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EI2GYB > ASTRO 06.12.25 14:46l 117 Lines 6837 Bytes #41 (0) @ WW
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Subj: A new look at TRAPPIST-1e, an Earth-sized, habitable-zone e
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A new look at TRAPPIST-1e, an Earth-sized, habitable-zone exoplanet
Of the seven Earth-sized worlds orbiting the red dwarf star TRAPPIST-1, one
planet in particular has attracted the attention of scientists. This planet
orbits the star within the "Goldilocks zone"-a distance where water on its
surface is theoretically possible, but only if the planet has an atmosphere.
And where there is water, there might be life.
Two recent scientific papers detail initial observations of the TRAPPIST-1
system obtained by a research group using NASA's James Webb Space Telescope,
published in The Astrophysical Journal Letters. In these publications, the
authors, including Sukrit Ranjan with the University of Arizona Lunar and
Planetary Laboratory, present a careful analysis of the results so far and
offer several potential scenarios for what the planet's atmosphere and surface
may be like.
While these reports are intriguing and show progress toward characterizing the
nearest potentially earth-like exoplanet, Ranjan urges caution in a third
paper, also appearing in The Astrophysical Journal Letters, arguing that more
rigorous studies are needed to determine whether TRAPPIST-1e has an atmosphere
at all and whether preliminary hints of methane detected by James Webb are
indeed signs of an atmosphere or have their origin with its host star.
The TRAPPIST system, so named after the survey that discovered it-"Transiting
Planets and Planetesimals Small Telescope project"-is located about 39
light-years from Earth. It resembles a miniature version of our solar system.
The star and all its planets would comfortably fit inside the orbit of planet
Mercury. A "year" for any given TRAPPIST planet lasts mere days by Earth
standards.
"The basic thesis for TRAPPIST-1e is this: If it has an atmosphere, it's
habitable," said Ranjan, who is an assistant professor at LPL. "But right now,
the first-order question must be, 'Does an atmosphere even exist?'"
To answer this question, researchers aimed the space telescope's powerful
Near-Infrared Spectrograph (NIRSpec) instrument at the TRAPPIST system as
planet TRAPPIST-1e transited-or passed in front of-its host star. During a
transit, starlight filters through the planet's atmosphere-if there is one-and
is partially absorbed, allowing astronomers to deduce what chemicals it may
contain. With each additional transit, the atmospheric contents become clearer
as more data is collected.
The four transits of TRAPPIST-1e studied by the team revealed hints of methane.
However, because TRAPPIST-1e's star is a so-called M dwarf, about one tenth the
size of our sun and only slightly larger than Jupiter, its unique properties
call for extra caution when interpreting data, Ranjan said.
"While the sun is a bright, yellow dwarf star, TRAPPIST-1 is an ultracool red
dwarf, meaning it is significantly smaller, cooler and dimmer than our sun," he
explained. "Cool enough, in fact, to allow for gas molecules in its atmosphere.
We reported hints of methane, but the question is, 'Is the methane attributable
to molecules in the atmosphere of the planet or in the host star?'"
To rule on this question, Ranjan and colleagues simulated scenarios in which
TRAPPIST-1e might have a methane-rich atmosphere and evaluated the probability
for each of them. In the most likely scenario among the ones tested, the planet
resembled Saturn's methane-rich moon, Titan. However, the work showed that even
that scenario was very unlikely.
"Based on our most recent work, we suggest that the previously reported
tentative hint of an atmosphere is more likely to be 'noise' from the host
star," Ranjan said. "However, this does not mean that TRAPPIST-1e does not have
an atmosphere-we just need more data."
Ranjan pointed out that while James Webb is revolutionizing exoplanet science,
the telescope was not originally designed to study small, Earth-like exoplanets.
"It was designed long before we knew such worlds existed, and we are fortunate
that it can study them at all," he said. "There is only a handful of
Earth-sized planets in existence for which it could potentially ever measure
any kind of detailed atmosphere composition."
New answers could come from NASA's Pandora mission, currently in development
and slated for launch in early 2026. Led by Daniel Apai, professor of astronomy
and planetary sciences at the U of A Steward Observatory, Pandora is a small
satellite designed to characterize exoplanet atmospheres and their host stars.
Pandora will monitor stars with potentially habitable planets before, during
and after they transit in front of their host stars.
In addition, researchers hope that an ongoing, larger round of observations and
new analytical techniques could finally tip the scale in one way or another.
Currently, the collaboration is focusing on a technique known as dual transit:
by observing the star when both TRAPPIST-1e and TRAPPIST-1b, the innermost and
airless planet of the system, pass in front of their star at the same time.
"These observations will allow us to separate what the star is doing from what
is going on in the planet's atmosphere-should it have one," Ranjan said.
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