- 3473 - EXOPLANETS - discoveries are accelerating? A third planet was found orbiting nearby star , “Proxima Centauri”. August, 2016, astronomers had discovered an exoplanet orbiting in neighboring Proxima Centauri. Based on Radial Velocity measurements ( Doppler Photometry), the discovery team estimated that the planet was roughly the same size and mass as Earth.
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------------- 3473 - EXOPLANETS - discoveries are accelerating?
- In 2020, this planet was confirmed by follow-up observations.
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- In that same year, a second exoplanet (Proxima “c“) roughly seven times the mass of Earth (a Super-Earth or mini-Neptune) was confirmed. They detected a third exoplanet around Proxima Centauri – Proxima “d“! This Mars-sized planet orbits about halfway between its host star and Proxima “b” and is one of the lightest exoplanets ever discovered.
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- In addition to confirming the existence of Proxima b, astronomers spotted the first hints of a signal corresponding to an object with a five-day orbit. Since the signal was so weak, the team had to conduct follow-up observations with ESPRESSO to confirm that it was due to a planet.
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- Similar to Proxima b and c, the planet was confirmed using the Radial Velocity Method, where slight changes in a star’s position indicate the possible presence of planets.
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- Proxima d has a minimum mass of 0.26 Earth masses (twice the mass of Mars), making it the lightest exoplanet ever measured using the Radial Velocity Method. Because Proxima b is so light, its gravitational influence is so small that it only causes Proxima Centauri to move back and forth at around 40 centimeters per second
( 1.44 kilometers / hour; 0.89 miles per hour ).
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- It orbits its star at a distance of about 0.029 AU, 4 million kilometers;
2,485,485 miles, which is less than a tenth of Mercury’s distance from the Sun.
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- The Proxima Centauri star system consists of three confirmed exoplanets, with orbital periods of five days (Proxima d), eleven days (Proxima b), and five years (Proxima c).
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- The radial velocity technique has the potential to unveil a population of light planets, like our own, that are expected to be the most abundant in our galaxy and that can potentially host life as we know it.
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- This discovery not only demonstrates the way exoplanet studies have grown by leaps and bounds in recent years. It has also made Proxima Centauri even more appealing to astronomers.
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- With three exoplanets (in six years) discovered around this closest stellar neighbor, the research potential is immeasurable. These activities will benefit tremendously from the James Webb Space Telescope (JWST), which will start gathering light soon.
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- Exoplanet surveys using the ESPRESSO instrument will benefit from the Extremely Large Telescope (ELT), which is scheduled to become operational by 2027. Between its 39.3 meter, (130 ft) primary mirror, 4.2 m (14 ft) secondary mirror, and an advanced suite of instruments ,which includes a spectrograph, coronograph, and adaptative optics.
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- Outside of our closest neighbor planetary system other planets have been found in the habitable zone of a White Dwarf star that is 117 lightyears away.
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- Most stars will end their lives as white dwarfs. White dwarfs are the remnant cores of once-luminous stars like our Sun, but they’ve left their lives of fusion behind and no longer generate heat. They’re destined to glow with only their residual energy for billions of years before they eventually fade to black.
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- Could life eke out an existence on a planet huddled up to one of these fading specters?
For life to exist around a white dwarf, the white dwarf would have to have planets in its slowly shrinking habitable zone. These planets are in the habitable zone of the white dwarf about 117 light-years away.
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- This is the first time astronomers have detected any kind of planetary body in the habitable zone of a white dwarf. The researchers observed “WD1054-226” for 18 nights with the ESO’s New Technology Telescope (NTT) at their La Silla Observatory, observing dips in starlight as something passed between us and the star.
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- They used the NTT’s ULTRACAM high-speed camera to capture data images of the white dwarf. They also examined data on the same star from NASA’s Transiting Exoplanet Survey Satellite (TESS.)
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- The team found dips in light that they interpret as 65 clouds of planetary debris. The clouds are evenly spaced and orbit the white dwarf every 25 hours. What causes such regularity?
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- The researchers say that a planet must be there, which forces these debris clouds into a precise orbital pattern. They say the planet is similar in size to rocky planets in our Solar System and that it’s only about 2.5 million kilometers (1.55 million miles) from the star. That’s about 1.7% of the distance between Earth and the Sun.
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- Alongside the regular dips in starlight is an ever-present obscuration that the team says is debris in a planetary disk around the star. These structures are in a region that would have been overcome when the white dwarf went through its preceding red giant phase.
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- It’s doubtful that any of these structures could have survived the red giant phase, so they must have formed more recently in the aftermath. If there is a planet in the habitable zone, it can’t be a hold-over from the star’s previous life as a main-sequence star.
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- If all of the circumstances lined up just right life would potentially have about two billion years to do its thing on the purported planet, with one of those billions in the future.
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- The first three nights of ULTRACAM observations of WD1054-226 shows a notable and easily recognized recurring feature, the double-dip structure that recurs every 25.2 hours, and occurs just before hours 2, 27, and 52. Using this structure as a visual anchor, the adjacent, antecedent, and subsequent transits can all be seen to have the same morphology over all three nights.
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- These bodies are kept in an evenly-spaced orbital pattern because of the gravitational influence of a nearby major planet. Without this influence, friction and collisions would cause the structures to disperse, losing the precise regularity that is observed. A precedent for this ‘shepherding’ is the way the gravitational pull of moons around Neptune and Saturn helps to create stable ring structures orbiting these planets.
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- The possibility of a major planet in the habitable zone is exciting and also unexpected. More evidence is necessary to confirm the presence of a planet. We cannot observe the planet directly, so confirmation may come by comparing computer models with further observations of the star and orbiting debris.
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- If there are indeed clouds of material orbiting the white dwarf, they’re likely outside the Roche limit. Debris clouds probably come from collisions or tidal disruption events. From a dynamical and evolutionary perspective, the origin of the large occulting clouds is likely the result of tidal disruption or collisions in the vicinity of the Roche limit.
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- The “Roche Limit” is the distance a planet can get close to a star before being torn apart by the star’s gravity.
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- It’ll be up to further observations with the James Webb Space Telescope to provide better data. The JWST has the power to better define the debris disk and its components. But if there is a roughly Earth-sized rocky planet there, it’s an intriguing possibility with liquid water potential.
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- Marginally habitable situations may be relatively common in the Milky Way and the Universe. Life might arise countless times and never evolve the complexity that life on Earth has become. The Moons of our Solar System might harbor life for some time. Mars may have harbored life for some time. Now, maybe, we can add white dwarf planets to that list.
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February 20, 2022 EXOPLANETS - discoveries are accelerating? 3473
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