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http://www.spaceanswers.com/deep-space/what-do-we-know-about-the-oort-cloud/

It holds dwarf planets and it’s poisonous – that’s just two facts about this comet-laden object

1. It extends up to a light year from the Sun

The sphere of this icy cloud is thought to surround the Sun at up to a distance of 50,000 AU, making its total diameter nearly two light years. Its outer edge is a nearly quarter of the distance from the Sun to its nearest stellar neighbour, Proxima Centauri.

2. It’s where comet Hale-Bopp was born

Whereas short-term comets with orbital periods of up to 200 years, like Halley, came from the Kuiper Belt, 1997′s stunning long-period comet Hale-Bopp probably coalesced from the icy material that makes up the Oort Cloud.

3. It’s made up of trillions of icy bodies

Not including the countless smaller particles, there are several trillion icy objects with a diameter of over a kilometre making up the Oort Cloud. It’s difficult to be sure of its total mass, but it’s thought to be in the region of five times that of the Earth.

4. It’s extremely poisonous

The Oort Cloud is made up of organic ices including water, methane and ethane. It also houses carbon monoxide and hydrogen cyanide, both of which can be deadly as a gas in enclosed spaces. Ironically, hydrogen cyanide is also thought to be a precursor to the compounds that played a role in the origins of life on Earth.

5. It might be home to an undetected star

In the 1980s, physicist Richard Muller proposed a theory that the Oort Cloud could be home to a small companion star to the Sun, a brown or red dwarf. The idea was that Nemesis, as it was called, passed through part of the Oort Cloud every 26 million years, scattering particles across the Solar System and bombarding the planets with comets.

6. It was once part of the inner Solar System

When the Solar System was forming 4.5 billion years ago, the Oort Cloud was gradually coalescing over the span of the inner Solar System. It’s thought that as the gas giants moved in the outer Solar System, the object that made up the Oort Cloud were flung out to their current orbit.

7. It would take the latest spacecraft 30 years to get there

It’s technically part of the Solar System, but despite that it would still take the latest spacecraft technology 30 years to travel up to 750 billion kilometers (466 billion miles) to reach its inner edge. Currently an ideal craft for that purpose would be a Solar Sail.

8. Two dwarf planet-like objects have been discovered there

Objects of around 450 kilometers (280 miles) in diameter have been discovered in the Oort Cloud within the last ten years. One of them, Sedna, has an extreme orbital period of 11,400 years that takes it from around 76 AU to 1,000 AU away from the Sun.

9. It defines the border of the Solar System

It’s a common misconception that the orbits of the outer planets and Pluto mark the edge of the Solar System, but in fact the gravitational influence of the Sun extends much further. This is evidenced by the hold it still has on the objects in the Oort Cloud, many times that distance away.

10. It might not actually exist

The sphere of the Oort Cloud was hypothesized to exist around our Solar System and other similar planetary systems by astronomer Jan Oort in 1950. Since then, astronomers have tracked objects moving through it but are yet to make direct observations of the cloud itself.

http://www.spaceanswers.com/deep-space/what-do-we-know-about-the-oort-cloud/

1.1)

AU is 

an astronomical unit (abbreviated au;^[1] sometimes AU,^[2] a.u.^[3][4] and ua^[5]) is a unit of length, roughly the distance from the Earth to the Sun. However, that distance varies as the Earth orbits the Sun, from a maximum (aphelion) to a minimum (perihelion) and back again once a year. Originally, each distance was measured through observation, and the au was defined as their average, half the sum of the maximum and minimum, making the unit a kind of medium measure for Earth-to-Sun distance. It is now defined more precisely as 149597870700 metres (about 93 million miles).^[6]

The astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System. However, it is also a fundamental component in the definition of another critical unit of astronomical length, the parsec.

http://en.wikipedia.org/wiki/Astronomical_unit

1.2)

About Proxima Centauri

The star Proxima Centauri lies a scant 4 light-years from Earth, making it the closest stellar neighbor to our own sun and a perfect target for the Hubble Space Telescope.

In this Hubble telescope photo, Proxima Centauri shines as a bright point-like object, but that appearance is deceiving. The star is actually invisible to the naked eye when viewed from the surface of Earth.

Proxima Centauri possesses a very low average luminosity, and a mass only about an eighth of the sun, according to a NASA image description. Despite this dimness, occasionally the brightness of Proxima Centauri increases. Astronomers call it a "flare star," as convection processes within the star's body give rise to random, powerful changes in brightness.

[...]

Scientists used the Hubble Space Telescope's Wide Field and Planetary Camera 2 (WFPC2) to capture the new view of Proxima Centauri. The image does not show the other two stars which make up a triple star system with Proxima Centauri. Its two companions, Alpha Centauri A and B, lie outside the frame. Hubble acquired the image in 1996, and NASA unveiled it in 2013.

The Alpha Centauri star system is home to at least one alien planet, Alpha Centauri Bb, which orbits the B star. It is the closest known exoplanet to Earth.

http://www.space.com/23475-proxima-centauri-hubble-telescope-photo.html

The sun's closest stellar neighbors are three stars in the Alpha Centauri system. The two main stars are Alpha Centauri A and Alpha Centauri B, which form a binary pair. The third star, which may or may not be part of the system, is Proxima Centauri. It is about 4.22 light-years from Earth and is the closest star other than the sun.

[...]

By itself, Alpha Centauri A is the fourth brightest star in the sky; just a bit dimmer, by 0.02 of a magnitude, than Arcturus. It is a yellow star of the same type (G2) as the sun, and it is about 25 percent larger. Alpha Centauri B is an orange K2-type star, slightly smaller than the sun. Proxima Centauri is a red dwarf about seven times smaller than the sun, or one-and-a-half times bigger than Jupiter. All three stars are a bit older — 4.85 billion years old — than the sun, which is about 4.6 billion years old.

[...]

Astronomers announced in October 2012 that they had detected an Earth-size planet orbiting Alpha Centauri B. The newfound world, known as Alpha Centauri Bb, is about as massive as Earth, but its surface may be covered with molten rock, researchers said. The existence of the planet suggests that undiscovered worlds may lurk farther away from its star — perhaps in the habitable zone, that just-right range of distances where liquid water can exist.

Read full article here: http://www.space.com/18090-alpha-centauri-nearest-star-system.html