Pluto is often assumed to be the coldest place in the solar system due to its great distance from the sun, orbiting billions of miles beyond the gas giants. This remote position naturally leads to extremely low temperatures. However, identifying the true coldest point requires a deeper look, not only at the major planets but also at smaller, less-known regions.
The Definitive Answer: Identifying the Coldest Major Planet
Despite its frigid distance, Pluto is not considered the coldest major planet in the solar system, primarily because it is no longer classified as one. The title of the coldest of the eight official planets falls to the ice giants, Uranus and Neptune. Neptune, being the farthest planet from the sun, has the lowest average temperature, measured at approximately -330°F (-200°C) at the top of its clouds.
Uranus, which orbits closer to the sun than Neptune, paradoxically holds the record for the coldest measured temperature within a major planet’s atmosphere: -371.56°F (-224.2°C). This unexpected difference is likely due to Uranus’s distinct lack of internal heat radiating outward. Neptune, in contrast, emits more than twice the energy it absorbs from the sun. This internal heat dynamic prevents Neptune’s atmosphere from reaching the deep-freeze extremes observed on Uranus.
Pluto’s Extreme Environment and Temperature Profile
Pluto’s surface temperature typically ranges between a low of about -400°F and a high of -369°F. This range is directly linked to its highly elliptical orbit, which brings it closer to the sun at certain points in its 248-year journey. The dwarf planet’s coldness is also influenced by its composition, which includes volatile ices like nitrogen, methane, and carbon monoxide.
The presence of these volatile ices creates a thin, seasonal atmosphere that dramatically impacts its temperature profile. When Pluto is closer to the sun, some of the surface ices sublimate, turning directly into gas to form a temporary atmosphere. As Pluto moves farther away, this gas freezes and snows back down onto the surface. The sublimation process itself consumes heat, acting like a natural refrigerant that helps keep Pluto’s surface extremely cold.
Pluto was reclassified as a dwarf planet in 2006 by the International Astronomical Union (IAU). This resulted from a formal definition requiring a planet to have “cleared the neighborhood” around its orbit. Pluto is located in the Kuiper Belt and shares its orbital path with many other objects, meaning it has not achieved gravitational dominance in its region. This classification means that while Pluto is extremely cold, its status as a dwarf planet removes it from the conversation of the coldest planet.
Beyond the Planets: The Solar System’s Absolute Coldest Regions
The search for the absolute coldest measured location in the solar system leads away from the distant planets and toward small, permanently shadowed regions. These spots are found in deep craters near the poles of airless bodies, such as the Moon and Mercury, where the sun’s light never reaches. The tilt of the Moon’s axis is slight, allowing the rims of polar craters to cast shadows that perpetually shield the crater floors.
In these permanently shadowed regions, temperatures can plummet far lower than on Pluto’s surface. Data from NASA’s Lunar Reconnaissance Orbiter measured temperatures within these lunar craters as low as -397°F (-238°C). Other measurements have recorded spots as cold as -414°F (-248°C) in craters like Hermite near the Moon’s north pole. Without an atmosphere to circulate heat and with no direct sunlight for billions of years, these areas radiate their meager heat into space, creating perfect “cold traps.” These small, nearby regions hold the record for the lowest temperatures yet measured in the solar system.