Astronomy Picture of the Day . Solar Flares Cause Sun Quakes . ... Water World . ... Water (Dihydrogen Oxide, H2O) is a truly remarkable chemical compound, fundamental to life on Earth. Earth is the only planet in the Solar System where the present surface temperature and pressure allow the three forms of water, solid (ice), liquid (ocean), and gas (water vapor condensing in clouds) to exist simultaneously. An Extrasolar Planet? ... Isn't the Sun round? ... M83: A Barred Spiral Galaxy . ...