True colour Io mosaic from the Galileo mission


Image and text courtesy APOD, credit: Galileo Project, JPL, NASA

The strangest moon in the Solar System is bright yellow. This picture, an attempt to show how Io would appear in the “true colors” perceptible to the average human eye, was taken in 1999 July by the Galileo spacecraft that orbited Jupiter from 1995 to 2003. Io’s colors derive from sulphur and molten silicate rock. The unusual surface of Io is kept very young by its system of active volcanoes. The intense tidal gravity of Jupiter stretches Io and damps wobbles caused by Jupiter’s other Galilean moons. The resulting friction greatly heats Io’s interior, causing molten rock to explode through the surface. Io’s volcanoes are so active that they are effectively turning the whole moon inside out. Some of Io‘s volcanic lava is so hot it glows in the dark.

Update: The exoplanet Kepler-186f orbiting an early M dwarf: Emeline Bolmont et al., arXiv preprint pdf, has now been confirmed by the Gemini and Keck observatories, and is published (Elisa V. Quintana et al.., Science, 2014 DOI: 10.1126/science.1249403). A 1D model simulation given by Bolmont requires an atmosphere with 0.5-5 bars of carbon dioxide (depending on the amount of nitrogen also present) to raise the surface temperature above the freezing point of water, and the planet has a 130 day orbit around the M1 dwarf. Orbiting at the outer edge of the habitable zone of the star, it receives just one third of the energy at its surface than the Earth does from the Sun.


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