NASA: Venus May Once Have Been Habitable

Venus may have had a shallow liquid-water ocean and habitable surface temperatures for up to 2 billion years of its early history, according to computer modeling of the planet’s ancient climate by scientists at NASA’s Goddard Institute for Space Studies (GISS) in New York.

Observations suggest Venus may have had water oceans in its distant past. A land-ocean pattern like that above was used in a climate model to show how storm clouds could have shielded ancient Venus from strong sunlight and made the planet habitable. Credits: NASA
Observations suggest Venus may have had water oceans in its distant past. A land-ocean pattern like that above was used in a climate model to show how storm clouds could have shielded ancient Venus from strong sunlight and made the planet habitable.
Credits: NASA

The findings, published this week in the journal Geophysical Research Letters, were obtained with a model similar to the type used to predict future climate change on Earth.

“Many of the same tools we use to model climate change on Earth can be adapted to study climates on other planets, both past and present,” said Michael Way, a researcher at GISS and the paper’s lead author. “These results show ancient Venus may have been a very different place than it is today.”

Venus today is a hellish world. It has a crushing carbon dioxide atmosphere 90 times as thick as Earth’s. There is almost no water vapor. Temperatures reach 864 degrees Fahrenheit (462 degrees Celsius) at its surface.

Scientists long have theorized that Venus formed out of ingredients similar to Earth’s, but followed a different evolutionary path. Measurements by NASA’s Pioneer mission to Venus in the 1980s first suggested Venus originally may have had an ocean. However, Venus is closer to the sun than Earth and receives far more sunlight. As a result, the planet’s early ocean evaporated, water-vapor molecules were broken apart by ultraviolet radiation, and hydrogen escaped to space. With no water left on the surface, carbon dioxide built up in the atmosphere, leading to a so-called runaway greenhouse effect that created present conditions.

Previous studies have shown that how fast a planet spins on its axis affects whether it has a habitable climate. A day on Venus is 117 Earth days. Until recently, it was assumed that a thick atmosphere like that of modern Venus was required for the planet to have today’s slow rotation rate. However, newer research has shown that a thin atmosphere like that of modern Earth could have produced the same result. That means an ancient Venus with an Earth-like atmosphere could have had the same rotation rate it has today.

Another factor that impacts a planet’s climate is topography. The GISS team postulated ancient Venus had more dry land overall than Earth, especially in the tropics. That limits the amount of water evaporated from the oceans and, as a result, the greenhouse effect by water vapor. This type of surface appears ideal for making a planet habitable; there seems to have been enough water to support abundant life, with sufficient land to reduce the planet’s sensitivity to changes from incoming sunlight.

Way and his GISS colleagues simulated conditions of a hypothetical early Venus with an atmosphere similar to Earth’s, a day as long as Venus’ current day, and a shallow ocean consistent with early data from the Pioneer spacecraft. The researchers added information about Venus’ topography from radar measurements taken by NASA’s Magellan mission in the 1990s, and filled the lowlands with water, leaving the highlands exposed as Venusian continents. The study also factored in an ancient sun that was up to 30 percent dimmer. Even so, ancient Venus still received about 40 percent more sunlight than Earth does today.

 

“In the GISS model’s simulation, Venus’ slow spin exposes its dayside to the sun for almost two months at a time,” co-author and fellow GISS scientist Anthony Del Genio said. “This warms the surface and produces rain that creates a thick layer of clouds, which acts like an umbrella to shield the surface from much of the solar heating. The result is mean climate temperatures that are actually a few degrees cooler than Earth’s today.”

The research was done as part of NASA’s Planetary Science Astrobiology program through the Nexus for Exoplanet System Science (NExSS) program, which seeks to accelerate the search for life on planets orbiting other stars, or exoplanets, by combining insights from the fields of astrophysics, planetary science, heliophysics, and Earth science. The findings have direct implications for future NASA missions, such as the Transiting Exoplanet Survey Satellite and James Webb Space Telescope, which will try to detect possible habitable planets and characterize their atmospheres.
Present-day Venus has a crushing carbon dioxide atmosphere 90 times thicker than Earth’s with clouds of sulfuric acid and a surface temperature of 864 degrees Fahrenheit (462 degrees Celsius). In short, it’s pretty bad for life as we know it. Even our most robust landers have only survived a short time on Venus. Scientists have long suspected that Venus started with very similar components as Earth, but its development simply took a different path. Using the same climate models created to track global warming on Earth, scientists have extrapolated what Venus might have been like a few billion years ago.

Based on topographical data, Venus probably had a shallow sea covering much of its surface in the past. It still had more dry land than Earth, though. That would have limited the amount of water evaporation from Sun exposure, and thus the greenhouse effect from water vapor. The Sun was also about 30% less bright two billion years ago. The GISS analysis takes into account Venus’ slow rotation, too. A single day on Venus is equal to 117 Earth days. Each spot is exposed to sunlight for two months at a time, which would have led to a thick layer of clouds and rain on ancient Venus. This also served to reduce solar heating on the surface. The result was an average temperature several degrees cooler than Earth today.

However, Venus was not stable in this state. When the sun increased in brightness, this tenuous balance was lost as harsh ultraviolet radiation broke water molecules in the atmosphere apart. Hydrogen was lost to space and carbon dioxide built up. A runaway greenhouse effect took hold and Venus became in uninhabitable hellscape we know today. These findings could help inform future NASA missions like the James Webb Space Telescope, which will search for exoplanets that may have things in common with ancient Venus.
Ancient Venus may have been habitable, according to a new NASA study that suggests that the planet had a shallow liquid-water ocean and cooler surface temperatures for up to 2 billion years of its early history.

The findings were obtained with a computer model of the planet’s ancient climate, similar to the type used to predict future climate change on Earth.

“These results show ancient Venus may have been a very different place than it is today,” said Michael Way, a researcher at NASA’s Goddard Institute for Space Studies (GISS) in New York.

Venus today has a carbon dioxide atmosphere 90 times as thick as Earth’s. There is almost no water vapour.

Temperatures reach 462 degrees Celsius at its surface, researchers said.

Scientists long have theorised that Venus formed out of ingredients similar to Earth’s, but followed a different evolutionary path.

Measurements by NASA’s Pioneer mission to Venus in the 1980s first suggested Venus originally may have had an ocean.

However, since Venus is closer to the Sun than Earth and receives far more sunlight, the planet’s ocean evaporated, water-vapour molecules were broken apart by ultraviolet radiation, and hydrogen escaped to space.

With no water left on the surface, carbon dioxide built up in the atmosphere, leading to a so-called runaway greenhouse effect that created present conditions.

Until recently, it was assumed that a thick atmosphere like that of modern Venus was required for the planet to have today’s slow rotation rate.

However, newer research has shown that a thin atmosphere like that of modern Earth could have produced the same result.

That means an ancient Venus with an Earth-like atmosphere could have had the same rotation rate it has today.

The GISS team postulated ancient Venus had more dry land overall than Earth, especially in the tropics. That limits the amount of water evaporated from the oceans and, as a result, the greenhouse effect by water vapour.

This type of surface appears ideal for making a planet habitable; there seems to have been enough water to support abundant life, with sufficient land to reduce the planet’s sensitivity to changes from incoming sunlight.

Researchers simulated conditions of a hypothetical early Venus with an atmosphere similar to Earth’s, a day as long as Venus’ current day, and a shallow ocean consistent with early data from the Pioneer spacecraft.

“Venus’ slow spin exposes its dayside to the Sun for almost two months at a time,” co—author and fellow GISS scientist Anthony Del Genio said.

“This warms the surface and produces rain that creates a thick layer of clouds, which acts like an umbrella to shield the surface from much of the solar heating,” Del Genio said.

“The result is mean climate temperatures that are actually a few degrees cooler than Earth’s today,” he said.
For a 2-billion-year-long span, ending about 715 million years ago, Venus was likely a much more pleasant spot that it is today. To observe Venus now is to witness a dry and toxic hellscape, where the planet heats up to a scorching 864 degrees Fahrenheit. A super-strong electric wind is believed to suck the smallest traces of water into space. With apologies to Ian Malcolm, life as we know it could not find a way.

But travel back in time a few billion years or so. Ancient Venus, according to a new computer model from NASA, would have been prime solar system real estate, to the point it may have been downright habitable.

NASA’s Goddard Institute for Space Studies, in a report published Thursday in the journal Geophysical Research Letters, calculated that the average surface temperature 2.9 billion years ago was about 50 degrees Fahrenheit. Such temperature would have made Venus, surprisingly for a planet closer to the Sun, a bit chillier than Earth was at the time.

To determine the ancient temperatures of Venus, NASA scientists applied a computer model similar to the ones used to predict the future of Earth climate. The simulations relied on topographical data from the Magellan mission, a spacecraft that in the early 1990s mapped 98 percent of the surface of Venus with radar.

“Many of the same tools we use to model climate change on Earth can be adapted to study climates on other planets, both past and present,” said Michael Way, a Goddard researcher and the lead author of the new study, in a press release. “These results show ancient Venus may have been a very different place than it is today.”

Old Venus would have orbited a Sun about 30 percent dimmer than present-day Sol. Due to its proximity Venus would still be baked in unearthly amounts of sunlight. But the GISS simulation revealed that, when Venus’s extremely slow daily rotation is taken into account, unusual weather patterns emerge.

Venus is strange in that it rotates so slowly – 243 Earth days per spin – it actually completes a yearly orbit of the sun before its day is over. That is, a Venusian year is shorter than Venusian a day. Were there to be a shallow ocean on Venus at the time, the sun would have churned some of the liquid sea into a thick cloud layer. The net effect would have been like the flap of foil across a car windshield.

Those ancient Venusian clouds would act “like an umbrella to shield the surface from much of the solar heating,” said GISS’s Anthony Del Genio in the press release. “The result is mean climate temperatures that are actually a few degrees cooler than Earth’s today.”

Exactly when Venus overheated remains a mystery. Despite how hot and dry our solar system twin is today — Venus is about the same size as Earth, and possibly within the so-called “Goldilocks zone” of habitable worlds — the odds seem increasingly good it may have had the right conditions for life a long, long time ago.
Researchers used climate models to calculate that Venus might have had a shallow ocean of liquid water and temperatures that could have allowed life to exist for up to two billion years of its early history.

The atmosphere is 90 times as thick as the air on Earth and scientists had thought this was largely caused by the difference between the two planets’ rate of spin. A day on Venus lasts 117 Earth days because it spins on its axis at a much slower rate.

But recent research showed that Venus could have had an atmosphere similar to the Earth’s today.
The first signs that Venus once had an ocean were discovered by NASA’s Pioneer mission in the 1980s.

Venus is closer to the sun than Earth and receives far more sunlight. This caused the ocean to evaporate, water-vapour molecules were broken apart into hydrogen and oxygen by ultraviolet radiation and the hydrogen escaped to space.

With no water left on the surface, carbon dioxide built up in the atmosphere and led to a runaway greenhouse gas effect that created present searing heat.

Michael Way, a researcher at Nasa’s Goddard Institute for Space Studies (GISS) in New York, said: “Many of the same tools we use to model climate change on Earth can be adapted to study climates on other planets, both past and present.

“These results show ancient Venus may have been a very different place than it is today.”

Colleague Anthony Del Genio added: “In the GISS model’s simulation, Venus’ slow spin exposes its dayside to the sun for almost two months at a time.

“This warms the surface and produces rain that creates a thick layer of clouds, which acts like an umbrella to shield the surface from much of the solar heating.

“The result is mean climate temperatures that are actually a few degrees cooler than Earth’s today.”

In a statement, Nasa said it was thought that Venus may have had more land than Earth.

“This type of surface appears ideal for making a planet habitable. There seems to have been enough water to support abundant life, with sufficient land to reduce the planet’s sensitivity to changes from incoming sunlight,” it added.

One of the factors they had to take into consideration was the ancient sun was up to 30 per cent dimmer.

“Even so, ancient Venus still received about 40 per cent more sunlight than Earth does today,” the statement said.


(Source: NASA)

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