Since the formation of the earth, meteorites, dust and asteroids have been raining down on it. Shouldn’t it keep getting bigger over time? ntv.de asks planetary researcher Ulrich Köhler. And he knows of another effect that turns the calculation upside down.
Nobody was there when it happened. But it is believed that planet Earth was formed by small chunks of rock lumping together into an ever larger sphere. This happened in the infancy of the solar system when a gigantic disk of dust and gas orbited the sun. The larger the young earth became, the more material it attracted. To this day, the rock rain continues in a weakened form. So is the earth still growing?
“Tons of meteorites, dust and asteroids from space rain down on earth,” says Ulrich Köhler, planetary geologist at the Institute for Planetary Research at the German Aerospace Center (DLR), to ntv.de. The amount is tiny compared to the total mass of the earth. But in some years there is also a lot more: “66 million years ago, a billion times more mass than usual came to earth at one fell swoop,” says Köhler. It was the asteroid that wiped out the dinosaurs. But even that was only a billionth the mass of Earth.
The question now is: Can the earth also lose mass back to space? After all, for almost 70 years, mankind has been launching rockets and satellites into space. NASA’s new moon rocket, for example, weighs more than 2,600 tons with a full tank. “But rockets fall back to earth,” says Köhler. The fuel in the tanks also remains in the atmosphere after burning.
Only the payload of the rockets stays in space, at least for a certain amount of time. Over the decades, more than 10,000 tons are said to have accumulated, which – in working order or as space junk – are orbiting the earth and the sun. The material from the lower orbits eventually falls back into the atmosphere where it burns up. Only a few space probes have penetrated deep into the solar system and can be regarded as a – vanishingly small – loss of mass for the earth.
But there is a much more powerful leak above our heads: the atmosphere. It is constantly exposed to particle radiation from space. “When this radiation hits the upper atmosphere, molecules are hit and shot up, and the ionized atoms and molecules are accelerated so much that they can escape the Earth’s gravity,” explains Köhler. About 100,000 tons of mass disappear into space every year.
“On Mars you can see that a planet can lose almost its entire atmosphere over time due to radiation,” says Köhler. However, this is not to be feared on Earth, since volcanoes are constantly replenishing new gas. In addition, due to its greater mass, the earth can hold the air molecules better than Mars – and it is also better protected from solar winds thanks to its magnetic field. Still, the annual loss in mass is undeniable.
So the calculation is relatively simple: the earth gains around 50,000 tons per year from dust and rock from space, and around 100,000 tons loses its atmosphere. In the end, that leaves a minus of 50,000 tons. So the mass of the earth decreases over time. So will people soon have to move closer together?
Putting the annual mass loss in relation to the total mass of the earth should provide some relief. In total, the earth weighs 5.972 trillion tons. With a loss of 50,000 tons per year, it would take more than 100 quadrillion years for the earth to disappear completely. But the sun alone has an expected remaining lifespan of only 5 billion years – before the earth could disappear, it will be long gone.
By the way: In the 19th century, a theory emerged according to which the earth had grown significantly over millions of years: the so-called earth expansion theory. Among other things, researchers wanted to use it to explain why the once connected supercontinent Pangea burst apart – the earth as a rising cake. The problem: There is no known mechanism that could explain this type of expansion. The earth expansion theory therefore no longer plays a role today.
