The newly discovered planets orbit an ultracool dwarf star and one is in the habitable zone, making it a prime target for further investigation.
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An illustration of two super-Earths orbiting a red dwarf
star. (Image credit: Mark Garlick/Science Photo Library via Getty Images) |
An international team of astronomers has discovered two new
super-Earths orbiting a distant ultracool dwarf star located 100 light-years
away from Earth.
The newly spotted exoplanets orbit the second coolest star
ever found with planets around it. The inner planet of the system, designated
LP 890-9b, is around 30% larger than Earth and rapidly orbits the dwarf star in
just 2.7 Earth days. The second planet, called LP 890-9c, is slightly larger,
at around 40% the size of Earth, and completes its orbit in around 8.5 Earth
days. Astronomers believe this second planet is in the habitable zone of its star,
where it is neither too hot nor too cold to support the existence of liquid
water at its surface.
The inner planet was originally identified as an exoplanet
candidate by the Transiting Exoplanet Survey Satellite (TESS), which spots
exoplanets as they cross the face of their stars as seen from Earth, causing a
tiny drop in light output. It was then confirmed by telescopes of the Search
for Habitable Planets Eclipsing Ultra-cool Stars (SPECULOOS) project operated
by the University of Birmingham in the U.K. (In addition to LP 890-9, the
system is sometimes referred to as TOI-4306 or SPECULOOS 2 to recognize these
two observers.)
The SPECULOOS team then searched the system for additional
exoplanets, which revealed the second world that TESS missed.
"TESS searches for exoplanets using the transit method, by monitoring the brightness of thousands of stars simultaneously, looking for slight dimmings that might be caused by planets passing in front of their stars," Laetitia Delrez, an exoplanetary scientist at the University of Liège in Belgium and lead author of a paper detailing the discovery, said in a statement. "However, a follow-up with ground-based telescopes is often necessary to confirm the planetary nature of the detected candidates and to refine the measurements of their sizes and orbital properties."
This follow-up work is particularly important in the case of
cool stars like LP 890-9 because much of their light registers as infrared, to
which TESS's sensitivity is limited.
That weakness isn't shared by the SPECULOOS project
telescopes, which are located in Chile and on Tenerife, an island just west of
Morocco. These telescopes are equipped with cameras that are very sensitive to
near-infrared light.
"The goal of SPECULOOS is to search for potentially
habitable terrestrial planets transiting some of the smallest and coolest stars
in the solar neighborhood," Michaël Gillon, an astronomer at the
University of Liège and SPECULOOS project principal investigator, said in the
same statement. "This strategy is motivated by the fact that such planets
are particularly well suited to detailed studies of their atmospheres and the
search for possible chemical traces of life with large observatories, such as
the James Webb Space Telescope (JWST)."
Gillon compared the discovery of these planets around the
cool star LP 890-9 to finding the exoplanets of the TRAPPIST-1 system, centered
on what is currently the coolest star ever found to have planets orbiting it.
Of the seven known exoplanets around TRAPPIST-1, three are
in the habitable zone, which has made the system a prime target for deeper
investigation. And the fact that one of these newly discovered worlds occupies
the habitable zone of LP 890-9 makes further investigation of the system almost
equally enticing.
"This gives us a license to observe more and find out whether the planet has an atmosphere, and if so, to study its content and assess its habitability," Amaury Triaud, an astrophysicist at the University of Birmingham and SPECULOOS working group leader, said.
Next, the scientists hope to study the atmosphere of
SPECULOOS-2c, possibly with JWST, which recently detected carbon dioxide in the
atmosphere of an exoplanet.
"It is important to detect as many temperate
terrestrial worlds as possible to study the diversity of exoplanet climates and
eventually to be in a position to measure how frequently biology has emerged in
the cosmos," Triaud concluded.
Reference: Research Paper
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