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posted by Fnord666 on Tuesday September 12 2017, @12:14AM   Printer-friendly
from the peek-a-boo dept.

Astronomers have identified exoplanets from which potential life forms are likely to be able to observe a transit of one of our solar system's planets:

"The detection of thousands of extrasolar planets by the transit method naturally raises the question of whether potential extrasolar observers could detect the transits of the Solar System planets," they wrote in a paper published [open, DOI: 10.1093/mnras/stx2077] [DX] last month in the Monthly Notices of the Royal Astronomical Society.

[...] The transit method only works if a planet is aligned in a way that it crosses the star. In the Solar System, the terrestrial planets – Mercury, Mars, Earth and Venus – are more likely to be spotted in this way than the gas and ice giants – Jupiter, Saturn, Uranus and Neptune. Up to three planets in various combinations can be seen at any one time, the researchers found. The next step is to find which boundaries are located in the best positions to observe more than one of the terrestrial planets crossing the Sun, and count up the number of exoplanets inside these "transit zones."

Katja Poppenhaeger, co‑author of the study and assistant professor at Queen's University Belfast, estimated that "a randomly positioned observer would have roughly a 1 in 40 chance of observing at least one planet. The probability of detecting at least two planets would be about ten times lower, and to detect three would be a further ten times smaller than this." A full sweep shows there are currently 68 known exoplanets that are in a good spot to catch a planet transiting the Sun. From this list, nine of them are temperate and have sizes similar to Earth, but none are considered to be habitable. That doesn't mean the chances of aliens potentially spying on Earth are completely zero. The researchers estimate that there are ten other unconfirmed exoplanets that have more favorable conditions of sustaining life, and are within the transit zones.


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  • (Score: 2) by FatPhil on Tuesday September 12 2017, @12:37PM (5 children)

    by FatPhil (863) <pc-soylentNO@SPAMasdf.fi> on Tuesday September 12 2017, @12:37PM (#566703) Homepage
    Ah, OK, smearing the orbits' precession (I'm using loose terminology - I mean anything that causes the planet to deviate from a perfect ellipse) over the sphere by ignoring the time dimension, yeah that might get it closer to that magnitude of number - "will ever get a chance to see at least one transit". However, is there enough time to spear the orbits over so much of the sphere, I don't know?

    If she's not done the hard maths required to come up with a believable number, then I would still reserve the right to call fake. Simply being lined up with the ecliptic does *not* mean there'll be a possible transit; if spacey (and timey-wimey) stuff worked like that, there'd be a solar eclipse every 29 days, and the moon's *way* bigger (to the earth) than any planet (is to the sun).
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  • (Score: 0) by Anonymous Coward on Tuesday September 12 2017, @04:53PM (1 child)

    by Anonymous Coward on Tuesday September 12 2017, @04:53PM (#566835)

    The reason we don't have a solar eclipse every month (or alternatively, never) is that the earth orbits the sun. Other stars don't orbit the sun.

    • (Score: 2) by FatPhil on Tuesday September 12 2017, @09:26PM

      by FatPhil (863) <pc-soylentNO@SPAMasdf.fi> on Tuesday September 12 2017, @09:26PM (#566965) Homepage
      > The reason we don't have a solar eclipse every month (or alternatively, never) is that the earth orbits the sun.

      What utter, utter, codswallop.

      The moon occludes millions of stars all the freaking time, and we don't rotate around any of those suns.
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  • (Score: 3, Interesting) by dx3bydt3 on Tuesday September 12 2017, @05:46PM (2 children)

    by dx3bydt3 (82) on Tuesday September 12 2017, @05:46PM (#566873)

    That sentence would then be more accurate to say, "a randomly positioned observer would have roughly a 1 in 40 chance of observing at least one planet... eventually". Venus and Mercury have the greatest inclination of their orbits, and Mercury takes over 230,000 years for the orbital ellipse to make one full rotation against the background stars.

    • (Score: 2) by FatPhil on Tuesday September 12 2017, @09:34PM (1 child)

      by FatPhil (863) <pc-soylentNO@SPAMasdf.fi> on Tuesday September 12 2017, @09:34PM (#566967) Homepage
      And after those 230000 years, has it painted a filigree of stripes, or has it filled in all the gaps?
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      • (Score: 3, Interesting) by dx3bydt3 on Tuesday September 12 2017, @11:20PM

        by dx3bydt3 (82) on Tuesday September 12 2017, @11:20PM (#567007)

        Oh, stripes indeed, but it turns out, if my math is right they all overlap handily. The precession of mercury's orbit is 5.5 arcseconds per year, and it is inclined by under 7°. if I didn't mess up a few decimal places, that means that in one earth year, Mercury's perihelion height change relative to some invariable plane would amount to only 1/16 of the planet's diameter. And that's using earth years, so roughly 4 times as many Mercury years, so only 1/66th of Mercury's diameter per orbit.

        disclaimer: I have had a few glasses of wine, and my only references are the top hits on google.