Like the ninth planet? – Planets with extreme orbits not an anomaly at all

Planets with giant orbits – such as the possible ninth planet in the solar system – are not an anomaly at all, but a normal by-product of the chaotic formation phase of solar systems. At least, that is the result of simulations by an international research team that has modeled various planetary systems and their development. In the process, planets were repeatedly catapulted into particularly large and eccentric orbits, in which they were nevertheless stabilized. Exoplanets with large semi-major axes of the ellipse between 100 and 10,000 astronomical units (AU) are therefore likely to be much more common than assumed.

Not so unlikely in the solar system

As the group led by André Izidoro from Rice University in the US state of Texas explains, it has been a mystery for years how large planets could end up in such wide orbits and that they are sometimes thousands of times further away from them than the Earth is from the sun. There have also been repeated references to a planet orbiting far away in the solar system, which has recently attracted more attention as “Planet 9”. The simulations have now provided a possible answer to the question and suggested that such planets are a not-so-rare part of planetary systems. The work is presented in the scientific journal Nature Astronomy.

The simulations have now suggested that planets are regularly pushed into particularly wide orbits in the chaotic early phase of a star system. In the star clusters in which this normally happens, they are then often stabilized by other stars and orbit their stars, decoupled from the processes in the inner system. As soon as the stars that have formed together have moved further apart, these planets would be frozen in their orbits, so to speak. Unstabilized planets would instead leave their system altogether and form the population of lonely planets that we are only just beginning to understand.

In the solar system, the research team has identified two phases in which a large planet could be ejected in this way. This was the case during the formation of Uranus and Neptune, and later during the instability phase of the gas giants. Overall, they see a probability of “up to 40 percent” that an object of the postulated size of the theoretical ninth planet was catapulted to the edge of the solar system. Overall, they believe that around one in every one thousand-star systems should have such an extremely distant exoplanet, with different composite planetary systems being differently efficient in their positioning.

Is there another large planet – and if so, where?

There has long been speculation about another planet far out in the solar system. Because Pluto has not been counted as a planet for almost 20 years, such a celestial body would be the ninth planet. Astronomers Mike Brown and Konstantin Batygin from the California Institute of Technology (Caltech) in particular have been conducting extensive research on the subject and have repeatedly published papers on the subject. Just a few days ago, an international research team presented direct evidence of such a planet, but it would not match the one the two Californians suspect in the solar system. A newly discovered dwarf planet with an extreme orbit also does not fit in with Brown and Batygin's theories.

(mho)