Astronomers and planetary scientists conduct extensive research in Antarctica. They operate telescopes at the south pole, launch instruments on balloons, and hunt for meteorites on the Antarctic ice. The balloon missions, launched in southern summer, take advantage of the 24-hour daylight to power solar cells and maintain a steady altitude without the need to drop ballast. They climb to about 130,000 feet, and can remain aloft for weeks or months. They follow circular wind currents that circle the continent, allowing the payload to drop back on the Antarctic ice at the end of a mission. Scientists from the United States and other countries conduct weeks-long searches for meteorites on the ice. Few terrestrial rocks are found atop the ice fields deep in Antarctica, so there's a good probability that any rocks on the ice fell from space.