Why is Jupiter not a star due to its large size?

The smallest known main-sequence star in the Milky Way is a red dwarf called EBLM J0555-57Ab, located 600 light-years from Earth. With an average radius of nearly 59,000 kilometers, this star is only slightly larger than the planet Saturn. Therefore, this red dwarf is the smallest known star that has hydrogen fusion in its core; The process that provides the star’s energy to burn until the end of its life.

In the solar system, there are two objects bigger than the mentioned star. One of them is the sun; But the other is the planet Jupiter , whose radius reaches 69,911 kilometers; But why is Jupiter a planet and not a star according to these dimensions?

The answer to the above question is simple: Jupiter does not have enough mass to support the hydrogen-to-helium fusion process. The star EBLM J0555-57Ab is nearly 85 times more massive than Jupiter. If this star was a little lighter, it would not be able to perform the hydrogen fusion process; But if the solar system had a different structure, would it be possible for the planet Jupiter to shine as a star?

There are different groups of objects that can be classified as failed stars. These objects are called brown dwarfs and can fill the gap between gas giants and stars. The mass of brown dwarfs starts at 13 times the mass of Jupiter. These objects are heavy enough to support nuclear fusion, but this fusion is not of ordinary hydrogen but of deuterium or heavy hydrogen. Deuterium is an isotope of hydrogen that has one proton and one neutron in its nucleus instead of just one proton. The temperature and pressure of deuterium fusion is lower than the temperature and pressure of hydrogen fusion.

Since deuterium fusion occurs at lower mass, temperature and pressure, it is one of the steps to reach hydrogen fusion for stars whose accretion process continues and absorb the surrounding mass; But some objects never reach the required mass for hydrogen fusion.

Shortly after the discovery of brown dwarfs in 1995, these objects were called failed stars or ambitious planets, but numerous studies show that the formation of these objects like stars was from cloud collapse, not core accumulation; Some brown dwarfs do not even have enough mass to fuse deuterium, making them difficult to distinguish from planets.

Modeling shows that the upper limit of planetary mass and formation by core accretion method is less than 10 times the mass of Jupiter. As a result, the planet Jupiter is not included in the group of failed stars; But by thinking about the cause of this issue, we can get a better understanding of how the universe works. In addition, the planet Jupiter has a stormy, striped and twisted appearance, and the existence of humans would probably not be possible without this gas giant.

Why doesn’t Jupiter have big and bright rings like Saturn?

Considering the similarity of the planet Jupiter to its neighbor Saturn, it is natural to ask why this planet does not have clear and bright rings like Saturn. However, Jupiter has thin, narrow rings made up of dust that only shine when there is sunlight in the background. According to new research, these narrow rings lack brightness because the large Galilean moons prevent rocks and dust from accumulating around Jupiter. According to Stephen Kane, an astrophysicist at the University of California Riverside:

The fact that Jupiter doesn’t have brighter rings than Saturn has bothered me for a long time. If Jupiter had such rings, it would certainly appear brighter to us because this planet is much closer to Earth than Saturn.

Keen and his colleague Zhixing Li, an astrophysicist at Riverside University, ran a series of simulations of objects orbiting Jupiter to test the hypothesis of a giant ring system around Jupiter at some point in history. The aforementioned simulations considered the orbital motion of Jupiter and its four largest moons, known as the Galilean moons, which are: Ganymede (which is even larger than Mercury and is known as the largest moon in the solar system), Callisto, Io, and Europa. The researchers also included enough time for the formation of a ring system in their simulations. According to this modeling, Jupiter has not even had rings similar to Saturn in the past and is unlikely to have them in the future. Kane explains:

Giant and heavy planets have heavy moons and these moons prevent the formation of rings of matter. The Galilean moons of Jupiter, one of the largest in the Solar System, would quickly destroy any potential large rings that might be forming.

Jupiter has narrow rings, most of which are dust from moons and material that may have been thrown into space by impact events. On the other hand, much of Saturn’s rings are made up of ice, possibly fragments of comets, asteroids, or icy moons that have been broken apart by Saturn’s gravity.

We know that Saturn’s moons play a vital role in the formation and maintenance of its rings, But one or more large moons can also gravitationally disrupt the rings and drive the ice out of the planetary orbit and into an unknown region. Although most people think that Saturn is the only planet with rings, rings around planets are very common even in the solar system. For example, in addition to Jupiter, the solar system’s ice giants Uranus and Neptune both have narrow rings of gas and dust.

Compared to other planets, Uranus has a strong axial deviation and its orbital axis is parallel to the orbital plane. The position of the rings of this planet is adjusted accordingly. Probably, a mass collided with Uranus and led to its axial deviation, or possibly this planet once had huge rings that caused this deviation. Of course, rings are not limited to planets. A small body with a width of 230 km called Chariklo, which is located in the orbit between Jupiter and Uranus, also has rings.

Also, the dwarf planet Haumea in the Kuiper belt has a ring. Simulations show that rings around ice masses are common due to the gravitational interaction and removal of ice from these masses.

To us astronomers, the rings are like bloodstains on a crime scene wall. When we look at the rings of the giant planets, we find evidence of the events that caused this material to accumulate.

Anyway, now that Jupiter has no spectacular rings, let’s enjoy Saturn’s rings. The Planetary Science Journal has accepted this research and is available on the arXiv database.

Why do none of the moons of the solar system have rings?

We have many strange moons in our solar system. hot and cold moons; Moons with liquids and dusty moons. One lunar planet is walnut-shaped and another is potato-shaped; But among almost 300 moons that have been discovered so far, not even one of them has rings. This is really strange.

Of the eight planets in the solar system, half have rings of dust and ice that orbit their equator. It is thought that Mars once had a ring, and according to new research, even our blue planet probably had a ring similar to Saturn’s ring about 500 million years ago, which lasted for tens of millions of years.

In addition, some dwarf planets also have rings; Although astronomers have not yet been able to understand how these rings are formed. Even some asteroids have their own rings.

While investigating the concept of ringed moons outside our solar system, Mario Socercchia, an astrophysicist at the Universidad Adolfo Ibánez in Chile, and his colleagues became involved in the question of why moons in our own cosmic neighborhood lack rings. In an interview with Science Alert, he explains:

I believe we are unlucky to some extent; Because we started observing the universe during a period when these structures no longer exist. After doing this research, I was convinced that these rings probably existed in the past.

On the other hand, the only reason we see Saturn’s rings is because we are in the right place and time. For this reason, we see solar and lunar eclipses; Because the moon is gradually moving away from the earth and at some point it will be so far that it can no longer completely cover the sun.

I wonder what mythical and epic stories we will hear from the inhabitants of other worlds about ringed moons. I mean, how will their stories and culture about the moons of the rings be different from our stories? There are infinite possibilities.

The scientists’ research has been accepted for publication in the Journal of Astronomy and Astrophysics and is available in the archive database.