Night temperatures on Jupiter鈥檚 moon Io appear to be the same at the equator as they are at the poles. The temperature map, from NASA鈥檚 Galileo spacecraft, has surprised and puzzled scientists.
鈥淲e鈥檝e got a mystery image here,鈥� says Dave Rothery at the UK鈥檚 Open University.
On Io, as on Earth, regions near the equator get more direct sunlight during the day than the polar regions. Since the poles receive less solar energy, they don鈥檛 retain as much warmth at night and should be relatively cool. Unlike Earth, Io has no atmosphere to help with the heat retention.
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The temperature map comes from observations by Galileo鈥檚 photopolarimeter-radiometer (PPR) instrument during its 27th orbit of Jupiter, in February 2000.
Several of Io鈥檚 powerful volcanoes are shown as warm orange and yellow spots on the image (L-K is Lei-Kung Fluctus, L is Loki, Pe is Pele, M is Marduk and Pi is Pillan). Their temperatures can exceed 1200 掳C. The coldest areas, shown in blues and purples, get down to minus 180 掳C.
One possible explanation for the warm poles is that excess volcanic heat radiates there. Or the surface material near the pole may hold its heat better than the surface closer to the equator.
A third effect might be that the angle at which Io was viewed highlights at high latitudes those slopes which received more sunlight during the day.
Researchers hope that subsequent PPR observations of the polar regions of Io will clear up the mystery.