Halley՚s Comet, Origin and Orbit of Halley՚s Comet, Structure and Composition (For CBSE, ICSE, IAS, NET, NRA 2022)

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Halley՚s Comet

  • It is the first comet whose return was predicted and, almost three centuries later, the first to be imaged up close by interplanetary spacecraft.
  • It is arguably the most famous of all comets. I
  • t is a periodic comet that returns to Earth every 75 years.
  • The last time it was here was in 1986, and it is projected to return in 2061.
  • It is named after the English astronomer Edmond Halley, who examined the reports of a comet approaching the Earth in 1531,1607 and 1682.
  • He later concluded that these comets were the same returning over and over again.

Origin and Orbit of Halley՚s Comet

Origin and Orbit of Halleys Comet
  • The recent appearance of Halley՚s Comet in 1986 was greatly anticipated.
  • Astronomers first imaged the comet with the 200-inch Hale Telescope at Palomar Observatory in California on October 16,1982, when it was still beyond the orbit of Saturn at 11.0 AU from the Sun.
  • It is believed to have originated from the Kuiper Belt.
  • Some of the blocks of rock and ice – which are essentially the leftover matter from the formation of the Solar System some 4.6 billion years ago – are pulled deeper into the Solar System and become active comets.
  • It is classified under,
    • A periodic or a short-period comet: with the orbit lasting for 20 years or less.
    • Long-period comets: whose orbit lasts for thousands of years and that which originates from the Oort cloud.
  • The orbit of Halley՚s Comet around the Sun is highly elliptical and retrograde.
  • This means that it orbits around the Sun in the opposite direction to the planets. Due to its retrograde orbit, its velocity is highest relative to the Earth.
  • Its mass is estimated to be 242.5 billion tons and its average density to be 0.6 g/ .
  • It was observed that the gases ejected were made of 80 % water, 3 - 4 % carbon dioxide, 17 % carbon monoxide with traces of hydrocarbons.

Halley՚s in the Space Age

  • When Halley՚s Comet came by Earth in 1986, it was the first time we could send spacecraft up to look at it.
  • That was a fortunate occurrence, as the comet ended up being underwhelming in observations from Earth.
  • When the comet made its closest approach to the sun, it was on the opposite side of that star from the Earth
  • Making it a faint and distant object, some 39 million miles away from Earth.
  • Several spacecrafts successfully made the journey to the comet. This fleet of spaceships is sometimes dubbed the “Halley Armada.”
  • Two joint Soviet/French probes (Vega 1 and 2) flew nearby, with one of them capturing pictures of the heart or nucleus of the comet for the first time.
  • The European Space Agency՚s Giotto got even closer to the nucleus, beaming back spectacular images to Earth.
  • Japan sent two probes of its own (Sakigake and Suisei) that also obtained information on Halley.

Structure and Composition

  • When Halley approaches the Sun, it expels jets of sublimating gases from its surface, which knocks it very slightly off its orbital path.
  • So, this process causes the comet to form a bright tail of ionized gas (ion tail) , and a faint one made up of dust particles.
  • The ion tail is also known as a coma (a small atmosphere) which spans up to 100,000 km across and consists of volatiles such as water, methane, ammonia, and carbon dioxide.
  • It is expected to be seen next in 2061.
  • As expected, some are choosing to prepare for the worst, indicating the end of life. Others are contemplating if they will live long enough to witness it.

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