“Hot Jupiter blows its top” appears to be a metaphor or imaginative way of describing a dramatic occurrence or situation surrounding a hot Jupiter exoplanet. A “Hot Jupiter” is a type of gas giant exoplanet that is comparable to Jupiter in size and composition but orbits relatively close to its parent star, resulting in high temperatures. These planets are notorious for their tremendous temperatures and strange atmospheric conditions.
The planet HAT-P-32b is shedding so much helium from its atmosphere that the trailing gas tails are among the biggest structures yet observed on any planet beyond our solar system. Three-dimensional (3D) simulations aided in the modeling of the planet’s atmospheric flow. The scientists hope to widen their planet-observing net and survey 20 additional star systems to find more planets losing their atmosphere and learn about their evolution.
A planet roughly 950 light years from Earth could be the planet equivalent of Yosemite Sam, blowing its atmosphere ‘top’ in a spectacular way. According to researchers, the planet HAT-P-32b is losing so much of its atmospheric helium that the trailing gas tails are among the largest structures yet known of an exoplanet, a planet outside our solar system.
Based on data from the Hobby-Eberly Telescope at the University of Texas at Austin’s McDonald Observatory, three-dimensional (3D) simulations on the Texas Advanced Computing Center’s Stampede2 supercomputer assisted in modeling the movement of the planet’s atmosphere. The scientists intend to broaden their planet-observing net and examine 20 more star systems in order to identify more planets shedding their atmospheres and learn more about their evolution.
One of the potential explanations is that maybe the planets are losing their mass/ If we can capture planets in the process of losing their atmosphere, then we can study how fast the planet is losing its mass and what are the mechanisms that cause their atmosphere to escape from the planet.
Zhoujian Zhang
“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. And 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,” said Zhoujian Zhang, a postdoctoral fellow in the Department of Astronomy & Astrophysics, University of California Santa Cruz.
Zhang is the lead author in a study on the helium tail detected from HAT-P 32b that was published in Science Advances in June 2023. The science team used data from the Habitable Planet Finder spectrograph, an instrument on the Hobby-Eberly telescope, which provides high spectral resolution of light in near-infrared wavelengths.
The planet HAT-P-32b was discovered in 2011 using spectroscopic data from the Hungarian-made Automated Telescope Network. It’s known as a ‘hot Jupiter,’ a gas giant similar to our neighboring planet Jupiter, but with a radius twice as large. This hot Jupiter hugs closely in orbit to its host star, about three percent the distance from the Earth to the Sun. Its orbital period – what we consider a year here on Earth — is only 2.15 days, and this proximity to the star scorches it with both long and short-wave radiation.
The main motivation for the scientists’ interest in studying hot Jupiters is their pursuit of the mystery of the Neptunian desert, the inexplicable relative scarcity on average of intermediate-mass planets, or sub-Jupiters, with short orbital periods.
“One of the potential explanations is that maybe the planets are losing their mass,” Zhang offered. “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-32b process in action.”
The light used in the investigation was emitted by the star HAT-P-32 A. It’s slightly hotter and larger than our sun. The examined light is not simply starlight. As the planet passes in front of the star, the starlight is filtered the most by the planet’s gaseous atmosphere for only a few hours. When the spectra were studied, this filtering, known as absorption, revealed properties of the transiting planet, in this case, massive discharges of helium.
Zhang and colleagues separated the starlight into its component frequencies using a technique known as transmission spectroscopy, similar to how a prism separates sunlight into a rainbow spectrum. Gaps in the spectrum suggest that light is being absorbed by elements in HAT-P-32b’s gaseous environment.
“What we see in our data is that when the planet is transiting the star, we see there’s deeper helium absorption lines. The helium absorption is stronger than what we expect from the stellar atmosphere. This excess helium absorption should be caused by the planet’s atmosphere. When the planet is transiting, its atmosphere is so huge that it blocks part of the atmosphere that absorbs the helium line, and that causes this excess absorption. That’s how we discovered the HAT-P-32b to be an interesting planet,” Zhang said.
It became more interesting as they developed 3D hydrodynamical simulations of the HAT-P-32b and host star, led by Antonija Oklopi of the Anton Pannekoek Institute for Astronomy at the University of Amsterdam, and Morgan MacLeod of the Harvard-Smithsonian Center for Astrophysics.
The simulations investigated the connections between planetary outflow and star winds in the extrasolar system’s tidal gravitational field. The models depicted columnar tails of planetary outflow both leading and trailing the planet along its orbital path, with excess helium absorption even distant from the transit spots that corresponded to observations. Furthermore, the simulations predict that the atmosphere will be completely destroyed in around 4 x 10e10 Earth years.
“We made use of TACC’s Stampede2 system’s Intel Skylake nodes for our calculations,” MacLeod stated. “This computation involves tracking flow as it moves away from the planet, from a slow-moving subsonic ‘atmosphere’ to a supersonic wind.” The HAT-P-32b system has a large-scale outflow that is similar in size to the planet’s orbit around the star. These requirements, taken combined, indicate the necessity for a robust, high-accuracy method for solving three-dimensional gas dynamics.”
The modelers utilized the Athena++ hydrodynamic software and a custom problem setup to do their calculation on Stampede2. With it they solve the equations of gas dynamics in a rotating frame of reference that matches the planet’s orbital motion. Athena++ is a Eulerian code — the flow is discretized with volume elements — and they used nested layers of mesh refinement to capture the large-scale star-planet system along with the much smaller scale of the atmosphere near the planet’s surface.
“Using the TACC HPC systems is a joy,” remarked MacLeod. “A few factors come into play here, the first and most important of which is the level of support. When I have an issue, I can phone the support line, get help, and get back to doing what I do best: science. Second, rather of performing a single full-scale calculation, I spend the great bulk of my effort creating and validating model findings. The TACC systems are extremely well prepared for this situation, which greatly accelerates development. In these situations, the ability to execute test computations through development queues or submit larger calculations of varying sizes in the lead-up to an eventual final model is critical and effective.”
In the future, the scientists plan to continue developing complex 3D models that capture features like atmospheric mixing of gases and even winds within the atmosphere on more distant worlds hundreds or even thousands of light years away.
