Thanks to Masterworks for sponsoring today’s video.
The Moon is our closest celestial neighbour. It’s the brightest object in the night sky,
an unusually large natural satellite for a planet of our size, and so close that its gravitational
pull slightly lengthens our day. Thanks to this proximity, we’ve been able to observe, photograph,
and even visit it. We know more about the Moon today than we do about any other celestial body
in the solar system – apart from Earth. And yet, there are things about it that remain a complete
mystery. Thanks to high-definition photographs captured by the Lunar Reconnaissance Orbiter, some
of these mysteries are finally coming to light. What can we learn from these incredible images?
And what amazing discoveries lie just around the corner?
I’m Alex McColgan and you are watching Astrum. Join with me today and you will see some of the
most recent, spectacular and puzzling images of the Moon, captured in breath-taking detail by
the Lunar Reconnaissance Orbiter. The LRO has been scanning the Moon’s surface since 2009.
It’s equipped with a powerful camera, capable of taking high-definition photos, which it sends to
NASA’s Planetary Data System. The LRO can send up to 155 gigabytes of data per day,
or 55 terabytes per year. By comparison, New Horizons took a full two years to transmit the
data from its one Pluto flyby. Although the LRO was launched over a decade ago,
it’s still operational, and we are constantly learning new things about the lunar surface
thanks to its high-powered camera and topographic mapping capabilities.
Let’s take a look at one of these images. At first glance, it may seem unremarkable,
but a deeper look tells a different story. See those two large, round depressions? Those are
impact craters, much like countless others that blanket the lunar surface.
But if we zoom out, we see that these craters are located on an unusual domelike structure. This is
Mons Gruithuisen Gamma. Look how the western side of the dome appears lighter where the Sun’s light
is reflecting off its steep slope. By contrast, the western sides of the craters are plunged
into shadow due to their low elevation. Shadows on the moon are so dark compared to Earth due to the
absence of Rayleigh scattering in an atmosphere. The Moon has no atmosphere, so the only light that
reaches shadowy regions are reflections from the lunar surface itself, which isn’t actually that
reflective. It is generally very dark, with an average albedo of 0.12, about as dark as wet soil.
Directly to the dome’s east is a dark shadow cast by the dome itself,
and it gives you a sense of how tall it is. The dome is towering, with a slope of up to 20 degrees
and rising 1500 meters above the lunar surface. With a diameter of 20 kilometres, it’s equivalent
to the metro area of a midsize city. That’s pretty massive! Zooming out further, we see that the dome
is surrounded by darker and much flatter terrain. This plain, or mare, is the result of basaltic
lava flows that flooded the topographic lows around 4 billion years ago, resulting in the
even surface you see now. Think of it like ice cream dripping into the crevices of a wafer cone.
Zooming out further still, we see a second dome located to the southeast of Mons Gruithuisen
Gamma. This is Mons Gruithuisen Delta, and it’s even bigger than its cousin,
towering 1800 meters above the surrounding surface and spanning 27 kilometres in diameter.
The dark basalt plain that surrounds both domes is part of a vast mare known as Oceanus Procellarum,
or “Ocean of Storms,” which covers a full 10.5% of the lunar surface.
I don’t know about you, but I think “ocean” is a fitting word. The domes look a bit like islands!
It is believed that the Gruithuisen Domes, like the Oceanus Procellarum, were formed
by ancient lava flows. But why did they leave these unusual structures? Believe it or not,
there may be clues here on Earth. This is Mount Saint Helens, an active stratovolcano located
in America’s Pacific Northwest. Maybe you can tell where I’m going with this. As you can see,
it’s shaped a bit like a dome. Stratovolcanoes like this one
are the result of pyroclastic flows of silica-rich materials like rhyolite, dacite or andesite.
Once expelled from the Earth’s crust, these high viscosity lavas move slowly as they cool,
hardening into domelike or conical formations over time. We suspect that the Gruithuisen Domes,
like terrestrial stratovolcanoes, are made of highly silicic material,
and recent thermal measurements taken by the LRO’s Diviner instrument support this theory,
suggesting that the domes are compositionally different from their surrounding plain.
So, unlike the Moon’s basalt lavas, which settled into smooth, low-lying surfaces,
these more viscous, silica-rich lavas extruded slowly, like thick molasses,
eventually cooling and leaving the massive domes you see now. But here's where it gets strange.
On Earth, stratovolcanoes like Mount Saint Helens are a unique product of water and plate tectonics.
At the convergence of two tectonic plates, a subduction zone can occur
where colder and denser material from an oceanic plate is thrust under the less dense plate and
back into the Earth’s blazing hot mantle. The remelted material results in silica-rich magmas
like rhyolite or dacite, which then rise. But unlike here on Earth, neither liquid water nor
plate tectonics are present on the Moon. So how did these silica-rich magmas form?
We’re not sure! One explanation suggests that when lunar magma had nearly cooled and crystalized,
it left a residual liquid that could have been extremely rich in silica.
The problem, however, is that this process, known as fractional crystallization, would produce only
small quantities of silicic material, which wouldn’t be nearly enough to explain a massive
27-kilometre goliath like Mons Gruithuisen Delta.
A second model suggests that silicic materials formed when basalt magma rose
upward, causing rocks on the lunar surface to partially melt and form rhyolites and dacites.
If this were indeed the case, then the Gruithuisen Domes should be nearly the same
age as the surrounding basalt plain. We don’t know if this is true yet, but future research
could shed light on both the chronology and composition of these mysterious structures.
To me, the most exciting part is that we may be just a few years away from getting an
answer. NASA plans to send a Commercial Lunar Payload Services rover to this region in 2025.
This mission will explore the Moon’s surface and collect rock samples that should shed light,
not just on the mysterious Gruithuisen Domes, but on lunar volcanism in general.
And high-definition images taken by the LRO, like the ones we’ve been studying today,
will provide NASA with crucial information for selecting a safe and navigable landing spot.
It’s exciting to imagine how this mission will add to our current understanding of the Moon
with on-the-ground imaging and rock samples, and honestly, I can’t wait. Which of the two theories
to explain the formation of the Gruithuisen Domes do you think sounds more plausible? I’d love to
hear your ideas in the comments! So, there we have it. Almost everything you could want to
know about the Moon’s Gruithuisen Domes and the unsolved mystery of how these massive, eerily
Earth-like structures came to exist. I hope I earned your like and subscription today!
The Moon may look boring at a first glance, but to me, it’s like art. Speaking of which,
did you know the Apollo 12 lander had an Andy Warhol drawing smuggled aboard?
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Thanks for watching! If you want more of the Moon, check out the playlist here. And if
you found value in these videos, please consider supporting me as a member or on Patreon, with an
added bonus of having your name added to the end of my videos. All the best, and see you next time.