WednesdaySeptember 29, 2010

(Scattered Disk, Oort Cloud)

The Launch PadWednesday, 9/29/10

On which of the following planets would it currently

be impossible to successfully land a spacecraft on the surface? Why?

A. VenusB. Mercury

C. MarsD. Jupiter

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The Scattered DiskThe scattered disc is a distant region of the Solar System that is sparsely populated by icy dwarf planets, a subset of the broader

family of trans-Neptunian objects. The scattered disc objects (SDOs) have orbital eccentricities ranging as high as 0.8, inclinations as

high as 40°, and perihelia greater than 30 astronomical units

The Scattered DiskThese extreme orbits are believed to be the result of gravitational "scattering" by the gas giants, and the objects continue to be subject to perturbation by the

planet Neptune. While the nearest distance to the Sun approached by scattered objects is about 30–35 AU, their

orbits can extend well beyond 100 AUThis illustration shows two planets orbiting

about a common star. The outer planet takes more time to complete an orbit than the inner

planet, so once per orbit the inner planet overtakes the outer planet. When the planets

are at a, the outer planet exerts a gravitational perturbation that accelerates the inner planet, advancing the body ahead of its normal path. When the planets reach b, the

reverse is true and the inner planet is decelerated. This perturbing influence is what

led to the discovery of the planet Neptune.

The Scattered DiskThis makes scattered objects among the most distant and cold objects in the Solar System. The innermost portion of the scattered disc overlaps with a torus-shaped region of

orbiting objects known as the Kuiper belt, but its outer limits reach much farther away from the Sun and farther above and

below the ecliptic than the belt proper.

The Oort CloudThe Oort cloud is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or

nearly a light-year, from the Sun.This places the cloud at nearly a

quarter of the distance 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 the Oort cloud's distance.

The outer extent of the Oort cloud defines the gravitational

boundary of our Solar System.

The Oort CloudThe Oort cloud is thought to

comprise two separate regions: a spherical outer

Oort cloud and a disc-shaped inner Oort cloud, or

Hills cloud.Objects in the Oort cloud are largely composed of

ices, such as water, ammonia, and methane.Astronomers believe that the matter comprising the Oort cloud formed closer to the Sun and was scattered far out into space by the

gravitational effects of the giant planets early in the Solar System's evolution.

The Oort CloudAlthough no confirmed direct

observations of the Oort cloud have been made, astronomers believe that it is the source of all long-period and Halley-type comets entering the inner Solar

System and many of the Centaurs and Jupiter-family

comets as well.The outer Oort cloud is only loosely bound to the Solar System, and thus is easily

affected by the gravitational pull both of passing stars and of

the Milky Way Galaxy itself.These forces occasionally

dislodge comets from their orbits within the cloud and send

them towards the inner Solar System.

The Oort CloudBased on their orbits,

most of the short-period comets may

come from the scattered disc, but some may still have originated from the

Oort cloud.

Although the Kuiper belt and the farther scattered disc have been observed and mapped, only four

currently known trans-Neptunian objects

(90377 Sedna, 2000 CR105, 2006 SQ372 and 2008 KV42 ) are considered possible

members of the inner Oort cloud.