A new NASA mission will capture images of Earth\u2019s invisible \u201chalo,\u201d the faint light given off by our planet\u2019s outermost atmospheric layer, the exosphere, as it morphs and changes in response to the Sun. Understanding the physics of the exosphere is a key step toward forecasting dangerous conditions in near-Earth space, a requirement for protecting Artemis astronauts traveling through the region on the way to the Moon or on future trips to Mars. The Carruthers Geocorona Observatory will launch from NASA\u2019s Kennedy Space Center in Florida no earlier than Tuesday, Sept. 23.<\/p>\n
In the early 1970s, scientists could only speculate about how far Earth\u2019s atmosphere extended into space. The mystery was rooted in the exosphere, our atmosphere\u2019s outermost layer, which begins some 300 miles up. Theorists conceived of it as a cloud of hydrogen atoms \u2014 the lightest element in existence \u2014 that had risen so high the atoms were actively escaping into space.<\/p>\n
But the exosphere reveals itself only via a faint \u201chalo\u201d of ultraviolet light known as the geocorona. Pioneering scientist and engineer Dr. George Carruthers<\/a> set himself the task of seeing it. After launching a few prototypes on test rockets, he developed an ultraviolet camera ready for a one-way trip to space.<\/p>\n In April 1972, Apollo 16 astronauts placed Carruthers\u2019 camera on the Moon\u2019s Descartes Highlands, and humanity got its first glimpse of Earth\u2019s geocorona. The images it produced were as stunning for what they captured as they were for what they didn\u2019t.<\/p>\n \u201cThe camera wasn\u2019t far enough away, being at the Moon, to get the entire field of view,\u201d said Lara Waldrop, principal investigator for the Carruthers Geocorona Observatory. \u201cAnd that was really shocking \u2014 that this light, fluffy cloud of hydrogen around the Earth could extend that far from the surface.\u201d Waldrop leads the mission from the University of Illinois Urbana-Champaign, where George Carruthers was an alumnus.<\/p>\n Today, the exosphere is thought to stretch at least halfway to the Moon. But the reasons for studying go beyond curiosity about its size. \u201cWe\u2019ve never had a mission before that was dedicated to making exospheric observations,\u201d said Alex Glocer, the Carruthers mission scientist at NASA\u2019s Goddard Space Flight Center in Greenbelt, Maryland. \u201cIt\u2019s really exciting that we\u2019re going to get these measurements for the first time.\u201d<\/p>\n<\/p>\n
As solar eruptions reach Earth, they hit the exosphere first, setting off a chain of reactions that sometimes culminate in dangerous space weather storms. Understanding the exosphere\u2019s response is important to predicting and mitigating the effects of these storms. In addition, hydrogen \u2014 one of the atomic building blocks of water, or H2O \u2014 escapes through the exosphere. Mapping that escape process will shed light on why Earth retains water while other planets don\u2019t, helping us find exoplanets, or planets outside our solar system, that might do the same.
NASA\u2019s Carruthers Geocorona Observatory<\/a>, named in honor of George Carruthers, is designed to capture the first continuous movies of Earth\u2019s exosphere, revealing its full expanse and internal dynamics.<\/p>\n