Credit: shaulliv, Flickr.

Mars is a barren and desolate place that’s totally inhospitable for life — at least on its surface. At the same time, however, Mars exhibits Earth-like features: the day/night rhythm is very similar to ours (a Martian day lasts 24 hours, 39 minutes and 35 seconds), it has water that can be extracted from its poles and subsurface, and is believed to have once been rich in liquid water.

For these reasons, some scientists have proposed terraforming the Red Planet into our second home in the solar system. The challenges are numerous, however, and according to a new study, it might be impossible to undertake because the planet doesn’t have enough CO2 to sustain a thick-enough atmosphere.

A leaky planet

Terraforming is the process of transforming a hostile, extraterrestrial environment into one suitable for human life. One of the biggest challenges we face in terraforming Mars is the planet’s lung-emptying thin atmosphere, which is just 6/1000^th that of Earth’s atmosphere (judging by atmospheric pressure at the surface). Your body would boil if left exposed on the Martian surface — if the extreme cold, UV radiation, and lack of oxygen didn’t kill you first.

In order to both raise the surface temperature and the atmosphere’s thickness, a terraforming project on Mars would have to dump copious amounts of greenhouse gases into the planet’s atmosphere, either by delivering them from Earth — such as CFCs, or Freon, gasses that are 17,700 times more potent than carbon dioxide at trapping heat — or by releasing the carbon dioxide trapped in the ice and beneath the surface. The Martian atmosphere is already 96 percent carbon dioxide.

A new study published in Nature Astronomy, however, suggests that there simply isn’t enough CO2 available on Mars that we could release and bring its atmospheric pressure to terraforming levels. In the most optimistic scenario, we might be able to raise Mars’ atmospheric pressure from 0.6 percent that of Earth’s to 7 percent. Relatively speaking, that’s a huge jump, but still not nearly enough to make life bearable at surface level, according to the new NASA-sponsored study, led by Bruce Jakosky of the University of Colorado, Boulder.

The researchers tallied the amount of easily-vaporizable materials — such as CO₂ and H₂O — on the planet, the abundance of volatiles locked up on and below the surface, and the loss of gas from the atmosphere to space. About 20 years-worth of spacecraft observational data was used for this study, collected by NASA’s Mars Reconnaissance Orbiter, the Mars Odyssey spacecraft, and NASA’s MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft.

“Our results suggest that there is not enough CO₂ remaining on Mars to provide significant greenhouse warming were the gas to be put into the atmosphere; in addition, most of the CO₂  gas is not accessible and could not be readily mobilized. As a result, terraforming Mars is not possible using present-day technology,” said Jakosky in a press release.

The various sources of CO2 on Mars and their estimated potential contributions to Martian atmospheric pressure. Credits: NASA Goddard Space Flight Center.

The most accessible CO₂ deposit is in the polar ice caps. One can imagine vaporizing the ice caps by spraying dust on them to absorb more solar radiation, or as Elon Musk once jokingly said, “Nuke ’em!”. However, this procedure would only contribute enough of the greenhouse gas to double the Martian pressure — to 1.2 percent that of Earth’s.

Mars might actually have a lot of carbon trapped in minerals inside the crust, but these are buried so deep that it would require enormous resources to recover them. What’s more, the extent of these deep deposits is unknown.

In its distant past, billions of years ago, the Martian climate once supported liquid water at the surface. However, back then it used to have a thick atmosphere, which has since been stripped away by solar radiation and solar winds. Rivers, streams, lakes, even oceans seem to once have dotted the Martian landscape but then they vanished — at least some of the water escaped into space, then some more of it may have been boiled away after the Red Planet lost its magnetic field. Now, all of that water and CO₂ is gone forever.

The news didn’t seem to shake Elon Musk, one of the most vocal proponents of Mars terraformation. Taking to Twitter on Monday, Musk said there are actually copious amounts of CO2 on Mars.

There’s a massive amount of CO2 on Mars adsorbed into soil that’d be released upon heating. With enough energy via artificial or natural (sun) fusion, you can terraform almost any large, rocky body.

— Elon Musk (@elonmusk) July 31, 2018

The SpaceX and Tesla CEO linked to a 1993 paper authored by Robert Zubrin and Chris McKay, which found that “CO2 may be released by planetary warming, and as the CO2 atmosphere thickens, positive feedback is produced which can accelerate the warming trend.” Zubrin chipped in the Twitter thread to clarify.

I wrote this paper in 1993 with Chris McKay. It shows why #Mars can be terraformed. There is positive feedback- we warm Mars a few degrees C with CF4. this will cause CO2 to outgas from the soil.That will warm Mars more, releasing more CO2,resulting in a Runaway greenhouse effect

— Robert Zubrin (@robert_zubrin) August 1, 2018

Contrary to Jakowski, the required CO2 is almost certainly there. If the soil contains 1% adsorbed CO2 by wt, it will contain enough CO2 in the top 200 m to give Mars a 300 mb (5 psi) atmosphere – same pressure as Skylab – or Mt Everest. No need for spacesuits on such a Mars.

— Robert Zubrin (@robert_zubrin) August 1, 2018

Whatever the case may be, terraforming is certainly a lofty goal for humanity. But these numerous challenges ought to remind us just how lucky we are to live on such a hospitable planet. If there’s such a thing as paradise, we’re living in it.