Related topics: stars , solar system , exoplanet , nasa , earth
Planet
hideA planet (from Greek πλανήτης, from the verb πλανώμαι planōmai I wander), is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.[a]
The term planet is ancient, with ties to history, science, myth, and religion. The planets were originally seen by many early cultures as divine, or as emissaries of the gods. Even today, many people believe in astrology, which holds that the movement of the planets affects people's lives, although such a causation is rejected by the scientific community. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. Even now there is no uncontested definition of what a planet is. In 2006, the IAU officially adopted a resolution defining planets within the Solar System. This definition has been both praised and criticized, and remains disputed by some scientists.
The planets were thought by Ptolemy to orbit the Earth in deferent and epicycle motions. Though the idea that the planets orbited the Sun had been suggested many times, it was not until the 17th century that this view was supported by evidence from the first telescopic astronomical observations, performed by Galileo Galilei. By careful analysis of the observation data, Johannes Kepler found the planets' orbits to be not circular, but elliptical. As observational tools improved, astronomers saw that, like Earth, the planets rotated around tilted axes, and some share such features as ice-caps and seasons. Since the dawn of the Space Age, close observation by probes has found that Earth and the other planets share characteristics such as volcanism, hurricanes, tectonics, and even hydrology. Since 1992, through the discovery of hundreds of extrasolar planets (planets around other stars), scientists are beginning to understand that planets throughout the Milky Way Galaxy share characteristics in common with our own.
Planets are generally divided into two main types: large, low-density gas giants, and smaller, rocky terrestrials. Under IAU definitions, there are eight planets in the Solar System. In order from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four gas giants, Jupiter, Saturn, Uranus, and Neptune. The Solar System also contains at least five dwarf planets: Ceres, Pluto (originally classified as the Solar System's ninth planet), Makemake, Haumea and Eris. With the exception of Mercury, Venus, Ceres and Makemake, all of these are orbited by one or more natural satellites.
As of June 2009, there are 353 known extrasolar planets, ranging from the size of gas giants to that of terrestrial planets.
For more information about Planet, read the full article at
Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.
News tagged with planets
New Horizons Crosses a Threshold: Closer to Pluto than Earth
Space & Earth / Space Exploration
9 hours ago |
4.7 / 5 (7) |
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(PhysOrg.com) -- The new year approaches with New Horizons zooming past another milestone: the NASA spacecraft is now closer to target planet Pluto than its home planet, Earth.
A New Method of Estimating Stellar Distances
Dec 21, 2009 |
4.4 / 5 (14) |
2
(PhysOrg.com) -- The star Chi Cygni is located about 550 light-years away, in the direction of the constellation of Cygnus the Swan. It is a notable star because, unlike the sun which still burns hydrogen ...
Avatar's moon Pandora could be real
Dec 17, 2009 |
4.3 / 5 (27) |
10
In the new blockbuster Avatar, humans visit the habitable - and inhabited - alien moon called Pandora. Life-bearing moons like Pandora or the Star Wars forest moon of Endor are a staple of science fiction. ...
Astronomers discover 'tilted planets'
Dec 22, 2009 |
4.6 / 5 (16) |
4
(PhysOrg.com) -- University of Exeter, UK, research has added to a growing evidence that several giant planets have orbits so tilted that their orbits can be perpendicular or even backwards relative to their ...
Astronomers Find Super-Earth Using Amateur, Off-the-Shelf Technology (w/ Video)
Dec 16, 2009 |
4.9 / 5 (28) |
10
(PhysOrg.com) -- Astronomers announced today that they have discovered a "super-Earth" orbiting a red dwarf star 40 light-years from Earth. They found the distant planet with a small fleet of ground-based ...
New planet discoveries suggest low-mass planets are common around nearby stars (w/ Video)
Dec 14, 2009 |
4.8 / 5 (19) |
14
(PhysOrg.com) -- An international team of planet hunters has discovered as many as six low-mass planets around two nearby Sun-like stars, including two "super-Earths" with masses 5 and 7.5 times the mass of ...
Rare Scottish mineral may indicate life on Mars
Space & Earth / Space Exploration
Dec 10, 2009 |
3.7 / 5 (22) |
7
(PhysOrg.com) -- A team of NASA (National Aeronautics and Space Administration) scientists is looking for clues about life on Mars in an earthy clay mineral found only in Aberdeenshire in Scotland.
First Direct Imaging of a Young Binary System
Dec 15, 2009 |
4.9 / 5 (17) |
2
(PhysOrg.com) -- A team of astronomers from The Graduate University for Advanced Studies, the National Astronomical Observatory of Japan, and other universities have captured the first direct image of a young ...
Giant Planet Set for a Cataclysmic Show
Dec 16, 2009 |
4.9 / 5 (16) |
4
(PhysOrg.com) -- A team of Chinese astronomers have discovered a giant planet close to the exotic binary star system QS Virginis. Although dormant now, in the future the two stars will one day erupt in a violent ...
WISE satellite blasts off on space-map mission
Space & Earth / Space Exploration
Dec 14, 2009 |
4.8 / 5 (6) |
4
NASA launched Monday a new breed of satellite called WISE on a mission to orbit Earth and map the skies to find elusive cosmic objects, including potentially dangerous asteroids.
Spitzer Telescope Observes Baby Brown Dwarf
Nov 23, 2009 |
4.8 / 5 (13) |
0
(PhysOrg.com) -- NASA's Spitzer Space Telescope has contributed to the discovery of the youngest brown dwarf ever observed -- a finding that, if confirmed, may solve an astronomical mystery about how these ...
Superior Super Earths
Space & Earth / Space Exploration
Nov 30, 2009 |
4.6 / 5 (55) |
15
Super Earths are named for their size, but these planets - which range from about 2 to 10 Earth masses - could be superior to the Earth when it comes to sustaining life. They could also provide an answer to ...
Exoplanets Clue to Sun's Curious Chemistry
Nov 11, 2009 |
4.6 / 5 (21) |
15
(PhysOrg.com) -- A ground-breaking census of 500 stars, 70 of which are known to host planets, has successfully linked the long-standing "lithium mystery" observed in the Sun to the presence of planetary systems. ...
Cloudy with a chance of pebble showers: Simulation suggests rocky exoplanet has bizarre atmosphere
Sep 29, 2009 |
4.7 / 5 (26) |
12
(PhysOrg.com) -- So accustomed are we to the sunshine, rain, fog and snow of our home planet that we find it next to impossible to imagine a different atmosphere and other forms of precipitation.
Found: The planet that shouldn't exist (w/ Video)
Aug 26, 2009 |
4.4 / 5 (19) |
21
(PhysOrg.com) -- The 'most unlikely' discovery of a new planet which could spiral into its star within the next 500,000 years, has been made by Scottish astronomers.
