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A SETI-based Look at New Horizons

Using eleven of the Allen Telescope Array’s 6.1-meter dishes, the SETI Institute and the Radio Astronomy Laboratory at the University of California (Berkeley) have detected the New Horizons spacecraft on its way to Pluto/Charon. New Horizons transmits an 8.4 GHz carrier signal that showed up readily on the SETI Prelude detection system. What I hadn’t realized was that snagging distant spacecraft transmitters is a standard part of SETI operations, as Jill Tarter notes in this brief article on the event posted at the New Horizons site:

“We look forward to checking in with New Horizons as a routine, end-to-end test of our system health. As this spacecraft travels farther, and its signals grow weaker, we will be building out the Allen Telescope Array from 42 to 350 antennas, and thus can look forward to a long-term relationship.”

Image: New Horizons as tracked by the Allen Telescope Array. This plot shows 678 hertz (Hz) of spectrum collected over 98 seconds. The New Horizons signal can be easily seen as a bright diagonal line, drifting at rate of -0.6 > Hz/second. Credit: SETI Institute.

Just how long-term a relationship it may be is shown by this second image, the result of combining fifteen of the ATA’s antennae in October to detect the carrier from Voyager 1. The most distant of all man-made objects, Voyager transmitted from 108 AU, a signal described by Tarter as reliable and ‘…with a very high signal to noise ratio.’ New Horizons may be a newcomer compared to the 37-year old Voyager, but it will doubtless offer fodder for the ATA’s antenna farm for decades to come. The method at work here is called ‘beamforming,’ a way to process the incoming signal that allows multiple antennae to function together with maximum directionality.

Image (click to enlarge): Integrated power from Voyager 1 spacecraft over 192 second observation. Credit: SETI.

Combining signals from a host of different antennae so that detectors can do their work is no easy task, but it’s heartening to this SETI skeptic that the capabilities of the Allen Array are wide. Tarter described them in a recent Space.com posting:

One of the good things about the ATA is that there are likely to be many stars that are visible at any one time within its large field of view, so with multiple beamformers, and multiple detectors, we can explore multiple stars simultaneously, at different frequencies if we want. Furthermore, we can do this while our astronomy colleagues are mapping the sky for hydrogen gas, or large biogenic molecules, or other phenomena of scientific interest to them. This multiplexing potential is a new and exciting innovation that will speed up the SETI searching in the next decades.

Thus, while a new generation of SETI signal detectors called SonATA (SETI on the ATA) goes through its shakedown (a recent success in tracking the relatively nearby Rosetta spacecraft was a success), we can continue to do interesting radio astronomy with the same instrumentation. That’s a satisfying situation in the context of continuing debate about SETI methods and the best ways to optimize our chances for finding the signal of an extraterrestrial civilization. And it points to the growing maturity of the kind of interferometry used here, linking numerous small antennae on the impressive new hardware of the growing Allen site.

Comments on this entry are closed.

  • Tibor November 11, 2008, 11:31


    this is a very interesting aspect of deep space probes. Related to this, I think it is worth to think about the following questions:

    * May ETI find / detect our spacecraft in deep space?
    * May ETI detect the communication signals we exchange with our deep space probe (in both directions, i.e. not only signals sent by the spacecraft back to Earth but signals sent from the Earth to the spacecraft as well)?

    I am wondering if there are any estimates of detectability of such a communication.

    Of course, the questions can be asked in the reverse mode as well: can we detect an ETI spacecraft?


  • Ron S November 11, 2008, 12:18

    Tibor, the signal power from any of our interplanetary spacecraft is quite low, perhaps on order of 100 watts or so. This is very insignificant in comparison to leakage from a large number of ordinary commercial sources on Earth. The only reason we can detect spacecraft is both the antennas on the spacecraft and on Earth are high-gain and pointed at each other. Of course if the power plant lasts and the spacecraft enters into a neighboring and occupied stellar system then…maybe.

    The technique being used at the Allen array is standard procedure for any instrument – to calibrate it against a known signal that challenges but does not exceed the capabilities of the instrument. Distant spacecraft are ideal for this.

  • ljk November 11, 2008, 13:28

    In addition to Sol type stars, we should also be looking at
    those objects at the edge of the Milky Way galaxy and beyond
    that only radiate in the infrared.

  • Tibor November 12, 2008, 15:05


    I agree with you on the signals we receive from a spacecraft now. But just for completeness, what about uplink signals, even if they are rare? Should not they be much stronger, perhaps comparable to planetary radar beacons? At least re transmission power, if not for duration. E.g., I would like to know how strong / long were the “awakening” signals sent to Pioneer 10 in the last contact attempts?

    Anybody out there with such knowledge?

  • ljk November 12, 2008, 15:39

    Seth Shostak is predicting an ETI detection within two decades:


  • Adam November 12, 2008, 19:15

    Hi All

    Larry, those infrared sources on the Rim, are you thinking they’re migratory ATCs like the Cirkovic/Bradbury scenario postulates? Alternatively looking for beacons towards the Core might work as per the Benford3 scenario. Hopefully the ATA can be used for both.

  • Ron S November 12, 2008, 22:08

    Here my summary of the salient words in the Universe Today article on Shostak that ljk referenced:

    “… could become … assuming … yet to be built … actually happens … estimated … assumptions … should be able … predicted … estimate …”

    Tibor, perhaps the best example are those occasions when a large dish with a powerful transmitter attached is used to catch the attention of a satellite or spacecraft that is tumbling or otherwise disoriented, since its own directional antenna pointed elsewhere makes the receiver somewhat deaf. I can vaguely recall Arecibo being used at least once this way. Sorry that I don’t know more. This would still, of course, be a stray and directional signal that would be most difficult to detect.

  • ljk November 12, 2008, 23:21

    I am thinking we should keep all our options open.

    I don’t necessarily have an issue with looking for signals
    from Sol-type star systems, but I also think that SETI
    needs to expand its scanning realms beyond what was
    laid down back in the 1960s and 1970s.

    Just as we can only find the largest planets around other
    suns at present, our current search levels will only allow
    us to find the more advanced technological cultures, thus
    we should assume such beings have moved beyond living
    on planets around G class stars. This means Dyson Shells
    and Matroishka/Jupiter Brains, as two examples.

    This includes looking for ETI probes in our Sol system,
    though admittedly if they wanted to hide from us in
    interplanetary space to observe us without disrupting
    our natural behavior, it would not be very difficult.

  • ljk November 13, 2008, 11:01

    Ron S., you are thinking of the SOHO satellite that was almost
    lost just over 10 years ago. Arecibo and the Deep Space Network
    were used to recover it and the craft is still returning images and
    data on Sol:


    Other methods of looking for ETI signals are to monitor supernovae,
    which would make great natural celestial beacons where a society
    might aim transmissions in the direction directly opposite to where
    a SN appears in space.



    Other celestial objects as SETI synchronizers:


  • ljk November 25, 2008, 10:50


    Two new SETI searches see first light

    November 21, 2008

    The Search for Extraterrestrial Intelligence is picking up steam. The folks over at the Berkeley SETI group now have 7 separate searches underway at infrared, visible and radio wavelengths.

    Today, Andrew Siemiona and pals outline the two newest programs which have recently seen first light and are hunting for pulses just a few hundred nanosceonds long. By contrast, most searches up till now have looked only for pulses a few seconds long.

    The first, a project called Fly’s Eye at the Allen Telescope Array in northern California, can watch huge areas of the sky up to 100 degrees square and spot pulses as short as 0.625 ms

    The second is called Astropulse at the Arecibo Observatory in Puerto Rico and will be 30 times more sensitive than any search gone before.

    The early results from these searches are being processed on the SETI@Home network which the authors claim is the second most powerful supercomputer on the planet.

    Nevertheless, it looks as if they have long hard slog ahead of them: ET hasn’t revealed herself just yet.

    Ref: arxiv.org/abs/0811.3046: New SETI Sky Surveys for Radio Pulses