A Recent Comet Impact on Neptune

Did a large, icy comet smash into Neptune two centuries ago? That's the picture that is emerging from the latest measurements of gases in the atmosphere of the giant blue planet.

At a meeting this week of the American Astronomical Society in Miami, Fla., Paul Hartogh, project scientist for the Herschel mission, the European Space Agency's infrared observatory satellite, described the mission's first results for the Solar System. These include measurements of abnormally high levels of carbon monoxide in Neptune's stratosphere--a possible trace of a comet impact.

Emmanuel Lellouch, an astronomer at the Paris Observatory, first published the idea five years ago, on the basis of far less certain measurements made by a 30-metre radio telescope on the mountain Pico Veleta in Spain. "We are becoming more confident," says Lellouch, who is a co-author with Hartogh on a forthcoming paper concerning the Herschel results in the journal Astronomy & Astrophysics.…

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