Artistic impression of the Venusian surface and atmosphere (without annotations)
PR Image eso2015f
Phosphine signature in Venus’s spectrum
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An international team of astronomers
today announced the discovery of a rare molecule — phosphine — in the
clouds of Venus. On Earth, this gas is only made industrially or by
microbes that thrive in oxygen-free environments. Astronomers have
speculated for decades that high clouds on Venus could offer a home for
microbes — floating free of the scorching surface but needing to
tolerate very high acidity. The detection of phosphine could point to
such extra-terrestrial “aerial” life.
“When we got the first hints of phosphine in Venus’s spectrum, it was a shock!”, says team leader Jane Greaves of Cardiff University in the UK, who first spotted signs of phosphine in observations from the James Clerk Maxwell Telescope (JCMT),
operated by the East Asian Observatory, in Hawaiʻi. Confirming their
discovery required using 45 antennas of the Atacama Large
Millimeter/submillimeter Array (ALMA)
in Chile, a more sensitive telescope in which the European Southern
Observatory (ESO) is a partner. Both facilities observed Venus at a
wavelength of about 1 millimetre, much longer than the human eye can see
— only telescopes at high altitude can detect it effectively.
The international team, which includes researchers from the
UK, US and Japan, estimates that phosphine exists in Venus’s clouds at a
small concentration, only about twenty molecules in every billion.
Following their observations, they ran calculations to see whether these
amounts could come from natural non-biological processes on the planet.
Some ideas included sunlight, minerals blown upwards from the surface,
volcanoes, or lightning, but none of these could make anywhere near
enough of it. These non-biological sources were found to make at most
one ten thousandth of the amount of phosphine that the telescopes saw.
To create the observed quantity of phosphine (which
consists of hydrogen and phosphorus) on Venus, terrestrial organisms
would only need to work at about 10% of their maximum productivity,
according to the team. Earth bacteria are known to make phosphine: they
take up phosphate from minerals or biological material, add hydrogen,
and ultimately expel phosphine. Any organisms on Venus will probably be
very different to their Earth cousins, but they too could be the source
of phosphine in the atmosphere.
While the discovery of phosphine in Venus’s clouds came as a surprise, the researchers are confident in their detection. “To
our great relief, the conditions were good at ALMA for follow-up
observations while Venus was at a suitable angle to Earth. Processing
the data was tricky, though, as ALMA isn’t usually looking for very
subtle effects in very bright objects like Venus,” says team member Anita Richards of the UK ALMA Regional Centre and the University of Manchester. “In
the end, we found that both observatories had seen the same thing —
faint absorption at the right wavelength to be phosphine gas, where the
molecules are backlit by the warmer clouds below,” adds Greaves, who led the study published today in Nature Astronomy.
Another team member, Clara Sousa Silva of the Massachusetts Institute of Technology in the US, has investigated
phosphine as a “biosignature” gas of non-oxygen-using life on planets
around other stars, because normal chemistry makes so little of it. She
comments: “Finding phosphine on Venus was an unexpected bonus! The
discovery raises many questions, such as how any organisms could
survive. On Earth, some microbes can cope with up to about 5% of acid in
their environment — but the clouds of Venus are almost entirely made of
acid.”
The team believes their discovery is significant because
they can rule out many alternative ways to make phosphine, but they
acknowledge that confirming the presence of “life” needs a lot more
work. Although the high clouds of Venus have temperatures up to a
pleasant 30 degrees Celsius, they are incredibly acidic — around 90%
sulphuric acid — posing major issues for any microbes trying to survive
there.
ESO astronomer and ALMA European Operations Manager Leonardo Testi, who did not participate in the new study, says: “The
non-biological production of phosphine on Venus is excluded by our
current understanding of phosphine chemistry in rocky planets'
atmospheres. Confirming the existence of life on Venus's atmosphere
would be a major breakthrough for astrobiology; thus, it is essential to
follow-up on this exciting result with theoretical and observational
studies to exclude the possibility that phosphine on rocky planets may
also have a chemical origin different than on Earth.”
More observations of Venus and of rocky planets outside our
Solar System, including with ESO’s forthcoming Extremely Large
Telescope, may help gather clues on how phosphine can originate on them
and contribute to the search for signs of life beyond Earth.
More Information
This research was presented in the paper “Phosphine Gas in the Cloud Decks of Venus” to appear in Nature Astronomy.
The team is composed of Jane S. Greaves (School of Physics
& Astronomy, Cardiff University, UK [Cardiff]), Anita M. S. Richards
(Jodrell Bank Centre for Astrophysics, The University of Manchester,
UK), William Bains (Department of Earth, Atmospheric, and Planetary
Sciences, Massachusetts Institute of Technology, USA [MIT]), Paul Rimmer
(Department of Earth Sciences and Cavendish Astrophysics, University of
Cambridge and MRC Laboratory of Molecular Biology, Cambridge, UK),
Hideo Sagawa (Department of Astrophysics and Atmospheric Science, Kyoto
Sangyo University, Japan), David L. Clements (Department of Physics,
Imperial College London, UK [Imperial]), Sara Seager (MIT), Janusz J.
Petkowski (MIT), Clara Sousa-Silva (MIT), Sukrit Ranjan (MIT), Emily
Drabek-Maunder (Cardiff and Royal Observatory Greenwich, London, UK),
Helen J. Fraser (School of Physical Sciences, The Open University,
Milton Keynes, UK), Annabel Cartwright (Cardiff), Ingo Mueller-Wodarg
(Imperial), Zhuchang Zhan (MIT), Per Friberg (EAO/JCMT), Iain Coulson
(EAO/JCMT), E’lisa Lee (EAO/JCMT) and Jim Hoge (EAO/JCMT).
An accompanying paper by some of team members, titled “The
Venusian Lower Atmosphere Haze as a Depot for Desiccated Microbial
Life: A Proposed Life Cycle for Persistence of the Venusian Aerial
Biosphere”, was published in Astrobiology in August 2020. Another related study by some of the same authors, "Phosphine as a Biosignature Gas in Exoplanet Atmospheres", was published in Astrobiology in January 2020.
The European Southern Observatory (ESO) is the foremost
intergovernmental astronomy organisation in Europe and the world’s most
productive ground-based astronomical observatory by far. It has 16
Member States: Austria, Belgium, the Czech Republic, Denmark, France,
Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal,
Spain, Sweden, Switzerland and the United Kingdom, along with the host
state of Chile and with Australia as a Strategic Partner. ESO carries
out an ambitious programme focused on the design, construction and
operation of powerful ground-based observing facilities enabling
astronomers to make important scientific discoveries. ESO also plays a
leading role in promoting and organising cooperation in astronomical
research. ESO operates three unique world-class observing sites in
Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the
Very Large Telescope and its world-leading Very Large Telescope
Interferometer as well as two survey telescopes, VISTA working in the
infrared and the visible-light VLT Survey Telescope. Also at Paranal ESO
will host and operate the Cherenkov Telescope Array South, the world’s
largest and most sensitive gamma-ray observatory. ESO is also a major
partner in two facilities on Chajnantor, APEX and ALMA, the largest
astronomical project in existence. And on Cerro Armazones, close to
Paranal, ESO is building the 39-metre Extremely Large Telescope, the
ELT, which will become “the world’s biggest eye on the sky”.
The Atacama Large Millimeter/submillimeter Array (ALMA),
an international astronomy facility, is a partnership of ESO, the U.S.
National Science Foundation (NSF) and the National Institutes of Natural
Sciences (NINS) of Japan in cooperation with the Republic of Chile.
ALMA is funded by ESO on behalf of its Member States, by NSF in
cooperation with the National Research Council of Canada (NRC) and
the Ministry of Science and Technology (MOST) and by NINS in cooperation
with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and
Space Science Institute (KASI). ALMA construction and operations are led
by ESO on behalf of its Member States; by the National Radio Astronomy
Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on
behalf of North America; and by the National Astronomical Observatory of
Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO)
provides the unified leadership and management of the construction,
commissioning and operation of ALMA.
With a diameter of 15m (50 feet) the James Clerk Maxwell Telescope (JCMT)
is the largest single dish astronomical telescope in the world designed
specifically to operate in the submillimetre wavelength region of the
electromagnetic spectrum. The JCMT is used to study our Solar System,
interstellar and circumstellar dust and gas, evolved stars, and distant
galaxies. It is situated in the science reserve of Maunakea, Hawaiʻi, at
an altitude of 4092m (13 425 feet). The JCMT is operated by the East
Asian Observatory on behalf of NAOJ; ASIAA; KASI; CAMS as well as the
National Key R&D Program of China. Additional funding support is
provided by the STFC and participating universities in the UK and
Canada.
Links
Contacts
Jane Greaves (study author)
Cardiff University
Cardiff, UK
Email: GreavesJ1@cardiff.ac.uk
Anita Richards (study author)
UK ALMA Regional Centre and University of Manchester
Manchester, UK
Email: a.m.s.richards@manchester.ac.uk
Clara Sousa Silva (study author)
Massachusetts Institute of Technology
Cambridge, USA
Tel: +1 617 253 6283
Email: cssilva@mit.edu
Leonardo Testi (contact for independent comment on the study)
European Southern Observatory
Garching bei München, Germany
Tel: +49 89 3200 6541
Email: ltesti@eso.org
Dave Clements (study author)
Imperial College
London, UK
Email: d.clements@imperial.ac.uk
Paul Rimmer (study author)
University of Cambridge
Cambridge, UK
Email: pbr27@cam.ac.uk
William Bains (study author)
Massachusetts Institute of Technology
Cambridge, USA
Email: bains@mit.edu
Bárbara Ferreira
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6670
Cell: +49 151 241 664 00
Email: pio@eso.org
Source: ESO/News