Through the history of space exploration so
far, we’ve debated where the earth’s atmosphere ends, and space begins. And your surprise
for the day is that according to newly unearthed observations, our atmosphere is way bigger
than we ever thought. Like it goes past the moon.
We’ve mostly defined space as the vast expanse of the rest of the universe that exists past
the Kármán Line, which exists roughly 100 kilometers above mean sea level. Now according
to Federation Aeronautique Internationale—the organization officially in charge of determining
these kinds of rules—after the Kármán line, you are in space.
The reasoning behind this is after 100 kilometers, the earth’s atmosphere becomes too thin
for a conventional aeronautic vehicle like an airplane to stay in flight without reaching
orbital velocity—so you have to switch to more specialized astronautic vehicles.
But if you thought this was gonna be simple—it’s not. Even though the FAI’s Karman line designation
is commonly recognized, there’s actually no official international consensus over where
space technically begins. Some astrophysicists say it should actually be 80 kilometers above
the mean sea level because of the way that orbital momentum acts on satellite objects.
NASA and the U.S. air force also define space as starting about 80 kilometers above the
Earth’s surface, and those who cross that line officially become astronauts.
OK, so the definition of space is up in the air, but what even is the atmosphere? Yes,
it’s the bubble of gases that shield and insulate the earth from the aggressive radiation
of the sun and the cold dark depths of space, but like most complex things, it’s got layers:
The troposphere, with all our fun weather and necessary gases for breathing and surviving;
The stratosphere, where commercial airlines fly when possible because there’s usually
less turbulence; the mesosphere, where most meteors burn up and the highest layer at which
clouds can form; Then comes the thermosphere, which is where that tricky Kármán line
lives—this is where astronauts begin to experience weightlessness, and is where the
ISS orbits! That means that technically, our most commonly defined line of where space
begins is still in Earth’s atmosphere. And then finally, there’s the exosphere,
the final layer between us and outer space, made up of super spaced out hydrogen and helium
atoms slowly dissipating out to nothing up to 200,000 kilometers away from earth’s
surface...or so we thought. We actually haven’t previously really known where the exosphere
ends and outer space begins, we just know that those extremely sparse gases gradually
fade out into a vacuum. But a team of astronomers has recently dropped
a total bombshell. When the cloud of gases in the exosphere reflects the Sun’s UV light,
it creates a luminosity, a glow that we can see, called the geocorona. These new observations
of the geocorona indicate that the exosphere may extend up to 630,000 kilometers away from
earth—a distance that includes the moon! So technically, the moon is in the Earth’s
atmosphere! This realization is thanks to an instrument
called the Solar Wind Anisotropies Instrument, or SWAN. SWAN was able to measure and analyze
the full extent of the geocorona, making us think about our atmosphere in a whole new
way. See, sunlight interacts with the hydrogen
atoms of the exosphere at a wavelength called Lyman-alpha radiation, which is something
astrophysicists can measure when looking at cosmological structures in deep space. Observing
Lyman alpha radiation can tell us about the distribution of matter in space, and help
us think about how the universe expanded. It’s also a wavelength that’s absorbed
by the inner layers of our atmosphere, so we can’t see it from Earth. But from SWAN’s
position in space, it was able to see and measure both--and it extended far beyond what
we were expecting. So while this discovery is remarkable in many
ways, not the least of which is that technically no one has ever left earth’s atmosphere—it
won’t change space travel for us in most practical ways. It’s far more important
for informing the future of our observations of space.
The new results also show that sunlight compresses the hydrogen atoms of the exosphere, producing
pockets of denser geocorona, with the corresponding Lyman alpha radiation, depending on the sun’s
position. So space telescopes that make measurements from within the confines of the exosphere
will need to take a new Lyman-alpha baseline level--and the bunching of the geocorona--into
account when observing the night sky...hopefully letting us peer further, and with greater
accuracy. One last amazing thing about this piece of
information is that this isn’t even new research—these observations were made by
SWAN in the late 90’s, and were only JUST dug out of the archives for further analysis!!
What other startling discoveries could be lurking in a cupboard somewhere? Make sure
to subscribe for all your space updates, like this video here. Thanks so much for watching
and I’ll see you next time on Seeker.
