Like asteroids, comets are leftovers from the formation of different stuff. Each is an irregular ball of icy slush, frozen gases, and dark minerals just a few miles or kilometers wide. Like planets, some comets orbit the Sun on a predictable schedule. Halley's comet, the most famous of these weird wanderers, drops by earth every 76 years or so, it's not due for its next visit until July 2061.
Where do comets come from?
Comets originate far out in the solar system-some from the Kuiper belt of icy bodies beyond the orbit of Neptune, and others from a more distant region known as the Oort cloud
Unwelcomed visitors.
Until relativity recently in human history, the appearance of comets was thought to symbolize doom and upheaval. For instance
Caesar's comet:- This onetime visitors was heralded by the Romans to mark the assassination, debate whether the comet actually existed.
Halley's comet:- Our most famous visitor's regular appearances were blamed for the overthrow of an English king in 1066 and the later outbreak of the Black Death plague. The Catholic Church declared Halley an agent of evil in 1456,but that didn't stop the comet from coming.
Shoemaker-levy:- Discovered in modern times, this heavenly body demonstrated the destruction power of comets when it broke apart and slammed into the gas giant Jupiter in 1994, creating dark marks up to twice the size of earth in the planet's atmosphere.
What happens when comets head in our direction ?
As a comet nears the sun, ice and dust boils from its icy center-called nucleus-to form an atmosphere known as a coma. Sunlight blows gas and dust from this coma to create spectacular tails. Some tails reach 100 million miles160 million km long and can be seen from earth. Like asteroids, comets occasionally collide with planets and have the potential to cause massive destruction.
How could we defend earth from a large asteroid or comet.
In 2013 NASA announced its 'Grand challenge' to locate any nasty asteroid heading our way and prevent their impact, rock-stopping options include.
Nu cling IT:- Attack the asteroids with a nuclear missile, smashing it into space dust.
Ramming IT:- Launch a rocket directly into the asteroid to break it in half or divert its course.
Blasting IT:- Target the asteroid with a space-based laser to vaporize it before it gets too close.
Redirecting IT:- Mount rocket engines to the asteroid's surface to change its course 'so' it misses earth.
What is an asteroid?
Asteroids are chunks of rock that orbit the Sun and wander around the solar-system. They're the rubble left over from the solar system formation roughly 4.6 billion years ago. An asteroid is made of the same stuff under your feet-rock, bits of metal, maybe some carbon.
Where do they come from?
Scientist estimates that million of the pint-size planeloads orbit the Sun in the asteroid belt, a stretch of space between the orbits of Mars and Jupiter. Some scientist believes the asteroid belt is from the rubble of a planet that never formed.
Isn't It too dangerous to visit the asteroid belt?
Although movie portray asteroid belts as spaceship - jumbles of rock, our solar system's real asteroid belt isn8 nearly so treacherous. The average distance between rocks is nearly a million miles. Which would give spaceship pilots plenty of wiggle room.
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