Astronomers have found an exoplanet with a leaky atmosphere. HAT-P-32b, a gas giant located 923 light-years away is losing its atmosphere at a fast pace, and the scientists have discovered the extent of this loss. The exoplanet is 1.8 times the radius of Jupiter and is spitting out gas to form two tails, which are larger than any other structures we have ever found associated with an exoplanet. The tails are created as HAT-P-32b’s atmosphere spills over, and they span more than 53 times the radius of the exoplanet. The lead author of the study, astrophysicist Zhoujian Zhang, comments on the discovery, saying, “It is exciting to see how gigantic the extended tails are compared to the size of the planet and its host star.” He adds that other planets might also have extended escaping atmospheres that are waiting to be discovered.
HAT-P-32b is a puffy world with a low density, just 10% that of Jupiter’s. It orbits its star at a very close distance of just 2.15 days. The star is a little bigger and hotter than the Sun, and the exoplanet is heated to a temperature of around 1,836 Kelvin (2,845 Fahrenheit, 1,562 Celsius). The heat makes HAT-P-32b so puffy, but it’s also what’s stripping away its atmosphere. Previous observations had noted this effect in action but had not captured the true extent of the atmospheric destruction wrought by the star.
The Observations and Findings
The astronomers studied HAT-P-32b using transits, which is when an exoplanet orbits between us and its star. As the exoplanet blocks some of the star’s light, it causes the star’s light to fluctuate slightly on a regular basis, dimming. However, when an exoplanet with an atmosphere passes in front of its host star, some of that star’s light travels through the atmosphere, causing changes to the spectrum as some wavelengths are absorbed and re-emitted by elements and compounds in the gas. These can be picked out and traced to the substances causing them, like a chemical fingerprint.
The team used the Hobby-Eberly Telescope at the McDonald Observatory in Texas to observe HAT-P-32b over several nights, to piece together data covering its complete orbit, not just the 3 hours it takes to transit. They analyzed the spectra, looking for variations in the gases known to be leaking from HAT-P-32b’s atmosphere. The astronomers found that the tails are enormous. The exoplanet is puffing up so much that it’s spilling over the point at which the gas can remain gravitationally bound to the planet, ejecting vast amounts of material out into the space around the star. The team’s calculations suggest that the exoplanet is losing around 33.8 trillion tons of gas per year.
At that rate, it will take the exoplanet’s atmosphere around 40 billion years to evaporate entirely. This is almost triple the current lifespan of the Universe of 13.8 billion years, and it could help astronomers interpret other leaky gas exoplanets on close orbits with their stars. The lead author of the study, Caroline Morley of the University of Texas at Austin, comments on the findings, saying, “Our findings on HAT-P-32b may help us understand how other planets and their stars interact. We are able to take high-precision measurements on hot Jupiters, like this one, and then apply our findings to a wider range of planets.”
The discovery of HAT-P-32b suggests that many more leaky exoplanets with giant tails may be out there, waiting for us to look. The exoplanet is not the first leaky exoplanet that we have found, and some even share some similarities with the transits of HAT-P-32b. The discovery could help us better understand how planets and their stars interact, as well as the evolution of exoplanets.