Discovery
of 30 exocomets
in a
young planetary system
Découverte de
30 exocomètes dans un système planétaire jeune
VERION FRANÇAISE
Scientific Reports 12, 5855 (2022) https://www.nature.com/articles/s41598-022-09021-2
The paper published by Scientific Reports
(Springer Nature) presents the detection of 30 exocomets in the young planetary
system of β Pictoris. These comets orbiting a star other than the Sun were
discovered through observations obtained with the NASA's TESS observatory. This
work has been made by a the team led
by Alain Lecavelier des Etangs of the Institut d'astrophysique de Paris (CNRS,
Sorbonne Université) including a student
from the École nationale supérieure des mines de
Paris, researchers from the
Institut d'astrophysique de Paris (IAP-CNRS, Sorbonne Université), the Observatoire
de Haute Provence, Laboratorio Nacional
de Astrofisica in Brasil, Laboratoire d’études
spatiales et d’instrumentation en astrophysique (Observatoire de Paris-CNRS, PSL,
Sorbonne Université, Université Paris Cité), the Leiden Observatory
in the Netherlands, and the Institut de planétologie
et d'astrophysique de Grenoble (CNRS, UGA). The analysis of the observations obtained by the TESS satellite allowed
the determination of the size of the nuclei of these 30 comets, which are
between 3 and 14 kilometers in diameter.
Even better, the large number of detections
allows to determine the size distribution of these celestial objects, i.e. how
many small comets there are relative to the number of large comets. This is the
first time that the size distribution of small bodies is measured in an
extrasolar system. Or, in other words, it is only the second planetary system
after the Solar System for which we have information on the size distribution
of its constituent objects.
The knowledge of the size distribution of
comets and asteroids is important because this distribution is the direct
result of processes that took place during planetary formation. This is why a
lot of work has been done to measure it precisely in the Solar System. Today,
for the first time, it is measured elsewhere.
In the paper published by Scientific Reports
(Springer Nature), it is shown that the size of exocometary nuclei in the
β Pictoris planetary system is strikingly similar to that observed in the
Solar System comets. The observed distribution corresponds precisely to the
distribution expected in the case of a population of objects that results from
a cascade of collisions and fragmentations.
This new result shows the importance of
collisions in the processes that determine the size of objects. It is known
that the fall of comets on Earth is a serious candidate for the origin of water
on our planet. Therefore, the similarity between the formation history of
comets in the planetary system of Beta Pictoris and in the Solar
System may have important implications for the existence of water on
planets in other planetary systems. All this shows the importance of the
interactions between planets and small bodies such as asteroids or comets,
because they determine the shape of planetary systems and the history of the
objects which compose it.
Fig. 1. Distribution
of the size of exocomets discovered in the β Pictoris planetary system.
While 16 exocomets are between 3 and 4
kilometers in diameter, only 4 have a diameter between 6 and 8 kilometers and
only one comet has a diameter between 8 and 10 kilometers. This rapid decrease
in the number of objects for large sizes is characteristic of objects produced
by collision and fragmentation.
Credit: A. Lecavelier des Etangs, IAP-CNRS
(https://www.iap.fr/users/lecaveli/BetaPic_exocomets_en/Images/Histogram_EN.PNG)
Fig. 2. Artist's impression
of the exocomets in orbit around the star β Pictoris.
Credit: ESO/L. Calçada
(https://www.eso.org/public/images/eso1432a)
Fig. 3. Light curves
of an exocomet transit, as predicted and observed for β Pictoris.
The left plot shows the light curve of β Pictoris observed with TESS during
the transit of an exocomet in front of this star on January 2, 2019 (Lecavelier
des Etangs et al. 2022; see also Zieba et al. 2019;
Pavlenko et al. 2022).
The right plot shows the theoretical light
curve of an exocomet transit predicted more than 20 years ago by A.
Lecavelier des Etangs, A. Vidal-Madjar & R. Ferlet (Astronomy &
Astrophysics 1999).
Credit: A. Lecavelier des Etangs, IAP-CNRS
(https://www.iap.fr/users/lecaveli/BetaPic_exocomets_en/Images/TESS_LC_EN.PNG)
(https://www.iap.fr/users/lecaveli/BetaPic_exocomets_en/Images/Theo_LC_EN.PNG)
Fig. 4. Exocomet size
distribution in the β Pictoris planetary system.
The size of each of the 30 exocomets is shown
by a blue square. The red line indicates the expected distribution for a
population of objects produced by collisions.
Credit: A. Lecavelier des Etangs, IAP-CNRS
(https://www.iap.fr/users/lecaveli/BetaPic_exocomets_en/Images/Distribution_EN.PNG)
Title and
abstract of the paper
"Exocomets size
distribution in the β Pictoris planetary system"
Alain
Lecavelier des Etangs1,*, Lucie Cros1,2, Guillaume
Hébrard1,3, Eder Martioli1,4, Marc Duquesnoy5,
Matthew Kenworthy6, Flavien Kiefer1,5,
Sylvestre Lacour5, Anne-Marie Lagrange5,
Nadège Meunier7, and Alfred Vidal-Madjar1
1Institut d’Astrophysique de Paris, CNRS, UMR 7095,
Sorbonne Université, 98 bis bd Arago, 75014 Paris, France
2Ecole nationale supérieure des mines de Paris, Université PSL, 60
boulevard Saint-Michel, 75272 Paris, France
3Observatoire de Haute-Provence, 04870 St Michel l’Observatoire,
France
4Laboratorio Nacional de Astrofisica, Rua Estados Unidos
154, 37504-364, Itajuba - MG, Brazil
5LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne
Université, Univ. Paris Diderot, Sorbonne Paris Cité,
5 place Jules Janssen,
92195 Meudon, France
6Leiden Observatory, Leiden University, Leiden, The Netherlands
7Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
*lecaveli@iap.fr
To be published by Scientific Reports (Springer Nature) 2022
Embargoed
until Thursday April 28, 2022, 10 am (UK time)
ABSTRACT
The star β Pictoris harbors a young planetary system of
about 20 million years old, which is characterized by the presence of a gaseous
and dusty debris disk, at least two massive planets and many minor bodies. For
more than thirty years, exocomets transiting the star have been detected using
spectroscopy, probing the gaseous part of the cometary comas and tails.
The detection of the dusty component of the
tails can be performed through photometric observations of the transits. Since
2018, the Transiting Exoplanet Survey Satellite has observed β Pic for a total of 156 days. Here
we report an analysis of the TESS photometric data set with the identification
of a total of 30 transits of exocomets. Our statistical analysis shows that the
number of transiting exocomet events (N) as a function of the absorption depth
(AD) in the light curve follows a power law in the form dN(AD)
∝ AD−α, where α = 2.3 ±0.4. This distribution of absorption
depth leads to a differential comet size distribution proportional to R−γ, where γ = 3.6 ±0.8, showing a striking
similarity to the size distribution of comets in the Solar system and the
distribution of a collisionally relaxed population (γD = 3.5).