Comets

1705

Comets are wandering bodies of ice, rock and organic compounds that can be several miles in diameter. Space Comet is celestial body which orbits in elliptical or parabolic around the Sun.Comets - Space Comet picture

Facts about Comets

* Known Comets: About 5200
* Other names: dirty snowballs or cosmic snowballs

What is a Space Comet?

Comets are small, irregularly shaped bodies composed of a mixture of rock, organic molecules and frozen gases. When in the proximity of the Sun, they are usually characterised by a long tail which is composed of material vaporised off the comet body.

Origins

Some originate from the Edgeworth-Kuiper Belt, beyond Neptune, and some from the Oort cloud, a spherical shell comprised of millions of bodies at the edge of our solar system.

Space Comet are thought to have created major changes to Earth’s early atmosphere and climate by striking Earth billions of years ago. They may have delivered the first carbon-based molecules to our planet.

Orbit

The orbit of a Comet usually takes them to the cold and dark outermost reaches of the solar system.

Composition

A comet consists of:

1.  A Nucleus
2.  A Coma
3.  A Dust Tail
4.  Ion Trail

When comets venture into the more intense sunlight of the inner solar system, the ices on the comet nucleus begin to melt and fall away. The wake of particles forms the comet’s tail, which can be hundreds of miles long and can often be seen from Earth.

Name

Most are named after their discovers – person or spacecraft.

Halley’s Comet

Halley’s Comet is named after Edmund Halley (1656-1742). Halley was the first person to predict the return of a comet to the inner solar system in a regular orbit. Halley’s Comet orbits the Sun every 76 years. The most recent appearance was in 1986. Halley’s Comet will be next visible from Earth in 2061.

Halley’s comet orbital period is on average 76 years, however its orbital path can vary due to to gravitational fields of the major planets. In the last 2000 years, it has varied by as much as four years.

Famous Comets:

Other famous Space Comets are: Comet Neat, Comet Machholz (official designation C/2004 Q2), Hale-Bopp has an orbital period of 4026 years.

The visit of the Hale-Bopp comet in 1997 gave one of the brightest views of a comet since 1811, visible even from brightly lit cities.

Long Period Comets

Long Period Comets (Non-periodic comets) are comets that do not have confirmed observations at more than one perihelion passage and generally have orbital periods of 200 years or more.

Comet Hale-Bopp – discovered July 23, 1995.

Exocomets

Exocomet is a comet which exists outside the Earth’s solar system that orbits stars other than the sun and can also be found in interstellar comets. First exocomet system was discovered in 1987 around Beta Pictoris. 11 exocomets have been been found (2017).


Spacecraft – Missions to a Comet

First spacecraft to visit a come was NASA’s International Comet Explorer (ICE). It flew past comet Giacobini-Zinner in 1985.

European Space Agency’s Giotto flew by and studied Halley’s Comet in 1986.

NASA’s Deep Impact sent an impactor into Comet Tempel 1 in order to study the impact.

Stardust Spacecraft was the first sample return mission to collect dust samples from the coma of a comet and return these to Earth. NASA’s Stardust mission target was Comet Wild 2. Stardust mission was extend and it visited Comet Tempel 1 in 2011.

European Space Agency’s Rosetta was first spacecraft to orbit a comet. Rosetta’s Philae lander made the first soft landing on a comet. The comet was called  67P/Churyumov–Gerasimenko (67P).


History

* In the 1070s a comet is shown in the Bayeux Tapestry which depicted a chronicle of the Battle of Hastings of 1066. The comet referred to later was called Halley’s Comet.

* In 1705 Edmond Halley published that the comets of 1531, 1607 and 1682 comets were the same. He predicted it would return in 1759. At a later date it was named Halley’s Comet.

* First Comet Flyby by NASA’s International Comet Explorer on 11 September 1985.

* ESA’s Giotto was the first spacecraft to make close up observations of a comet. It flew past Halley’s comet in 1986.

* In 1994 Comet Shoemaker-Levy 9 collided into Planet Jupiter.

* Comet Hyakutake was discovered on 31 January 1996 by Yuji Hyakutake (Japanese astronomer).  It was dubbed The Great Comet of 1996.

Rosetta spacecraft was launched in 2004 and arrived at Comet 67P/Churyumov-Gerasimenko on 6 August 2014. Rosetta was the first mission to rendezvous with a comet.

* On 4 July 2005 the impactor from the Deep Impact spacecraft collided with Comet Tempel 1. It created an impact crater. This allowed scientists to study the interior of the comet nucleus.

* NASA extended Deep Impact mission and called it EPOXI. It flew by Comet Hartley 2 on 31 December, 2007.

* NASA extended Stardust mission in 2007 and called it NExT. Stardust spacecraft visited Comet Tempel 1 in February 2011 where it viewed the impact crater from the Deep Impact mission of 2005.

* In 2011 Herschel Space Observatory found the first evidence of Earth-like water in a comet.

*  Philae Lander was the first spacecraft to land on a comet. It landed on 12 November 2014 on Comet 67P/Churyumov-Gerasimenko.


Did you know?

Perihelion means the closest point in a comet’s orbit to the Sun.


Books:

Comet by Carl Sagan, Ann Druyan (Contributor)
From Amazon.comAmazon.co.uk

Impact!: The Threat of Comets and Asteroids
by Gerrit L. Verschuur
From Amazon.comAmazon.co.uk

Shoemaker by Levy by David H. Levy
From Amazon.comAmazon.co.uk


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