Using the Atacama Large Millimetre/submillimeter Array (ALMA), in which the
European Southern Observatory (ESO) is a partner, astronomers have
unambiguously detected the presence of a disk around a planet outside our
Solar System for the first time. The observations will shed new light on how
moons and planets form in young stellar systems.
"Our work presents a clear detection of a disk in which satellites could be
forming," says Myriam Benisty, a researcher at the University of Grenoble,
France, and at the University of Chile, who led the new research published
today in The Astrophysical Journal Letters. "Our ALMA observations were
obtained at such exquisite resolution that we could clearly identify that
the disk is associated with the planet and we are able to constrain its size
for the first time," she adds.
The disk in question, called a circumplanetary disk, surrounds the exoplanet
PDS 70c, one of two giant, Jupiter-like planets orbiting a star nearly 400
light-years away. Astronomers had found hints of a "moon-forming" disk
around this exoplanet before but, since they could not clearly tell the disk
apart from its surrounding environment, they could not confirm its
detection—until now.
In addition, with the help of ALMA, Benisty and her team found that the disk
has about the same diameter as the distance from our Sun to the Earth and
enough mass to form up to three satellites the size of the Moon.
But the results are not only key to finding out how moons arise. "These new
observations are also extremely important to prove theories of planet
formation that could not be tested until now," says Jaehan Bae, a researcher
from the Earth and Planets Laboratory of the Carnegie Institution for
Science, U.S., and author on the study.
Planets form in dusty disks around young stars, carving out cavities as they
gobble up material from this circumstellar disk to grow. In this process, a
planet can acquire its own circumplanetary disk, which contributes to the
growth of the planet by regulating the amount of material falling onto it.
At the same time, the gas and dust in the circumplanetary disk can come
together into progressively larger bodies through multiple collisions,
ultimately leading to the birth of moons.
But astronomers do not yet fully understand the details of these processes.
"In short, it is still unclear when, where, and how planets and moons form,"
explains ESO Research Fellow Stefano Facchini, also involved in the
research.
"More than 4000 exoplanets have been found until now, but all of them were
detected in mature systems. PDS 70b and PDS 70c, which form a system
reminiscent of the Jupiter-Saturn pair, are the only two exoplanets detected
so far that are still in the process of being formed," explains Miriam
Keppler, researcher at the Max Planck Institute for Astronomy in Germany and
one of the co-authors of the study.
"This system therefore offers us a unique opportunity to observe and study
the processes of planet and satellite formation," Facchini adds.
PDS 70b and PDS 70c, the two planets making up the system, were first
discovered using ESO's Very Large Telescope (VLT) in 2018 and 2019
respectively, and their unique nature means they have been observed with
other telescopes and instruments many times since.
The latest high resolution ALMA observations have now allowed astronomers to
gain further insights into the system. In addition to confirming the
detection of the circumplanetary disk around PDS 70c and studying its size
and mass, they found that PDS 70b does not show clear evidence of such a
disk, indicating that it was starved of dust material from its birth
environment by PDS 70c.
An even deeper understanding of the planetary system will be achieved with
ESO's Extremely Large Telescope (ELT), currently under construction on Cerro
Armazones in the Chilean Atacama desert. "The ELT will be key for this
research since, with its much higher resolution, we will be able to map the
system in great detail," says co-author Richard Teague, a researcher at the
Center for Astrophysics | Harvard & Smithsonian, U.S.. In particular, by
using the ELT's Mid-infrared ELT Imager and Spectrograph (METIS), the team
will be able to look at the gas motions surrounding PDS 70c to get a full 3D
picture of the system.
This research was presented in the paper "A Circumplanetary Disk Around PDS
70c" to appear in The Astrophysical Journal Letters.
More information:
"A Circumplanetary Disk Around PDS 70c" Astrophysical
Journal Letters (2021). DOI:
Tags:
Space & Astrophysics