The hunt for
habitable planets may have just gotten far more narrow
Scientists had long hoped and theorized that the
most common type of star in our universe called an M dwarf — could host nearby
planets with atmospheres, potentially rich with carbon and perfect for the
creation of life. But in a new study of a world orbiting an M dwarf 66 light-years
from Earth, researchers found no indication such a planet could hold onto an
atmosphere at all.
Without a carbon-rich
atmosphere, it’s unlikely a planet would be hospitable to living things. Carbon
molecules are, after all, considered the building blocks of life. And the
findings don’t bode well for other types of planets orbiting M dwarfs, said
study co-author Michelle Hill, a planetary scientist and a doctoral candidate
at the University of California, Riverside.
“The pressure from
the star’s radiation is immense, enough to blow a planet’s atmosphere
away,”
M dwarf stars are
known to be volatile, sputtering out solar flares and raining radiation on
nearby celestial bodies.
But for years, the
hope had been that fairly large planets orbiting near M dwarfs could be in a
Goldilocks environment, close enough to their small star to keep warm and large
enough to cling onto its atmosphere.
The nearby M dwarf,
however, could be too intense to keep the atmosphere intact, according to the new study, which was published in The Astrophysical
Journal Letters.
A similar phenomenon
happens in our solar system: Earth’s atmosphere also deteriorates because of
outbursts from its nearby star, the sun. The difference is that Earth has
enough volcanic activity and other gas-emitting activity to replace the
atmospheric loss and make it barely detectable, according to the research.
However, the M dwarf planet examined in the study, GJ 1252b, “could have 700 times more carbon than Earth has, and it still wouldn’t have an atmosphere. It would build up initially, but then taper off and erode away,” said study coauthor and UC Riverside astrophysicist Stephen Kane, in a news release.
Where is started and how
it’s going
GJ
1252b orbits less than a million miles from its home star, called GJ_1252. The
planet reaches sweltering daytime temperatures of up to 2,242 degrees
Fahrenheit (1,228 degrees Celsius), the study found.
The
existence of the planet was first suggested by NASA’s Transiting Exoplanet
Survey Satellite, or TESS, mission. Then, astronomers ordered the nearly
17-year-old Spitzer Space Telescope to set its sights on the area in January
2020 — less than 10 days before Spitzer was
deactivated forever.
The
investigation into whether GJ 1252b had an atmosphere was led by astronomer Ian
Crossfield at the University of Kansas and involved a collection of researchers
from UC Riverside, NASA’s Jet Propulsion Laboratory, Caltech, the University of
Maryland, Carnegie Institution for Science, the Max Planck Institute for
Astronomy, McGill University, the University of New Mexico, and the University
of Montreal.
This illustration shows one possible scenario for the hot,
rocky exoplanet called 55 Cancrie, which is nearly two times as wide as Earth.
Data from NASA's Spitzer Space Telescope showed that the planet has extreme temperature
swings. - NASA/JPL-Caltech/NASA/JPL-Caltech
They
pored over the data produced by Spitzer, searching for emission signatures, or
signs that a gaseous bubble could encase the planet. The telescope captured the
planet as it passed behind its home star, allowing researchers to “look at the
starlight as it’s passing through the atmosphere of the planet,” giving a
“spectral signature of the atmosphere” — or lack thereof, Hill said.
Hill
added that she wasn’t shocked to find no signs of an atmosphere, but she was
disappointed. She’s looking for moons and planets in “habitable zones,” and the
results made looking at worlds circling the ubiquitous M dwarf stars slightly
less interesting.
Researchers
hope to get even more clarity about these types of planets with the help of the
James Webb Space Telescope, the most powerful space telescope to date.
Webb
will soon set its sights on the TRAPPIST-1 system, “which
is also an M dwarf star with a bunch of rocky planets around it,” Hill noted.
“There’s
a lot of hope that it will be able to tell us whether those planets have an
atmosphere around them or not,” she added. “I guess the M dwarf enthusiasts are
probably holding their breath right now to see whether we can tell whether
there’s an atmosphere around those planets.”
There
are, however, still plenty of interesting places to hunt for habitable worlds.
Apart from looking to planets farther away from M dwarfs that could be more
likely to retain an atmosphere, there are still roughly 1,000 sun like stars
relatively near Earth that could have their own planets circling within
habitable zones, according to the UC Riverside post about the study.