Astronomers have expanded the search for extraterrestrial intelligence into a new realm with detectors tuned to infrared light.

The idea was first proposed by Charles Townes, the late UC Berkeley scientist whose contributions to the development of lasers led to a Nobel Prize, in a paper [1] published in 1961.

Pulses from a powerful near-infrared laser could outshine a star, if only for a billionth of a second. Interstellar gas and dust is almost transparent to near-infrared, so these signals can be seen from greater distances. It also takes less energy to send the same amount of information using infrared signals than it would with visible light.

Scientists have searched for radio signals for more than 50 years and expanded their search to the optical realm more than a decade ago. But instruments capable of capturing pulses of infrared light have only recently become available.

“We had to wait for technology to catch up,” said Shelley Wright, an Assistant Professor of Physics at the University of California, San Diego who led the development of the new instrument while at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics.

The new instrument, called NIROSETI (near-infrared optical SETI), will also gather more information than previous optical detectors by recording levels of light over time so that patterns can be analyzed to for potential signs of other civilizations.

NIROSETI has been installed at the University of California’s Lick Observatory on Mt. Hamilton east of San Jose and saw first light on March 15. Lick Observatory has been the site of several previous SETI searches, including an instrument to look in the optical realm, which Wright built as an undergraduate student at UC Santa Cruz.

Near-infrared dramatically extends search for ET



Because near-infrared light penetrates farther through gas and dust than visible light, this new search will extend to stars thousands rather than merely hundreds of light years away.

Also, the success of the Kepler Mission, which has found habitable planets orbiting stars both like and unlike our own, has prompted the new search to look for signals from a wider variety of stars. Last week, researchers from the Australian National University and the Niels Bohr Institute in Copenhagen announced that new calculations show that billions of the stars in the Milky Way will have one to three planets in the habitable zone (where there is the potential for liquid water and thus where life could exist).

NIROSETI could uncover new information about the physical universe as well. “This is the first time Earthlings have looked at the universe at infrared wavelengths with nanosecond time scales,” said SETI scientist and optical SETI pioneer Dan Werthimer of UC Berkeley, a key NIROSETI researcher. “The instrument could discover new astrophysical phenomena, or perhaps answer the question of whether we are alone.”

The group also includes famed SETI pioneer Frank Drake of the SETI Institute and UC Santa Cruz, who serves as a senior advisor to both past and future projects and is an active observer at the telescope.

Drake pointed out several additional advantages to a search in this new realm. “The signals are so strong that we only need a small telescope to receive them. Smaller telescopes can offer more observational time, and that is good because we need to search many stars for a chance of success.” he said. The receivers are also much more affordable that those used on radio telescopes.

“There is only one downside: the extraterrestrials would need to be transmitting their signals in our direction,” Drake said, though he sees a positive side to that limitation. “If we get a signal from someone who’s aiming for us, it could mean there’s altruism in the universe. I like that idea. If they want to be friendly, that’s who we will find.”

Or perhaps it could mean there’s someone out there looking to harm us, as Stephen Hawking has warned.

Funding for the project is from Bill and Susan Bloomfield.

How NIROSETI works

The search for extraterrestrial signals (SETI) began in 1960, when Frank Drake searched for microwave radio waves at a microwave “waterhole” frequency of 1,420 MHz (21 cm). In 1997, Werthimer’s group at UC Berkeley extended the search, testing the first pulsed multiple detector system in the optical (light) domain and launching “optical SETI” (OSETI).

NIROSETI has now taken the next step. NIROSETI is a telescope designed to detect pulsed laser signals emitted at specific near-infrared wavelengths (900 to 1700 nm, longer than visible light). The assumption is that a distant civilization could signal its existence by transmitting a code consisting of two or more extremely short laser pulses in a period less than .5 nanosecond and at extremely high power (enough to exceed the light emitted from their sun for that very brief period of time to rule out the sun as a source).

The NIROSETI project is described in detail in the journal SPIE Proceedings [2] and in an open-access arXiv version [3] of the paper.

Abstract of A near-infrared SETI experiment: probability distribution of false coincidences

A Search for Extraterrestrial Life (SETI), based on the possibility of interstellar communication via laser signals, is being designed to extend the search into the near-infrared spectral region (Wright et al, this conference). The dedicated near-infrared (900 to 1700 nm) instrument takes advantage of a new generation of avalanche photodiodes (APD), based on internal discrete amplification. These discrete APD (DAPD) detectors have a high speed response (< 1 GHz) and gain comparable to photomultiplier tubes, while also achieving significantly lower noise than previous APDs. We are investigating the use of DAPD detectors in this new astronomical instrument for a SETI search and transient source observations. We investigated experimentally the advantages of using a multiple detector device operating in parallel to remove spurious signals. We present the detector characterization and performance of the instrument in terms of false positive detection rates both theoretically and empirically through lab measurements. We discuss the required criteria that will be needed for laser light pulse detection in our experiment. These criteria are defined to optimize the trade between high detection efficiency and low false positive coincident signals, which can be produced by detector dark noise, background light, cosmic rays, and astronomical sources. We investigate experimentally how false coincidence rates depend on the number of detectors in parallel, and on the signal pulse height and width. We also look into the corresponding threshold to each of the signals to optimize the sensitivity while also reducing the false coincidence rates. Lastly, we discuss the analytical solution used to predict the probability of laser pulse detection with multiple detectors.