According to the Math, it’s Highly Unlikely That an Intelligent Civilization is Located at Alpha Centauri

In December of 2020, the world got a bit of a pre-holiday surprise when it was announced that astronomers at the Parkes radio telescope in Australia had detected a “tantalizing” signal coming from Proxima Centauri (the red dwarf companion of the Alpha Centauri system). Afterward, researchers at Breakthrough Listen consulted the data on the signal – Breakthrough Listen Candidate 1 (BLC1) – and noted the same curious features.

However, the scientific community has since announced that the signal is unlikely to be anything other than the result of natural phenomena. This was also the conclusion reached by Amir Siraj and Prof. Abraham Loeb of Harvard University after they conducted a probability assessment on BLC1. Like the vast majority of candidate radio signals discovered to date, this one appears to be just the forces of nature saying hello.

Continue reading “According to the Math, it’s Highly Unlikely That an Intelligent Civilization is Located at Alpha Centauri”

The WOW Signal Probably Didn’t Come from Aliens, or Comets as You Recently Heard

On August 15th, 1977, astronomers using the Big Ear radio telescope at Ohio State University detected a 72-second radio signal coming from space. This powerful signal, which quickly earned the nickname the “Wow! signal”, appeared to be coming from the direction of the Sagittarius Constellation, and some went so far as to suggest that it might be extra-terrestrial in origin.

Since then, the Wow! signal has been an ongoing source of controversy among SETI researchers and astronomers. While some have maintained that it is evidence of extra-terrestrial intelligence (ETI), others have sought to find a natural explanation for it. And thanks a team of researchers from the Center of Planetary Science (CPS), a natural explanation may finally have been found.

In the past, possible explanations have ranged from asteroids and exoplanets to stars and even signals from Earth – but these have all been ruled out. And then in 2016, the Center for Planetary Science – a Florida-based non-profit scientific and astronomical organization – proposed a hypothesis arguing that a comet and/or its hydrogen cloud could be the cause.

This was based on the fact that the Wow! signal was transmitting at a frequency of 1,420 MHz, which happens to be the same frequency as hydrogen. This explanation was also appealing because the movement of the comet served as a possible explanation for why the signal has not been detected since. To validate this hypothesis, the CPS team reportedly conducted 200 observations using a 10-meter radio telescope.

This telescope, they claim, was equipped with a spectrometer and a custom feed horn designed to collect a radio signal centered at 1420.25 MHz. Between Nov. 27th, 2016, and Feb. 24th, 2017, they monitored the area of space where the Wow! signal was detected, and found that a pair of Solar comets (which had not been discovered in 1977) happened to conform to their observations, and could therefore have been the source.

Spectra obtained from these comets – P/2008 Y2(Gibbs) and 266/P Christensen – indicated that they were emitting a radio frequency that was consistent with the Wow! signal. As Antonio Paris (a professor at the CPS), described in a recent paper that appeared in the Journal of the Washington Academy of Sciences:

“The investigation discovered that comet 266/P Christensen emitted a radio signal at 1420.25 MHz. All radio emissions detected were within 1° (60 arcminutes) of the known celestial coordinates of the comet as it transited the neighborhood of the ‘Wow!’ Signal. During observations of the comet, a series of experiments determined that known celestial sources at 1420 MHz (i.e., pulsars and/or active galactic nuclei) were not within 15° of comet 266/P Christensen.”

The Wow! signal represented as “6EQUJ5”. Credit: Big Ear Radio Observatory/NAAPO

The team also examined three other comets to see if they emitted similar radio signals. These comets – P/2013 EW90 (Tenagra), P/2016 J1-A (PANSTARRS), and 237P/LINEAR – were selected randomly from the JPL Small Bodies database, and were confirmed to emit a radio signal at 1420 MHz. Therefore, the results of this investigation conclude that the 1977 “Wow!” Signal was a natural phenomenon from a Solar System body.

However, not everyone is convinced. In response to the paper, Yvette Cendes – a PhD student with the Dunlap Institute at the University of Toronto – wrote a lengthy response on reddit as to why it fails to properly address the Wow! signal. For starters, she cites how the research team measured the signal strength in terms of decibels:

“I have never, ever, EVER used dB in a paper, nor have I ever read a paper in radio astronomy that measured signal strength in dB (except perhaps in the context of an instrumentation paper describing the systems of a radio telescope, i.e. not science but engineering.) We use a different unit in astronomy for flux density, the Jansky (Jy), where 1 Jy= ?230 dBm/(m2·Hz). (dB is a log scale, and Janskys are not.)”

Another point of criticism is the lack of detail in the paper, which would make reproducing the results very difficult – a central requirement where scientific research is concerned. Specifically, they do not indicate where the 10-meter radio telescope they used came from – i.e. which observatory of facility it belonged to, or even if it belonged to one at all – and are rather vague about its technical specification.

Spectra obtained from an area in the direction of the Sagittarius constellation. Credit: The Center for Planetary Science

Last, but not least, there is the matter of the environment in which the observations took place, which are not specified. This is also very important for radio astronomy, as it raised the issue of interference. As Cendes put it:

“This might sound pedantic, but this is insanely important in radio astronomy, where most signals we ever search for are a tiny fraction of the man-made ones, which can be millions of times brighter than an astronomical signal. (A cell phone on the moon would be one of the brighter radio astronomy sources in the sky, to give you an idea!) Radio Frequency Interference (RFI) is super important for the field, so much that people can spend their careers on it (I’ve written a chapter on my thesis on this myself), and the “radio environment” of an observatory can be worth a paper in itself.”

Beyond these apparent incongruities, Cendes also states that the hypothesis for the experiment was flawed. Essentially, the Big Ear searched for the same signal for a period of 22 years, but found nothing. If the comet hypothesis held true, there should be an explanation as to why no trace of the signal was found until this time. Alas, one is lacking, as far as this most recent study is concerned.

“And now you likely have an idea on why one-off events are so hard to prove in science,” she claims. “But then, this is really the major reason the Wow! signal is unsolved to this day- without a plausible explanation, [without] additional data, we just will never know.”

Though it may be hard to accept, it is entirely possible that we may never know what the Wow! signal truly was – whether it was a one-off event, a naturally-occurring phenomena, or something else entirely. And if the comet hypothesis should prove to be unverifiable, then that is certainly good news for the SETI enthusiasts!

While the elimination of natural explanations doesn’t prove that things like Wow! signal are proof of alien civilizations, it at least indicates that this possibility cannot be ruled out just yet. And for those hopeful that evidence of intelligent life will be someday found, that’s really the best we can hope for… for now!

Further Reading: Journal of the Washington Academy of Sciences, Astronomer Here!

Weekly Space Hangout – June 9, 2017: Dr. Jeffrey Forshaw Presents “Universal: A Guide to the Cosmos”

Host: Fraser Cain (@fcain)

Special Guest:
Dr. Jeffrey Forshaw is a British particle physicist with an interest in quantum chromodynamics (QCD) which is the study of the behavior of subatomic particles. Dr. Forshaw is the co-author (with Brian Cox) of Universal: A Guide to the Cosmos, which sends readers on an inspirational journey of scientific exploration.


Sarah Marquart ( / @SagaofSarah)

Their stories this week:

ALMA Finds Ingredient of Life Around Infant Sun-like Stars

Wow! Mystery Signal From Space Finally Explained

We use a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (, which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!


The WSH recently welcomed back Mathew Anderson, author of “Our Cosmic Story,” to the show to discuss his recent update. He was kind enough to offer our viewers free electronic copies of his complete book as well as his standalone update. Complete information about how to get your copies will be available on the WSH webpage – just visit for all the details.

If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Universe Today, or the Universe Today YouTube page

‘Wow!’ Signal Was…Wait For It…Comets

The Wow! signal. Credit: Big Ear Radio Observatory and North American AstroPhysical Observatory (NAAPO)
The Wow! signal recorded on August 15, 1977. The ones, twos and threes indicate weak background noise. Letters, especially those closer to the end of the alphabet, represent stronger signals. The “6EQUJ5” is read from top to bottom (see graph below) and shows the signal rising from “6” to “U” before dropping back down to “5”. Credit: Big Ear Radio Observatory and North American AstroPhysical Observatory (NAAPO)

Comets get blamed for everything. Pestilence in medieval Europe? Comets! Mass extinctions? Comets! Even the anomalous brightness variations in the Kepler star KIC 8462852 was blamed for a time on comets. Now it looks like the most famous maybe-ET signal ever sifted from the sky, the so-called “Wow!” signal, may also be traced to comets.

Say it ain’t so!

The Big Ear Observatory, on the grounds of Ohio Wesleyan University, operated from 1963-1998. It was part of Ohio State University's long-running Search for Extraterrestrial (SETI) program. The observatory was torn down in 1998 to make room for a golf course. Credit: / NAAPO
The Big Ear Observatory, on the grounds of Ohio Wesleyan University, operated from 1963-1998. It was part of Ohio State University’s long-running Search for Extraterrestrial (SETI) program. The observatory was torn down in 1998 to make room for a golf course. Credit: / NAAPO

In August 1977, radio astronomer Jerry Ehman was looking through observation data from the Ohio State’s now-defunct Big Ear radio telescope gathered a few days earlier on August 15. He was searching for signals that stood apart from the background noise that might be broadcast by an alien civilization. Since hydrogen is the most common element in the universe and emits energy at the specific frequency of 1420 megahertz (just above the TV and cellphone bands), aliens might adopt it as the “lingua franca” of the cosmos. Scientists here on Earth concentrated radio searches at and around that frequency looking for strong signals that mimicked hydrogen.

Ehman’s searches turned up mostly background noise, but that mid-August night he spotted a surprise — a vertical column with the alphanumerical sequence “6EQUJ5″ that indicated a strong signal at hydrogen’s frequency. Exactly as predicted. Big Ear picked up the signal from near the 5th magnitude star Chi-1 Sagittarii in eastern Sagittarius not far from the globular cluster M55.

Astonished by the find, Ehman pulled out a red pen, circled the sequence and wrote a big “Wow!” in the margin. Ever since, it’s been called the Wow! signal and considered one of the few signals from space that defies explanation. Before we look at how that may change, let’s make sense of the code.

Plot of signal strength vs time of the Wow! signal on August 15, 1977. Credit: Maksim Rossomakhin
Plot of signal strength vs time of the Wow! signal on August 15, 1977. The signal rose and fell during the 72 seconds observation window. Credit: Maksim Rossomakhin

Each digit on the chart corresponded to a signal intensity from 0 to 35. Anything over “9” was represented by a letter from A to Z. It was probably the “U” that knocked Ehman’s socks off, since it indicated to a radio burst 30 times greater than the background noise of space.

In Big Ear’s 35 years of operation, it was the most intense, unexplainable signal ever recorded. What’s more, it was narrowly focused and very close to hydrogen’s special frequency.

Big Ear listened for just 72 seconds before Earth’s rotation carried the signal’s location out of “view” of antenna.  Since the radio array had two feed horns, the transmission was expected to appear three minutes apart in each of the horns, but only a single one ever picked it up.

Despite follow-up observations by Ehman and others (more than 100 studies were made of the region) the signal was gone. Never heard from again. Nor has anything else like it ever been recorded anywhere else in the sky.

Careful scrutiny eliminated earthbound possibilities such as aircraft or satellites. Nor would anyone have been transmitting at 1420 MHz since it was within a protected part of the radio spectrum used by astronomers and off-limits to regular broadcasters. The nature of the signal implied a point source somewhere beyond the Earth. But where?

On August 15, 1977, periodic comets 266P/Christensen and 335P/Gibbs would have both been very close to the small swath of sky south of Chi Sagittarii where the Wow! signal was received. Diagram: Bob King, source: Stellarium
On August 15, 1977, periodic comets 266P/Christensen and 335P/Gibbs would have both been very close to the narrow swath of sky south of Chi Sagittarii where the Wow! signal was received. Could they be implicated? Diagram: Bob King, source: Stellarium

If it really was an attempt at alien contact, why try only once and for so short a time interval? Even Ehman doubted (and still doubts) an extraterrestrial intelligence origin, but a much more recent suggestion made by Prof. Antonio Paris of St. Petersburg College, Florida may offer an answer. Paris earlier worked as an analyst for the U.S. Department of Defense and returned to the “scene of the crime” looking for any likely suspects. After studying astronomical databases, he discovered that two faint comets,  266P/Christensen and 335P/Gibbs, discovered only within the past decade, had been plying the very area of the Wow! signal on August 15, 1977.

A huge cloud of hydrogen surrounded Comet Hale-Bopp when it neared the Sun in the spring of 1997. Ultraviolet light, charted by the SWAN instrument on the SOHO spacecraft, revealed a cloud 100 million kilometres wide and diminishing in intensity outwards (contour lines). It far exceeded the great comet's visible tail (inset photograph). Although generated by a comet nucleus perhaps 40 kilometres in diameter, the hydrogen cloud was 70 times wider than the Sun itself (yellow circle to scale)
A huge cloud of hydrogen surrounded Comet Hale-Bopp when it neared the Sun in 1997. Ultraviolet light, charted by the SWAN instrument on the SOHO spacecraft, revealed that the cloud far exceeded the great comet’s visible tail (inset photo) —  70 times wider than the Sun itself (yellow circle to scale at right). Credit: SOHO (ESA & NASA) and SWAN Consortium / inset: Dennis di Cicco

If you recall, a comet has two or three basic parts: a fuzzy head or coma and one or two tails streaming off behind. Invisible to earthbound telescopes, but showing clearly in orbiting telescopes able to peer into ultraviolet light, the coma is further wrapped in a huge cloud of neutral hydrogen gas.

As the Sun warms a comet’s surface, water ice or H2O vaporizes from its nucleus. Energetic solar UV light breaks down those water molecules into H2 and O. The H2 forms a huge, distended halo that can expand to many times the size of the Sun.

Paris published a paper earlier this year exploring the possibility that the hydrogen envelopes of either or both comets were responsible for the strong 1420 MHz signal snagged by Big Ear. On the surface, this makes sense, but not all astronomers agree. First off, if comets are so radio-bright in hydrogen light, why don’t radio telescopes pick them up more often? They don’t. Second, some astronomers doubt that the signals from these comets would have been strong enough to be picked up by the array.

image of the full page of the computer printout that contains the "Wow!" signal. Credit:
Image of the full page of the computer printout that contains the “Wow!” signal. Credit: Big Ear Radio Observatory and North American AstroPhysical Observatory (NAAPO)

A quick check on 266P and 335P at the time of the signal show them both around 5 a.u. from the sun (Jupiter’s distance) and extremely faint at magnitudes 22 and 27 respectively. Were they even active enough at those distances to form clouds big enough for the antenna to detect?

Paris knows there’s only one way to find out. Comet 266P/Christensen will swing through the same area again on Jan. 25, 2017, while 335P/Gibbs follows suit on January 7, 2018. Unable to use an existing radio telescope (they’re all booked up!), he’s begun a gofundme campaign to purchase and install a 3-meter radio telescope to track and analyze the spectra of these two comets. The goal is $20,000 and Paris is already well on his way there.

It would be a little bit sad if the Wow! signal turned out to be a “just a comet”, but the possibility of solving a 39-year-old mystery would ultimately be more satisfying, don’t you think?

A Fine Pair of Lunar Occultations for North America This Weekend

Heads up, North American residents: our Moon is about to blot out two naked eye stars on Friday and Saturday night.

Such an event is known as an occultation, an astronomical term that has its hoary roots in astronomy’s pseudoscience ancestor of astrology. An occultation is simply when one astronomical body passes in front of another from our line of sight. There’s nothing quite like watching a star disappear on the dark limb of the Moon. In a universe where events often transpire over periods of time longer than a human life span, occultations are abrupt affairs to witness.

Close double stars have also been teased out of occultation data, winking out in a quick, step-wise fashion. If an occultation such as the two this weekend occurs while the Moon is waxing towards Full, we get the added advantage of watching the action on the leading dark limb of the Moon during convenient early evening hours.

Beta Capricorni on the dark limb of the Moon Saturday night. (Created by the author using Starry Night).
Beta Capricorni on the dark limb of the Moon Saturday night. (Created by the author using Starry Night).

First up is the occultation of the +3.9th magnitude star Rho Sagittarii on Friday night, October 11th. Central conjunction for this occultation occurs at 00:40 Universal Time (UT) early on the morning of the 12th. The Moon will be at a 51% illuminated waxing gibbous phase, having passed First Quarter just prior to the start of the occultation at 7:02 PM EDT/23:02 UT on the 11th. The sunset terminator line at the start of the occultation will bisect the central U.S., and observers east of the Mississippi will get to witness the entire event. The southern graze line will cross Cuba and Guatemala. Note that the Moon will also pass its most southern declination for this lunation just two days prior on October 9th at 23:00 UT/7:00 PM EDT, at a declination of -19.6 degrees.  This is one of the Moon’s most southern journeys for 2013, meaning that it will still ride fairly far to the south in the sky during this weekend’s occultations.

The occultation of Rho Saggitarii by the Moon for the night of October 11th. (rendered using Occult 4.1.02 software).
The occultation of Rho Sagittarii by the Moon for the night of October 11th. the dashed line indicates where the occultation will occur in the daytime; east of this region, the occultation occurs after sunset. (rendered using Occult 4.1.02 software).

Rho Sagittarii is an F-type star 122 light years distant. Stick around until February 23rd, 2046, and you’ll get to see an even rarer treat, when the planet Venus occults the very same star. Just south of the Rho Sagittarii pair lies the region from which the Wow! Signal was detected in 1977.

The Moon moves at an average speed of just over a kilometre a second in its orbit about the Earth, and traverses roughly the apparent distance of its angular size of 30’ in one hour. The duration of occultations as seen from their center line take about an hour from ingress to egress, though its much tougher to watch a star reappear on the bright limb of the Moon!

And the night of Saturday, October 12th finds the 62% illuminated waxing gibbous Moon occulting an even brighter star across roughly the same region. The star is +3.1 magnitude Beta Capricorni, which also goes by the Arabic name of Dabih, meaning “the butcher.”  Dabih is also an interesting double star with a +6th magnitude component 3.5’ away from the +3rd magnitude primary. Dabih is an easy split with binoculars, and it will be fun to watch the two components pass behind the Moon Saturday night. This occultation also occurs the night of October 12th which is traditionally Fall Astronomy Day. If you’re hosting a star party this coming Saturday night, be sure to catch the well-timed occultation of Beta Capricorni! The central conjunction for this event occurs at 01:27 UT on the morning of the 13th, and North American observers east of the Rockies will get to see the entire event.

(Rendered using Occult software).
The occultation footprint of Beta Capricorni for the night of October 12th. (Rendered using Occult software).

Beta Capricorni is 328 light years distant, putting the physical separation of the B component at about a third of a light year away from the primary star at 21,000 astronomical units distant. “Beta B” thus takes about 700,000 years to orbit its primary! It’s also amazing to think that those fusion-born photons took over three centuries to get here, only to be rudely “interrupted” by the bulk of our Moon in the very last second of their journey.

And be sure to keep an eye on the primary star as it winks out, as it’s a known spectroscopic triple star with unseen companions in respective 9 and 1374 day orbits. Dabih may just appear to “hang” on the jagged lunar limb as those close companions wink out in a step-wise fashion.

Both occultations are bright enough to watch with the naked eye, although a standard set of 10x 50 binoculars will provide a fine view. The ingress of an occultation is also an excellent event to catch on video, and if you’ve got WWV radio running audio in the background, you can catch the precise time that the star disappears from your locale.

Note: WWV radio is still indeed broadcasting through the ongoing U.S. government shutdown, though they’re operated by NOAA & the NIST.

The International Occultation and Timing Association is always interested in reports of occultations carried out by amateur astronomers. Not only can this reveal or refine knowledge of close double stars, but a series of occultation observations from precisely known locations can map the profile of the lunar limb.

Be sure to catch both events this U.S. Columbus Day/Canadian Thanksgiving Day weekend, and send those pics in to Universe Today!

Precise timings for the ingress and egress of each lunar occultations for major North American cities can be found at the following pages:

– Rho Sagittarii

– Beta Capricorni

35 Years Later, the ‘Wow!’ Signal Still Tantalizes


Since the SETI program first began searching for possible alien radio signals a few decades ago, there have been many false alarms but also instances of fleeting signals of interest which disappeared again as quickly as they had appeared. If a potential signal doesn’t repeat itself so it can be more carefully observed, then it is virtually impossible to determine whether it is of truly cosmic origin. One such signal in particular caught astronomers’ interest on August 15, 1977. The famous “Wow!” signal was detected by the Big Ear Radio Observatory at Ohio State University; it was thirty times stronger than the background noise but lasted only 72 seconds and was never heard again despite repeated subsequent searches.

In a new book titled The Elusive Wow, amateur astronomer Robert Gray chronicles the quest for the answer to this enduring puzzle.

When the signal was first seen in the data, it was so pronounced that SETI scientist Jerry Ehman circled it on the computer printouts in red ink and wrote “Wow!” next to it. It appeared to fit the criteria for an extraterrestrial radio signal, but because it wasn’t heard again, the follow-up studies required to either confirm or deny this were not possible. So what was it about the signal that made it so interesting?

First, it did appear to be an artificial radio signal, rather than a natural radio emission such as a pulsar or quasar. The Big Ear telescope used a receiver with 50 radio channels; the signal was only heard on one frequency, with no other noise on any of the other channels. A natural emission would cause static to appear on all of the frequencies, and this was not the case. The signal was narrow and focused, as would be expected from an artificial source.

The Big Ear Radio Observatory. Credit: Big Ear Radio Observatory / North American AstroPhysical Observatory / Ohio State University

The signal also “rose and fell” during the 72 seconds, as would be expected from something originating in space. When the radio telescope is pointed at the sky, any such signal will appear to increase in intensity as it first moves across the observational beam of the telescope, then peak when the telescope is pointed straight at it and then decrease as it moves away from the telescope. This also makes a mere computer glitch a less likely explanation, although not impossible.

What about satellites? This would seem to be an obvious possible explanation, but as Gray notes, a satellite would have to be moving at just the right distance and at just the right speed, to mimic an alien signal. But then why wasn’t it observed again? An orbiting satellite will broadcast its signal repeatedly. The signal was observed near the 1420 MHz frequency, a “protected spectrum” in which terrestrial transmitters are forbidden to transmit as it is reserved for astronomical purposes.

There may be a bias in thinking that any alien signals will be like ours which leak out to space continuously, ie. all of our radio and TV broadcasts. That is, “normal” radio emissions from every-day type technologies which could easily be seen on an ongoing basis. But what if they were something more like beacons, sent out intentionally but only on a periodic basis? As Gray explains, radio searches to date have tended to look at many different spots in the sky, but they will only examine any particular spot for a few minutes or so before moving on to the next. A periodic signal could easily be missed completely, or if seen, it may be a long time before it is seen again.

Of course, it is also possible that any other civilizations out there might not even use radio at all, especially if they are more advanced than us (while other intelligent life might be behind us, as well). A newer branch of SETI is now searching for artificial sources of light, like laser beams, used as beacons.

So where does this leave us? The “Wow!” signal still hasn’t been adequately explained, although various theories have been proposed over the years. Perhaps one day it will be observed again, or another one like it, and we will be able to solve the mystery. Until then, it remains a curiosity, a tantalizing hint of what a definite signal from an extraterrestrial civilization might look like.

More information is available at the Big Ear Radio Observatory website.