Latest news with #TOI6894b
WIRED
09-07-2025
- Science
- WIRED
A Giant Planet and a Small Star Are Shaking Up Conventional Cosmological Theory
Jul 9, 2025 7:00 AM A gas giant comparable in size to Saturn has been found orbiting a small red dwarf star. The discovery is making experts reconsider conventional notions of how planets form. An illustration of the giant gas planet TOI-6894b orbiting the small, dim red dwarf star TOI-6894. Illustration: University of Warwick/Mark Garlick Many of the stars in the Milky Way galaxy are small, dim red dwarfs—stars much smaller than the sun in both size and mass. TOI-6894, located far away from Earth, is one of them. Astronomers previously thought a star like this could not have large planets circulating it, because its mass is only about 20 percent of the sun, meaning its planetary system—generated from materials surrounding the star—would not have contained enough mass to form a giant body like Saturn or Jupiter. But when observing TOI-6894, an international research team detected a clear transit signal—a temporary decrease in a star's brightness caused by a planet passing across it. This newly discovered planet, named TOI-6894b, blocks 17 percent of the star's light, indicating the planet is fairly large. The signal was picked up by the Transiting Exoplanet Survey Satellite (TESS), an observation instrument launched by NASA to hunt for planets orbiting stars outside of our solar system. This makes TOI-6894 'the lowest mass star known to date to host such a planet,' said Edward Bryant, Astrophysics Prize Fellow at the University of Warwick, in a press statement. The finding appears to upend conventional theory on how planets are formed. 'This discovery will be a cornerstone for understanding the extremes of giant planet formation,' Bryant said. Astronomers at University College London and the University of Warwick, as part of a global collaboration with partners in Chile, the US, and Europe, trawled through the data of about 91,000 red dwarf stars observed by TESS before discovering the planet TOI-6894b. After that, the nature of TOI-6894b was clarified by additional observations made with other telescopes. According to these, TOI-6894b's radius is slightly larger than Saturn's, but its mass is only about half that of the ringed giant. Its density is extremely light at only 0.33 g/cm³, indicating that it is an expanding gas planet. TOI-6894 is nearly 40 percent smaller than the previous record for the smallest star with a planet of this size. This fact poses a serious contradiction to conventional theories of planet formation. The widely accepted planetary formation model, the 'core-accumulation theory,' proposes that a ring of dust and rocks—known as protoplanetary disk—forms around a star, and that materials in this disk then gather together to form the cores of planets. After starting out this way, larger gas planets then accrete gases around their cores to become gigantic. But if the mass of the star is small, the mass of its protoplanetary disk tends to be small as well. In such a scenario, the nucleus necessary for the formation of a giant gas planet will not grow. Based on this theory, it is estimated that more than 120 times more solid matter than that of the Earth would be required to form TOI-6894b. However, the observed disk surrounding the star TOI-6894 contains only 58 times the mass of the Earth at most. This raises the possibility of an alternative planet-formation mechanism existing. One suggestion by Bryant and the team is that planets could form by gradual gas accumulation, without the initial formation of a massive core. 'Alternatively, it could have formed because of a gravitationally unstable disc,' Bryant says. 'In some cases, the disc surrounding the star will become unstable due to the gravitational force it exerts on itself. These discs can then fragment, with the gas and dust collapsing to form a planet.' However, the press statement goes on to explain that neither of these theories can could completely explain the formation of TOI-6894b, based on the data gathered. For now the planet's origin remains a mystery. Analyzing the atmosphere of the newly discovered exoplanet might yield answers; it is possible that chemical traces of its formation process remain. Observations of TOI-6894b by the James Webb Space Telescope over the next 12 months are expected to reveal details about its interior structure and atmospheric composition, which will have a major say on whether current theories about planet formation are supported or new ones are needed. The discovery may force us to rethink our unified model of planet formation, says Andrés Jordán of the Millennium Astrophysics Institute at Adolfo Ibáñez University in Chile. Years of steady observations are pushing the limits of theory, and it may even be time to fundamentally rethink our estimates of the total number of giant planets in the galaxy. This story originally appeared on WIRED Japan and has been translated from Japanese.
Yahoo
04-06-2025
- General
- Yahoo
A Super-Tiny Star Gave Birth to a Giant Planet And We Don't Know How
A giant conundrum has been found orbiting a teeny tiny red dwarf star just a fifth of the size of the Sun. Such small stars were thought to be incapable of producing giant planets. But there, in its orbit, appears to be unmistakable evidence of an absolute unit: a gas giant around the size of Saturn. TOI-6894b, as the exoplanet is named, has 86 percent of the radius of Jupiter. At just 23 percent of the radius and 21 percent of the mass of the Sun, its parent TOI-6894 is the smallest star yet around which a giant world has been found. "I was very excited by this discovery," says astrophysicist Edward Bryant of the University of Warwick in the UK, who led the large international research team. "We did not expect planets like TOI-6894b to be able to form around stars this low-mass. This discovery will be a cornerstone for understanding the extremes of giant planet formation." Planets are born from the material that's left over from the formation processes of its host star. Stars form when a dense clump of material in a cloud of gas and dust collapses under gravity. Material from that cloud spools around the spinning protostar in a disk that feeds the star's growth; when the star is large enough to push the material away with its stellar wind, growth stops. The remaining material is what makes planets. The dust clumps together, gradually building worlds that end up orbiting the star. Here's the thing, though. The amount of material in the disk is thought to be proportional to the mass of the star. The reason tiny red dwarf stars shouldn't be able to make giant planets is because there just oughtn't be enough material to do so. Nevertheless, these strange, 'impossible' systems show up from time to time, suggesting not just that giant planets can form around tiny stars, but that the process is not all that uncommon. We don't have a good handle on just how common it is, so Bryant and his team embarked on a mission to scour TESS data for clues. "I originally searched through TESS observations of more than 91,000 low-mass red-dwarf stars looking for giant planets," he says. "Then, using observations taken with one of the world's largest telescopes, ESO's VLT, I discovered TOI-6894b, a giant planet transiting the lowest mass star known to date to host such a planet." Exoplanets are usually found via a technique known as the transit method. When an exoplanet orbiting a star passes between us, the observers, and the star, that star's light dims minutely. Astronomers can determine the presence of an exoplanet by looking for periodic dips in the star's light. It's usually a tiny signal that takes quite a bit of analysis to find. When the researchers looked at TOI-6894, they found its light dimming by an absolutely whopping 17 percent. According to the team's observations of the transits, that would make the diameter of the star about 320,000 kilometers (200,000 miles), while the exoplanet is around 120,000 kilometers across. Follow-up observations to see how much this giant exoplanet's gravity affects the orbital motion of the star revealed the mass of TOI-6894b. It's just 17 percent of the mass of Jupiter, suggesting an exoplanet atmosphere that is light and fluffy. This is exciting for a few reasons. Because the exoplanet has such deep transits, it's a perfect candidate for atmosphere study. During those transits, some of the star's light filters through the diffuse atmosphere. As it does so, it can become altered by the atoms and molecules therein, allowing scientists to literally see what TOI-6894b is made of. A team of astronomers has already applied for time with JWST to perform these atmospheric studies. Because the exoplanet is quite cool (temperature wise, but also just in general), they expect to find a lot of methane. "This system provides a new challenge for models of planet formation, and it offers a very interesting target for follow-up observations to characterize its atmosphere," says astrophysicist Andrés Jordán of the Millennium Institute of Astrophysics in Chile. Hopefully, these studies will also shed some light on how TOI-6894b formed. There are two scenarios astronomers prefer for gas giants: a gradual accumulation of material from the bottom up, or the direct collapse of an instability in the protoplanetary disk. Based on the team's observations, neither scenario quite works. More detail on the composition of TOI-6894b could help tease out which is the more likely pathway for the formation of giant worlds orbiting tiny stars. "It's an intriguing discovery. We don't really understand how a star with so little mass can form such a massive planet!" says astrophysicist Vincent Van Eylen of University College London. "This is one of the goals of the search for more exoplanets. By finding planetary systems different from our Solar System, we can test our models and better understand how our own Solar System formed." The discovery has been published in Nature Astronomy. Water Discovered Around a Young, Sun-Like Star For First Time June's Full Moon Will Be The Lowest in The Sky For Decades. Here's Why. The Milky Way Might Not Crash Into The Andromeda Galaxy After All
