According to a new NASA-funded study, the oft-idealized future of Mars as a habitable world of blues, reds and greens remains little more than fertile ground for science fiction.
In a new paper published in the journal Nature Astronomy, Bruce Jakosky of the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder, and Christopher Edwards from the department of physics and astronomy at Northern Arizona University, Flagstaff, reveal how Mars might never regain the wet and warm character of its early days — even with human intervention.
"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," Jakosky told Phys.org.
To terraforming hopefuls, this lack of CO2 is a complete and total bummer.
Mars as it may have appeared some 4 billion years ago. (Photo: ESO/M. Kornmesser)
Some 4 billion years ago when the planet was young, Mars is believed to have had a thick, warm atmosphere, an active iron and nickel core, and a magnetic field to help protect it from solar winds. Under these conditions, and based on the observed presence of what are assumed to be ancient shorelines on the surface, it's estimated that large shallow seas once covered as much as a third of the red planet.
And then something went terribly wrong. Mars's core went from active to dormant, its magnetic field weakened, and solar winds and/or impacts from comets or asteroids slowly stripped the planet of its atmosphere. The water that didn't evaporate as the surface cooled and dried up became locked up in ice at the poles.
For those with an eye for terraforming Mars, hope has always hinged on the planet having substantial carbon reserves in both its rocks and ice to one day extract and use to once more thicken its atmosphere. In September 2015, during an appearance on "The Tonight Show" with Stephen Colbert, SpaceX founder Elon Musk suggested nuclear weapons might do the trick.
"Drop thermonuclear weapons over the poles," he said.
Like other ideas I outlined in a post titled "5 ways to terraforms Mars without nuclear weapons," the point of Musk's explosive idea was to release the massive amounts of CO2 assumed locked up in the Martian poles, like this:
By detonating thermonuclear weapons over the poles, humanity could effectively provide the nudge that's needed to perhaps trigger a runaway greenhouse effect on Mars. The bombs would release heat, which in turn would melt the carbon dioxide frozen at the poles and, in theory, help to immediately thicken Mars' thin atmosphere. As sunlight is trapped by the C02, the temperature would rise, more ice would melt, and so on.
Gone with the (solar) wind
Artist's rendering of how, without a strong magnetic field, the sun's solar wind and radiation slowly strip the planet of its atmosphere. (Photo: NASA/GSFC)
To come up with the most accurate inventory yet of Mars's carbon dioxide potential, Jakosky and Edwards scoured two decades of data collected from NASA's Mars Reconnaissance Orbiter, Mars Odyssey spacecraft and NASA's MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft. Nearly every possible terraforming idea was considered, with all coming up short on the necessary CO2 to create a warm, thick atmosphere.
"The atmospheric pressure on Mars is around 0.6 percent of Earth's," explains Bill Steigerwald, science writer for NASA's Goddard Space Flight Center, in the Phys.org article. "With Mars being further away from the Sun, researchers estimate a CO2 pressure similar to Earth's total atmospheric pressure is needed to raise temperatures enough to allow for stable liquid water. The most accessible source is CO2 in the polar ice caps; it could be vaporized by spreading dust on it to absorb more solar radiation or by using explosives. However, vaporizing the ice caps would only contribute enough CO2 to double the Martian pressure to 1.2 percent of Earth's, according to the new analysis."
As for the Martian soil, the researchers estimate that even if humans were somehow able to strip mine away the surface of Mars down to 300 feet, the harvested CO2 from this process would only contribute less than 5 percent to the required pressure.
The team concludes that simply too much of Mars' atmosphere has been stripped away by solar wind and radiation. According to estimates, the atmosphere that presently remains will entirely disappear over the next 2 billion years. The CO2 and water once present is vast quantities, they add, is likely gone forever.
"There is not enough CO2 left on Mars in any known, readily accessible reservoir, if mobilized and emplaced into the atmosphere, to produce any significant increase in temperature or pressure," they write.
Mars as a stepping stone
While dreams of skipping through Martian fields might be dashed for now, it's likely that the red planet will still one day host human colonists in our mission to explore the solar system. The technology hurdles required for that may yet appear daunting, but at least for Jakosky, they're questions better pondered than terraforming.
"We're getting away from the science here, but I would question the rationale for terraforming to begin with," he told Wired. "Having a back-up planet in case we screw this one up, or it gets screwed up from external drivers, I think is a poor argument. It's a lot easier to keep this one pleasant and with a clement climate than it is to change the Mars environment."