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Halley՚s Comet, Origin and Orbit of Halley՚s Comet, Structure and Composition
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
- 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 activecomets.
- 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.