From Simple English Wikipedia, the free encyclopedia
The
Oort cloud
, or
Opik?Oort cloud
,
[1]
is a cloud of
comets
and other objects.
Astronomers
believe it is way beyond the
orbits
of
Pluto
and the
Kuiper belt
. The Oort cloud is believed to be the source of long-period
comets
in the
Solar System
.
[2]
The Oort cloud may lie about 50,000
AU
, or nearly a
light-year
, from the
Sun
.
[3]
This means the cloud is nearly a quarter of the way to
Proxima Centauri
, the nearest
star
to the Sun.
The
Kuiper belt
and
scattered disc
, the other two reservoirs of
trans-Neptunian objects
, are less than one-thousandth of the Oort cloud's distance. The outer limit of the Oort cloud defines the boundary of the
Solar System
and the region of the Sun's gravitational dominance.
[4]
The
Dutch
astronomer
Jan Hendrik Oort
published the Oort cloud idea in 1950. The Oort cloud was named after him, as were the Oort comet, and
Oort constants
.
[5]
The Oort cloud takes up a lot of space and is thought to have
trillions
of comets about tens of
millions
of
kilometers
apart.
The Oort cloud is made up of an inner Oort cloud and an outer Oort cloud. The outer cloud is weakly bound to the Sun; long-term comets are thought to come from there. The Inner cloud is also called the
Hills cloud
and maybe the maker of comets.
The objects in the Oort cloud are believed to consist of much ice. Since the object
1996 PW
was found to be a rocky body in an orbit typical of long-period comets, it is believed that rocky objects might be in the Oort cloud.
The Oort cloud is thought to be the remains of a disk made out of gas that surrounded the Sun long ago.
[3]