There is currently one accepted model as the most likely explanation for how the Earth formed: the gradual accretion of asteroids. However, there are facts about our planet’s composition that are difficult to explain.
A new paper, a combination of experiment and modeling, suggests a new formation pathway that more closely matches Earth’s features.
“The prevailing theory in astrophysics and cosmology is that the Earth is made up of cartilaginous asteroids,” says planetary scientist Paolo Sozzi, of ETH Zurich in Switzerland. These are relatively small clumps of rock and metal that formed early in the solar system. that’s the problem. The theory is that there is no mixture of these chondrites that can explain the exact composition of Earth, which is much poorer in light and volatile elements like hydrogen and helium than we expected.
There are a lot of question marks about the planet formation process, but scientists have managed to piece together an overall picture. When a star forms from a dense mass of matter in a molecular cloud of dust and gas in space, the surrounding matter forms a spinning disk and sinks toward the growing star.
And this disk of dust and gas not only contributes to the star’s growing environment—the small densities within that vortex also collapse into smaller, cooler clumps. Small particles first collide with static electricity and then with gravity and stick together to form larger and larger objects that can eventually become a planet. This model is called accretion and is strongly supported by observational evidence.
But if the rocks that stick together are chondrites, a big question remains about what lighter, volatile elements are missing.
Scientists have offered various explanations, including heat generated during collisions that could vaporize some of the lighter elements.
However, this does not necessarily follow either: according to recent experimental work, heat vaporizes lighter isotopes of elements with fewer neutrons. But lighter isotopes are still found on Earth in roughly the same proportions as chondrites.
So the researchers explored another possibility: that the rocks that joined together to make Earth were not cartilaginous asteroids from Earth’s general orbital neighborhood, but minor planets. These are the larger bodies, the “seeds” of the planets, that have grown large enough to have a defined core.
They ran an N-body simulation, changing variables such as the number of minor planets in a “Grand Tack” scenario in which Jupiter first moves closer to the Sun and then returns to its current position.
Under this scenario, Jupiter’s motion in the early solar system would have had a very disturbing effect on the smaller rocks orbiting it, scattering the smaller planets into the inner disk.
The simulations were designed to produce the inner solar system we see today: Mercury, Venus, Earth, and Mars. The team found that a diverse mix of minor planets with different chemical compositions could reproduce the Earth as we see it today. In fact, Earth was the most likely outcome of the simulations.
This could have important implications not only for the Solar System, and for understanding the changing compositions of its rocky planets, but also for other planetary systems elsewhere in the galaxy.
The team’s research has been published in the journal Nature Astronomy.
Source: Lebanon Debate
