Certain parts of Earth get as chilly as the Red Planet, but it's less common for whole regions to get so frigid. It happens when the jet stream gets buckled, which lets cold air move south. We've seen this before; you might remember polar vortex headlines from past years.
The cold air from a sunless Arctic is meeting warmer air coming up from the Atlantic. That leads to a fierce low-pressure storm on the leading edge of that buckle — and rock-bottom temperatures in its wake.
Weather experts say this storm is unusually strong, but scientists aren't sure if human-driven climate change will make kinks in the jet stream more common. Recent research shows it does happen, but we don't have many cold-weather examples to compare to this storm.
And no matter now long the cold lasts, it probably won't be as bad as Mars at its worst. There, the rover Curiosity measured temperatures more than 110 degrees below zero during the coldest part of its winter.