ALMA maps Europa’s temperature

ALMA maps Europa’s temperature

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A terrestrial volcano is hotter than its surroundings. The same is true for geysers like the ones in Yellowstone National Park in the United States, or in the El Tatio geyser field in northern Chile. The reason: the interior of the Earth is hotter than its surface, and volcanoes and geysers are places where this internal heat escapes, thanks to geological activity.

What is true for the Earth is also true for Europa, one of the four largest moons of the giant planet Jupiter. Europa is about the size of our own moon. Because it is so far away from the sun, its surface is completely frozen – the temperature never rises above minus 160 degrees Celsius. But below the thick ice crust is a deep subsurface ocean of liquid water. Just like Earth, Europa’s interior is hotter than its surface.

Scientists believe that the icy surface of Europa is relatively young: between 20 and 180 million years old. A young surface suggests that there is still geological activity going on in Europa. If so, there may be places on the surface where internal heat escapes into space. There may even be ice volcanoes or geysers!

To find out which parts of the surface are warmer than average, astronomers have made the first temperature maps of Europa. Even very cold objects emit a tiny amount of infrared and sub-millimeter radiation. ALMA was able to detect this radiation, and to create a global temperature map of Europa’s surface.

The map is pretty crude. The smallest details that ALMA could distinguish are about 200 kilometers wide. Still, the map clearly shows that some parts of the surface are a bit warmer than average (‘a bit less cold’ would be a better description). Also, in the northern hemisphere of Europa, ALMA discovered a large area that is colder than its surroundings.

Astronomers will now be able to compare ALMA’s temperature map to detailed photos of Europa’s surface, made by the American Galileo space probe. Thus, they hope to find regions on Europa with enhanced geological activity. Future spacecraft might go there to look for ice volcanism or geysers.


Europa is one of the four large moons of Jupiter. The others are Io, Ganymede, and Callisto. The four moons were discovered in 1610 by Italian astronomer Galileo Galilei. Europa is a little bit smaller than our own moon. It is special because it has a very deep subsurface ocean of liquid water. In fact, there’s more water below the surface of Europa than in all the seas and oceans on Earth combined! Some scientists think that the ocean of Europa could harbor primitive micro-organisms.


The ALMA observations of Europa were carried out by Samantha Trumbo. Samantha is a PhD candidate in planetary sciences at the California Institute of Technology (Caltech) in Pasadena. She worked together with her thesis advisor Mike Brown (also at Caltech) and with Bryan Butler of the National Radio Astronomy Observatory. ALMA observed Europa four times, from different directions, enabling Samantha and her colleagues to create a global temperature map. The results have been published in The Astrophysical Journal, a professional magazine of astronomy.