Science Today

Hot “Cometary” Planet

HD 209458b stands out among the 463 other exoplanets for many reasons. According to the Discover blog 80beats, it has a nickname (Osiris) and in the eleven years since first spotting it, we’ve learned a lot about it:

We know it’s 153 light years away, that it has water in its atmosphere, and that it orbits its star in three and a half days at a distance 100 times closer than Jupiter is to the sun.

And, last week, University of Colorado scientists using the Hubble Space Telescope confirmed another remarkable fact about the gas giant: the heat of its star and the stellar winds are whipping its atmosphere into a comet-like tail coming off of the planet. The study was published in The Astrophysical Journal.

Hubble’s Cosmic Origins Spectrograph (COS) detected the heavy elements carbon and silicon in the planet’s super-hot, 2,000-degree-Fahrenheit atmosphere. This detection revealed the parent star is heating the entire atmosphere, dredging up the heavier elements and allowing them to escape the planet in the form of gas.

Some of that gas is coming off the planet at pretty fast speeds, heading in the direction toward Earth. Lead author and astronomer Jeffrey Linsky, PhD, said that:

We found gas escaping at high velocities, with a large amount of this gas flowing toward us at 22,000 miles per hour. This large gas flow is likely gas swept up by the stellar wind to form the comet-like tail trailing the planet.

Although this extreme planet is being roasted away by its star, it won’t be destroyed anytime soon. At almost the same mass as Jupiter, “It will take about a trillion years for the planet to evaporate,” according to Linsky.

Image credit: NASA, ESA, and G. Bacon (STScI)