At a meeting earlier this year, some experts took some time out of their schedules to have an intriguing discussion – what if Mars and Venus swapped places?
The question was raised at the Comparative Climatology of Terrestrial Planets III meeting at the Lunar and Planetary Institute in Houston, Texas in August. Here researchers were discussing the environments of rocky worlds in our Solar System and beyond.
But according to NASA, a thought experiment about switching our two neighboring planets was also discussed. Of course, it was just a bit of fun – as far as we know we haven’t invented a planet-moving machine yet – but there was some interesting science to come out of it.
Mars has a mass of one-tenth that of Earth, whereas Venus has a fairly similar mass. The former orbits within the current habitable zone of the Sun, while the latter orbits slightly within the inner edge. Of course, neither look habitable now – Mars has an average surface temperature of -60°C (-80°F), with temperatures reaching 460°C (860°F) on Venus owing to its thick atmosphere. So what if we switched them?
“Modern Mars at Venus’s orbit would be fairly toasty by Earth standards,” said Chris Colose, a climate scientist based at the NASA Goddard Institute for Space Studies, wrote Elizabeth Tasker for NASA.
Mars today has a thin atmosphere, blasted away by the Sun when it lost its magnetic field for unknown reasons. Were we to move Mars to Venus’ orbit today, it's unlikely the temperatures would be high enough to release enough carbon dioxide trapped on the planet to thicken the atmosphere much.
Even if it could be thickened, without a magnetic field Mars couldn’t cling onto its atmosphere, meaning the chances of liquid water existing would be slim. “I suspect it would just be a warmer rock,” said Colose.
As for Venus, interestingly its temperature doesn’t rely on the Sun that much; move it to the orbit of Mars, and it would still remain largely similar as its atmosphere is in equilibrium. Over a long time, however, it might be that the planet starts to cool. Otherwise, the only option is to take it beyond the orbit of Mars.
“It seems that simply switching the orbits of the current Venus and Mars would not produce a second habitable world,” wrote Tasker. But had Venus originally formed in the position of Mars, a planet of that size may have fared better at holding onto its atmosphere.