Migrating Orbit Causes Extreme Seasons on Gas Giant

We might think that it’s bad enough dealing with Australia’s weather and seasons, but you haven’t seen this new exoplanet’s extreme swings. While here in Australia we sometimes mark our seasons more by what is happening rather than the temperature (such as cyclone season, bushfire season, and magpie season), a new exoplanet discovered by researchers at the University of Southern Queensland (USQ) experiences seasons which differ in temperature by thousands of degrees and are marked by aluminium rain.

The international research team was led by Pennsylvania State University graduate Jiayin Dong, and included USQ graduate student Alexis Heitzmann and astrophysics lecturer Dr George Zhou. USQ’s MINERVA-Australis facility at the Mount Kent Observatory in Queensland was used to discover the new exoplanet TOI-3362 b. 

“The University of Southern Queensland is in partnership with NASA JPL to provide the US astronomical community with access to MINERVA-Australis,” Mr Heitzmann said.

“This is the first major result to be published from this new partnership.  

“We run Australia's only set of telescopes dedicated to studying planets around other stars.

“Collaborating with our colleagues at the Pennsylvania State University, we discovered the planet TOI-3362 b using NASA's Transiting Exoplanet Survey Satellite space telescope.

“We then used MINERVA-Australis to confirm the orbit of the planet, revealing the highly unusual path the planet follows.”

The exoplanet the researchers have discovered is particularly unusual as researchers have caught it in the act of migrating in its orbit. The planet is currently moving from a wide circular orbit to one much closer to its host star. This act of migration is causing the planet to have an unusual elliptical orbit, a phenomenon that has only been seen twice before. 

“It's like looking at a flock of migratory birds - most of the time you see them wading in the water or on far off islands,” Mr Heitzmann said.  

“Every now and then, you see a flock flying overhead – on the move.”

TOI-3362 b is a gas giant, and as its orbit migrates it is expected to become a “hot Jupiter” in the far future. A hot Jupiter is a gas giant which has an orbit closer to its Sun, unlike Jupiter in our Solar System which is relatively far away. 

One of the main hypotheses as to how hot Jupiters are created is that they form further away from their host star and then migrate into a closer orbit throughout their life, a process being seen in TOI-3362 b.

“TOI-3362 b is one such planet caught in the act of migration, where its eccentric orbit is a transitional stage,” Mr Heitzmann explained. 

“If this is indeed the case, it is a great advance towards solving the mystery of how very close orbit giant exoplanets are formed.”

“Its uniqueness also renders it a privileged target for future atmospheric studies using the soon to be launched James Webb Space Telescope.”

TOI-3362 b’s unusual orbit has resulted in the exoplanet experiencing rapid and extreme seasons. During the planet’s year, which only lasts just over 18 days, the temperature on the surface fluctuates by 1000’s of degrees. These extreme temperature differences are thought to cause aluminium rain to fall on the planet’s surface in winter, when the planet is at its furthest from its star, due to aluminium in the atmosphere evaporating and forming clouds in the summer.

“The planet experiences a surface temperature of more than 2200 degrees in the summer and its winters are, in contrast, only around 500 degrees,” Mr Heitzmann said.

“Due to this extreme difference of temperature on the planet, aluminium present in TOI-3362 b’s atmosphere evaporates, forming clouds in summer which rain down in winter. 

“This is more than fun speculation, it's something we can measure - we plan to use some of the biggest telescopes on Earth to peek at the atmosphere of TOI-3362 b.”

So while Australian seasons can feel a bit wild at times, it’s hard to imagine just how extreme they can get throughout the rest of the universe on planets like TOI-3362 b.