Editorials

PASADENA — After years of garnering less attention than its sexier Jovian sisters, the crater-covered moon Callisto is getting closer attention than ever this week from NASA. 

But alas — it turns out the National Aeronautics and Space Administration is just using Callisto to get closer to that fireball of a moon, Io. 

The Galileo spacecraft, on its third and final tour of Jupiter and its satellites, will make its closest pass at Callisto yet, coming within just 76 miles of the Mercury-sized moon early Friday morning. 

NASA is using Callisto’s gravity to better position Galileo for passes at Io in August and October to determine whether the intensely volcanic moon creates its own magnetic field. 

“The main reason we’re flying so close to Callisto is to set up flybys of Io,” said Eilene Theilig, Galileo project manager at NASA’s Jet Propulsion Laboratory. 

Callisto is “sort of the ugly duckling of the moons,” said Galileo project scientist Torrence Johnson. Io’s volcanoes, evidence of water close to the surface of Europa and two-toned Ganymede have all generated more scientific excitement. 

But Callisto, which bears craters billions of years old, still has a thing or two to teach scientists.  

NASA will use the flyby to examine small craters to follow up on earlier imaging of the moon that showed fewer craters than researchers expected. 

Galileo also will examine Jupiter this week, mapping its clouds and searching in particular for dark clouds known as “brown barges,” which haven’t been seen since NASA’s Voyager spacecraft flew by in 1979. 

In August, Galileo will pass within about 220 miles of Io to see whether a volcanic plume spotted five months ago is still active. 

Galileo was originally scheduled to end its mission four years ago, but it has continued to bring back useful data despite being bombarded with more than three times as much radiation as it was designed to withstand. NASA plans on sending Galileo on three more passes of Io and one of the small inner moon Amalthea before the probe plunges into Jupiter’s atmosphere in 2003.