Planetary Defence Part 1: Introduction to Asteroids and Comets
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| E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz, Austria (http://www.sternwarte.at) / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0) |
The Chicxulub Crater in Mexico, spanning over 110 miles in width, marks the spot where, 66 million years ago, 'an asteroid the size of a mountain' [1] struck the Earth. The asteroid travelled at a speed of around 40,000 miles per hour [1] before pummelling the planet with an 'explosive yield estimated at 100 trillion tons of TNT.' [1] This is 'two million times stronger than the most powerful man-made bomb’ [2]. The immense impact of the asteroid is believed to have caused mass extinction including that of the dinosaurs.
Although
they are rare occurrences, scientists have tried to find ways to protect the
planet from asteroid and comet attacks which could potentially have devastating
consequences as shown by the dinosaur-ending event 66 million years ago.
Asteroids
vs Comets
Asteroids
are small bodies, usually around ‘1,000 km (600 miles) or less in diameter,’ [3]
that orbit the sun. The majority of asteroids are found in the Main Asteroid
Belt located in the region between Mars and Jupiter. Similarly, comets are also
defined as small bodies orbiting the sun [4].
The
main distinction between a comet and an asteroid is what they are made of: asteroids
consist of ‘metals and rocky material’ [5] whilst a comet has ‘a
substantial fraction of its composition made up of volatile ices’ [4].
This difference comes as a result of asteroids forming closer to the sun ‘where
it was too warm for ices to remain solid.’ [5] The ice sublimates
when a comet approaches the sun to form ‘a cloud known as the coma.’
[4][6] Comets can be easily distinguished from asteroids due to the
presence of the two comet tails – the dust and ion tails. The dust tail is
formed when ‘radiation from the sun pushes dust particles away from the coma.’ [6]
Meanwhile, charged particles from the sun ‘convert some of the comet’s
gases into ions.’ [6]
Planets
were formed in the early Solar System by gravity drawing dust and rock orbiting
the sun together. [7] However, not all of this material was used to
construct planets as the formation of Jupiter halted the creation of new
planets. The gravitational force of this large planet caused ‘the small bodies
to collide with one another, fragmenting them into asteroids.’ [7]
Comets
are believed to have been formed ‘on the fringes of the [protoplanetary] disk,
far from the sun’s heat.’ [8] A protoplanetary disk is ‘a disk of
gas […] and dust […] orbiting a newly formed star.’ [9] Here, ‘fine
grains of dust coated with frozen gases and water ice began clumping together’
and over time evolved into comets. [8]
In Part 2 (phys-talk.blogspot.com/2020/03/planetary-defence-part-2-detection-and.html), I will look into methods used to detect and deflect asteroids and comets.
Sources:
5. http://coolcosmos.ipac.caltech.edu/ask/181-What-is-the-difference-between-an-asteroid-and-a-comet-
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