“New Research Explains the Relative Stability of the Inner Solar System Planets”

SPACE — Earth might not have been there, destroyed in a brutal collision between planets. That’s because of the orbits of the inner solar system planets; Mercury, Venus, Earth and Mars, so messed up.

In fact, modeling suggests the inner orbiting planets should have collided with each other by now. However, that didn’t happen. The secret that controls the destiny of this planet has long puzzled scientists. However, scientists are now coming up with new claims.

Research published May 3, 2023 in the journal Physical Review X claims it can explain the reasons for the stability of the Earth and its companions. Through a deep dive into models of planetary motion, the researchers found that the motion of the inner planets is constrained by certain parameters that act as a tether holding back the system’s chaos.

Scroll to read

Scroll to read

As well as providing a mathematical explanation for the alignments found in the solar system, this new research insight could help scientists understand the trajectories of exoplanets around other stars.

Planets are unpredictable

Planets are constantly tugging on one another’s gravity, and that slight pull keeps making tiny adjustments to the planet’s orbit. The outer planets (Jupiter and so on), which are much larger, are more resistant to minor tugs and so maintain relatively stable orbits.

The problem of trajectories for inner planets, however, is still too complex for scientists to solve with precision. In the late 19th century, the mathematician Henri Poincare proved that it was mathematically impossible to solve the equations governing the motion of three or more interacting objects (often known as the three-body problem).

As a result, the uncertainties in the details of the planet’s initial position and velocity have continued to grow over time. In other words: It is possible to take two scenarios where the distances between Mercury, Venus, Mars and Earth differ only slightly. In one scenario, the planets will collide with each other and in another scenario, they will deflect each other.

The time it takes for two tracks with almost the same initial conditions to deviate by a certain amount is called the Lyapunov time of a chaotic system.

In 1989, Jacques Laskar, astronomer and director of research at the National Scientific Research Center and Paris Observatory and co-author of the new study, calculated Lyapunov times characteristic of the orbits of the inner solar system planets. He found Lyapunov only needed 5 million years.

“That means you’re basically losing one digit every 10 million years,” Warriors told Live Science.

So, for example, the initial uncertainty of the planet’s position is 15 meters, 10 million years later this uncertainty becomes 150 meters. After 100 million years, another 9 digits are lost, giving an uncertainty of 150 million kilometers, equivalent to the distance between the Earth and the sun. “Basically you don’t know where the planet is,” Warriors said.

100 million years may sound like a long time, but our own solar system is over 4.5 billion years old. The absence of dramatic events like planetary collisions or planets being knocked out of all that chaotic motion has long puzzled scientists.

Laskar then looked at the problem in a different way. It simulates the trajectory of the inner planet over the next 5 billion years, stepping from one moment to the next. He found the probability of a planetary collision was only 1 percent. Using the same approach, he calculated, it would take an average of about 30 billion years for one of the planets to collide.

Survive in Chaos

Delving into the math, Laskar and his colleagues claim to have identified so-called symmetries or ‘quantities retained’ in gravitational interactions. “Symmetry creates a practical barrier in the chaos of planetary wanderings,” claims Warriors.

The quantity that arises remains almost constant and inhibits certain chaotic movements, but does not prevent total chaos. Laskar gave an example, like the raised lip of a dinner plate, it will prevent food from falling from the plate, but not totally prevent it from falling. “We can thank this quantity for the apparent stability of our solar system,” he said.

Professor of Planetary Science at the University of Arizona, Renu Malhotra highlighted how subtle or ingenious the mechanisms identified in the study were. “It is interesting that the orbits of the planets of our solar system show very weak chaos,” he said.

In another work, Laskar and colleagues are looking for clues as to whether the number of planets in the solar system was once different from what we see today. Even so, all the stability claimed in the study is still in question.

For one thing, did the retained quantity always occur over billions of years, before life evolved? Source: LiveScience