One of the major wonders of space is meteor showers, which are beautiful to watch.
But today we will not talk about their beauty. We will talk about how these can be catastrophic
if they hit Earth in the future. Meteors have always been a cause of fear for humans. They have
been responsible for many extinction events and other destruction on Earth before. In April 2018,
the B612 Foundation reported, “It’s 100 percent certain we’ll be hit [by a devastating asteroid],
but we’re not 100 percent certain when.” Throughout recorded history, hundreds of
Earth impacts (and exploding bolides) have been reported, with some occurrences causing deaths,
injuries, property damage, or other significant localised consequences.
Impact craters are found on every continent on Earth, but they are most common in parts
of Australia, Europe and North America. This is not because the surface of these areas has changed
so little that craters have been preserved. So in this video we will understand what are these
impact events? Why are they caused? Have they happened before on Earth and caused damage?
How do we prepare to deal with them? So just relax in your seat and enjoy the video.
But before this, lets take a step back and discuss what are Meteorite? A Meteorite is a piece of rock
from outer space that strikes the surface of the Earth. A Meteoroid is a meteorite before
it hits the surface of the Earth. Meteors are glowing fragments of rock matter from outside
the Earth’s atmosphere that burn and glow upon entering the Earth’s atmosphere. They are more
commonly known as shooting stars. Some meteors, particularly larger ones, may survive passage
through the atmosphere to become meteorites, but most are small objects that burn up completely
in the atmosphere. They are not, in reality, shooting stars. Fireballs are dazzling meteors.
They can be classified in mainly three types- Stony meteorites, Iron meteorites and Stony-Iron
meteorites. So where do they come from? Well, most of the meteorites are fragments of larger bodies
called part bodies. They can be either minor planets or asteroids from the solar system. These
parent bodies can originate from many sources. Asteroids are the major source of these fragments
or meteorites and mainly originate from deep space. The major sources are - The Asteroid belt
and The Oort cloud. The asteroid belt is located between the orbits of Mars and Jupiter. It
comprises a swarm of about 100,000 objects called asteroids. Asteroids are small rocky bodies with
irregular shapes that have a cratered surface. About 3,500 or more of these asteroids have been
officially classified, and their orbital paths are known. The Oort Cloud is a theoretical cloud of
predominantly icy planetesimals proposed to surround the Sun at distances ranging from
2,000 to 200,000 AU. We have already made a video on The Oort Cloud before, so you can go watch it
after this video and know more about it. These asteroids are sometime thrown towards the Earth
by many factors and some of them have orbits that get them close to the Earth. Some even cross the
orbital path of the Earth and are known as Apollo objects. All the objects that pass close to Earth
are refereed to as Near-Earth Objects. About 150 NEOs with diameters between 1 and 8 km are known,
but this is only a fraction of the total number. Many NEOs will eventually collide with the Earth.
These objects have unstable orbits because they are under the gravitational influence
of both the Earth and Mars. So, now let’s talk about what is an Impact event?
When a large object from the space hits the Earth’s surface it deforms the site
and forms an impact. When a meteorite collides with the Earth, it can form an impact carter-
a bowl-shaped hollow in the Earth’s surface. Space rocks have produced craters in the way throughout
Earth’s life, especially when the planet was young around 4 Billion years ago.
Craters of between 1m and more than 1,000 km wide exist in large numbers on planets and moons
throughout the solar system. About 150 have been found on the Earth. So, how are they formed?
All craters whether on Earth or another planet or moon are formed much in the same way. An impacting
meteorite blasts surface material from the point of impact and produces a crater. The size of the
crater depends on the size of the original rock. A 30-m space rock hitting the earth can produce a
crater 1 km in diameter. The meteorite on entering the Earth’s atmosphere breaks up as it meets the
friction of the atmosphere. Frictional heating will cause the object to heat and glow. Melting
and even vaporisation of the outer parts of the object will begin, but if the object is large
enough, solid material will remain when it impacts the surface of the Earth. The outer layer of the
rock is shattered as the meteorite impacts the Earth. Shock waves move through the surface as
the meteorite burrows into the earth and the heat and compression causes an explosion and blasts a
crater into the Earth’s surface. Impacts of large meteorites have never been observed by humans.
Much of our knowledge about what happens next must come from scaled experiments.
As the solid object plows into the Earth, it will compress the rocks to form a depression
and cause a jet of fragmented rock and dust to be expelled into the atmosphere. This material
is called ejecta. The impact will send a shock wave into the rocks below, and the rocks will be
crushed into small fragments to form a breccia. Some ejecta will be hot enough to vaporise,
and the heat generated by the impact could be high enough to actually melt the rock at the
site of the impact. The shock wave entering the Earth will first move in as a compressional wave
(P-wave), but after passage of the compressional wave an expansion wave (rarefaction wave) will
move back toward the surface. This will cause the floor of the crater to be uplifted and may also
cause the rock around the rim of the crater to bent upward. Faulting may also occur in the rocks
around the crater, causing the crater to become enlarged, and have a concentric set of rings.
The ejecta will eventually settle back to the Earth’s surface forming an ejecta blanket thick
near the crater rim and thins outward from the
crater. Rocks below the crater that were not melted by the impact
will be intensely fractured. All of this would happen in a matter of 1 to 2 minutes.
The total mass of extraterrestrial objects that strike the Earth is about 107 to 109 kg/year.
We also know this as the Meteorite flux, which means the total mass of the extraterrestrial
object that strikes the Earth. The frequency at which they strike depends on the size of objects.
There is an inverse relation between the size of the object and the frequency at which they strike.
The smaller the object greater is the frequency. Asteroids with a 1 km (0.62 mi) diameter strike
Earth every 500,000 years on average. Large collisions with a diameter of 5 km or more-
happen once every 20 million years. What we mean by this? It simply means that tons of
micrometeorites strike the Earth each day. But because of their small size, they either burn up
or settle slowly to the surface. Meteorites with a diameter of about 1mm strike the Earth nearly
every 30-45 seconds. After entering the Earth’s atmosphere, the friction of passage through the
atmosphere generates enough heat to melt or vaporise the objects that we sometimes also
call shooting stars. The velocities at which small meteorites have impacted the Earth range from 4
to 40 km/sec. Larger objects would not be slowed down much by the friction associated with passage
through the atmosphere, and thus would impact the Earth with high velocity. Calculations show that a
meteorite with a diameter of 30 m, weighing about 300,000 tons, traveling at a velocity of 15 km/sec
(33,500 miles/hour) would release energy equivalent to about 20 million tons of TNT.
Meteorite impacts have a large effect on Earth. Though we as humans do not know of
what the effects of an impact of a large meteorite. But we can try to make calculations
and scale the effect of the impacts. Some of them are-
1. Earthquakes- They can cause catastrophic earthquakes of up to 13 Richter scales, causing
damage to almost everything. These earthquakes can have deadly aftershocks very high in magnitude.
2. The enormous quantities of dust put into the atmosphere would block incoming solar radiation.
The dust could take months to settle back to the surface. Meanwhile, the Earth would be in
a state of continual darkness, and temperatures would drop throughout the world, generating
global winter like conditions. A similar effect has been postulated for the aftermath of a nuclear
war (termed a nuclear winter). Blockage of solar radiation would also diminish the ability
of photosynthetic organisms, like plants, to photosynthesise. Since photosynthetic
organisms are the base of the food chain, this would seriously disrupt all ecosystems.
3. If the impact occurred in the oceans, a giant tsunami would be generated. For a 10
km-diameter object the leading edge would hit the seafloor of the deep ocean basins before
the top of the object had reached sea level. We estimate the tsunami from such an impact
would produce waves from 1 to 3 km high. These could easily flood the interior of continents.
4. Large amounts of nitrogen oxides would result from combining
Nitrogen and Oxygen in the atmosphere because of the shock produced by the impact. These
nitrogen oxides would combine with water in the atmosphere to produce nitric acid,
which would fall back to the surface as acid rain, resulting in the acidification of surface waters.
These were some of the significant effects that such an impact will have on Earth.
It is estimated that in any given year the odds that you will die from an
impact of an asteroid or comet are between 1 in 3,000 and 1 in 250,000.
So how do we humans prepare for this impact event in the coming future? What is our
preparation? Well, we should certainly not take inspiration from Hollywood. We also know this
process as Asteroid impact avoidance. Asteroid impact avoidance comprises several methods
by which near-Earth objects (NEO) could be diverted, preventing destructive impact events.
Past collisions with extraterrestrial bodies have had major effects on the evolution of the
world . Some 4.4 billion years ago, for instance , a Mars-size planetoid seems to possess struck
our young planet, throwing out enough debris to make our moon. And an outsized impact may have
caused the extinction of the dinosaurs 65 million years ago. Even today cosmic impacts are clear.
Various collision avoidance techniques have different trade-offs regarding metrics
such as overall performance, cost, failure, risks, operations, and technology readiness.
There are various methods for changing the course of an asteroid/comet.These can be differentiated
by various types of attributes such as the mitigation (deflection or fragmentation),
energy source (kinetic, electromagnetic, gravitational, solar/thermal, or nuclear), and
approach strategy (interception, rendezvous, or remote station). In 1998 scientists and Congress
approved the Space-guard Survey which had a goal of identifying 90% of all NEOs with a size greater
than 1 km.In September 2011, NASA announced that they had identified 93% of all NEOs of this size
and that of the total number estimated to exist (989) they had identified 911. For mid-sized NEOs,
with sizes between 100 m and 1 km, 5,200 have been found and are being tracked, but it is estimated
that there are still over 15,000 of such bodies that have not yet been discovered. Asteroids have
always been a threat to our existence.We already have seen this year asteroids passing very close
to the Earth. Though there are no detailed plans but we are constantly working on them.
So what do you think about these Impact events? Do you think we are under-prepared for such event
and need to address this issue? Let us know your views and questions in the comment section below.
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