Cold spot (astronomy)
A cold spot is a region of anomalously low nighttime surface temperature surrounding a young impact crater on an airless planetary surface. Hypervelocity impacts displace and rarefy material, and ejecta falls to form a “fluffy” surface layer that is less densely packed than surrounding regolith. The resulting region of low surface density has a lower thermal inertia than other material and cools faster after sunset.
On the Moon's surface, these ray-like spots extend 10 to 100 times the radius of the impact crater and are 2–10 Kelvin cooler than the surrounding lunar surface. Depending on size, cold spots fade to background levels after roughly 0.5–1 million years as successive impacts and seismic waves recompact the material. They cover over 1% of the lunar surface.
The phenomenon was first observed by Apollo 17, which carried an infrared radiometer. Cold spots were systematically characterized and mapped by planetary scientist Joshua Bandfield and collaborators in 2011 using data from the Diviner Lunar Radiometer Experiment (DLRE) on NASA's Lunar Reconnaissance Orbiter. Over 2,200 cold spots have been identified on the lunar surface between the latitudes 50° N and 50° S, with source craters ranging from 43 meters to 2.3 kilometers in diameter.
Cold spots have been found only on the Moon but are predicted to be present on Mercury and other airless bodies.