On 24 August 2006, the General Assembly of the International Astronomical Union held a meeting. Astronomers discussed a topic together, "What kind of celestial body can be counted as a planet?" "
Why are astronomers discussing this topic? It turns out that Pluto, the solar system's "ninth planet," has been controversial since its discovery. Astronomers debate whether Pluto is a real planet. Eventually, after heated discussions, astronomers redefined planets. Pluto was demoted. Since then, the idea of the eight planets of the solar system has become the mainstream view.
Planets of the Solar System
So what is a planet? Scientists define it this way.
First of all, the planet must be a celestial body rotating around the star. Second, planets need to have enough mass to keep themselves in a spherical shape. Third, the planet must be able to clear the area near its orbit, and there can be no larger objects than it in its orbital range.
After scientists define planets this way, there are only eight objects in the solar system that meet all three conditions at the same time. That is what we are now referring to as the eight planets of the solar system.
planet
Planets orbit stars. There are eight planets around the Sun. There are about 150 billion to 400 billion stars in the Milky Way. Are there any planets around them? The answer is yes. Scientists have reportedly found about 4,000 planets in the universe beyond the solar system. So which is the largest planet in the universe that scientists have discovered so far?
In July 2015, scientists at ETH Zurich discovered a planet beyond the solar system through the Southern Observatory in Europe. Scientists call it HD 100546b. This is a giant gas giant planet. This planet is currently the largest planet ever found in the universe.
Imaginary image of HD 100546b, the largest planet in the known universe
How big is this planet? HD 100546b is about 335 light-years away and orbits a star called HD 100546. Its diameter is about 9,865 million kilometers. Let's compare it to Earth and Jupiter and other celestial bodies to see how big the largest known planet in the universe is.
We live on Earth, and the world we live in is very huge for human beings. The diameter of the Earth is 12,756 km. However, In the solar system, Earth is not yet the largest planet. Earth ranks only fifth among the eight planets in the solar system. The largest planet in the solar system is Jupiter. Jupiter is 142984 kilometers in diameter. It is 11 times the diameter of the Earth, more than 1300 times the volume of the Earth, and 318 times the mass of the Earth.
Earth and Jupiter
In front of Jupiter, the earth is as small as a small glass marble in front of a basketball.
The feeling of the Earth in front of Jupiter
However the diameter of the planet HD 100546b is a staggering 9865 million kilometers. It is almost 7 times the diameter of Jupiter and more than 77 times the diameter of the Earth. So based on the multiples of their diameter difference, we can simply calculate that HD 100546b is 343 times the volume of Jupiter and more than 450,000 times the volume of Earth.
In other words, the largest known planet in the universe can hold more than 340 Jupiters and more than 450,000 Earths! The size of this planet is no less than that of the Sun. The diameter of the Sun is 1,392,000 km, which is only 1.4 times the diameter of HD 100546b. It is even 5 times larger in diameter than the Sun's stellar neighbor, Proxima Centauri.
HD100546b compared to Jupiter, Sun, and Earth
Interestingly, scientists have found that this is a very young planet. HD 100546b was formed around 5 million to 10 million years ago. Scientists have found that the planet is still in a planetary disk, and it is also gathering gas and dust. That said, the planet HD100546b is currently in its infancy with planet formation. It's still growing up.
The situation in the early days of the formation of the solar system was similar to what the star HD100546 is like today. Primitive Jupiter also accumulated gas and dust in the planetary disk, slowly becoming the largest gas giant in the solar system. The planet HD 100546b is already 20 times the mass of Jupiter, but it is still growing. If this continues, what will it look like?
Planetary disks around early stars
Sometimes we wonder why Jupiter doesn't become a self-luminous star like the Sun. The fundamental reason is that jupiter's mass is still too small. If Jupiter's mass reaches 7% of the Sun's mass, that is, its mass increases by a factor of 70, it will have enough mass to trigger an internal nuclear fusion reaction to become a star.
While HD 100546b is still growing, if there is enough material in the surrounding planetary disk, it is possible to increase its mass to 7% of the Sun and trigger an internal nuclear fusion reaction to become the smallest star. In that case, it would not be the largest planet in the universe, but a companion star 100546 star HD.
The smallest star red dwarf
Once HD 100546b becomes a star, its volume will be greatly reduced. Because of its own huge mass, it will greatly increase its density. At that time, it was not as large as Jupiter.
However, HD100546b may face another fate. If its mass doesn't reach the minimum standard for becoming a star, it becomes a brown dwarf, a celestial body that scientists jokingly refer to as a "failed star."
Brown dwarfs
In any case, for a celestial body that is still in its growth stage, its future is full of infinite possibilities. Isn't that true of people either? What do you think about that?
More exciting content, welcome to pay attention to rabbitski to talk about science. Let's talk about interesting scientific knowledge!