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----------------------------- 2702 - EXOPLANETS - new discoveries?
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- A few years ago, people were bemoaning the fact that Pluto had been demoted from its being the ninth planet in the Solar System to one of three dwarf planets.
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- With the proper planets of our solar system ending with Neptune, many of the older mnemonics for remembering their order had to be scuttled.
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- At the same time that astronomers demoted Pluto and regularized the Solar System, they delivered a bounty of new worlds to ponder. Thanks to arduous ground-based studies of nearby stars, and to the dazzling successes of NASA’s Kepler mission, we now have a catalog of over 1,700 “new” planets orbiting hundreds of other stars.
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- 340 of these are new “planetary systems” with over 850 planets between them; some such systems have up to six worlds orbiting their star!
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- In a single decade we have discovered that our solar system is not unique among the nearly 1 trillion stars in the Milky Way. Based on the Kepler survey, we have identified over 100 exoplanets that are “Earth-sized“, and of these, a handful are just the right distance from their star for liquid water to potentially exist on their surfaces!
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- Water is the staff of life. Without it you cannot even begin the chemistry of life. In November 2013 scientists announced that one fifth of all Sun-like stars in the Milky Way have an Earth-sized planet in the “water zone.” With one fifth of the 1 trillion Milky Way stars being Sun-like, this works out to a whopping 40 billion Earth-like planets with liquid water potentially existing on their surfaces.
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- That’s a lot of opportunities for the chemistry of life to commence. On Earth this happened only a few hundred million years after the surface of Earth cooled enough for standing water to exist. Then bacteria emerged and dominated the planet for the next 4 billion years.
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- Through the efforts of ground-based telescopes and NASA’s Hubble and Spitzer Space Telescopes, astronomers have been able to study the atmospheres of over 50 of these new worlds. Water, carbon dioxide, methane, sodium, and water vapor have all been detected in these planetary atmospheres, along with actual clouds in the atmospheres of these planets.
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- Would you believe that there are planets so hot that they are evaporating right before our eyes? One planet has an atmosphere hot enough to have clouds of iron gas and raindrops of liquid iron raining down on the planet’s surface.
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- For some of the more massive, Jupiter-sized planets, it could even rain diamonds! The star is orbited by an object that is circled by a ring system much larger than Saturn’s rings. The mass of the enigmatic object is not known; it could be a brown dwarf or a low-mass star instead of a planet.
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- Because the exoplanet catalog includes nearly 1,000 other planets that transit their stars, we can eventually study their atmospheres too. The goal is to find an Earth-sized, water-supporting “Goldilocks planet” with an atmosphere showing trace amounts of oxygen.
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- Earth’s atmosphere is 22-percent oxygen because Earth has a biosphere created over the eons by bacteria and plant life. Because oxygen reacts quickly with other compounds and rocks to oxidize them, only a planet with an extensive biosphere can continuously regenerate such a massive amount of atmospheric oxygen.
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- If astronomers do detect an exoplanet with a significant oxygen atmosphere, that can only mean an alien biosphere has created it. Many of us feel that it is only a matter of time, perhaps a few decades, before enough planetary atmospheres will have been surveyed to find one with such life signs. When that day dawns, we will have written a new chapter in the search for life and be able to actually estimate how much life exists in the universe!
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- We are on the threshold of such a discovery as the catalog of exoplanets fattens from hundreds to thousands, and hence to tens of thousands in the near future. We know that planetary systems are not rare in the Milky Way. We know that small planets like Earth handsomely outnumber the giant planets like Jupiter, and we know that planets do find themselves in the “water zone” from time to time. Statistically, over 40 billion of these Earth-like worlds may exist in the vastness of our Milky Way.
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- So far we have discovered some of these distant worlds through glitches in the movement of their parent stars, or the brief diminution of their star light, but we now have a tally of 17 exoplanets that have been directly imaged as faint dots of light near their parent stars.
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- The closest of these orbits the star Fomalhaut, located 25 light years from Earth. Larger than Jupiter, and with a distance from Fomalhaut that is four times the distance between Neptune and our Sun, this planet takes over 1,500 years to complete one orbit.
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- So we are living in an enchanting time when we have broken out of our parochial Solar System chauvinism and now get to see the bigger and richer picture of innumerable planetary systems strewn throughout our galaxy, and the bountiful opportunities for life that may very well exist there.
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- New discoveries made by NASA’s Transiting Exoplanet Survey Satellite (TESS), the telescope that has spotted a number of strange new worlds circling star systems.
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- From Tatooine-like systems to habitable worlds to starry eclipses, TESS has been busy uncovering the universe's oddities since launching in 2018. A follow-up to the prolific Kepler mission, which discovered about 70 percent of the approximately 4,000 exoplanets known to science today.,,
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- TESS is scheduled to scan 200,000 of the night's brightest stars for insight into their solar systems. It's expected to conduct this survey over the course of two years, focusing on small chunks of the night sky at a time.
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- The satellite, which has four cameras that snap pictures once every 30 minutes, has a leg up on Kepler, and can study stars that are 30 to 100 times brighter. Ultimately, scientists hope the project will help us understand the composition of different solar systems, uncover mysteries about potentially habitable worlds, and unlock secrets about life elsewhere in the universe.
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- TESS has discovered its first Earth-sized planet in the habitable zone of a distant star. Its orbit sits in the sweet spot, where liquid water could exist on its surface. The exoplanet is at a short distance from Earth, only 101.5 light-years away.
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- TESS’s star, an M dwarf star, is about 40 percent of the sun’s size and mass and nearly half as hot at the surface. The planet sits just inside the habitable zone, orbits around its star every 37 days, and is about 20 percent larger than Earth. It doesn’t get as much energy from its own star as we do from Earth, receiving about 86 percent of the solar energy felt here on Earth. Researchers also suspect the planet is tidally locked, meaning only one side faces its star during orbit.
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- It’s difficult to say what conditions might be like on the exoplanet, but scientists believe it sits within the realm of habitability. Using the information currently available about the exoplanet’s orbit, size and other solar system conditions, scientists are able to create models of likely environments. A tidally locked planet would have vastly different cloud systems than what you might find here on Earth.
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- In the 20 computer models that simulated its environment, several of them were habitable. One model revealed a watery world with an atmosphere chiefly composed of carbon dioxide, when another described a scenario in which the exoplanet could be rocky and have landscapes shaped by strong winds that sweep from the exoplanet’s night side to its sunny side.
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- Another exoplanet lives within a two-star system and is a type of exoplanet called a circumbinary planet. These types of planets are extremely difficult to spot. It is almost seven times larger than earth, between the size of Neptune and Saturn. It also has a very strange orbit. The depth and duration of the orbit fluctuate and its transit in front of the two stars is odd, occurring every between 93 and 95 days.
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- The two stars orbit each other every 15 days. One of them is 10 percent more massive than the Sun, and other is about one-third the mass of the Sun. No other planets have been observed in the solar system.
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- During its mission, Kepler discovered 12 circumbinary planets in a total of 10 systems, but most of the exoplanets found in those systems were larger. These are easier to spot because they're more visible when they slide in front of their stars.
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- TESS data also revealed evidence that the well-studied star Alpha Draconis and a nearby companion star regularly eclipse each other. The super star is located about 270 light-years away in the constellation Draco.
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- About 5,000 years ago, the star was considered to be a guiding light in the night sky—a North Star directing the ancient Egyptians and other ancient civilizations. Thanks to Earth's precession, or its cyclical 26,000-year wobble, that role is now played by Polaris, the North Star.
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- TESS, launched in April 2018, hunts for planets using the "transit method," looking for telltale dips in stellar brightness caused by orbiting worlds crossing stars’ faces from the satellite’s perspective. This same strategy was used to great effect by NASA’s Kepler space telescope, which discovered about 70% of the roughly 4,000 known exoplanets.
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- TESS found three different planets circling a star. One of the other planets is a red dwarf about 40% as massive, 40% as wide and 50% as hot as Earth’s sun. The innermost world is roughly Earth-sized and completes one orbit every 10 Earth days. The center planet is 2.6 times bigger than our planet, meaning it’s likely a gassy “mini-Neptune,” and zips around every 16 days.
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- The outermost known planet in the system, is the really intriguing one. It’s just 20% larger than Earth and completes one orbit every 37 days. The alien world receives 86% of the stellar energy that Earth gets from the sun, putting it in the habitable zone (at least as it’s traditionally defined).
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- All three planets may be tidally locked, always showing it the same face just as Earth’s moon only ever shows us its near side. But tidal locking doesn’t necessarily preclude the possibility of life on an alien world, astronomers say.
- In 11 months of data, we saw no flares from the star, which improves the chances this planet is habitable and makes it easier to model its atmospheric and surface conditions.
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- TRAPPIST-1 is a dwarf star that lies just 40 light-years away from us and hosts seven Earth-size planets, three of which appear to be in the habitable zone. The system is a prime candidate for observation by NASA’s James Webb Space Telescope, which is scheduled to launch in 2021.
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- James Webb should be able to probe the TRAPPIST-1 worlds’ atmospheres for potential biosignature gases, such as methane and oxygen.
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- And in-depth observations of light that has streamed through the atmosphere on its way to Earth could tell us a great deal about conditions on the alien world’s surface, which remain a total mystery at the moment. It’s exciting because no matter what we find out about the planet, it’s going to look completely different from what we have here on Earth.
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- April 8, 2020 2702
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--------------------- Thursday, April 9, 2020 -------------------------
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