This is the strongest evidence yet of a rocky planet beyond our solar system with an atmosphere.
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An artist concept of TOI-561 b and its host star. JWST has
found the strongest evidence yet of an atmosphere around the rocky exoplanet,
challenging assumptions that ultra-hot super-Earths cannot hold onto air.
(Image credit: NASA/STScI) |
Astronomers using the James Webb Space Telescope (JWST) say
they have found the strongest evidence yet for an atmosphere around a rocky
world outside our solar system.
The findings challenge the prevailing wisdom that relatively
small planets orbiting extremely close to their stars cannot sustain
atmospheres.
The ultra-hot super-Earth, TOI-561 b, is the innermost of at
least three planets circling a 10-billion-year-old star located about 280
light-years from Earth. The planet orbits at just one-fortieth the distance
between Mercury and the sun, completing a full orbit in under 11 hours.
That extreme proximity places it in a class of
ultra-short-period super-Earths that are heated to temperatures high enough to
melt rock. Under such conditions, scientists generally expect planets to lose
any atmosphere due to intense stellar radiation, leaving behind bare, airless
rock. But observations from NASA's TESS space telescope have shown TOI-561 b
has an unusually low density for a purely rocky world, suggesting that another
explanation may be needed.
"It must have formed in a very different chemical
environment from planets in our own solar system," Johanna Teske, a staff
scientist at the Carnegie Earth and Planets Lab in Washington D.C. who led the
new paper, said in a statement.
To test whether the planet has an atmosphere, the team used
the JWST's NIRSpec instrument to measure the temperature of TOI-561 b's
dayside. In May 2024, JWST observed the planet–star system continuously for
more than 37 hours, capturing four full orbits. Scientists focused on moments
when the planet passed behind its star, events known as "secondary
eclipses" when the planet's own light briefly disappeared. By measuring
the tiny drop in the system's total brightness during each eclipse, the team
could isolate the planet's infrared glow and directly determine its dayside
temperature.
If TOI-561 b had no atmosphere, its dayside should reach
roughly 4,900 degrees Fahrenheit (2,700 degrees Celsius). Instead, the JWST
measured a temperature much cooler, around 3,100 degrees Fahrenheit (1,700
degrees Celsius). To understand why, the researchers tested a range of possible
surfaces and atmospheric types to see which could reproduce the signal observed
by JWST.
"We really need a thick volatile-rich atmosphere to
explain all the observations," study co-author Anjali Piette of the
University of Birmingham said in the statement. "Strong winds would cool
the dayside by transporting heat over to the nightside."
The team suggests the planet may maintain a balance between
its molten surface and its atmosphere, allowing gases to cycle between them and
potentially replenishing its atmosphere.
"While gases are coming out of the planet to feed the
atmosphere, the magma ocean is sucking them back into the interior," study
co-author Tim Lichtenberg of the University of Groningen in the Netherlands
said in the statement. "It's really like a wet lava ball."
The results open the door to probe the interiors and
geological activity of such extremely hot rocky planets by studying their
atmospheres, the researchers note.
The findings were published on Dec. 11 in the The
Astrophysical Journal Letters.