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Canada as cold as Mars? Is this for real? Well, yes, and no

Scott Sutherland
Meteorologist/Science Writer

Thursday, January 11, 2018, 9:00 AM - With a severe blast of Arctic cold pushing down over most of Canada for weeks, the comparisons with Mars started popping up again. Is this for real, though? Is it really as cold as Mars across parts of Canada? Well, yes, and no. Let's break it down.

Note: As of Jan 11, 2018, REMS data from Curiosity, up to Jan 9, 2018, is now publicly available, revealing the temperatures on the Red Planet over the Christmas holidays. The information in the article has been updated to reflect this new data.

Temperatures across Canada and the northern United States plunged around Christmas, due to a lobe of the polar vortex dipping far south over North America. On the afternoon of Thursday, December 28, this resulted in the two opposite ends of the country being the only places in Canada where temps were warmer than -10oC (not including the wind chill).

Temperatures across Canada as of 3 p.m. EST, on Thursday, Dec 28, 2017.

The temperatures and wind chills across across Saskatchewan, Manitoba, northern and eastern Ontario and into Quebec, and especially those in the territories, were so cold that they invoked an otherworldly feeling! Even up north, in Yellowknife and Whitehorse, average temperatures for that time of year are roughly 10 degrees warmer than what residents were seeing!

We don't even have to delve into the fictional, say with Star Wars' planet Hoth, to get a good comparison for this kind of frigid weather. Conveniently, NASA has a weather station positioned on the planet next door, roughly 75 million km farther from the Sun than Earth. The Curiosity rover, which is located in Gale Crater, on Mars, has been sending back daily weather readings since August 2012.

The Rover Environmental Monitoring Station (REMS) is a pair of sensors, positioned on Curiosity's mast, that gather weather data, and we can see daily records of air temperature, ground temperature, UV radiation and atmospheric pressure from REMS. The instrument also gathers humidity data, which is used in scientific research, and it was designed to measure wind direction and speed as well, but damage to one of the two sensors during landing prevents reliable wind measurements.

Curiosity's REMS instrument, located on its mast, measures weather data on the surface of Mars. Credit: NASA/JPL/Scott Sutherland

Curiosity records both air and ground temperature separately, by directly sensing the air around the REMS instrument, about 2 metres above the ground, and by measuring the infrared radiation emitted by the ground. It does this to keep a running track of them both, as there is typically a significant difference between these two values, especially during the day.

On Mars, the ground and air are heated by the same processes we see in action here on Earth. Sunlight directly warms the ground. That heat is directly transferred to the air molecules closest to the ground, which sets up convection in the air, while the ground also emits infrared radiation, which is absorbed by greenhouse gases in the air.

There are a some big differences for Mars, though. First, the sunlight isn't as intense, due to Mars being an average of 75 million km farther away from the Sun, so there's less energy being absorbed by the ground. Second, the surface is barren, with no plants or bodies of liquid water to absorb and retain heat. Third, Mars' atmosphere is extremely thin compared to Earth's, with an average atmospheric pressure of 6 millibars, compared to Earth's average of 1013 millibars, and that extremely thin air is mostly concentrated very close to the ground.

So, compared to what happens on Earth, less heat is stored in Mars' surface, the thin air conducts less of that heat away from the ground and absorbs less of the infrared radiation emitted by the ground, and what heat is transferred to the air mostly stays in the air right next to the ground. Thus, if you measured the temperature at 1 metre and 2 metres above the Martian ground, the air at 2 metres up is going to be significantly colder.

From up-to-date readings taken by Curiosity's weather station, the rover experienced a maximum air temperature of -18oC on Sol 1918 (the equivalent of Dec 28 here on Earth), and a maximum ground temperature of -5oC.

That means that several locations throughout Canada were at least as cold, and in many places colder, than Mars!

Hold on a second, though. Taking a look at the overnight low temperatures Curiosity measured on that same day, the air temperture got down to -77oC! Even with the wind chill, Regina was "only" at -44 by Friday morning! So, we definitely can't compare low temperatures. Due to its thin atmosphere, Mars just cools off far more quickly than Earth does during the night.

Data from the REMS instrument, from Curiosity Sol 1918, or Dec 28, 2017 here on Earth. Credit: NASA/Centro de Astrobiologia

Location matters!

There's another important factor to consider for these temperatures, which we haven't discussed yet. Location, or more specifically, latitude.

The Curiosity rover just happens to be in Mars' tropics, as Gale Crater is located at 5oS latitude. For comparison, here on Earth, that would be roughly in the middle of the Indonesian rainforest!

A comparison of the Curiosity Rover's position on Mars with where it would be on Earth. Credit: Google/Scott Sutherland

Mars' southern hemisphere is in winter right now, although Curiosity doesn't experience much seasonal variation at its latitude. If we moved the rover up to 50oN latitude on Mars, though, to match the latitude of Regina, the temperatures it just recorded would be much colder, even in the midst of summer!

Viking 2, which NASA landed on Mars in September of 1976, touched down at 47oN latitude, which is a bit closer to the latitude of Regina and Winnipeg here on Earth. At the time of its landing, Mars' northern hemisphere was roughly a third of the way through summer, and the lander read daily temperature variations of between -30oC and -90oC. As the days (or Sols) ticked away, it started to get colder and colder as the autumnal equinox passed for the lander and winter approached. By its 300th day on the red planet, getting close to winter solstice, Viking 2 was recording daily high tempertures of -101oC and daily lows of -111oC! The lowest recorded temperature ever seen on Earth is -89.2oC, at Soviet Vostok Station in Antarctica, on July 21, 1983. There's no way that anywhere in Canada would see such extreme cold!

Interested in keeping up on Mars weather? Head to NASA's REMS website for further updates

Sources: NASA | NASA JPL | The Planetary Society

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