Geological features don't usually grow overnight, but the Artemis Corona, an almost perfectly circular bump on Venus the size of Alaska, just got five times bigger. Researchers creating highly detailed new Venusian maps noticed a ring of ridges beyond the originally assumed diameter of Artemis, suggesting that the previously described bulge (inset) was just the tip of a gigantic swelling of land (white circle). The scientists now believe Artemis to be the largest such protuberance in the solar system, with a diameter of 13,000 kilometers, greater than the distance between Los Angeles and Sydney. Given its size and shape, the researchers—who report  their findings this month in Geology—suggest that an enormous spout of lava rising from deep inside the planet, called a mantle plume, is the only known process that could have formed Artemis. Similar activity in Earth's mantle produced the 2500-kilometer wide Mongolian-Manchurian steppe .