Why hasn't E.T. phoned Earth? Maybe aliens are waiting for the exact right moment.

An artist's illustration of two alien planets around a red sun.
An artist's illustration of two alien planets around a red sun. Aliens on such a planet might choose to beam signals toward Earth when they are directly between Earth and their own sun. (Image credit: Mark Garlick/Science Photo Library via Getty Images)

Aliens may be waiting until a cosmic version of "high noon" to send out their signals to us, scientists have suggested. 

In a new study, researchers hunted for technological signs of E.T. during the moments when exoplanets pass directly in front of their suns, from Earth's point of view. These exact moments could be the perfect chance for an alien world to beam out a signal to Earthlings in an attempt to make contact. 

"Exoplanetary transits are special because they can be calculated by both us on Earth, as the observers, and also any potential technological species in the exoplanetary system itself, as the transmitters," said study leader Sofia Sheikh (opens in new tab), a postdoctoral researcher in radio astronomy at the Search for Extraterrestrial Intelligence (SETI) Institute. These transits, then, are a predictable and repetitive time during which aliens might think to send messages and Earthlings might look to receive them. 

Related: 12 possible reasons we haven't found aliens 

"This strategy helps us narrow down the huge question of where and when to look for a message in the vast reaches of space," Sheikh told Live Science in an email. 

The new study, published Dec. 9 on the preprint site arXiv (opens in new tab) and scheduled for peer-reviewed publication in The Astronomical Journal, did not find any evidence of chatty aliens. But the study only searched a dozen far-off planets. In the future, they plan to look further with a variety of telescopes. 

Related: Is it time to send another message to intelligent aliens? Some scientists think so. (opens in new tab)

Since radio technology was invented in the late 19th century, Earth has been leaking transmissions into space — and occasionally, as with the famed Arecibo Message of 1974 (opens in new tab), has sent them out deliberately in hopes of contacting any intelligent extraterrestrial that might be listening. Hoping that intelligent alien civilizations might also leak out technological signals, or technosignals, researchers also scan the galaxy for radio waves (opens in new tab) that might have originated from alien tech. 

But the galaxy is a big place, so a key question is where to look. Sheikh and her team settled on eavesdropping on far-off exoplanets as they pass in front of their suns, in what is known as a "Schelling point" — a solution to a problem that two individuals tend to default to if they aren't communicating with one another. In other words, the moment of planetary transit just seems the logical moment to connect from the point of view of both the transmitter and receiver. 

Sheikh and her colleagues used West Virginia's Robert C. Byrd Green Bank Telescope to search for radio signals from 12 exoplanets whose transits were observable during a brief window in March 2018. They detected plenty of radio signals — almost 34,000, in fact — but 99.6% of those could be dismissed out of hand as interference from Earthbound communications. A group of trained citizen scientists did the work of examining the signals. 

In the end, all but two of the signals were determined to be due to interference. The remaining two, a couple of short bursts from Kepler-1332b and Kepler-842b — both potentially rocky planets larger than Earth — were deemed worthy of further follow-up. However, Sheikh said, those two are also almost certainly due to interference and are not real messages. 

Nevertheless, she said, the study was proof that the search method can work. The researchers plan to tackle more observations in the future at the SETI Institute's Allen Telescope Array in California. 

Originally published on LiveScience.com (opens in new tab).

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Stephanie Pappas
Live Science Contributor

Stephanie Pappas is a contributing writer for Space.com sister site Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz. 

  • Helio
    The argument that a transit is a great time to send us messages seems nuts. The background noise could not be worse. The SOHO spacescope, and others in L1, would be useless if they weren't using a halo orbit to keep them outside the apparent disk of the Sun.

    SWAIM?
    Reply
  • COLGeek
    In transit as define by what reference point (either end and with what offset given the distance between both planets)? I agree with Helio, this seems to make little practical sense.
    Reply
  • rod
    ET phoning home, buzzing Earth, and UAP/UFO reports are a popular theme :)

    https://forums.space.com/threads/pentagon-releases-its-long-awaited-2022-ufo-report.59562/
    https://forums.space.com/threads/10-things-we-learned-about-aliens-or-the-lack-thereof-in-2022.59344/
    https://forums.space.com/threads/why-havent-aliens-contacted-earth-new-fermi-paradox-analysis-suggests-were-not-that-interesting-yet.59267/
    https://forums.space.com/threads/why-have-aliens-never-visited-earth-scientists-have-a-disturbing-answer.55892/
    Reply
  • COLGeek
    rod said:
    ET phoning home, buzzing Earth, and UAP/UFO reports are a popular theme :)

    https://forums.space.com/threads/pentagon-releases-its-long-awaited-2022-ufo-report.59562/
    https://forums.space.com/threads/10-things-we-learned-about-aliens-or-the-lack-thereof-in-2022.59344/
    https://forums.space.com/threads/why-havent-aliens-contacted-earth-new-fermi-paradox-analysis-suggests-were-not-that-interesting-yet.59267/
    https://forums.space.com/threads/why-have-aliens-never-visited-earth-scientists-have-a-disturbing-answer.55892/
    No kidding. Does generate lots of clicks and theories, though.
    Reply
  • billslugg
    It might be advantageous to wait 1/4 of a year and transmit 90° from the direction to your star. Any receiving antenna would have the transmitting planet as far off to one side from the star as possible.
    Reply
  • Helio
    billslugg said:
    It might be advantageous to wait 1/4 of a year and transmit 90° from the direction to your star. Any receiving antenna would have the transmitting planet as far off to one side from the star as possible.
    Yes. We have direct images of a number of exoplanets thanks to coronagraphs. The greater the elongation, the less the noise.
    Reply
  • Jan Steinman
    I don't understand what this even means, given the distances involved.

    Our nearest star is about four and a quarter years away at the speed of light.

    Would aliens on a planet circling Proxima Centauri (for example) send us radio signals when their planet was directly between their star and ours, or at a point in time that was about ninety days before that point, so that by the time the signal reached us, it would look like it was coming from the transiting planet?

    Or would they be sending such a signal when we, the target, were either transiting, or would be transiting in 0.2465 of one of our years?

    I guess I don't understand the goal of the timing, or I'd understand the timing better.
    Reply
  • billslugg
    If you are on a planet and you want to send a signal to other far away planets you need to alert your potential audience of your existence so they will turn their antennas towards you. One way to do that is to always be sending your signal in a direction opposite of your Sun. This way, anyone who just happened to be looking at your Sun would see your planet in transit and, at the same time would be right in the middle of the transmitted signal. They would think "Look, there is a planet crossing that Sun, I wonder if it might be sending a signal" and they would point their receiver antenna towards it and be able to hear the signal.
    One problem with this is that they would also be pointing their antenna directly at the star, all of which are very noisy in the radio spectrum. We suggest they modify their strategy and wait until they are as far from their Sun as possible as viewed by any potential receiver. That would be exactly 1/4 of a local year from a transit. In that case they would be somewhat removed sideways from the star and we might hear their signal better.
    Reply
  • Rick From CT
    The most logical reason we haven't been contacted by aliens, or even detected any alien transmissions, is they don't use radio waves. My favorite theory is they've seeded the universe with quantum entangled communications devices that allow instantaneous communications regardless of distance. Something like the ansible device described in Enders Game. If we could find a way to tune into that, we'd really have something. I suspect contact will happen naturally as our work with quantum entanglement evolves.
    Reply
  • Jan Steinman
    Rick From CT said:
    they've seeded the universe with quantum entangled communications devices that allow instantaneous communications…
    Violates Bell's Theorem. Three smart guys (ACZ) recently got Nobel Prizes for validating Bell.

    Quantum entanglement is expected to be useful in cryptography, but not in superluminal communications.
    Reply