UFO spotted over Antarctica?

While a definitive explanation has not been found, several elements suggest a prosaic answer.

The supposed UFO appears more or less directly over the research station; it also appears to be nearly perfectly round and about the right size for a balloon. Neumayer-Station III, a scientific research station, carries out tests and experiments in a wide variety of areas, including geophysics, meteorology and atmospheric chemistry.

Weather balloons are used extensively to study and sample the atmosphere at different times and altitudes above Antarctica.