Thu, 19 May 2022

Montreal [Canada], January 23 (ANI): A recent study provided new insights into what seasons looked like on a planet outside our solar system.

The study, led by McGill University, was published in 'The Astronomical Journal'.

The research opened up with one aspect of the atmosphere on XO-3b, one of a class of exoplanets (planets outside our solar system), which was that, the winds were so strong that they moved at the speed of sound. It is known as hot Jupiters. The eccentric orbit of the planet also led to seasonal variations hundreds of times stronger than what we experience on Earth.

The researchers also suggested that the oval orbit, extremely high surface temperatures (2,000 degrees C- hot enough to vaporize rock) and "puffiness" of XO-3b revealed traces of the planet's history. The findings will potentially advance both the scientific understanding of how exoplanets form and evolve and give some context for planets in our own solar system.

Hot Jupiters are massive, gaseous worlds like Jupiter, that orbit closer to their parent stars than Mercury is to the Sun. Though not present in our own solar system, they appeared to be common throughout the galaxy. Despite being the most studied type of exoplanet, major questions remained about how they form. Could there be subclasses of hot Jupiters with different formation stories? For example, did these planets take shape far from their parent stars -- at a distance where it's cold enough for molecules such as water to become solid -- or closer. The first scenario fit better with theories about how planets in our own solar system were born, but what would drive these types of planets to migrate so close to their parent stars remained unclear.

To test those ideas, the authors of the recent McGill-led study used data from NASA's retired Spitzer Space Telescope to look at the atmosphere of exoplanet XO-3b. They observed eccentric seasons and measured wind speeds on the planet by obtaining a phase curve of the planet as it completed a full revolution about its host star.

"This planet is an extremely interesting case study for atmospheric dynamics and interior evolution, as it lies in an intermediate regime of planetary mass where processes normally neglected for less massive hot Jupiters may come into play," said Lisa Dang, the first author of the paper and a PhD student at McGill University's Department of Physics. "XO-3b has an oval orbit rather than the circular orbit of almost all other known hot Jupiters. This suggests that it recently migrated toward its parent star; if that's the case, it will eventually settle into a more circular orbit."The eccentric orbit of the planet also led to seasonal variations hundreds of times stronger than what we experience on Earth. Nicolas Cowan, a McGill professor explained: "The entire planet receives three times more energy when it is close to its star during a brief sort of summer, than when it is far from the star."The researchers also re-estimated the planet's mass and radius and found that the planet was surprisingly puffier than expected. They suggested that the possible source of this heating could be due to leftover nuclear fusion.

Observations by Gaia, an ESA (European Space Agency) mission, found that the planet was puffier than expected which indicated its interior may be particularly energetic. Spitzer observations also hinted that the planet produced much of its own heat as XO-3b's excess thermal emission wasn't seasonal -- it's observed throughout the year on XO-3b. It might be possible that the excess warmth was coming from the planet's interior, through a process called tidal heating. The star's gravitational squeeze on the planet oscillated as the oblong orbit took the planet farther and then closer to the star. The resulting changes in interior pressure produced heat.

For Dang, this unusual hot Jupiter provided an opportunity to test ideas about which formation processes might produce certain characteristics in these exoplanets. For example, could tidal heating in other hot Jupiters also be a sign of recent migration? XO-3b alone won't unlock the mystery, but it served as an important test for emerging ideas about these scorching giants. (ANI)

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