Deceber 21, 2010 by Istvan
I admit it. From time to time I lose track of robotic missions. Especially to the outer system, they take long enough to get places that after I watch their launches with excitement and anticipation, I let them drop off my radar for years at a time, only checking now and then to see how much longer we have before an encounter.
Thus it was with some excitement I realized yesterday that Dawn reaches Vesta in 2011. And of course, it’s New Year’s, so 2011 isn’t far-off anymore: it’s now.
Dawn is exciting for three reasons. Number one, it’s yet another ion-drive propulsion mission. That’s awesome because chemical rockets are fine for getting to LEO, but beyond that, well, we need better. Lots better. I grew up reading stories about “space rangers” with “ion ultradrive” on their cruisers. So with every robotic mission that uses ion propulsion, we practice, refine, and improve that technology for future missions, making them faster and more reliable.
Number two, Dawn is going to Ceres and Vesta. We’ve had a few asteroid flyby missions in the past decades, and a few rendezvous missions, such as NEAR Shoemaker and Hayabusa, which were great successes. Dawn isn’t a flyby – it will visit both rocks for extended periods (hurray for that ion engine again, for making this possible), with cutting-edge instruments. The targets are interesting. Ceres is a dwarf planet – something we’ve never visited before. Planetary scientists should be on the edges of their seats, because surprises are guaranteed. Vesta, on the other hand, is also one of the largest asteroids, but it is expected to have an unusual composition. It is understood to have melted entirely in the distant past, and also been subject to a serious impact much more recently. That recent impact is how we know about the melting – pieces have reached Earth as meteorites, and spectroscopic comparisons with observations of the asteroids have matched that rubble to Vesta! Vesta’s the brightest asteroid, meaning high surface albedo. Should we hope for some water ice, which is a high-albedo material, or something more interesting? Water ice itself would be pretty interesting! So the data from these rocks will increase our knowledge of asteroid formation and evolution, and teach us about a class of objects we’ve never really scrutinized before.
This is great stuff, so what’s reason number three to care about Dawn? I’ll rant about this over and over: Ceres and Vesta aside, asteroids are possibly the Most Important target for any of our space programs, unmanned, manned, whatever. Even more so than Mars (barely). Why?
Even perfect planets like our own are hard to work with. It takes serious energy to move anything to space from the surface, and it takes some care to get anything safely down. Landing something on another planet like Mars incurs these costs and risks twice. The biggest handicap to all our space efforts is launch energy, represented by the launch cost per kilogram. The biggest risk to our probes, after launching them, is landing them somewhere else. With debris like asteroids and comets, this energy cost is hardly an issue, because of their tiny gravity. Just getting our equipment there is the real challenge for us today.
Getting to asteroids and comets is worthwhile, because our direct mineral studies of meteorites (and our spectroscopic examinations of comets) indicate these objects have materials we’re going to want, now and in the future. The abundance of platinum group metals and rare earth elements in asteroids (as compared with Earth’s crust) makes them potentially quite valuable, if we could just move the ores back here (or refine them in situ and then move the results here). We expect these ores would be even easier to get to on an asteroid a few hundred meters across, as opposed to digging through a similar distance (or more) of Earth’s crust (which is also likely denser). Furthermore, one of our best means of beating that launch cost problem I mentioned is to avoid sending all the fuel our equipment needs along with it. If a mission is manned, air and water are requirements too, which is even more mass you have to send along. If we get these things from a comet or asteroid, especially an asteroid that has other minerals we need…suddenly we’re talking about a cheaper, more sustainable space program that can actually return value to Earth industries. Therefore, we really need to know about asteroids, to learn whether these ideas are pie-in-the-sky, or whether there really is pie waiting for us, in the sky.
But the real deal on asteroids is this: we have no reason to believe habitable worlds are common around other stars. Earth is still likely to be a rare gem. Even near-habitable worlds like Mars, where landing and living there takes serious effort, are not yet known to be commonplace either. Asteroids and comets, however, are expected to be practically everywhere, in any planetary system around any star and even around stars that lack real planets. If we can learn to live off asteroids and comets, getting the materials and metals we need for shelter and industry, getting the volatiles like air and water we need to live and travel, then our species can go anywhere, live anywhere, around any star, no matter what else we find there. Forever.
Habitable worlds we may yet find, and that will be all to the good. Other life we may find, and that will teach us something also. But asteroids are the real diamonds. Asteroids are the Future.