Judith Korth, one of
four Chalmers astronomers involved in the study, recently published in Nature Astronomy, explains why
this planetary system is of particular interest:
is unique. TOI-500 hosts four low-mass planets where the innermost planet has
an orbital period of around 13 hours (TOI-500b). Such ultra-short-period
planets (USPs) usually show a particular architecture of high-inclined orbits
with respect to the outer planets in the system and are thought to be the outcome
of so called high-eccentricity migration, where very elliptical orbits gradually become more and more circular from the star’s tidal forces”, says
planets in the TOI-500 system, however, show orbits on a similar plane, and
thus, TOI-500 is the first system that could have formed via a different
formation scenario, namely the low-eccentricity migration described in the article”.
Slow and steady migration towards the star
scientific community unanimously agrees that a planet like TOI-500b could not
have formed in its current position, but that it must have originated in a more
external area of the protoplanetary disk, and then migrated much closer to
its star. However, there is still a lot of debate on the migration process, but
it is common opinion that it usually takes place in a violent way, a process
that can involves collisions between planets which set the planets on non-circular
and inclined orbits, migrating towards smaller orbits that become increasingly
In the recent
article, however, the authors present simulations with which they demonstrate
that the planets around TOI-500 may have formed on almost circular orbits
further out in the system, and then performed a slow and steady migration during
2 billions years, in which the planets, without colliding with each other, move
along orbits that remain almost circular but gradually smaller and smaller.
research, published in the prestigious journal Nature Astronomy was led by Luisa Maria
Serrano and Davide Gandolfi of the Physics Department of the University and
featured Chalmers astronomers Judith Korth, Carina Persson, Iskra Georgieva and Malcolm
TOI similar to Earth - and also very different
closest to the star, named TOI-500b, is a so called Ultra-Short Period (USP)
planet , as its orbital period is just 13 hours . It is also considered an
Earth analogue, that is, a rocky planet similar to the Earth in radius, mass
and density. However, its proximity to the star makes it so hot (around 1350 degrees Celsius) that its surface is most likely an immense expanse of lava.
has a size and mass similar to Earth but in reality, it is very different from
Earth due to its short orbital period. It is called an Earth-analog, meaning
that it has a similar bulk density as our Earth. This does not mean that the
planet is also as habitable as our Earth. It is quite the opposite, due to its
vicinity to the star the planet is very hot and its surface consists most
likely of a lava ocean”, says Judith Korth and continues.
another similarity to our own Earth could exist for TOI-500b. It could have a
secondary atmosphere. I think this will trigger further atmospheric studies in
the future which may also give us information about our own atmosphere”.
was initially identified by NASA 's TESS (Transiting Exoplanet Survey Satellite)
space telescope which searches for exoplanets using the so called transit
method. This method identifies planets that periodically obscure their home star,
causing a decrease in the light received on Earth. The planet was subsequently
confirmed thanks to an intense observation campaign conducted by European
Southern Observatory (ESO). The data cover an entire year and their analysis,
combined with that of the TESS data, made it possible to measure the mass,
radius, and orbital parameters of the inner planet.
An extraordinary planetary system
measurements also made it possible to discover 3 additional planets, with
orbital periods of 6.6, 26.2 and 61.3 days. TOI-500 is an extraordinary
planetary system for understanding the dynamic evolution of planets”, says project
leader Davide Gandolfi, University of Turin.
Judith Korth, of the Department of Space, Earth and Environment at Chalmers, was involved in the dynamical studies:
if the system shows transit timing variations that could help us to constrain
the planetary and orbital parameters. Unfortunately, this was not the case
since the dynamics of the system are dominated by the secular dynamics rather
than the resonant dynamics. Furthermore, I studied the long-term stability of
the system and tested if we could refine the upper mass limits of the outer
planets since we have only the Msini (minimum mass) from the radial velocities.
Since the system could have formed via low-eccentricity migration, I also
studied the dynamics within a smaller range of mutual inclinations but for a
longer time span.”
demonstrates the importance of combining the discovery of systems hosting close
USP-type planets with numerical simulations to test the possible migratory
processes that may have brought them to the current configuration.
data over long periods of time allows us to study the internal architecture of
systems similar to TOI-500 and to understand how the planets settled on their
orbits”, concludes Davide Gandolfi, University of Turin.
article A low-eccentricity migration pathway for a 13-h-period Earth analoguein a four-planet system in Nature Astronomy.
Images from Nasas exoplanet catalog.
The text is written by Christian Löwhagen, Chalmers, based on the press release from the University of Turin: Dalla missione della NASA alle osservazioni UniTo: TOI-500, un sistema planetario di quattro pianeti con un processo di migrazione peculiare - Il pianeta più vicino alla stella è molto simile alla Terra...