Could mini-Neptunes be irradiated ocean planets?

Date:
July 20, 2020
Source:
CNRS
Summary:
New research suggests that the low density of mini-Neptunes could
be explained simply by the presence of a thick layer of water.



FULL STORY ==========================================================================
Many exoplanets known today are 'super-Earths', with a radius 1.3 times
that of Earth, and 'mini-Neptunes', with 2.4 Earth radii. Mini-Neptunes,
which are less dense, were long thought to be gas planets, made up of
hydrogen and helium.


==========================================================================
Now, scientists at the Laboratoire d'Astrophysique de Marseille (CNRS/Aix- Marseille Universite'/Cnes)1 have examined a new possibility, namely
that the low density of mini-Neptunes could be explained simply by the
presence of a thick layer of water that experiences an intense greenhouse effect caused by the irradiation from their host star.

These findings, recently published in The Astrophysical Journal Letters,
show that mini-Neptunes could be super-Earths with a rocky core surrounded
by water in a supercritical state2, suggesting that these two types of exoplanet may form in the same way. Another paper recently published in Astronomy &Astrophysics, involving in France scientists mainly from the
CNRS and the University of Bordeaux3, focused on the effect of stellar irradiation on the radius of Earth-sized planets containing water. Their
work shows that the size of the atmospheres of such planets increases considerably when subject to a strong greenhouse effect, in line with
the study on mini-Neptunes.

Future observations should make it possible to test these novel hypotheses
put forward by French scientists, who are making major contributions to
our knowledge of exoplanets.

Notes 1. In collaboration with a researcher at the Laboratoire
Atmosphe`res et Observations Spatiales (CNRS/UVSQ/Sorbonne Universite')
2. Supercritical water exists at very high pressures and temperatures.

3. The French scientists work at the Laboratoire d'Astrophysique de
Bordeaux (CNRS/Universite' de Bordeaux) and used a planetary atmosphere
model developed at the Laboratoire de Me'te'orologie Dynamique (CNRS/ENS Paris/Ecole Polytechnique -- Institut Polytechnique de Paris /Sorbonne Universite').


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


========================================================================== Journal References:
1. Olivier Mousis, Magali Deleuil, Artyom Aguichine, Emmanuel Marcq,
Joseph
Naar, Lorena Acun~a Aguirre, Bastien Brugger, Thomas Gonc,alves.

Irradiated Ocean Planets Bridge Super-Earth and Sub-Neptune
Populations.

The Astrophysical Journal, 2020; 896 (2): L22 DOI:
10.3847/2041-8213/ ab9530
2. Martin Turbet, Emeline Bolmont, David Ehrenreich, Pierre Gratier,
Je're'my Leconte, Franck Selsis, Nathan Hara, Christophe
Lovis. Revised mass-radius relationships for water-rich rocky
planets more irradiated than the runaway greenhouse limit. Astronomy
& Astrophysics, 2020; 638: A41 DOI: 10.1051/0004-6361/201937151 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200720101806.htm

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