Take a moment to consider the Earth’s formation and the land beneath your feet. It’s easy to forget the intricate complexities of the planet that serves as our home base, supplying us with air, water, and gravity.
For a long time, scientists thought it took over 100 million years for Earth to form. They also assumed that water, our life source, was a lucky gift from water-rich asteroids like comets. However, a groundbreaking study from the University of Copenhagen suggests something else entirely.
“We demonstrate that Earth’s formation occurred through the rapid accumulation of small, millimeter-sized pebbles,” says Professor Martin Bizzarro of the Globe Institute, who played a crucial role in this study.
“This mechanism facilitated the Earth’s formation in merely a few million years. Our findings suggest that Earth’s water isn’t a happy accident, but rather an inevitable byproduct of its formation.”
These revolutionary results suggest not only a more rapid creation of our planet than we previously believed but also point to the presence of water as an expected outcome of this formation process. This information is vital in understanding more about not just our planet but also those orbiting stars outside our solar system.
“Given this new planet formation mechanism, the possibility of habitable planets existing elsewhere in the galaxy increases dramatically,” Bizzarro adds. It’s worth noting that habitability is the potential for a planet to possess the necessary ingredients for life to flourish. Water is a critical ingredient.
Associate Professor Martin Schiller, another significant contributor to this study, offers his perspective on the debate surrounding planet formation.
“There’s a longstanding theory that planets gradually form through the collision of celestial bodies, incrementally expanding their size over 100 million years. In such a scenario, Earth’s water would owe its existence to a chance event,” he explains.
For instance, Earth’s water could have originated from icy comets bombarding our planet during the final stages of its formation.
“If this was the actual formation process, then Earth’s possession of water is a fortunate accident, significantly reducing the likelihood of water existing on planets beyond our solar system,” Schiller notes.
Contrary to this perspective, the researchers of this new study put forward a fresh theory on Earth’s creation.
“In the vicinity of the young Sun, there existed a disk where planets were burgeoning. This disk was teeming with tiny dust particles. Once a planet reached a certain size, it acted akin to a vacuum cleaner, swiftly sucking up all that dust. This mechanism enabled it to reach Earth’s size in a few million years,” explains Isaac Onyett, a Ph.D. student and the study’s corresponding author.
This ‘vacuum cleaner’ effect played a critical role not only in Earth’s formation but also in ensuring water was delivered to our planet.
“The disk also held a multitude of icy particles. The dust vacuuming process concurrently captures a portion of this ice, contributing to water’s presence during Earth’s formation, rather than relying on a lucky event 100 million years later,” adds Onyett.
The new understanding of these mechanisms greatly enhances the probability of water’s presence on other planets.
“This theory would predict that every Earth-like planet formation will result in water. Therefore, any planet orbiting a star the size of the Sun in another planetary system should possess water, provided it’s at the right distance,” says Bizzarro.
To gain these insights, the researchers utilized silicon isotopes, enabling them to decipher the mechanisms and timescales of planet formation. They analyzed the isotopic composition of over 60 different meteorites and planetary bodies.
This established genetic relationships between rocky planets like Earth and Mars and other celestial objects. The strategy facilitated the identification of the building blocks that formed Earth and the process by which they assembled.
Planet formation is a complex process that begins within dense regions of dust and gas in space. Here we explain the traditional theory of how planets form.
Planet formation starts in nebulae, which are vast, dense clouds of gas and dust in space. Within these nebulae, there are regions called molecular clouds, where the dust and gas are dense enough to collapse under their own gravitational pull.
As a molecular cloud collapses, it often forms a rotating disk of material. At the center of this disk, a protostar begins to form as the gravity pulls more and more material inward. This is the beginning of a new solar system.
Around the protostar, the remaining material forms a flat, rotating disk called a protoplanetary disk. This disk consists of gas, dust, and larger solid particles. This is the environment in which planets begin to form.
In the protoplanetary disk, small dust particles start sticking together in a process called accretion, forming larger and larger clumps. As these clumps grow, their increased gravity allows them to pull in more material, eventually forming planetesimals – bodies that are large enough to have their own gravity but are not yet full-fledged planets.
Two paths of planet formation are currently proposed – core accretion and disk instability.
This is the most widely accepted model for planet formation. In this process, a planetesimal continues to gather more material, gradually growing into a protoplanet. Over millions of years, these protoplanets can gather enough material to become planets. Gas giants, like Jupiter and Saturn, form when a protoplanet gathers a massive amount of gas from the disk.
In this model, a portion of the disk becomes gravitationally unstable and collapses under its own weight to form a planet. This model is often used to explain the formation of gas giants, as it allows for planets to form quickly before the gas in the disk dissipates.
After a planet forms, it can migrate – move closer to or farther from the star. This happens because of gravitational interactions with the remaining material in the disk. This is one explanation for why we find gas giants, which we’d expect to form far from the star where there’s more material, very close to their stars.
Eventually, the material in the disk is either accreted onto planets, pushed out of the system by solar winds, or incorporated into smaller bodies like asteroids and comets. This leaves a relatively clear solar system with planets in stable orbits.
The final stage of planet formation involves a period of heavy bombardment, where leftover planetesimals collide with the newly formed planets. This can cause significant changes to a planet’s surface and can even deliver important materials, like water.
These stages outline a general process. Not all planets will follow this exact path, and there’s still much we don’t know about planet formation.
For instance, our understanding of the formation of “exoplanets” – planets around other stars – is continually evolving, as we discover planets with a vast range of sizes, compositions, and orbits that challenge our existing models.