Did Venus ever have oceans?

Date:
October 13, 2021
Source:
Universite' de Gene`ve
Summary:
The planet Venus can be seen as the Earth's evil twin. At first
sight, it is of comparable mass and size as our home planet,
similarly consists mostly of rocky material, holds some water and
has an atmosphere. Yet, a closer look reveals striking differences
between them: Venus' thick CO2 atmosphere, extreme surface
temperature and pressure, and sulphuric acid clouds are indeed a
stark contrast to the conditions needed for life on Earth. This
may, however, have not always been the case. Previous studies
have suggested that Venus may have been a much more hospitable
place in the past, with its own liquid water oceans. A team of
astrophysicists investigated whether our planet's twin did indeed
have milder periods.

The results suggest that this is not the case.



FULL STORY ==========================================================================
The planet Venus can be seen as the Earth's evil twin. At first sight,
it is of comparable mass and size as our home planet, similarly consists
mostly of rocky material, holds some water and has an atmosphere. Yet,
a closer look reveals striking differences between them: Venus' thick CO2 atmosphere, extreme surface temperature and pressure, and sulphuric acid
clouds are indeed a stark contrast to the conditions needed for life on
Earth. This may, however, have not always been the case. Previous studies
have suggested that Venus may have been a much more hospitable place in
the past, with its own liquid water oceans. A team of astrophysicists
led by the University of Geneva (UNIGE) and the National Centre of
Competence in Research (NCCR) PlanetS, Switzerland, investigated whether
our planet's twin did indeed have milder periods. The results, published
in the journal Nature, suggest that this is not the case.


========================================================================== Venus has recently become an important research topic for
astrophysicists. ESA and NASA have decided this year to send no less
than three space exploration missions over the next decade to the second closest planet to the Sun. One of the key questions these missions aim to answer is whether or not Venus ever hosted early oceans. Astrophysicists
led by Martin Turbet, researcher at the Department of Astronomy of the
Faculty of Science of the UNIGE and member of the NCCR PlanetS, have
tried to answer this question with the tools available on Earth. "We
simulated the climate of the Earth and Venus at the very beginning of
their evolution, more than four billion years ago, when the surface of
the planets was still molten," explains Martin Turbet. "The associated
high temperatures meant that any water would have been present in the
form of steam, as in a gigantic pressure cooker." Using sophisticated three-dimensional models of the atmosphere, similar to those scientists
use to simulate the Earth's current climate and future evolution, the
team studied how the atmospheres of the two planets would evolve over
time and whether oceans could form in the process.

"Thanks to our simulations, we were able to show that the climatic
conditions did not allow water vapour to condense in the atmosphere of
Venus," says Martin Turbet. This means that the temperatures never got
low enough for the water in its atmosphere to form raindrops that could
fall on its surface. Instead, water remained as a gas in the atmosphere
and oceans never formed. "One of the main reasons for this is the clouds
that form preferentially on the night side of the planet. These clouds
cause a very powerful greenhouse effect that prevented Venus from cooling
as quickly as previously thought," continues the Geneva researcher.

Small differences with serious consequences Surprisingly, the
astrophysicists' simulations also reveal that the Earth could easily have suffered the same fate as Venus. If the Earth had been just a little
closer to the Sun, or if the Sun had shone as brightly in its 'youth'
as it does nowadays, our home planet would look very different today. It
is likely the relatively weak radiation of the young Sun that allowed the
Earth to cool down enough to condense the water that forms our oceans. For Emeline Bolmont, professor at UNIGE, member of PlaneS and co-author
of the study, "this is a complete reversal in the way we look at what
has long been called the 'Faint Young Sun paradox'. It has always been considered as a major obstacle to the appearance of life on Earth!" The argument was that if the Sun's radiation was much weaker than today,
it would have turned the Earth into a ball of ice hostile to life. "But
it turns out that for the young, very hot Earth, this weak Sun may have
in fact been an unhoped-for opportunity," continues the researcher.

"Our results are based on theoretical models and are an important
building- block in answering the question of the history of Venus,"
says study co-author David Ehrenreich, professor in the Department
of Astronomy at UNIGE and member of the NCCR PlanetS. "But we will
not be able to rule on the matter definitively on our computers. The observations of the three future Venusian space missions will be
essential to confirm -- or refute -- our work." These prospects
delight Emeline Bolmont, for whom "these fascinating questions
can be addressed by the new Centre for Life in the Universe,
which has just been set up within the UNIGE's Faculty of Science." ========================================================================== Story Source: Materials provided by Universite'_de_Gene`ve. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Martin Turbet, Emeline Bolmont, Guillaume Chaverot, David
Ehrenreich,
Je're'my Leconte & Emmanuel Marcq. Day-night cloud asymmetry
prevents early oceans on Venus but not on Earth. Nature, 2021 DOI:
10.1038/s41586- 021-03873-w ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211013114018.htm

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