This research helps us understand the potential for these planets to have the elements to support life. Some of these exoplanets could even be our interstellar neighbors, with four potentially within 30 light-years of our Sun and the closest likely to be about 20 light-years from us. Our galaxy holds an estimated 300 million of these potentially habitable worlds, based on results in a study using Kepler data. The spacecraft was retired in 2018, but discoveries are still being made using its data.Īccording to research released in October 2020, about half the stars similar in temperature to our Sun could have a rocky planet capable of supporting liquid water on its surface. She is also the project scientist for Kepler's extended mission, known as K2. "We're still trying to figure out how big a planet can be and still be rocky," said Jessie Dotson, an astrophysicist at NASA's Ames Research Center in California's Silicon Valley. Much more data are needed, including a better understanding of how a planet's size relates to its composition. But that doesn't change one of the most astonishing conclusions after more than 20 years of observation: Planets in the habitable zone are common. Newer data showed that the number is likely smaller – possibly between 2 and 12.Īt first glance, that might seem disappointing: fewer rocky, potentially habitable worlds among the thousands of exoplanets found so far. One analysis of discoveries by NASA’s Kepler Space Telescope indicated that 20 to 50 percent of the stars in the sky are likely to have small, potentially rocky planets in their habitable zones. The more we study, the more our understanding can change. How many terrestrial planets are out there? If they have thin atmospheres, they would be unlikely to contain the heavy molecules of Earth, such as carbon dioxide. TRAPPIST-1f, g and h are far enough from the host star that any water they might possess could be frozen as ice across these surfaces. In terms of size, density and the amount of radiation it receives from its star, this is the most similar planet to Earth. It is mysterious why TRAPPIST-1e has a much rockier composition than the rest of the planets. Like TRAPPIST-1c, it does not necessarily have a thick atmosphere, ocean or ice layer – making these two planets distinct in the system. Scientists were surprised that TRAPPIST-1e is the only planet in the system slightly denser than Earth, suggesting it may have a denser iron core than our home planet. Scientists are uncertain whether it has a large atmosphere, an ocean or an ice layer – all three of these would give the planet an "envelope" of volatile substances, which would make sense for a planet of its density (less than half that of Earth). TRAPPIST-1d is the lightest of the planets – about 30 percent the mass of Earth. TRAPPIST-1c also likely has a rocky interior, but with a thinner atmosphere than planet b. TRAPPIST-1b, the innermost planet, is likely to have a rocky core, surrounded by an atmosphere much thicker than Earth's. Credit: NASA/JPL-Caltechīased on available data, here are scientists' best guesses about the appearances of the planets: This artist's concept shows what the TRAPPIST-1 planets may look like, based on available data about the planets' diameters, masses and distances from the host star, as of February 2018. Future study of this unique planetary system could reveal conditions suitable for life. This system of seven rocky worlds – all of them with the potential for water on their surface – is an exciting discovery in the search for life on other worlds. In 2017, NASA announced the discovery of the most Earth-sized planets found in the habitable zone of a single star, called TRAPPIST-1. As we continue checking off items on the habitability list, we'll draw closer and closer to finding a world bearing recognizable signs of life. ![]() ![]() We will gain a better understanding of temperatures on the surface. Key factsįuture space telescopes will be able to analyze the light from some of these planets, searching for water or a mixture of gases that resembles our own atmosphere. While these characteristics don't guarantee a habitable world – we can't quite tell yet if these planets really do possess atmospheres or oceans – they can help point us in the right direction. We've found rocky planets in Earth's size range, at the right distance from their parent stars to harbor liquid water (this is known as the habitable zone). These faraway worlds may have gaseous atmospheres, but that’s not a defining feature. In general, terrestrial planets have a bulk composition that is dominated by rock or iron, and a solid or liquid surface. The third planet from its star is illustrated here with a narrow band of water between the hot day side and icy night side of the planet.
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