Red Moon

TA SHU 1 yueliang de fenmian The Birth of the Moon

Now, my friends, I am on the moon. A very strange thing to say. Also to experience, but aside from the weird lightness of my body here, I must admit that the idea is even stranger than the reality. At least so far. But this is just because it is such a very strange idea. I am standing on the moon. Sitting, actually. And because of that, I am now very interested to discover: what is this place? What is the moon? And to understand this, we have to go right back to the beginning.

The solar system began as a swirl of dust. Not like our dust, dust isn’t quite the right word for it, because bits of all the elements were included in this swirling mass of particles, and it was a lumpy swirl to begin with, because of gravity. Then it got lumpier as time passed and gravity caused the lumps to come together, one way or another.

The lightest elements were the most common and the most likely to clump together, and by the nature of their distribution and their intrinsic qualities, most of these elements clumped at the center of this particular dust cloud. Feng shui principle number one: gravity. In the Chinese system of primary qua as described in the Yijing, the Book of Change, gravity would be kun, in other words, the yin in yin-yang. It works on everything equally and without exception. Nothing escapes it. So in the case of this swirl of dust, most of the particles fell in toward the center, and finally they massed so hugely that the pressure of their own weight caused them to catch fire. It was a nuclear fusion fire, in which atoms crush together and release energy, and so the sun ignited. The two lightest elements, helium and hydrogen, mostly clumped inward and ended up in the sun—ninety-nine percent of the solar system’s hydrogen and helium is in the sun—but smaller whirlpools of these elements formed our four gas giants, Jupiter, Saturn, Uranus and Neptune.

The heavier elements—which were mostly created in the stupendous explosions called supernovas—bumped around the solar system closer to the sun, gathering and clumping into balls that were molten from the energy of their impacts, and from gravity’s crushing draw inward onto themselves. These clumps grew as they ran into one another, forming eventually the rocky planets Mercury, Venus, Earth and Mars. The asteroid belt would have become another one of these rocky planets, but the gravity of nearby Jupiter kept pulling all these bits of a planet away from one another, until those that were not jerked into the sun or out of the solar system ended up in the wide band they are in now.

Each of the four rocky planets was made of smaller planetesimals, which attracted one another and ran into one another and then held together. This process was cumulative, which means that near the end of the process, around four and a half billion years ago, the collisions were often between quite large planetesimals—really they were small planets at this point, making their final combinations. Each of the four rocky planets we ended up with shows signs of gigantic collisions in their final years of accumulation. Mars’s northern hemisphere is four kilometers lower than its southern hemisphere, and is now regarded as the impact basin of a giant impactor. Mercury is far denser and more metallic than it should be given the expected spread of elements, and it’s now postulated that a giant impact with another planetesimal knocked away much of its surface and mantle, which flew out into its orbit. These chunks of Mercury would have fallen back onto it and recoalesced eventually, but being so close to the sun, many pieces were driven by the photon wind of sunlight out of Mercury’s orbit, ending up eventually on Venus, or even the Earth.

Venus shows signs of a giant impact that hit with an angular momentum that stopped its rotation in its tracks, so that even now it spins very slowly, and in the opposite direction to the other planets.

Then there is Earth and its moon, a moon so immense compared to its planet’s size that it is proportionately by far the biggest satellite in the solar system. How did that happen? The theory is this: in the beginning, up to around 4.51 billion years ago, there were two planets that had coalesced in Earth’s orbit, called now Earth and Theia, or Gaia and Theia. They were almost the same size, and Theia was in the L5 position of Earth, which is a gravitational resonance point along Earth’s orbit that makes an equilateral triangle with the sun and the Earth. Lagrange positions are pretty stable, but there are other powerful gravitational bodies in the system, and so a time came when some pull from Jupiter or Venus, or both together in a cosmic coincidence, yanked Theia out of its place and sent it spinning toward Earth. Its approach appears to have resembled Ptolemy’s epicycles, little orbits spiraling along in a bigger orbit, and as the two planets came together, their mutual attraction caused them to accelerate at each other. Theia also seems to have been rapidly spinning. When they finally collided, it appears to have been an almost direct hit, with a very high angular momentum.

On impact the two bodies first merged and then exploded violently outward, throwing a great splash of hot stone and metal in a liquid spray that surrounded the hot spinning mass remaining in the middle. The spray of fragments was cast into space in a doughnut-shaped band around the newly formed and now bigger planet, which had been set spinning so fast by the collision that each day took about five hours.

That big combined mass was Earth as we know it now. The melted fragments in their doughnut-shaped band, which planetologists now call a synestia, quickly (meaning in just a century or so) recollected and coalesced into our moon, a ball one-quarter the size of Earth, but only one-tenth its mass, because the material that had been thrown outward was made mostly of surface and mantle materials, lighter than core materials. Both Theia’s and Earth’s cores ended up inside Earth. The ball of recollected materials in space was the moon.

Luna. In China we usually call the tutelary spirit Chang’e, a great goddess. Sometimes Yu Nu. In the Greek myths, Selene. And Selene’s mother was Theia—thus the scientists’ name for the impactor planetesimal. This lost planet is in fact not lost, but rather a part of all of us. Theia’s atoms are in every body of every human.

In the four and a half billion years since that time, the moon’s and Earth’s gravitational influence on each other has caused Earth’s rotation to slow to twenty-four hours a day, while the moon is now tidally locked, and rotates on its axis in the same time it takes to complete an orbit around Earth. On they go in their spiral dance, and the tides caused by the tug of the moon on the Earth’s oceans had a huge impact on the development of life on Earth.

What to make of this story? Hard to believe! Vast, earth-shattering collisions, followed by billions of years of spiral dancing—these are what made the peaceful harmonious world we live on, and made also this dead white rock in space, this moon. One collision, but with two very different outcomes, almost entirely dependent on gravity and the other laws of physics. That’s something to ponder. Worlds in collision! And then different outcomes, including some very good ones.

Of course we would not want any such thing to happen again to us now! That would mean disaster. And the motions of the physical cosmos are not the same as the operations of human history. Not even close. Analogies always deceive more than they reveal; I am no fan of analogies, I do not use them. Even metaphor, that mental operation we use with almost every word we speak, is slippery and deceptive. I always speak as plainly as I can.

And yet language, and therefore thought, is a strange and imprecise game of metaphors and analogies, one that we must play to stay alive. So now I want to suggest that even if there is a Theia looming out there in the orbit of our collective history, spiraling in toward us—as perhaps there is—and even if it has already been dislodged from its Lagrange point and is now bearing down on us, such that it is about to collide with some already-existing Gaia inside us, as seems inevitable, gravity and inertia being what they are—this has happened before. And the results, no matter how catastrophic at first, can still eventually turn to the good.