What's next -- how do you work with a $200 million collector?
The Stardust@home collaboration has now identified several candidate features in the aerogel that may
be the tracks of the first contemporary interstellar dust particles ever brought back to Earth for study (or, they may be something else). We have examined several of these as well as we can through the microscope in the Cosmic Dust Laboratory. Several have passed this cut -- that is, they are still very promising -- and we can't wait to find out what they really are.
Unfortunately, it is very difficult to get good images of tracks in the aerogel tiles while they are still in the flight tray (as many of you have pointed out). So to make further progress, we will need to remove the tracks from the collector.
We are considering two options. The first is to extract the tiles containing these candidate tracks from the collector. This will enable us to examine the tracks in transmitted light, which gives much improved visibility, particularly at very high magnification (we currently have to use reflected light illumination). There are two principal risks in doing this. First, because the aerogel may be somewhat distorted during extraction, we may partially lose the ability to accurately determine where on the sky the particle originated. This could compromise our ability to distinguish between interstellar dust and interplanetary dust. Second, the aerogel is very fragile; it could just fall apart if we try to remove it from the tray. We do have a flight spare that we could practice with, but we know from our experience with the cometary aerogel that it has changed somewhat in space; it has become more brittle. We don't think that either of these issues is very serious, but they have to be considered carefully.
The second option is to extract the track directly from the aerogel in a "keystone", using an extraction technique that we developed here at Berkeley specifically for Stardust and have been using successfully for several months on the cometary collector. Here we use robotically-controlled micromanipulators and extremely sharp glass needles to machine the aerogel, and extract tracks in tiny doorstop-shaped wedges of aerogel that we call "keystones". The visibility of tracks in these tiny keystones is superb (see picture below). But we would be doing the keystone microsurgery either over or next to the entire collector. We would have to build in numerous safeguards to be absolutely sure that nothing could endanger the collector.
If this were almost any other project, we could afford to take risks and try some things out. But the interstellar collector is practically priceless(well, not exactly priceless, but it would cost at least $200 million to get another one). So we have to be incredibly careful, and we have to make sure that we've thought this through extremely thoroughly.
Fortunately, a situation like this has come up before. In the late 1960's, when the Apollo missions were bringing back rocks from the Moon, NASA recognized that they needed a way to oversee the handling of these incredibly precious samples. So NASA organized a committee of scientists called the Curation and Analysis Planning Team for Extraterrestrial Materials (CAPTEM
) to oversee the curation of the Moon rocks -- that is, to advise NASA on how to store and distribute them. Even though it's been nearly 40 years, this committee is still very busy making recommendations to NASA on the curation and distribution of all kinds of extraterrestrial samples to scientists all over the world. These include the Apollo moon rocks, which are still in very heavy demand, but now also include samples from the Genesis
mission and now Stardust.
A subcommittee of CAPTEM has been organized for the oversight and allocation of the Stardust samples. Amazingly, it's called the Stardust Sample Allocation Subcommittee (SSAS). The Stardust@home project director, Andrew Westphal, is on this subcommittee. The SSAS will meet on Sept 18-19 in at the Lunar and Planetary Institute (LPI
) in Houston near NASA's Johnson Space Center. (See the ARES
website). At this meeting, we will decide on a course of action, then make a recommendation to the CAPTEM committee that will meet at LPI near the end of October. We will keep the Stardust@home collaboration informed as this careful decision-making proceeds.
This is the frustrating part: this is going to take a while. There is just no other way. We have to be very, very careful with these precious samples. After all, they belong to all the American people, who paid for the mission.
Finally, a word about the huge advantage of doing sample-return missions. Stardust, like Apollo and Genesis, brought back samples from space that can be studied simultaneously by hundreds of scientists all over the world. Many, if not most, of the scientific instruments that are now being used to analyze Apollo samples couldn't have even been imagined in the 1960's. Even in the case of Stardust, some of the instruments that are now being used didn't exist when Stardust was launched in 1999. Some other instruments, like the synchrotrons that we mentioned in an earlier news item, are the size of shopping malls, and could never practically be flown in space. As long as we're careful, these same samples will be studied by our grandchildren using instruments that we cannot imagine today. They will be answering questions that we don't even know how to pose.