as "planets" but at least one of them is classified as a "world".

[dhd40]

On July 7, 2007 NASA will launch its next explorer into the Solar System. This spacecraft's destinations are the asteroids Ceres and Vesta, where it will help answer many unknowns about the formation and structure of these minor planets. ...

Read the full blog entry

I can´t remember where I´ve read it. But I remember that it said that celestial bodies below approx. 500 km diameter will not be of spherical shape, those bigger than approx. 500 km will be of spherical shape (approximately, of course). Ceres and Vesta seem to confirm this. Is there any physical explanation for this? Is density (g/cm³) of minor importance?

[Amber Robot]

Um, I obviously don't agree with the new definition of planet. By that definition, Earth is not a planet. Even if you ignore the Moon, which is hard, almost all Aten asteroids cross Earth's orbit.

The definition is poorly worded, but the idea behind it is good. Read What is a Planet? by Steven Soter and then let me know of your opinion.