Eccentric exoplanet discovered

Date:
January 7, 2022
Source:
University of Bern
Summary:
An international research team has discovered a sub-Neptune
exoplanet orbiting a red dwarf star.



FULL STORY ==========================================================================
Led by the University of Bern, an international research team has
discovered a sub-Neptune exoplanet orbiting a red dwarf star. The
discovery was also made thanks to observations performed by the SAINT-EX observatory in Mexico. SAINT- EX is run by a consortium including the
Center for Space and Habitability (CSH) at the University of Bern and
the National Center of Competence in Research NCCR PlanetS.


==========================================================================
"Red dwarfs" are small stars and thus much cooler than our Sun. Around
stars like these, liquid water is possible on planets much closer to
the star than in our solar system. The distance between an exoplanet
and its star is a crucial factor in its detection: the closer a planet
is to its host star, the higher the probability that it can be detected.

In a study recently published in the journal Astronomy & Astrophysics, researchers led by Dr. Nicole Schanche of the Center for Space and
Habitability CSH of the University of Bern report the discovery of the exoplanet TOI-2257 b orbiting a nearby red dwarf. Nicole Schanche is
also a member of the National Center of Competence in Research PlanetS,
which the University of Bern runs together with the University of Geneva.

A special telescope is part of the solution Exoplanets that are very
far from our solar system cannot be observed directly with a telescope
-- they are too small and reflect too little light. However, one way to
detect such planets is the transit method. This involves using telescopes
to look for dips in the star's brightness that occur when planets pass
in front of the star. Repeated observations of the dips in the star's brightness give precise measurements of the planet's orbital period around
the star, and the depth of the transit allows researchers to determine
the planet's diameter. When combined with planet mass estimates from
other methods, such as using radial velocity measurements, the planet
density can be calculated.

Planet TOI-2257 b was initially identified by data from NASA's Transiting Exoplanet Survey Satellite TESS space telescope. The small star was
observed for a total of four months, but the gaps between observations
meant that it was not clear whether the decrease in brightness could
be explained by the transit of a planet with an orbit of 176, 88, 59,
44 or 35 days.



========================================================================== Observation of the star with the Las Cumbres Observatory Global Telescope subsequently ruled out the possibility that a planet with a 59-day orbital period was causing the drop in brightness. "Next, we wanted to find out
if the 35-day orbital period could be possible," explains Nicole Schanche.

The Mexico-based SAINT-EX telescope, co-operated by the CSH and the
NCCR PlanetS, is purpose-built to study red dwarfs and their planets in
more detail.

SAINT-EX is an acronym that stands for Search And characterIsatioN
of Transiting EXoplanets. The project was named in honor of Antoine de
Saint- Exupe'ry (Saint-Ex), the famous writer, poet and aviator. SAINT-EX observed a partial transit of TOI-2257 b and was able to confirm the exoplanet's exact orbital period around its star, 35 days. "Another 35
days later, SAINT-EX was able to observe the entire transit, which gave us
even more information about the properties of the system," says co-author Robert Wells from the CSH, who was involved in the data processing.

A temperate planet with an irregular orbit With its 35-day orbital
period, TOI-2257 b orbits the host star at a distance where liquid water
is possible on the planet, and therefore conditions favorable for the
emergence of life could exist. Planets in this so-called "habitable zone"
near a small red dwarf star are easier to study because they have shorter orbital periods and can therefore be observed more often. The radius of TOI-2257 b (2.2 times larger than Earth's) suggests that the planet is
rather gaseous, with high atmospheric pressure not conducive to life.

"We found that TOI-2257 b does not have a circular, concentric orbit,"
explains Nicole Schanche. In fact, it is the most eccentric planet
orbiting a cool star ever discovered. "In terms of potential habitability,
this is bad news," Nicole Schanche continues. "While the planet's
average temperature is comfortable, it varies from -80DEGC to about
100DEGC depending on where in its orbit the planet is, far from or close
to the star." A possible explanation for this surprising orbit is that
further out in the system a giant planet is lurking and disturbing the
orbit of TOI 2257 b. Further observations measuring the radial velocity
of the star will help confirm the eccentricity and search for possible additional planets that could not be observed in transit.

Candidate for observation with JWST The James Webb Space Telescope (JWST), which successfully launched on December 25, will revolutionize research
into exoplanet atmospheres. In order to prioritize good candidates for observations with the JWST, a transmission spectroscopy metric (TSM)
was developed that rates different system properties.

TOI-2257 b is well positioned with respect to TSM and is one of the most attractive sub-Neptune targets for further observations. "In particular,
the planet could be studied for signs of features such as water vapor
in the atmosphere," Nicole Schanche concludes.

========================================================================== Story Source: Materials provided by University_of_Bern. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. N. Schanche, F. J. Pozuelos, M. N. Gu"nther, R. D. Wells, A. J.

Burgasser, P. Chinchilla, L. Delrez, E. Ducrot, L. J. Garcia,
Y. Go'mez Maqueo Chew, E. Jofre', B. V. Rackham, D. Sebastian,
K. G. Stassun, D.

Stern, M. Timmermans, K. Barkaoui, A. Belinski, Z. Benkhaldoun,
W. Benz, A. Bieryla, F. Bouchy, A. Burdanov, D. Charbonneau,
J. L. Christiansen, K. A. Collins, B.-O. Demory, M. De'vora-Pajares,
J. de Wit, D. Dragomir, G. Dransfield, E. Furlan, M. Ghachoui,
M. Gillon, C. Gnilka, M. A.

Go'mez-Mun~oz, N. Guerrero, M. Harris, K. Heng, C. E. Henze,
K. Hesse, S.

B. Howell, E. Jehin, J. Jenkins, E. L. N. Jensen, M. Kunimoto, D. W.

Latham, K. Lester, K. K. McLeod, I. Mireles, C. A. Murray,
P. Niraula, P.

P. Pedersen, D. Queloz, E. V. Quintana, G. Ricker, A. Rudat,
L. Sabin, B.

Safonov, U. Schroffenegger, N. Scott, S. Seager, I. Strakhov,
A. H. M. J.

Triaud, R. Vanderspek, M. Vezie, J. Winn. TOI-2257 b:
A highly eccentric long-period sub-Neptune transiting a
nearby M dwarf. Astronomy & Astrophysics, 2022; 657: A45 DOI:
10.1051/0004-6361/202142280 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220107121438.htm
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