The Earth’s atmosphere is described as a fragile coat wrapping around the planet, comparable in scale to an apple’s skin protecting the fruit. For more than half a century, even before the Apollo 16 mission captured the first ultraviolet images of Earth, researchers knew that the outermost atmospheric layer — the geocorona — extends far beyond the denser, surface-level air that we breathe.
Now, a new study from Space Physics redefines the boundaries of our planet, based on overlooked data collected at the end of the last millennium. The report concludes that the edges of the atmosphere actually extend more than 391,000 miles from the planet’s surface, about twice as far as our moon. SCIENCE of planets space science universe science
This doesn’t mean you can go moonwalking without a spacesuit, said Jean-Loup Bertaux, a study coauthor and planetologist. The hydrogen molecules that make up the outer atmosphere are so sparse that this region is still considered a vacuum. Any spacecraft traveling through it wouldn’t notice a thing or be slowed by drag. SCIENCE of planets space science universe science
It does mean, however, that humankind has yet to leave the Earth’s atmosphere. The moon, the farthest point ever reached by astronauts, orbits well within the geocorona. SCIENCE of planets space science universe science
All of this challenges the way we see our planet’s borders. NASA considers a space traveler to be an astronaut when they climb higher than 50 miles above the planet’s surface. The Fédération Aéronautique Internationale, which judges world records for aeronautic travel, uses the Kármán line — set at 100 kilometers above sea level — to denote the “edge of space.” SCIENCE of planets space science universe science
With this new knowledge, high-powered telescopes on the moon or in Earth’s orbit will also need to account for — and filter out — the geocorona’s bright ultraviolet light when looking out into the universe. This would make it easier to scan the cosmos. SCIENCE of planets space science universe science
And if those telescopes spot planets out in the galaxy with the same halo that surrounds our Earth, that light could someday be used to locate habitable planets far from our own interstellar front door. SCIENCE of planets space science universe science