Artist’s impression of Mars four billion years ago
Artist’s impression of Mars four billion years ago
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A primitive ocean on Mars held more water than Earth’s Arctic Ocean, and covered a greater portion of the planet’s surface than the Atlantic Ocean does on Earth, according to new results published today. An international team of scientists used ESO’s Very Large Telescope, along with instruments at the W. M. Keck Observatory and the NASA Infrared Telescope Facility, to monitor the atmosphere of the planet and map out the properties of the water in different parts of Mars’s atmosphere over a six-year period. These new maps are the first of their kind. The results appear online in the journal Science today.
About four billion years ago, the young planet would have had enough
water to cover its entire surface in a liquid layer about 140 metres
deep, but it is more likely that the liquid would have pooled to form an
ocean occupying almost half of Mars’s northern hemisphere, and in some
regions reaching depths greater than 1.6 kilometres.
“Our study provides a solid estimate of how much water Mars once had, by determining how much water was lost to space,”
said Geronimo Villanueva, a scientist working at NASA’s Goddard Space
Flight Center in Greenbelt, Maryland, USA, and lead author of the new
paper. “With this work, we can better understand the history of water on Mars.”
The new estimate is based on detailed observations of two slightly
different forms of water in Mars’s atmosphere. One is the familiar form
of water, made with two hydrogen atoms and one oxygen, H2O. The other is HDO, or semi-heavy water, a naturally occurring variation in which one hydrogen atom is replaced by a heavier form, called deuterium.
As the deuterated form is heavier than normal water, it is less
easily lost into space through evaporation. So, the greater the water
loss from the planet, the greater the ratio of HDO to H2O in the water that remains [1].
The researchers distinguished the chemical signatures of the two
types of water using ESO’s Very Large Telescope in Chile, along with
instruments at the W. M. Keck Observatory and the NASA Infrared Telescope Facility in Hawaii [2]. By comparing the ratio of HDO to H2O,
scientists can measure by how much the fraction of HDO has increased
and thus determine how much water has escaped into space. This in turn
allows the amount of water on Mars at earlier times to be estimated.
In the study, the team mapped the distribution of H2O and
HDO repeatedly over nearly six Earth years — equal to about three Mars
years — producing global snapshots of each, as well as their ratio. The
maps reveal seasonal changes and microclimates, even though modern Mars
is essentially a desert.
Ulli Kaeufl of ESO, who was responsible for building one of the
instruments used in this study and is a co-author of the new paper,
adds: "I am again overwhelmed by how much power there is in remote
sensing on other planets using astronomical telescopes: we found an
ancient ocean more than 100 million kilometres away!"
The team was especially interested in regions near the north and
south poles, because the polar ice caps are the planet’s largest known
reservoir of water. The water stored there is thought to document the
evolution of Mars’s water from the wet Noachian period, which ended about 3.7 billion years ago, to the present.
The new results show that atmospheric water in the near-polar region
was enriched in HDO by a factor of seven relative to Earth’s ocean
water, implying that water in Mars’s permanent ice caps is enriched
eight-fold. Mars must have lost a volume of water 6.5 times larger than
the present polar caps to provide such a high level of enrichment. The
volume of Mars’s early ocean must have been at least 20 million cubic
kilometres.
Based on the surface of Mars today, a likely location for this water
would be the Northern Plains, which have long been considered a good
candidate because of their low-lying ground. An ancient ocean there
would have covered 19% of the planet’s surface — by comparison, the
Atlantic Ocean occupies 17% of the Earth’s surface.
“With Mars losing that much water, the planet was very likely wet
for a longer period of time than previously thought, suggesting the
planet might have been habitable for longer,” said Michael Mumma, a senior scientist at Goddard and the second author on the paper.
It is possible that Mars once had even more water, some of which may
have been deposited below the surface. Because the new maps reveal
microclimates and changes in the atmospheric water content over time,
they may also prove to be useful in the continuing search for
underground water.
[1] In oceans on Earth there are about 3200 molecules of H2O for each HDO molecule.
[2] Although probes on the Martian surface and orbiting the planet can provide much more detailed in situ measurements, they are not suitable for monitoring the properties of the whole Martian atmosphere. This is best done using infrared spectrographs on large telescopes back on Earth.
More information
This research was presented in a paper entitled “Strong water isotopic anomalies in the Martian atmosphere: probing current and ancient reservoirs”, by G. VIllanueva et al., to appear online in Science on 5 March 2015.
The team is composed of G.L. Villanueva (NASA Goddard Space Flight Center, Greenbelt, USA; Catholic University of America, Washington, D.C., USA), M.J. Mumma (NASA Goddard Space Flight Center), R.E. Novak (Iona College, New York, USA), H.U. Käufl (ESO, Garching, Germany), P. Hartogh (Max Planck Institute for Solar System Research, Göttingen, Germany), T. Encrenaz (CNRS — Observatoire de Paris-Meudon, Paris, France), A. Tokunaga (University of Hawaii-Manoa, Hawaii, USA), A. Khayat (University of Hawaii-Manoa) and M. D. Smith (NASA Goddard Space Flight Center).
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. 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, the world’s most advanced visible-light astronomical observatory and two survey telescopes.
VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
Four programmes at NASA Headquarters in Washington, D.C., supported this work: Mars Fundamental Research, Planetary Astronomy, Planetary Atmospheres, and NASA Astrobiology.
Links
Contacts:
Geronimo Villanueva
Goddard Space Flight Center
Greenbelt MD, USA
Tel: +1 301 286 1528
Email: geronimo.villanueva@nasa.gov
Michael Mumma
Goddard Space Flight Center
Greenbelt MD, USA
Email: Michael.J.Mumma@nasa.gov
Ulli Käufl
ESO
Garching bei München, Germany
Email: hukaufl@eso.org
Richard Hook
ESO education and Public Outreach Department
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
