In the early days of the Solar System, baby Earth may have taken much less time to form than we previously thought.
According to an analysis conducted in February 2020, there is evidence that most of the Earth took only 5 million years to come together, several times longer than current models suggest.
This review is a significant contribution to our current understanding of planetary formation, suggesting that the mechanisms may be more varied than we think, even among planets of the same type, located in the same neighborhood: rocky planets like Mars and the Land.
You see, we’re not really 100 percent sure how planets form. Astronomers have a pretty good general idea, but the finer details … well, they’re pretty hard to spot in action.
The broad outlines of the planetary formation process are tied to star formation itself. Stars form when a group in a cloud of dust and gas collapses on itself under its own gravity, and begins to spin. This causes the surrounding dust and gas to start spinning around you, like water spinning around a drain.
As it rotates, all of that material forms a flat disk, which feeds on the growing star. But not the entire disk will be sucked: what remains is called the protoplanetary disk and continues to form the planets; That is why all the planets in the Solar System are more or less aligned in a plane plane around the Sun.
When it comes to planetary formation, it is believed that small bits of dust and rock on the disk will begin to stick electrostatically. Then, as they grow in size, so does their gravitational pull. They begin to attract other groups, through casual interactions and collisions, increasing in size until they are an entire planet.
For Earth, this process was thought to take tens of millions of years. But an analysis of the iron isotopes found in the Earth’s mantle suggests otherwise, according to scientists at the University of Copenhagen in Denmark.
In its composition, Earth appears to be different from other bodies in the Solar System. Earth, Moon, Mars, meteorites – they all contain natural isotopes of iron, such as Fe-56 and lighter Fe-54. But the Moon, Mars, and most meteorites have similar abundances, while Earth has significantly less Fe-54.
The only other rock that has a composition similar to Earth’s is a rare type of meteorite called CI chondrites. The interesting thing about these meteorites is that they have a composition similar to the Solar System as a whole.
Imagine if you had to get all the ingredients for a bolognese. Mix them all together in a large pot: that’s the protoplanetary disk and later the Solar System. But if you scattered your ingredients in a bunch of smaller pots, with different proportions of each ingredient, you now have the individual planets and asteroids.
What makes CI chondrites special is that, in this analogy, they are like little pots containing the initial proportions of ingredients for a full bolognese. So having one of these space rocks on hand is like having a microcosm of the dust that spun in the protoplanetary disk at the dawn of the Solar System, 4.6 billion years ago.
According to current planetary formation models, if things just came together, the iron abundances in Earth’s mantle would be representative of a mix of all different types of meteorites, with higher Fe-54 abundances.
The fact that the composition of our planet is only comparable to IC dust suggests a different formation model. Rather than rocks hitting together, researchers believe Earth’s iron core formed early through a shower of cosmic dust, a process faster than the accumulation of larger rocks. During this time, the iron core formed, sucking up the iron early.
Then, when the Solar System cooled, after its first hundreds of thousands of years, CI dust from further away could migrate inward, to where Earth was forming. It spread all over the Earth, basically overwriting the iron in the mantle.
Because the protoplanetary disk, and the large amounts of IC dust that could have rained down on Earth, only lasted for about 5 million years, Earth must have accumulated within this time period, the researchers concluded.
“This added CI powder overprinted the iron composition in the Earth’s mantle, which is only possible if most of the previous iron had already been removed from the core,” explained planetary geologist Martin Schiller of the University of Copenhagen. .
“That is why the nucleus formation must have happened early.”
If this model of “cosmic dust” accumulation is how Earth formed, this research also means that other planets in other parts of the Universe could have formed in this way.
This not only expands our understanding of planetary formation, but could have implications for our understanding of life within the Universe. It could be that this type of planetary formation is a prerequisite for conditions conducive to life.
“We now know that planet formation occurs everywhere. That we have generic mechanisms that work and make planetary systems. When we understand these mechanisms in our own solar system, we can make similar inferences about other planetary systems in the galaxy. Including at what point and how often water accumulates, “said cosmochemist Martin Bizzarro of the University of Copenhagen.
“If the theory of early planetary accumulation really is correct, water is likely to be just a by-product of the formation of a planet like Earth, making the ingredients of life, as we know it, more prone to be found in other parts of the Universe. ” “
The research was published in Scientific advances.
A version of this article was first published in February 2020.
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