The crater Faustini, on the south pole of the moon, where temperatures reached -238 C, is seen in the upper centre of this photo, taken by NASA's Lunar Reconnaissance Orbiter. (Associated Press/NASA)

Astronomers have found the coldest spot ever measured in our solar system and it's closer than you'd think.

NASA's Lunar Reconnaissance Orbiter, launched in June, recently returned its first data, including temperatures from the moon's surface. Dark spots inside craters near the moon's south pole registered a daytime temperature of –238 C, the lowest temperature measured in our solar system outside a lab.

The spot is permanently in shadow, never receiving any heat from the sun, so it's colder than the average temperature on Pluto, which is 40 times farther away from the sun.

The Diviner Lunar Radiometer Experiment on the orbiter measured a surface temperature on the moon one degree colder than any measured on Pluto and just 35 degrees warmer than absolute zero, the coldest temperature possible.

"After decades of speculation, Diviner has given us the first confirmation that these strange, permanently dark and extremely cold places actually exist on our moon," said science team member Ashwin Vasavada of NASA's Jet Propulsion Laboratory in Pasadena, Calif.

The coldest spots were found in small craters inside larger ones, named Faustini, Shoemaker and Haworth, in the southern polar region of the moon. Some of the craters were previously unexplored, so they don't have names yet.

These supercold crevices are important because they can freeze and trap volatile chemicals, such as water and methane.

"It is safe to conclude that the temperatures in these supercold regions are definitely low enough to cold-trap water ice, as well as other more volatile compounds, for extended periods," David Paige, a UCLA professor of planetary science, said in a news release.

These cold traps were first theorized 50 years ago, and Diviner is now showing astronomers where they are and how cold they get, Paige said.

Future astronauts colonizing the moon could mine water trapped in craters. The frozen volatile chemicals could also give astronomers clues about the formation of the solar system.

The Lunar Reconnaissance Orbiter began taking measurements just a week ago, after entering orbit around the moon in June. The probe circles the moon about 50 kilometres above the surface, providing the first close-up look of the moon's surface in a decade.

The surface of the moon has an average daytime temperature of 107 C and at night the average temperature drops to –153 C. The daily temperature swing is among the most extreme seen in the solar system.

The Lunar Reconnaissance Orbiter also found further evidence of hydrogen on the moon, which could point to water ice trapped under the moon's surface.