Astronomers have discovered an exoplanet with a tail, like a gigantic comet. The planet, known as WASP-69b, is slowly evaporating in the radiation of its host star.
WASP-69b is a gas giant that orbits very close to its host star, meaning it’s a kind of planet often called a Hot Jupiter. That alone isn’t too exciting – those are some of the most commonly found exoplanets out there, because their size and proximity to stars makes them easy to detect.
But what’s weird about WASP-69b is its long luxurious tail, which would give it the appearance of a gigantic comet. The intense radiation from the star – the stellar wind – is not only boiling off the planet’s atmosphere, but also sweeping it into a long stream like a comet’s tail.
In a new study, astronomers used the KECK Observatory in Hawaii to examine WASP-69 b in more detail, revealing the full extent of its tail. They found that it stretches some 580,000 km (360,000 miles), which is roughly one and a half times the distance from Earth to the Moon.
“Work by previous groups showed that this planet was losing some of its atmosphere and suggested a subtle tail or perhaps none at all,” said Dakotah Tyler, first author of the study. “However, we have now definitively detected this tail and shown it to be at least seven times longer than the planet itself.”
The team says “at least” because they actually ran out of observation time before they saw the end of the tail. There’s no telling how far it truly extends, but it likely changes over time anyway, as the stellar wind changes.
WASP-69b seems to be losing gas – mostly hydrogen and helium – at a rate of about 200,000 tons per second. That sounds like it’s draining fast, but it shakes out to about one Earth’s mass every billion years or so. That means in its estimated lifespan so far the planet has lost about two Earth’s worth of gas – and there’s plenty more where that came from.
“At around 90 times the mass of Earth, WASP-69b has such a large reservoir of material that even losing this enormous amount of mass won’t affect it much over the course of its life,” said Tyler. “It’s in no danger of losing its entire atmosphere within the star’s lifetime.”
The research was published in The Astrophysical Journal. You can see an animation of the tail in the video below.
WASP 69b 2K
