Was Venus Once a Waterworld?

by Nancy Atkinson on June 24, 2010

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Venus Monitoring Camera image taken in the ultraviolet (0.365 micrometres), from a distance of about 30,000 km. Credits: ESA/MPS/DLR/IDA

Ever read Isaac Asimov’s 1950′s novel “Lucky Starr and the Oceans of Venus”? Maybe Asimov wasn’t so wrong about Venus after all. Analyzing data from ESA’s Venus Express, planetary scientists are looking at the possibility that the planet may have once harbored oceans, and potentially could have been habitable when during its early history.

While Earth and Venus are comparable in size, they otherwise seem completely different. Earth is a lush, clement world teeming with life, while Venus is hellish, its surface roasting at temperatures higher than those of a kitchen oven.

The biggest difference between the two planets is that Venus has very little water, while Earth is bathed in it. Were the contents of Earth’s oceans to be spread evenly across the world, they would create a layer 3 km deep. If you were to condense the amount of water vapor in Venus’ atmosphere onto its surface, it would create a global puddle just 3 cm deep.

But scientists are beginning to think that billions of years ago, Venus probably had much more water. Venus Express has confirmed that the planet has lost a large quantity of water into space, by measuring the rate of how much hydrogen and oxygen is escaping into space, as the Sun’s ultraviolet radiation beats down on the planet and breaks up water molecules.

Venus Express has measured the rate of this escape and confirmed that roughly twice as much hydrogen is escaping as oxygen. It is therefore believed that water is the source of these escaping ions. It has also shown that a heavy form of hydrogen, called deuterium, is progressively enriched in the upper echelons of Venus’s atmosphere, because the heavier hydrogen will find it less easy to escape the planet’s grip.

“Everything points to there being large amounts of water on Venus in the past,” says Colin Wilson, Oxford University, UK. But that does not necessarily mean there were oceans on the planet’s surface.

Eric Chassefière, Université Paris-Sud, France, has developed a computer model that suggests the water was largely atmospheric and existed only during the very earliest times, when the surface of the planet was completely molten. As the water molecules were broken into atoms by sunlight and escaped into space, the subsequent drop in temperature probably triggered the solidification of the surface. In other words: no oceans.

Although it is difficult to test this hypothesis it is a key question. If Venus ever did possess surface water, the planet may possibly have had an early habitable phase.

Even if true, Chassefière’s model does not preclude the chance that colliding comets brought additional water to Venus after the surface crystallized, and these created bodies of standing water in which life may have been able to form.

There are many open questions. “Much more extensive modelling of the magma ocean–atmosphere system and of its evolution is required to better understand the evolution of the young Venus,” said Chassefière.

When creating those computer models, the data provided by Venus Express will prove crucial.

The Venus Express team are meeting this week to discuss their latest findings at the International Venus Conference in Aussois, France.

Source: ESA

About 

Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

Torbjorn Larsson OM June 27, 2010 at 1:08 PM

Venus goes through periods as a complete magma planet.

Not according to the latest research. Ribbon tessera terrain (RTT) “represents some of Venus’s oldest surfaces, and is widely accepted as forming prior to postulated global catastrophic resurfacing.” Apparently “~30% of Venus has rtt exposed at the surface or shallowly buried (>0.75 km).”

This challenges the catastrophe hypothesis. Now, as a layman I don’t know if any of this is good. Apparently it is an old controversy in the background, where the terrain imagery interpretation from the Magellan onwards of no large craters have been challenged by researchers like Hamilton:

“Conventional analyses assign to a fraction of the most distinct old structures origins by plumes, diapirs, and other endogenic processes, and ignore the rest. [...]

A continuum of increasing degradation, burial, and superposition connects the younger and truly pristine young impact structures with the most modified of the ancient structures. Younger craters of the ancient family are superimposed on older ones in impact-definitive cookie-cutter bites and are not deflected as required by endogenic conjectures. Four of the best-preserved of the pre-“pristine” circular structures are huge, with rimcrests 800–2000 km in diameter, and if indeed of impact origin, must have formed, by analogy with lunar dating, no later than 3.8 Ga. Much of the venusian plains is seen in topography to be saturated with overlapping 100–600 km circular structures, almost all of which are disregarded in conventional accounts. Several dozen larger ancient plains basins reach 2500 km in diameter, are themselves saturated with midsize impact structures, and may date back even to 4.4 Ga.”

Of course, eventually these protracted to and fro’ risk devolving into meaningless pattern recognition. Without being able to read the paywalled away papers, the RTT evidence sounds a bit more promising.

My layman take FWIW (i.e. not much): Extraordinary claims like catastrophic resurfacing, not seen anywhere else to my knowledge, needs extraordinary evidence. However, apparently the evidence is even less than ordinary to some. At the very least it seems like an open question?!

Aqua June 28, 2010 at 6:12 PM

Enigmatic Venus may soon reveal some of her long hidden/veiled secrets as current and future missions gather and send back data…

1) Why does Venus rotate backwards?
2) Why is that rotation so slow?
3) What has caused the surface to be continually ‘reworked’?
4) What conditions created its sulfuric acid atmosphere?
5) Why doesn’t Venus have a magnetic field like Earth?
6) What happened to the water on Venus?
7) Did Venus ever harbor life?
8) How were the strangely flattened volcanic landforms created?

The list friends, goes on and on… WHICH is why we’ve gone there and will go there again and again.

Torbjorn Larsson OM June 28, 2010 at 11:19 PM

3) What has caused the surface to be continually ‘reworked’?

That is possibly a matter of some contention, which would have been more clearly seen and possibly discussed if ever my previous comment gets out of moderation.

I’ll repeat it here but without the offending links then:

Venus goes through periods as a complete magma planet.

Not according to the latest research. Ribbon tessera terrain (RTT) “represents some of Venus’s oldest surfaces, and is widely accepted as forming prior to postulated global catastrophic resurfacing.” Apparently “~30% of Venus has rtt exposed at the surface or shallowly buried (>0.75 km).”

This challenges the catastrophe hypothesis. Now, as a layman I don’t know if any of this is good. Apparently it is an old controversy in the background, where the terrain imagery interpretation from the Magellan onwards of no large craters have been challenged by researchers like Hamilton:

“Conventional analyses assign to a fraction of the most distinct old structures origins by plumes, diapirs, and other endogenic processes, and ignore the rest. [...]

A continuum of increasing degradation, burial, and superposition connects the younger and truly pristine young impact structures with the most modified of the ancient structures. Younger craters of the ancient family are superimposed on older ones in impact-definitive cookie-cutter bites and are not deflected as required by endogenic conjectures. Four of the best-preserved of the pre-“pristine” circular structures are huge, with rimcrests 800–2000 km in diameter, and if indeed of impact origin, must have formed, by analogy with lunar dating, no later than 3.8 Ga. Much of the venusian plains is seen in topography to be saturated with overlapping 100–600 km circular structures, almost all of which are disregarded in conventional accounts. Several dozen larger ancient plains basins reach 2500 km in diameter, are themselves saturated with midsize impact structures, and may date back even to 4.4 Ga.”

Of course, eventually these protracted to and fro’ risk devolving into meaningless pattern recognition. Without being able to read the paywalled away papers, the RTT evidence sounds a bit more promising.

My layman take FWIW (i.e. not much): Extraordinary claims like catastrophic resurfacing, not seen anywhere else to my knowledge, needs extraordinary evidence. However, apparently the evidence is even less than ordinary to some. At the very least it seems like an open question?!

Torbjorn Larsson OM June 28, 2010 at 11:22 PM

HTML fail. It was supposed to be:

Venus goes through periods as a complete magma planet.

Paul Eaton-Jones June 29, 2010 at 12:03 AM

I seem to remember an article in Scientific American [?] /Astronomy [?] or somesuch from 15 or so years ago which suggested that the bigger impact craters did date from 4GYA when the venusian atmosphere was not as thick and the paucity of later/smaller impact craters was due to the fact that as the atmosphere thickened so it stopped all but the largest asteroids/meteors getting to the surface.

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