Our universe is full of stones in many forms and sizes. Today, in this
post, we'll look at those stones and rocks. This post is going to be
exciting because you will learn about several kinds of celestial rocks and
much more. Welcome to our blog, CosmicWisdom, where we discuss Astronomical
objects and structures with little to no use of math. Without wasting any
time, let's begin.
Introduction:
When you look at the stones and pebbles on the ground, you don't like them,
don't you? That's why you are always trying to keep them out of your house
and porch. So let's do something different, pick one of them and throw it at
a speed of 11.2 Km/s. No matter how you throw, just throw. It will never
come back to you. It will fly into space, where something interesting will
happen in our scientific communities. They will search it, catalog, pray,
give it a name, and observe its trajectory. Isn't it fascinating that the
same piece of stone, which had no respect on Earth, but somehow arrived and
is floating in space, around the Earth? Now, it is attracting the scientific
communities and social media. So, the Asteroids, meteors, comets, centaurs,
and trojans are basically the same, only varying in size, location, and
composition more or less.
That's why we will call them celestial rocks to refer to them all at once.
As many of us know that such objects form in accretion disks by condensation
of dust and gas, which takes a few thousand years to become
pebbles.
They continue to collide and stick or break with one another. Gradually,
they acquire the size of little stones, then rocks, larger rocks, then
finally they become mini asteroids and meteors. If they are lucky, they
become minor planets. Such a phase, from dust grains to small rocky pieces,
is called the planetesimal phase, which is really important for planets,
moons, and asteroids. Today, we are going to look at them closely and try to
understand their variations.
Dust:
Yeah, dust grains are crushed pieces of stone. These are the most available
things on our planet, our neighborhood, and nearby planets. Almost all over
the cosmos. Not only in the cosmos, we humans, animals, plants, or anything
which is on our earth, except tiny Microbes, meaning viruses, viroids, and
prions, are the only living beings that are not covered by dust. Newborn
babies are the cleanest humans, but when we wrap them with a blanket, they
become contaminated by dust, so nothing on Earth is dustless. What we call
the cleanest water it's impossible to purify to a zero dust percentage. By
the way, dust also has side effects and benefits, like we create buildings
and infrastructures, while it causes us several diseases and
allergies.
Technically speaking, less than a millimeter in size particle considered a
dust. We're not discussing how they form on either Earth or in space. These
dusts may have different properties, like Terrestrial dust contains
Magnesium, Silicon, Iron, and calcium compounds. Silica is one of the most
abundant substances on Earth, which is found in common sand or soil. Solar
dust will consist of hydrogen plasma, electrons, protons, and other
elements. That's the difference in the dust of various places.
Likewise, Planet Mars has dust with Iron oxide, which gives it a reddish
look to its rocks and sands. Venus has Basaltic sands, which come from its
constant volcanic eruptions and high-pressure winds. Remember, Sand, rock,
soil, or other similar things will have a similar composition to their
Nebula where they formed. However, their chemistry changes in course of
time. Due to ionizing radiations, planetesimal collisions, and other
factors, their chemistry has been affected. Thus, they can create 120,000
different compounds and mixtures only from 12 elements.
Pebble:
These are slightly larger than dust grains, almost 4 to 64 mm. These are
also one of the most common ingredients of rocky planets. In space, their
large concentration can be found in planetary and cometary rings. These
may form from either the condensation of the accretion disk or the impact
of rocks. These are basic ingredients of rings and sometimes stellar
disks.
Planetesimal pebbles will be different from the ring's particles because
planets form in later stages of the planetesimal phase, when they collide
together, break into several chunks, and keep fragmenting further, which
creates pebble-sized particles that may be trapped in a planet's
gravitational field. Gradually, they align along with the equator and
orbit the planet. Each of these particles will behave like a natural moon,
but on a smaller scale. Rings can be formed around any celestial object
with sufficient gravity and appropriate conditions. No matter whether it's
a planet, comet, asteroid, dwarf planet, or even moon.
We have a dwarf planet, Haumea, in our solar system in the Kuiper belt.
Which has a ring system like Gas giant planets. It's pretty thin and
obscure, though. It tells us how stable the Kuiper objects are. Contrary
to it being often denoted as a delicate zone full of rocks and stones. At
least there is enough silence to form a ring system. In actuality, those
particles are located very far from each other. Imagine 10 rocks are
orbiting the sun at millions of km from each other. That's why they don't
collide with each other. We're stopping our discussion on pebbles because
we'll see them tend to later in the Rings sections. Likewise, we are
directly jumping to larger rocks, about a few meters to a hundred
meters.
Meteor:
These rocks are the smallest in commonly known free-floating, solar
system objects. Their size varies from dust grain to nearly a meter. They
orbit the sun, like a planet. When they are visible from Earth's surface,
they suddenly appear like a long, thin glowing line, which usually lasts
for less than a second. These are often called shooting stars. They've got
3 main variations by name and timings. Let's see them.
i. Meteoroid:
Rocks that orbit the sun and haven't yet collided with anything in space,
called meteoroids. They are usually less than a meter. If they advance
toward Earth or any other planet. As soon as it enters in gravitational
field of the planet, it gets aggressively pulled toward the planet's
center.
ii. Meteor:
We call it free-falling, but since planets are rotating, they won't fall
directly; instead, they may travel some distance or even orbit the planet,
depending on their trajectories. It starts to lose some of its material by
atmospheric friction. To feel this, ride on a fast-moving bike, and your
hair, clothes, and body parts will feel a kind of tactile sensation as if
somebody is touching your front body, with a whoosh sound. This sensation
usually happens 60-80 Kmh speeds in a vehicle, but Meteor travels at a
speed of around 260,000 Kmh. These speeds are enough to shred their parts
and burn them due to friction. That's why they appear as a thin line,
which is called Meteor.
In technical terms, this is the right moment to call them a shooting star
or meteor, but we commonly refer to all its different phases like
Meteoroid, meteor, and meteorite. Remember, anything thin, glowing
line-like structure, if seen falling on the ground but doesn't hit the
surface, whether it's an Asteroid, meteoroid, comet, fragments of moons or
planets, will still be called a meteor.
iii. Meteorite:
All of the above objects, if they hit the ground, then their fragments
called meteorites. They are usually hard rocks that manage to hit the
ground. All the soft parts burned in the sky. Many people who
experienced a large meteorite nearby said it felt like an Artillery
shell was falling in the surrounding meaning it hit the ground with an
eardrum-piercing Swoosh or whoosh noise. They cause much damage if they
are large enough, and sometimes they create craters.
According to an estimate, every day around 4000-5000 meteoroids are
tracked, while only 17-20 hit the Earth. In addition, millions of dust
and small pebble-like objects burn in the atmosphere, creating meteors.
Debris Disk:
This is made by millions of small and large stones and icy particles,
which can be found around moons, planets, Stars, or around nowhere, just
in space. These may consist of the aftermath of heavy collisions. Don't
be confused with planetesimals because they form before the collisions,
right after the accretion disk particles' aggregation, while Debris
forms when the aggregated particles orbit in random orbits at different
speeds with different trajectories and collide with each other. Some of
them transform into large planet-sized spheres. Unused particles find
their appropriate place to orbit the star; nevertheless, 20% particles
never settle in their optimal zones, instead they may wander around
planetary orbits or anywhere they can find a safe zone.
Since our solar system has two distinct regions on the basis of
temperature and distance from the sun. The inner or closer region to the
sun mostly consists of rocky particles, which is why rocky planets or
smaller planets (Mercury, Venus, Earth, and Mars) are made of rocks and
dust; hence, the trojans, meteoroids, asteroids, and moons are all made
of rocks.
In the opposite of this zone, it is called the ice zone or outer zone,
where icy particles are abundant. Hence, we have Jupiter, Saturn, Uranus,
and Neptune's moons are mostly made of icy stones. Therefore, 90% of
objects like Centaurs, Trojans, and moons will contain icy materials
except gas giants, which are mostly gases, but they also contain ice
particles.
That distinction gave the idea of the frost line, which was hypothesised
to understand the varying configuration of the solar system. This line is
considered around the asteroid belt. If you cross this line, you will see
the icy objects instead of the rocky ones, and the solar system will have
changed. They have several types, let's see them in depth.
Ring:
|
|
Ringed Planet
|
We all know about Rings of Saturn, which is a debris disk made after the
collision and fragmentation of nearby objects. Remember, all types of
objects and structures we are talking about are no more different than a
junkyard, where all the fragments and pieces of various items can be
found. When such an object breaks into many pieces, some particles fall
into larger objects due to gravity, the other particles orbit in
different paths to the large objects, and some other pieces are launched
away due to gravitational influence. Whatever is left, first they orbit
or fall into the large object, but later on, they align with the equator
and behave like natural moons or moonlets. That's how rings form; they
may form around any object with a strong gravitational field, including
stars, planets, asteroids, or moons.
|
|
Inside its Ring
|
We have 4 gas giant planets. Jupiter's rings are mostly made of dust
grains and rocks, which reflect less light and are almost invisible. The
rest of the 3 planets' rings contain icy particles and reflect much light,
which is why Saturn's rings are bright enough and have been known as the
Jewel of the Solar System. The same happens with Uranus and Neptune's
rings, but they receive less light.
Saturn's moon Rhea is known for its controversial ring system. Chariklo
and Chiron are the centaurs bearing ring systems, Quaoar and Haumea are
Kuiper belt objects having rings.
Asteroid:
They are found in the Inner solar system and near the orbits of planets;
some of these are trojans, meteoroids, or just large rocks that orbit
the sun. Their large concentration is found between the orbits of Mars
and Jupiter. This zone is called the Asteroid belt, which is not a
ring-like structure of rocks of different sizes; instead, these rocks
are thousands of km apart from each other. However, there are some zones
or clusterings of such rocks, and they are often represented in social
media and sci-fi films. These groupings are not so large, as you can see
in the first image.
There are some famous asteroids like 4-Vesta, Ceres, Eros, and Bennu.
Most of the asteroids are named after famous personalities or places,
and sometimes mythological characters. Even though the Ceres is an
asteroid but its size is comparable to dwarf planets; Since it meets all
the criteria for a dwarf planet as defined by the IAU (International
Astronomical Union), that's why it's been classified as a Dwarf planet
living in the Asteroid field, while its brothers and sisters reside in
the Kuiper belt.
Trojan:
These are a few hundred meters to kilometers in size, rocks that orbit
the sun in a planet's orbit and don't easily collide with major planets.
in whatever planet's orbit they are found, they are classified according
to the planet's trojans, like Earth trojans, Jupiter trojans, Saturn
Trojans, etc. their speed and trajectory saves them from the collision
or becoming a moon of these planets. There are some rare cases where
planets can capture these rocks and force them to orbit. Most of the
Moons of the gas giants are captured trojans.
Trojans of Jupiter have two distinct groups named the Trojan camp and
the Greek camp, which are based on their orbital stability points or
Lagrangian points. Meaning, if they leave these points, they may either
fall into Jupiter or be thrown away from their orbits.
Currently, there are 1 Trojan of Venus, Earth's 2, Mars' 4, around 1
million of Jupiter, Saturn's 1, Uranus' 2, and Neptune's orbit has 15
Trojans. Remember, these are highly unstable numbers; one day you observe
5 Trojans of a planet, and the next day they may leave or be destroyed by
planetary moons or other external factors. Therefore, they are temporary.
Centaur:
Icy or rocky large objects of the same size as asteroids, but reside
beyond the asteroid belt. In general terms, between Jupiter and
Neptune's orbits, small icy objects are called Centaurs. They are
counterparts of inner asteroids found in the inner solar system. These
may also become Meteors if they are falling on planets nearby.
Comet:
|
|
A Comet orbiting its star
|
These are very special rocks that indeed orbit the sun, but in a highly
elliptical orbit, unlike a planet, moon, or asteroid. Another striking
difference is that when they come close to the sun, their outer layers
start to shred and leave a several-thousand-kilometer tail. This is a kind
of photoevaporation.
If you look at the comet in the outer solar system, it will look more like
an asteroid, but when it gets closer to the sun, intense heat tries to strip
off the water, ice, or carbon dioxide in the outer layers rapidly. Sometimes
comets can break into pieces, but mostly they survive.
|
|
Comet: Far from Its Star
|
Their aphelion (farthest point from the parent) and perihelion (closest
point from the parent) have a vast difference. Since they orbit in a highly
eccentric orbit, it's common to have a huge difference between those two
points. These two characteristics make the comet unique.
There are some famous comets like Halley, Hale-Bopp bopp and Shoemaker-Levy
levy-9. The comet Halley has an orbital period of around 76 Earth years,
meaning, when Earth is about to complete its 76th orbit of the sun, Halley
comes closer to the sun. Here are some famous comets and their orbital
periods, meaning how long they will come back near Earth, and you can have a
romantic candlelight dinner underneath a glowing comet in the night sky, or
take some legendary photographs or selfies with a comet.
One more thing, Comets have two types according to their orbital periods.
One completes its orbit in a few decades or centuries (less than 200 years),
while another category comes again after thousands or millions of years.
Hence, they are called Short or long-period comets.
