In 2007, NASA launched the Dawn spacecraft bound for the solar system’s second largest asteroid – Vesta. It entered the orbit of Vesta in July of 2011 and will continue in orbit until August of this year, after which it will be bound for the largest asteroid – Ceres – which it will reach in 2015.
The press conference about Dawn’s findings today centered on Vesta’s Rheasilvia Crater and its age. Rheasilvia is a massive impact crater with a central peak – Rheasilvia Mons – which ranks as the tallest known mountain in the solar system (with Olympus Mons a close second). The material ejected by the impact amounts to about 250,000 cubic miles, and makes up around six percent of the material in the asteroid belt, including the Vesta family of asteroids. Some of it has even reached Earth, so that scientists knew what to look for when launching this mission to Vesta. Evidence now clearly indicates that the impact occurred a billion years – much more recently that the majority of impacts on the Moon, which occurred over three billion years ago. According to the researchers in the conference, this puts constraints on ideas about solar system dynamics – the way objects have moved around the solar system since its formation.
Vesta is also of interest because it is a legitimate proto-planet – it could have been the heart of a new planet or been incorporated into another planet at the beginning of the solar system. This is another attempt by us to piece together our past.
There are two items of particular interest to me with regard to this mission: the ion thrusters on Dawn, and the likelihood that we can duplicate the mission now that there’s some interest among billionaries to go asteroid mining. A panelist called asteroid mining a “tough sell,” but noted that Dawn was essentially on a prospecting mission much like the type that would have to be done for any asteroid that miners might be interested in. So, lessons learned from this mission will help us to conduct similar missions more efficiently.
On the ion thruster front, there was solid good news. Ion drives produce continuous thrust over long lifetimes and, on deep space missions, can produce higher velocities than chemical rockets. They are not useful for ground-to-space launches or anything that requires significant thrust, but are ideal when there is a lot of time available to accelerate. Just to give you an idea, Dawn can accelerate from 0 to 60 mph in four days – so ion thrusters are definitely not for the impatient. Dawn’s ion thrusters performed better than expected, allowing it to definitely extend its mission to its second target – Ceres. This is excellent news and really extends our abilities in space.