Ancient Venus may have looked a whole lot like Earth
According to computer modelling, theplanet Venus could have once been habitable, hosting a shallow-waterocean, and surface temperatures hospitable to life. The simulationsare based on present-day observations of Venus, paired with dataharvested by previous NASA missions that visited the enigmatic planet.
Often referred to as Earth's twin,current-day Venus is anything but. The tortured world's atmosphere,which is believed to be roughly 90 times as thick as that of our ownplanet, has led to a runaway greenhouse effect, resulting in surfacetemperatures of 864 ºF(462 ºC).
However, it is possible that, in itsancient past, this hellish world could have sincerely deserved themoniker of Earth's twin. In the 1980s NASA's Pioneer spacecraftobserved clues that a water ocean may once have existed on Venus.Now, a team of scientists from NASA's New York-based GoddardInstitute for Space Studies has run computer simulations designed tomodel Venus' ancient atmosphere, and come up with some surprisingresults.
The computer model employed for thesimulations is similar in nature to those used to forecast theeffects of climate change on Earth. For the purpose of thesimulations, the researchers had Venus rotate at the same speed thatit does today.
Digital Venus was given an atmospheresimilar to that of present day Earth, and furnished withtopographical features based on data harvested by NASA's Magellanmission that visited the planet in the 1990s. The researchers thenfilled the low-lying areas of the planet with a shallow ocean,leaving only the highlands exposed.
According to the team, landmasses onancient Venus would have been much dryer than their Earthlyequivalent. This fairly mundane characteristic could have played avital part in keeping the planet's greenhouse gas problem at bay, asless water vapour would escape from the ground via evaporation.
It was discovered that Venus' slowrotational period of 117 Earth days, in conjunction with the ancientanalogue of our Sun used in the study, combined to create ahospitable surface temperature only a few degrees cooler than thetemperature on present-day Earth.
The slow spin of the planet, whichwould expose areas of the surface to the glare of the Sun for monthsat a time, allowed the heat from our star to evaporate enough waterto create a kind of cloud shield. This barrier mitigated some of ourSun's heating influence, which, whilst younger and less hot in thesimulations than it is today, would still have bathed the planet in40 percent more sunlight than that received by present-day Earth.
Itis estimated that this Earth-like Venus could have remained habitable in this way foraround 2 billion years.
However, eventually, the sheer quantityof sunlight striking the planet worked to evaporate the oceans ofancient Venus. Subsequently, ultraviolet light broke down theresulting water vapor particles into their constituent elements.Once the majority of the hydrogen had escaped into space, all thatremained was a dense, carbon dioxide-dominated atmosphere shroudingthe lifeless planet we see today.
The evidence for the habitability ofVenus-like planets could help inform the search for exoplanets withthe potential to harbor life. These exoplanets may now present amore attractive prospect for the next generation of ground-based andorbital observatories, including the much anticipated James Webb Space Telescope.