Until not so long ago, the word “exoplanet” seemed more typical of speculation than astronomy. Isaac Newton already dropped in the ‘Scholium Generale’ of the Principia Mathematica that fixed stars could be the center of systems similar to ours, but science needed centuries to prove it. It was not until the late 1980s that the first signs of planets outside the Solar Systemalthough we had to wait until 1992 to confirm for the first time the existence of worlds beyond the Sun, around the pulsar PSR B1257+12.
In recent decades, the pace of discoveries has skyrocketed thanks to increasingly precise instruments, which have allowed us to locate worlds that are as strange as they are fascinating. The Kepler space telescope, for example, identified Kepler-16b, a planet with “two suns” more than a decade ago, reminiscent of Tatooine from Star Wars. Since then we have cataloged a huge variety of exoplanets, but now the James Webb telescope presents an especially striking find: a world of boiling lava that, to the surprise of astronomers, is colder than theoretical models predict.
An extreme world that questions what we know
With a radius approximately 1.4 times that of Earth, TOI-561 b is an extreme super-Earth orbiting a star located about 280 light years away, in the constellation Sextans. NASA describes it as the innermost planet of a system made up of four worlds, with an immediate peculiarity: it completes an orbit in less than eleven hours. Its proximity is so extreme, barely 0.01 astronomical units, that the daytime hemisphere must greatly exceed the melting point of rocks. Everything points to a planet trapped by its star in a tidal lock, with eternal day on one side and perpetual night on the other.
One of the peculiarities that most puzzles researchers is the low density of TOI-561 b. Astronomer Johanna Teske, lead author of the study, explains that “it is not a super-puff, but it is less dense than one would expect with a composition similar to that of the Earth.” The team envisioned the planet having a small iron core and a mantle made up of less compact minerals, a possibility that would fit the chemistry of its star. As it is a very old G-type star, about 10 billion years old and poor in iron, located in the thick disk of the Milky Way, it is plausible that the planet emerged in a primordial environment different from that of the Solar System.
Still, the exotic composition did not resolve all the unknowns, and the team began to consider another possibility: that TOI-561 b was involved through a thick atmosphere. The idea is striking because the models indicate that small planets subjected to such intense irradiation for billions of years should have lost their gases long ago. NASA reminds us, however, that some worlds of this type show signs that they are not simple bare rocks. That nuance opened the door to thinking that the low density could be due, in part, to a volume inflated by a substantial layer of gases.
To test the idea of a dense atmosphere, the team turned to a technique that James Webb has used on other rocky worlds: measuring the disappearance of some of the infrared glow as the planet passes behind its star. Using the NIRSpec spectrograph, the researchers estimated the temperature of the illuminated hemisphere and compared it to what would be expected for a surface without heat-distributing gases. If TOI-561 b were a bare rock, its temperature would be around 2,700 ºC. However, observations placed that value close to 1,800°C, a difference too large to ignore.
The unexpectedly low temperature makes sense if TOI-561 b is enveloped by a dense, volatile-filled atmosphere. In that case, the winds would transport heat from the illuminated hemisphere to less hot areas, which would reduce the infrared emission received by the telescope. Gases capable of absorbing part of the radiation before it escapes into space also come into play, something that coincides with the models evaluated by the team. YoIt is even possible that silicate clouds exist that reflect the light of the star and contribute to cooling the upper layers of the atmosphere.
To explain how TOI-561 b maintains such a resilient atmosphere, the researchers propose a mechanism in which magma and gases are in constant exchange. Tim Lichtenberg points out that as the interior releases volatile compounds into the atmosphere, the ocean of molten rock recaptures some of them, reducing the loss to space. This process requires a planet exceptionally rich in volatile substances, very different from Earth in its initial composition. In Lichtenberg’s words, it would be “like a ball of wet lava,” a description that well sums up the extreme nature of the find.
The observations that have allowed us to reconstruct this scenario are part of James Webb’s General Observers 3860 program. For more than 37 hours, the telescope continuously tracked the system as TOI-561 b completed nearly four full orbits, a record that offers a rare glimpse of how its brightness varies along the way. With that volume of data, the team is now analyzing how the temperature changes around the planet and what clues it provides about the composition of its atmosphere. This set of data, still being analyzed, points to a more complex world than was intuited in the first observations.
The case of TOI-561 b shows that even the most extreme worlds can hold surprises. Far from just a scorched rock, Webb’s observations describe a dynamic system in which magma, atmosphere, and stellar radiation interact in ways we don’t yet fully understand. As Johanna Teske points out, “What’s really exciting is that this new data set It’s opening even more questions than it’s answering.“The research continues, and each new analysis seems to confirm that this planet belongs to a category that we are only beginning to know.
Artistic images | POT
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