Scientists discover new exoplanet with an atmosphere ripe for study


Date:
June 9, 2021
Source:
University of New Mexico
Summary:
Scientists have discovered a new, temperate sub-Neptune sized
exoplanet with a 24-day orbital period orbiting a nearby M dwarf
star. The recent discovery offers exciting research opportunities
thanks to the planet's substantial atmosphere, small star, and
how fast the system is moving away from the Earth.



FULL STORY ==========================================================================
An international group of collaborators, including scientists from
NASA's Jet Propulsion Laboratory and The University of New Mexico,
have discovered a new, temperate sub-Neptune sized exoplanet with
a 24-day orbital period orbiting a nearby M dwarf star. The recent
discovery offers exciting research opportunities thanks to the planet's substantial atmosphere, small star, and how fast the system is moving
away from the Earth.


==========================================================================
The research, titled TOI-1231 b: A Temperate, Neptune-Sized Planet
Transiting the Nearby M3 Dwarf NLTT 24399, will be published in a
future issue of The Astronomical Journal. The exoplanet, TOI-1231 b,
was detected using photometric data from the Transiting Exoplanet Survey Satellite (TESS) and followed up with observations using the Planet
Finder Spectrograph (PFS) on the Magellan Clay telescope at Las Campanas Observatory in Chile. The PFS is a sophisticated instrument that detects exoplanets through their gravitational influence on their host stars. As
the planets orbit their hosts, the measured stellar velocities vary periodically, revealing the planetary presence and information about
their mass and orbit.

The observing strategy adopted by NASA's TESS, which divides each
hemisphere into 13 sectors that are surveyed for roughly 28 days,
is producing the most comprehensive all-sky search for transiting
planets. This approach has already proven its capability to detect
both large and small planets around stars ranging from sun-like down
to low-mass M dwarf stars. M dwarf stars, also known as a red dwarf,
are the most common type of star in the Milky Way making up some 70
percent of all stars in the galaxy.

M dwarfs are smaller and possess a fraction of the sun's mass and have
low luminosity. Because an M dwarf is smaller, when a planet of a given
size transits the star, the amount of light that is blocked out by the
planet is larger, making the transit more easily detectable. Imagine an Earth-like planet passing in front of a star the size of the sun, it's
going to block out a tiny bit of light; but if it's passing in front of
a star that's a lot smaller, the proportion of light that's blocked out
will be larger. In a sense, this creates a larger shadow on the surface
of the star, making planets around M dwarfs more easily detectable and
easier to study.

Although it enables the detection of exoplanets across the sky, TESS's
survey strategy also produces significant observational biases based on
orbital period. Exoplanets must transit their host stars at least twice
within TESS 's observing span to be detected with the correct period by
the Science Processing Operations Center (SPOC) pipeline and the Quick
Look Pipeline (QLP), which search the 2-minute and 30-minute cadence
TESS data, respectively. Because 74 percent of TESS' total sky coverage
is only observed for 28 days, the majority of TESS exoplanets detected
have periods less than 14 days. TOI-1231b's 24-day period, therefore,
makes its discovery even more valuable.

NASA JPL scientist Jennifer Burt, the lead author of the paper, along
with her collaborators including Diana Dragomir, an assistant professor
in UNM's Department of Physics and Astronomy, measured both the radius
and mass of the planet.



========================================================================== "Working with a group of excellent astronomers spread across the globe,
we were able to assemble the data necessary to characterize the host star
and measure both the radius and mass of the planet," said Burt. "Those
values in turn allowed us to calculate the planet's bulk density and hypothesize about what the planet is made out of. TOI-1231 b is pretty
similar in size and density to Neptune, so we think it has a similarly
large, gaseous atmosphere." "Another advantage of exoplanets orbiting
M dwarf hosts is that we can measure their masses easier because the
ratio of the planet mass to the stellar mass is also larger. When the
star is smaller and less massive, it makes detection methods work better because the planet suddenly plays a bigger role as it stands out more
easily in relation to the star," explained Dragomir. "Like the shadow
cast on the star. The smaller the star, the less massive the star,
the more the effect of the planet can be detected.

"Even though TOI 1231b is eight times closer to its star than the Earth
is to the Sun, its temperature is similar to that of Earth, thanks to
its cooler and less bright host star," says Dragomir. "However, the
planet itself is actually larger than earth and a little bit smaller
than Neptune -- we could call it a sub-Neptune." Burt and Dragomir,
who actually initiated this research while they were Fellows at MIT's
Kavli Institute, worked with scientists specializing in observing and characterizing the atmospheres of small planets to figure out which
current and future space-based missions might be able to peer into
TOI-1231 b's outer layers to inform researchers exactly what kinds of
gases are swirling around the planet. With a temperature around 330
Kelvin or 140 degrees Fahrenheit, TOI-1231b is one of the coolest,
small exoplanets accessible for atmospheric studies discovered thus far.

Past research suggests planets this cool may have clouds high in their atmospheres, which makes it hard to determine what types of gases surround them. But new observations of another small, cool planet called K2-18
b broke this trend and showed evidence of water in its atmosphere,
surprising many astronomers.



========================================================================== "TOI-1231 b is one of the only other planets we know of in a similar
size and temperature range, so future observations of this new planet
will let us determine just how common (or rare) it is for water clouds
to form around these temperate worlds," said Burt.

Additionally, with its host star's high Near-Infrared (NIR) brightness,
it makes an exciting target for future missions with the Hubble Space
Telescope (HST) and the James Webb Space Telescope (JWST). The first set
of these observations, led by one of the paper's co-authors, should take
place later this month using the Hubble Space Telescope.

"The low density of TOI 1231b indicates that it is surrounded by
a substantial atmosphere rather than being a rocky planet. But
the composition and extent of this atmosphere are unknown!" said
Dragomir. "TOI1231b could have a large hydrogen or hydrogen-helium
atmosphere, or a denser water vapor atmosphere.

Each of these would point to a different origin, allowing astronomers
to understand whether and how planets form differently around M dwarfs
when compared to the planets around our Sun, for example. Our upcoming
HST observations will begin to answer these questions, and JWST promises
an even more thorough look into the planet's atmosphere." Another way
to study the planet's atmosphere is to investigate whether gas is being
blown away, by looking for evidence of atoms like hydrogen and helium surrounding the planet as it transits across the face of its host star.

Generally, hydrogen atoms are almost impossible to detect because their presence is masked by interstellar gas. But this planet-star system
offers a unique opportunity to apply this method because of how fast
it's moving away from the Earth.

"One of the most intriguing results of the last two decades of exoplanet science is that, thus far, none of the new planetary systems we've
discovered look anything like our own solar system," said Burt. "They're
full of planets between the size of Earth and Neptune on orbits much
shorter than Mercury's, so we don't have any local examples to compare
them to. This new planet we've discovered is still weird -- but it's one
step closer to being somewhat like our neighborhood planets. Compared
to most transiting planets detected thus far, which often have scorching temperatures in the many hundreds or thousands of degrees, TOI-1231 b is positively frigid." In closing, Dragomir reflects that "this planet joins
the ranks of just two or three other nearby small exoplanets that will be scrutinized with every chance we get and using a wide range of telescopes,
for years to come so keep an eye out for new TOI1231b developments!" ========================================================================== Story Source: Materials provided by University_of_New_Mexico. Original
written by Steve Carr.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jennifer A. Burt, Diana Dragomir, Paul Mollie`re, Allison
Youngblood,
Antonio Garci'a Mun~oz, John McCann, Laura Kreidberg, Chelsea
X. Huang, Karen A. Collins, Jason D. Eastman, Lyu Abe, Jose
M. Almenara, Ian J. M.

Crossfield, Carl Ziegler, Joseph E. Rodriguez, Eric E. Mamajek,
Keivan G.

Stassun, Samuel P. Halverson, Steven Jr. Villanueva, R. Paul
Butler, Sharon Xuesong Wang, Richard P. Schwarz, George R. Ricker,
Roland Vanderspek, David W. Latham, S. Seager, Joshua N. Winn,
Jon M. Jenkins, Abdelkrim Agabi, Xavier Bonfils, David Ciardi,
Marion Cointepas, Jeffrey D. Crane, Nicolas Crouzet, Georgina
Dransfield, Fabo Feng, Elise Furlan, Tristan Guillot, Arvind
F. Gupta, Steve B. Howell, Eric L. N. Jensen, Nicholas Law, Andrew
W. Mann, Wenceslas Marie-Sainte, Rachel A. Matson, Elisabeth
C. Matthews, Djamel Me'karnia, Joshua Pepper, Nic Scott, Stephen
A. Shectman, Joshua E. Schlieder, Franc,ois-Xavier Schmider,
Daniel J. Stevens, Johanna K. Teske, Amaury H.M.J. Triaud, David
Charbonneau, Zachory K. Berta-Thompson, Christopher J. Burke, Tansu
Daylan, Thomas Barclay, Bill Wohler, C. E. Brasseur. TOI-1231 b:
A Temperate, Neptune-Sized Planet Transiting the Nearby M3 Dwarf
NLTT 24399. Submitted to arXiv, 2021 [abstract] ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/06/210609084613.htm

--- up 4 weeks, 5 days, 22 hours, 45 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)