Telescopes like ALMA can detect the thermal ‘glow’ emitted even by cold objects like Europa, hence providing important clues about the hidden processes taking place there.

An ALMA image of Jupiter’s moon Europa, in which ALMA has been able to map thermal variations across its entire surface. For comparison, a Hubble image of Jupiter is shown in the background.

Credit: ALMA (ESO/NAOJ/NRAO), S. Trumbo et al.; NRAO/AUI NSF, S. Dagnello; NASA/Hubble

Unlike optical telescopes, which can only detect sunlight reflected from planetary bodies, millimetre-wave radio telescopes like ALMA can detect the thermal ‘glow’ that is naturally emitted even by relatively cold objects in our Solar System, including comets, asteroids and moons. At its hottest point, Europa’s surface temperature never exceeds 160 degrees below zero. This is cold, but just the right temperature to emit infrared radiation in different amounts and frequencies depending on whether it is emitted from higher or lower temperature regions – radiation that ALMA can capture and analyse with unprecedented resolution, giving us these unique results. Equally unique is the resulting opportunity to understand and study the surface of this moon with so many mysteries.

A young and enigmatic surface

As Europa is an oceanic world with potential geological activity, its surface temperatures are of great interest as they may provide important clues to the nature of the processes taking place. Indeed, observations suggest that beneath Europa’s thin layer of ice lies an ocean of salty water in contact with a rocky core. Europa also appears to have a relatively young surface, with an age of between 20 and 180 million years, which would indicate the presence of thermal or geological processes that have not yet been identified.


“ALMA Thermal Observations of Europa”, S. Trumbo et al. The Astrophysical Journal.

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