A Planet with a Tail

An artist's interpretation of how extrasolar planet HD 209458b may look.
Image: NASA, ESA, and G. Bacon (STScL)

A giant gas extrasolar planet, HD 209458b, has recently been confirmed to possess a tail, resembling something like that of a comet. The planet is similar to Jupiter, but unlike Jupiter it orbits very close to its star, completing an orbit every 3.5 days¹.

The planet, about 153 light-years from Earth, has been heavily studied since its initial discovery because it was one of the first discoveries of an extrasolar planet transiting its star. This is a special case where the orbit of the planet allows it to eclipse its star, as seen from the Earth. The rare position essentially allows astronomers to study the atmosphere of the planet, finding out what chemicals make it up (the process is detailed for a similar case here). Astronomers studying HD 209458b discovered that the planet’s atmosphere contains heavy elements including carbon and silicon. Since the atmosphere is exposed to the scorching heat of the star due to their close proximity, the heavy elements can escape.

Eventually, these materials come together to form a large flow of gas coming out from the planet. On the Earth, astronomers have detected the gas to be coming towards us at 22,000 miles per hour. When the stellar wind from the star picks up the gas, the tail, resembling one of a comet’s, is formed. Still, despite the large outflow of gas, the planet is not likely to completely “evaporate” anytime soon. It is estimated that it will take a trillion years for that to happen.

The recent finding is important in that it further helps us realize how our star is not unique in harboring planets, as the numerous other discoveries of extrasolar planets have proved. However, perhaps more importantly, it shows the intense variety of what can be found in the universe.

Footnotes

1: Extrasolar planets are planets that are found outside of our solar system, orbiting other planets. Recently, there has been an explosion in the discovery of extrasolar planets, and the number of total extrasolar planets discovered so far is currently a little over 450.