Science Gazette

Seasons on a planet beyond our solar system have been shown in new ways

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Observations of a hot Jupiter might help us learn more about the formation and development of planets.

Imagine being in a location where the winds are so powerful that they travel faster than sound. That’s only one feature of XO-3b’s atmosphere, which belongs to the hot Jupiters class of exoplanets (planets beyond our solar system). Seasonal changes on Mars are hundreds of times greater than on Earth due to the planet’s eccentric orbit.

Imagine being in a location where the winds are so powerful that they travel faster than sound. That’s only one feature of XO-3b’s atmosphere, which belongs to the hot Jupiters class of exoplanets (planets beyond our solar system). Seasonal changes on Mars are hundreds of times greater than on Earth due to the planet’s eccentric orbit. A McGill-led research team has published a report that sheds fresh light on what seasons might be like on a planet beyond our solar system. The round orbit, extraordinarily high surface temperatures (2,000 degrees C, hot enough to melt rock), and “puffiness” of XO-3b, according to the astronomers, disclose evidence of the planet’s past. The discoveries might help scientists better understand how exoplanets arise and evolve, as well as provide context for planets in our own solar system.

Hot Jupiters are enormous gaseous planets that circle their parent stars closer than Mercury orbits the Sun. They seem to be ubiquitous across the galaxy, despite not being found in our own solar system. Despite being the most researched exoplanet type, there are still many unanswered issues concerning how they develop. Could there be several types of hot Jupiters, each with its own creation story? Do these planets, for example, form distant from their parent stars, at a distance where it’s cold enough for molecules like water to solidify, or closer? The first scenario is more consistent with beliefs about how planets in our own solar system are formed, but it’s unknown what would cause these planets to travel so close to their parent stars.

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To put such theories to the test, researchers from McGill University looked at the atmosphere of exoplanet XO-3b using data from NASA’s decommissioned Spitzer Space Telescope. By collecting a phase curve of the planet as it completed a full rotation around its host star, they were able to discern eccentric seasons and calculate wind speeds on the planet.

Examining the dynamics of the atmosphere and the development of the interior

“This planet is an extremely interesting case study for atmospheric dynamics and interior evolution because it lies in an intermediate regime of planetary mass where processes normally ignored for less massive hot Jupiters may come into play,” says Lisa Dang, a PhD student at McGill University’s Department of Physics and the first author of a paper recently published in The Astronomical Journal. “XO-3b has an oval orbit, unlike virtually all other known hot Jupiters, which have circular orbits. This indicates that it has lately moved closer to its parent star; if so, it will soon settle into a more circular orbit.”

Seasonal changes on Mars are hundreds of times greater than on Earth due to the planet’s eccentric orbit. “The whole planet gets three times more energy when it is near to its star during a short type of summer than when it is distant from the star,” says Nicolas Cowan, a McGill professor.

The researchers also recalculated the planet’s mass and radius, discovering that it was considerably puffier than previously thought. They speculate that residual nuclear fusion might be the cause of this warmth.

Tidal heating causing excessive warmth and puffiness?

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The planet is puffier than predicted, according to observations by Gaia, an ESA (European Space Agency) mission, indicating that its innards may be highly active. Spitzer data also suggest that the planet generates a significant amount of its own heat, since XO-3b’s excess thermal emission is year-round on the planet. It’s likely that the extra heat is coming from the planet’s interior, thanks to a phenomenon known as tidal heating. As the planet’s oblong orbit moves it further and then closer to the star, the star’s gravitational pull on it oscillates. Heat is produced as a consequence of the changes in internal pressure.

For Dang, this very hot Jupiter presents a chance to test theories about which creation processes could result in certain exoplanet features. Could tidal heating on other hot Jupiters, for example, also be a hint of recent migration? XO-3b will not solve the puzzle on its own, but it will serve as a critical test for new theories regarding these raging titans.

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