New candidates presented at the Meteoritical Society Conference in New York

At the 2010 Meteoritical Society Conference in New York, we reported on the further analysis of track 30 (Orion and Sirius), and reported the exciting discovery of two more promising interstellar dust candidates, tracks 34 and 37. Track 30 was analyzed by Alex Simionovici, Laurence Lemelle, and colleagues on beamline ID22 at the European Radiation SynchrotronFacility (ESRF). Alex and his colleagues oriented track 30 so that Orion and Sirius could be analyzed separately. X-ray fluorescence spectra showed the presence in each of iron, chromium, nickel and manganese. We already knew that the major elements present are aluminum in Orion and magnesium in Sirius. Orion appears to contain crystalline material.

Track 34 was discovered by Naomi Wordsworth, who has named it Hylabrook. This track has been analyzed at Berkeley at the Scanning Transmission X-ray Microscope (STXM) beamline 11.0.2 at the Advanced Light Source (ALS) by Anna Butterworth and Tolek Tyliszczak, and also by Frank Brenker, Sylvia Schmitz, Bart Vekemans and colleagues on beamline ID13 at ESRF. Hylabrook is one magnesium-rich particle, and has minor concentrations of iron, chromium, and nickel. X-ray diffraction at ID13 shows that it is crystalline.

Finally, just hours before the MetSoc conference Anna and Tolek analyzed track 37 on the STXM beamline at the ALS. They found that it is carbon-rich and has a minor concentration of iron. At this point, we know nothing more about it, on purpose. Despite the fact that there was much more precious beamtime available, we stopped the analysis in order to carefully plan the next steps. Organic material in track 37 could be damaged by too much exposure to x-rays, so we will do careful planning before doing any further analysis on this track.

Things have been happening so fast here that we have not yet had time to contact the discoverer of track 37 to give him or her a chance to name it, but will do this shortly. We can tell you that track 37 is from tile I1092, which is all new data scanned and searched for the first time in Phase 3.

We emphasize that these particles are only candidates — they could still be false alarms. What we do know about these is that their trajectories are consistent with an origin in the interstellar dust stream, and their composition does not seem to be consistent with spacecraft material, with the exception of track 37, which might be a piece of ejecta from an impact on the phenolic heatshield on
the sample return capsule. The carbon-to-oxygen ratio in this sample tentatively seems higher than that in phenolic, but only further analysis will tell.

Our challenge now is to develop extremely reliable techniques for extracting these particles from their picokeystones, in order to do detailed mineralogy and petrology using Transmission Electron Microscopes, and to measure isotopes using ion microprobes. The ratio of the isotopes oxygen-18 to oxygen-17 in the galaxy is about 4.1 +/- 0.1, while the solar system value is about 5.2. So it will be important to measure oxygen isotopes in our interstellar dust candidates to confirm that they are indeed interstellar. The instruments for doing these measurements exist in several laboratories around the world, but we don’t yet have an adequate technique for preparing these tiny samples in their aerogel picokeystones for these kinds of analyses. The risk of losing the particles in the process of preparing them for analysis is currently unacceptably high.

The challenge of developing the reliable techniques will be fun and challenging.