SETI “Wow!” Signal Wasn’t Chatty Aliens After All — It Was a Fizzing Comet

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Big Ear Radio Observatory

On Aug. 15, 1977 at 10:16 p.m. ET Ohio State University’s Big Ear radio telescope detected a curious signal from deep space. Nearly 40 years later, we finally know what caused it and, sadly, it’s not aliens.

For decades, the signal has been the strongest piece of “go-to” evidence that intelligent extraterrestrials are out there in our galaxy. When found by astronomer Jerry Ehman on that fateful night, the 72-second signal — that had been recorded on a computer printout — certainly stood out.

While pointing at three star systems called Chi Sagittarii in the constellation of Sagittarius, Big Ear had picked up a powerful burst of radio waves. To the untrained eye, the assortment of printed digits might not mean much, but as I wrote in 2016, those letters and numbers could hold the answer to the biggest question we’re currently asking of the universe: Are we alone?

The Big Ear printout contains a bunch of apparently random numbers and letters, but Ehman’s red pen circles a cluster of digits “6EQUJ5” with other circles around a “6” and “7” on separate columns. This particular code first uses the numbers 1-9 and then the alphabet A-Z to denote signal strength. As the burst suggests, the signal strength hit “6” and then blasted through the letters reaching a peak of “U” before subsiding back into the numerical scale at “5.” There was then a slight wave trailing the main signal (hence the circled “6″ and “7″). The wave profile of the “Wow!” signal is graphically envisaged here. (Discovery News, April 18, 2016)

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Maksim Rossomakhin

The maddening thing about the Wow! signal has always been a lack of replication. To science, one random signal in the dark proves nothing. It would be like trying to plot a trend line on a graph with one data point. More data is obviously needed and yet, since 1977, there’s been no other radio signal quite like it.

Curious, yes. Definite proof of chatty aliens? A solid nope.

So, when researching other possible causes of the Wow! signal that were also rare occurrences (but not aliens), Antonio Paris of St Petersburg College, Fla. (and an ex-analyst of the US Department of Defense), suggested that the signal might have been generated by one of two comets that serendipitously drifted into the line of sight of the Big Ear radio telescope.

In 1977, neither 266P/Christensen and 335P/Gibbs were known of (they were discovered in 2006 and 2008 respectively) and Paris calculated that both comets would have been in the right place in the sky when the Wow! signal was recorded.

What’s more, the Wow! signal has a frequency of 1420MHz — the same frequency that neutral hydrogen radiates at. Hydrogen is abundant in our universe, so this frequency is commonly observed in astronomy.

At first blush, observing in this frequency to look for alien transmissions might seem like a fool’s errand; if the universe is humming in hydrogen noise, why would aliens bother using that frequency to ping their extraterrestrial neighbors?

Through SETI logic, the frequency of neutral hydrogen might be used by advanced civilizations as a kind of interstellar water cooler. It is the most abundant signal in the universe, every intelligent life-form would know this. So why not use 1420MHz as THE frequency to communicate across the light-years in hopes that other civilizations might already be tuned in?

But a SETI signal would need to stand out from the crowd — it would need to be powerful and possess other qualities that hint at its artificial nature. But should a comet quickly pass through the observing window of a radio telescope, Paris predicted that the received 1420MHz signal might mimic that of an artificial source.

And this year, an opportunity presented itself. Comet 266P/Christensen would pass through the sky in a similar orbital position as it did in 1977. During an observing campaign from November 2016 to February 2017, Paris studied the radio frequencies coming from the region and from the comet itself. He also compared these observations with other known comets.

The upshot: 266P is indeed producing a strong 1420MHz signal, as are other comets.

“The results of this investigation, therefore, conclude that cometary spectra are detectable at 1420 MHz and, more importantly, that the 1977 “Wow!” Signal was a natural phenomenon from a solar system body,” he writes in a study published in the Journal of the Washington Academy of Sciences

It appears that, in this case, the signal wasn’t aliens trying to make contact with us; it was a chance comet that just happened to be in the right place at the right time.

So, back to that alien megastructure

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NASA Uses Gravitational Wave Detector Prototype to Detect ‘Space Mosquito’ Splats

Artist impression of ESA LISA Pathfinder in interplanetary space (ESA)

Imagine speeding down the highway and plowing into an unfortunate swarm of mosquitoes. Now imagine that you had the ability to precisely measure the mass of each mosquito, the speed at which it was traveling and the direction it was going before it exploded over your windscreen.

Granted, the technology to accomplish that probably isn’t feasible in such an uncontrolled environment. Factors such as vibration from the car’s motor and tires on the road, plus wind and air turbulence will completely drown out any “splat” from a minuscule insect’s body, rendering any signal difficult to decipher from noise.

But move your hypothetical “car and mosquitoes” into space — as silly as that may sound — and things become a lot less noisy. And now NASA is measuring its own special kind of “mosquito splat” signal by using a rather unlikely space experiment.

The European LISA Pathfinder spacecraft is a proof of concept mission that’s currently in space, orbiting a region of gravitational stability between the Earth and the sun — called the L1 point located a million miles away. The spacecraft was launched there in late 2015 to carry out precision tests of instruments that will eventually be used in the space-based gravitational wave detector eLISA. Inside the payload is a miniaturized laser interferometer system that measures the distance between two test masses.

When launched in 2034, eLISA (which stands for Evolved Laser Interferometer Space Antenna) will see three spacecraft, orbiting the sun at the L1 point, firing ultra-precise lasers at one another as part of a space-based gravitational wave detector. Now we actually know gravitational waves exist — after the US-based Laser Interferometer Gravitational-wave Observatory (or LIGO) detected the space-time ripples created after the collisions of black holes — excitement is building that we might, one day, be able to measure other phenomena, such as the ultra-low frequency gravitational waves that were created during the Big Bang.

But the only way we can do this is to send stunningly precise interferometers into space, away from our vibration-filled atmosphere to stand a chance of detecting some of the faintest space-time rumbles in our cosmos that would otherwise be drowned out by a passing delivery truck or windy day. And LISA Pathfinder is currently out there, testing a tiny laser interferometer in a near-perfect gravitational free-fall, making the slightest of slight adjustments with its “ultra-precise micro-propulsion system.”

Although LISA Pathfinder is a test (albeit a history-making test of incredible engineering ingenuity), NASA thinks that it could actually be used as an observatory in its own right; not for hunting gravitational waves, but for detecting comet dust.

Like our mosquito-windscreen analogy, spacecraft get hit by tiny particles all the time, and LISA Pathfinder is no exception. These micrometeoroides come from eons of evaporating comets and colliding asteroids. Although measuring less than the size of a grain of sand, these tiny particles zip around interplanetary space at astonishing speeds — well over 22,000 miles per hour (that’s 22 times faster than a hyper-velocity rifle round) — and can damage spacecraft over time, slowly eroding unprotected hardware.

Therefore, it would be nice if we could create a map of regions in the solar system that contain lots of these particles so we can be better prepared to face the risk. Although models of solar system evolution help and we can estimate the distribution of these particles, they’ve only ever been measured near Earth, so it would be advantageous to find the “ground truth” and measure them directly from another, unexplored region of the solar system.

This is where LISA Pathfinder comes in.

As the spacecraft gets hit by these minuscule particles, although they are tiny, their high speed ensures they pack a measurable punch. As scientists want the test weights inside the spacecraft to be completely shielded from any external force — whether that’s radiation pressure from the sun or marauding micro-space rocks — the spacecraft has been engineered to be an ultra-precise container that carefully adjusts its orientation an exact amount to directly counter these external forces (hence the “ultra-precise micro-propulsion system”).

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When LISA Pathfinder is struck by space dust, it compensates with its ultra-precise micro-thrusters (ESA/NASA)

This bit is pretty awesome: Whenever these tiny space particles hit the spacecraft, it compensates for the impact and that compensation is registered as a “blip” in the telemetry being beamed back to Earth. After careful analysis of the various data streams, researchers are learning a surprising amount of information about these micrometeoroides — such as their mass, speed, direction of travel and even their possible origin! — all for the ultimate goal of getting to know the tiny pieces of junk that whiz around space.

“Every time microscopic dust strikes LISA Pathfinder, its thrusters null out the small amount of momentum transferred to the spacecraft,” said Diego Janches, of NASA’s Goddard Space Flight Center in Greenbelt, Md. “We can turn that around and use the thruster firings to learn more about the impacting particles. One team’s noise becomes another team’s data.”

So, it turns out that you can precisely measure a mosquito impact on your car’s windshield — so long as that “mosquito” is a particle of space dust and your “car” is a spacecraft a million miles from Earth.

NASA put together a great video, watch it:

Aside: So it turned out that I inadvertently tested the “car-mosquito” hypothesis when driving home from Las Vegas — though some of these were a lot bigger than mosquitoes…

When Stardust Met Tempel, a Love Story

Comet Tempel 1 near Stardust-NExT close approach (NASA)
Comet Tempel 1 near Stardust-NExT close approach (NASA)

A NASA spacecraft, a lonely comet and a Valentine’s date with no comparison.

Last night, NASA’s veteran Stardust-NExT mission successfully visited its second comet, Tempel 1. Having already been visited by NASA’s Deep Impact mission in 2005, it’s hard not to wonder whether Tempel 1 was a little apprehensive. Deep Impact did lob a refrigerator-sized copper impactor into the comet’s surface during the 2005 encounter, so I think we can forgive the comet some pre-date jitters.

Fortunately, Stardust was the perfect date (no impactors, silverware, dishes or bottles were thrown), just a peaceful flyby, during which the spacecraft beamed dozens of photos back to Earth. To quote Joe Veverka, Stardust-NExT principal investigator: “It was 1,000 percent successful!”

Alas, although the date was a success, there won’t be the sound of wedding bells any time soon. Stardust is now powering away from the comet at a breakneck speed. Was it something Tempel 1 said?

For more on this Valentine’s rendezvous, have a read of my Discovery News article “Stunning Photos from a Comet Near-Kiss.”

Oh yes, and I got bored, so I created a rough animation of the flyby. Enjoy!