The largest object in the Main Asteroid Belt between Mars and Jupiter is Ceres, an odd, water-rich proto-planet roughly the size of Texas (590 miles in diameter). Scientists have long puzzled about the origin of the bright white spot near the equator, which we recently learned is two bright spots. We'll soon know a lot more about it as NASA's Dawn spacecraft has nearly reached Ceres. It's already captured shots of the planet (above) and will soon go into a polar orbit at 13,500 km (8,300 miles) before descending to a survey altitude of 4,430 km (2,800 miles). Eventually, it'll drop as low as 1,480km (950 miles) to capture high resolution mapping data and 3D images of Ceres. Once the mission is over it'll remain the asteroid's orbiting buddy forever.
Its first approach to Ceres will be beamed live from the Slooh community observatory starting at 1PM ET today. Unfortunately, Dawn will take fewer photos during this phase than planned due to the failure of two reaction wheels. Given that it's already visited Mars and Vesta, another dwarf planet in the region, a few glitches are understandable. Despite the issues, we're expecting the same spectacularly detailed images we saw of Vesta. That should help clear up theories as to what the white spots are, which have ranged from ice-gorged craters to cryo-volcanoes. Not to be biased, but we're definitely pulling for the volcanoes.