Last week, a team of scientists led by Vladimir Pushkarev, director of the Russian Centre of Arctic Exploration, rappelled down into a mysterious crater that appeared earlier this year in the Yamal Peninsula of northern Siberia. Ever since three such craters were discovered in July, theories have abounded as to their origins; everything from aliens to stray missiles has been considered and discredited.

Vladimir Pushkarev/Russian Centre of Arctic Exploration via the Siberian Times

Attempts to descend into the crater over the summer failed, but with temperatures dipping down to 12°F (-11°C), the frozen hole was sturdy enough to support climbing gear. The accessible portion of the crater is 54 feet (16.5 meters) deep, at the base of which is a frozen lake thought to be around 34 feet (10.5 meters) deep.

Vladimir Pushkarev/Russian Centre of Arctic Exploration via the Siberian Times

The team took a number of scientific measurements to better understand these newly-formed craters. "They did radiolocation tests at a depth of 200 meters, took probes of ice, ground, gases, and air. Now they all went back to their institutes and labs and will work on the material," Pushkarev explained to The Siberian Times. "The next stage is processing of the gathered information. Then we plan to explore the surrounding area, comparing images from space, and even those taken in the 1980s, to understand if there are—or were—some similar objects."

Vladimir Pushkarev/Russian Centre of Arctic Exploration via the Siberian Times

Although none of the results have been reported yet, two main theories have emerged to explain the relatively sudden formation of the craters. One such theory posits that the site is an example of a "pingo," a hole created when a large underground deposit of ice melts, leaving behind a sunken cavern. Alternatively, Russian scientist Igor Yeltsov, the deputy head of the Trofimuk Institute, suggests that, like the so-called Bermuda Triangle, this Siberian crater was formed by an underground explosion of methane that resulted from the warm climactic conditions above compounded by the geological fault lines below.

Vladimir Pushkarev/Russian Centre of Arctic Exploration via the Siberian Times

"I have heard about this idea of a phenomenon like the Bermuda Triangle, but I repeat, our scientists need to work on their materials first and only then draw some definite conclusions," Pushkarev said. "At the moment we do not have enough information."