March 5, 2021
Description
Originally published here: Exoplanets scaled one in 120 million by tato_713 - Thingiverse
The concept of this post is to compare the size in the same scale of various Earth sized exoplanets with the Earth itself or other astronomical bodies like Neptune. Although there are thousands exoplanets confirmed, I made only some of the most notorious ones with known diameter, and nearly Earth sized (up to 2.5 its diameter). The models are just spheres scaled one in 120 million, to compare with terrestrial planets; one in 250 million; and one in 500 million for the biggest ones.
The file's names explained: name_1_x_10_y.stl is 1 : x* 10^y. So _1_6_10_7 is 1:600000000 or one in 60 million.
Proxima b is the closest exoplanet known to the Solar System, the closest within the habitable zone of its star, the only known planet in the nearest star, Proxima Centauri, and the only one confirmed in the Alpha Centauri system. As is it said, the host star for the planet is part of the Alpha Centauri system, orbiting the two main stars Alpha Centauri A (Rigil Kentaurus) and B (Toliman). Proxima is a flare M type red dwarf while the others are G (Sun like) and K type (orange star) respectively. Flare stars are randomly emit huge flares that could have devastating effects on a close orbit planet atmosphere, unless it has a strong magnetic field.
Luyten b is the fourth closest planet in the habitable zone. It's orbiting the Luyten's Star, which is a red dwarf, that unlike Proxima Centauri, it's relatively inactive. This planet is classified as a super-Earth, a planet bigger than Earth, but smaller than Neptune, it isn't related with its composition.
This planet was at the time of its discovery, the closest known rocky planet. It orbits a K type star. It is in the hot zone of its system, which means that water cannot be liquid on its surface. It is one of the few exoplanets with a detected atmosphere. The star is visible to the naked eye, and is one of the oldest star know with 11 billion of years.
The HD 219134 system has at least 5, and possibly 7, planets; of which the two most close to the star has known diameter. HD 219134 c is the second one, also with a possible atmosphere. The rest of the planets of this system are also more massive.
Trappist-1 is one of the best studied exoplanets. It has 7 Earth sized planets that transit in front of the host star, viewed from the Solar System. It is an ultra-cool red dwarf slightly larger than Jupiter. All of the planets orbits very close to the star, comparable with the distance between the Earth and the Moon, so a planet of the system is visible from the surface of the others. The planet b (the closest to the star) has a Venus like atmosphere mainly composed of CO2 and it is inferred to have water vapor because of its low density.
Trappist-1 c is, like the b, a Venus like planet with water vapor atmosphere, too hot to be liquid. Like most if not all the planet on the system it is likely tidal locked to the star.
Trappist-1 d is the smallest and less densest planet of the Trappist-1 system. It is between the size of Mars and Earth. This planet orbits the inner edge of the habitable zone, but it is likely tidal locked.
The e planet is one of the most Earth like one know, well within the habitable zone, slightly smaller, and nearly the same density of our planet. The habitability of the red dwarf planets is cuestionable, mostly because of the tidal lock. The always-day hemisphere may be too hot, while the night one may be too cold. It could be that in the border line between the hemispheres, the air is warm enough to sustain Earth like conditions. Also if the atmosphere is thick enough, it could distribute more efficiently the air temperature.
Trappist-1 f is about the size of Earth, but two third its mass. This low density is consistent with a water rich world (20% of its mass, contrast to the 0.02% of Earth's mass). This means that it is probably an ocean world, with a combination of water vapor atmosphere, liquid ocean and large ice blocks.
Like other members of this system, Trappist-1 g appear to be composed of high amounts of water, in this case in form of ices. It is the biggest planet of the system, although most of them are similar in size. Because of their proximity, the planet of the Trappist-1 system are locked in an orbital resonance, similar to the moons of Jupiter, Io, Europa and Ganymede.
The h planet is the outermost one of the Trappist-1 system. It has about the same size and density of that of Mars, but is though to be composed 5% of water ice. It is unlikely that this planetary system has many bigger planets in larger orbits, because their effects on the star light must be detectable, as well as their transits in front of the star.
55 Cancri was one of the firsts star system to be discovered with more than two exoplanets. It is binary star system of a K type star (55 Cancri A), which has all the 5 known planets of the system, and a smaller M type red dwarf (55 Cancri B). Only the e planet of this system, nicknamed Janssen, has a known radius, because its proximity to the star makes possible the transits. It could be a carbon planet, a planet composed of silicate rock and iron core like Earth, but with a thick crust and mantle of carbonaceous material. This hypothetical type of planet may have layers of graphite and diamond below its surface, and high amount of hydrocarbons like methane in the surface, as well as carbon monoxide, dioxide, and smog in the atmosphere. In the Solar system there aren't large carbon based bodies, only the C-type asteroids (like 253 Mathilde) are mainly composed of carbonaceous material.
Because its low density Gliese 1214 b could be mainly water in composition. Ocean worlds are theorised to have a thick ice layer at the bottom the ocean, that prevents the exchange of other-than-water nutrients from the mantle, which left poor conditions for the life as we know. Gliese 1214 b could also be a smaller version of ice giants like Neptune and Uranus.
Kepler-37 b at the time of its discovery was the smallest planet know. It is also the smallest one known to orbit a Sun like star. It is a bit larger than the Moon. By its proximity to the star and the small size it is likely to be rocky in composition, like the moon, but the exact composition is unknown yet because the mass and density of any planet of the system cannot be determined.
COROT-7 b was the first planet known to be terrestrial. Because its proximity to the COROT-7 star and its high density, it is a candidate for a chthonian planet, an hypothetical kind of planet that is the remnant rocky core of an ice or gas giant which atmosphere was stripped off by the stellar winds.
BD+20594 b is the 594th entry in the +20° zone of the Bonner Durchmusterung catalogue (the "b" is because is the first planet of the system); in the Kepler program is K2-56, indicating that it is from the second part of the program. It is one of the proposed mega-Earth. Contrary to the term "super-Earth" that reference only the size, mega Earths are planets 2 or more times the Earth radius, that are composed of terrestrial compounds, that is, they are not gas gigant, and have a perceptible interface between the gas and liquid.
This is the first planet known around a white dwarf. It is also the smaller planetary object, being smaller than Pluto , so it is not guaranteed that it meets the requirements for being a planet. It can be vaporizing by in host remnant star. Life conditions around a white dwarf are unclear, the luminosity of these bodies is too weak, so the habitable zone is too short. Also, volatile materials like water and hydrogen may have being eroded by stellar wind. White dwarf are usually the size of Earth, so transits in front of them are rare. The host white dwarf of this planetary object is posted here.
Kepler-10 b was the first planet confirmed to be a terrestrial planet. Like most of the planets discovered by transit method, it orbits very close to its host star. This is because this method is extremely biased to this kind of planets. It is very likely that Kepler-10 b has a dry surface, like that of Mercury.
Kepler-10 c is probably a mini-Neptune, a super-Earth with the composition of that of ice giants. It also sometimes applies to hydrogen planets smaller than Neptune. For these planets, the term "gas dwarf" may be more accurate.
Although the exact mass of this planet is unknown, it's thought to be an ocean planet, a theoretical kind of planet dominated by water ocean environment.
One of the smallest and recent planets discovered. It is too close to its star, so it's uninhabitable.
Kepler 62 is a 5 known planet system K-type star. This kind of star is an intermediate between M-type red dwarf and G-type Sun-like star, called "dwarf orange". The lighter the star, the longer its life. Their life is longer to that of Sun like stars, and they are less likely to have the problems of red dwarfs, like the tidal locking of the planet and the probability of being a flare star. The b planet is a typical super-Earth planet, in the hot zone of the star.
c is a Mars sized exoplanet with the stellar flux of that of Mercury.
d is the biggest planet known of the system, and orbits in the "Venus zone" of the star, where the planet is too hot for having liquid water in its surface, but it is not close enough to deplete its atmosphere. By its density it is something between a small version of Neptune and a gigant version of Venus.
e is in the limit of size (1.6 Earth's masses) in which a planet is expected to be a big rocky planet or an small gaseous planet. It lays within the habitable zone.
f orbits in the outer part of the habitable zone of its star, meaning that it could be covered of ice if it hasn't a substancial atmosphere to retain the heat.
Sometimes called "Earth 2.0", this planet is important because is the first nearly certain terrestrial planet orbiting whit in the habitable zone of a G-type star. The orbital period is similar to that of Earth. This kind of planet are difficult to detect since planets that far from its star are less likely to transit in front of the star viewed from Earth.
Another candidate for being a mega-Earth planet.
The Kepler-11 system is compact compared with Solar System, althogh there could be more planets that not transit the star. All the 6 known planets orbit within the orbit of Venus. The star is G-type, slithly heavier that the Sun. All the planets are bigger than the Earth, and the biggest, about the size of Neptune or Uranus.
Type: Planet. Gas dwarf.
This is a super-Earth planet in a Venus-like orbit around a Sun-like star.
This system is known for being analogous in planet distribution to the Solar System. It has 8 known planets, the first 3 are likely terrestrial, the next 3 are in the range of super-Earth size, and the last 2 are jovian planets by they size. It is one of the farthest known multiple planet system discovered by the Kepler mission.
This planet is known for being discovered using a machine learning algorithms on the transit data.
This planet is one of the first, and the few, Earth-like planet discovered using gravity microlesing, the detection of the lens effect that a exoplanet does of a background star. This method allows to detect planets with long orbital period, because they must be separated enough of they stars. Prior to the Kepler mission it was the most Earth-like exoplanet known.
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