Ultrahot planet hides under a gas blanket ⚡ экспресс
Ultra-short-period (USP) exoplanets (radius up to 2 R⊕, period ≤1 day) are typically stripped of volatile atmospheres by intense stellar irradiation, as evidenced by densities and eclipse observations matching bare rock. TOI-561 b (density 4.3±0.4 g·cm⁻³) stands out with an anomalously low density for an Earth-like composition, pointing to an odd interior (e.g., a coreless structure) or a secondary volatile-rich atmosphere. We present the first dayside emission spectrum of TOI-561 b, captured by JWST's NIRSpec in the 3–5 μm range. High-significance data rule out a bare rocky surface: instead of the expected ~3000 K, the dayside is cooled by a thick volatile envelope. This overturns the total atmospheric desiccation hypothesis for highly irradiated planets, confirming that planet-scale magma oceans can preserve substantial volatiles, and unlocks geophysical exploration of ultra-hot super-Earths through atmospheric observations.
For a long time, planets squeezed right up against their star were thought to be bare rocky spheres. Temperatures in the thousands of degrees strip away any gas envelope. But the James Webb Space Telescope showed: the ultrahot exoplanet TOI-561 b is wrapped in a dense blanket of gases.
The planet completes a full orbit around the star in just 10 hours. It was expected that its dayside would heat up to 3000 °C and glow in infrared light like a furnace. But the spectrum—the splitting of light into colors—revealed a much fainter glow. This means a warm layer of atmosphere, like a blanket, traps the heat near the surface.
Where did it come from? The likely source is an ocean of molten magma.
So the planet acquired a new gas envelope that lasts longer than expected. The surprise is that, at nearly the size of Neptune, this world weighs as much as Mars—a fluffy giant among scorching rocks.
🎯 At Neptune's size, TOI-561 b weighs as much as Mars—one of the fluffiest super-Earths.
🎬 The magma ocean on TOI-561 b brings to mind Mustafar—the fiery world from Star Wars.