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Planetary science

Comet leaves a trail in the air

Nature volume 392, pages 754–755 (1998)Cite this article

* 29th Lunar and Planetary Science Conference, Houston, Texas, 16-20 March, 1998.

The large interplanetary dust particles known as cosmic spherules can be collected from the sea floor and from polar ice. But melting on atmospheric entry and subsequent alteration on Earth lead to changes in composition that limit their usefulness as samples of extraterrestrial material. The place to find nearly pristine IDPs is the stratosphere. Since 1974, NASA has flown decommissioned U-2 spy planes at about 20 km altitude, with simple impact collectors mounted under the wings. These planes are usually ‘ships of opportunity’, collecting dust while performing other research, so it can take months for a collector to accumulate the 30-40 hours of exposure required to harvest a useful crop of a few hundred IDPs, ranging from about 5 to 50 μm across. IDPs are identified as extraterrestrial by the presence of solar-flare particle tracks, implanted noble-gas atoms from the solar wind, and by non-terrestrial isotope ratios of hydrogen, nitrogen and oxygen. Most IDPs also have major-element compositions that are similar to those of the primitive meteorites known as carbonaceous chondrites, consistent with an origin in comets or certain types of asteroid. Specifically, the more porous IDPs are thought to come from comets1. But without any samples of certified comet dust for comparison (or samples of asteroids, other than the highly biased selection provided by meteorites), the connection has been hard to prove.

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Figure 1: Mother and child? The comet Schwassmann-Wachmann 3, and (left) an interplanetary dust particle captured by a high-flying aircraft.

JIM SCOTTI/NASA SCOTT MESSENGER

Notes

  1. * 29th Lunar and Planetary Science Conference, Houston, Texas, 16-20 March, 1998.

References

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    Laura Garwin

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  1. Laura Garwin
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Garwin, L. Comet leaves a trail in the air. Nature 392, 754–755 (1998). https://doi.org/10.1038/33793

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