CHEOPS finds unique planetary system

Date:
January 25, 2021
Source:
University of Bern
Summary:
The CHEOPS space telescope detects six planets orbiting the star
TOI-178.

Five of the planets are in a harmonic rhythm despite very different
compositions - a novelty.



FULL STORY ========================================================================== Musical notes that sound pleasant together can form a harmony. These
notes are usually in a special relationship with each other: when
expressed as frequencies, their ratios result in simple fractions, such
as four-thirds or three-halves. Similarly, a planetary system can also
form a kind of harmony when planets, whose orbital period ratios form
simple fractions, regularly attract each other with their gravity. When
one planet takes three days to orbit its star and its neighbor takes two
days, for example. Using the CHEOPS space telescope, scientists, led by astrophysicist Adrien Leleu of the Center for Space and Habitability of
the University of Bern, the University of Geneva and the National Center
of Competence in Research PlanetS, found such relationships between five
of six planets orbiting the star TOI-178, located over 200 light years
away from Earth. The results were published in the journalAstronomy
and Astrophysics.


==========================================================================
A missing piece in an unexpected puzzle "This result surprised us, as
previous observations with the Transiting Exoplanet Survey Satellite
(TESS) of NASA pointed toward a three planets system, with two planets
orbiting very close together. We therefore observed the system with
additional instruments, such as the ground based ESPRESSO spectrograph
at the European Southern Observatory (ESO)'s Paranal Observatory in
Chile, but the results were inconclusive.," Leleu remembers. When
he and his colleagues first proposed to investigate the system more
closely, they were therefore not sure what they would find. The high
precision and target-pointing agility of CHEOPS was required to bring
clarity, but that turned out to be more difficult than expected. "After analyzing the data from eleven days of observing the system with CHEOPS,
it seemed that there were more planets than we had initially thought,"
Leleu says. The team identified a possible solution with five planets and decided to invest another day of precious observation time on the system
to confirm. They found that there were indeed five planets present with
orbital periods of around 2, 3, 6, 10 and 20 days respectively.

While a system with five planets would have been quite a remarkable
finding in itself, Leleu and his colleagues noticed that there might be
more to the story: the system appeared to be in harmony. "Our theory
implied that there could be an additional planet in this harmony;
however its orbital period needed to be very nearly 15 days.," Leleu
explains. To check if their theory was in fact true, the team scheduled
yet another observation with CHEOPS, at the exact time that this missing
planet would pass by -- if it existed. But then, an accident threatened
to cancel their plans.

Prediction confirmed despite near-collision "Just before the time of
the observation, a piece of space debris threatened to collide with
the CHEOPS satellite," as co-author and Professor of Astrophysics at
the University of Bern, Yann Alibert, recalls. Therefore, the control
center of the European Space Agency (ESA) initiated an evasive maneuver
of the satellite and all observations were interrupted. "But to our great relief, this manoeuver was done very efficiently and the satellite could
resume observations just in time to capture the mysterious planet passing
by," as Nathan Hara, co- author and astrophysicist from the University
of Geneva reports. "A few days later, the data clearly indicated the
presence of the additional planet and thus confirmed that there were
indeed six planets in the TOI-178 system," Hara explains.



==========================================================================
A system that challenges current understanding Thanks to the precision
of CHEOPS' measurements as well as previous data from the TESS mission,
the ESO's spectrograph ESPRESSO, and others, the scientists could not
only measure the periods and sizes of the planets of 1.1 to 3 times the
radius of the Earth, but also estimate their densities. With that came
another surprise: compared to the harmonic, orderly way the planets
orbit around their star, their densities appear to be a wild mixture.

"It is the first time we observe something like this," as ESA Project
Scientist Kate Isaak points out and adds that "in the few systems we
know with such a harmony, the density of planets steadily decreases as
we move away from the star. In the TOI-178 system, a dense, terrestrial
planet like Earth appears to be right next to a very fluffy planet with
half the density of Neptune followed by one very similar to Neptune."
As Adrien Leleu concludes, "the system therefore turned out to be one
that challenges our understanding of the formation and evolution of
planetary systems." CHEOPS -- in search of potential habitable planets
The CHEOPS mission (CHaracterising ExOPlanet Satellite) is the first of
ESA's newly created "S-class missions" -- small-class missions with an
ESA budget much smaller than that of large- and medium-size missions,
and a shorter timespan from project inception to launch.



========================================================================== CHEOPS is dedicated to characterizing the transits of exoplanets. It
measures the changes in the brightness of a star when a planet passes in
front of that star. This measured value allows the size of the planet
to be derived, and for its density to be determined on the basis of
existing data. This provides important information on these planets --
for example, whether they are predominantly rocky, are composed of gases,
or if they have deep oceans. This, in turn, is an important step in
determining whether a planet has conditions that are hospitable to life.

CHEOPS was developed as part of a partnership between the European Space
Agency (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.

CHEOPS began its journey into space on Wednesday, December 18, 2019
on board a Soyuz Fregat rocket from the European spaceport in Kourou,
French Guiana. Since then, it has been orbiting the Earth on a polar
orbit in roughly an hour and a half at an altitude of 700 kilometers
following the terminator.

The Swiss Confederation participates in the CHEOPS telescope within
the PRODEX programme (PROgramme de De'veloppement d'EXpe'riences
scientifiques) of the European Space Agency ESA. Through this programme, national contributions for science missions can be developed and built by project teams from research and industry. This transfer of knowledge and technology between science and industry ultimately also gives Switzerland
a structural competitive advantage as a business location -- and enables technologies, processes and products to flow into other markets and thus generate added value for our economy.

More information: https://cheops.unibe.ch Bernese space exploration:
With the world's elite since the first moon landing When the second
man, "Buzz" Aldrin, stepped out of the lunar module on July 21, 1969,
the first task he did was to set up the Bernese Solar Wind Composition experiment (SWC) also known as the "solar wind sail" by planting it in
the ground of the moon, even before the American flag. This experiment,
which was planned and the results analysed by Prof. Dr. Johannes Geiss
and his team from the Physics Institute of the University of Bern,
was the first great highlight in the history of Bernese space exploration.

Ever since Bernese space exploration has been among the world's elite. The numbers are impressive: 25 times were instruments flown into the upper atmosphere and ionosphere using rockets (1967-1993), 9 times into the stratosphere with balloon flights (1991-2008), over 30 instruments were
flown on space probes, and with CHEOPS the University of Bern shares responsibility with ESA for a whole mission.

The successful work of the Department of Space Research and Planetary
Sciences (WP) from the Physics Institute of the University of Bern was consolidated by the foundation of a university competence center, the
Center for Space and Habitability (CSH). The Swiss National Fund also
awarded the University of Bern the National Center of Competence in
Research (NCCR) PlanetS, which it manages together with the University
of Geneva.

Exoplanet research in Geneva: 25 years of expertise awarded a Nobel Prize CHEOPS will provide crucial information on the size, shape, formation and evolution of known exoplanets. The installation of the "Science Operation Center" of the CHEOPS mission in Geneva, under the supervision of two professors from the UNIGE Astronomy Department, is a logical continuation
of the history of research in the field of exoplanets, since it is here
that the first was discovered in 1995 by Michel Mayor and Didier Queloz, winners of the 2019 Nobel Prize in Physics. This discovery has enabled the Astronomy Department of the University of Geneva to be at the forefront
of research in the field, with the construction and installation of HARPS
on the ESO's 3.6m telescope at La Silla in 2003, a spectrograph that
remained the most efficient in the world for two decades to determine the
mass of exoplanets. However, this year HARPS was surpassed by ESPRESSO,
another spectrograph built in Geneva and installed on the VLT in Paranal.

CHEOPS is therefore the result of two national expertises, on the one hand
the space know-how of the University of Bern with the collaboration of
its Geneva counterpart and on the other hand the ground experience of the University of Geneva supported by its colleague in the Swiss capital. Two scientific and technical competences that have also made it possible to
create the National Center of Competence in Research (NCCR) PlanetS.


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


========================================================================== Journal Reference:
1. A. Leleu, Y. Alibert, N. C. Hara, M. J. Hooton, T. G. Wilson,
P. Robutel,
J.-B. Delisle, J. Laskar, S. Hoyer, C. Lovis, E. M. Bryant,
E. Ducrot, J.

Cabrera, J. Acton, V. Adibekyan, R. Allart, C. Allende Prieto,
R. Alonso, D. Alves, D. R. Anderson, al. Six transiting planets and
a chain of Laplace resonances in TOI-178. Astronomy & Astrophysics,
2021; DOI: 10.1051/0004-6361/202039767 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/01/210125144528.htm

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