Scientists already knew that the lowest temperatures ever measured on Earth were on a frozen ice ridge in eastern Antarctica, near the South Pole. But they recently discovered that temperatures there can drop even lower than those previously measured.

Tiny valleys near the top of Antarctica's ice sheet reach temperatures of nearly minus 100 degrees Celsius (minus 148 degrees Fahrenheit) during the long, dark polar winter. As they report this week in Geophysical Research Letters, the team thinks this is about as cold as it can possibly get in our corner of the solar system.

When the researchers first announced they had found the coldest temperatures on Earth five years ago, they determined that persistent clear skies and light winds are required for temperatures to dip this low. But the new study adds a twist to the story: Not only are clear skies necessary, but the air must also be extremely dry, because water vapour traps some heat in the air.

The researchers observed the valleys where the super cold, super dry air is denser than the slightly warmer air around it, so it falls into the hollows and becomes trapped. This allows the snow surface and the air above it to cool further, until the clear, calm, dry conditions change and the cold air mixes with warmer air tighter in the atmosphere.

"In this area, we see periods of incredibly dry air, and this allows the heat from the surface of the snow to radiate into space more easily," said Ted Scambos, a senior research scientist at the National Snow and Ice Data Centre at the University of Colorado-Boulder."It's a place where Earth is so close to its limit, it's almost like another planet," he added. For the temperature to drop that low, clear skies and dry air need to persist for several days. Temperatures could drop a little lower if the conditions lasted for several weeks, but that's extremely unlikely to happen, Scambos said.

The measurement smashes the previous record for the coldest known air temperature in the natural world: a frigid minus 128.6°F felt in 1983 at the Russian Vostok Station, not far from the South Pole. Humans can't inhale air that cold for more than a few breaths - it would cause our lungs to bleed. Russian scientists ducking out to check on the weather station would wear masks that warmed the air before they breathed it in.