Beyond Earth

Planets and dwarf planets of the Solar System (Sizes to scale, distances not to scale)
The deepest visible-light image of the universe from the Hubble Ultra Deep Field telescope
NGC 4414 is a spiral galaxy in the constellation Coma Berenices about 56,000 light years in diameter and approximately 60 million light years from Earth
Main articles: Outer space, Universe, and Extraterrestrial life

Outer space, also simply called space, refers to the relatively empty regions of the universe outside the atmospheres of celestial bodies. Outer space is used to distinguish it from airspace (and terrestrial locations). There is no discrete boundary between the Earth's atmosphere and space, as the atmosphere gradually attenuates with increasing altitude. Outer space within the solar system is called interplanetary space, which passes over into interstellar space at what is known as the heliopause.

Outer space is certainly spacious, but it is far from empty.[citation needed] Outer space is sparsely filled with several dozen types of organic molecules discovered to date by microwave spectroscopy, blackbody radiation left over from the big bang and the origin of the universe, and cosmic rays, which include ionized atomic nuclei and various subatomic particles. There is also some gas, plasma and dust, and small meteors. Additionally, there are signs of human life in outer space today, such as material left over from previous manned and unmanned launches which are a potential hazard to spacecraft. Some of this debris re-enters the atmosphere periodically.

Although the planet Earth is currently the only known body within the solar system to support life, current evidence suggests that in the distant past the planet Mars possessed bodies of liquid water on the surface.[75] For a brief period in Mars' history, it may have also been capable of forming life. At present though, most of the water remaining on Mars is frozen. If life exists at all on Mars, it is most likely to be located underground where liquid water can still exist.[76]

Conditions on the other terrestrial planets, Mercury and Venus, appear to be too harsh to support life as we know it.[citation needed] But it has been conjectured that Europa, the fourth-largest moon of Jupiter, may possess a sub-surface ocean of liquid water and could potentially host life.[77]

Recently, the team of Stéphane Udry have discovered a new planet named Gliese 581 g, which is an extrasolar planet orbiting the red dwarf star Gliese 581.[citation needed] Gliese 581 g appears to lie in the habitable zone of space surrounding the star, and therefore could possibly host life as we know it.
















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