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Super Earths in the ancient solar system?


This scenario was suggested by Konstantin Batygin, a researcher at Caltech that deals with planetary sciences, and Gregory Laughlin of the University of California in an article appearing in this week in Proceedings of the National Academy of Sciences (PNAS).
A study prepared by researchers at Caltech and the University of California at Santa Cruz argue that the Earth belongs to a second generation of planets. It seems that the inner solar system could have hosted a number of Super Earths, planets bigger than Earth but smaller than Neptune, long before Mercury, Venus, Earth and Mars were formed. If so, these planets would have disappeared long ago, destroyed and fallen towards the Sun billions of years ago because of the shift of Jupiter, first inward and then outward, which occurred in the early life stages of the solar system.

modello-sistema-solare

Credit: K.Batygin/Caltech

This scenario was suggested by Konstantin Batygin, a researcher at Caltech that deals with planetary sciences, and Gregory Laughlin of the University of California in an article appearing in this week in Proceedings of the National Academy of Sciences (PNAS). The results of their simulations suggest the possibility of a new scenario, which could respond to a number of outstanding questions about the current composition of the solar system and the Earth itself. For example, this paper explains why the terrestrial planets in our solar system have masses relatively low in comparison with the planets in orbit around other Sun-like stars.
“Our work indicates that the migration of Jupiter inward and outward may have destroyed a first generation of planets and laid the foundation for the formation of the terrestrial planets, depleting the total mass of the solar system as we know it today “says Batygin. “All this is perfectly suited to some recent developments in the understanding of how the solar system evolved, as well as how to fill in some gaps.”
Thanks to the recent survey of exoplanets, or planets in solar systems other than our own, we know that about half of all Sun-like stars in our galactic neighborhood have planetary systems. Yet these systems seem very different from ours. In our solar system space within the orbit of Mercury is basically empty, there is a handful of debris, probably asteroids with orbits close to that land that have moved to the inside, but no doubt there are planets. This is in sharp contrast to what is observed in most of the extrasolar planetary systems. These systems typically have one or more planets more massive than the Earth in orbits closer to its star than Mercury is, and very few objects at greater distances.
“It seems that the solar system today does not represent what is common in our galaxy, we are a special case,” says Batygin. “However there is no reason to think that the channel more frequent formation of planets in the galaxy should not take place here too. It is much more likely that subsequent changes have altered the original composition of the solar system. ”
According to Batygin and Laughlin, the key to understanding why the solar system has become as it stands today is Jupiter. Their model incorporates the so-called scenario “Grand Tack”, proposed for the first time in 2001 by a group of Queen Mary University of London and later revised in 2011 by a team of the Observatory of Nice. This scenario says that during the first few million years of the solar system, when the planets were still submerged in a disk of gas and dust around a relatively young Sun, Jupiter has become so massive, gravitationally influential that it was able to create an opening in the disc. And while the Sun attracted the disk of gas to itself, even Jupiter began to move inland, as if it were pulled from a huge conveyor belt.
“Jupiter would continue in that direction and would end up falling on the Sun, if it were not for Saturn,” explains Batygin. Saturn was formed after Jupiter, but was pulled towards the Sun at a faster rate, thus allowing them to recover. Once the two massive planets were found close enough, they engaged in a particular type of report called orbital resonance, or their periods of revolution are such as to be expressible as a ratio of integers. In an orbital resonance 2: 1, for example, Saturn complements two orbits around the Sun in the same time taken by Jupiter to perform a single orbit. Being in a relationship of this type, the two bodies would begin to exert gravitational influence on each other.
“This resonance has allowed the two planets to open a gap in mutual disc, and started ceded mutually angular momentum and energy, almost like a rhythmic dance,” says Batygin. At one point, moving forward and forth would have caused the expulsion of all the gas present between the two planets, a condition that would reverse the direction of migration of planets sending them back to the outer areas of the solar system. (Hence, the “tack”, literally “turn”, the scenario Grand Tack: planets migrate inward, and then change course dramatically, something like a boat that turns around a buoy).
In a previous model, developed by Bradley Hansen of the University of California at Los Angeles, the terrestrial planets in their orbits end current with their masses present as a result of a particular set of circumstances. Such circumstances require that 10 million years after the formation of the Sun all bricks that will form then the inner solar system, called planetesimals, occupy a ring that extends from 0.7 to 1 astronomical unit (1 astronomical unit is the average distance from the Sun to the Earth ). According to the scenario Grand Tack, the outer edge of this ring would be drawn from Jupiter as it moved toward the Sun on its “conveyor belt”, creating a vacuum in the disc until the current Earth orbit.
Konstantin Batygin believes the answer may lie in the primordial Super Earths. The open area of the inner solar system corresponds almost exactly to the orbital portion where the Super Earths are. It is therefore reasonable to assume that this region, in the primordial stages of the solar system, has been cleared of a group of planets of the first generation who did not survive.
The calculations and simulations produced by Batygin Laughlin show that while Jupiter moved inward, dragged along all the planetesimals that where met along the way, leading them towards the sun. While the planetesimals were approaching the Sun, their orbits become more elliptical. These new more elongated orbits allowed the planetesimals, especially those with radii of the order of 100 km, to penetrate previously unexplored regions of the disk, triggering a cascade collision between debris. In fact, the calculations show that during this period each planetesimal would have collided with another object, at least once every 200 years, with such violence to crack and fall toward the Sun.

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