Life needs liquid water. Closer to the Sun it boils away, farther out it freezes. The green band shows where it can be liquid. Move the Earth.
The edges of the band: the calculation of Kopparapu et al., 2013. The Solar System stretches to Neptune at 30 such distances; the band takes up less than one. The planets and the Sun are enlarged on screen.
The axis of the Earth is tilted by 23.4°. The seasons come from this: warmth reaches the north and the south in turn, and one can live on almost the whole planet. The Moon holds this tilt.
With the Moon the tilt wanders only from 22.1° to 24.5°. Without it, by the calculation of Jacques Laskar (Nature, 1993), it would change chaotically from 0° to nearly 85°. Mars has no large moon, and its axis wobbles just like that. On screen the Moon is closer than it really is.
The Sun strikes the planets with two kinds of radiation. The first is a stream of charged particles, the solar wind (yellow dots). The magnetic field turns it aside. The second is hard ultraviolet (violet rays). The ozone shield holds it back at a height of 15–35 km. Switch off either shield.
The pink rings are the radiation belts: there the field holds the particles it has caught. There is one more wall among them, and the next screen is about it.
Mars: the magnetic field went out, and the solar wind carried off most of the atmosphere (measured by the NASA MAVEN spacecraft). There is so little ozone that if the whole layer were pressed down to the pressure at the surface, it would make a film 3 mm thick. It holds back almost all the dangerous ultraviolet. The green rings at the poles are the auroras. Losses on screen are sped up millions of times.
The magnetic field does more than turn particles aside. It catches some of them and holds them in two rings around the planet. These are the radiation belts, discovered in 1958. In the outer belt electrons race at nearly the speed of light: “killer electrons”, which put satellites out of action.
In 2014 NASA probes found that these electrons cannot come closer to the Earth than 11 thousand kilometers. The boundary is sharp, like a wall of glass (the white shell), and it holds even through strong magnetic storms.
The authors of the discovery explain it this way: cold plasma around the Earth scatters the electrons, and they leak inward too slowly. Daniel Baker, who led the work, compared the boundary to the force shield in “Star Trek”. Astronauts fly beneath this wall.
Baker et al., Nature, 2014, the Van Allen Probes. Distances on screen are to scale: the boundary lies at 2.8 Earth radii from its center.
The Sun is 400 times larger than the Moon and almost exactly 400 times farther away. That is why their disks are the same size in the sky. When the Moon stands in front of the Sun, it covers the Sun completely, and the corona becomes visible. Move the Moon.
The Moon ranges from 356 to 407 thousand km: when it is closer the eclipse is total, when it is farther a ring remains. Nowhere else in the Solar System does a satellite cover the Sun so exactly. Helium was discovered in the eclipse of 1868, and the theory of Einstein was tested in 1919.
Each condition on its own can be called luck. But all of them are needed at once, on one planet and at one time.
About six thousand planets have already been found around other stars. There is no second Earth among them, and not one confirmed trace of life either.
The paleontologist Peter Ward and the astronomer Donald Brownlee gathered these conditions in the book Rare Earth (2000) and came to this conclusion: planets with complex life ought to be extremely rare in the Universe. Neither of them is a theologian.
True: one can live only where living is possible. But that does not answer why such a place exists at all.
Billions of tries would help if the whole matter were the planet. But on a finished planet life still has to appear: the DNA code, the cell factory, the proton turbines. There the count is not in planets.
To win one lottery is luck. But here the win is in four at once: in the laws of physics, in the planet, in the cell and in the code. When one person wins every draw in a row, nobody says “lucky”. They look for the one who arranged it.
Seven people live on the ISS. Thousands of engineers supply them with air, warmth and protection. The Earth does the same for eight billion, without a single failure.
A house with heating, water, air and a roof against the weather does not appear by itself. It is built for the one who will live in it. The Earth was prepared for you. The Bible calls the Builder by name: God.
“The highest heavens belong to the LORD, but the earth he has given to mankind.”
Psalm 115:16
“He stretches out the north over the void and hangs the earth on nothing.”
Job 26:7, written thousands of years before the first photograph from space
The One who prepared a home for you wants you to know the Owner. He knows you and wants you to know Him.
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