Category: exoplanets

Since the discovery of the first world beyond the solar system in the 1990s, astronomers have become adept at spotting extrasolar planets, or exoplanets. But while NASA's exoplanet catalog has burgeoned to over 6,000 confirmed entries, moons around these worlds, known as exomoons, have proved elusive.

In fact, we have failed to make a single confirmed discovery of an exomoon despite being certain that just as the planets of the solar system have their own natural satellites, worlds in other star systems must have them too.

Now, this controversial drought of exomoons may have become even more confusing and, frankly, weird. That is because while studying a strange star system called CD-35 2722 with the Very Large Telescope (VLT), astronomers have discovered an object that could be an exomoon, or it could be something that forces us to rethink our very definition of what a "moon" is and what a "planet" is.

The star CD-35 2722 is located around 73 light-years away and has around half the mass of the sun. It is orbited by a "failed star" or brown dwarf. These stellar bodies get their unfortunate nickname because they form like other stars but fail to gather enough mass to trigger the fusion of hydrogen to helium in their cores. In terms of mass, brown dwarfs are more massive than the largest gas giant planets, but smaller than the smallest stars, usually with around 13 to 80 times the mass of Jupiter, or around 0.013 to 0.08 times the mass of the sun.

The newly discovered object in CD-35 2722 is certainly moon-like, but rather than orbiting a planet as the moons in the solar system do, it orbits the system's brown dwarf.

"This system is somewhat hard to define using solar-system-based words like 'planet' and 'moon.' The exosatellite is clearly massive enough to be a planet, but it does not orbit a star, though it orbits an object that orbits a star," team leader Kevin Hoy of the Universidad Diego Portales and the Millennium Nucleus of Young Exoplanets and their Moons (YEMS) in Chile, said in a statement.

"Being the third wheel in this system makes us want to call it a moon, even if it is nothing like the small, rocky moons we have in our system."

The team's research was published on Wednesday (July 22) in the journal Nature.

Erm... It's definitely an exosatellite

The team currently isn't able to definitively claim this object in CD-35 2722 is an exomoon, because that would require really nailing down a new definition of what a moon is.

"The satellite we report is a giant gaseous body orbiting a highly massive companion, itself several times the mass of Jupiter. We have a clear delineation between the planets and the sun in the solar system, so defining things like moons is simple," team member Alice Zurlo of the Universidad Diego Portales said. "In the CD-35 2722 system, where we are blurring the lines between stars, planets, and moons, the whole thing becomes more complicated to describe."

Zurlo and colleagues can, however, confidently claim this is an exosatellite, meaning it is a first-of-its-kind detection no matter what the future holds for its classification.

It is hoped that the Extremely Large Telescope (ELT) currently under construction in Chile, will make a massive impact in the hunt for exomoons, and now, other exosatellites.

Until these objects begin to be uncovered, one thing this discovery re-emphasizes is something that astronomers have been gleefully discovering ever since the first exoplanet was spotted: planetary systems come in a variety of diverse, weird and wonderful forms.

This might be the closest we've gotten to finding a planet that could support life: Astronomers have detected an atmosphere around an Earth-like, rocky planet orbiting in the habitable zone around its star, a monumental first.

The rocky planet, called LHS 1140 b, is 48-light-years away from Earth and according to this new research, it has an atmosphere that contains helium. It is also the first rocky planet to have an atmosphere be detected directly. This is the first rocky planet to be found with an atmosphere that is also in the habitable zone, meaning it's at the right distance away from its star for liquid water to potentially exist on the planet. As we continue to search the cosmos for planets that can be considered "habitable," this planet checks more boxes than almost anything we've ever seen.

"We have actually detected directly the helium present in the atmosphere itself, and that's the first direct detection for any rocky exoplanet, which is really exciting … and then there's this added bonus that it's in the habitable zone, which is super exciting for astrobiology and habitability and searching for life," lead author Collin Cherubim, who recently earned his Ph.D. from Harvard University, told Space.com. "It feels kind of surreal."

What's this planet like?

Let's explore this planet and the system where it "lives."

This exoplanet, or planet outside of our solar system, was first discovered in 2017 by a team led by astronomer Jason Dittmann who is now a co-author on this new discovery.

"This planet was found like 10 years ago, and we're just now saying, okay, that's an atmosphere," Dittman told Space.com. "We're slowly narrowing the gap and checking these boxes … we're finding a planet that's rocky, a planet that's of the right temperature and now … it's like okay, we finally found one that has an atmosphere."

And being a rocky planet, "there's definitely a surface … it's made of rocks," Dittman said. What does the planet's surface look like? We can't say yet, but the researchers who found this planet's atmosphere think there's a good chance it could have water.

While it orbits a red dwarf star, which is smaller and cooler than the sun, it orbits closer than we do to our star, maintaining a temperature that keeps the planet in the "Goldilocks zone" where liquid water could exist on its surface.

"It probably also has a lot of water," Cherubim said. "If it has some amount of atmosphere that can provide a bit of a greenhouse effect, which we know that it does now … it will very likely be what we consider to be habitable conditions on Earth, and conditions that would likely support liquid water."

So is it Earth-like? While it's certainly not an Earth copy, this planet can be considered Earth-like in two main ways, Cherubim shared. One: its overall composition. The planet is rocky, likely with an iron core and (now we know) it has an atmosphere. And two: the planet's temperature is just right for liquid water, which is necessary for life at least as far as we understand it on our planet.

Finding an atmosphere

The discovery of the first exoplanet was confirmed just over 30 years ago. Since then, scientists have found over 6,000 exoplanets and counting. And while a few rocky planets have been found in their star's habitable zone, it wasn't until now that an atmosphere has been confirmed around a rocky planet in the habitable zone.

One reason why scientists have had a hard time finding such planets with atmospheres is their stars. LHS 1140 b orbits the most common type of star, a red dwarf, which is about one-third the size of our sun. This type of star remains active for a lot longer than stars like our sun. This activity means it releases bursts of extreme radiation like solar flares and coronal mass ejections. And typically, the extreme radiation around these stars totally strips the atmospheres from the planets orbiting them, so astronomers have wondered if planets orbiting these stars can have an atmosphere at all.

"This discovery is a big deal because it's showing that at least this rocky planet has retained an atmosphere over billions of years," Cherubim said. It's "a bona fide, robust way of saying yes, atmospheres can survive on rocky exoplanets."

It's possible that other gases beyond helium are in the planet's atmosphere, and it's possible that some of its atmosphere was previously stripped away by its star's radiation. But the red dwarf that this planet orbits is roughly 6 billion years old, a few billion years older than the age at which their extreme radiation activity begins calming down. So while some helium is still slowly escaping the planet's atmosphere over time, the team expects the planet to retain an atmosphere, Dittman shared. After all, even Earth's helium is slowly escaping our own atmosphere.

The proof is in the atmosphere

To prove that this planet has an atmosphere, the team started with a prediction that Cherubim made during graduate school. It all started with a theoretical model and a sneaking suspicion that there must be rocky exoplanets with atmospheres other than Earth.

"This came out of a very specific prediction from a planetary evolution model that I actually developed myself, from scratch, from first principles, for my Ph.D. as a theorist, and I made a very specific prediction about this planet," Cherubim said. "And then I went out and did a pretty unexpected, weird thing using this technique that's typically reserved for observing giant planets, and I used it for a rocky planet, which nobody has done before.

"And lo and behold, I made this measurement that was actually consistent with my prediction. And it was really nice to kind of close the whole loop of the scientific method."

The team took the theoretical model that Cherubim developed in graduate school and put it to the test using the Warm Infrared Echelle (WINERED) Spectrograph on the Magellan Observatory in Chile. And with their observations, they were able to see LHS 1140 b and another planet both transit, or pass in front of, their star in the same night. With this spectrographic data, they could identify the signatures of molecules in the atmospheres of these planets as they passed in front of the star. And while one planet yielded no results, this planet showed a direct, undeniable helium signature.

Are there aliens?

When looking at a planet that is rocky, has an atmosphere, and is in the habitable zone (meaning it could have liquid water), the question of life comes up quite quickly.

But the researchers don't have enough data to make that conjecture. "I'm not claiming this planet has life," Cherubim made clear. With further investigation, scientists could better understand what else might be in this planet's atmosphere, and they could confirm if it has water. Further observations might not be able to confirm habitability or identify any life on the planet, but they could at least help us to better understand planets like this.

With this being the first planet of its kind discovered, further exploration will help us to put the pieces together. But it is certainly a major step forward in the eternal human quest to answer the question: are we alone?

This work was described in a study published in the journal Science.

It has taken over ten years, but astronomers have finally won a prolonged game of cosmic hide-and-seek with a planet hiding around the star Beta Pictoris. The extrasolar planet, or exoplanet, is known as Beta Pictoris d. It is found 63 light-years away and has two planetary siblings, which were caught some time ago.

This new exoplanet is 100 times fainter than its sibling Beta Pictoris b, which was the first planet discovered in the system. That makes Beta Pictoris d the faintest exoplanet ever seen from Earth.

Like its previously discovered sibling, Beta Pictoris d is a gas giant. However, unlike Beta Pictoris b and Beta Pictoris c, it is much further away from its parent star and is thus much cooler than its siblings. The newly discovered world is also smaller than the previously seen world around Beta Pictoris. While both Beta Pictoris b and Beta Pictoris c have around 10 times the mass of Jupiter each, Beta Pictoris d has only around 2.4 times the mass of the solar system's most massive world. That makes it one of the lightest exoplanets ever directly imaged by a ground-based telescope.

"Planet d, it seems, has been playing a game of hide-and-seek with us for over a decade, and only now can we say ‘found you!’" team member Jayne Birkby an astronomer at the University of Oxford in the UK, said in a statement.

The discovery of Beta Pictoris d helps clear up a puzzle regarding a disk of dust and debris in this planetary system, which is theorized to be made of the leftovers of planet formation. That is because this newly found world has exactly the right mass and location needed to explain both the odd shape of this debris disk and its location.

11 years of hide-and-seek

The team behind this discovery wasn't initially looking for a third planet around Beta Pictoris. Instead, they were simply attempting to learn more about the system's first planet.

"This was a serendipitous discovery," team co-leader Ben Sutlieff, an astronomer at the University of Edinburgh said. "We initially wanted to look more at a known planet in the system, Beta Pictoris b, to see how it changed over time."

That was until they spotted telltale signs of another planet around the same star. Delving back into 11 years of archival data, the team found the third planet lurking in various images.

To consider how impressive it is to directly image a planet outside the solar system, consider that of the over 6,000 worlds in NASA's exoplanet catalog, less than 100 were discovered using direct imaging. Such detections are so tricky because they require picking out the thermal glow of a planet from the glare of its parent star.

Catching a direct image of an exoplanet as faint as Beta Pictoris d is a major step forward for this technique.

"The new planet is 100 times fainter than Beta Pictoris b, the famous planet in the same system, making it the faintest exoplanet ever imaged directly from Earth," team co-leader and European Southern Observatory researcher Markus Bonse said.

The discovery of Beta Pictoris d makes the Beta Pictoris system just the second in which more than two worlds have been directly imaged. The first was HR 8799, which is located around 133 light-years away.

"Systems with multiple directly imaged exoplanets are the 'holy grails' of discoveries, because they can teach us a lot about what different exoplanets are like in the same formation environment," Sutlieff said

Thus, the discovery of Beta Pictoris d via direct imaging should encourage further direct imaging of planetary systems which may also harbor faint planets. This is an investigation that could be picked up by the Extremely Large Telescope (ELT), currently under construction in the Atacama Desert of northern Chile.

"Planets seem to have friends," team member Beth Biller, of the University of Edinburgh in the UK, said. "Many of the famous directly imaged exoplanet systems seem to have multiple giant planets in the same system, and likely there are even more lower-mass planets hiding in these systems that might be revealed with instruments on the ELT."

The team's research was published on Wednesday (July 15) in The Astrophysical Journal Letters.

Clouds formed from vaporized rock could create the ultimate thermal insulation on one of the most common types of exoplanets discovered so far — the sub-Neptunes — raising temperatures so high that these worlds' solid surfaces melt and turn into oceans of magma.

"This work takes us one step closer to answering the question of what these mysterious worlds are made from," said astronomer Luis Welbanks, of Arizona State University, in a statement.

Sub-Neptunes are planets larger than Earth but smaller than Neptune. They are especially mysterious since we do not have a world of this type in our solar system. They are thought to contain a rocky core surrounded by a deep atmosphere, but not much else is known about their composition and structure. Their atmosphere could be hydrogen-rich like Jupiter's, or it could be abundant with water vapor and carbon-based organic molecules. In some cases, they might even be habitable under the hycean world paradigm, wherein a thick hydrogen atmosphere encases a global ocean of liquid water.

The James Webb Space Telescope (JWST) is busy probing the atmosphere of several sub-Neptunes to try and learn more about their bulk composition because their atmosphere should be representative of what such planets are made from, but results so far have been inconclusive.

Atmospheres of sub-Neptunes are deep and dense, meaning crushing pressures close to the boundary between the atmosphere and the solid body of the world can turn minerals into vapor that forms clouds. These minerals include aluminium oxide, iron, magnesium silicate, manganese sulfide, potassium chloride, sodium sulfide and zinc sulfide.

Using detailed computer simulations, a team led by Sagnick Mukherjee of Arizona State University explored what effect these clouds could have on both the surface and atmosphere of a sub-Neptune.

They showed that when these mineral clouds form deep down, they act as efficient insulating blankets that trap heat (and lots of it) leaking out from the core of the planet.

"Among the sub-Neptunes currently being studied with JWST, we were amazed to find that cloud-driven heating can raise the temperature at the planet's atmosphere–interior boundary by roughly over 1,400 to 2,600 degrees Celsius [2,550–4,712 degrees Fahrenheit]," said Mukherjee.

At the same time, because heat is being prevented from escaping, the upper atmosphere cools noticeably.

With all that heat retained close to the surface, the rock begins to melt.

"For some of the planets we modeled, that extra heat is enough to melt the planet's surface, creating a magma ocean," said team-member Matthew Nixon of Arizona State University.

These potential magma planets include GJ 1214b, which orbits a red dwarf star 48 light-years away. At one time it was thought to be a cool water-world, but JWST's discovery in 2025 of metallic vapors and carbon-dioxide haze in GJ 1214b's atmosphere rule this out, and now it seems that its surface, undetectable beneath the thick atmosphere, could be completely molten.

However, the presence of magma oceans opens up possibilities for more complex atmospheric chemistry. Gas seeps out of the magma and diffuses into the atmosphere, in theory enriching it in oxygen, silicon hydride and silicon monoxide, while going the other way the magma absorbs ammonia, methane and water vapor from the atmosphere. In other words, the atmosphere becomes enriched by material from underground, while also becoming depleted in some gases that astronomers would expect to see in greater abundance.

This means that JWST's attempts to learn about the bulk composition of a sub-Neptune exoplanet from the spectrum of its atmosphere could be skewed by this exchange of gases between a magma ocean and the atmosphere. The extra heating deep down will also impact the future of these sub-Neptune planets, since the extra heat will keep their lower atmosphere bloated and prevent the planet from contracting over billions of years.

If the findings are correct, they could place a huge obstacle on sub-Neptunes being habitable. Even if the boundary between the atmosphere and solid body of the planet isn't hot enough to form magma, it would still render the surface too hot to support liquid water or life.

The findings were published on July 8 in Astrophysical Journal Letters.

NASA's exoplanet-hunting spacecraft TESS (Transiting Exoplanet Survey Satellite) has a new method for detecting worlds beyond the solar system. The technique relies on a phenomenon introduced by Einstein in his 1915 theory of gravity, general relativity, called gravitational microlensing.

The exoplanet in question is called Gaia23bra b. The first hints of this exoplanet were found in 2023 by the now-retired Gaia space telescope via the slight brightening of a star caused by a microlensing event.

TESS usually spots planets by the tiny drop in the light output from their parent star as they cross, or transit, its face. This technique is most effective for very large gas giants that orbit close to their star, so it most likely wouldn't work for Gaia23bra b, which has 1.6 times Jupiter's mass but orbits its star at a similar distance to Jupiter's orbit around the sun. Additionally, the transit method employed by TESS usually has a search radius of around 150 light-years. Gaia23bra b, however, orbits an orange dwarf star about 80 percent the size of the sun that is located 40,000 light-years away. Thus, to confirm the existence of this world, TESS had to learn a new trick.

"When TESS launched, no one expected it to ever be capable of finding this kind of planet," team member Diana Dragomir of the University of New Mexico said in a statement. "The discovery implies that there are probably other so-called microlensing planets hiding in TESS's data that we hadn't previously thought to look for."

Microlensing and the hunt for exoplanets

To understand what microlensing is, first we have to consider what general relativity says about the effect of objects with mass on space itself. Mass causes the very fabric of space and time, united as 4-dimensional spacetime, to warp. Gravity arises from that curvature. The greater the mass, the more extreme the warping and thus the greater the force of gravity.

Here is the cool part: light usually travels in a straight line, but when the very fabric of spacetime is curved, it has to follow that path. So when light from a background object passes a foreground object, the light bends around it. The bigger the mass and the closer to that mass the light passes, the more its path is curved. That means light from the same source can reach our telescopes at different times. This causes an amplification of the background source.

This phenomenon of gravitational lensing has been used to great effect to study ancient galaxies that would usually be too distant and faint to see when they are gravitationally lensed by foreground galaxy clusters.

Obviously, planets have a heck of a lot less mass than clusters of galaxies, but they can still cause a slight gravitational lensing effect. That is micro-lensing, and it can be used to hunt planets.

Of the around 6,000 known exoplanets, only around 5 percent have thus far been discovered using microlensing. That is compared to around 75% found using the transit method TESS usually depends upon.

Gaia23bra b was first hinted at when it acted as a gravitational lens, passing between Earth and a background star, causing the ever-so-slight brightening of that star. The exciting thing about TESS successfully using microlensing is that this offers a complementary technique of exoplanet detection capable of detecting planets that the transit method might miss.

"With microlensing, we can find smaller planets with greater orbital distances, including worlds in the habitable zone of their star and even farther away," team member Mallory Harris of the University of New Mexico said. "Microlensing events happen once, and they're gone — they don't repeat. I like to joke that we'll probably find the first Earth analog with microlensing, and then wave at it as it goes by because we'll never see it again.

And, if you will excuse the pun, the future is bright for microlensing. That is because it is one of the techniques that NASA's next project, the Nancy Grace Roman Telescope, will use.

Roman will scour the very heart of the Milky Way where stars are tightly packed together, hunting microlensing events which should be common in such a dense stellar region. NASA scientists predict that this will lead to Roman discovering around 1,000 microlensing exoplanets on top of the estimated 100,000 transiting worlds it is predicted to detect.

"This is a bit like a preview of the microlensing NASA's Nancy Grace Roman Space Telescope will do. The key to Roman's microlensing survey is its dense time coverage targeting the galactic bulge," team member Michael Fausnaugh of Texas Tech University said. "The TESS mission uniquely provides these rapid observations for stars in other parts of the galaxy, and pairing the two opens up prospects for understanding planet formation in a diverse population of stars.

"Since microlensing finds solar system-like planets, this offers a new chance to understand how planetary systems like our own vary in different regions of the galaxy."

The team's research was published on July 1 in The Astrophysical Journal Letters.

A potentially habitable rocky world has been found in the habitable zone around a red dwarf just 25 light-years from us.

However, faced with a hostile wind of radiation from its host star, it remains unclear whether this new exoplanet supports an atmosphere, or the possibility of life. Nevertheless, astronomers are celebrating the discovery.

"This one's exciting," said Paul Robertson of the University of California, Irvine, in a statement. "It's one of our closest cosmic neighbors. Twenty-five light years sounds like a long way, but the Milky Way is about 100,000 light years across, so in that respect it's our next-door neighbor."

The planet, designated GJ 3378b, orbits the faint red dwarf star in the constellation of Camelopardalis, the Giraffe. It was discovered in 2024 by French astronomers using the Canada–France–Hawaii Telescope in Mauna Kea, but American astronomers have revised those initial findings, revealing that the planet is possibly more like Earth than we realized.

All we know for sure is the mass and the orbit of GJ 3378b. We do not yet know whether it is like Earth or not – it could have land and sea and clouds and life, or it could be airless and cratered.

The planet is not seen to transit, or pass in front of its star, blocking its light from our vantage point. Instead, GJ 3378b was detected by the effects of its gravity tugging on its parent star. This causes the star to wobble around the center of mass that it shares with the planet, a wobbling that is betrayed by a Doppler shift in the star's light that can be measured by its spectra, the wavelengths of light that it emits.

When it was discovered in 2024, its mass was measured to be 5.26 times the mass of Earth, putting it in mini-Neptune territory of being a larger, mostly gaseous world. However, by taking a second look at the planet using two different telescopes, Robertson's team was able to show that the planet's true mass is 2.3 times the mass of Earth. This means that it is closer to being a rocky super-Earth instead.

Furthermore, the same observations found that GJ 3378b's orbital period is 21 days, not the 25 days that had originally been measured. This means that the planet is closer to the star than had been thought, sitting comfortably within the habitable zone where temperatures will be suitable for liquid water on the surface of a planet with an atmosphere. So from that point of view, the chance of GJ 3378b being habitable, if not inhabited, seems fair.

"This super-Earth gets about 90% of the radiation from its host star that Earth gets from its sun, so it's right in the sweet spot," said Robertson.

One significant problem, however, is that red dwarfs spit out harmful torrents of radiation in fierce gusts of their stellar winds, which can strip away a planet's atmosphere. This raises the question, does GJ 3378b even have an atmosphere?

Currently there is no way to tell. The James Webb Space Telescope (JWST) has been probing for atmospheres around other rocky worlds orbiting red dwarfs, such as those in the TRAPPIST-1 system. It does so by transit spectroscopy, where an atmosphere wrapped around a planet absorbs some of the star's light filtering through it, leaving dark absorption lines in the star's spectrum.

Unfortunately, GJ 3378b does not transit its star. This means that astronomers will have to wait until the 2040s, when NASA's Habitable Worlds Observatory will hopefully launch, to answer the question of whether GJ 3378b really does have an atmosphere or not.

Still, astronomers are hopeful. GJ 3378b is right on the edge of the zone where planets are expected to be seriously battered by radiation, meaning it could have escaped the worst. If so, there might be more than just an atmosphere for the Habitable Worlds Observatory to discover.

"The ultimate goal is biosignatures," said University of Texas at Austin astronomer Michael Endl in a separate statement. "We really want to know, are we alone in the universe? We are still in the reconnaissance phase of our solar neighborhood, trying to find the planets around the nearest stars because those will be the easiest ones to detect a biosignature on."

"This planet brings us one step closer to knowing all of our neighbors and, ultimately, which might be hospitable for life."

The findings were reported on June 30 in The Astrophysical Journal.

Hot Jupiters are some of the most extreme planets in the universe, blazing gas giants like Jupiter or Saturn that exist so close to their stars that they complete orbits in a matter of days. Now, new research may rewrite the definition of these planets that make the solar system look a little bit mundane.

The extrasolar planet, or exoplanet, at the heart of this rethink is CoRoT-2 b, a world with 3.5 times the mass of Jupiter and 1.5 times the size of our solar system's largest planet, located around 696 light-years away. It orbits its star in just 41 hours or so.

What is so strange about CoRoT-2 b? Most hot Jupiters are tidally locked, meaning they have one side that permanently faces their stars, a "dayside," and a "nightside" that faces out into space in perpetuity. However, a new investigation of CoRoT-2 b seems to show that this hot Jupiter isn't tidally locked, and that is a big surprise, one that challenges all our assumptions about these extreme exoplanets.

"I really like looking at the weird ones — finding planets that don't fit the standard picture — and doing some mystery solving," team leader Aurora Kesseli of the NASA Exoplanet Science Institute (NExScI) said in a statement.

"Now we can see that a one-size-fits-all model does not work, even for planets that we've been studying for a long time. Every time we look at another hot Jupiter, we learn something new to help refine our models, which are useful for understanding not only hot Jupiters, but for all types of exoplanets."

The cosmic dance of hot Jupiters

For rocky planets, tidal locking would result in an incredibly hot dayside and a much cooler nightside, divided by a perpetual sunset. However, the situation for gas giants is somewhat more complicated because of their swirling atmospheres.

This means while hot Jupiters have day and night sides, they usually possess large hot spots on the dayside, shifted slightly towards the direction of their rotation and their orbit around the host star. CoRoT 2b defies this expectation too, possessing a hotspot in the opposite direction of its orbit. Kesseli and the team investigated three possible reasons for this abnormality.

"The conditions for tidal locking are important for astronomers to understand because the habitable zone for planets around M dwarfs is within the tidal locking zone, where we expect tidal locking to happen pretty quickly," Kesseli said. "The way that a planet rotates greatly affects how the planet distributes its heat, and therefore affects its habitability, so for a planet that is tidally locked, the temperatures, winds, and climates are going to look completely different than those of a planet that is not tidally locked."

Measuring the velocity of CoRoT-2 b, Kesseli and colleagues found that one day on this hot Jupiter is about three Earth days, which is almost twice as long as its year which lasts around 1.5 Earth days. This means that its day is much shorter than its year; by the time CoRoT-2 b completes one rotation, it has made almost two orbits of its parent star.
"I was very pleasantly surprised when I tried a bunch of methods, and I was like, 'Aha! This is actually like one of the three hypotheses!' Seeing the data pretty clearly pointing towards one of them was just really exciting," Kesseli said.

The next step for Kesseli is to discover what is causing the slow rotation of CoRoT-2 b.

"Hot Jupiters are the first type of planet where we have been able to really explore and refine our models of their climates," said Kesseli. "With the next generation of telescopes like the Habitable Worlds Observatory and the Extremely Large Telescope, we’ll be able to do more in-depth measurements across more planets, maybe even potentially habitable ones."

The team's research was presented at the 248th meeting of the American Astronomical Society in Pasadena, California, and has been published on the paper repository site arXiv.

What is rarer than discovering a "super-puff" planet with densities much (much) lower than those of the solar system gas giants? Discovering two orbiting the same star.

That is exactly what astronomers have done, finding two extrasolar planets, or exoplanets, that are super-puff siblings orbiting the same star. Both planets, designated TOI-791 b and TOI-791 c, have densities lower than that of cotton candy, making them the lightest exoplanets ever seen.

"Only a handful of these super-puffy planets are known, and it is even rarer to find two in the same system," team leader George Dransfield of Oxford University said in a statement. "Their extremely low densities make them fascinating targets for understanding how planetary systems form and evolve."

The two planets orbit a dwarf star called TOI-791, which is located around 1,110 light-years from Earth. Both planets are around the same size as Jupiter, but the solar system's most massive planet has a density 28 times greater than TOI-791 c and 35 times greater than TOI-791 b.

The low density of these exoplanets aren't their only remarkable quality, however. The super-puff siblings are also locked in a rare dance that sees the inner planet complete five orbits as the outer planet completes three orbits. This is known as a 5:3 mean-motion resonance.

As TOI-791 b and TOI-791 c complete this orbital tango, they gravitationally tug on each other, causing changes in their transits of their parent star, with transits representing the moments these planets cross the star's face from our vantage point. These transits are some of the longest ever seen, lasting 11 hours per planet, and were integral to discovering the worlds.

If you cross me....

TOI-791 b and TOI-791 c were first identified as candidate planets in 2019 and 2023, respectively, when the Planet Hunters citizen scientist group assessed data from NASA's exoplanet-hunting spacecraft TESS (Transiting Exoplanet Survey Satellite).

TESS hunts planets using the transits they make of their host stars from its position around Earth. These planetary transits cause a tiny dip in light from the star that TESS can detect.

Dransfield and colleagues then measured the size and density of these planets using data from telescopes across the globe, including the ASTEP (Antarctic Search for Transiting ExoPlanets) telescope at Concordia Station in Antarctica, to discover the planets are rare super-puff gas giants.

The discovery could help solve the puzzle of how super-puff planets actually form. The prevailing theory suggests super-puff planets form in distant, cold regions in the disks of gas and dust that surround their parent stars. This allows gas to accumulate around small solid cores, leading super-puffs to gather vast atmospheres of hydrogen and helium.

Further investigation of TOI-791 b and TOI-791 c could help sort between this formation route and other birth mechanisms for super-puffs.

"This system offers a unique laboratory for understanding how super-puff planets form and evolve," team member Amaury Triaud of the University of Birmingham said in the statement. "We propose to carry out space-based observations using the James Webb Space Telescope to assess if the puffy atmosphere contains carbon, nitrogen, and oxygen-bearing species, revealing new insight into how these unusual planets formed."

The team's research was published on Thursday (June 25) in the journal Monthly Notices of the Royal Astronomical Society.

Using NASA's exoplanet-hunting spacecraft TESS (Transiting Exoplanet Survey Satellite), scientists have discovered a planetary system that scientists are calling "improbable." It could change how we think about the mechanisms behind planet formation.

The reason for the unusual arrangement of this planetary system is a failed star or brown dwarf designated TOI-201 c. Objects like this get the slightly unfair nickname of "failed stars" because, despite forming from a collapsing cloud of gas and dust like other stars, they fail to gather enough mass to trigger nuclear fusion of hydrogen to helium in their cores. Brown dwarfs have masses between 13 and 80 times that of Jupiter, or 0.013 to 0.08 the mass of the sun. That puts them right between the most massive planets and the smallest stars.

TOI-201 c is on a highly elliptical orbit, taking 2,881 days to orbit its star, which has resulted in planets including a super-Earth named TOI-201 d and a warm Jupiter named TOI-201 b, forming in a narrow zone within its orbit, something that isn't just new to astronomers; it is completely unexpected based on planetary formation models.

The 5.8-day orbit of TOI-201 d and the 53-day orbit of TOI-201 b are both perfectly aligned with the orbit of the brown dwarf. The brown dwarf creates gravitational instability at distances equivalent to the distance between Mars and the sun, but this didn't prevent planets from forming in the system.

"This discovery provides a crucial insight into how planets form even around massive, eccentric objects," team member and INAF researcher Aldo Bonomo said in an emailed statement.

The system challenges the idea that gas giant planets form at distances equivalent to 2 to 3 times the distance between Earth and the sun in the disks of gas and dust that surround stars during their infancy.

"The presence of the brown dwarf on such an elliptical orbit forced the planets to form and survive by occupying the innermost and hottest edges of the primordial disk," team member Luca Naponiello of the National Institute for Astrophysics (INAF) said in the statement. "Furthermore, the data show that during the close approach of the brown dwarf, the warm Jupiter undergoes strong and sudden variations in its transit timing, bearing witness to an intense and vigorous dynamic interaction currently underway between the two giants."

The system was discovered by TESS using a rare mono-transit event, which describes a planetary body making one crossing of the face of its star, causing a dip in starlight. This was followed by an observing campaign conducted from the ground.

It is extremely rare to discover objects like TOI-201 c with such long and eccentric orbital periods using transits they make of their parent star. This brown dwarf is the first one of these objects to have its mass confirmed, making it an important step forward in astronomy.

"It [TOI-201c] is the transiting object with the longest orbital period for which the mass is known," Naponiello said.

The team's results were published on Wednesday (June 17) in the journal Nature.