Our solar system has more than a hundred moons. Only 3
of those are in the inner solar system. These are our very own moon and Mars’
Phobos and Deimos. Almost all of the remaining ones are satellites of the gas
giants. At the time of writing, 79 of those belong to Jupiter and 82 belong to
Saturn. Why is it these gas giants have so many moons? It has to do
with their massive size and the distance from the sun.
SIZE MATTERS!
Gravity plays an important in game of acquiring more natural
satellites. More massive an object is, more easily it can pull an object
towards it and then eventually into its orbit. The gas giants are absolutely
massive. The smallest giant, Uranus is 15 times more massive than the earth. So
no wonder they have so many moons.
Speaking of the gas giants, Uranus has 27 and Neptune has
14. Even comparing with the other two gas giants, Jupiter and Saturn have the most
number of moons. The reason is already mentioned and it is almighty gravity.
Jupiter is the biggest planet in our solar system and hence can trap more
object than any other planet. It can significantly change the trajectory of
various bodies fly past its sphere of influence. Saturn, being the second most
massive planet, has similar effect on nearby objects.
LOCATION MATTERS!
Other than their gravitational influence, the gas giants are
ideally located to trap objects. They are much farther away from the sun than
the terrestrial worlds. They can easily trap a small objects coming their way
i.e. in their gravitational influence. Jupiter is most ideally placed out of
all the planets for this. It is 3.5 times as far away from sun as Mars is from
the sun. It has a huge gravitational influence. It is about 318 more massive
than our earth. That is pretty big. This influence outweighs the force due to
other planets and the sun near the giant and hence, it is easy for it to
capture rocky worlds. So basically, to capture a huge number of moons, size
definitely matters!
Fun Fact: For the longest time, Jupiter held the record for
most number of moons in the solar system. But that changed recently. A team from Carnegie Institute of Science discovered 20 more moons orbiting Saturn
than was previously known taking the number of moons for Saturn up to 82
closely beating Jupiter. These numbers can change, however, as many more moon
may be there to be discovered around these planets.
WHY DO ROCKY PLANETS HAVE NO OR LESS MOONS?
The rocky planets, on the other hand, are small and contest
with the sun. The influence of sun is far greater than the
planets. This is the reason why Mercury and Venus have no moon while
earth has one moon which was a result of a catastrophic event. Mars is a bit
far away from sun and nearer to the asteroid belt and therefore caught 2 small
irregular shaped rocks. They are so small that they could not meet the
requirements for being round. More on that in this article.
The story of our moon is different from the moon of the gas
giants. As mentioned earlier, it was a result of a catastrophe and not
capturing an object flying past it making our moon the most unique in the solar
system. It is hypothesized that in the early solar system, Earth collided with
a Mars sized body known as Theia. This resulted in ejection of vaporized chunks
of Earth’s crust into the space. Due to gravity, these ejected particles stuck
together and formed our moon. This is why moon is so similar to earth in its
composition.
MOONS OF JUPITER AND SATURN
The Jovian system is very interesting. It is like a mini
solar system with so many objects going around the planet. Jupiter almost
behaves like a sun. But can it ever become a star? No, at least not our Jupiter. Here’s more on it. The rings of the planet and its 79 satellites make up this system. The
four biggest moons were the first ones to be discovered. They were discovered
by Galileo in 1610 and hence they are called Galilean moons. The fours moons
are Ganymede, Io, Europa and Callisto. Io is closest to planet while Callisto
is the farthest. Europa is the smallest but the most interesting out of all the
moons in the solar system. It is covered with an icy crust below which there
are oceans of liquid water. What’s more interesting is that due to
gravitational effects of Jupiter, tides are created which in turn keeps the
water warm. If you want to discover life out there, you wouldn’t be blamed to
look towards Europa!
Jupiter’s biggest moon, Ganymede, is larger than Mercury. It
is the 9th largest object in the solar system. In fact, it
could have been a planet on its own if it wasn’t in the gravitational grasp of
Jupiter. The same is true for Titan, the largest moon of Saturn. It is even
bigger than Ganymede.
CONCLUSION
In conclusion, we found that gravity of Jupiter and Saturn
is the main reason why they have so many moons. Along with this, their position
from the sun makes it ideal for it to trap objects flying past it. There’s no
competition for Jupiter and Saturn whether somebody is talking about size or
the number of moons.
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