What’s the News: If you were to bring a glass of water to Mars, the liquid would instantly boil because the Red Planet’s carbon dioxide atmosphere is so thin: The vapor pressure of the water easily surpasses the weak atmospheric pressure, sending water molecules flying off quickly into the atmosphere. However, ancient shorelines and river-like features indicate that Mars had a watery past, leading researchers to wonder what happened to Mars’ once-thicker atmosphere. Now, data from the Mars Reconnaissance Orbiter has uncovered a massive deposit of solid CO2 at the south pole that could double the planet’s atmospheric pressure if it were released as gas. “If you double the amount of CO2 in the atmosphere, it’s quite possible that you could have liquid water,” planetary scientist Philip James of the Space Science Institute in Boulder told Scientific American. “People have suggested that this could happen, and now it looks like it could be possible.”
How the Heck:
- As the Mars Reconnaissance Orbiter flies past Mars’s south polar cap, it sent radar waves at the planet, which reflect off surfaces within the ice and travel back to the orbiter.
- These reflected signals look different depending on what materials the waves are traveling through, and in the latest fly-by, researchers imaged deeper into the ice cap and found that the reflected signals resembled the reflective properties of dry ice.
- By calculating the area and depth of this dry-ice signal, the scientists discovered that that this Martian material accounts for upwards of 12,500 cubic kilometers (which is a lot; think about a cubic kilometer) of solid CO2.
What’s the Context:
- Previously, scientists had only found a couple hundred cubic kilometers of dry ice near Mars’s south pole. This new find increases Martian dry ice estimates by 30 times and “is about 80 percent of the current CO2 content of the entire atmosphere.”
- Without a massive moon to stabilize its axial tilt, Mars’s axial tilt changes up to 40 degrees every 100,000 years. When this happens, and the south pole points toward the sun, sunlight can vaporize the dry ice, releasing it into the Martian atmosphere. If all of the known dry ice on Mars were to vaporize, it would nearly double the atmospheric pressure, and could support enough liquid water to “account for some of the [water-carved] features,” say the researchers.
- From finding big stashes of ice on Mars to evidence that transient liquid water might possibly exist on the Red Planet, scientists have been searching high and low for water deposits.
- Recently, scientists have imaged the entire southern ice cap in 3D.
Not So Fast: The amount of atmospheric pressure accounted for by the solid CO2 is impressive, and may allow for liquid water to be present without instantaneously vaporizing, but researchers don’t think it’s enough to account for large amounts of running water. That’s because a thicker CO2 atmosphere would also cause more dry ice deposits on the Martian surface, which would reflect sunlight and leave Mars slightly cooler.
The Future Holds: Other scientists are working on calculating the abundance of carbonate rocks, another possible repository of CO2 on Mars.
Reference: Roger J. Phillips et al. “Massive CO2 Ice Deposits Sequestered in the South Polar Layered Deposits of Mars.” Science. DOI: 10.1126/science.1203091
Image: Image: NASA/JPL-Caltech/University of Rome/Southwest Research Institute