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EI2GYB > ASTRO 28.09.23 00:04l 135 Lines 6740 Bytes #999 (0) @ WW
BID : 20207_EI2GYB
Read: GUEST
Subj: New insights into the atmosphere and star of an exoplanet
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New insights into the atmosphere and star of an exoplanet
Date:
September 25, 2023
Source:
University of Montreal
Summary:
A new study of the intriguing TRAPPIST-1 exoplanetary system has
demonstrated the complex interaction between the activity of the system's star
and its planetary features.
Astronomers led by a team at Universit‚ de Montr‚al has made important progress
in understanding the intriguing TRAPPIST-1 exoplanetary system, which was first
discovered in 2016 amid speculation it could someday provide a place for humans
to live.
Not only does the new research shed light on the nature of TRAPPIST-1 b, the
exoplanet orbiting closest to the system's star, it has also shown the
importance of parent stars when studying exoplanets.
Published in Astrophysical Journal Letters, the findings by astronomers at
UdeM's Trottier Institute for Research on Exoplanets (iREx) and colleagues in
Canada, the U.K. and U.S. shed light on the complex interplay between stellar
activity and exoplanet characteristics.
Captured the attention
TRAPPIST-1, a star much smaller and cooler than our sun located approximately
40 light-years away from Earth, has captured the attention of scientists and
space enthusiasts alike since the discovery of its seven Earth-sized exoplanets
seven years ago. These worlds, tightly packed around their star with three of
them within its habitable zone, have fueled hopes of finding potentially
habitable environments beyond our solar system.
Led by iREx doctoral student Olivia Lim, the researchers employed the powerful
James Webb Space Telescope (JWST) to observe TRAPPIST-1 b. Their observations
were collected as part of the largest Canadian-led General Observers (GO)
program during the JWST's first year of operations. (This program also included
observations of three other planets in the system, TRAPPIST-1 c, g and h.)
TRAPPIST-1 b was observed during two transits -- the moment when the planet
passes in front of its star -- using the Canadian-made NIRISS instrument aboard
the JWST.
"These are the very first spectroscopic observations of any TRAPPIST-1 planet
obtained by the JWST, and we've been waiting for them for years" said Lim, the
GO program's principal Investigator.
She and her colleagues used the technique of transmission spectroscopy to peer
deeper into the distant world. By analysing the central star's light after it
has passed through the exoplanet's atmosphere during a transit, astronomers can
see the unique fingerprint left behind by the molecules and atoms found within
that atmosphere.
'Just a small subset'
"This is just a small subset of many more observations of this unique planetary
system yet to come and to be analysed," adds Ren‚ Doyon, Principal Investigator
of the NIRISS instrument and co-author on the study. "These first observations
highlight the power of NIRISS and the JWST in general to probe the thin
atmospheres around rocky planets."
The astronomers' key finding was just how significant stellar activity and
contamination are when trying to determine the nature of an exoplanet. Stellar
contamination refers to the influence of the star's own features, such as dark
spots and bright faculae, on the measurements of the exoplanet's atmosphere.
The team found compelling evidence that stellar contamination plays a crucial
role in shaping the transmission spectra of TRAPPIST-1 b and, likely, the other
planets in the system. The central star's activity can create "ghost signals"
that may fool the observer into thinking they have detected a particular
molecule in the exoplanet's atmosphere.
This result underscores the importance of considering stellar contamination
when planning future observations of all exoplanetary systems, the sceintists
say. This is especially true for systems like TRAPPIST-1, since the system is
centred around a red dwarf star which can be particularly active with starspots
and frequent flare events.
"In addition to the contamination from stellar spots and faculae, we saw a
stellar flare, an unpredictable event during which the star looks brighter for
several minutes or hours," said Lim. "This flare affected our measurement of
the amount of light blocked by the planet. Such signatures of stellar activity
are difficult to model but we need to account for them to ensure that we
interpret the data correctly."
A range of models explored
Based on their collected JWST observations, Lim and her team explored a range
of atmospheric models for TRAPPIST-1 b, examining various possible compositions
and scenarios.
They found they could confidently rule out the existence of cloud-free,
hydrogen-rich atmospheres -- in other words, there appears to be no clear,
extended atmosphere around TRAPPIST-1 b. However, the data could not
confidently exclude thinner atmospheres, such as those composed of pure water,
carbon dioxide, or methane, nor an atmosphere similar to that of Titan, a moon
of Saturn and the only moon in the Solar System with its own atmosphere.
These results are generally consistent with previous (photometric, and not
spectroscopic) JWST observations of TRAPPIST-1 b with the MIRI instrument. The
new study also proves that Canada's NIRISS instrument is a highly performing,
sensitive tool able to probe for atmospheres on Earth-sized exoplanets at
impressive levels.
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