Related topics: stars · solar system · earth · nasa · orbit

Biofinder advances detection of extraterrestrial life

An innovative scientific instrument, the Compact Color Biofinder, developed by a team of University of Hawai'i at Mānoa researchers, may change the game in the search for signs of extraterrestrial life.

Modeling electrolyte transport in water-rich exoplanets

Oceans on water-rich exoplanets may be enriched with electrolytes, including salts such as sodium chloride, suggests a modeling study published in Nature Communications. The research proposes electrolytes can be transported ...

Software upgrade for 19-year-old martian water-spotter

The MARSIS instrument on ESA's Mars Express spacecraft, famous for its role in the discovery of signs of liquid water on the Red Planet, is receiving a major software upgrade that will allow it to see beneath the surfaces ...

Webb's mid-infrared spectroscopy will reveal molecules, elements

NASA's James Webb Space Telescope team continues to work its way through the 17 science instrument modes. This week they checked off numbers (5) NIRCam grism time series and (4) imaging time series, both used to study exoplanets ...

Martian meteorite upsets planet formation theory

A new study of an old meteorite contradicts current thinking about how rocky planets like the Earth and Mars acquire volatile elements such as hydrogen, carbon, oxygen, nitrogen and noble gases as they form. The work is published ...

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Planet

A 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.

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