Right now, scientists have no idea whether or not life exists on Neptune, and conditions there appear to be extremely hostile to life. To find life on Neptune, the planet would have to have an energy source for bacteria life to take advantage of and a steady supply of liquid water.
More than 30 times farther from the sun than Earth, ice giant Neptune is the only planet in our Solar System that is not visible to the naked eye, and it was predicted for the first time through mathematics before its discovery. Although the farthest planet from the sun, ice giant Neptune is a frequent pitstop of popular culture and novels. Neptune is called one of two ice-giant planets in the Solar System (the other being its close twin, Uranus).
Neptune, like its close-twin Uranus, is an ice giant, a subclass of a giant planet, as ice giants are smaller in size and contain higher concentrations of volatiles than Jupiter and Saturn. Neptune gives up 2.5 times the amount of heat that Neptunes absorbed from the Sun, whereas Uranus, although closer to the Sun, does not - this is pretty weird, considering that the compositions of ice giants are quite similar. Neptune and Uranus demonstrate that planets formed under similar conditions can deliver both extremes.
That is why Uranus is soft, aquamarine, while Neptune is cerulean, the bluest planet in our Solar System - the ideal contrast to Neptune. NASA's Kepler spacecraft found the most common kind of planet in the galaxy is somewhere in between the sizes of Earth and Neptune: a super-Earth, whose similarities in our solar system are nonexistent and whose creation is thought almost impossible. Super-Earths are the most common kind of planet in our galaxy, says Dr. Ingo Waldmann, an extrasolar planet researcher at University College London, U.K., and one of the scientists who reported that a watery world called K2-18 b exists. Super-Earths are possible places for extraterrestrial life.
Similar ice-ocean worlds Exoplanets in between Earths and Neptunes size - super-Earths and mini-Neptunes - show distinct structures, scientists think. This may be true for worlds as small as Earth, super-Earths, or even some sub-Neptunes (any planet smaller in radius than Neptune but larger than our planet, Earth). After the nine-year mission, most of the exoplanets that are currently known are, in fact, rocky planets, ranging in size from the Earth to Neptune.
Stretching the limits of the largest telescopes in the world, astronomers saw only a few planets up close. Scientists have found thousands of planets over the past few years, but so far, no undisputed observations have been made of the moons surrounding any of them.
When not bickering over this, planet scientists are searching for Planet Nine, a hypothetical world presumably circling the sun past Neptune, the existence of which might explain the odd orbits of a few distant celestial bodies. Ground-based telescopes have found massive planets weighing a few times as much as Jupiter, orbiting their stars at a distance of more than double the distance from the sun as Neptune--another area in which ideologues believe large planets cannot have grown. One of the first, most stunning systems found in direct imaging was that around star HR 8799, which has four planets ranging in orbits beyond those of Saturn, out to more than double that of Neptune.
More recently, scientists have begun to think that a handful of Jupiter's and Saturn's moons may also have life-bearing conditions. Water-rich exoplanets and icy moons such as Jupiters, Europa, and Saturns Enceladus are potential targets for astrobiologists looking for signs of life elsewhere in the cosmos.
Life forms in these waters do not require oxygen to survive, and they may help us better understand the possibilities of life on other planets, including exoplanets. Until recently, the assumption was that, for the many water-rich exoplanets larger than Earth but smaller than the Earth's moon Neptune, the ices formed deep within the planets will prevent important minerals from reaching water near the surface. Because of immense pressures on the bottoms of the oceans of Super-Earths and Mini-Neptunes, high-pressure ices would form thick mantles around an exoplanet's core, sealing the mineral-rich rocks from reaching the seas above.
Exoplanet surveys seemed to find many super-cooked Jupiters and small Neptunes around other stars. However, the potential liquid-water-bearing rocky planets were still in short supply before the Kepler era. By the mid-2010s, Kepler had shown that Earth-sized worlds were common; it had even found some potentially habitable ones passing in front of their stars, such as a pair that Kaltenegger had modeled for Borucki. Meanwhile, in 2016, astronomers found the closest star to Earth, Proxima Centauri, has a potentially habitable planet about Earth's size.
The planet lies in what astronomers call a habitable zone, and its temperature may be suitable for life to thrive there. At a stroke, the so-called habitable zone--where liquid water, and thus, thought to be life, is feasible in any planetary system--would extend up to an impressive 30AU. The search for moons beyond our solar system has revealed yet another possible lunar world, one larger than the Earth, orbiting the planet Earth, which is similar in size to Jupiter.
The planet, and its other possible lunar world, orbits a sun-like star more than 5,000 light-years away, according to a report in Nature Astronomy. When Pluto was discovered, Pluto was considered to be the planet. At the same time, Neptune became the second-farthest-known planet, except during the 20-year period from 1979-1999, when Pluto's elliptical orbit brought it closer than Neptune to the sun. Neptune's largest moon, Triton, was discovered soon afterward, although no other moons among the planets remaining 13 known were located by telescopes before the 20th century.
Voyager 2 acquired this side-on view of Triton, the largest satellite of Triton, just after it closed...[+] to the moon and passed through its shadow on Aug. 25, 1989. Key to Trident's mission was the use of an eclipse of the sun from Triton -- only as seen by the spacecraft -- with Neptune in its background. Being the brightest that Triton has ever been, the opposition also means Neptune--currently hanging out in Aquarius in its 165-year-long orbit around the sun--rises to the east during the setting sun, setting to the west during sunrise.
For now, Triton is circling Neptune at the edges of the Solar System, complete with its geysers, nitrogen atmosphere, and possible internal oceans. As the planet furthest from the Sun, in theory, it should be able to bask in the glow of its Neptune spot on the cosmic rostrum. In future years, if NASA followed a scientific consensus recommendation and sent a probe to Uranus, Neptune would be the only planet humanity has yet to visit with a dedicated mission.
When planetary scientists looked at recent telescope observations that spanned almost two decades, they expected to see signs that Neptune was gradually warming. Initially, the biggest gaseous giants close to their star, the warm Jupiter, seemed the most abundant, but as a growing number of super-Earths have piled up, scientists have been baffled by their abundance.
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