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Astronomy

The comet no one saw

Nature volume 405, pages 285–287 (2000)Cite this article

With all the work that is going into searching for near-Earth asteroids (NEAs), one might think that any comets approaching Earth would also be discovered. It is expected that, with some increase in the current effort, all near-Earth objects greater than 1 km in diameter will be catalogued within a couple of decades. So how is it possible that a moderately bright comet could be discovered by a spacecraft designed for quite a different purpose and yet never be seen by NEA surveys or, for that matter, by any other observer?

The Solar Wind Anisotropies (SWAN) instrument on the Solar and Heliospheric Observatory (SOHO) spacecraft was designed to study the solar wind that separates our immediate neighbourhood from interstellar gas. But according to Mäkinen et al.1 (writing on page 321 of this issue), images taken by SWAN in the summer of 1997 reveal the presence of five comets in the southern sky, one of which had not been seen by any observers when it was bright.

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Figure 1: SWAN full-sky map at Lyman-α wavelengths.

FMI/SERVICE D'AERONOMIE

References

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  1. Department of Astronomy University of Maryland, College Park, 20742-2421, Maryland, USA

    Michael F. A'Hearn

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  1. Michael F. A'Hearn
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Correspondence to Michael F. A'Hearn.

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A'Hearn, M. The comet no one saw. Nature 405, 285–287 (2000). https://doi.org/10.1038/35012723

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