Space News & Blog Articles

When we think of Jupiter-type planets, we usually picture massive cloud-covered worlds orbiting far from their stars. That distance keeps their volatile gases from vaporizing from stellar heat, similar to what we’re familiar with in our Solar System. So, why are so many exoplanets known as “hot Jupiters” orbiting very close to their stars? That’s the question astronomers ask as they study more of these extreme worlds.

It turns out that hot Jupiters don’t actually start life snuggled up so close. Instead, they form much farther away from their stars in the protoplanetary nebula. That leads to the question: how did they migrate inward? The answer has been “we aren’t sure” from the planetary science community. However, astronomers at MIT, Penn State University, and a host of other institutions think they’ve got a handle on a better answer. They’ve found a hot Jupiter “progenitor.” That’s a juvenile version of a Jovian world slowly turning from cold to hot. The clues lie in its orbit and may give insight into how other planets evolve.

This new world is called TIC 241249530 b and it lies about 1,100 light-years away from us. Instead of circling its star in an almost circular elliptical orbit (our Jupiter does around the Sun), this one is in a highly elliptical orbit. That squished “egg-shaped” path takes it very close to its star (like about 10 times closer than the orbit of Mercury. Then, it heads out to about the distance that Earth lies from the Sun. Not only is that a weird orbit, but it gets weirder. The path is “retrograde”. That means its direction of travel is counter to the star’s rotation. Think of it like this: the star rotates one way and the planet orbits the opposite way.

Both the highly elliptical orbit and the retrograde path tell planetary scientists that the formerly “cool” Jupiter-like world is evolving into one of those hot Jupiters. Now, if that isn’t strange enough, the star the planet is orbiting is actually a binary star. That means it has a stellar companion. Over time, successive interactions between the two orbits—of the planet and its star—force the planet to migrate ever closer to its star. That forces its elliptical orbit to change to a tighter, more circular one. That’ll take about a billion years and that’s when the planet will be fully evolved into a Hot Jupiter.

An orbital comparison of this evolving hot Jupiter if it existed in our Solar System. Courtesy NOIRLab.

Venus is known for being really quite inhospitable with high surface temperatures and Mars is known for its rusty red horizons. Even the moons of some of the outer planets have fascinating environments with Europa and Enceladus boasting underground oceans. Recent observations from the James Webb Space Telescope show that Ariel, a moon of Uranus, is also a strong candidate for a sub surface ocean. How has this conclusion been reached? Well JWST has detected carbon dioxide ice on the surface on the trailing edge of features trailing away from the orbital direction. The possible cause, an underground ocean!

Uranus is the seventh planet in the Solar System and has five moons. Ariel is one of them and is notable for its icy surface and fascinatingly diverse geological features. It was discovered back in 1851 by William Lassell who funded his love of astronomy from his brewing business! The surface of Ariel is a real mix of canyons, ridges, faults and valleys mostly driven by tectonic activity. Cryovolcanism is a prominent process on the surface which drives constant resurfacing and has led to Ariel having the brightest surface of all Uranus’ moons. 

Studying Ariel closeup reveals that the surface is coated with significant amounts of carbon dioxide ice. The trailing hemisphere of Ariel seems to be particularly coated in the ice which has surprised the community. At the distance of Uranian system from the Sun, an average of 2.9 billion kilometres, carbon dioxide will usually turns straight into a gas and be lost to space, it’s not expected to freeze!

Until recently, the most popular theory that supplies the carbon dioxide to Ariel’s surface is interactions between its surface and charged particles in the magnetosphere of Uranus. The process known as radiolysis breaks down molecules through ionisation. A new study just published in the Astrophysical Journal Letters suggests an intriguing alternative, the carbon dioxide molecules are expelled from Ariel, possibly from a subsurface liquid ocean!

A team of astronomers using JWST have undertaken a spectral analysis of Ariel and compared the results with lab based findings. The results revealed that Ariel has some of the most carbon dioxide rich deposits in the solar system. The deposits are not just wisps and trace amounts instead adding up to about 10 millimetres across the trailing hemisphere. Furthermore, the results also showed signals from carbon monoxide too which should not be there given the average temperatures. 

When the James Webb Space Telescope was launched it came with a fanfare expecting amazing things, much like the Hubble Space Telescope. One of JWST’s most anticipated target was TRAPPIST-1. This inconspicuous star is host to seven Earth-sized planets, with at least three in the habitable zone. The two inner planets are airless worlds but so far there has been no word of the third planet, the first in the habitable zone. The question is why and what makes it so tricky to observe?

TRAPPIST-1 is a red dwarf star about 41 light years in the constellation Aquarius. The interest in the planets in the habitable zone is that the conditions could allow for the existence of liquid water. The seven planets were discovered through transit photometry where tiny drops in brightness of the star are observed due to the passage of the planets in front of the star.  The planets that orbit the star all have fairly short orbital periods from 1.5 days to 20 days. The result of this is that their transits across the stellar surface often overlap. 

The launch of the JWST in 2021 reignited the interest in exoplanet studies. Its predecessor the Hubble Space Telescope was never expected to last as long to JWST was able to complement the famous telescope. Setting itself apart from Hubble by its advanced infrared capability, JWST was ideally placed to study exoplanet atmospheres. Fundamental to the operation of the JWST is a large, multi-segment mirror measuring 6.5 metres in diameter and a whole host of sophisticated instruments. 

A team of astronomers have been studying TRAPPIST-1 and its system of planets using JWST, exploiting its infrared capabilities. Using a technique known as transmission spectroscopy the starlight is explored as it passes through the planetary atmospheres as they pass in front of the star. Studying the light in this way can reveal the elements in the atmosphere. Three years in though and challenges have slowed them down. 

Now, a paper published in Nature Astronomy highlights the challenges they faced and proposes how to overcome them. Top of the list relates to the non uniformity of a star. Those interested in solar astronomy will already be familiar with sun spots, flares and other solar phenomenon. These are seen on stars too and regions where cooler regions form can often harbour water vapour, playing havoc with transmission spectra and making it difficult to identify elements in the planetary atmosphere rather than in the star. This is known as stellar contamination.