Seven Earth-sized planets orbit a frigid star in the TRAPPIST-1 solar
system, around 40 light years from our sun.
New information on TRAPPIST-1 b, the planet in the TRAPPIST-1 solar system
nearest to its star, has been made available to astronomers by the James
Webb Space Telescope (JWST). These new discoveries shed light on how
measurements of exoplanets in the habitable zone of cold stars might be
impacted by the star. Liquid water can still be found on the surface of the
circling planet in the habitable zone.
Researchers Ryan MacDonald, a NASA Sagan Fellow and astronomer at the
University of Michigan, and his team published their findings in the journal
The Astrophysical Journal Letters.
"We found no evidence of an atmosphere surrounding TRAPPIST-1 b in our
observations. This indicates that the planet may be made entirely of rock,
have clouds high in the sky, or have an atmosphere that is too thin to be
detected due to a highly heavy chemical like carbon dioxide, according to
MacDonald. "However, we do observe that the star is by far the most
significant factor influencing our observations, and this will have the same
effect on other planets within the system."
The main objective of the team's research was to determine how much
information could be gleaned about the star's influence on planet
observations in the TRAPPIST-1 system.
"It will be much, much harder to detect any atmospheric signals when we
look at the planets in the habitable zone—TRAPPIST-1 d, e, and f—if we don't
figure out how to deal with the star now," MacDonald stated.
After seven Earth-sized exoplanets were discovered in 2017 in the potential
exoplanetary system TRAPPIST-1, a star about 40 light-years distant from
Earth that is considerably smaller and colder than our sun, astronomers and
space enthusiasts alike have been interested in this system. These planets,
which are closely clustered around their star and three of which are in its
habitable zone, have raised expectations for the discovery of possibly
habitable planets outside of our solar system.
Utilizing a method known as transmission spectroscopy, Olivia Lim of the
Trottier Institute for Research on Exoplanets at the University of Montreal
conducted the investigation and provided crucial information about the
characteristics of TRAPPIST-1 b. Astronomers can detect the distinct imprint
that the molecules and atoms in the exoplanet's atmosphere leave behind by
examining the light emitted by the central star after it has traveled past
it during a transit.
Michael Meyer, an astronomy professor at the University of Montreal,
stated, "These observations were made with the NIRISS instrument on JWST,
built by an international collaboration led by René Doyon at the University
of Montreal, under the auspices of the Canadian Space Agency over a period
of nearly 20 years." Being a part of this partnership was an honor, and it
was really thrilling to witness discoveries like these, which characterize
varied planets orbiting neighboring stars because to NIRISS's unique
capabilities.
Know your planet and star.
The study's main discovery was the importance of pollution and star
activity in determining an exoplanet's composition. The term "stellar
contamination" describes how the star's natural properties, including as
brilliant areas known as faculae and dark regions known as spots, might
affect measurements of an exoplanet's atmosphere.
The researchers discovered strong evidence that the transmission spectra of
TRAPPIST-1 b and, probably, the other planets in the system are
significantly shaped by stellar pollution. The activity of the central star
can produce "ghost signals" that could lead an observer to believe they have
found a certain chemical in the exoplanet's atmosphere.
This finding emphasizes how crucial it is to take stellar pollution into
account while organizing upcoming observations of any exoplanetary system.
This is particularly true for systems like TRAPPIST-1, which revolve around
a red dwarf star that exhibits periodic flare outbursts and starspot
activity.
Lim stated, "We observed a stellar flare, an erratic event during which the
star looks brighter for several minutes to hours, in addition to the
contamination from stellar spots and faculae." "Our assessment of the
quantity of light blocked by the planet was impacted by this flare. Although
these stellar activity characteristics are challenging to model, we must
take them into consideration to make sure that the data is appropriately
interpreted."
Running a series of millions of models to explore the full range of
properties of cool starspots, hot star active regions, and planetary
atmospheres that could explain the JWST observations the astronomers were
seeing, MacDonald played a crucial role in modeling the impact of the star
and looking for an atmosphere in the team's observations.
Nothing noteworthy to observe about TRAPPIST-1 b
The quest for Earth-sized exoplanets with an atmosphere has made all seven
of the TRAPPIST-1 planets intriguing prospects; nevertheless, TRAPPIST-1 b
faces more challenging circumstances than its siblings due to its close
closeness to its star. Its surface temperature ranges from 120 to 220
degrees Celsius, and it gets four times as much solar energy as Earth.
Nonetheless, of all the candidates in the system, TRAPPIST-1 b would be the
simplest to identify and characterize if it had an atmosphere. A greater
signal is produced during TRAPPIST-1 b's transit since it is the hottest
planet in the system and the planet nearest to its star. Because of all
these things, TRAPPIST-1 b is an important but difficult observation
target.
The researchers carried out two separate atmospheric retrievals, a method
to ascertain the type of atmosphere present on TRAPPIST-1 b, based on
observations, to account for the influence of stellar pollution. Before the
data were examined, star pollution was eliminated in the first method.
MacDonald's second method involved modeling and fitting both the planetary
atmosphere and stellar pollution at the same time.
The results showed that the predicted stellar pollution alone might match
TRAPPIST-1 b's spectra in both scenarios. This implies that there isn't any
proof of a substantial atmosphere on the planet. This kind of conclusion is
still highly significant since it indicates to astronomers the kinds of
atmospheres that don't fit the data that have been seen.
Lim and her colleagues investigated a variety of atmosphere models for
TRAPPIST-1 b, looking at many probable compositions and situations based on
their accumulated JWST data. High trust was placed on the exclusion of
atmospheres rich in hydrogen and devoid of clouds. This indicates that
TRAPPIST-1 b does not seem to have a distinct, prolonged atmosphere.
The information, however, was insufficient to definitively rule out thinner
atmospheres, such as ones made entirely of water, carbon dioxide, or
methane, as well as atmospheres like to Titan's, Saturn's moon and the only
moon in the solar system with a sizable atmosphere. These findings, the
first spectrum of a TRAPPIST-1 planet, are in general in agreement with
earlier JWST observations of the dayside of TRAPPIST-1 b, which the MIRI
instrument saw in a single hue.
These discoveries will guide next JWST and other telescope observation
programs, advancing our knowledge of exoplanetary atmospheres and possible
habitability as astronomers continue to study more rocky planets in the
vastness of space.
Provided by
University of Michigan
