Reported by Reference News Network on July 5. On May 9, American Fun Science website published an article titled "Scientists Discover Secret of 'Symmetry' Protecting Earth from Chaos in Space." The author is Anna Deming and content is composed as follows:
Earth probably shouldn't exist.
This is because orbits of "inner planets" of solar system - Mercury, Venus, Earth and Mars - are mixed up, and, according to models, they should have already collided. However, this has not yet happened.
A new research paper published May 3 in journal Physical Review X may finally explain why.
By studying patterns of planetary motion, researchers found that movement of planets in inner belt is determined by certain parameters that act as "tethers" that keep solar system under control. In addition to providing a mathematical explanation for apparent harmony of our solar system, new study's findings could also help scientists understand orbits of planets around other stars.
The planets are constantly pulling on each other with gravitational pull, and these pulls are constantly adjusting orbits of planets. The "outer planets" are much larger, more resistant to these relatively small pulls, and thus remain relatively stable in their orbits.
However, question of trajectories of planets in inner belt remains too complex to be fully resolved. In late 19th century, French mathematician Henri Poincaré demonstrated that it was mathematically impossible to solve equations involving motion of three or more interacting bodies, often referred to as "three-body problem". As a result, there is uncertainty about details of planet's initial position and speed growth over time. In other words, two scenarios are possible when Mercury, Venus, Mars and Earth are at slightly different distances: in one case, planets collide, in other they drift.
In a chaotic solar system, time it takes for two orbits with almost identical initial conditions to separate is called "Lyapunov time". In 1989, Jacques Rascal, an astronomer at French National Center for Scientific Research and co-author of a new study, calculated that Lyapunov time constant for planetary orbits in inner solar system was only 5 million years.
"Essentially, this means losing one digit every 10 million years," Rascal told Fun Science. years, nine more digits will be lost, resulting in an uncertainty of 150 million kilometers, which is equivalent to distance between Earth and Sun. "We basically have no idea where this planet is," Rascal said.
While 100 million years may seem like a long time, solar system itself ismore than 4.5 billion years, and absence of dramatic events such as planetary collisions or ejection of planets from a chaotic system of motion, has always puzzled scientists.
Lascar then approached question in a different way: he modeled trajectories of planets in belt for next 5 billion years, from one moment to next. He found that there was only a 1% chance of planets colliding. Using same method, he calculated that, on average, any collision of planets takes about 30 billion years.
Deepening into this mathematical problem, Rascal and his colleagues for first time identified a "symmetry" or "conservation" in gravitational interactions that "creates a practical barrier to chaotic motion of planets."
The number of these naturally occurring (planets) stays about same, which moderates some of chaotic movement but doesn't completely stop it, much like raised edges of a dinner plate keep food from falling off plate but don't stop it. t Block it completely. We can thank this (planetary) population for making our solar system seem stable.
Renu Malhotra, professor of planetary science at University of Arizona, highlighted how subtle mechanisms revealed in this study are. Interestingly, "the orbits of planets in our solar system show unusually little turmoil," Malhotra, who was not involved in study, told Fun Science.com.
Lascall and his colleagues are looking elsewhere for clues to see if number of planets in our solar system is different from what we see now. Although today stability of planetary orbits in our solar system is obvious, question of whether this was always case for billions of years before appearance of life remains open.