Wednesday, September 23, 2009

Priorities for Asteroids and Comets - Part 1

For the next several postings, I'll be exploring the priorities set for planetary exploration in Decadal Survey White Papers by each of the Analysis Groups that advise NASA. There are four groups that I know of: MEPAG (Mars), VEXAG (Venus), OPAG (outer planets), and SBAG (small bodies). These groups are composed of scientists active within their disciplines (although it is common for scientists to be active in two or more groups).

The goal of the Decadal Survey is recommend a set of planetary science priorities that translates into a set of mission and research goals to be funded by NASA. In a previous job, I developed product roadmaps for a high technology company. Ultimately, a roadmap distills a set of options into the mix of mission (or products) that fit within budget constraints to produce the highest return (in science or profit). The Decadal Survey is looking to each of the Analysis Groups to recommend the priorities within its own discipline. (Mechanisms have been put in place to seek input from other sources in the planetary science community, too.)

In this blog entry, I'll start with the priorities recommended by SBAG for exploring asteroids (near Earth to the Trojan that share their orbit with Jupiter) and comets. I start here because the White Papers from this community most clearly set out (so far as I've found in my reading to date) priorities within each of their sub-disciplines. It's perhaps easier for SBAG to have clear priorities at this point. While single SBAG White Papers cover literally thousands of bodies, White Papers for other disciplines focus on single aspects of a single world (for example, atmospheric studies at Venus) or a single body (a Uranus orbiter).

White Papers tend to follow a common outline. They start by showing why the study of the object or phenomenon is scientifically compelling, then discuss the key outstanding questions, and then establish measurement priorites to answer those questions. For comets and asteroids, the scientific rational is essentially the same. These bodies represent the most unaltered worlds left from the formation of the solar system. Studying them will reveal the conditions and processes of the early solar system.

For asteroids, "The sheer diversity of asteroids is their most compelling feature. They are a reservoir of information on a huge range of solar system history, chemistry, physical processes, and evolution. Because they often are collisional fragments, asteroids are windows into processes that are hidden on the terrestrial planets by time, geochemical evolution, or simply deep burial."

For comets, "Comets represent the most unaltered (i.e., primitive) samples of the early Solar System and, even though new results have shown that the surfaces of short period comets have undergone major evolutionary modifications, carefully selected samples can still be expected to provide key information on the processes of planetary formation during the first few hundred million years of Solar System history."

The priorities for asteroids are set out in three papers, one for main belt and Trojan asteroids, another for near-Earth asteroids, and a third for comets. The priorities for each are similar:
  1. Maintain active programs of telescopic research and laboratory studies. The sheer diversity of theses bodies allows telescopic observations to lead to new understandings of these worlds while laboratory studies allow scientists to interpret findings from telescopic and spacecraft missions.
  2. Make Discovery missions ($425M per mission) the highest priority for exploring these worlds. The diversity of these worlds means that a mission to almost any of them can make a significant contribution to the field. The comet White Paper goes so far as to recommend increasing the frequency of Discovery missions from to every 18 to 24 months (from the current approximately every 3.3 year frequency).
  3. Fly a New Frontiers mission ($650M per mission) to address a high priority target.
  4. In the case of cometary exploration, perform technology development to enable a future Flagship mission (>$1B) to return frozen samples from a comet.
The next blog entry will list priorities for specific missions.

You can find all the SBAG white papers and white papers on these bodies submitted by the rest of the science community at

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