Sunday, May 23, 2010
I missed the exact date on this one, but it was probably about five or so days ago. Looking at Dawn's current position, it's finally now closer to Vesta than to Mars. Dawn made a flyby of Mars over a year ago (February 2009) and since it's using an ion engine it has an extremely gentle trajectory where it simply matches its orbit over time with the object it intends to approach as opposed to a regular probe that will go directly to an object, fire its engines at full blast and drastically change its trajectory in order to go into orbit and not go flying by.
So here's where it is now:
Vesta is now 0.4272 AU away, and Mars 0.4556 AU. Dawn is now the first probe to be closer to Vesta than any other major object...unless by chance it's Rosetta, as you can see here. It's a bit hard to tell as Vesta being an asteroid isn't quite as aligned to the orbital plane as the rest of the planets, and thus is off by seven degrees. With every major planet (IOW not Ceres or Pluto) you can more or less calculate their orbits as if they were on a two-dimensional surface, but since Vesta looks like this:
and thus Dawn is actually moving to go under the orbital plane a bit, as that area on the right in darker blue is where Vesta will be when they meet:
Anyway, it's now just 64 million km away, or 166 times the distance from the Earth to the Moon. In contrast, Earth is 317 million km away from Vesta now which is 825 times.