This video is sponsored by Magellan TV.
Welcome back to Launch Pad, I'm Christian Ready, your friendly neighborhood astronomer.
And I'm sure by now, you probably have heard that astronomers have detected an alien signal
coming from the closest star to our solar system.
Or more than likely, they did not. It's a very interesting bit of news but there's a
lot more we don't yet know publicly. That's because the story was leaked to the Guardian
before the science team completed their analysis. We don't really. know who leaked the information,
but astronomers with the Breakthrough Listen Initiative - who are working on the signal
- did confirm the information in the leak is correct.
It was, apparently, a radio-loud, narrowband signal broadcast designated BLC-1 for "Breakthrough
Listen Candidate 1".
Now to be clear, the most likely explanation is that BLC-1 is just some new kind of radio
interference from human technology and not an actual alien signal. But then again, there
are other characteristics about this signal that are really strange, and it seems like
what they found was exciting enough to get leaked to the media.
Already, it's being compared to the famous Wow! signal. This was a loud burst of energy
that was detected by the Ohio State University's Big Ear radio antenna in August of 1977. It
lasted for 72 seconds and was never heard from again.
BLC-1, on the other hand seems to have lasted for about 3 hours. And, because it was detected
with the largest steerable radio dish in the southern hemisphere, was localized to a 16
arcminute-wide circle around Proxima Centauri.
At least, that's what the news is reporting. I'll admit I wasn't sure I would even make
this video because without a research paper, there's no way to know what the team actually
determined. But there's been so much chatter among astronomers on Twitter and my curiosity
was definitely piqued. Besides, this was probably the most on-brand-for-2020 story that we could
close out the year with. So now that the space cat is out of the nebula, we may as well talk
about what we do know about the signal, how astronomers search for extraterrestrial communications,
and what this signal could really be.
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So, about that candidate signal. Well, it was found in archival data from the Parkes
radio telescope taken in April 2019. At the time it was observing Proxima Centauri, which
at 4.2 light-years is the closest star to the solar system. It's a small red dwarf star
that orbits the Alpha Centauri binary star once every 547,000 years. It's currently on
the near side of its orbit, hence the name "Proxima".
The star is home to two known planets, Proxima b and c. Proxima b is roughly an Earth-sized
planet that orbits the star once every 11 days. That puts the planet at about 0.05 astronomical
units from Proxima. But because Proxima has such a low surface temperature, 0.05 AU puts
the planet in the star's so-called "habitable zone"; that is, it orbits at a distance where
liquid water could exist on the planet's surface, assuming, of course it has any water.
Proxima's second planet is about 7 Earth masses and orbits much further at 1.5 AU from the
star. That makes the planet either a "Super Earth" or a "Mini Neptune". Either way, it's
probably too cold to be capable of supporting even simple microbial life, let alone a civilization
capable of broadcasting.
However, we don't know anything about the planets' compositions because they're both
too close to Proxima to be imaged in a telescope. We only know of their existence by the gravitational
pull they exert on the star, causing Proxima to oscillate back and forth as they orbit.
Red dwarf stars are notorious for having violent, powerful flares. The Parkes telescope was
monitoring Proxima in 2019 to catch the radio emission from flare events. The Breakthrough
Listen astronomers discovered the signal in October 2020 when they were looking through
the 2019 data.
Specifically, they're looking for signals that are very strong and are confined to a
narrow band of frequencies called a "beam". Radio signals occur naturally in the Universe
and come from virtually everywhere, but even the most concentrated radio sources produce
signals that are tens of thousands of hertz wide. Artificial beams have a frequency range
of just a few hertz.
There's nothing in nature that we know of that concentrates so much power into so narrow
a beam. That's why astronomers have been looking for signals like this since the 1960's as
part of the Search for Extraterrestrial Intelligence, or SETI.
Of course, tight radio beams are everywhere on Earth. Radio broadcasts, cell phones, TV
transmissions, you name it, they're all emitting these tight, modulating radio beams.
So how can we tell if a radio signal is originating here on Earth or is coming from outer space?
Well, take a look at this plot. It's a signal from the Voyager 1 spacecraft. The horizontal
axis is frequency - measured in megahertz - and the vertical axis is time, going up
in 10 second increments. Notice that over time, the beam "drifts" from higher to lower
frequencies. This is because the signal is acquired when the source is rising in the
telescope's sky, so the telescope is initially rotating toward the source. This causes the
beam to be doppler shifted to a relatively high frequency. As Earth continues to rotate,
less and less of the telescope's motion is directed toward the source, and the beam doppler
shifts to a lower or "redder" frequency.
Another technique is to temporarily point the telescope away from the target and see
if the signal disappears. This is called "nodding". If the signal disappears when the telescope
nods off the target, it's probably really coming from the direction to the source.
Of course, there are plenty spacecraft and satellites out there, which add up to billions
of false signals that can be acquired in a single night. That's why a lot of computer
time goes into winnowing out all of those human-caused signals. Only those that make
it through a complex series of filters are actually seen by astronomers.
In the case of BLC 1, there are a number of characteristics that don't resemble satellite.
First, the signal seems to have lasted for 3 hours. Satellites in low earth orbit would
have crossed Parkes' sky in just a few minutes.
Geostationary and geosynchronous satellites orbit much farther away, and can linger above
a give location on Earth up to 24 hours a day. But geosynchronous orbits are confined
to a ring about Earth's equator. Proxima Centauri lies 63 degrees south of the celestial equator.
That leaves another kind of orbit called Molniya orbits. They're named after the Soviet communications
and spy satellites that began using these orbits in the 1960's. They're highly inclined
to the equator and have high eccentricities, allowing long dwell times over a given location
at mid latitudes. So, a spacecraft could broadcast to a receiver on the ground at a mid latitude
for hours at a time.
Now, if there's one silver lining to the fact that this was leaked before publication, it
may be that astronomers not involved in the research have been talking about this quite
a bit on Twitter and doing some parallel research of their own.
For example, Jason Wright at Penn State asked Jonathan McDowell at the Center for Astrophysics
if there are any Molniya satellites that hang over New South Wales, Australia. As far as
McDowell could ascertain, no, there aren't. The only active Molniya satellites all have
northern apogees. But Proxima lies 63 degrees south of the celestial equator.
That doesn't necessarily rule out a Molniya spacecraft, however. Spacecraft in such orbits
would have to perform stationkeeping maneuvers to maintain their orbits. There are some derelict
spacecraft on orbits that precessed from a northern to a southern apogee. But those spacecraft
are 1980's-era relics that have long since died. It's unclear why any of them would suddenly
start broadcasting again.
One kind of spacecraft we can certainly rule out are the interplanetary probes. The pioneer
spacecraft died out a long time ago. Both Voyagers and New Horizons aren't anywhere
in the sky close to Centaurus, let alone Proxima. Spacecraft orbiting other planets never find
themselves that far south in the sky, either because all planets follow the ecliptic and
never get further south than 23.5 degrees.
The signal itself was picked up at a frequency of 982.002 MHz. Interestingly, that's pretty
close in frequency to the so-called "watering hole" where interference from water vapor
in Earth's atmosphere, free electrons throughout the Galaxy, and other molecules are at a minimum.
But Michael Fidler, a retired Air Traffic Controller and amateur astronomer, pointed
out that the frequency band between 960 and 1215 megahertz is reserved worldwide for aeronautical
navigation, and 982 MHz in particular is used as part of the Instrument Landing System at
some airports.
Fidler also noticed the Parkes airport is only 15 miles away from the Parkes telescope,
but doesn't use 982 MHz as part of its instrument landing system.
Now of course, astronomers involved in SETI are pretty familiar with radio interference,
so it's hard to imagine this getting leaked if the signal weren't genuinely interesting.
For example, the beam has a drift, but rather than a drift to lower frequencies, it appears
this signal was drifting toward higher frequencies. In other words, it seems to be approaching
the telescope faster than Earth can carry the telescope away from the signal. That could
be due to an aircraft approaching the telescope, a spacecraft approaching Earth, or even a
transmitter on another planet rotating toward Earth during the broadcast.
The signal is also unmodulated, so instead of carrying a message like an artificial radio
transmission, it's monotone and steady, like a dialtone.
On the one hand, that doesn't sound like smart way to send a message. But on the other, it
could be it actually is modulated, but is modulated so quickly that we just don't know
that it's modulated at all. Or maybe it's unmodulated on purpose, as a way for an intelligent
civilization to stand out from all of the artificial signals that we generate. But then
again, we generate a lot of unmodulated radio interference.
Now, bear in mind, everything we know of publicly comes from the press reports. But one key
thing that is missing thus far is independent confirmation. It's entirely likely the Parkes
telescope just picked up radio interference from a moving source. Or, Parkes didn't pick
up anything at all and what looks like a signal was accidentally introduced into the data
after the fact. Or, it could have been a deliberate hack, because why not? That's why independent
confirmation of any signal, preferably with another telescope located elsewhere, is essential.
Unfortunately, there aren't many telescopes in the southern hemisphere with the sensitivity
of Parkes. The Atacama Large Millimeter Array in Chile is an extremely sensitive radio observatory,
but because it operates in the microwave part of the spectrum, it's only sensitive to frequencies
that are much higher than Parkes, starting at about 84 GHz.
The Square Kilometer Array is actually a pair of large radio arrays in Africa and Australia,
and they could potentially follow up on the signal, but they haven't come online yet.
Having a large array would allow the signal to be rediscovered but pinpointed in the sky.
Assuming of course that whoever send the signal decided to repeat. An individual radio telescope
has notoriously low resolution, so even though Parkes is the largest single-dish antenna
in the southern hemisphere, the signal could have originated anywhere in a 16 arcminute-wide
circle around Proxima. That's about half the diameter of the full Moon.
It's hard to imagine the team announcing an unambiguous detection of an alien signal
without independent confirmation. At best, they couldn't rule out alien origin, but without
confirmation, we'll be left with another Wow! situation.
Besides, an alien civilization transmitting from Proxima, the closest star to the solar
system? That seems just a little too convenient, doesn't it? That was my thinking, at least.
But Jason Wright pointed out that point-to-point transmission takes a lot of energy to reach
long distances. For example, you can call anyone in the world on your cell phone, even
though it uses a very low-power transmitter. That's because the signal from one phone is
routed to the other via a series of cell phone towers. Each tower receives the signal and
amplifies it before transmitting it to the next tower. The process repeats at nearly
the speed of light until it's received by the destination phone.
Alien civilizations are out there communicating, setting up a network of transmitters would
ultimately be the most energy efficient way of doing it. Sure, it would take a few million
years to set up the network, but once that's done, you'd be good to go. If you wanted to
communicate with Earth at some point in the future, dropping off a transmitter at Proxima
might wouldn't be a bad idea.
It's an interesting, but I'm a little bit skeptical about that one. Still, there's no
question the signal is also very interesting. For now we'll have to give the team an opportunity
to finish up their work and get their results vetted through peer review and publication.
If I had to bet, my guess is that this result will help refine future SETI work.
Obviously, a lot of the challenges with searching for alien radio signals could be addressed
if we could build radio telescopes on the far side of the Moon. That's really the only
place in the entire solar system that is shielded from Earth's radio emission.
In fact, I made a video about putting telescopes on the Moon, so if you'd like to learn more
about that, I'll see you over there when we're done here.
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Until next time, stay home, stay healthy, and stay curious, my friends.