There's an invisible halo surrounding Earth, generated by faint light given off by our planet's outermost layer as it interacts with the Sun.
Understanding more about this outer layer, known as the exosphere, could help keep future astronauts safe during journeys to the Moon or even Mars.
More about Earth
A new mission from NASA is about to launch to study and photograph this strange quirk of the Earth-Sun system.
The Carruthers Geocorona Observatory launched on 24 September 2025 from NASA's Kennedy Space Center.
Seeing the unseeable
How far does Earth's atmosphere stretch out into space?
The exosphere, our atmosphere’s outermost layer, begins about 480km (300 miles) up.
It's seen only as a faint helo of ultraviolet light, called the 'geocorona'. And yes, you guessed it, humans can't naturally see ultraviolet light with our own eyes.
A scientist and engineer named Dr. George Carruthers decided to take a look at it in the early 1970s.
Carutthers developed an ultraviolet camera that was placed on the Moon in April 1972 by Apollo 16 astronauts, giving humanity its first glimpse of the geocorona.
"The camera wasn’t far enough away, being at the Moon, to get the entire field of view," says Lara Waldrop, principal investigator for the Carruthers Geocorona Observatory.
"And that was really shocking – that this light, fluffy cloud of hydrogen around the Earth could extend that far from the surface."
Now, scientists think the exosphere could stretch halfway to the Moon – at least.
We need to learn more
There are two main reasons we need to learn more about the geocorona, and those reasons are protecting astronauts and learning more about distant planets.
That's because as eruptions from the Sun hit our planet, they smash into the exosphere first.
That sets off a chain reaction of events that can result in dangerous space weather, which is the term given to the effects of the Sun's powerful influence across the Solar System.
Strong Solar Storms can be dangerous for astronauts working in Earth orbit, but even more so for astronauts making the journey to the Moon, or even Mars.
Secondly, understanding more about how solar storms cause hydrogen to escape through our exosphere could help scientists learn more about why Earth retains water while other planets don't.
That could help us find and study planets beyond our Solar System – known as exoplanets – where the same thing happens.
NASA says the Carruthers Geocorona Observatory, named after George Carruthers, could capture the first continuous videos of Earth’s exosphere, revealing how big it is and how it works.
"We’ve never had a mission before that was dedicated to making exospheric observations," says Alex Glocer, Carruthers mission scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
"It’s really exciting that we’re going to get these measurements for the first time."
Launching the mission
The Carruthers spacecraft launched on a SpaceX Falcon 9 rocket along with NASA’s IMAP (Interstellar Mapping and Acceleration Probe) spacecraft and the National Oceanic and Atmospheric Administration’s SWFO-L1 (Space Weather Follow On – Lagrange 1) space weather satellite.
All three will eventually reach Lagrange point 1, a gravitationally-stable location between Earth and the Sun.
Carruthers’ two-year science phase will begin in March 2026, capturing images of the exosphere using two ultraviolet cameras.
"The near-field imager lets you zoom up really close to see how the exosphere is varying close to the planet," Glocer says.
"The wide-field imager lets you see the full scope and expanse of the exosphere, and how it’s changing far away from the Earth’s surface."
The cameras will track hydrogen atoms as they move through the exosphere and out into space.
"Understanding how that works at Earth will greatly inform our understanding of exoplanets and how quickly their atmospheres can escape," Waldrop says.
In other words, by learning more about how Earth's atmosphere works, we may be able to learn more about how to search for other Earth-like planets – even life – elsewhere in the Universe.
