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To support an Earth-like atmosphere for about 4.6 billion years (Earth's current age), a moon with a Mars-like density is estimated to need at least 7% of Earth's mass. [20] One way to decrease loss from sputtering is for the moon to have a strong magnetic field of its own that can deflect stellar wind and radiation belts.
Irregular moons are probably minor planets that have been captured from surrounding space. Most irregular moons are less than 10 kilometres (6.2 mi) in diameter. The earliest published discovery of a moon other than Earth's was by Galileo Galilei, who discovered the four Galilean moons orbiting Jupiter in 1610. Over the following three ...
This is a list of exoplanets within the circumstellar habitable zone that are either under 10 Earth masses or smaller than 2.5 Earth radii, and thus have a chance of being rocky. [ 3 ] [ 1 ] Note that inclusion on this list does not guarantee habitability, and in particular the larger planets are more unlikely to have a rocky composition. [ 4 ]
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]
The planet has 6.9 Earth masses and 1.8–2.4 Earth radii, and with its close orbit receives 40 percent more stellar radiation than Earth, leading to surface temperatures of about 60° C. [ 145 ] [ 146 ] [ 147 ] HD 40307 g , a candidate planet tentatively discovered in November 2012, is in the circumstellar habitable zone of HD 40307 . [ 148 ]
The mass of the star and the distance from the star set the tidal habitable zone. A planet tidally locked has one side of the planet facing the star, this side would be very hot. The face away from the star would be well below freezing. A planet too close to the star will also have tidal heating from the star. Tidal heating can vary the planet ...
Although the Moon is Earth's only natural satellite, there are a number of near-Earth objects (NEOs) with orbits that are in resonance with Earth. These have been called "second" moons of Earth or "minimoons". [2] [3] 469219 Kamoʻoalewa, an asteroid discovered on 27 April 2016, is possibly the most stable quasi-satellite of Earth. [4]
The study of extraterrestrial atmospheres is an active field of research, [1] both as an aspect of astronomy and to gain insight into Earth's atmosphere. [2] In addition to Earth, many of the other astronomical objects in the Solar System have atmospheres. These include all the giant planets, as well as Mars, Venus and Titan.