Apollo 17,
NASA's final voyage to the Moon, completes its mission
to collect Moon rocks and perform gravity and
seismic activity experiments. After spending 75 hours
on the Moon's surface and exploring more than 22 miles
in the lunar rover, astronauts Jack Schmitt
and Eugene Cernan prepare for their journey home. As Commander Cernan
approaches the lunar module, he readies himself to take the
last human steps on the Moon. (high-pitched beep) SHATNER:
In just over a decade,
NASA's Apollo program had successfully developed
and executed a space exploration mission that allowed 12 people
to walk on Earth's moon. But how much do we really know about the giant gray sphere
that hangs in our sky? What, precisely, is a moon? And just what makes it
different from our planet or other planets
in the universe? PASCAL LEE:
A planet is a large object that's going independently
around a star. And so, what a moon is, is an object that is not going
directly around a star but around a planet as the planet itself
goes around the star. So the Earth, for example,
has a very large moon. Many of the planets
in our solar system have moons. Every one of these objects
are little worlds of their own. (thunder crashes) VERONICA BRAY:
A lot of people think of moons as like our moon. It's kind of black-and-white, cold, dead,
geologically inactive. But it's relatively boring compared to what we know
of some other moons. For example,
Pan looks like a flying saucer or a-a ravioli. Hyperion looks like
a sea sponge, with all of these strange pits
in its surface. And then we look
at Jupiter's moon Io, which is the most volcanically
active body in the solar system, covered with yellows
and oranges. We know of something like 300
moons in the solar system today, and we are always
discovering more. Each of these objects has a unique
and distinctive geology, it's a different color,
it has a different history. Each one is kind of
a puzzle piece in understanding
the solar system. SHATNER:
You could say that many
of the bizarre moons that circle
our neighboring planets make the Earth's moon
seem rather dull. But a closer look reveals
that our gray companion is the perfect partner for creating a thriving
environment on our planet. The size, proximity
and singularity of our moon make our home world
quite unique. Earth is the only terrestrial
planet in the solar system that has a major moon. Mercury and Venus
don't have moons. Mars has some
little captured moons. We are unique in that
we are a terrestrial planet that has this moon that is huge. The Moon is very unusual
in that it is about one quarter the size of
the Earth in terms of diameter. It's very big,
compared to planet Earth. Our moon is humungous. Even the largest moons
of our solar system-- when we look at Ganymede
and Titan, the large worlds
of Jupiter and Saturn-- they're nothing in comparison to
the size of those giant planets. And then we look at the Moon, and it is huge
compared to the Earth. SHATNER:
It turns out
that this solitary, large moon has helped make our planet
the livable world that it is. LEE:
The Moon's motion
around the Earth is so regular that cultures
have created calendars, in many cases, reliant
on the cycles of the Moon. It's a timepiece,
in terms of when is a good time to grow crop,
to plant, to harvest. The other thing
is that the Moon has a physical influence
on the Earth. BRAY:
If we didn't have
the large moon that we have, we would have much more wobble
of our spin axis, which would lead
to more extreme seasons. We also wouldn't have tides. So, that has implications for the development
of life on Earth. Life wouldn't have
been able to develop from the seas
to the land so easily if we didn't have a moon. REBECCA BOYLE:
we are very lucky
that we have our moon here to stabilize our spin, to stabilize the tilt
of our planet on its axis and stabilize
its own rotation around the sun. And the Moon
is one of the things that keeps us safe
from the gravitational bullying of Jupiter or other planets. It safeguards the climate
of Earth through this action. We're very lucky to have
a large moon stabilizing us.