The SETI Institute's Allen Telescope Array (ATA) was recently used to seek out artificial signals from Tabby's Star. Alas, no signal was detected.
Nov. 8, 2011 --
Despite the occasional report of an extraterrestrial sighting, be it through a microscope revealing curious shapes in a meteorite or a photo of wispy lights taken at the blurry end of a camera lens, aliens have yet to make contact with humans. Even the White House yesterday put out a statement declaring that the federal government "has no evidence that any life exists outside our planet, or that an extraterrestrial presence has contacted or engaged any member of the human race." Humans may not yet have encountered life outside of our planet, but many scientists see it as an inevitability. In 1960, astronomer Frank Drake came up with the now eponymous equation which provided an estimate of the number of civilizations in our galaxy. Although scientists continue to debate the application of his formula as well as alternatives, Drake's own solution to the equation is 10,000 civilizations, suggesting intelligent, technologically advanced life outside our planet is common. How these different civilizations, including our own, find each other is an important question for anyone here on Earth looking for extraterrestrials. Explore how aliens might stumble upon our planet -- and how we might actually spot them first.
BLOG: ARE UFOS ALIEN? NO!
Before we can began to search the skies, we have to start by narrowing down our options. Sticking within our own galaxy is a good start, since we're more likely to spot a neighbor closer to us than one further away. Astronomers may also elect to focus their attention on stars closer to the center of the Milky Way, where 90 percent of its stars are clustered. Furthermore, the stars here are a billion times older than the sun, giving life more time to develop biologically and technologically. Many stars are unsuitable for nurturing life, and even stars that do have the appropriate "spectral type" may host exoplanets inhospitable to life due to their location relative to their parent star, size or composition. These criteria would not only help us find aliens, but also help them find us. After all, Earth would stand out as a hospitable planet, according to a paper published in 2007 in Astrophysical Journal.
If aliens are looking for us, they're scanning the same, vast, dark and mostly empty expanse of space that we are. It's a good thing then that we're leaving the lights on to make it easier to find us. According to Abraham Loeb, of Harvard University and Edwin Turner, from Princeton University, by scanning the skies for artificial illumination as opposed to naturally occurring light sources, both human and extraterrestrial astronomers might be able to find signs of life. Existing telescopes would be able to see a city the size of Tokyo as far as the edges of our solar system.
BLOG: CITY LIGHTS COULD REVEAL ET
For more than 25 years, the SETI Institute has been scouring the skies for signs of alien life. However, long before the institute was established, scientists have tried to catch a communication signal from another world. Scientists looking for alien signals use a combination of optical and radio telescopes, such as the one seen here. Dropping in on a signal without knowing the source of the communication is the tricky part, however, and researchers narrow down their search by targeting specific kinds of stars. With their citizen science program, SETI@home, the institute has enlisted three million additional observers analyzing data for traces of an alien signal.
BLOG: MAN LOOKS FOR ALIENS, LOSES JOB
Have aliens already stopped by for a visit, even though we weren't at the door to meet them? If they have, shouldn't they have left something behind? An artificial object of alien origin could be lurking in our solar system without our knowledge. As Discovery News' Ray Villard explains: "In a paper published in the 1960s, Carl Sagan, using the Drake Equation, statistically estimated that Earth might be visited every few tens of thousands of years by an extraterrestrial civilization." Further out beyond our solar system, aliens may have left what essentially amount to interstellar billboards large enough to be seen by, say, a planet-hunting telescope like Kepler. These last two scenarios, of course, envision an extremely technologically advanced civilization well beyond the engineering capabilities of humankind. At the same time, humans have sent spacecraft beyond the solar system, including Pioneer 10 and 11 as well as Voyager 1 and 2. All of these spacecraft are equipped with what are essentially calling cards for the human race -- small plaques in the case of the Pioneer spacecraft and golden records for the Voyager spacecraft (seen here).
SCIENCE CHANNEL: Top 10 Alien Sightings
Humans may rely primarily on fossil fuels as their primary means of energy, but that doesn't mean extraterrestrials in a far off civilization have the same power source. Solar power could be one option, though not quite with the same black panels we use on Earth. A super civilization could even tap into a black hole to meet its energy needs. If aliens are tapping to these cosmic bodies, that should make them all the more detectable from Earth. How would we know whether an alien race was relying on a black hole as a source of energy? As Discovery News' Ray Villard explains: "Tell-tale evidence would come from measurements that showed the black hole weighed less than 3.5 solar masses. That's the minimum mass for crushing matter into a black hole via a supernova core-collapse."
In one of the most unusual -- and highly unlikely -- first-contact scenarios, aliens would be able to recognize us by the level of greenhouse gas emissions we pump into our atmosphere. Not only that, according to a hypothesis put forward by researchers affiliated with NASA and Pennsylvania State University (though not directly tied with either institution), but aliens may use that as cause to wipe out the human race. In this bizarre set of circumstance, aliens view human advancement as a destructive force spiraling out of control. To avoid the threat of a future adversary, extraterrestrials clear out the competition.
BLOG: TO SAVE THE GALAXY, DESTROY HUMANITY
After all the public excitement surrounding the star KIC 8462852 and its weird transit signal as spotted by NASA’s Kepler Space Telescope, the SETI Institute decided to expedite plans to point a powerful radio antenna at the nearby star in the hope of detecting any artificial transmissions emanating from that location. Sadly (or not, depending on how you view the discovery of an intelligent alien civilization living in our cosmic backyard), the first pass drew a blank.
So, is this “case closed” for the possibility of an alien megastructure around KIC 8462852? Well, not really, but it does make a vanishingly slim chance of aliens even more vanishingly slim.
But before we discuss what SETI has (or, indeed hasn’t) found, a quick recap.
Aliens! Or Not
In September, astronomers and citizen scientists published a paper describing a “bizarre” transit signal recorded by Kepler, outlining a few possible causes for the phenomenon around KIC 8462852 — informally known as “Tabby’s Star.” On 2 occasions during Kepler’s prime observing run, huge transits were detected around the star.
Usually, Kepler will detect periodic dips in star brightness and the amount of dimming relates to the size of the exoplanet passing in front of the star. Typically, for a small exoplanet, this dip in brightness is of the order of a couple of percent. But the two transit signals detected around Tabby’s Star were dramatic. The first transit dipped by 15 percent, but the second transit (that consisted of several objects passing in front of the star over several weeks) dipped to as much as 22 percent. The strength of the transit and its multi-object nature was unprecedented.
Many natural phenomena were explored and the researchers eventually focused on the possibility of a swarm of comets as being the most likely culprit. A nearby star, they argued, may have destabilized comets in Tabby’s Star’s Oort cloud (a hypothetical region surrounding a star containing countless billions of icy bodies), nudging a huge number of comets toward the star, blocking its light from view.
This explanation certainly fits many of the transit’s characteristics, but during an interview with The Atlantic, astronomer Jason Wright, an astronomer from Penn State University, discussed an alternate avenue of study that he wanted to investigate. On many occasions since, Wright and other astronomers have cautioned against jumping to the alien conclusion — after all, there are other, more likely natural explanations — but when faced with an unprecedented transit signal, why not explore the most extreme possibilities?
As with any speculation about aliens, the slim possibility of this Kepler signal being artificial caused an eruption of interest. While many scientists vented frustration at the frenzy of interest surrounding an unlikely scenario, whether they liked it or not, suddenly everyone was interested in Kepler science and hypotheses of an advanced alien civilization living in our galaxy. In my personal view, so long as the discussion remained planted firmly in the science, and not conspiracy theories and nonsense, this was no bad thing — especially as professional scientists were planning on investigating the possibility themselves.
Allen Telescope Array
So, if not comets, what could be causing the bizarre transit signal? Taking the age of our galaxy into consideration, it’s not such a stretch to think that if life is common in the Milky Way, perhaps there’s a vastly more advanced civilization to our own out there that has the ability to build huge solar energy collectors, say, around their host star. This speculation would certainly fit a Type II Kardashev civilization that has the ability to build huge megastructures around a star (much like a Dyson Sphere) to collect huge quantities of energy. Perhaps Kepler’s transit signal was several vast solar collectors passing in front of the star?
While it’s fun to think up all the possible structures an intelligent alien race might build, seeing a star dim a couple of times is hardly proof that aliens are out there. It’s not even evidence, especially when Occam’s Razor reminds us that there are other explanations out there with far fewer assumptions (i.e. the exocomet explanation). But in the interest of using Tabby’s Star as a point of scientific interest and respond to the huge public interest in the star, SETI Institute scientists turned to the their Allen Telescope Array (ATA) to “listen in” on the location.
The ATA is located a few hundred miles north of San Francisco, Calif., in the Cascade Mountains, consisting of 42 6-meter diameter radio antennae. The ATA was aimed at Tabby’s Star for 2 weeks and listened out for 2 specific radio signals. The first signal, of a narrow-band 1 Hz bandwidth, might be used as a “hailing signal”, according to the SETI Institute, for advanced alien civilizations to announce their presence. The second signal may be of a more broad-band emission that could signify an alien presence through the leakage of beamed propulsion in the star system. Beamed propulsion is one hypothetical method that could be used to power spacecraft in the future, so if there’s an alien megastructure around that star, there would likely be spacecraft too, possibly sporting this propulsion method.
“This is the first time we’ve used the Allen Telescope Array to look for relatively wide-band signals, a type of emission that is generally not considered in SETI searches,” said SETI Institute scientist Gerry Harp in a news release.
But on this first 2 week pass, the ATA didn’t detect either type of signal emanating from Tabby’s Star:
Analysis of the Array data show no clear evidence for either type of signal between the frequencies of 1 and 10 GHz. This rules out omnidirectional transmitters of approximately 100 times today’s total terrestrial energy usage in the case of the narrow-band signals, and ten million times that usage for broad band emissions. —
This finding provides an upper limit on our ability to detect these most powerful signals — if these hypothetical aliens possess the energy required to build vast structures around stars, they will certainly have the energy required to generate such powerful beacons. But say if they’re not deliberately transmitting? Well, that might explain why we’re not hearing the narrowband “hailing” signal. Say if there’s little activity around these structures? That might explain why there’s little radio “leakage” from the star. What if these are structures left in orbit by a bygone alien civilization? Perhaps they’re monuments of an empire that is long gone. A fascinating thought.
Once again, we’re speculating about what these hypothetical aliens are or are not, but the SETI investigation certainly rules out certain scenarios.
“The history of astronomy tells us that every time we thought we had found a phenomenon due to the activities of extraterrestrials, we were wrong,” said SETI Institute astronomer Seth Shostak. “But although it’s quite likely that this star’s strange behavior is due to nature, not aliens, it’s only prudent to check such things out.”
It’s very easy to give every reason why the Kepler signal from Tabby’s Star is not aliens — as it most likely isn’t — but collecting more data from other observatories taking different approaches certainly isn’t a waste of time when on the trail of tracking down the slim possibility of intelligent extraterrestrial life in our galaxy.
Source: SETI Institute