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For a stable orbit the ratio between the moon's orbital period P s around its primary star P p must be < 1 ⁄ 9, e.g. if a planet takes 90 days to orbit its star, the maximum stable orbit for a moon of that planet is less than 10 days.
Planetary habitability in the Solar System is the study that searches the possible existence of past or present extraterrestrial life in those celestial bodies. As exoplanets are too far away and can only be studied by indirect means, the celestial bodies in the Solar System allow for a much more detailed study: direct telescope observation, space probes, rovers and even human spaceflight.
[72] Extremophiles are Earth organisms that live in niche environments under severe conditions generally considered inimical to life. Usually (although not always) unicellular, extremophiles include acutely alkaliphilic and acidophilic organisms and others that can survive water temperatures above 100 °C in hydrothermal vents.
Surface planetary habitability is thought to require an orbit at the right distance from the host star for liquid surface water to be present, in addition to various geophysical and geodynamical aspects, atmospheric density, radiation type and intensity, and the host star's plasma environment. [2]
NASA has pointed out that normal adults have ten times as many microbial cells as human cells in their bodies. [3] They are also nearly everywhere in the environment and, although normally invisible, can form slimy biofilms. [3] Extremophiles have adapted to live in some of the most extreme environments on Earth.
In 1962, Mariner 2, the first successful mission to Venus, measured the planet's temperature for the first time, and found it to be "about 500 degrees Celsius (900 degrees Fahrenheit)." [ 14 ] Since then, increasingly clear evidence from various space probes showed Venus has an extreme climate, with a greenhouse effect generating a constant ...
The two most common reasons in favor of colonization are the survival of humans and life independent of Earth, making humans a multiplanetary species, [6] in the event of a planetary-scale disaster (natural or human-made), and the commercial use of space particularly for enabling a more sustainable expansion of human society through the ...
Red dwarfs [12] are the smallest, coolest, and most common type of star. Estimates of their abundance range from 70% of stars in spiral galaxies to more than 90% of all stars in elliptical galaxies, [13] [14] an often quoted median figure being 72–76% of the stars in the Milky Way (known since the 1990s from radio telescopic observation to be a barred spiral). [15]