![]() Try your hand at a little exoplanet exploration of your own with NASA’s citizen science project. If you're excited about the possibility of civilizations in space, check out what's new at the SETI Institute, an organization dedicated to the search for extraterrestrial intelligence. Kepler showed that, on average, every star has at least one planet. Researchers use the idea of a habitable zone to narrow down which exoplanets might be good candidates in the search for extraterrestrial life.Īs of early 2023, NASA's Kepler Space Telescope and TESS missions have detected and cataloged more than 5,000 exoplanets, according to the NASA Exoplanet Archive, and those represent just a tiny fraction of the planets we're likely to discover as we keep looking. Why is the habitable zone important for the search for life? But there is evidence that an ocean may have once flowed on Mars, and NASA's Perseverance rover is still busily sampling for microbial life that could be hidden below the planet's surface. Mars is at the far, chilly edge of the sun's habitable zone. But as a result, we may be overlooking even better conditions for life than those on Earth because our view is too narrow. To be fair, we have only one frame of reference. Some researchers say that isn't a coincidence after all, we created the idea of "habitable zones" to look for planets like ours. That atmosphere eliminates the possibility of life (as we would recognize it) on the planet's surface.Įarth is squarely in the middle of the sun's habitable zone. However, Venus' runaway greenhouse atmosphere makes the planet even hotter than Mercury, which is much closer to the sun. Venus is just far enough away from the sun for the planet to have the possibility of hosting liquid water, according to NASA. Venus, Earth and Mars all orbit within the sun's habitable zone. Which solar system planets are in the habitable zone? So, the width of the goldilocks zone is about 0.8 AU or about 120 million km (about 75 million miles). Venus orbits about 0.7 AU (1 AU = 1 Astronomical Unit) from the sun and Mars about 0.5 AU. For our solar system, there are various definitions, so to take an example where Venus' orbit defines the inner boundary, and Mars' orbit the outer boundary. This depends on the type of star and the theoretical assumptions that are used to determine whether liquid water might be stable on the surface of a planet. Since the Goldilocks zone is based on theoretical modeling and certain assumptions, some definitions may barely include Venus' orbit or Mars' orbit if the models yield planets different than Venus or Mars that could potentially have liquid water on the surface. Venus is too hot, Mars too cold, and Earth is just right. In our solar system, the Earth is clearly in the Goldilocks zone with much of its surface covered by liquid water. Just right in this case is distances from a star that could allow stable liquid water on the surface of a planet. Similarly, planets too close to their star are too hot, those too far away or too cold, whereas those in the Goldilocks zone are just right. In that story Goldilocks would find two extremes, then would find things that were "just right" for her. ![]() ![]() The Goldilocks zone is a reference to the fairy tale Goldilocks and the Three Bears. Bruce Betts is Chief Scientist and LightSail Program Manager for The Planetary Society, the world's largest space interest group. ![]()
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