AMALTHEA, one of Jupiter’s inner moons, may be a loose jumble of pieces rather than a solid object.
Planetary scientists already knew the volume of the 270-kilometre potato-shaped moon, but only measured its mass when NASA’s Galileo probe made a close pass on 5 November. The results show that the moon’s density is close to that of water ice, John Anderson of NASA’s Jet Propulsion Laboratory told the American Geophysical Union last week. The surface appears to be made of dense rock, so the low average density means the moon may be more than 50 per cent empty space, says…
