Quick Facts
Worlds of astrobiology
Venus is the second planet from the Sun and approximately the same mass and size of Earth. The volcanic surface of Venus is a blisteringly hot 864 Fahrenheit (462 °C), but that is mostly due to its thick carbon dioxide greenhouse atmosphere, which traps heat. Although Venus is an Earth-like planet in the solar system’s habitable zone, it is not habitable for life as we know it.Distance From Star (AU)Orbital Period In DaysTemperature (Kelvin)MassRadiusFlux
Earth’s surface is 71% water and 29% land. The surface is in a constant state of change due to the shifting of tectonic plates that make up the planet’s crust. Earth’s atmosphere is 78% nitrogen, 21% oxygen, and 1% other gases. Most of this oxygen is produced by photosynthetic plants. Because oxygen on Earth is a signature of life, astrobiologists are looking for an abundance of this “biosignature” gas on other planets.
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Although Mars today is a cold desert world, various missions sent by NASA and other space agencies have found evidence the planet was warmer in the past, with lakes and rivers on the surface. Mars still does have water, frozen solid at the poles and also beneath the surface. Future missions to the Red Planet will search for evidence that life ever arose there, or even exists in protected niches today.
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The largest body in the asteroid belt, Texas-sized Ceres is believed to be 25 percent water ice by mass. Scientists believe it may have a layer of frozen water beneath its heavily cratered surface. Ceres has a thin water vapor atmosphere which may be produced by ice volcanoes, or by ice near the surface sublimating (transforming directly from solid to gas) on the dwarf planet’s daylight side.
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Callisto is the third largest moon in the Solar System. The outermost of Jupiter’s Galilean satellites, Callisto’s interior is thought to be a large icy mantle surrounding a small rocky core. Callisto is the most heavily cratered object in the Solar System, with the oldest landscape. This is because it has not had geologic activity altering its surface over the last 4 billion years.
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Jupiter’s moon Ganymede is the largest moon in our solar system. It has a metallic iron core that generates a magnetic field, a rocky mantle, and an outer layer of ice that is perhaps 800 km thick. The surface ice layer has a complex geological history, with darker cratered areas and lighter regions covered with grooves and ridges as high as 700 meters that run for thousands of kilometers along the surface. .
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Jupiter’s moon Europa is thought to be one of the most promising places for life in our Solar System. Underneath the water ice shell, Europa has a global ocean of salty water, and most likely has hydrothermal vents dotting the ocean floor. To properly explore Europa for signs of life, missions need to drill down through the top ice layer which is thought to be 15 to 25 kilometers thick.
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Io is the most volcanic body in the solar system. Because of its widely varying orbit around Jupiter, Io is subjected to tremendous tidal forces that cause its surface to bulge up and down (or in and out) by as much as 100 meters. The colorful surface material is thought to be either molten sulfur and its compounds, or silicate rock.
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Titan is Saturn's largest moon. It is surrounded by a thick chemical smog and only certain kinds of telescopes and cameras can see through the haze to the surface. Not only is Titan’s dense, complex atmosphere of great interest to scientists, it also has an eerily Earth-like landscape, except that its flowing rivers and lakes are liquid methane and ethane, while the mountains are solid water ice.
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This tiny moon of Saturn blasts icy water vapor geysers, which refresh the surface and generate a halo of fine ice dust around Enceladus. These geysers indicate that the interior of the moon may be liquid today, even though it should have frozen eons ago. The surface of Enceladus is varied, with craters, fissures, smooth plains, and corrugated terrain.
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This moon is thought to have once been a Kuiper Belt Object that became trapped in Neptune’s gravity. Triton has a crust of frozen nitrogen, an icy mantle, and a core of rock and metal. The surface of Triton is sparsely cratered, with smooth plains, mounds, and round pits formed by icy lava flows. Triton's volcanic activity is driven by seasonal heating from the Sun.
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This Super-Earth planet orbits the red-dwarf star Gliese 832. If the planet’s atmosphere is like Earth’s, the planet Gliese 832-c might experience large seasonal shifts. However, a denser atmosphere (something expected for Super-Earths) could easily make this planet too hot for life and a "Super-Venus" instead.
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The planet Gliese 667 C-c is located on the inner edge of the habitable zone. The exact surface temperature depends on a number of yet unknown factors: it could be a pleasant 30°C if we assume a planetary atmosphere that is similar to Earth’s. However, a more massive atmosphere would result in Venus-like conditions.
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If we assume the atmosphere of Gliese 163-c is a scaled up version of Earth’s, then its surface temperature might be around 60°C — too hot for complex life (plants and animals are not able to survive at temperatures above 50°C). However, plenty of microbial life forms can thrive at those temperatures or higher. The star it orbits, Gliese 163, is a red dwarf 50 light years away, in the Dorado constellation.
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Kepler 438-b is thought to be a rocky planet. The star this planet orbits is a red dwarf in the constellation Lyra, about 470 light-years away. Located within the habitable zone, the planet was announced as being as being one of the most Earth-like planets, in terms of size and temperature, yet found. However, given the uncertainty about its mass and atmosphere, this planet also could be a just slightly cooler Venus.
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Kepler 186-f is on the outer edge of the habitable zone, in a similar position as the planet Mars is in our Solar System. It could be rocky like Earth, or a lower density ocean planet with a thick atmosphere. SETI Researchers used the Allen Telescope Array to listen for radio emissions from the Kepler-186 system in March and April of 2014, but no signals attributable to extraterrestrial technology were found.
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Scientists don't know if Kepler-22b has a predominantly rocky, gaseous or liquid composition, but it does have a nearly-year-long orbit around a G-class star similar to our Sun. If it has an atmosphere similar to Earth’s, then its temperature would be just right for liquid water.
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Kepler 20-f orbits a star similar to our Sun, but in a very tight orbit. Because of this, its temperature is thought to be around 430 degrees Celsius—hot enough to melt lead — making Kepler 20F too hot to be habitable for life as we know it. Scientists believe the planet is rocky with an atmosphere of water vapor.
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Kepler 62-e is a Super-Earth exoplanet in the habitable zone. The star it orbits is slightly smaller and cooler than our Sun, and would appear slightly peach-colored to the naked eye. Kepler 62-e may be a terrestrial or water-ice-dominated planet. One modeling study suggests it is likely that planets in Kepler 62-e’s size range are completely covered by oceans.
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When the discovery of this planet was first announced, it was described as one of the most Earth-like planets, in terms of size and temperature, yet found. Later analysis, however, has shown that the planet is likely more analogous to Venus, and thus not likely to be habitable.
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Planetary dataExoplanet DiscoveriesPlanets outside our Solar System are known as “exoplanets” or “extrasolar planets.” Discoveries made by the Kepler Space Telescope must be confirmed by follow-up observations before astronomers can say with confidence they have discovered a planet orbiting a distant star.
Data source:www.exoplanets.org / Habitable Exoplanets Catalog
Small Bodies: Asteroids, Comets & MeteoritesImpacts of Life
Asteroids and comets have delivered water and organic chemicals to Earth since its birth, perhaps aiding the origin of life. But larger impacts can also put an end to life — such as the Chicxulub asteroid that caused the dinosaurs to go extinct 65 million years ago.
The facts and figures —100 tons
Each day, more than 100 tons of material from asteroids and comets falls toward Earth. Most of it is destroyed by friction as it passes through our atmosphere. If one hits the ground it is called a meteorite.
Where in the world is Astrobiology
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