The Moon Guards Her Secrets: Part V

Death of the Moon

Last week in Part IV, I blogged about how the Moon may have created life on Earth. But death is also a part of the Moon's story.


Photo credit NASA

Yes, one day the Moon will die. All things must end. The universe is built on a cycle of creation and decay.

In the 4.5 billion years since the Moon formed, it's been slowly slipping away from Earth. Its original orbital path less than 20,000 miles from Earth's surface has slowly increased over time to the roughly 239 million mile oval it tracks today.

This is partly due to the interaction with the tidal bulge created by the Moon's gravity on Earth. The tidal bulge is slightly ahead of the Moon's orbit because the Earth spins faster than the orbital speed. This speeds up the Moon and at the same time pushes it further away from Earth. It isn't being pushed out very quickly--only about 4 centimeters (or 1.6 inches) per year--but over vast amounts of time, the distance grows.

As the space between the Moon and Earth grows, the Moons orbit will also slow until it takes 47 days to revolve around the Earth, meaning our "months" will stretch by approximately 17 days. But that's not the only thing that will be affected. Our "days" will also stretch, because the rotation of the Earth will slow down, until what was a single day now lasts 47. The span of time for months and days on Earth will become the same.

In its younger days, the Moon was 80% larger in our sky than it is today. Billions of years from now, it will appear only as a dot among the stars.


Photo credit NASA

But as the Sun begins to expand into a red dwarf at the end stages of its life about 5 billion years from now, it will create much denser solar winds that will begin to push against the Moon. This will ultimately put a drag on the Moon's orbit and send it into a death spiral with the Earth, until it reaches a point only 11,470 miles (18,470 kilometers) above our planet--a point called the Roche limit-- where gravitational forces will rip it asunder.

In death, the Moon will break into pieces that form a ring around the Earth once more, just as it did at its birth.

If humankind is still alive to see the Moon's swan song, it will be a beautiful sight--a great arc of debris forming a ring around planet. Until those pieces begin to fall back to Earth, creating a destructive asteroid bombardment.

As the destruction continues, the two worlds will again fuse into one, but the process will destroy all life that might still survive on Earth. So the death of our Moon also means the death of our world.

Or at least, that's the theory. It's possible that the Earth, or both the Earth and the Moon, could escape destruction altogether. Science uses mathematics and observation to determine what they think will happen in the very distance future, but in reality no red giant sun has ever been observed in this phase of its life, so the universe might yet have some surprises in store.

And with that, this series has now come to a close. I hope you've enjoyed May Moon Month and that you might have discovered as many big surprises reading these blogs as I found writing them.

Photo credit NASA

Intrigued with reading a few stories with a lunar bent? Below are several SFR stories with settings on the Moon.

Grand Master's Game by Aurora Springer involves an alien attack on Moon Station before moving on to other points in the galaxy. The author recommends this book to readers who "favor action adventures in space with aliens, dragons, and a sprinkle of humor."

Mako's Bounty by Diane Dooley begins on Lunar Base before moving to Earth. "For nine long months Vin Sainte has been fleeing the bounty hunter from one temporary refuge to the next. Now he’s got Mako exactly where he wants her."

Moonlight by Aeon Igni takes place in a mining operation on the Moon. "What’s it like to live on the moon? Let me tell you, it’s not a damned picnic. After a personal tragedy struck my life, I signed up for service on the moon. My name is Belle, and I’ve been here for six years now, mining Helium 3 for the Moon Rock Mines Corporation."

And here's an interesting article involving lunar eclipses:
SF Thought Experiment: Fun with Total Eclipses on author Carol Van Atta's blog.

In a month or two, I'll have a new two-part series: How Magnetism Saved the Universe. More surprises ahead. Turns out, gravity isn't the only galaxy-forming heavyweight in our universe. Magnetism played a very important role, too. But just like our Moon, magnetism has a very dark side.

Resources:
How the Universe Works: Secret History of the Moon, Science Channel S4/E6 (2015)
Space.com: Earth's Moon Destined to Disintegrate
PhysLink.com: The Fate of Our Moon
StarrySkies.com: The Primal and Future Moon

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