- 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“.
--------------------------- 2891 - EXOPLANETS - thousands have been found?
- How does the “transit method” work and why is it successful?
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- In using the transit method we look for repetitive short dimmings of a star, which are caused by a planet passing in front of the star when viewed from Earth. This event is called a “transit“.
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- When you look at a randomly chosen star, however, you typically don't know if it has a transiting planet or even a planet at all. In order to find new transits, astronomers typically have to look at a star for a very long time and without pause, typically for weeks and sometimes for years to observe multiple orbits of the transiting planet.
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- But even that is not enough. For the transit method to work, we need to be in the orbital plane of the planet around its star, when seen from Earth. On average, this is only the case for about every hundredth exoplanet. So we need to observe hundreds and thousands of stars continuously.
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- The transit method success is based on the continuous observation of a large number of stars by NASA's Kepler Space Telescope. Kepler has discovered thousands of exoplanets since 2009, in total more than half of all the exoplanets known today.
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- The procedure for exoplanet transit searches has been improved by refraining from the “data binning“. Part of the increased computer workload can be absorbed by modern CPU power, but we also had to design the computer code from scratch to make it as efficient as possible. Now it even works on a standard laptop. So you can even find an exoplanet on a train journey with a laptop on your knees.
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- How many overlooked exoplanets have you been able to track down? 18 discoveries in the Kepler data. KOI-456.04 is the 19th exoplanet that we have identified and that has previously been overlooked by the standard search techniques.
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- They have detected another few dozen candidates, which we are currently studying in more detail before we report them to the community. We don't want a measurement error to be identified as a planet.
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- During the nine years of operation, Kepler recorded measurement data from about 150,000 stars.
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- How do we decide which stars are worth a second, closer look?
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- The careful selection of the stars to be re-examined was crucial to our previous discoveries. Rather than just randomly choose one of the 150,000 stars from the Kepler mission they focused on the second part of the mission, the so-called K2 mission, in which transiting planets had already been discovered around a total of 517 stars.
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- To check if this method is truly better than the previous methods, we simply revisited all the brightness measurements of these 517 stars and looked for additional planets that might have been missed so far.
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- As a result, we not only found all the previously known exoplanets, but we also discovered 18 new ones. That may not sound like much, 18 out of 517. It's not just the number of planets that's important though. More important is the fact that all of our newly discovered planets are about the same size as Earth and thus much smaller than most known exoplanets. Of course that's why they had initially been missed.
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- After sifting through the K2 data, we have now extended our search to the more than 4000 light curves from the first Kepler mission from 2009 to 2013. And again they were successful. The 1.9 Earth radius planetary candidate is KOI-456.04 orbiting the sun-like star Kepler-16.
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- Why is KOI-456.04 as a planetary candidate? The signal of this presumed planet passes one of our statistical tests with a probability of 85 percent. That means the chances are 85 out of 100, or almost six to one, that this signal is genuinely caused by a planet and not by a random statistical variation of the data or by an instrumental effect.
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- Six to one is a good bet. But as astronomers we want the signal to have a probability of 99 percent, a chance of ninty-nine to one, before we would formally grant the planetary status to the candidate. KOI-456.04 still remains a good candidate.
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- Why is it important to examine a single star system so closely? What do we learn from such an individual case? Humanity invests considerable funds and work but also heart & soul in follow-up observations of the most interesting exoplanets or planetary candidates. Even though financial investments in space research are only about one thousandth of the military budget, we do not want to waste the valuable observation time.
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- In some sense, observation time of ground- and space-based telescope is worth billions of Euros or Dollars and we certainly want to avoid spending that time on an interesting observational target only to find that the target does not exist.
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- That's why we went to great pains in our study to statistically determine the planetary status. Strictly speaking, this characterization of the planet, or planet candidate, was by far the most time-consuming part.
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- Researchers had succeeded in discovering KOI-456.04 in May 2019, after only a few days of computer-aided searches of the data. The next step, the extremely complex characterization of the planetary system around the star Kepler-160, took a long time.
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- Next time we will be faster and it won't take us another year to do the candidate vetting after first detection. And the good news is that we have already found a few dozen more promising candidates in the Kepler data.
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- Using the transit method of detection, the Kepler Space Telescope examined over 530,000 stars and discovered over 2,600 explanets in nine years. TESS, the successor to Kepler, is still active, and has so far identified over 1,800 candidate exoplanets, with 46 confirmed.
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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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- By chasing that second transit down astronomers have found longer period planets. 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. This planet is out at a thirty-five days orbit, which is a much longer period than we usually find them.
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- “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 1,000°C.
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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, they turned to the Next Generation Transit Survey (NGTS) in Chile.
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- NGTS 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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- NGTS has twelve state-of-the-art telescopes, which means that we 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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- The astronomers had 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 signaled a second transit of the suspected exoplanet. Finally, on the night of October 24, 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 160 Celsius (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.
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- These results highlight the synergy between space telescopes like TESS, and more nimble, economical facilities like NGTS. 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.
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- This highlights the power of high-precision ground-based photometric facilities in revealing longer-period transiting exoplanets that TESS alone cannot discover. There are hundreds of single transits detected by TESS that will be monitored 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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- Discovering life outside our solar system is the motivator for all this effort and expense. What will we do then?????????????????????????????
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----------------------------- See other reviews about exoplanets;
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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 6, 2020 2891
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--------------------- --- Monday, November 9, 2020 ---------------------------
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