Nature reveals why "hot Jupiters" move in reverse?

A study published today in the journal Nature led by Samdar Naoz, a former researcher from Tel Aviv University who is posted in the USA answers the riddle of why many planets in other solar systems move in the opposite direction to the direction of their sun's rotation and why quite a few of them, including those larger than the planet Jupiter are in close proximity to their sun. The research also brings new insights into our solar system

Over 500 planets outside the solar system have been discovered since 1995. However, due to the development of technology, only in recent years have astronomers noticed that some of them rotate their suns in opposite directions. Many of these planets are called hot Jupiters because they are as big as Jupiter or bigger than it (sometimes even more), but unlike the situation in the solar system where the planet Jupiter is very far from the Sun, these are planets that are very close to their Sun, so much so that it takes them days Few orbit their sun, compared to the almost three months it takes for the closest planet to the sun, Mercury, to orbit it.

How did these planets come from their position in the middle of the solar system to such a close proximity to the sun and especially why a considerable proportion of them - about half - move in the opposite direction. These two puzzles are solved at once in a study, the results of which are published today in the journal Nature, led by Dr. Samdar Naoz, a postdoctoral researcher at Northwestern University, together with Dr. Will Farr, Prof. Yoram Litvik (also a former Israeli , but completed his studies in the USA), Prof. Fred Racio and PhD student Jean de Sedia.

According to Dr. Naoz, who completed her third degree at the School of Astronomy and Astrophysics at Tel Aviv University, the very discovery contradicted a long-standing theory of the formation of solar systems, and which was mainly based on our solar system, which turned out to be an anomaly in the landscape where all the planets move with the axis of rotation of the sun, and more or less in the plane of its equator. "When you look at the other solar systems that have been discovered, you see that half of the planets whose rotation axis can be measured are above or below the equatorial plane and that in half of these planets, the planets move in opposite directions.
This required the team at Northwestern to slightly change and rebuild the theory of the creation of the solar systems, by adding another, external body that influences it. In the existing theory it is said that initially there is a cloud of gas and dust that begins to swirl. Then the sun is formed in its center, and in its equatorial plane the planets are formed from the remnants of the gas cloud that continue to surround it in the same plane and in the same direction in which it also rotates around its axis.

By adding an external factor to the model - a planet or companion star (an additional sun in double star systems) is above the equator, and it pulls the planets to it somewhat. By using the old Newton's laws and the tidal forces acting on the planet once it got close enough to its sun, the researchers were able to build a mathematical model, prove it and build a simulation based on it. According to the model, Dr. Naoz explains: "In order to show the phenomenon and simplify the explanation, we focused on a system that has a sun and one more planet, such as Jupiter, which is at a distance of Jupiter from its sun, and another planet with an elliptical orbit that affects the Jupiter-like planet that is initially located In an almost circular orbit in the equatorial plane and in the direction in which the sun rotates around an axis in the initial phase. When a system exists in such a configuration, you see that little by little, the influence of the outer body begins to affect the orbit of the inner planet and it begins to oscillate between its original orbit and an elliptical orbit.

When it rises above the equatorial plane or descends below it, its orbit is circular and when it is close to the plane, its orbit is very elliptical. Over time, its orbit becomes more and more elliptical until one of the foci becomes very close to the Sun and then it has the possibility of trapping it in a close orbit with the help of tidal forces."

So far there is an explanation of how a planet like Jupiter reached an orbit where it orbits the sun at a short distance, but why in 50% of cases it also orbits it in the opposite direction to the direction of rotation?

According to Dr. Naoz, from the model he built, it turned out that the fluctuations between the shape of the track and the height of the track above the plain are so great, that in about fifty percent of the cases the track turns upside down." Now the question is at what stage in its orbit does the sun catch it, if it happens to catch it when it is in the direction opposite to the direction of its self-circulation, that will be the direction in which it will circle it forever.
"Our model is suitable for observations, it is also quite simple and mainly relies on Newton's laws, on a process that has been known since the sixties, the problem is that the way the model was used for fifty years there was an error. The physics is there, people simply made a mistake in the way they did the calculations for fifty years, our Tzut corrected the error and now he explains the calculations very well." Dr. Naoz concludes.