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How Many Planets Are Like The Earth?
We know that there are not really any planets like the Earth in our Solar System. Mars comes the closest but its atmosphere is far too thin, it is very cold compared to Earth, and it is much smaller than the Earth, about one-third the size. Venus is closest to the Earth in size, but due to an extremely high level of carbon dioxide in its atmosphere – about 96 percent compared to one-third of one percent for Earth – and its much closer proximity to the Sun than Earth, Venus has extremely hot temperatures that are completely inhospitable to any type of life as we know it.
So there are not any Earth-like planets in our own Solar Systems, but what about planets outside our Solar System, in other star systems? Well, there’s a good chance that could be a completely different story.
Recent years has already seen the discovery of a number of planets that seem to be tantalizingly like the Earth. Our improved state of technology has enabled us to locate these planets beyond anything that could have been done only a relatively short time ago. The vast majority of these are within a thousand light-years or less of Earth, and we’ll go into more detail about some of the best candidates for Earth-like planets in the next section.
But this is just the beginning – the whole Universe may be absolutely full of planets similar to the Earth – as our technology improves and gets better and better in the years, decades, and centuries ahead we will find more and more of them.
After all, it is now estimated that there could be around 500 million Earth-like planets in the Milky Way Galaxy alone, and about 2 trillion galaxies in the observable Universe, 16 billion light-years in all directions from Earth. And what may lie beyond the cosmological event horizon of 16 billion light-years, beyond which we can never really hope to explore(the light from that part of the Universe can never reach us), we can scarcely imagine.
Planets Most Like Earth
One great example of an Earth-like planet is Gliese 667Cc which orbits the third star in a triple star system called Gliese 667 – this planet is located about 23.62 light years from Earth and is visible in the constellation Scorpius. Gliese 667Cc is orbiting the red dwarf star Gliese 667C in the middle of a habitable zone. This planet has been called a super Earth-like planet – it has about 3.7 times the mass of the Earth and an equilibrium temperature of approximately 39.6 degrees Fahrenheit.
Kepler 22b is an Earth-like planet orbiting Kepler 22, a star very much like our own Sun, about 638 light years from Earth and visible in the constellation Cygnus. Although it has a mass about twice that of Earth and an equilibrium temperature of around 12.2 degrees Fahrenheit, the composition of Kepler 22b is probably not like that of the Earth, although what it precisely is remains unknown at this time.
Another super Earth-like planet is Kepler 69c – this is a planet orbiting around the star Kepler 69, which is about 2430 light years from Earth and visible in the constellation Cygnus.
This planet is approximately 6 times as massive as Earth and believed to have a rocky surface and an equilibrium temperature of 527 degrees Fahrenheit(any oceans probably would have boiled away long ago, accounting for its being significantly more massive than Earth), which would be too hot for life as we currently know it. Kepler 69c may be more like the planet Venus in our Solar System with a runaway greenhouse effect.
Kepler 62f is also classified as a super Earth-like planet and orbits in the habitable zone of Kepler 62, a star which is smaller and cooler than our Sun, about 1200 light years from the Earth and visible in the constellation Lyra.
It is about 2.8 times as massive as the Earth, is believed to have large oceans, and has an equilibrium temperature of approximately -85 degrees Fahrenheit. Although this equilibrium temperature is somewhat cooler than the Earths it is still well within the range which would be favorable for the evolution of alien life forms.
Also enhancing the possibility of some sort of alien life, besides the oceans and temperature, is the fact that Kepler 62 is currently believed to be a very stable star with an extremely long lifespan in the range of about 30 billion years.
Kepler 186f is a planet which very closely resembles the Earth in size with a mass about 1.4 times that of Earth and an equilibrium temperature of about -121 degrees Fahrenheit, significantly colder than Earth but still in the range where life of some sort could evolve, especially since some areas of the planet would be warmer.
Orbiting in the habitable zone of the red dwarf star Kepler 186 it is about 582 light years from Earth, visible in the constellation Cygnus. This planet is definitely a good candidate for some type of alien life and is certainly worthy of further study.
Kepler 442b is a planet which excites scientists since it is about 2.3 times as massive as the Earth with an equilibrium temperature of -40 degrees Fahrenheit – some areas of the planet would be quite a bit warmer than this so the chance of some type of alien life evolving there is very significant.
The relation of Kepler 442b’s mass to its volume indicates that it probably has a solid rocky surface. Whether or not there is a significant amount of water, which is crucial to the evolution of any form of life as we know it, is still an open question and more research needs to be done.
Kepler 452b is another Earth-like planet often called Earth 2.0, or Earth’s cousin. Orbiting in a habitable zone around Kepler 452, which is a star very much like our own Sun, it is about 1402 light years from Earth and can be seen in the constellation Cygnus.
This planet has a mass about 5 times that of the Earth and probably has a solid rocky surface since it’s radius is only around 50 percent greater than the Earths.
Kepler 452b has been called Earth 2.0 in large part because it has an equilibrium temperature of about 17 degrees Fahrenheit, slightly warmer than the Earths, and it orbits around Kepler 452 about every 385 days, very close to the Earths 365 days. This planet is definitely a prime candidate for some sort of alien life and should be studied intensely. Who knows, there may even be some type of intelligent alien civilization there!
Other Planets Like Earth
Luyten b | GJ 273b
Luyten b, also known as GJ 273b, orbits within the habitable zone of a red dwarf called Luyten’s Star in the constellation Canis Minor about 12.2 light years away from Earth. It is the third closest potentially habitable exoplanet; only Proxima Centauri b and Ross 128 b are closer to Earth.
Luyten b is classified in the lower range of Super-Earth planets since it is about 2.9 times as massive as the Earth with a radius about 1.5 times as much; Earth-like(meaning an Earth-like composition) planets generally must have a mass no greater than 1.4 times that of the Earth. Because of this relationship of mass to the radius, it is likely to have a solid rocky surface.
It orbits very close to its host star about every 18.6 days at a distance of about 8.463 million miles – it is less likely to be tidally locked since there is a higher degree of eccentricity(about .10) in its orbit causing a spin-orbit resonance to occur.
This planet receives a stellar incident flux(similar to the solar wind from the Sun) from its host star only about 6 percent greater than the Earth receives from the Sun, it may have an atmosphere similar to Earth, and the average surface temperature is about 66 degrees Fahrenheit, which is very close to the Earths.
All of this makes Luyten be one of the most Earth-like planets that has ever been found. Since it’s host star, Luyten’s Star is very stable and quiet and not prone to stellar flares, Luyten b is very likely to retain an atmosphere for billions of years to come. If the atmosphere is thick enough, heat will be distributed very evenly around the planet, greatly increasing its habitability.
The Earth Similarity Index(ESI), where Earth has a value of 1, is about .91 for Luyten b which gives it one of the highest ESIs of any exoplanet thus far discovered. The habitability potential of Luyten b is in fact so high that an organization called METI – Messaging Extraterrestrial Intelligence – sent a message towards the planet in October 2017 which contained music and scientific information with the hope of contacting any extraterrestrial civilization which might exist there.
Proxima Centauri b
Proxima Centauri b is the closest known Earth-like planet orbiting in the habitable zone of the red dwarf star Proxima Centauri(part of a triple star system) 4.2 light years(25 trillion miles) from Earth and visible in the constellation Centaurus.
It orbits around the parent star Proxima Centauri in only about 11.2 Earth days at a distance of 4.6 million miles. Although, as mentioned, it orbits in the habitable zone of Proxima Centauri, the planet is subject to stellar wind pressures over 2000 times that of the solar wind experienced by the Earth. This fact greatly lessens the chances of any type of existing life, though it is not absolutely impossible.
Ross 128 b
Ross 128 b is an Earth-sized exoplanet which orbits in the innermost part of the habitable zone of Ross 128, a red dwarf star with only about 17 percent of the mass of the Sun and 20 percent of the radius, and is about 11 light years away, located in the constellation of Virgo. This makes Ross 128 b the second closest potentially habitable exoplanet to Earth.
This planet is actually the nearest exoplanet to Earth which is orbiting around a quiet and relatively stable red dwarf star which is about 9.5 billion years old – this makes Ross 128 b an excellent candidate for some type of extraterrestrial life.
Ross 128 b is roughly 1.35 times as massive as Earth with a radius about 1.1 times that of Earth. This seems to suggest that it has a mostly solid rocky surface with a gravity of approximately 1.12 times that of the Earth.
Ross 128 b orbits very close to Ross 128 with its year lasting only 9.9 Earth days. Although this planet is very possibly tidal locked to the parent star, meaning each side respectfully has perpetual day and night, its temperature is believed to be very similar to that of Earths, increasing the chances of habitability for some form of existing life.
Tau Ceti e
Tau Ceti e is an exoplanet orbiting the host star Tau Ceti in a habitable zone at a mean distance of 51336000 miles – Tau Ceti is a stable Sun-like star about 11.9 light years from Earth in the constellation Cetus. Tau Ceti has an apparent magnitude of 3.5 and can be seen from the Earth with the naked eye.
Tau Ceti has a significant debris disk surrounding it – ten times that of our Sun – so Tau Ceti e would suffer much more impacts than Earth. Tau Ceti makes an orbit around its host star every 168 days and has a mass about 3.93 times that of the Earth.
In addition to this, if Tau Ceti e has an atmosphere it’s surface temperature would be around 154 degrees Fahrenheit, making it somewhat less hospitable to life.
Tau Ceti f
Tau Ceti f is the second of 5 planets(this number is still not certain) orbiting Tau Ceti in a habitable zone about 11.9 light years from Earth. It is currently classified as a Super-Earth planet with about 2.66 times the mass of the Earth making an orbit around Tau Ceti at a distance of 125550000 miles every 642 days.
Although orbiting in the temperate zone of Tau Ceti, recent research findings indicate that Tau Ceti f has occupied this habitable zone for less than one billion years, which means there may not have been enough time for any significant form of life to evolve.
Wolf 1061c is a planet orbiting at the inner edge of the habitable zone of the red dwarf star Wolf 1061 about 13.8 light years from Earth in the constellation Ophiuchus. Wolf 1061 is believed to have a potential lifetime of about 400 to 500 billion years which would be around 40 to 50 times that of the Sun. With a mass of about 4.3 times that of Earth and a radius over 1.5 times as large, Wolf 1061c is thought to have a rocky surface with a slightly higher density than Earth.
The surface gravity of Wolf 1061c is about 1.6 times that of the Earth, it orbits the parent star Wolf 1061 about every 17.9 days, and its equilibrium temperature is thought to be about -58 degrees Fahrenheit. It orbits Wolf 1061 at a mean distance of only about 7.8 million miles which increases the possibility that one side of the planet is always locked toward the parent star.
This means that there is a strong possibility of extreme temperature differences between the day and night side of Wolf 1061c which in itself would lessen the chances of life, but there is also a significant possibility of more moderate temperatures at the terminator zone between the day and night sides. This would increase the chances that liquid water could exist and that some form of alien life could evolve.
Trappist-1 is an ultra-cool red dwarf star slightly larger than the planet Jupiter but much more massive which is located about 39.6 light years from Earth and visible in the constellation Aquarius. It has only about 8 percent of the mass of our Sun and as such is very close to the boundary between brown dwarf stars and hydrogen fusion stars(like the Sun). With these attributes, Trappist-1 has the ability to live 4 to 5 trillion years, which is 400 to 500 times longer than the Sun.
Seven terrestrial type planets have been detected using the Spitzer Space Telescope orbiting Trappist-1 in the temperate zone, with 3 of these having a very high potential of habitability – Trappist-1e, Trappist-1f, and Trappist-1g – this is more potentially habitable planets than have been detected in any other star system so far.
Trappist-1b is very close in size to the Earth with an estimated mass 12 percent great than Earth and radius only 2 percent greater – almost identical. It orbits Trappist-1 at a distance of 1069500 miles every 1.5 Earth days – only 36 hours. Research has shown that the surface is mostly rocky with probably less than 5 percent of it consisting of water. It is believed to have a surface gravity about 81 percent that of Earth.
Since it has a stellar flux about 4 times that of the Earth’s solar wind, it may have a very thick Venusian type atmosphere. The surface temperature of Trappist-1b is estimated at about 890 degrees Fahrenheit, which is hotter than the surface of Venus. Needless to say, Trappist-1b is certainly inhospitable to any form of life as we know it.
This planet orbits the host star Trappist-1 at a distance of about 1469400 miles approximately every 2.42 days, which is about 58 hours. Its mass is about 15.6 percent greater than Earths with a radius of 9.5 percent greater. It is the third largest planet of the Trappist-1 system and the most massive overall. The surface gravity is about 96.6 percent that of Earths.
Trappist-1c is believed to be very similar to Trappist-1b with a mostly rocky composition and also a thick Venusian like atmosphere, although somewhat thinner than Trappist-1b. It is also currently thought to be much too hot to support life.
Trappist-1d orbits its host star Trappist-1 at a very close distance of about 2072040 miles every 4.05 days, which is about 97 hours. It lies in the innermost region of the temperate zone of Trappist-1 and has about 29.7 percent the mass of Earth and a radius of 78.4 percent. The surface gravity is approximately 48.3 percent that of the Earth.
The host star Trappist-1 has a very low luminosity so, despite its very close orbit, Trappist-1d receives only about 4.3 percent more stellar flux than the Earth. This planet is believed to have a mostly rocky surface with the possibility of some oceans, atmosphere, and perhaps some ice. Trappist-1d has an equilibrium temperature of roughly 48 degrees Fahrenheit, somewhat warmer than Earths. The composition of its atmosphere, as well as its suitability for life, has yet to be determined.
The exoplanet Trappist-1e orbits Trappist-1 very closely at a distance of about 2723305 miles every 6.1 Earth days which is approximately 146 hours. It has a mass of about 77.2 percent that of Earth and a radius of about 91 percent. The surface gravity is 93 percent that of Earth.
Trappist-1e has a stellar flux of about 60 percent that of what the Earth receives from the Sun and an equilibrium temperature of roughly -16.7 degrees, a little bit cooler than Earth. With a density of approximately 1.024 times that of the Earth, almost identical, Trappist-1e is believed to have a very Earth-like composition with a solid rocky surface.
It has been confirmed to have a compact atmosphere similar to the terrestrial planets in our Solar System with a very high potential of being an ocean world very similar to Earth which would be very favorable to the evolution of some sort of alien life. With an Earth Similarity Index of .87, Trappist-1e has one of the highest habitability potentials of any exoplanet discovered so far.
Trappist-1f also orbits in the habitable zone of its host star, Trappist-1, at a distance of 3441000 miles approximately every 9.2 days, which is about 221 hours. The mass of Trappist-1f is about 68 percent that of the Earth with the radius being roughly 4.5 percent greater. There is a surface gravity of about 62 percent that of Earth.
It is thought that Trappist-1f has a rocky surface surrounded by a very dense gaseous and steamy atmosphere – this very dense atmosphere may heat up the planet to around 2060 degrees Fahrenheit which would be extremely hot.
However, since it is thought that Trappist-1f is tidally locked to its host star, with perpetual daylight on one side and night on the other side, there would be a distinct terminator zone where more moderate temperatures might exist giving some possibility of life.
The exoplanet Trappist-1g orbits in the habitable zone of Trappist-1 at a mean distance of 35340000 miles about every 12.35 days which is 296 approximately hours. This orbit has an eccentricity of only .00208, giving the planet a very stable climate.
Trappist-1g has both a mass and radius about 15 percent larger than Earth although it has a density of only 76 percent of Earth and surface gravity of 87.1 percent. The temperature is believed to be around -110 degrees Fahrenheit – it receives only about 25 percent of the stellar flux that the Earth receives from the Sun.
These findings indicate that Trappist-1g is most likely covered with a thick layer of ice although a huge global ocean or a very thick atmosphere is possible. The evolution of life on Trappist-1g might be possible, although the conditions would probably be harsh.
Trappist-1h is the outermost planet in the system of Trappist-1. It orbits the host star slightly outside what is considered the habitability zone at the frost line at a distance of 5756700 miles approximately every 18.87 days, or about 453 hours. It has a mass 33.1 percent that of Earth and a radius of 77.3 percent with a surface gravity of about 55.5 percent.
This planet receives only about 13 percent of the stellar flux that the Earth does and has a temperature estimated at around -155 degrees Fahrenheit, a little colder than the south pole of the Earth. The density of Trappist-1h is very close to that of Mars in our Solar System, so it is quite possible that there is some water, probably in the form of a thick ice shell. It might be possible for life to evolve on Trappist-1g, but the conditions would be very harsh.
We will keep searching for Earth 2, another planet so similar to Earth that it could almost be identical. A planet that might have some type of intelligent life, perhaps even advanced civilizations that may even be not so different from our own.
This civilization could have beings which appear similar to us, or they may be quite different. They may be in a similar stage of technological progress or be far more advanced than we can even imagine. If they are more advanced, what we could learn from them might leap us ahead to a future that would seem like magic today.
We don’t know whether they would be a benevolent or a war-like species like we are, although the former would seem more likely for a civilization to reach an advanced state. But they would probably be curious about the Cosmos like we are; after all curiosity is one of the most important attributes of intelligence, a trait that has enabled us to learn and progress to our current state of technology.
So out there among the countless stars, there may very well be a large number of planets much like the Earth with intelligent beings looking up at the stars from their world and wondering about them. Perhaps one day in the more distant future we will have the technology, along with the curiosity, to go visit them.
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