Hot hydrogen atoms in Earth's upper atmosphere found

New York: A team of University of Illinois researchers has discovered the existence of hot atomic hydrogen (H) atoms in an upper layer of Earth's atmosphere known as thermosphere.

This finding significantly changes current understanding of the H distribution and its interaction with other atmospheric constituents.

Because H atoms are very light, they can easily overcome a planet's gravitational force and permanently escape into interplanetary space.

The ongoing atmospheric escape of H atoms is one reason why Earth's sister planet, Mars, has lost the majority of its water.

In addition, H atoms play a critical role in the physics governing the Earth's upper atmosphere and also serve as an important shield for satellites in low-earth orbit against the harsh space environment.

"Hot H atoms had been theorized to exist at very high altitudes, above several thousand km, but our discovery that they exist as low as 250 km was truly surprising," said Lara Waldrop, assistant professor of electrical and computer engineering and principle investigator of the project.

The result suggests that current atmospheric models are missing some key physics that impacts many different studies, ranging from atmospheric escape to the thermal structure of the upper atmosphere.

The results also show that the presence of such hot H atoms in the thermosphere significantly affects the distribution of the H atoms throughout the entire atmosphere.

The origin of such hot H atoms, previously thought not to be able to exist in the thermosphere, is still a mystery.

"We know that there must be a source of hot H atoms, either in the local thermosphere or in more distant layers of the atmosphere, but we do not have a solid answer yet," said Waldrop in a paper published in the journal Nature Communications.