Earth's atmosphere stretches out to the moon - and beyond

February 20, 2019 by Claudia Mignone, American Geophysical Union

The gaseous layer that wraps around Earth reaches up to 630,000 kilometers away, or 50 times the diameter of our planet, according to a new study based on observations by the ESA/NASA Solar and Heliospheric Observatory, SOHO, and published in AGU's Journal of Geophysical Research: Space Physics.

"The moon flies through Earth's atmosphere," says Igor Baliukin of Russia's Space Research Institute, lead author of the paper presenting the results. "We were not aware of it until we dusted off observations made over two decades ago by the SOHO spacecraft."

Where our atmosphere merges into outer space, there is a cloud of hydrogen atoms called the geocorona. One of the spacecraft instruments, SWAN, used its sensitive sensors to trace the hydrogen signature and precisely detect how far the very outskirts of the geocorona are. These observations could be done only at certain times of the year, when the Earth and its geocorona came into view for SWAN.

For planets with hydrogen in their exospheres, water vapor is often seen closer to their surface. That is the case for Earth, Mars and Venus.

Read more at: https://phys.org/news/2019-02-earth-atmosphere-moon.html#jCp