Our solar system is divided into inner solar system
consisting of the rocky worlds and the outer solar system consisting of the gas
giants and the objects beyond them. But these two regions are conveniently
separated by a field of rocks and debris of different sizes called the asteroid
field. Why is it that this field exists between Mars and Jupiter and not
anywhere else? This to me is a fascinating question.
One of these two planets is, in a way, responsible for
this, the planet being Jupiter. Jupiter, being massive, influences everything
in its neighborhood with its gravity. There are areas in the asteroid belt
where anything can be diverted into different orbits due to Jupiter’s gravity.
These areas are called Kirkwood gaps. These gaps are locations of orbital
resonance of Jupiter.
Orbital resonance refers to the phenomena when
orbiting objects exerts regular and periodic gravitational influence on each
other, commonly due to the orbital periods of the bodies being related to each
other by a ratio of small numbers.
Within 3.5 AU from the Sun, in the asteroid belt, these
resonances create Kirkwood gaps. Asteroids are ejected from these locations due
to repeated disturbances. However, some
asteroids are temporarily present in and around these gaps. This increases the eccentricity
of the asteroid orbit, meaning the orbit is more “squashed”. These are ejected
out of orbit when they encounter the inner planets.
Because of presence of these gaps due to influence of
Jupiter’s gravity, the objects present in this region could not club together
and form a planet. Basically, Jupiter prevented a planet to be formed in the
asteroid field. But, as the gaps are present in specific locations, not all
asteroids were ejected for their orbits. Also, the regions of the gaps have a
very low density of the asteroids, naturally. Even if these rocks were to be
form a planet by coming together, the planet would be very tiny. The entire
mass of the asteroid belt is about 4% of our Moon.
While planets formed relatively early in the solar
system by collisions and coming together of dusts and rocks and different
materials called “planetesimals”. Asteroids
are left over rocks and objects that just couldn’t form planets 4.6 billion
years ago. Birth of Jupiter prevented their formation creating Kirkwood gaps
between Mars and Jupiter. Today, Kirkwood gaps are main source of near Earth
asteroids. We may be killed because of these someday. Thank you, Jupiter, I guess? Some asteroids may also exit solar
system because of these gaps.
In a few million years, many of the asteroids will
break out of the resonance due to gravitational interaction with other planets.
This may cause many of these asteroids to escape.
Asteroids may
seem very uninteresting but they are pretty fascinating. They are found in
various sizes and shapes. Largest asteroid (which is also a Dwarf Planet) is named Ceres with a diameter of
950km. It is also considered a dwarf planet. The smallest ones may only be a
few feet wide. Another interesting thing is that some asteroids are known to
have their own moons. About 150 known asteroids contain one or more moons
orbiting them. There are even binary asteroids where the asteroids go around
each other.
They are classified according to their composition-
1. C
type asteroids- about two third of all asteroids fall under this category. They
are very dark with an average albedo (brightness/ ability of an object to reflect light)) of about 0.06. Their compositions
are similar to the sun and are found in the outer region of the asteroid belt.
2. S
type asteroids- they are comparatively brighter with average albedo of 0.16 and
are composed of iron and magnesium silicates. They are found in the inner
region of the belt.
3. M
type asteroids- they are the brighter than the other with average albedo of
0.19 and are composed of iron. They are found in the middle region of the belt.
Conclusion
We
found out that Jupiter is mainly responsible for both formation of asteroids or
their inability to form a planet and the location where they are found i.e. between
mars and Jupiter. We also discussed different kinds of asteroids and some
interesting facts about them.
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