TRAPPIST-1
TRAPPIST-1 is an intriguing system of seven Earth-sized exoplanets orbiting a cooler, smaller red dwarf star located approximately thirty-nine light-years from Earth. Discovered through the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, the first three planets were identified in 2016, with the remaining four confirmed in early 2017. Notably, three of these planets reside in the habitable zone, an area where conditions may allow for liquid water, a crucial factor for the potential for life. The planets range in size, with the largest being about 1.12 times the size of Earth. However, their proximity to the star raises concerns over harmful radiation exposure, which could impact their atmospheres and the possibility of sustaining life.
While they are estimated to be between 5.4 and 9.8 billion years old—older than Earth—the TRAPPIST-1 planets are thought to have experienced significant environmental challenges. Observations suggest that some may have once hosted liquid water, but intense ultraviolet radiation could have stripped it away. Future research, particularly with the James Webb Space Telescope, aims to analyze the atmospheres of these planets through spectroscopy to search for signs of water and other chemical compositions that could hint at habitability. This system continues to capture the interest of astronomers and the public alike, as it holds potential insights into the nature of planetary systems beyond our own.
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TRAPPIST-1
TRAPPIST-1 is a system of extrasolar planets orbiting a star about thirty-nine light-years from Earth. The planets are noteworthy in that they are all about the same size as Earth, and several are located in a zone that may allow for the presence of liquid water—a key component for the possibility of life. The TRAPPIST-1 system orbits a star smaller and cooler than the Sun. They are also much closer to their star, with all seven orbiting within the distance Mercury orbits the Sun. The first three planets were discovered in 2016; the remaining four were identified in February 2017. The system was named after the Transiting Planets and Planetesimals Small Telescope (TRAPPIST), a telescope in Chile that identified the first three planets.
Background
The first exoplanets—planets orbiting a star outside the solar system—were discovered in January 1992. Astronomers detected two planets orbiting the rapidly spinning remains of a star that ended its life in a supernova explosion. The rocky exoplanets were dead worlds, constantly bombarded by radiation from the collapsed star. In 1995, astronomers discovered the first exoplanet orbiting a star the size of the Sun. The planet, 51 Pegasi b, was a gas giant about the size of Jupiter. It orbited so close to its star that its year lasted four days.
By 2022, the National Aeronautics and Space Administration (NASA) had discovered 5,021 exoplanets. Some were gas giants, like Jupiter and Saturn, and others were rocky terrestrial planets, like Earth. The first rocky exoplanet, Kepler-10b, was discovered in 2011 by the Kepler Space Telescope. Kepler-10b orbited so close to its star that its surface temperature was hotter than molten lava. For the possibility of life to exist, a planet must circle its star at a distance in which liquid water is capable of forming on its surface. This distance is known as the habitable zone.
If a planet is too close to its star, any water would boil away; too cold, and it would be locked in ice. Astronomers estimate the temperature range of the habitable zone to be within about 5 degrees Fahrenheit (-15 degrees Celsius) to 239 degrees Fahrenheit (115 degrees Celsius). In this range, water can remain in liquid form; even at the extremes of the range, water can remain liquid under certain circumstances. The first known Earth-sized exoplanet located in the habitable zone of its star is Kepler-186f, which was discovered in 2014. Scientists do not see the discovery as proof that life exists on Kepler-186f, only that conditions on its surface may be similar to those that allowed life to form on Earth.
Overview
In May 2016, astronomers working with the TRAPPIST telescope at the La Silla Observatory in Chile announced that they had discovered three planets orbiting a star designated as 2MASS J23062928-0502285. The planets were identified by their shadows cast as they orbited in front of the star. The star is classified as a red dwarf, a cooler, Jupiter-sized star about twelve times less massive than the Sun. The planets' discovery was later confirmed by several ground-based telescopes and NASA's Spitzer Space Telescope, an infrared telescope in Earth's orbit. While observing the star, Spitzer discovered the remaining four TRAPPIST-1 planets.
The seven planets are most likely rocky and are roughly the size of Earth—the largest has a radius about 1.12 times that of Earth and the smallest about .75 times that of Earth. The closest planet orbits within 1.1 million miles (1.8 million kilometers) of its star; the furthest orbits at a distance of 5.6 million miles (9 million kilometers). In contrast, Mercury, the closest planet to the Sun, orbits at an average distance of 36 million miles (58 million kilometers). The planets are believed to be between 5.4 and 9.8 billion years old—older than Earth, which is about 4.6 billion years old. They were given the designations TRAPPIST-b through TRAPPIST-h. Three of the outer four planets—dubbed e, f, and g—are within the habitable zone of their star.
A potentially damaging factor for the possibility of life, however, is that all seven planets may have been bombarded by deadly radiation from their star. The closeness of the planets to each other may have helped funnel charged radiative particles from the star toward the planets' atmospheres. Earth is subject to a stream of similar charged particles from the Sun, but its magnetic field protects it from the harmful radiation. If Earth's magnetic field received the same amount of radiation as the TRAPPIST-1 planets, it would most likely fail.
Scientists have speculated that at one point in their past, the TRAPPIST planets may have had large amounts of liquid water. The inner planets, however, likely received considerable amounts of ultraviolet radiation from the star and would have lost any liquid water that once existed. Observations made by the Hubble Space Telescope have suggested that the outer planets, especially the three in the habitable zone, may have avoided enough of a direct ultraviolet hit that they have maintained some liquid water.
Astronomers have further speculated that an electromagnetic field generated by the star may have heated the closest four planets enough for volcanic activity to occur. On the second and third planets—TRAPPIST-c and TRAPPIST-d—this heating may even have resulted in the formation of oceans of liquid magma beneath the surface. If the theory holds true, these planets could be covered in erupting volcanoes.
As the planets travel in front of the star, some of its light passes through their atmospheres. As this light reaches telescopes in Earth's orbit, astronomers can study it to gain hints at the chemical composition of the atmospheres. On December 25, 2021, NASA launched the James Webb Space Telescope, a more advanced telescope that will study this light by separating it into its distinct wavelengths—a process known as spectroscopy. Astronomers hope the Webb telescope will provide answers to many of their questions, including a determination if water exists on any of the TRAPPIST-1 planets.
Bibliography
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