How many planets can the solar system have?
Our solar system has eight planets, but How many planets like Mars or Jupiter could orbit
within our solar system without causing damage to Earth? How many planets fit in
the solar system? Let's find out!
What is a planet? To define approximately how many
planets could fit inside our solar system, we must first remember precisely what " Planet " means.
In astronomy, a planet is a celestial body that orbits around a star and is
large enough to have gravity, which allows it to have a spherical shape.
In our solar system, eight known planets orbit the Sun. Each planet
is unique in its size, composition, and environmental conditions. For example,
Venus is the hottest planet in the solar system, while Neptune is the coldest and most distant.
Planets formed from the disk of gas and dust surrounding the star they orbit.
Small objects form as the disk cools and condenses, which merges to form planets.
The composition of a planet depends on its distance from the star and the number of materials
available in the protoplanetary disk; thus, if the disk has many complex materials such as carbon,
iron, or zinc, the resulting planet will be rocky, while the formation disk is composed
mainly of gases such as hydrogen and helium the resulting planet will be a gas giant.
Dwarf planet Then we have
the more minor brothers of the planets, the dwarf planets. Although it is colloquially
believed that the main difference between dwarf planets and Planets is size, this is not true.
The main difference between a planet and a dwarf planet is that a dwarf
planet has not "cleared its orbit" from other objects, whereas a planet has.
This means that a dwarf planet orbits the Sun, just like a planet, but there are other objects
in or near its orbit that it hasn't ejected, and every so often, they get in its way.
A dwarf planet collides or passes very close to various objects on its way around the Sun,
mainly asteroids, unlike a planet that has wholly swept its orbit of any other
object and doesn't bump into anything during its entire path around the Sun.
In 2006, the International Astronomical Union (IAU) established a formal definition of a planet,
which established three criteria for an object to be classified as a planet, these are:
1: It must orbit the Sun 2: Have enough mass to have a spherical shape and
3: To have cleared its orbit of other objects entirely it might
encounter on its way around the Sun. If an object does not meet these three
requirements, it cannot be classified as a planet. There are several recognized dwarf planets in our
solar system: Ceres, Pluto, Haumea, Makemake, and Eris, with more expected to be discovered.
But even though they don't meet the strict definition of a planet,
dwarf planets are essential for understanding the evolution and diversity of the solar system.
How small can a planet be? If we want to fill the solar system
with planets, let's think about the smallest ones first, one way we could put several planets in
orbit around the sun without their gravitational fields affecting Earth is to make them very small.
This is because the smaller a planet is, the less mass it is;
the less mass it is, the less its gravitational force of attraction.
That said, let's remember that the second requirement for an object
to be called a planet is that it HAVE ENOUGH MASS TO HAVE A SPHERICAL SHAPE.
But what mass is this? For an object to be spherical,
it must have enough mass and gravity to compress its material toward the center and balance its
gravitational force in all directions. This minimum mass necessary to achieve the spherical
shape depends on the composition of the object and the gravitational force it experiences.
In general, it is estimated that an object needs to have a mass of at least a few tenths of the
mass of the Moon to achieve the spherical shape. However, this is only a rough estimate, as the
exact amount of mass needed can vary depending on the composition and density of the object, as
well as the speed of rotation and other factors. For example, the dwarf planet Ceres, which lies in
the asteroid belt between Mars and Jupiter, has a mass of about 0.00015 times the mass of Earth but
is large enough to be spherical due to its gravity. By comparison, the asteroid Vesta, which
is significantly smaller than Ceres and has a mass of only about 0.00002, the mass of Earth, is
not spherical due to its lower mass and gravity. In summary, the mass required for an object to be
spherical can vary depending on composition, density, and other factors, but in general,
a mass of at least a few tenths of the mass of the Moon is needed to achieve this shape.
That is to say that if there were an object the size of Ceres orbiting the Sun
in orbit free of asteroids, it should strictly be classified as a Planet.
Well, we already have a minimum size, now follow the distance. What is the
minimum distance at which we could place planets the size of Ceres?
This is a more difficult question since the planets do not always have the same distance.
Let's remember that the orbits of the planets around the sun are not circular but elliptical,
so sometimes they move towards and away from the sun, but they
also move towards and away from each other. The minimum distance in which the planets can
be separated depends on many factors, such as the mass, the orbital speed, and the gravitational
disturbances of other celestial bodies in the solar system; it must also be considered
that the planets sometimes get very close and this it does not produce any change on Earth.
There are specific orbital configurations where the planets can be relatively close to each other.
For example, during a Mars "opposition" event, the minimum distance between the
two planets may be about 55 million kilometers when Earth is directly between the Sun and Mars.
Another close configuration with Earth occurs during Venus's "inferior conjunction" when
Venus is between Earth and the Sun. The minimum distance between the two
planets can be about 40 million kilometers. In our solar system, that is the minimum
distance between two planets, but things change if we look at other solar systems.
Orbital resonance Orbital resonance
or orbital synchronization is a phenomenon that occurs when two or more celestial bodies are so
close that the orbit of one affects the other. Several planetary systems have been found to
have planets with orbits in sync, especially when the planets are very close. One of these
systems is the Kepler-223 planetary system, located about 1,200 light-years away from us.
Kepler-223 consists of four similar-sized planets with nearly circular orbits and are
arranged in a chain. The two outer planets are in 4:3 orbital resonance, which means that for
every four complete orbits of the outer planet, the inner planet completes three full orbits.
The two inner planets in the system are also in 4:3 orbital resonance with each
other, meaning that for every four complete orbits of the inner planet,
the outer planet completes three full orbits. This type of orbital resonance is believed to be
due to gravitational interactions between planets as they orbit their host star. As the planets
gravitationally interact, they can transfer orbital energy, synchronizing their orbits.
This phenomenon can also be seen in our solar system on the Moons of Jupiter,
where the orbits of Io and Europa have a 2:1 resonance, meaning that for every two
turns Io completes, Europa completes 1. In turn, Io and Ganymedes have a 4:1 resonance;
that is to say, for every four turns that Io makes, Ganymedes makes 1.
Jupiter and Saturn also have orbital periods in a 5:2 resonance. This means
that for every five turns around the Sun that Jupiter makes, Saturn makes 2.
The orbital synchronization between planets is given by their proximity, size, and mass,
so the more significant the planets' mass and proximity in the solar system, the probability
that they are synchronized will increase. Knowing this, the number of planets the
solar system could host will depend mainly on their size, and its distance.
The minimum size could be similar to that of the dwarf planet Ceres and the minimum distance would
be the minimum distance between Earth and Venus, which is approximately 40 million kilometers.
Suppose they are minor planets like Earth or smaller like Pluto or Ceres.
In that case, they will be able to fit a large amount, considering that in our solar system,
there are at least 20 objects that have similar sizes to Ceres, especially the
natural satellites of the gaseous planets. It is impossible to calculate an exact
amount. But, it is possible to determine that could fit at least twice as many planets as
there are currently could fit in our solar system without their gravitational force
interfering with the orbits of other planets. And if we removed the gas giants and replaced them
with more minor rocky planets, even more, would fit since rocky planets are so much more minor. So
a solar system with up to 30 small rocky planets could exist without any problem, although so far
nothing like this has been discovered. How big can a planet be?
If we go to the other extreme, there are also mass limits on the side of the giant planets,
although in this case, the limits between what is and what is not a planet are not so clear.
The International Astronomical Union established in 2006 that the mass limit of a planet is 13
times the mass of Jupiter. This figure was established because it was calculated that
once this mass limit is reached or exceeded, the planet would begin to be crushed by gravity,
which would cause the atoms in the core to fuse and then become a Star.
However, years later, when we discovered massive exoplanets, we found exoplanets
equal to or larger than Jupiter, which orbited extremely close to their star.
These planets were classified as " hot Jupiters " because their surface temperatures are often
scorching, often exceeding 1,000 degrees Celsius. That is, these planets have identical temperatures
to brown dwarfs. Brown dwarfs are a type of "failed star," that is,
a substellar object that is located on the border between stars and planets since they
have a mass more significant than that of the planets but does not reach the mass necessary
to initiate nuclear fusion in their core, which would prevent them from becoming true stars.
This classification was created because they wanted to implement a way to divide the border
between planets and stars, but then... What about the Hot Jupiters? Are they gas giants,
or are they brown dwarfs? It is not yet clear even to astronomers.
As we can see, the classification of what is and what is not a planet is not clear
when we analyze the maximum limits, and this is important if we want to fill our solar system
with massive planets like Jupiter or brown dwarfs. There would be no place for so many;
we could only place two or a maximum of three planets like Jupiter before
the orbit of one interferes with the other; this would cause a gravitational attraction
in which they would end up colliding and merging into a single object, possibly forming a star.
In the universe, there are examples of stellar systems where two or more of these objects can
quietly orbit their host star. But, although the distances between each planet are enormous,
our solar system is relatively small compared to others. There could not be as many giant
planets as Jupiter without their immense gravitational pull endangering life on Earth.