New research by scientists from Harvard University, NASA’s Jet Propulsion Laboratory and the UK Centre for Astrobiology shows that widespread regions of the surface of Mars could be made habitable to photosynthetic life via a solid-state analogue to Earth’s greenhouse effect. Through experiments and modeling under Martian environmental conditions, the team demonstrated that a 0.8 to 1.2-inch (2-3 cm) thick layer of silica aerogel — a translucent, styrofoam-like material — could transmit sufficient visible light for photosynthesis, block hazardous UV radiation and raise temperatures underneath it permanently to above the melting point of water, without the need for any internal heat source.
“This regional approach to making Mars habitable is much more achievable than global atmospheric modification,” said Harvard University’s Dr. Robin Wordsworth, lead author of the study.
“Unlike the previous ideas to make Mars habitable, this is something that can be developed and tested systematically with materials and technology we already have.”
Dr. Wordsworth and colleagues were inspired by a phenomenon that already occurs on Mars.
Unlike Earth’s polar ice caps, which are made of frozen water, polar ice caps on Mars are a combination of water ice and frozen carbon dioxide. Like its gaseous form, frozen carbon dioxide allows sunlight to penetrate while trapping heat. In the summer, this solid-state greenhouse effect creates pockets of warming under the ice.
“We started thinking about this solid-state greenhouse effect and how it could be invoked for creating habitable environments on Mars in the future,” Dr. Wordsworth said.
“We started thinking about what kind of materials could minimize thermal conductivity but still transmit as much light as possible.”
The researchers landed on silica aerogel, one of the most insulating materials ever created.
Silica aerogels are 97% porous, meaning light moves through the material but the interconnecting nanolayers of silicon dioxide infrared radiation and greatly slow the conduction of heat.
“Silica aerogel is a promising material because its effect is passive,” said co-author Dr. Laura Kerber, a research scientist at NASA’s Jet Propulsion Laboratory.
“It wouldn’t require large amounts of energy or maintenance of moving parts to keep an area warm over long periods of time.”
In the study, a thin layer of silica aerogel allowed light from a lamp tuned to simulate Martian sunlight to heat the surface beneath it by up to 150 degrees Fahrenheit (65 degrees Celsius) — enough to raise temperatures on the Martian surface and melt water ice.
“Spread across a large enough area, you wouldn’t need any other technology or physics, you would just need a layer of this stuff on the surface and underneath you would have permanent liquid water,” Dr. Wordsworth said.
The team’s work was published this week in the journal Nature Astronomy.
R. Wordsworth et al. Enabling Martian habitability with silica aerogel via the solid-state greenhouse effect. Nature Astronomy, published online July 15, 2019; doi: 10.1038/s41550-019-0813-0