The Planet Slowly Bleeding Into Space

There's a planet out there bleeding into space — its atmosphere streaming off into a tail, like a comet the size of a gas giant.

HD 209458b orbits eight times closer to its star than Mercury is to our Sun — a full year in just three and a half days. The day side glows around a thousand degrees Celsius, and the night side never gets a moment of true cool.

It's a Hot Jupiter — a gas giant that spiraled into the wrong place. Astronomers call what's happening to it 'photoevaporation': the star's X-rays and ultraviolet light heat the upper atmosphere so hard the gas escapes into space. Hubble actually caught the hydrogen streaming off — a comet-like tail trailing the planet. Early estimates clocked the loss at around 10,000 tons every second. Sounds apocalyptic — but this world is so massive it would take longer than the age of the universe to strip it bare. Smaller Hot Jupiters, though? They may not be so lucky.

And here's the part that's wild: those 'super-Earths' we keep finding everywhere — the most common planets in the galaxy — some astronomers suspect a few of them might be the stripped cores of Hot Jupiters that lost everything. The most abundant worlds we know of could include the bones of dead gas giants.

Follow The Cosmic Vault — the universe is stranger than you think.