José Manuel Nieves

Updated:02/27/2020 20: 03h


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Our daily routine does not even allow us to suspect it, but the Universe is a dangerous place and life, on any planet that is found, faces numerous threats that could eliminate it in a rapid and brutal stroke. One of those threats, asteroids, solar flares or nearby supernovae apart, is that the planet in question is “swept” and expelled from its own solar system. A team of researchers from the Tehran University of Technology has made the numbers and discovered that Earth seems to be safe from a similar catastrophe … or almost. Your results have just been published in « ArXiv ».

An event of these characteristics always has a clear culprit: gravity, the absolute owner of everything that moves in the Universe. In fact, the same force that manages to keep a planet around a star for countless millions of years can also, suddenly send that planet to the depths of space, condemning him to wander alone for the rest of his days. Conditions that, as far as we know, are completely incompatible with life.

In recent years, astronomers have found a growing number of “wandering planets,” space vagrants who do not orbit around any star and wander aimlessly in the vast interstellar space. How many of them could have been expelled in this way from the systems in which they were born?

The complicated gravity

Gravity seems a simple thing, but it is not. Especially when more than two objects interact at the same time. It is enough to consider only three bodies orbiting each other so that the associated mathematics become intractable and it is, in practice, impossible to predict exactly how that system will evolve, which becomes chaotic. The call ” problem of the three bodies », in fact, has brought scientists who try in vain for centuries, over and over again, to find solutions that allow them to calculate their relative positions at any given time. The problem is that with three objects, any small deviation or change can lead to massive alterations in a surprisingly short time.

In other words, what seems like a calm and serene situation at one time, such as the Earth orbiting the Sun, can become dangerously unstable at the next moment.

What if a wandering star approaches?

And while it is true that the other planets in our system also affect and modify the Earth’s orbit, they are too small to cause major problems. Very different, however, would be the case of a wandering star that, on its way, would pass near us. Which, by the way, happens with relative frequency.

If a star gets close enough to the Solar System, could start changing the Earth’s orbit. At the point of maximum approach, our planet would get some additional energy, a gentle “pull” gravitational from the visitor. It would not be too much, but if the same thing happened year after year, our planet could add enough energy to get away from the Sun, leave the “habitable zone” (the distance to the Sun that allows the existence of water in a liquid state) and even if sufficient gravitational pulls occur, the one necessary to overcome the attraction of the Sun and leave the Solar System permanently.

The fact that we are still here, however, means that such a scenario has not occurred, at least during the last four billion years. But that doesn’t mean it can’t happen in the future. And this is precisely where the work of Behzad Bojnordi-Arbab and Sohrab Rahvar, researchers at the Tehran University of Technology, is framed.

Simulate the end of the world

In their simulations, the two scientists considered all possible scenarios: different masses of incoming stars in all kinds of angles and with all kinds of speeds. It was about seeing what circumstances should occur for one of those approaches to result in the expulsion of the Earth from our planetary system.

One of his conclusions is that The faster the visiting star goes, the better it would be for us, since it would have little time to “spoil” our solar system. Even if the star equals our orbital velocity around the Sun (about 106,000 km / h) it would have to pass through Jupiter’s orbit to affect us enough to drive us out.

The slowest, most dangerous stars

On the contrary, slow-moving stars are much more dangerous. Y it would be enough to border our system of planets to cause a real carnage inside. Of course, the mass of the visiting star is of the utmost importance, as is the approach angle. For example, if the star passed along the plane of the Solar System, it would have a good chance of getting close enough to us to destabilize us. If it gets close enough, it could even get us to beheaded, so the issue of expulsion would take a back seat …

With all their simulations in hand, the researchers applied them to our galactic neighborhood, using our growing knowledge about the positions, masses and velocities of the stars around us. And in doing so, they discovered that, on average, our dear planet only has a probability between 15,000 orbital destabilization over the course of its history, just over 4 billion years. Or what is the same, for every 10,000 Earth-like planets in our neighborhood, only one would have been expelled from its system.

The dangerous heart of galaxies

Of course, these data are valid in the outer region of the Milky Way, where (luckily) our planet is, since the density of stars is much lower than that of the central regions of the galaxy. There, in effect, things would paint much worse, and the probability of an orbital catastrophe would be about 160 times higher.

One of the conclusions of the study, then, is that Galactic centers are places that can become very hostile for life. Apart from greater cosmic radiation, lethal to biology, we now also know that the density of stars can multiply the number of visiting stars and, therefore, of planets “torn” from their systems. If there were life in any of them, things could get really difficult.


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