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Exoplanets in the earth neighborhood

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  • Exoplanets in the earth neighborhood


    Past, present and future stars that can see Earth as a transiting exoplanet

    Nature volume 594, pages505–507 (2021)Cite this articleAbstract

    In the search for life in the cosmos, transiting exoplanets are currently our best targets. With thousands already detected, our search is entering a new era of discovery with upcoming large telescopes that will look for signs of ‘life’ in the atmospheres of transiting worlds. Previous work has explored the zone from which Earth would be visible while transiting the Sun1,2,3,4. However, these studies considered only the current position of stars, and did not include their changing vantage point over time. Here we report that 1,715 stars within 100 parsecs from the Sun are in the right position to have spotted life on a transiting Earth since early human civilization (about 5,000 years ago), with an additional 319 stars entering this special vantage point in the next 5,000 years. Among these stars are seven known exoplanet hosts, including Ross-128, which saw Earth transit the Sun in the past, and Teegarden’s Star and Trappist-1, which will start to see it in 29 and 1,642 years, respectively. We found that human-made radio waves have already swept over 75 of the closest stars on our list.

    © Copyright Original Source

    Unfortunately this is a pay site I may find other sources.
    Last edited by shunyadragon; 06-23-2021, 07:39 PM.
    Glendower: I can call spirits from the vasty deep.
    Hotspur: Why, so can I, or so can any man;
    But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

    go with the flow the river knows . . .


    I do not know, therefore everything is in pencil.

  • #2


    Scientists identify 29 planets where aliens could observe Earth

    Astronomers estimate 29 habitable planets are positioned to see Earth transit and intercept human broadcasts

    The scientists identified 1,715 star systems where alien observers could have discovered Earth in the past 5,000 years by watching it ‘transit’ across the face of the sun. Photograph: c/o CornellIan Sample Science editor
    @iansampleWed 23 Jun 2021 11.00 EDT For centuries, Earthlings have gazed at the heavens and wondered about life among the stars. But as humans hunted for little green men, the extraterrestrials might have been watching us back.

    In new research, astronomers have drawn up a shortlist of nearby star systems where any inquisitive inhabitants on orbiting planets would be well placed to spot life on Earth.

    © Copyright Original Source

    The scientists identified 1,715 star systems in our cosmic neighbourhood where alien observers could have discovered Earth in the past 5,000 years by watching it “transit” across the face of the sun.

    Among those in the right position to observe an Earth transit, 46 star systems are close enough for their planets to intercept a clear signal of human existence – the radio and TV broadcasts which started about 100 years ago.

    The researchers estimate that 29 potentially habitable planets are well positioned to witness an Earth transit, and eavesdrop on human radio and television transmissions, allowing any observers to infer perhaps a modicum of intelligence. Whether the broadcasts would compel an advanced civilisation to make contact is a moot point.

    “One way we find planets is if they block out part of the light from their host star,” said Lisa Kaltenegger, professor of astronomy and director of the Carl Sagan Institute at Cornell University in New York. “We asked, ‘Who would we be the aliens for if somebody else was looking?’ There is this tiny sliver in the sky where other star systems have a cosmic front seat to find Earth as a transiting planet.”

    Earthly astronomers have detected thousands of planets beyond the solar system. About 70% are spotted when alien worlds pass in front of their host stars and block some of the light that reaches scientists’ telescopes. Future observatories, such as Nasa’s James Webb Space Telescope due to launch this year, will look for signs of life on “exoplanets” by analysing the composition of their atmospheres.

    To work out which nearby star systems are well placed to observe an Earth transit, Kaltenegger and Dr Jackie Faherty, an astrophysicist at the American Museum of Natural History, turned to the European Space Agency’s Gaia catalogue of star positions and motions. From this they identified 2,034 star systems within 100 parsecs (326 light years) that could spot an Earth transit any time from 5,000 years ago to 5,000 years in the future.

    One star known as Ross 128, a red dwarf in the Virgo constellation, is about 11 light years away – close enough to receive Earth broadcasts – and has a planet nearly twice the size of Earth. Any suitably equipped life on the planet could have spotted an Earth transit for more than 2,000 years, but lost the vantage point 900 years ago. If there is intelligent life on any of the two known planets orbiting Teegarden’s star, 12.5 light years away, it will be in a prime position to watch Earth transits in 29 years’ time.

    At 45 light years away, another star called Trappist-1 is also close enough to eavesdrop on human broadcasts. The star hosts at least seven planets, four of them in the temperate, habitable zone, but they will not be in position to witness an Earth transit for another 1,642 years, the scientists write in Nature.

    The findings come as the US government prepares to publish a hotly anticipated report on unidentified flying objects (UFOs). The report from the Pentagon’s Unidentified Aerial Phenomena Task Force, which was set up to gain insights into the nature and origins of unknown aircraft, is not expected to reveal evidence of alien antics, or rule it out.

    Prof Beth Biller at Edinburgh University’s Institute for Astronomy, who was not involved in the Nature study, said the work could change how scientists approach Seti, the search for extraterrestrial life. “What was striking to me was how few of the stars within 100 parsecs could have viewed a transiting Earth,” she said.

    “The transit method requires a very precise alignment between the transiting planet, its star, and the sun for a given planet to be detectable, so this result is not surprising. Now I am curious about what fraction of the stars in the Gaia catalogue of nearby stars have the right vantage point to detect the Earth via other exoplanet detection methods, such as the radial velocity method or direct imaging!” [/cite]

    Last edited by shunyadragon; 06-23-2021, 07:43 PM.
    Glendower: I can call spirits from the vasty deep.
    Hotspur: Why, so can I, or so can any man;
    But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

    go with the flow the river knows . . .


    I do not know, therefore everything is in pencil.


    • #3
      Nature also had a news story about it as well which is accessible

      Source: The 2,000 stars where aliens would catch a glimpse of Earth

      Scientists searching for extraterrestrial life should narrow their hunt to stars and planetary systems that have an occasional view of the Earth as it passes in front of the Sun

      Astronomers have pinpointed more than 2,000 stars from where, in the not-too-distant past or future, Earth can occasionally be detected transiting across the face of the Sun.

      If there are aliens living on planets around those stars, with at least a similar level of technological advancement to our own species, then they would theoretically be able to spot us. They could even have observed as the amount of carbon dioxide in Earth’s atmosphere increased over the past several hundred years, since the industrial revolution.

      The work, reported in this week’s Nature1, offers a new way of thinking about the search for extraterrestrial life, says Lisa Kaltenegger, an astronomer at Cornell University in Ithaca, New York, who led the analysis. “Who has the cosmic front seat to see us?” she asks. “For whom would we be the aliens?”

      Those aliens would be the natural choice for Earthlings to look for, say the scientists — because they may have already had a chance to spot us, and thus might be primed to be ready for communications from Earth.

      Movement of stars over time

      Although previous studies have considered this question2,3,4, this is the first to incorporate the movement of stars over time, because stars can slide in or out of the narrow slice of the sky that happens to line up with both Earth and the Sun. With this information, the scientists were able to predict where Earth was visible from over the past 5,000 years or so of human civilization — and also predict where it will be visible another 5,000 years into the future.

      In doing so, the study expands astronomers’ thinking about which stars have “a better-than-average shot of discovering and characterizing the Earth,” says Sofia Sheikh, an astrobiologist at the Berkeley SETI Research Center in California.

      The discovery was made possible by the European Space Agency’s Gaia space observatory, which has compiled the best three-dimensional map of stars to date. Working with Jackie Faherty, an astronomer at the American Museum of Natural History in New York City, Kaltenegger analysed the Gaia map to see which stars have been, or will be, in a position where Earth briefly moves between them and our Sun.

      Because most of the sky lies in other planes to that of our Solar System, there’s just a tiny sliver where this is possible, she says. Of the more than 330,000 stars in the Gaia catalogue that are within 100 parsecs of Earth, just 2,043 happen to have the perfect viewing geometry.

      Of those, 1,715 are in the right locations to have spotted Earth in the past 5,000 years, and an additional 319 will have vantage points in the next 5,000 years (see 'All eyes on Earth'). Seven of the 2,034 are already known to host planets — but many more are likely to have worlds orbiting them, some of which may be suitable for life.

      The method assumed for spying Earth from elsewhere in the Galaxy is the same one that Earth-bound astronomers have used to discover thousands of exoplanets: detecting the light of a distant star dimming slightly and regularly, as an orbiting planet passes across its face.

      Good alien targets

      With the results of this study, astronomers searching for extraterrestrial life can now focus on stars and planetary systems that have a view of Earth and thus might already expect to hear from us. “It really helps in the hunting if you know where the prey is located,” says Seth Shostak, an astronomer at the SETI Institute in Mountain View, California.

      Of those stars, the authors further identified 75 that are close enough — within 30 parsecs — for radio waves from Earth to already have washed over them since humans started to produce them. Those might be particularly good targets, Kaltenegger says, because aliens there could have both seen and heard us by now.

      But other stars assume new prominence. For instance, astronomers know of seven Earth-sized planets orbiting the star TRAPPIST-1, 12 parsecs from Earth. TRAPPIST-1 will move into a position to see Earth as a transiting planet in the year 3663, say the study authors (see 'Some of the stars with known exoplanets that have a view of Earth').

      Astronomers and science-fiction writers have noted that civilizations could signal their existence by constructing artificial ‘megastructures’ that pass in front of their stars, briefly dimming their light in a characteristic way.

      Perhaps, some say, humanity should plan ahead for when eyes from the TRAPPIST-1 system might be cast in our direction. “Maybe we should think about installing a transiting megastructure for them to observe,” says René Heller, an astrophysicist at the Max Planck Institute for Solar System Research in Göttingen, Germany.


      © Copyright Original Source

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