Imagine a scorching world of molten rock, orbiting so close to its star that one side is perpetually bathed in hellish heat. This is TOI-561 b, a planet so bizarre it defies our understanding of how worlds can exist. Scientists have just discovered that this 'Wet Lava Ball' in space somehow clings to a thick atmosphere, challenging everything we thought we knew about planets in extreme environments. But here's where it gets controversial: how can a planet so close to its star, bombarded by intense radiation, possibly hold onto an atmosphere? Shouldn't it have been stripped away long ago?
This groundbreaking discovery, made using NASA’s Webb Space Telescope, has astronomers scratching their heads. TOI-561 b, located about 280 light-years from Earth, orbits a 10-billion-year-old star and is believed to have a vast magma ocean. Despite its proximity to its star—less than one million miles—it appears to be surrounded by a substantial atmosphere. This finding not only explains the planet’s unusually low density but also forces us to rethink our models of rocky planets beyond our solar system.
First spotted in 2020, TOI-561 b is the innermost of at least three planets orbiting an ancient G-type star, slightly smaller and cooler than our Sun. Its orbit is so tight that it’s likely tidally locked, meaning one side always faces its star. This extreme condition should make it impossible for an atmosphere to survive, as the star’s radiation would typically blast gases into space. Yet, here we are, faced with evidence that suggests otherwise.
‘What makes this planet truly remarkable is its unexpectedly low density,’ explains Johanna Teske, lead author of the study published in The Astrophysical Journal Letters. ‘It’s not as light and fluffy as a “super-puff” planet, but it’s less dense than we’d expect for a planet with Earth-like composition.’ This anomaly hints that TOI-561 b isn’t just a rocky world—there’s something more complex at play.
Using Webb’s Near-Infrared Spectrograph (NIRSpec), researchers measured the planet’s dayside temperature, expecting it to reach a scorching 4,900 degrees Fahrenheit (2,700 degrees Celsius) if it lacked an atmosphere. Instead, they found temperatures closer to 3,200 degrees Fahrenheit (1,800 degrees Celsius)—still blisteringly hot, but not hot enough to rule out an atmosphere. ‘We explored other possibilities, but none fit the data as well as a thick, volatile-rich atmosphere,’ says Anjali Piette, co-author of the study.
And this is the part most people miss: the researchers believe the planet’s magma ocean might be the key. ‘We think there’s a balance between the magma ocean and the atmosphere,’ explains Tim Lichtenberg, another co-author. ‘Gases escape from the planet to form the atmosphere, but the magma ocean pulls them back in, creating a dynamic equilibrium.’ This process, however, requires the planet to be far richer in volatile compounds than Earth, earning it the nickname ‘Wet Lava Ball.’
But here’s the real head-scratcher: how does a small planet, constantly bombarded by stellar radiation, manage to retain such a thick atmosphere? The answer remains a mystery, but it’s one that could revolutionize our understanding of planetary formation and survival in extreme conditions. Could TOI-561 b be a rare exception, or are there more ‘Wet Lava Balls’ out there waiting to be discovered? And what does this mean for our search for habitable worlds? Let us know your thoughts in the comments—do you think this planet’s atmosphere is a fluke, or is there something fundamental about planetary science we’re still missing?
