A Brazilian research team has proposed a new physical model to explain the origin of water on Earth and anywhere else in the solar system. This proposal, which is is unlike any other, before it, claims all this water — whether liquid, solid or gas — originated on Jupiter.

The total volume of water found on Earth varies, depending on who you ask and what factors they use to arrive at a number. There are several units of measurements to study oceans and terrestrial water. According to a report on Brazilian news agency Agencia Fapesp's website, if the unit of measurement is terrestrial oceans, some scientists speak of three to four of them, while others estimate dozens being present on Earth. These massive variations stem from the fact that the amounts of water in the planet’s hot mantle and its rocky crust are unknown. Therefore, this model considers the full range of estimates to make the findings.

It is a widely accepted idea that asteroids impacted the course of evolution of life on the planet. From the death of the dinosaurs to the formation of water, several phenomena that make Earth unique have been attributed to objects from the sky crashing into the planet.

“The idea that Earth’s water came predominantly from asteroids isn’t new. It’s practically a consensus among researchers. Our work isn’t groundbreaking in that sense. What we did was associate the asteroid contribution with the formation of Jupiter. Based on the resulting model, we ‘delivered to Earth’ amounts of water consistent with currently estimated values,” André Izidoro, scientist at São Paulo State University’s Guaratinguetá School of Engineering  and lead author of the study, was quoted in the report.  

“First of all, it’s important to leave aside the idea that Earth received all its water via the impacts of comets from very distant regions. These ‘deliveries’ also occurred, but their contributions came later and were far less significant in percentage terms,” Izidoro said. This means that water found on earth came to the region currently occupied by earth’s orbit even before the planet was formed, he added.

How the solar system evolved is crucial to understanding this new theory. There was a huge ball of gas and cosmic dust swirling around which collapsed due to gravity. A region inside this swirling ball becomes the mass center for this collapsed system. The gravitational pull of this center caused mass to accumulate until 4.5 billion years ago. Around this period, the center became so massive and hot that it began the process of nuclear fusion, which transformed it into a star we now call the sun.  

“Meanwhile, the cloud around the sun continued to orbit the center and its matter agglutinated to form a disk, which later fragmented to define protoplanetary niches,” said the report.

A specific region in this disk was water-rich and is estimated to have been several astronomical units (1 AU is the distance between Earth and the sun, about 93 million miles) from the newly formed sun. It couldn't have been closer because the sun's heat wouldn't allow it.

We know that Jupiter has a solid core with a mass equivalent to several times that of Earth. This core is surrounded by a thick and massive layer of gas. Jupiter could only have acquired this wrapping during the solar nebular phase where planets were splitting from the disk and gathering mass to form planets.

According to the study, this gravitational attraction of gas from the surroundings was extremely fast due to the vast size of Jupiter. “In the vicinity of the formation of the giant planet, located beyond the ‘snow line’, thousands of planetesimals orbited the center of the disk and, simultaneously, attracted each other.”

During this accumulation, many water-containing planetesimals were engulfed by proto-Jupiter while others were propelled to the outskirts of the solar system. The study found that a smaller number of these water-rich planetesimals were hurled into the disk’s inner region, delivering water to the material that later formed the terrestrial planets and the Asteroid Belt that are closer to the sun and couldn’t have formed their own water. 

“The period during which the Earth was formed is dated to between 30 million and 150 million years after the Sun’s formation,” Izidoro said. “When this happened, the region of the disk in which our planet was formed already contained large amounts of water, delivered by the planetesimals scattered by Jupiter and also by Saturn. A small proportion of Earth’s water may have arrived later via collisions with comets and asteroids. An even smaller proportion may have been formed locally through endogenous physicochemical processes. But most of it came with the planetesimals.”

The researchers used supercomputer simulations to study the gravitational interactions among multiple bodies, and introduced a “gas drag” to account for the space wind blowing in opposite direction of the planetesimals, similar to what a cyclist would feel from the air on her/his body. This gas drag helped herd the very elongated orbits of the planetesimals that were found around Jupiter when the solar system was still very young. These rocks were gradually ‘circularized’ and implanted into the asteroid belt, which by itself, could never have formed water.

The team released an animation to help us understand this complex space phenomenon. It shows the proto-planets growing as they accrete gas from the gas cloud, and their growth destabilizes planetesimals, scattering them in various directions.

The different colors assigned to the planetesimals serve merely to show where they were to begin with and how they were scattered. The gray area marks the current position of the Asteroid Belt. Time passes in thousands of years, as shown at the top of the animation.

A second animation adds a key ingredient, which are the migrations of Jupiter and Saturn to positions nearer the sun during their growth processes. It shows how these two large planets were, invariably, crucial to water formation in the solar system.