The coldest place in the solar system may be closer than we think
The temperature is not constant throughout the solar system
Shadowed lunar craters may not be as cold as the Oort Cloud, but the comparison depends on whether we consider the Oort Cloud to be part of the solar system or not.
Space is very, very cold. The temperature of outer space is minus 270.45 degrees Celsius, just above absolute zero, the point at which molecular motion stops.
This temperature isn't constant throughout the solar system, Live Science reported on April 16. So-called "empty" space—though it's not actually empty—is much colder than planets, moons, or asteroids, for example, because there's (practically) nothing to absorb the energy coming from the sun .
?But what is the coldest place in the solar system? And how does it compare to temperatures on Earth
Space is much colder than planets, moons or asteroids
How to measure the temperature of the universe
First, let’s pause for a moment to consider exactly how we measure temperatures in the universe. “Temperatures can be measured by observing the intensity of infrared and microwave radiation emitted from surfaces, and in the absence of such measurements, temperatures can be estimated based on the amount of sunlight that surfaces receive,” Ian Crawford, a professor of planetary science and astrobiology at Birkbeck College, University of London, UK, told Live Science in an email.
However, taking cosmic measurements is not easy, according to Don Polacco, professor of astronomy at the University of Warwick in the United Kingdom. “There is nothing direct in astronomy, mainly because you are always observing rather than interacting.”
So, while there are accurate ways to measure temperatures in space, there will always be room for refinement. “The temperatures are estimates, and the numbers you get depend on how strong your assumptions are and the model you use,” Polacco says.
So, with these points in mind, what is the coldest place in the solar system, at least according to current data? Is it Pluto, given its distance from the sun? In fact, the coldest place may be much closer to Earth.
The Moon's 'Shadiest' Craters Could Actually Be the 'Coldest Places in the Solar System'
Moon Craters and Double Shading
In 2009, NASA's Lunar Reconnaissance Orbiter, a robotic spacecraft designed to help scientists better understand conditions on the Moon, provided data suggesting that "shadowed craters" at the Moon's south pole could be the coldest place in the solar system.
This theory was later reinforced by graduate student Patrick O'Brien and his supervisor, Shane Byrne, both planetary scientists at the University of Arizona. During a talk at the Lunar and Planetary Science Conference in 2022, O'Brien and Byrne suggested that the moon's "most shadowed" craters could actually be "the coldest places in the solar system."
According to O'Brien and Byrne, a crater can be considered most shaded if it is "obscured not only from direct solar illumination but also from secondary heating sources, such as solar radiation reflected from nearby bright objects as well as thermal radiation emitted from those warm surfaces."
Pluto's average surface temperature is -232.75 degrees Celsius (-100 degrees Fahrenheit).
"Shaded" craters have rims high enough that sunlight doesn't reach the crater floor, which is why they're so cold, Polacco added.
O'Brien and Byrne's research suggests that because these "permanently shaded areas" have been "shielded" from solar light for billions of years, their craters could contain "cold spots" that contain not only "water ice, but also more volatile compounds and elements" such as carbon dioxide, carbon monoxide, nitrogen and argon. According to O'Brien and Byrne, the temperatures of these craters are estimated to be around -248.15 degrees Celsius, but they could be much colder.
Oort cloud
Crawford is confident in the research, saying, "I'm pretty sure these are the coldest temperatures in the inner solar system (from Mercury to Mars) and also colder than the average surface temperature of Pluto." Pluto's average surface temperature is minus 232.75 degrees Celsius, according to NASA.
Illustration of the Kuiper Belt and Oort Cloud and their relationship to our solar system
However, these shadowed lunar craters may not be as cold as the Oort Cloud, a shell of icy space debris far beyond the orbit of Neptune, Crawford said, noting that the comparison depends on whether we consider the Oort Cloud to be part of the solar system or not.
According to Northwestern University in Illinois, temperatures in the Oort Cloud can be as low as -268.15 degrees Celsius, which would be much colder than anything found on the Moon. However, if we don't include the Oort Cloud as part of our solar system, it's very likely that the coldest place in the solar system is in our nearest celestial neighbor.
Comparisons with Earth
On Earth, even the coldest and most extreme Antarctic temperatures are warmer than the moon's craters or the Oort Cloud. The coldest ground temperature ever recorded was on July 21, 1983, at Russia's Vostok research station in Antarctica, at minus 89.2 degrees Celsius, according to the World Meteorological Organization's Global Climate and Extremes Archive.
The coldest ground temperature ever recorded was -89.2°C (Ca' Foscari University)
However, scientists have created artificial temperatures lower than those that occur naturally on Earth, in craters on the Moon or even in the Oort Cloud. Last year, a team of German researchers broke the record for the coldest temperature ever reached in a laboratory: -273.15 degrees Celsius.
But when it comes to naturally occurring temperatures, our Moon's shadowed craters are the lowest temperature in our solar system, depending, of course, on the dependency of the Oort cloud.
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