Shulou(Shulou.com)11/24 Report--

When it comes to planetary rings, the first thing that comes to mind is Saturn's beautiful rings. Saturn is also the first planet to be found to have planetary rings. Several other giant planets in the solar system actually have their own rings, but most of them are not obvious. Although the average thickness of Saturn's rings is only 20 meters, its range is almost twice the radius of Saturn. Apart from Uranus, other planetary rings are at best a "hula hoop" compared to Saturn's rings.

Although Saturn's rings dominate the solar system, Saturn's rings are at best a "swimming circle" in the Milky way, which has hundreds of billions of stars. There must be exoplanets with giant rings, such as J1407b, which is called "Super Saturn".

The host star J1407 (V1400 Cen) of J1407 b is a sun-like star more than 400 light-years away. This star is almost the same as our sun in mass and size, except that it is too young, only about 1600 million years old, compared with the 4.6 billion-year-old sun, that is, a little baby just after the full moon.

In 2007, astronomers found that the brightness of the star suddenly dimmed, and after careful observation, there was a solar eclipse. The occurrence of a solar eclipse is not surprising, indicating that there may be planets around the star, and the transit will occur when the planets move between the star and us.

It's just that this eclipse is weird: when exoplanets are discovered by the transit method, because the exoplanets are very far away from us, the occlusion of the planets to the stars is very limited, and the changes in the brightness of the stars are very weak. But this eclipse is very deep, that is, it is blocked more.

Second, the usual eclipse process is usually very regular, but the whole occlusion process is very complex; and this eclipse is very long, lasting nearly two months. According to various signs, astronomers speculate that the star may be obscured by a gaseous giant planet with a huge planetary ring.

Planetary rings are familiar to us, and there are ready-made samples in the solar system. Although the origin of Saturn's ring is still controversial, many people believe that it may have been one of Saturn's moons, later hit by asteroids and other celestial bodies, or fell into Saturn's Roche limit due to orbital decay. Coupled with the fact that it is a celestial body made mainly of water ice, it is not very strong and is easily disintegrated by Saturn's tidal forces, forming a fragmented ring around Saturn.

So some scientists believe that J1407 b may also be due to tidal forces, disintegrating the celestial bodies around it, or simply being hit by a large celestial body, forming this ring-shaped wreckage.

But it soon became clear that something was wrong: if it was debris, it would be too big. Saturn's rings are still within Saturn's Roche limit, but the rings of J1407 b have far exceeded the Roche limit of the planet and are close to the radius of the Hill sphere.

The Hill ball can be understood as: if a small celestial body wants to become a planet's moon, you must be within the planet's gravitational control range, which is the planet's Hill ball.

One is the range where gravity is strong enough to tear celestial bodies apart, and the other is an area controlled only by gravity. You can imagine the gap between the two. Based on observational data, astronomers estimate that J1407b's rings are 180 million kilometers in diameter (about 1.2astronomical units), nearly 200 times the size of Saturn's rings. If J1407b is placed in the position of the sun, its rings will even reach the orbit of Venus. So some scientists believe that the rings of J1407 b should not be mature planetary rings like Saturn's rings, but the CSDs left when the planets are forming.

According to the theory of planetary formation, this was originally a gas disk gathered by gravity. After about millions of years, the embryo of the planet was born in the center of the disk, and the gas disk became a circumstellar disk. The peristellar disk continues to transport gas and dust to the central planet, acting as an accretion disk. When the gas in the circumstellar disk is stripped clean, because only solid dust and debris are left, the viscosity of the circumstellar disk will drop significantly, which will cause the entire disk to spread in all directions, and a huge annular planetary disk will be formed.

This circular disk is not as mature and stable as Saturn's rings, it is still in the transitional stage. The dust particles here gather into clusters and gradually evolve into the planet's moons, leaving gaps in the planetary disk, that is, the orbital areas that are cleared by the moons. The total mass of the J1407 b planetary disk is equal to that of the Earth, and astronomers have found that there seem to be some satellite objects here.

When it seemed that all the speculation was coming to light, a key question began to haunt astronomers.

From the first solar eclipse in 2007 to 2015, there was no similar solar eclipse on that star in eight years. So astronomy cannot know the orbital period of the planet, or even whether it is orbiting the star.

In 2018, 10 years after the first solar eclipse, astronomers collated a century of photographic data from 1890 to 1990, but still found no record of the star darkening. This time, however, astronomers have also made some preliminary judgments about the planet: it may be a gaseous giant planet 5 to 20 times the mass of Jupiter, orbiting the star J1407 in an elliptical orbit with a high probability of a period of 14 to 17 years. In other words, if the conjecture is correct, the planet should transit again between 2021 and 2024. However, as of 2023 today, we still do not see a second solar eclipse on J1407.

If J1407 b really has nothing to do with this star, and considering that it may have 20 times the mass of Jupiter (properly a brown dwarf), then this huge planetary ring may not be a planetary ring at all, but a separate planetary system.

In other words, J1407 b is actually a newly formed star (it is not a star, after all, it is not massive enough, it can only be regarded as a dead star), its peristellar disk is actually a protoplanetary disk, and the moons born here are actually planets. In the future, with the formation of the planets, the original planetary disk will gradually disappear, and a mini planetary system will be born.

However, this guess can only be said to be possible, but it is no more likely than the guess of the planets. At present, the mainstream view is that this is a planet with a highly eccentric orbit orbiting a star.

Whether it is an independent planetary system or the circumstellar disk of a planet, everything depends on evidence. After all, there is still some time to go before the forecast of 2024, and 2024 is not an accurate deadline, and the 14-17-year cycle is only a rough forecast based on the only observations.

If we do observe the transit of J1407 b again in the future, this time we should not only be able to judge whether it is a planet or not, but also have a more detailed understanding of it and its planetary rings. Because compared with those days, today we have a sharp weapon for the study of exoplanets, that is, the Weber Space Telescope.

The near-infrared spectrometer equipped by the Weber Telescope can not only reveal the particle size and composition of the ring, but even because the moons in these rings are still in the process of formation. so they can be identified if they have their own "satellite rings". Finally, whether J1407 b will transit again, let's wait and see.

This article comes from the official account of Wechat: Linvo says ID:linvo001, author: Linvo

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