- 2914 - EXOPLANETS - what it is like on frontline of discovery? We’re getting better and better at detecting exoplanets. Using the “transit method” of detection, the Kepler Space Telescope examined over 530,000 stars and discovered over 2,600 exoplanets in nine years. “TESS“, the telescope that is successor to Kepler, is still active, and has so far identified over 1800 candidate exoplanets, with 46 confirmed by 2020.
------------- 2914 - EXOPLANETS - what it is like on frontline of discovery?
- But what if, hidden in all that data, there were even more planets? Astronomers have found one of these “lost” planets, and that they think they’ll find even more inside the same data.
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- Every method of detection has an inherent selection bias. A single transit in front of a star is not enough to be considered a planet detection. At least two transits are needed. So with the transit method, detection is biased towards planets with short orbital periods. It’s also biased towards finding larger planets, which block more starlight causing a bigger dip in brightness.
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- The transit geometry imposes a strong selection bias for close-in orbits, and only a handful of well-characterized transiting exoplanets are known to have orbital periods longer than about 30 days.
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- Since TESS only looks at most sections of the sky for 27 days, it’s biased toward detecting planets that complete two transits in that time period, meaning it’s likely to find planets close to their stars. And those planets are bound to be hot ones; too hot for liquid water or for life.
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- Hidden in all of the TESS data are detections of single transits: planets that are too far from their stars to complete two transits while TESS is watching. Those planets are further away from their stars, and cooler than the typical hot planets we find closer to their stars.
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- These discoveries are rare but important, since they allow us to find longer period planets than other astronomers are finding. Longer period planets are cooler, more like the planets in our own Solar System.
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- ‘NGTS-11 b” orbits a star that’s about 620 light years away. It’s five times closer to its star than Earth is to the Sun, and its orbit is only 35 days. NGTS-11b has a temperature of only 160°C, cooler than Mercury and Venus. Although this is still too hot to support life as we know it, it is closer to the Goldilocks zone than many previously discovered planets which typically have temperatures above 1000°C.
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- “NGTS” is the name of the star. “a”, “b” , “c” etc. are the names of the planets orbiting that star.
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- TESS had to spot at least one transit. Then the team investigated that single transit, all aspects of the star, and all of the data on it. Once they determined that the single TESS transit was a viable candidate for follow-up.
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- In Chile is an array of twelve, small robotic telescopes designed to find exoplanets of Neptune size or smaller around bright stars. It can monitor stars for months on end, and is very precise.
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- The 12 NGTS telescopes in Chile can monitor multiple stars for months on end, searching for lost planets. The dip in light from the transit is only 1% deep and occurs only once every 35 days, putting it out of reach of other telescopes.
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- Single transits are common in TESS data, and before the team decided to use NGTS to investigate this one, they had to rule out other possibilities. They ruled out things like asteroids or other anomalies. They also searched data from the ESA’s Gaia mission for explanations for the dip in brightness, and looked for things like nearby eclipsing binaries. None of those could explain it, so only then did they turn to NGTS.
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- They observed the star with one of NGTS’s twelve ‘scopes for a total of 79 nights, and 105,642 exposures. They employed an algorithm to comb through all that data, looking for the right light curve that signalled a second transit of the suspected exoplanet. Finally, on the night of October 24th 2019, NGTS spotted it.
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- After detecting the second transit with NGTS, they turned to other follow-up observations. They used the “ESO’s Leonard Euler telescope“, and the “HARPS spectrograph” on the ESO’s 3.6 m telescope to get radial velocity measurements. All of that data ruled out a low-mass companion star as the cause of the transit.
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- After a detailed analysis of all that data, they were able to characterize NGTS-11 b more completely. It’s roughly the same size and mass as Saturn. It’s 0.81 Jupiter radii, and .034 Jupiter masses. It’s still hot compared to Earth, at about 320 F), but much cooler than Venus and Mercury.
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- There are hundreds of single transits detected by TESS that we will be monitoring using this method. These results highlight the synergy between space telescopes like TESS, and more nimble, economical facilities like NGTS.
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- The strategy of large investments of photometric follow-up with instruments such as NGTS thereby allows efficient confirmation of single-transit events without adding to the considerable pressure on high-precision radial-velocity instruments. This highlights the power of high-precision ground-based photometric facilities in revealing longer-period transiting exoplanets that TESS alone cannot discover.
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- After this success, the team plans to utilize their method to find even more “lost” planets in all of that TESS data. There are hundreds of single transits detected by TESS that we will be monitoring using this method.
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- This will allow us to discover cooler exoplanets of all sizes, including planets more like those in our own Solar System. Some of these will be small rocky planets in the Goldilocks zone that are cool enough to host liquid water oceans and potentially extraterrestrial life.
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- Over the next decade, several very powerful telescopes will come online. Observing time on these ‘scopes will be in high demand, and their range of targets will span a whole host of topics in astronomy, astrophysics, and cosomology.
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- Planets form in debris disks around young stars. But it’s hard to see inside those dusty disks and spot the actual planets with the telescopes and instruments we currently have. Now, a team of astronomers have released what they’re calling a “rogue’s gallery” of images of these disks, each one showing evidence of young planets.
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- The “Gemini Planet Imager” (GPI) is a precision instrument mounted on the 8-meter Gemini South telescope in Chile.
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- This study targeted young stars less than 500 million years old. They were nearby stars, within 150 parsecs (490 light years) of us. There were 104 stars, including 38 that were previously imaged. The researchers were also able to resolve 26 debris disks and 3 protoplanetary / transitional disks.
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- Six of the 26 circumstellar disks from the Gemini Planet Imager survey, highlighting the diversity of shapes and sizes these disks can take and showing the outer reaches of star systems in their formative years.
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- This study is an effort to screen targets for observing time with more powerful future telescopes, whose observing time will be in very high demand. ‘Scopes like the “James Webb Space Telescope“, the “Giant Magellan Telescope“, and the “Extremely Large Telescope” will be coming online in the next few years. They’ll be powerful enough to study exoplanets and the systems that host them in greater detail than current telescopes. But their power isn’t needed to find those planets initially.
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- It is often easier to detect the dust-filled disk than the planets, so you detect the dust first and then you know to point your James Webb Space Telescope or your “Nancy Grace Roman Space Telescope’ at those systems, cutting down the number of stars you have to sift through to find these planets in the first place.
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- Looking at the images of the disks in this study is like looking at the Kuiper Belt in our own Solar System. The Kuiper Belt is a frigid area in the distant Solar System, 40 times further from the Sun than Earth is. The material in the Belt, rocks, ice, and dust, was left over from the planet forming stage in our Solar System’s development.
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- The Kuiper Belt was named in honor of Dutch-American astronomer Gerard Kuiper, who postulated a reservoir of icy bodies beyond Neptune. The first Kuiper Belt object was discovered in 1992. We now know of more than a thousand objects there, and it's estimated it's home to more than 100,000 asteroids and comets there over 62 miles across.
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- Gemini captured 26 images of debris disks around stars. Of those, 25 had holes in the disks, which are evidence of a young planet sweeping up gas and dust as it forms. Some of them were previously known, but seven of the 26 are newly identified.
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- But the images of the 19 previously known ones were nowhere near as sharp as these new images. In most cases, the previous images are from ‘scopes that lack the GPI’s high resolution, so those images don’t show the same holes that indicate the presence of young, still-forming planets.
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- One of the things we found is that these so-called disks are really rings with inner clearings. GPI had a clear view of the inner regions close to the star, whereas in the past, observations by the Hubble Space Telescope and older instruments from the ground couldn’t see close enough to the star to see the hole around it.
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- One of the things that makes the GPI, “Gemini Planet Imager” so effective is its coronagraph. The venerable Hubble has a coronograph, which blocks the light of distant stars, making it easier to see other detail around the star. But it’s coronograph isn’t near as effective and high-tech as the GPI’s. Using its coronagraph, GPI is able to see to within one astronomical unit (AU) of the stars it targets.
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- The researchers used the GPI to look at stars that were exceptionally bright in the infrared. Not because of the output of the star itself. But because high infrared output indicates the presence of a disk, which emits infrared light. GPI is powerful enough to observe near-infrared (NIR) light scattered by tiny dust particles no larger than one micron, or a thousandth of a millimeter.
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- A ring of dust around the star HR 4796 A has neatly sculpted edges suggesting the presence of a large planet that is sweeping up gas and dust inside the disk of icy, rocky debris, much the way Neptune sculpts the inner edge of our Kuiper Belt.
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- There has been no systematic survey of young debris disks nearly this large, looking with the same instrument, using the same observing modes and methods. Astronomers detected 26 debris disks with very consistent data quality, where we can really compare the observations, something that is unique in terms of debris disk surveys.
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- The way these disks and stars were sampled in this survey serves a purpose in exoplanet study. For example, seven of the new disks were in a group of 13 that move together through space. All 13 were born in the same region at about the same time, making them a great target for deepening our understanding of exoplanet formation in young solar systems, and by extension, how our own system formed.
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- If you dial back the clock for our own solar system by 4.5 billion years, which one of these disks were we?
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- It is like the perfect fishing spot; our success rate was much greater than anything else we have ever done. Because all seven are around stars that were born in the same region at roughly the same time, that group itself is a mini-laboratory where we can compare and contrast the architectures of many planetary nurseries developing simultaneously under a range of conditions, something that we really didn’t have before.
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- All of the stars and disks are young, between tens of millions of years to a few hundred million years. That’s a very dynamic period for young solar systems, as planets form and migrate and as the overall architecture of the system takes form.
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- One star named HD 156623 did not have a hole in its disk. But it’s one of the youngest in the group. That fits in with our understanding of how solar systems form. A very young star shouldn’t have any planets yet, since the star itself has barely formed.
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- An image of the very young star HD 156623 and its disk found no evidence of a hole in the disk, which would signal the presence of a planet if it were there. PS1 and bg1 and bg2 are point sources and background objects that aren't a part of the disk.
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- When we look at younger circumstellar disks, like protoplanetary disks that are in an earlier phase of evolution, when planets are forming, or before planets have started to form, there is a lot of gas and dust in the areas where we find these holes in the older debris disks.
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- One of the fascinating aspects of studies like this is what it might tell us about our own home here in our Solar System. What would it have looked like if it had been imaged in its infancy.
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- If you dial back the clock for our own solar system by 4.5 billion years, which one of these disks were we? Were we a narrow ring, or were we a fuzzy blob? It would be great to know what we looked like back then to understand our own origins. That is the great unanswered question.
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- Our Solar System is a relatively, calm, sedate place compared to young solar systems. There is no way we’ll ever know what our own Solar System looked like in its infancy. But the same processes that formed our system are at play in every system. Ours might only be special because of our precious life-supporting Earth.
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- Our understanding of young stars, and the solar system that evolve around them is taking shape. Even ten years ago, we weren’t nearly as knowledgeable as we are now. When our next generation of telescopes comes online over the next decade or so, our knowledge will grow by leaps and bounds.
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- And this study will be part of it all. Here are more reviews about exoplanets:
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- 2891 - EXOPLANETS - thousands have been found? Exoplanets are planets orbiting the other stars, outside our solar system, in other solar systems that are far, far away. They have been found by searching astronomers Most exoplanets have been found using the “transit method“.
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- 2872 - EXOPLANETS - discovering more planets. On October 20, 2020, scientists revealed a series of 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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- 2847 - CHEOPS - exploring other planets. September, 2020, eight months after the space telescope CHEOPS started its journey into space. CHEOPS is the first European Space Agency mission dedicated to characterizing known exoplanets. Exoplanets are planets outside the Solar System. They were first discovered in 1995.
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- 2770 - EXOPLANETS - are we alone? Some significant developments need to happen before we can answer the question with any confidence: We will get better at detecting Earth-like planets in the habitable zone and even be able to detect what's in their atmospheres (if they have one).
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- 2702 - EXOPLANETS - new discoveries? If astronomers do detect an exoplanet with a significant oxygen atmosphere, that can only mean an alien biosphere has created it. It is only a matter of time 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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- 2280 - We know there is life in the Universe. We are living proof of that. But is there life on exoplanets which are planets around other suns outside our own solar system? Exoplanets are common, we have found over 4,000 but as for life we are the only evidence so far.
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- 2233 - EXOPLANETS- The TESS Space Mission. The next generation exoplanet hunter is TESS, Transiting Exoplanet Survey Satellite, has already found eight confirmed planets in its first four months of observing and some are unlike anything astronomers have seen before.
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- 2223 - for more of the details about the TESS spac3 mission.
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- 2145 - for more details about the Kepler space telescope. There are nearly 1 trillion stars in our galaxy. 20% pf them are similar to our Sun. So, there could be 20,000,000,000 earth-like planets with liquid water on the surface.
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- 2119 - Math discovers exoplanets. Detecting sinusoidal wobbles in the light spectrum will detect earth-like terrestrial planets orbiting other stars.
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- 2107 - Planets outside our own. This Review lists 8 more reviews about exoplanets-
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- November 23, 2020 2914
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--------------------- Tuesday, November 24, 2020 -------------------------
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