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posted by martyb on Friday March 04 2016, @05:35AM   Printer-friendly
from the look-at-what-can-look-at-you dept.

The Search for Extraterrestrial Intelligence could be more successful if a smaller number of targets with a higher probability of success are observed. In a new paper, two astrophysicists propose looking at the thin region of space where aliens could observe the Earth transiting the Sun, the same technique that the Kepler space observatory uses:

In a paper to published in the journal Astrobiology, and available now online, Heller and Pudritz turn the telescope around to ask, what if extraterrestrial observers discover the Earth as it transits the sun?

If such observers are using the same search methods that scientists are using on Earth, the researchers propose that humanity should turn its collective ear to Earth's "transit zone", the thin slice of space from which our planet's passage in front of the sun can be detected. "It's impossible to predict whether extraterrestrials use the same observational techniques as we do," says Heller. "But they will have to deal with the same physical principles as we do, and Earth's solar transits are an obvious method to detect us."

The transit zone is rich in host stars for planetary systems, offering approximately 100,000 potential targets, each potentially orbited by habitable planets and moons, the scientists say – and that's just the number we can see with today's radio telescope technologies. "If any of these planets host intelligent observers, they could have identified Earth as a habitable, even as a living world long ago and we could be receiving their broadcasts today," write Heller and Pudritz.

[...] Heller and Pudritz propose that the Breakthrough Listen Initiative, part of the most comprehensive search for extraterrestrial life ever conducted, can maximize its chances of success by concentrating its search on Earth's transit zone.

From The Register .

[Continues.]

The Search for Extraterrestrial Intelligence in Earth's Solar Transit Zone (open, DOI: 10.1089/ast.2015.1358)

We explore Earth's transit zone (ETZ), the projection of a band around Earth's ecliptic onto the celestial plane, where observers can detect Earth transits across the Sun. ETZ is between 0.520° and 0.537° wide due to the noncircular Earth orbit. The restricted Earth transit zone (rETZ), where Earth transits the Sun less than 0.5 solar radii from its center, is about 0.262° wide. We first compile a target list of 45 K and 37 G dwarf stars inside the rETZ and within 1 kpc (about 3260 light-years) using the Hipparcos catalogue. We then greatly enlarge the number of potential targets by constructing an analytic galactic disk model and find that about 105 K and G dwarf stars should reside within the rETZ. The ongoing Gaia space mission can potentially discover all G dwarfs among them (several 104) within the next 5 years. Many more potentially habitable planets orbit dim, unknown M stars in ETZ and other stars that traversed ETZ thousands of years ago. If any of these planets host intelligent observers, they could have identified Earth as a habitable, or even as a living, world long ago, and we could be receiving their broadcasts today.


Original Submission

Related Stories

Planetary Security - How to Hide the Activity of an Entire Planet 53 comments

Two astronomers at Columbia University have suggested earthlings could use lasers to conceal the presence of Earth from intelligent life on other planets:

RAS [Royal Astronomical Socitety] notes that several prominent scientists, including Stephen Hawking, have cautioned against humanity broadcasting our presence to intelligent life on other planets. Other civilizations might try to find Earth-like planets using the same techniques we do, including looking for the dip in light when a planet moves directly in front of the star it orbits.

These events — transits — are the main way that the Kepler mission and similar projects search for planets around other stars. So far Kepler alone has confirmed more than 1,000 planets using this technique, with tens of these worlds similar in size to the Earth. [Professor David] Kipping and [graduate student Alex] Teachey speculate that alien scientists may use this approach to locate our planet, which will be clearly in the "habitable zone" of the Sun, where the temperature is right for liquid water, and so be a promising place for life.

Hawking and others are concerned that extraterrestrials might wish to take advantage of the Earth's resources, and that their visit, rather than being benign, could be as devastating as when Europeans first travelled to the Americas.

[...] According to the authors, emitting a continuous 30 MW laser for about ten hours, once a year, would be enough to eliminate the transit signal, at least in visible light. The energy needed is comparable to that collected by the International Space Station in a year. A chromatic cloak, effective at all wavelengths, is more challenging, and would need a large array of tuneable lasers with a total power of 250 MW.

Previously:
Narrow SETI Targets by Looking at Places Where Earth Transits can be Seen
Kepler Extended Mission Finds More Exoplanets
NASA's Kepler Mission Discovers Earth-Like Planet In Sun-Like Star's Habitable Zone


Original Submission

SETI: Not Successful Because We Are Barely Even Looking? 35 comments

Smart aliens might live within 33,000 light-years of Earth. A new study explains why we haven't found them yet.

[An] upcoming study in The Astronomical Journal, which we learned about from MIT Technology Review, suggests humanity has barely sampled the skies, and thus has no grounds to be cynical. According to the paper, all searches for extraterrestrial intelligence, or SETI, have examined barely a swimming pool's worth of water from a figurative ocean of signal space. "We haven't really looked much," Shubham Kanodia, a graduate student in astronomy who co-wrote the study, said during a NASA "technosignatures" workshop in Houston, Texas on September 26.

[...] In their study, Kanodia and his colleagues built a mathematical model of what they consider a reasonably sized cosmic haystack.
Their haystack is a sphere of space nearly 33,000 light-years in diameter, centered around Earth. This region captures the Milky Way's bustling core, as well as many giant globular clusters of stars above and below our home galaxy.

They also picked eight dimensions of a search for aliens — factors like signal transmission frequency, bandwidth, power, location, repetition, polarization, and modulation (i.e. complexity) — and defined reasonable limits for each one. "This leads to a total 8D haystack volume of 6.4 × 10116m5Hz2s/W," the authors wrote. That is 6.4 followed by 115 zeros — as MIT Technology review described it, "a space of truly gargantuan proportions."

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  • (Score: 2) by opinionated_science on Friday March 04 2016, @05:47AM

    by opinionated_science (4031) on Friday March 04 2016, @05:47AM (#313448)

    First, I quite like the idea.

    Second, it reminds me of some of the written works where the question is asked "do we WANT them to know we are here?"

    Interesting times....if only we can avoid the cascade of possible cataclysms until we get a stardrive(tm) working ;-)

    • (Score: 3, Funny) by Gravis on Friday March 04 2016, @06:19AM

      by Gravis (4596) on Friday March 04 2016, @06:19AM (#313463)

      Second, it reminds me of some of the written works where the question is asked "do we WANT them to know we are here?"

      absolutely! there are multiple good possible outcomes from them knowing about us:

      1. they could share their knowledge and technology
      2. they could help us identify which humans are harmful to humanity (and eliminate them)
      3. they could help terraform and colonize the planets in our system
      4. they could finally tell us wtf that thing is on Donald Drumph's head
      5. they could wipe us out and take the planet for themselves.

      I am willing to risk the fate of mankind for those kinds of gains.

    • (Score: 4, Insightful) by maxwell demon on Friday March 04 2016, @06:44AM

      by maxwell demon (1608) on Friday March 04 2016, @06:44AM (#313475) Journal

      Of course SETI doesn't make any effort to make us known to them; it's an effort to make them known to us. However the best chance we have to find them is if they actively try to contact us (as that would mean they intentionally send us signals they think we might be able to receive), which of course requires that they already found us, even without us making any effort to make ourselves known.

      Of course, if they are there' it's in our interest to know that. Especially if they are hostile; you've got much better chances to defend against someone you know exist, than you have against someone whose existence you didn't even know of before they attacked.

      --
      The Tao of math: The numbers you can count are not the real numbers.
      • (Score: 0) by Anonymous Coward on Friday March 04 2016, @07:05AM

        by Anonymous Coward on Friday March 04 2016, @07:05AM (#313481)

        Of course SETI doesn't make any effort to make us known to them; it's an effort to make them known to us.

        https://en.wikipedia.org/wiki/Active_SETI [wikipedia.org]

      • (Score: 3, Informative) by frojack on Friday March 04 2016, @08:04AM

        by frojack (1554) on Friday March 04 2016, @08:04AM (#313502) Journal

        But SETI is still listening radio waves, no?

        So if we look at a list of exoplanets [wikipedia.org] those are just about all we could expect to hear from, given how long we've been listening. Our earliest listening attempts only started in 1959, and realistic attempts were much later.

        So we've only listened to signals from a sphere 57 light years in diameter. Any signals we might have heard would have had to been passing through that sphere's outer boundary sometime before 57 years ago or we wouldn't hear it.

        However, our radio signals since the inception of radio broadcasts extend out 100 light years or so. (Given alien detectors that could distinguish it from the universal background radiation.)

        Given that we can't "listen farther" by concentrating our efforts, I don't see the point in worrying about transit paths.

        Unless they were randomly transmitting to planets transiting stars (57 years ago), we have a better chance of picking up their broadcast transmissions. And those won't necessarily be from stars that see us in transit.

        --
        No, you are mistaken. I've always had this sig.
        • (Score: 2) by mhajicek on Friday March 04 2016, @02:17PM

          by mhajicek (51) on Friday March 04 2016, @02:17PM (#313643)

          Their detection of us is not limited to our radio transmissions. We've been able to analyze chemical content in exoplanet atmospheres as they transit; they could use that technique to detect airborne life. They also likely have technologies thousands of years more advanced than ours and may be able to image the ground with usable resolution.

          --
          The spacelike surfaces of time foliations can have a cusp at the surface of discontinuity. - P. Hajicek
          • (Score: 0) by Anonymous Coward on Friday March 04 2016, @03:18PM

            by Anonymous Coward on Friday March 04 2016, @03:18PM (#313692)

            wait. are you saying they can see me when I'm on a mountain and I go behind a bush to pee?
            why would we even WANT to talk to these perverts?!

        • (Score: 2) by meustrus on Friday March 04 2016, @05:50PM

          by meustrus (4961) on Friday March 04 2016, @05:50PM (#313815)

          So we've only listened to signals from a sphere 57 light years in diameter.

          You mean they have. We can listen to message sent from thousands of light years away, as long as they were sent thousands of years ago. It is only the very limited number of specific stars to which we sent active SETI [wikipedia.org] or cosmic call [wikipedia.org] signals which need to be in a sphere up to 42 light years in diameter (first one being sent in 1974).

          --
          If there isn't at least one reference or primary source, it's not +1 Informative. Maybe the underused +1 Interesting?
          • (Score: 2) by frojack on Friday March 04 2016, @06:43PM

            by frojack (1554) on Friday March 04 2016, @06:43PM (#313846) Journal

            Yes, that's what I was trying to say, even though I phrased it badly.

            If they sent a pulse signal 1000 years ago, and it arrived 60 years ago, we would have missed it.
            However, if they sent continuous radio broadcasts starting at the same time we may hear it.

            Same for our transmissions. (active SETI or regular broadcast).

            There is the caveat that the signal may be so weak that we (or they) won't be able to separate it from the Cosmic Background Radiation noise.

            --
            No, you are mistaken. I've always had this sig.
    • (Score: 0) by Anonymous Coward on Friday March 04 2016, @06:52AM

      by Anonymous Coward on Friday March 04 2016, @06:52AM (#313476)

      Why so vague about "some of the written works"?

  • (Score: 1, Interesting) by Anonymous Coward on Friday March 04 2016, @05:53AM

    by Anonymous Coward on Friday March 04 2016, @05:53AM (#313453)

    How does SETI avoid false positives? They must have seen thousands to millions of interesting but deemed to be false positive signals by now.

  • (Score: 1, Interesting) by Anonymous Coward on Friday March 04 2016, @06:37AM

    by Anonymous Coward on Friday March 04 2016, @06:37AM (#313473)

    "For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places."
    - Ephesians 6:12

    • (Score: 2) by frojack on Friday March 04 2016, @08:20AM

      by frojack (1554) on Friday March 04 2016, @08:20AM (#313507) Journal

      But only when Congress is in session.

        "No man's life, liberty or property are safe while the Legislature is in session."

      --
      No, you are mistaken. I've always had this sig.
    • (Score: 2) by tibman on Friday March 04 2016, @02:36PM

      by tibman (134) Subscriber Badge on Friday March 04 2016, @02:36PM (#313659)

      G’Quon wrote, “There is a greater darkness
      than the one we fight. It is the darkness of the soul that has lost its way.
      The war we fight is not against powers and principalities; it is against chaos
      and despair. Greater than the death of flesh is the death of hope, the death of
      dreams. Against this peril we can never surrender. The future is all around us,
      waiting, in moments of transition, to be born in moments of revelation. No one
      knows the shape of that future or where it will take us. We know only that it
      is always born in pain.”

      --
      SN won't survive on lurkers alone. Write comments.
  • (Score: 0) by Anonymous Coward on Friday March 04 2016, @08:00AM

    by Anonymous Coward on Friday March 04 2016, @08:00AM (#313500)

    That's not where you dropped them, but it's where you've got the best chance of seeing them.

    Same logic here.

    Hahha, I said "logic" in a sentence about SETI, which is the dumbest technical thing humans have ever wasted time, effort, and cold hard money, on.

    • (Score: 2) by wonkey_monkey on Friday March 04 2016, @08:22AM

      by wonkey_monkey (279) on Friday March 04 2016, @08:22AM (#313508) Homepage

      Same logic here.

      No, it isn't.

      --
      systemd is Roko's Basilisk
    • (Score: 2) by c0lo on Friday March 04 2016, @10:41AM

      by c0lo (156) Subscriber Badge on Friday March 04 2016, @10:41AM (#313549) Journal

      which is the dumbest technical thing humans have ever wasted time, effort, and cold hard money, on.

      When it was launched, what better plausible denial for ECHELON than SETI?

      --
      https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
  • (Score: 2) by Bot on Friday March 04 2016, @03:22PM

    by Bot (3902) on Friday March 04 2016, @03:22PM (#313698) Journal

    Xykryyyz shifted his attention to the signal, it was almost certainly not natural. Uwrlyyyz's attention merged in, the two of them briefly shared their impression in a session that we might render as telepathic dialogue:
    - it's that shithole again, much stronger now.
    - it's better focussed, not necessarily stronger overall.
    - do you feel they discovered us?
    - no, they are just trying smarter
    - a long way to go
    - a long way to go

    --
    Account abandoned.