Mars has many similarities to Earth. There are volcanoes, canyons, craters and - most importantly - water. Oh, and now NASA researchers have added another similarity to the list: ice ages.
Yup, thanks to radargrams taken from NASA's Mars Reconnaissance Orbiter (MRO), scientists now have physical measurements that suggest Mars is actually just now emerging from an ice age that ended some 400,000 years ago. That's quite the cold spell!
According to the team, researchers have previously predicted that the Red Planet experienced ice ages in the past using complex computer models, but they lacked actual measurements to back them up.
Those days are now over, because the team was able to use the MRO's Shallow Subsurface Radar (SHARAD) to take a look inside the planet's ice caps, giving them a glimpse into its past climate shifts.
While analysing these images, the researchers noticed that there's a line in the ice that indicates a boundary. Above this boundary, there's a layer of fresher ice that is completely uniform, which means it accumulated quickly compared to the lower layers under the 'boundary line', reports the team.
"The layers in the upper few hundred meters display features that indicate a period of erosion, followed by a period of rapid accumulation that is still occurring today," says astronomer Isaac Smith from the Planetary Science Institute in Tucson, Arizona.
To understand what this means, we need to talk about how ice ages happen on Mars. They occur as Mars starts to tilt, making its poles warmer than normal because they're getting more sunlight.
This causes water vapour to travel from the decreasing poles towards the equator, forming glaciers and ice formations (pretty much like everyone's mental image of an ice age). Then, when the tilt moves back, the poles freeze quickly and the ice near the equator melts.
Since the poles shrink quickly at the beginning of the ice age and then reform just as fast afterwards, it creates a layer of fresher ice, and that's exactly what the researchers found in their latest scans. Since the ice is still growing, it likely means that Mars is still recovering from this event that happened 400,000 years ago, based off of the evidence gathered by the team.
"This suggests that we have indeed identified the record of the most recent Martian glacial period and the regrowth of the polar ice since then," says Smith. "Using these measurements, we can improve our understanding of how much water is moving between the poles and other latitudes, helping to improve our understanding of the Martian climate."
So why is this such a big deal? Well, if we want to inhabit Mars one day, we're going to need a firm grasp of how its climate operates over time. This means understanding how its tilt can cause an ice age, an event that would likely spell disaster for an unprepared human civilisation.
Plus any studies that look into how water works on Mars are crucial if we want to grow plants or, you know, survive. After all, dying from dehydration is quite easy.
"We want to know the history of water," Smith said in a report by The Verge's Alessandra Potenza. "At some point, we're going to have some people there and we'd like to know where the water is. So there's a big search for that."
Not only will this allow us to understand more about Mars - our potential new home - but also about Earth. Scientists use climate models all of the time to look into how climates are changing on Earth. From understanding how climates affected past civilisations to understanding how Earth will look in the future, all of this is done with models. Because of this, researchers are always trying to improve them.
"Mars is relevant to Earth, because it has the same processes going on as Earth does, namely Milankovitch cycles," Smith told Space.com's Charles Q. Choi. "Mars serves as a simplified laboratory for testing climate models and scenarios, without oceans and biology, that we can then use to better understand Earth systems."
The team's findings were published in the journal Science.