Comets

A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma (a thin, fuzzy, temporary atmosphere) and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet. Comet nuclei are themselves loose collections of ice, dust, and small rocky particles, ranging from a few hundred meters to tens of kilometers across. Comets have been observed since ancient times and have historically been considered bad omens.

Comets have a wide range of orbital periods, ranging from a few years to hundreds of thousands of years. Short-period comets originate in the Kuiper Belt, or its associated scattered disc, which lie beyond the orbit of Neptune. Longer-period comets are thought to originate in the Oort Cloud, a spherical cloud of icy bodies in the outer Solar System. Long-period comets plunge towards the Sun from the Oort Cloud because of gravitational perturbations caused by either the massive outer planets of the Solar System (Jupiter, Saturn, Uranus, and Neptune), or passing stars. Rarehyperbolic comets pass once through the inner Solar System before being thrown out intointerstellar space along hyperbolic trajectories.

Comets are distinguished from asteroids by the presence of a coma or a tail. However, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System.These have somewhat blurred the distinction between asteroids and comets (see centaurs and asteroid terminology).

As of May 2010 there are a reported 3,976 known comets of which about 1,500 are Kreutz Sungrazers and about 484 are short-period.This number is steadily increasing. However, this represents only a tiny fraction of the total potential comet population: the reservoir of comet-like bodies in the outer solar system may number one trillion. The number visible to the naked eye averages roughly one per year, though many of these are faint and unspectacular.Particularly bright or notable examples are called "Great Comets".

Source : wikipedia

R2 [Robonaut 2] will aboard on ISS!

Almost 200 people from 15 countries have visited the International Space Station, but the orbiting complex has so far only ever had human crew members – until now.

Robonaut 2, the latest generation of the Robonaut astronaut helpers, is set to launch to the space station aboard space shuttle Discovery on the STS-133 mission. It will be the first humanoid robot in space, and although its primary job for now is teaching engineers how dexterous robots behave in space, the hope is that through upgrades and advancements, it could one day venture outside the station to help spacewalkers make repairs or additions to the station or perform scientific work.

R2, as the robot is called, will launch inside the Leonardo Permanent Multipurpose Module, which will be packed with supplies and equipment for the station and then installed permanently on the Unity node. Once R2 is unpacked – likely several months after it arrives – it will initially be operated inside the Destiny laboratory for operational testing, but over time both its territory and its applications could expand. There are no plans to return R2 to Earth.

Source : NASA

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