the zoo of exoplanets
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Since the discovery of first known exoplanets in 1992, orbiting the pulsar PSR 1257+12, we have found and confirmed over 5460 distinct and diverse worlds in more than 3930 star systems throughout our galaxy.
They can be broadly divided into gas giants similar to Jupiter or Saturn, ice giants such as Neptune, and rocky planets like Mercury, Venus and Earth, some of which might be conductive to life.
However, not all of them are similar to planets found in our own solar system; we have discovered many diverse exotic worlds such as hot jupiters with clouds of molten rock, water worlds covered by a world-spanning unfathomably deep superocean, red-hot lava planets or planets darker than coal.
With the help of scientific models and up-to-date information, this poster attempts to artistically visualize together over 1100 of known exoplanets of all the different types we have discovered so far, arranged by the amount of heat they receive from their stars, comparing their relative sizes and providing a window to how they might look like.
Using methods such as doppler spectroscopy, microlensing and transit photometry, we are able to estimate dimensions and mass of many planets with considerable accuracy, as well as calculate the amount of heat that reaches them from their star
Kepler Space Telescope in particular has provided the most valuable and accurate data.
Planets with a radius over 1.5 times of Earth are likely to be terrestrial planets with an interior made mostly of rock and metal, most of which having a solid surface. Beyond this point, planets are likely to accumulate more and more gases, eventually becoming more similar to a hot versions of uranus with a gaseous atmosphere seamlessly transitioning into a liquid mantle.
Just like planets in our own solar system, gas and ice giants around other stars would feature an atmosphere composed mostly of helium and hydrogen, their appearance dictated mostly by the presence of diverse hazes and clouds in different layers of their atmospheres.
Exoplanets colder than -200 C are expected to appear as blue or cyan globes with their upper atmosphere dominated with methane hazes, just like in case of Uranus and Neptune. Cold terrestrial planets might possess lakes and rivers of liquid hydrocarbons, just like Saturn’s moon Titan.
Exotic ice and gas planets even colder than Uranus could feature cryogenic clouds and rain made of liquid nitrogen, neon, carbon monoxide or oxygen.
Gas planets warmer than -200 C but colder than -90 C would feature clouds of methane and hydrogen sulfide and ammonia crystals in their upper atmosphere, coloring them in various shades and mixtures of red, yellow and white
Water clouds just like the ones we know on Earth would be present from between -80C to 80C, giving gas and ice giants a white or light blue appearance. Many of these planets could have habitable planet-sized moons. Smaller planets at this range could possess a water ocean, some of them being "water worlds" entirely covered in water or steam. Tholines could give red and orange hues to some of these planets.
Warmer gas giants would largely lack clouds in the upper atmosphere, with diverse hazes of sulfur compounds deeper in the atmosphere. Their clear upper atmosphere would scatter light, giving it a strong blue appearance with possible hints of cyan or green. Smaller planets would feature clouds and hazes of different sulfur compounds, making many appear like Venus but giving others different shades of yellow, orange and green
At between 300 C and 1100, planets would feature various soots, hydrocarbons, chlorides and sulfides, as well as clouds of salt deeper in the atmosphere giving planets a wide variety of colors and hues. Alkali metal compounds in the atmosphere absorb an exceptional amount of light, making planets significantly darker.
Planets warmer than 800 C are hot enough to visibly radiate a dull red color. Small rocky planets would likely have most of their atmospheres blown away by heat and solar wind and so would be bare, grey and rocky.
At even higher temperatures, the sheer heat would melt parts of the planets surface, creating lakes and oceans of lava.
The hottest gas giants are the most exotic - their cloud layers would be made of silicates, molten glass, or even corundum and iron. Rubies and sapphires could rain on some of these worlds
Planets close to their parent star are likely to be tidally locked, just like the Moon is to Earth. One side of the planet would perpetually face the star, with the other one shrouded in permanent darkness
Let's look at some of the more interesting exoplanets out of the many hundreds that can be found on the poster!
PSR-1620-26b, one of the oldest exoplanets known, orbits a binary system made of a white dwarf and a pulsar neutron star that spins around 100 times per second
COCONUTS-2b, with its orbital period at over 1 million years, didn't form around its parent star, but coalesced on its own from an accretion disk with too little mass to form a proper star, and has likely changed stars dozens of times during its journey floating across the galaxy. Its also the closest directly imaged exoplanet at 35 light years away.
TRAPPIST-1b is one of eight planets that orbit around a very small and dim red dwarf star. All planets in the system are likely to be terrestrial, 3 of them lying in the habitable zone. All of them would fit well within the orbit of Mercury, and planets come so close to each other that neighboring planets can appear as big and bright in the night sky as our moon.
Proxima B - a terrestrial exoplanet slightly bigger than the Earth, located in the habitable zone of Proxima Centauri, the nearest star to the solar system at 4.25 light years away. In the future, it is likely to be the first exoplanet we send a probe to. Using the Orion drive, designed to accelerate a spacecraft by continuously detonating thousands of thermonuclear bombs behind it, such a journey might take less then a century.
Kepler-277b - a "mega-earth" rocky planet almost as massive as Saturn, its sheer mass causing it to contract inwards. It has a solid surface and its surface gravity is crushingly powerful - over 10 times stronger than Earth's.
55 Cancri e - planet with a confirmed lava ocean covering all of its surface. The planets interior is likely to be heavily composed of carbon, most of which is in the form of diamond
TrES-2b, a hot gas giant, is the darkest known exoplanet, reflecting less than 1% of light from its star, making it than coal. This is because its atmosphere is rich in vaporized alkali metals, exceptionally good at absorbing light
KELT-9b - the hottest confirmed exoplanet. Its dayside temperature approaches 4320 C, enough to melt any known material. On its day side, molecules break into their component atoms. Its atmosphere contains vaporized titanium and iron, and its star covers over 35% of the planet's daytime sky.
Kepler-70b - Possibly the hottest exoplanet known, with its surface hotter than the surface of the Sun. Originally, it might have been a gas giant that had all of its gases stripped away by its star, leaving only a rock and metal coreThe planet will eventually be completely vaporized by the heat of its star
WASP-12b - a scorching hot jupiter located so close to its star it is being significantly stretched by tidal forces into the shape of an egg. Hot gas continuously escapes from its day side, siphoned by its hot star. It is estimated it will be completely consumed by its star in less than 10 million years, the same fate that awaits Mercury, Venus and possibly even the Earth.
PSR J1719-1438 is a hot super-dense planet orbiting a milisecond pulsar every 2 hours. Its orbit is so small it would fit within the interior of the Sun. The planets interior is largely made of carbon under high pressure, making most of its interior exotic forms of diamond. Billions of years ago, this celestial body might have been a star that had all its outer layers stripped bare by the pulsar, leaving only a planet-mass carbon and oxygen core.
Ring systems on the infographic are an artistic addition. Its very difficult to determine if a planet possesses or doesnt possess a ring system, but all 4 giant planets in the solar system possess some manner of rings. Just like Saturn, many exoplanets certainly possess a large permanent or temporary ring systems of different sizes and materials.