The Biggest Moon Discoveries of the Last Decade


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[♪ INTRO]
It’s been 50 years since humans last walked
on the Moon,
but that doesn’t mean we’ve stopped exploring
our closest neighbor.
Countries from all over the world have sent
robotic missions to study it,
but none has been as important, or as successful,
as NASA’s Lunar Reconnaissance Orbiter.
NASA launched the mission, often called LRO,
in 2009 as part of its Vision for Space Exploration program.
This was a long-term plan designed
to guide the U.S. space program
after the loss of the space shuttle Columbia.
The goal with LRO wasn’t just to do science,
but to pave the way for a new era of human exploration.
And while we have yet to send people back to the Moon,
we can definitely say the LRO has succeeded.
The things it’s teaching us about our closest neighbor
are transforming the way we think about the Moon,
and the information we’re learning from
it will make it much easier for future astronauts.
So, in honor of all it’s done so far, and
to celebrate its 10th birthday,
let’s look back at three of LRO’s biggest
accomplishments.
For one, this mission showed us that the Moon
is not as dry as we used to think.
When researchers examined lunar rocks brought
back by the Apollo astronauts,
they turned out to be almost completely waterless;
way drier than rocks found on Earth.
That painted a picture of a pretty arid Moon.
But some scientists suspected that frozen water
might be hiding out in the Moon’s deepest
craters, which the Apollo program didn’t visit.
Those spots are so deep that they’ve never
seen sunlight,
and can have surface temperatures colder than
Pluto, just 35°C above absolute zero.
Temperatures like that are too cold for water
to sublimate away,
and they make it possible for ice to survive
in the vacuum of space.
But just because water could exist on the
Moon didn’t mean it had to be there.
To find out more, LRO’s companion mission,
called LCROSS, took one for the team.
It sent part of its rocket to smash into the
Moon’s Cabeus crater,
sending a plume of surface debris into space.
Then, the LCROSS spacecraft and LRO studied
the light from this material
as it passed in front of the Sun, and researchers
later found that
the plume was full of grains
of mostly-pure water ice.
They pronounced this crater “wetter than
the Sahara.”
That might not sound very impressive, but
it showed us that ice can accumulate on the Moon,
and that this supposedly-arid place has pockets
full of frozen water.
Someday, that water could be used to help
astronauts on the Moon’s surface.
But even if not, it’s still pretty amazing
that it’s up there.
That’s not the only thing LRO has uncovered
in hidden ice, either.
In 2016, scientists published another big discovery
made by the orbiter: the Moon’s ancient poles.
Besides finding ice at today’s poles,
LRO found ice deposits offset by about 200
kilometers in opposite directions.
If you draw a line between them, it passes
directly through the Moon’s center.
Researchers interpreted this arrangement as
evidence of the Moon’s old poles,
meaning the Moon used to spin on a different axis.
Which isn’t unheard of in the solar system,
but still feels downright weird to think about.
Models show that that axis shifted around
3 billion years ago,
most likely as mass moved around deep below
the surface.
This process was slow.
The poles drifted only around 2 centimeters
every century,
but that was enough to knock the Moon off
kilter by about 5°,
like if Earth’s axis shifted from the South
Pole to Australia.
As sunlight leaked into the once-shady areas,
some of that old polar ice probably evaporated,
but the rest traced out the path of the moving
axis for us to uncover billions of years later.
Besides being cool, this finding is also significant
because
it helps us understand when the inside of
the Moon was molten,
which is important for studying how the Moon
changed and evolved.
I mean, it doesn’t give us a very specific
estimate, but you have to start somewhere!
Finally, although LRO is meant to study the
Moon,
it’s actually taught us a lot about the
entire solar system.
For instance, it took enough images for scientists
to create a detailed,
billion-year-long timeline of large asteroid
impacts on the Moon.
And this January, scientists reported that
that timeline revealed something strange:
Asteroid collisions seem to have more than
doubled around 290 million years ago.
While that’s interesting by itself, that
also tells us something surprising about Earth.
Scientists have known for a while that Earth has
surprisingly few craters older than 300 million years,
but they’d always assumed that the craters
had just eroded away.
Now, LRO is telling us that these aren’t
just gaps in the record,
there were simply fewer impacts back then
than the period that followed.
Scientists still don’t know exactly what
happened 290 million years ago,
but one idea is the sudden bombardment might
point to
large collisions in the asteroid belt between
Jupiter and Mars.
Whatever it was, though, the scars on the
Moon point to some major event in the distant past.
And figuring out what it was would help us
continue to understand
how the solar system has changed over its
lifetime.
Also, on a much broader note, cratering rates
on the Moon are also used
to determine the ages of surfaces all around
the solar system.
Like, when scientists first saw Pluto’s
smooth surface,
they assumed it was young because it doesn’t
have as many craters as the old lunar surface.
So the more we understand about the Moon’s
craters,
the more we can infer about all the other
objects out there.
Of course, even though LRO has taught us so
many specific things over the last decade,
it isn’t valuable just because of those
discoveries.
LRO is especially important because it lives
around the Moon.
That means that, if scientists find something
interesting,
they can ask questions and get answers without
having to wait for a new mission,
which is pretty unusual in planetary science.
Also, as much as space exploration is always
pushing new horizons,
LRO has shown us that there are still endless
things to explore right here in our neighborhood.
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[♪ OUTRO]

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