Hot Jupiter-like exoplanet expels a spiral cloud of helium

An exoplanet has been spotted releasing huge amounts of helium gas, leaving a spectacular trail in its wake as it orbits a star 950 light-years from Earth.

HAT-P-32 b is losing so much of its atmospheric helium that it has created one of the largest planetary structures yet discovered outside our solar system.

The planet is known as a “hot Jupiter” because it is roughly the size of Jupiter, but much hotter. Orbiting its host star at only about 5 million kilometres (slightly more than 3% the distance between the Earth and the Sun), HAT-P-32 b has an estimated equilibrium temperature of more than 1600°C. It orbits its host binary star system every 2.5 Earth days.

Originally discovered in 2004, HAT-P-32 b was confirmed as a planet in 2011. Its radius is more than twice that of Jupiter, but it is slightly less massive.

Analysis of the planet is published in Science Advances.

“We have monitored this planet and the host star with long time series spectroscopy, observations made of the star and planet over a couple of nights,” says co-author Zhoujian Zhang, a postdoctoral fellow in the Department of Astronomy & Astrophysics, University of California Santa Cruz. “What we found is there’s a gigantic helium gas tail that is associated with the planet. The tail is large – about 53 times the planet’s radius – formed by gas that’s escaping from the planet.”

Researchers used three-dimensional computer simulations to help model the flow of the planet’s atmosphere based on data from the Hobby-Eberly Telescope at the University of Texas’s McDonald Observatory.

Astronomers are interested in hot Jupiters because they may help explain a phenomenon known as the “Neptunian desert” – this is the relative scarcity of Neptune-sized planets which are an intermediate between the gas giants like Saturn and Jupiter, and the smaller rocky planets like Earth and Mars.

“One of the potential explanations is that maybe the planets are losing their mass,” Zhang says. “If we can capture planets in the process of losing their atmosphere, then we can study how fast the planet is losing their mass and what are the mechanisms that cause their atmosphere to escape from the planet. It’s good to have some examples to see like the HAT-P-32 b process in action.”

The scientists hope to survey 20 additional star systems to find more planets losing their atmosphere and learn about their evolution.

Sign up to our weekly newsletter

Please login to favourite this article.