Science & technology | Astrobiology

Icy moons with vast oceans are the latest candidates for alien life

A new mission to Jupiter will examine three of them

Citizen scientist Thomas Thomopoulos created this enhanced-color image using raw data from the JunoCam instrument. At the time the raw image was taken, the Juno spacecraft was about 44,000 miles (71,000 kilometers) above Jupiter's cloud tops, at a latitude of about 55 degrees south, and 15 times closer than Ganymede, which orbits about 666,000 miles (1.1 million kilometers) away from Jupiter.An observer at Jupiter's cloud tops within the oval shadow would experience a total eclipse of the Sun. Total eclipses are more common on Jupiter than Earth for several reasons. Jupiter has four major moons (Galilean satellites) that often pass between Jupiter and the Sun: in seven days, Ganymede transits once; Europa, twice; and Io, four times. And since Jupiter's moons orbit in a plane close to Jupiter's orbital plane, the moon shadows are often cast upon the planet.JunoCam captured this image from very close to Jupiter, making Ganymede's shadow appear especially large. Figure 1, created by citizen scientist Brian Swift using JunoCam data, illustrates the approximate geometry of the visible area, projected onto a globe of Jupiter.Image data: NASA/JPL-Caltech/SwRI/MSSS/Thomas ThomopoulosImage processing by Thomas Thomopoulos
Image: NASA/JPL-Caltech/SwRI/MSSS/Thoma

Astrobiology is a branch of science that, for now, lacks anything to actually study. Despite this lack of research subjects, however, the search for life beyond Earth has a few rules of thumb. The most important is “follow the water”. The unusual chemical properties of water make it vital for life on Earth. And, since the laws of chemistry are the same everywhere, it is not unreasonable to think that water may play the same role on other planets too.

This article appeared in the Science & technology section of the print edition under the headline “Needles in faraway haystacks”

Science & technology

April 8th 2023

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