First study with CHEOPS data describes one of the most extreme planets
in the universe

Date:
September 28, 2020
Source:
University of Bern
Summary:
CHEOPS keeps its promise: Observations with the space telescope
reveal details of the exoplanet WASP-189b - one of the most extreme
planets known.



FULL STORY ========================================================================== Eight months after the space telescope CHEOPS started its journey into
space, the first scientific publication using data from CHEOPS has been
issued. CHEOPS is the first ESA mission dedicated to characterising
known exoplanets.

Exoplanets, i.e. planets outside the Solar system, were first found in
1995 by two Swiss astronomers, Michel Mayor and Didier Queloz, who were
last year awarded the Nobel Prize for this discovery. CHEOPS was developed
as part of a partnership between ESA and Switzerland. Under the leadership
of the University of Bern and ESA, a consortium of more than a hundred scientists and engineers from eleven European states was involved in constructing the satellite over five years. The Science Operations Center
of CHEOPS is located at the observatory of the University of Geneva.


========================================================================== Using data from CHEOPS, scientists have recently carried out a detailed
study of the exoplanet WASP-189b. The results have just been accepted
for publication in the journal Astronomy & Astrophysics. Willy Benz,
professor of astrophysics at the University of Bern and head of the
CHEOPS consortium, was delighted about the findings: "These observations demonstrate that CHEOPS fully meets the high expectations regarding its performance." One of the most extreme planets in the universe WASP-189b,
the target of the CHEOPS observations, is an exoplanet orbiting the
star HD 133112, one of the hottest stars known to have a planetary
system. "The WASP-189 system is 322 light years away and located in
the constellation Libra (the weighing scales)," explains Monika Lendl,
lead author of the study from the University of Geneva, and member of
the National Centre of Competence in Research PlanetS.

"WASP-189b is especially interesting because it is a gas giant that orbits
very close to its host star. It takes less than 3 days for it to circle
its star, and it is 20 times closer to it than Earth is to the Sun,"
Monika Lendl describes the planet, which is more than one and a half
times as large as Jupiter, the largest planet of the Solar system.

Monika Lendl further explains that planetary objects like WASP-189b are
very exotic: "They have a permanent day side, which is always exposed to
the light of the star, and, accordingly, a permanent night side." This
means that its climate is completely different from that of the gas giants Jupiter and Saturn in our solar system. "Based on the observations using CHEOPS, we estimate the temperature of WASP-189b to be 3,200 degrees
Celsius. Planets like WASP-189b are called "ultra-hot Jupiters." Iron
melts at such a high temperature, and even becomes gaseous. This object
is one of the most extreme planets we know so far," says Lendl.

Highly precise brightness measurements "We cannot see the planet itself as
it is too far away and too close to its host star, so we have to rely on indirect methods," explains Lendl. For this, CHEOPS uses highly precise brightness measurements: When a planet passes in front of its star as
seen from Earth, the star seems fainter for a short time.

This phenomenon is called a transit. Monika Lendl explains: "Because
the exoplanet WASP-189b is so close to its star, its dayside is so
bright that we can even measure the 'missing' light when the planet
passes behind its star; this is called an occultation. We have observed
several such occultations of WASP-189b with CHEOPS," says Lendl. "It
appears that the planet does not reflect a lot of starlight. Instead,
most of the starlight gets absorbed by the planet, heating it up
and making it shine." The researchers believe that the planet is not
very reflective because there are no clouds present on its dayside:
"This is not surprising, as theoretical models tell us that clouds
cannot form at such high temperatures." And the star is special too
"We also found that the transit of the gas giant in front of its star is asymmetrical. This happens when the star possesses brighter and darker
zones on its surface," adds Willy Benz. "Thanks to CHEOPS data, we can
conclude that the star itself rotates so quickly that its shape is no
longer spherical; but ellipsoidal. The star is being pulled outwards at
its equator." continues Benz.

The star around which WASP-189b orbits is very different from the
sun. Monika Lendl says: "The star is considerably larger and more than
two thousand degrees Celsius hotter than our sun. Because it is so hot,
the star appears blue and not yellow-white like the sun." Willy Benz adds: "Only a handful of planets are known to orbit such hot stars, and this
system is the brightest by far." As a consequence, it forms a benchmark
for further studies.

In conclusion, Willy Benz explains: "We are expecting further spectacular findings on exoplanets thanks to observations with CHEOPS. The next
papers are already in preparation."

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


========================================================================== Journal Reference:
1. M. Lendl, Sz. Csizmadia, A. Deline, L. Fossati, D. Kitzmann,
K. Heng, S.

Hoyer, S. Salmon, W. Benz, C. Broeg. The hot dayside and asymmetric
transit of WASP-189 b seen by CHEOPS. Astronomy & Astrophysics,
2020; DOI: 10.1051/0004-6361/202038677 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200928090502.htm

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