Not as young as she looks: the moon feigns a false age
To this day, it is still unclear exactly when the moon formed. Dating of its rocks provides conflicting information. This could be because the moon's face was contoured when it was young.
The moon, shown here in a photograph from the International Space Station, appears young.
NASA
When Earth formed 4.54 billion years ago, there was no moon. Our home planet orbited the sun alone. But then there was a huge crash. A protoplanet the size of Mars hit Earth. The Moon formed from the material thrown into space by the collision. »id-doc-1if9sdnhi1″
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> When this happened is controversial. Some researchers date the Moon's age at 4.35 billion years, others claim that our companion is significantly older. In the journal Nature, a group of researchers now presents a model that resolves this contradiction. As a result, the Moon has undergone a kind of facelift that makes it appear 80 to 160 million years younger than it actually is. »id-doc-1if9tl9d51″
> »id-doc-1ifcjit3v0″ The moon was once very close to us »Article »
is-new-line-child=> According to the collision theory, the Moon formed in several stages. The hot material that was expelled from the Earth by the impact coalesced to form a new celestial body. At that time, the Moon orbited the Earth at a distance of 20,000 to 30,000 kilometers and appeared 15 to 20 times larger than it does today. »id-doc-1if9v58qv0″
> The Moon originally consisted of a core covered by an ocean of liquid magma. Over the next millions of years, this magma ocean began to cool. A solid mantle and crust of lunar rock formed. At the same time, the Moon moved further and further away from Earth. As it did, its originally circular orbit became more elliptical. »id-doc-1ifa11a921″
> To date these events, researchers use radioactive isotopes trapped in lunar rocks. These isotopes decay with a known half-life. If you measure how much of them remains today, you can calculate when the rock in the magma ocean froze. When the magma solidified, the exchange of radioactive isotopes with the environment ended. “At that point, the geological clock started ticking,” says Thorsten Kleine. The study’s co-author is director of the Max Planck Institute for Solar System Research in Göttingen. »id-doc-1ifa1g0881″
> Most samples of Moon rocks indicate that our companion formed 4.35 billion years ago and cooled rapidly. The Moon would therefore be 190 million years younger than Earth. The fact that the Moon has relatively few impact craters also speaks to its young age. »id-doc-1ifa299gt1″
> However, doubts have been raised about this dating for some time. Crystallized minerals were discovered in the moon rock that the Apollo astronauts brought back to Earth. These so-called zircons are extremely rare. Above all, they are over 4.35 billion years old. How these contradictory observations can be reconciled remains a mystery to this day. »id-doc-1ifaekqaq1″
> »id-doc-1ifcjk41n0″ The moon moves vigorously »Article »
is-new-line-child=> This is where the work of Kleine, Francis Nimmo of the University of California at Santa Cruz and Alessandro Morbidelli of the Côte d'Azur Observatory comes in. Based on model calculations, the three researchers postulate that the Moon was briefly exposed to strong tidal forces when it was about 120,000 kilometers from Earth. That's a third of its current distance. The gravitational forces of the Sun and Earth acted through the already cold Moon. Like dough being kneaded vigorously, it warmed up. »id-doc-1ifael8o90″
> The heat caused a partial liquefaction of the lunar mantle. At that time, Earth's satellite was similar to Jupiter's moon Io, which is one of the most volcanically active celestial bodies in the solar system. The heat was not limited to the interior. Hot lava rose to the surface through pipes and locally melted the lunar crust. »id-doc-1ifagpaej1″
> In a short time, all the rock formed up to that point melted. This reset the geological clock to zero, Kleine explains. This clock therefore does not indicate the age of the moon, but rather the time that has passed since the moon last melted. »id-doc-1ifavggc81″
> Only a few zircons remained. These heat-resistant crystals survived the Moon's lifting and therefore allow conclusions to be drawn about its approximate age. This age cannot yet be determined precisely, says Kleine. However, the Moon probably formed 4.43 to 4.51 billion years ago. »id-doc-1ifajmi2p1″
> The proposal by the three researchers reconciles the different views on the age of the Moon. It may also explain why the Moon has relatively few craters despite its age. The reason is that the existing craters were filled by rising lava. This clock only started ticking when the lunar crust solidified a second time, 4.35 billion years ago. "Everything now fits together nicely," says Kleine, summarizing the advantages of the new statement. »id-doc-1ifajonl80″
Geochemist Maria Schönbächler from ETH Zurich finds the three researchers' considerations plausible. The crucial question is whether tidal forces actually generated enough heat to melt the Moon in places. »Article»
>Find out more »https://www.nzz.ch/wissenschaft/alter-des-mondes-modell-erklaert-warum-der-mond-juenger-aussieht-als-er-ist-ld.1862836″
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