High above the ice in Antarctica, a group of enormous balloons was quietly tracking a phenomenon that could not be seen from the ground. In January 2013, Nasa's BARREL mission sent 20 balloons drifting through the polar winds, carrying instruments designed to detect faint X-rays produced when energetic particles entered Earth's upper atmosphere.

In 2013, balloons were launched by NASA near the North and South poles to study X-rays in Earths atmosphere as part of the Balloon Array for Radiation-belt Relativistic Electron…

High above the ice in Antarctica, a group of enormous balloons was quietly tracking a phenomenon that could not be seen from the ground. In January 2013, Nasa's BARREL mission…