‘Colder Than Mars’

NASA/JPL-Caltech/Malin Space Science Systems

I have a bone to pick with news stories that declare, hyperbolically, whenever a location is in the midst of a deep freeze, that it’s “colder than Mars”—stories like this one from CTV News or this one from The Atlantic.

What exactly do they mean by “colder than Mars”? Mars is a planet—one that, like Earth, has an atmosphere, albeit thin, and weather and seasons. Mars can get as cold as –143°C (–226°F) and as warm as 35°C (95°F) in spots. Mars’s mean temperature is –63°C (–82°F), which is colder than just about any population centre can get (and no, wind chill doesn’t count for this). So that can’t be it. (Besides, comparing a mean temperature to a local temperature would be an apples-to-oranges comparison. Earth’s mean temperature, for the record, is 15°C.)1

It turns out that what reporters really mean is the current temperature at Gale Crater, as measured by the Rover Environmental Monitoring Station on the Curiosity rover. It also turns out that there’s a handy widget that gives the current conditions as measured by REMS. As I write this, the air temperature on Mars is –19°C and the ground temperature is –6°C (the difference is because the air is so thin).

Since it’s –19°C right now where I live, yes, Mars—or at least Gale Crater, which is not the same thing (again: apples to oranges)—is just as cold. But temperatures as high as 20°C (68°F) and as low as –127°C (–197°F) have been recorded at Gale Crater. It’s no trick for a Martian summer to be warmer than a Canadian winter, but even the daytime highs of a Martian winter can be warmer than a Canadian winter. Because the air is so thin, the Martian surface heats quickly when it’s sunny, and the temperature can swing as much as 100 degrees.2

I know that hyperbole is an essential part of talking about how goddamn cold it is out there (see also: using wind chill instead of temperature), but honestly, Mars isn’t a useful point of reference.