Can Martian holes give climate clues? (Image: NASA/JPL-Caltech/MSSS)

Digging a hole on another world may settle a nagging question about Earth’s climate.

From about 1300 to 1870, much of the Earth is thought to have endured a long cold snap dubbed the Little Ice Age. If such a freeze occurred, it is usually blamed on a dip in solar activity, but there are other suspects such as volcanoes.

If the sun was responsible, we should see evidence of it across the solar system, says Ralph Lorenz of the Johns Hopkins University Applied Physics Lab in Laurel, Maryland. To settle the debate, he suggests digging a hole on Mars to see if it, too, had an ice age around that time.


Temperature changes spread downward through ice and soil, so a borehole will contain clues about past climate. The ice sheet in Greenland contains evidence of the Little Ice Age at a depth of about 60 metres, for instance.

“There is a clear signal of the Little Ice Age there,” Lorenz says. “As the surface temperature goes up and down, a thermal wave propagates downward. So the deep interior has a muted memory of it.”

Solar shortfall

Lorenz calculated that the shortfall in solar radiation needed to explain the Little Ice Age on Earth would mean that temperatures on Mars were about half a degree Celsius lower than they would have been otherwise. The full signal of such a chill would be readable 40 metres deep in the Martian soil, he says.

Drilling a hole on Mars is already on the cards: NASA’s 2016 InSight lander will drill 5 metres into Martian soil. That might be just deep enough to find a hint of an ice age.

“It does not drill deep enough to see the signature unambiguously, but conceivably the measurements will already be somewhat sensitive to it at 5 metres,” he says.

Bringing kit to Mars that will drill 40 metres down is a tall order, but there may be another option. In soil that conducts heat poorly, such as ash, the signal of any cold spell will have travelled down more slowly, and will thus be found at shallower depths. Lorenz recommends sending a probe to the planet’s ash-covered Medusa Fossae Formation.

Journal reference: Icarus, DOI: 10.1016/j.icarus.2014.11.021