February 26, 2015
Detecting signals from intelligent aliens is a lifelong quest of noted astronomer Frank Drake. He conducted the first modern search for extraterrestrial intelligence (SETI) experiment in 1960. More than five decades later, the hunt remains front-and-center for the scientist.
Drake also devised a thought experiment in 1961 to identify specific factors believed to play a role in the development of civilizations in our galaxy. This experiment took the form of an equation that researchers have used to estimate the possible number of alien civilizations — the famous Drake Equation.
The Drake equation is:
N = R*. fp. ne. fl. fi. fc. L
N = the number of civilizations in our galaxy with which radio-communication might be possible (i.e. which are on our current past light cone);
R* = the average rate of star formation in our galaxy
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
fl = the fraction of planets that could support life that actually develop life at some point
fi = the fraction of planets with life that actually go on to develop intelligent life (civilizations)
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into space
Drake constructed the “Arecibo Message” of 1974 — the first interstellar message transmitted via radio waves from Earth for the benefit of any extraterrestrial civilization that may be listening.
The message consists of seven parts that encode the following (from the top down):
The numbers one (1) to ten (10)
The atomic numbers of the elements hydrogen, carbon, nitrogen, oxygen, and phosphorus, which make up deoxyribonucleic acid (DNA)
The formulas for the sugars and bases in the nucleotides of DNA
The number of nucleotides in DNA, and a graphic of the double helix structure of DNA
A graphic figure of a human, the dimension (physical height) of an average man, and the human population of Earth
A graphic of the Solar System indicating which of the planets the message is coming from
A graphic of the Arecibo radio telescope and the dimension (the physical diameter) of the transmitting antenna dish
This is the message with color added to highlight its separate parts. The actual binary transmission carried no color information.
Space.com caught up with Drake to discuss the current state of SETI during an exclusive interview at the NASA Innovative Advanced Concepts (NIAC) 2015 symposium, which was held here from Jan. 27 to Jan. 29.
Drake serves on the NASA NIAC External Council and is chairman emeritus of the SETI Institute in Mountain View, Calif. and director of the Carl Sagan Center for the Study of Life in the Universe.
Space.com: What’s your view today concerning the status of SETI?
Frank Drake: The situation with SETI is not good. The enterprise is falling apart for lack of funding. While NASA talks about “Are we alone?” as a number one question, they are putting zero money into searching for intelligent life. There’s a big disconnect there.
We’re on the precipice. The other thing is that there are actually negative events on the horizon that are being considered.
Space.com: And those are?
They are the world’s two largest radio telescopes, and both of them are in jeopardy. There are movements afoot to close them down … dismantle them. They are both under the National Science Foundation and they are desperate to cut down the amount of money they are putting into them. And their choice is to just shut them down or to find some arrangement where somebody else steps in and provides funding.
So this is the worst moment for SETI. And if they really pull the rug out from under the Green Bank Telescope and Arecibo … it’s suicide.
Space.com: What happens if they close those down?
Drake: We’re all then sitting in our living rooms and watching science fiction movies.
Space.com: How about the international scene?
Drake: The international scene has gone down too because all the relevant countries are cash-strapped also.
There is a major effort in China, a 500-meter [1,640 feet] aperture spherical radio telescope. The entire reflector is under computer control with actuators. They change the shape of the reflector depending on what direction they are trying to look. The technology is very complicated and challenging. The Russians tried it and it never worked right. But … there are serious resources there.
Drake: You would think. All those planetary detections are the greatest motivator to do SETI that we ever had. But it hasn’t had any impact, at least yet.
Space.com: How do you reconcile the fact that exoplanet discoveries are on the upswing, yet mum’s the word from ET?
Drake: People say that all the time … saying that you’ve been searching for years and now you’ve searched thousands of stars and found nothing. Why don’t you just give up … isn’t that the sensible thing?
There’s a good answer to all that. Use the well-know equation and put in the parameters as we know them. A reasonable lifetime of civilizations is like 10,000 years, which is actually much more than we can justify with our own experience. It works out one in every 10 million stars will have a detectable signal. That’s the actual number. That means, to have a good chance to succeed, you have to look at a million stars at least — and not for 10 minutes — for at least days because the signal may vary in intensity. We haven’t come close to doing that. We just haven’t searched enough.
Space.com: What are we learning about habitable zones?
Drake: Actually the case is very much stronger for a huge abundance of life. The story seems to be that almost every star has a planetary system … and also the definition of “habitable zone” has expanded. In our system, it used to be that only Mars and Earth were potentially habitable. Now we’ve got an ocean on Europa … Titan.
The habitable zone goes out. A habitable zone is not governed just by how far you are from the star, but what your atmosphere is. If you’ve got a lot of atmosphere, you’ve got a greenhouse effect. And that means the planet can be much farther out and be habitable.
“Radio waving” to extraterrestrials. Outward bound broadcasting from Earth has announced humanity’s technological status to other starfolk, if they are out there listening.
Credit: Abstruse Goose
Space.com: What is your view on the debate regarding active SETI — purposely broadcasting signals to extraterrestrials?
Drake: There is controversy. I’m very against sending, by the way. I think it’s crazy because we’re sending all the time. We have a huge leak rate. It has been going on for years. There is benefit in eavesdropping, and you would have learned everything you can learn through successful SETI searches. There’s all kinds of reasons why sending makes no sense.
Frank Drake, center, with his colleagues, Optical SETI (OSETI) Principal Investigator Shelley Wright and Rem Stone with the 40-inch Nickel telescope at Lick Observatory in California. Outfitted with the OSETI instrument, the silver rectangular instrument package protrudes from the bottom of the telescope, plus computers, etc.
Credit: Laurie Hatch Photography
That reminds me of something else. We have learned, in fact, that gravitational lensing works. If they [aliens] use their star as a gravitational lens, they get this free, gigantic, super-Arecibo free of charge. They are not only picking up our radio signals, but they have been seeing the bonfires of the ancient Egyptians. They can probably tell us more about ourselves than we know … they’ve been watching all these years.
Space.com: Can you discuss the new optical SETI efforts that you are involved with? You want to search for very brief bursts of optical light possibly sent our way by an extraterrestrial civilization to indicate their presence to us.
Drake: It’s alive and well. We’ve gotten a couple of people who are actually giving major gifts. There’s no funding problem. There is a new instrument that has been built, and it’s going to be installed at the Lick Observatory [in California] in early March.
The whole thing is designed to look for laser flashes. The assumption is — and this is where it gets to be tenuous — the extraterrestrials are doing us a favor. It does depend on extraterrestrials helping you by targeting you. These stellar beams are so narrow that you’ve got to know the geometry of the solar system that you’re pointing it at. They want to communicate. They have to be intent on an intentional signal specifically aimed at us. That’s a big order. So there are required actions on the part of the extraterrestrials for this to work. The big plus is that it’s cheap and relatively easy to do.
See the full article here.
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