For centuries, the process by which the gas giants of the Solar System came to form: Jupiter, Saturn, Neptune and Uranus, much larger than rocky planets – the first has 318 times more mass than Earth and is 1,400 times bulkier – but lower in density due to its gaseous nature. But is everything in them gas?
There are discrepancies among scientists about the composition of the nucleus: some researchers, such as those at the University of Colorado, believe that it is a mixture of rock, metal and hydrogen; others, such as those from the University of California at Berkeley, point out that the heart of these celestial bodies could be a fusion of undefined elements.
And at the origin, the ‘planetary beans’
There are many mysteries surrounding these vaporous planets also called Jovians, although we are closer to knowing how they arose. And this thanks to the recent findings of a team of scientists from the Southwest Research Institute, in Boulder (USA), and Queen University, in Kingston (Canada). Led by Harold Levison, an astronomer specialized in planetary mechanics, these experts believe that the key lies in some planetary beans that will lead us to glimpse the origin of the four giants of our solar system.
The work, published a few months ago in the journal Nature , proposes that the gradual accumulation of objects of at most one meter in diameter – beans or seeds – can explain how these worlds were formed, and their approach predicts the creation of one. four gas giants per star. “As far as we know, this model is the first to reproduce the structure of the outer Solar System, with two gas giants, two other icy giants – Uranus and Neptune – and a pristine Kuiper belt,” explains Martin Duncan, one of the authors of the test.
The first works in the field of recreating planetary systems date back to the 1960s and assumed that these celestial bodies appeared by aggregation of particles contained in the cloud of dust and gas that surrounds a young star.
In later decades, some variables were introduced, such as gravitational interactions and collisions between planetoids –objects smaller than planets, but larger than asteroids and comets–, and it emerged that, in the protoplanetary disk, that is, the area around the star in which the planets are born, the first thing that forms are ice and rock cores that end up being the centers of these cosmic objects. Then, the interstellar gas and dust become attached to them, making them grow little by little.
Earth could take it easy; Jupiter, not so much
But this model had an Achilles heel: if we want an important atmosphere to accumulate, like that of any gas giant, we need a solid core of at least ten times the mass of the Earth. And, for this, many millions of years have to pass, something these titans do not have, because to grow they need to feed on the gas that surrounds their star, and this, ten million years after being born, has left its clean system of said element.
Therefore, the Earth and other rocky planets may take the thirty million years predicted by the theory to form, but the gas giants had to see the light twenty million years before, when the gas had not yet disappeared from the early Solar System. .
How to solve the riddle? Levison and his colleagues realized that the answer lay in what they called ” nugget accretion.” They thought that these should be formed at such a slow rate as to allow the planetesimals – aggregated from matter from which planets are born – have time to disperse their brethren from the disk of nuggets and thus keep all the pie.
“The growth of the nuclei takes some time to be able to drive its competitors away from the nuggets and starve them, so to speak,” explains astronomer Katherine Kretke, a member of the research team. What’s more, the surrounding gas could play an important role: the nuggets would spiral toward the core aided by a strong interstellar gas wind.
This new hypothesis provides a formation mechanism a thousand times faster than the traditional one: instead of similar objects being added together, a dominant object can swallow up the surrounding material quickly and drive similar objects away from where it is.
Only direct observation can solve the riddle
But can we verify this through observation? It is probable, since most of the extrasolar planets discovered so far are precisely gas giants; not surprisingly, they are the easiest to detect. In fact, a couple of recent findings could help us: that of a young Jupiter orbiting the star Eridani 51, sighted in December 2014 from the Gemini Observatory, in Chile, with about twenty million years and a mass twice that of Jupiter. ; and that of a ring with those planetary beans captured around the star DG Tauri in 2015 by a team of astronomers from the British universities of Saint Andrews and Manchester.
In the study of both phenomena may be the key to confirm that the mysteries of these gaseous colossi are no longer so indecipherable.
