Comet overlooked

In the data of the soho solar probe, a comet has now been discovered that no one had seen when it was close to earth

The impact of comet shoemaker-levy-9 on jupiter nearly six years ago has raised awareness of the danger posed to earth by similar impacts. Since then, several initiatives have been launched to identify celestial bodies that could pose a threat to earth. But these observation programs are still far from being able to cover all near-earth objects. Scientists of the finnish meteorological institute and the service d’aeronomie in france could now prove that in 1997 a comet was overlooked, although it must have been comparatively bright.

Comet overlooked

Impact of comet shoemaker-levy-9 on jupiter

The researchers were able to identify the comet using data from the swan (solar wind anisotropies) instrument aboard the soho (solar and heliospheric observatory) solar probe, which is stationed about 1.5 million kilometers from the earth. Das instrument dient eigentlich der beobachtung des sonnenwindes, der unsere unmittelbare kosmische nachbarschaft vom interstellaren gas absetzt. For this purpose, swan scans the entire sky daily in the ultraviolet range of the electromagnetic spectrum and measures the so-called lyman-alpha emission of hydrogen atoms. But it is also suitable for detecting comets, which also emit considerable amounts of this radiation.

Despite swan’s very low resolution potential, scientists were able to spot a total of 18 comets in the data from december 1995 to june 1998, but only 17 of those had also been observed in the optical range. Treasures on the basis of the available data showed that the brightness of the comet which remained undiscovered at that time must have been about 11. This would have made it easily accessible to terrestrial telescopes. That it was nevertheless overlooked, the researchers attributed to its eccentric orbit, which lay outside the areas on which observations are usually concentrated.

The orbits of comets are very diverse and most of them do not lie in the plane of the ecliptic in which planets and asteroids move. At the same time the potential consequences of a comet impact are estimated to be more devastating than those of an asteroid impact. With their discovery, the scientists therefore call for the development of an effective early warning system, using devices such as swan, which regularly scans the entire sky.