Mars-like ice rediscovered in Hawaii volcano, but might not last

I’m not sure what takes my breath away first: the low oxygen, or the rugged, alien landscape that spreads out majestically below my feet.

We are standing on the 4200-metre-high summit of Mauna Kea, a dormant volcano that forms the highest point in Hawaii. It’s easy to see why astronomers are interested in this cold, remote place: the red-brown basalt rocks and dry, barren surface immediately conjure up images of Mars.

It was in the crater below, in 1969, that scientist Alfred Woodcock dug beneath the rocky exterior and discovered a hidden ice world.

But when Norbert Schörghofer, an astronomer from the University of Hawaii at Manoa, stumbled across Woodcock’s papers and records decades later, he was baffled. How could ice persist in an area where the average temperature is 4 °C above freezing?

To help solve this puzzle, Schörghofer has enlisted the help of Matthias Leopold, a geophysicist and permafrost expert at the University of Western Australia in Perth. The goal of our expedition today is to use a technique called electrical resistivity tomography to find out whether the curious ice patch still exists.

If it does, it could help us understand how underground ice forms in similar locations on Mars, too.

Down into the crater

The first step is to carry the surveying equipment to the bottom of the 300-metre-wide crater, known as Pu’u Wekiu. This is easier said than done: the loose rocky soil causes a few ungraceful slides down the steep slope, and the crisp air and 40 per cent drop in oxygen make our breathing short and ragged.

Once we’ve applied enough sunscreen to protect ourselves against the fiercely bright sun, Schörghofer begins to check the temperature sensors he buried here in 2013. Disappointingly, the first two read above zero – no ice here.

But when we get to the third sensor, which is a metre deep in the centre of Woodcock’s old surveying area, Schörghofer lets out a whoop of excitement. The temperature here is freezing.

To probe further, Leopold spaces out 20 steel electrodes – each the size of a tent peg – across the surveying area. These generate an electric field that can find frozen ground up to 50 metres deep by measuring resistivity. Although this technique is less straightforward than drilling down to look for ice, it preserves the unique volcanic landscape that is sacred to local people.

Once the readings have been uploaded to Leopold’s laptop, there is good and bad news. The subsurface ice is still here, but its area has shrunk from 600 to 200 square metres over the last half-century, and its depth has halved from about 10 to 5 metres. Global warming may have played a part in this shrinkage, but it’s hard to tell without long-term trend data.

Working out the age of the ice would also be tricky, says Schörghofer. Radiocarbon dating could be used if plants or animals were trapped in the ice, but there is scarcely any life up here other than the occasional insect, such as the endemic wekiu bug.

Later, the researchers will combine geological and meteorological data to come up with a theory of how the buried ice exists. The most plausible explanation is that it forms at night, when temperatures drop below zero.

At this time, icy air can swirl down the steep crater and seep into the porous, rocky ground. Any underground ice formed in this process would normally melt in the daytime heat, but the patch sits in the area of the crater that receives the least sunlight.

Ice on Mars

In this way, Mauna Kea is one of the best models on Earth for studying ice in the tropics of Mars, says Schörghofer. Most ice on Mars is at the poles, but photos have identified signs of buried ice towards the equator. Just like with Pu’u Wekiu, these spots are found in the shadows inside steep craters that punctuate the planet’s surface.

Not much is known about ice at mid-latitudes on Mars, meaning this terrestrial ice patch is a precious window into how and why it forms.

But sadly, time is running out. Schörghofer believes the Mauna Kea ice will disappear over the next 50 years, as climate change ramps up air temperatures.

As we drive back down through the blanket of clouds and peel off our alpine clothes, the only hints of the otherworldly place from which we have come are the smears of volcanic ash on our faces.

But hopefully, this will not be my last trip to Mars.

Read more: Hunting for Mars-like life a kilometre below Earth’s surface