Where Earth’s atmosphere merges into outer space, there lingers a cloud of hydrogen atoms called the geocorona that extends beyond the moon. Its full extent was recently revealed in old data taken by the SOHO spacecraft. ESA
Three-quarters of Earth’s atmosphere sits within the bottom 6.8 miles (11 km). At the space station’s altitude of 250 miles (400 km), there’s next-to-no air. But the faint breath of Earth continues into space as the geocorona or exosphere, the outermost layer of the atmosphere. Older estimates put its size at around 1.5 Earth radii or 12,000 miles out in space. But a recent discovery based on observations by the Solar and Heliospheric Observatory (SOHO) shows that it goes much, much further — all the way to the moon and beyond!
The Earth and its hydrogen envelope, or geocorona, as seen from the moon. This ultraviolet picture was taken in 1972 by John Young, Apollo 16 commander. NASA
Scientists weren’t aware of how big it was until they took a look back at older observations made by the orbiting solar observatory. One of the spacecraft’s instruments picked up the signature of hydrogen up to 391,000 miles (630,000 km) above Earth’s surface or 50 ...