Getting the intergalactic message across is easier said than done

Scientists recently decoded the first confirmed alien transmission from outer space. It said:

"Please send 5x10 (to the 50th power) atoms of hydrogen to each of the five star systems listed below. Then, add your system to the top of the list and delete the system at the bottom. Transmit copies of this message to 100 different solar systems. If you follow these instructions, you are guaranteed that within 0.25 degrees of a galactic rotation you will receive in return sufficient hydrogen stores to power your own civilization until the universe reaches inevitable maximum entropy. This really works!"

OK, it's only a joke, a cosmic/comic chain letter that's no more likely to happen than, well, promises of chain letters of the terrestrial type. But that's not to say there isn't an alien civilization somewhere in the far reaches of space with the ability -- and desire -- to communicate.

Why else do serious scientists at SETI -- the Search for Extraterrestrial Life -- scan the heavens for alien signals? Why did NASA stick iconic plaques on its first interstellar probes?

Just recently SETI astronomers recorded a mysterious radio wave signal for the third time. Most researchers now dismiss the signal, dubbed SHGb02 (plus) 14a, as an artifact of random chance, cosmic noise or maybe just a glitch in the technology.

"The news was incredibly overplayed. There are always these anomalies," says Woodruff Sullivan, an astrobiologist at the University of Washington.

In 1961, a small group of space scientists gathered at the National Radio Astronomy Observatory in Green Bank, W.Va., to consider the subject of intelligent extraterrestrial life.

Much of the meeting focused on astronomer Frank Drake's new mathematical formula for estimating the likely number of alien civilizations in the galaxy capable of engaging in interstellar communication.

The Drake Equation, as it has come to be known, didn't prove anything, of course. It was based on numerous variables, most of which we still don't have any good numbers for. But the equation and the Green Bank meeting got people thinking about the challenges of communicating with alien life.

A year later, Soviet scientists gave it a shot, sending a pair of radar signals to Venus in Morse code. The first message read "MIR," the Russian word for peace and world. The second signal said "Lenin" and "SSSR" (the Russian acronym for the Soviet Union).

Neither message got a response, which probably isn't surprising, given the fact that Venus' atmosphere consists primarily of carbon dioxide with clouds of sulfuric acid and a mean surface temperature of 867 degrees. Surely there are more hospitable places to live in the universe.

Ten years later, in 1972, NASA launched the Pioneer 10 planetary probe, followed a year later by its twin, Pioneer 11. Tacked to antenna support struts on both probes were license-plate-sized, gold-anodized aluminum plaques etched with information intended for any extraterrestrials who might retrieve them during or after their missions to study Jupiter, Saturn and the outer planets of the solar system.

"The plaques were a last-minute effort," said Seth Shostak, a SETI astronomer. "It was realized that Pioneer would be the first human-made hardware to leave the solar system and never come back, so people thought it would be a good idea to install a builder's plaque."

The late astronomer and author Carl Sagan and Drake were hastily commissioned to design the plaques, which were engraved at a local bowling shop. The final etched message included schematics of a hydrogen atom, a binary number code, the Earthly origin of the probe and line drawings of a nude man and woman -- both of whom looked like they might have come straight from a Southern California beach.

Both probes are now well out of the solar system. Pioneer 10 is 7.6 billion miles from Earth; Pioneer 11 is similarly distant. Neither has been heard from since April 2001, when astronomers picked up a feeble signal from Pioneer 10 that measured just one billionth of a trillionth of a watt.

The Pioneer probes, which Shostak describes as a kind of "demo," helped inspire the next effort at interstellar talk: the so-called Arecibo Message, transmitted Nov. 16, 1974, from the massive 1,000-foot-diameter radio telescope at Arecibo, Puerto Rico.

The Arecibo Message was an electromagnetic version of the Pioneer plaques. It consisted of 1,679 bits of binary data that roughly described, among other things: our numbering system, the atomic numbers of certain key elements, the chemical structure of DNA, the Earth's population at the time and our location in the solar system. The radio signal was directed toward the globular cluster M13 in the Hercules constellation 25,000 light-years away, which means a reply cannot be expected for at least another 49,970 years.

After Arecibo, scientists returned to the idea of physical messages, attaching 12-inch gold-plated copper phonograph disks to the probes Voyager 1 and 2, both launched in 1977 and both ultimately destined for interstellar space.

Voyagers' disks were more sophisticated than Pioneers' plaques. They contained sounds and images meant to depict Earth's diversity of life and culture. There were recordings of humpback whales, crashing surf, elephant trumpeting and rocket launches, plus music from Bach and Chuck Berry and spoken greetings in 55 languages, some long-dead.

Each record was encased in a protective aluminum jacket etched with iconic schematics akin to Pioneers' and packaged with a cartridge, needle and user instructions (written in symbolic language).

The latest effort to communicate with possible alien life has been the most modest.

In 1999, a Houston-based company now called Team Encounter transmitted radio signals toward several stars located 51 to 71 light-years away. Dubbed "Cosmic Call" and sent from the Evpatoriya radio telescope in Ukraine, the series of binary code signals resembled the Arecibo message, containing descriptions of Earthly life, the solar system and some mathematical relationships. Reportedly, three similar transmissions have been made since, all seemingly to no avail.

What means do you use to communicate: physical objects such as plaque-bearing probes or electromagnetic transmissions, such as light or radio?

Once that's decided, what about the language and content of an interstellar message? Will recipients understand it? Do aliens know Morse code?

The first question recently came up for debate again when Christopher Rose, a physicist at Rutgers University, and Gregory Wright, an electrical engineer with Antiope Associates, also in New Jersey, published a paper in the journal Nature arguing that transmitting electromagnetic signals into space as a way of saying, "Hey, we're here!" was a waste of money.

If humanity wants to correspond with the cosmos, Wright and Rose write, it should send bulk mail: Messages inscribed onto physical matter and then launched toward planets or other celestial bodies deemed most likely to harbor responsive life.

The primary benefit of sending "messages in bottles," Rose and Wright said, is cost-efficiency. A radio transmission is faster. It travels at the speed of light. But the transmission spreads and dissipates as it moves through space. By the time a signal from the Arecibo radio telescope reaches Saturn, it has dipped below detection level. And once it passes a target, it's gone for good.

Sending a signal farther, say 10,000 light-years, would take a million billion times more energy than launching a message-bearing probe.

Conversely, wrote the researchers, physical messages aboard the Pioneer and Voyager space probes remain intact no matter how far they've traveled from Earth. Their primary drawbacks are numbers, size and speed. The handful of probes bearing messages are all very, very small in a very, very large space. Moreover, they're all moving relatively slowly.

Even traveling thousands of miles per hour, none of the Pioneer or Voyager probes will reach an interesting target soon. Voyager 1, for example, won't enter another planetary system for another 40,000 years. Pioneer 10 is headed toward the red star Aldebaran, 68 light-years away. Zipping along at 28,000 mph, it will get there in 2 million years.

All potential communication with potential extraterrestrials starts with some basic assumptions.

Assumption No. 1: Any alien recipient is at least as intelligent and technologically advanced as humans.

"We assume they have access to a radio telescope because obviously they would need to be doing some kind of SETI-like research themselves to detect our signal," said Yvan Dutil, a Canadian physicist who, with colleague Stephane Dumas, has overseen the Cosmic Call efforts.

"That means they need to be able to do the math to design their own radio telescope and be familiar with basic material physics to build it. It means they also have some sort of social organization because something like SETI is not likely to be the work of a lone individual."

Shostak put it another way: "Getting a message to bacteria on Mars would be a tough assignment."

Assumption No. 2: Everybody's speaking the lingua franca. In Hollywood, aliens speak English. In reality, experts say, a universal language more likely will be mathematics and physics.

"It goes to the assumption that the laws of physics are the same everywhere," said Robert Park, a professor of physics at the University of Maryland. "If aliens can figure out the laws, they're going to have numbers."

Still, there's no diminishing the toughness of the task. After the Green Bank conference, Frank Drake sent a coded message to his fellow participants. It was a sort of intellectual exercise. The message consisted of 1,271 ones and zeros (or bits) and was based on the key that 1,271 is the product of two prime numbers, 31 and 41. Even though all the recipients were human, spoke the same language and were familiar with Drake's work, only one scientist successfully decoded the cryptogram.

Communicating with pictures isn't necessarily easier. For one thing, what if E.T. can't see? Then there's understanding what you're seeing. Parts of the Pioneer plaques appear pretty obvious: the line drawings of a man and woman or the sequence of planets in our solar system, for example. But within the entire illustration lies a lot more embedded information, much of it based on the wavelength of photons and the transition frequency of hydrogen atoms.

"I've shown the plaque to lots of people, including some really bright students," said Park. "They couldn't make heads or tails of it."

The bottom line may be one of intent. If the idea is merely to make our presence known in the universe, then transmitting a strong, unnatural signal -- a radio or light transmission, for example -- might be enough.

"I've always gone for the idea of a beacon," Sullivan said. "It would be simple, a sort of 'I am here!' message that might also include some basic information about where to look for a weaker signal containing more information. That's easier said than done, however."

You need to add interstellar scintillation and the galactic noise halo to the equation as well.

There are two real sources of noise that limits the radio astronomer's ability to search for very weak signals. The galactic noise halo interferes with us below 1 GHz and noise due to earth's atmosphere interferes with us above about 10 GHz. This pretty much keeps all SETI searches (at least radio ones) between 1 and 10 GHz. Inside these two frequencies, from about 1.4 to 7 GHz the noise level drops off even further to near the 2.7 Kelvin Cosmic Microwave Background (CMB) that permeates all space. Hydrogen (H) molecules, the most abundant element in the universe, excite and emit (masers) at around the 1.4 GHz frequency (21 cm band) and the hydroxyl (OH) emits at around 1.65 GHz. This is where much of our radio astronomy and SETI research is concentrated. Since H + OH is water, the frequency gap between these two is often called the “Water Hole”.

Also SETI searches are not looking for intelligence riding on a signal itself. The scintillation of the interstellar medium will quickly make that unintelligible. What most current SETI searches are looking for, is the extremely narrowband signal (carrier) that the information rides on. Indeed as we evolve into more "spread spectrum" type signals, the carrier(s) will be harder to detect. However, I think that will be a temporary phenomena. As we spread out into the solar system, we again will require high power carriers to convey information from point to point. So there may be a naturally "quiet" period in many advanced races prior to then spreading through out their solar system.

(from: http://www.seds.org/~rme/seti.html)

"Given an effective radiated power of the transmitter (in watts), the effective area of the receiving antenna (in square meters), the excess receiver noise temperature of the receiver used (in K), the averaging time of the receiver (in seconds), and the accepted band-width of the signal (in Hz), the range at which we can detect a signal transmitted by an intelligent civilization, is:

R=8x10^-6(P_eA/T)^1/2(t/B)^1/4 light years.

Where the constant is calculated from 1/[9.4608x10 ¹⁵(4”pi”k)^½]. Here the constant is the number of meters per one light year, and k is the boltzmann constant."

So to offset some of the limitations, we (SETI searches in general) are looking for extremely narrow band CW waves that have been Doppler shifted due to planetary motions.

Here is an excerpt from a paper I wrote a while back: (note: I cannot get the symbols for Pi or lambda to work )

With any link, there is parameter called a link margin. This the margin of degradation before the Bit Error Rate (BER) becomes unacceptable. This margin must take into account signal attenuation due to distance, atmospheric conditions antenna gain, transmitter power, frequency, etc.

The energy of an electromagnetic wave is directly proportional to its frequency. The Energy (E) equals Planck’s constant (h) times the speed of light (c) divided by the frequency of the wave (“lambda”): E = hc/”lambda” or in other words since c = “lambda”*v (v is frequency) then E = h v

Whereas Planck’s constant describes the nature of matter and energy at the atomic levels. Planck’s constant is; 6.626 x 10^-34 Joule-second. A joule is the amount of energy exerted when a force of one (1) newton is applied over a displacement of one meter, which is also equivalent to one (1) watt of power radiated for one second.

All of these equations lead up to the simple fact that the shorter the wavelength, the higher the energy of the wave.,

The following are just a few of the things that affect link margin (being able to receive data):

1. The frequency of the wave
2. RF interference (local radio noise, solar RFI, another satellite, etc)
3. Bit rate of the data
4. Antenna elevation (such as a 5° contact with the satellite versus 85°)
5. Atmospherics (rain, clouds, snow and the like)
6. Solar affects (sunspots, geomagnetic storms, solar flares and storms, etc)
7. Antenna gain and size
8. Radiated power from the transmitter
9. Antenna type (omni, dish, yagi, etc)
10. Antenna efficiency (efficiency of the LNA and the like)

All of these items must be taken into account by the RF engineer whenever he/she is designing the link. I have defined a few of the terms you may run across that are used by the engineers when describing or computing link margins.

FSL (Free Space Loss)

Loss in free space is a function of frequency squared plus distance squared plus a constant. Free space means transmission without absorption or reflection of energy. Expressed in decibel form, the free space loss is:

(FSL)dB = 20log(4"pi"d/"lambda")

Where "lambda" is wavelength.

EIRP: (Effective Isotropically Radiated Power).

Dish Antennas are a very directional antenna. This allows most of the radiated power to be broadcast in a single direction. EIRP is the power received that the antenna appears to broadcast as if it was an isotropic radiator. Thusly it is the product of the gain of the antenna and the transmitter power.

EIRP can be calculated using the following formula: EIRP_dBW = P₀ + L_t + G₁ where P₀ is the power out of the transmitter, L_t is the transmission line loss, and G₁ is the gain of the antenna.

E_b/N₀: (Energy per Bit Noise Density Ratio)

This is the efficiency of the digital communications with respect to the noise on the link. N₀ is commonly measured by the received bit energy to noise density ratio E_b/N₀.

C/N₀: (Carrier to Noise Ratio).

C equals Carrier power received and N equals the noise of the ground system.

G/T: (Gain-to-Noise Temperature Ratio)

Basically this is a ratio of the Gain of the ground station antenna to the Noise temperature of the ground station RF equipment.

Putting this all together gives us a “feel” for the link budget:

The link budget is a tabular method of calculating the space communications systems parameters. So the total equation would look something like this:

C/N₀ = EIRP – FSL_dB – (other losses) + G/T_dB/K - k

Where FSL is the free space loss, k is Boltzmann’s constant (1.3806 x 10^-23 joule/K) expressed in dBW or dBm, and the “other losses” may include:

· Polarization loss
· Pointing loss
· Off-contour loss
· Gaseous absorption losses
· Atmospheric effects (such as rainfall)
· Localized interference

Note: off contour loss refers to spacecraft antennas that are not earth coverage, such as spot beams, zone beams, or multiple beam antennas.

Since I mentioned noise temperature, I thought I would add the following:

Astronomers use temperature to represent the strength of detected radiation. Any body with a temperature above -273 deg C (approximately absolute 0) emits electromagnetic radiation (EM). This thermal radiation isn't just in the infrared but is exhibited across the entire electromagnetic spectrum. (Note: it will have a greater intensity (peak) at a specific area of the EM spectrum depending on its temperature). For example, bodies at 2000 K (Kelvin), the radiation is primarily in the infrared region and at 10000 K, the radiation is primarily in the visible light region. There is also a direct correlation between temperature and the amount of energy emitted, which is described by Planck's law.

When the temperature of a body decreases, two things happen. First, the peak shifts in the direction towards the longer wavelengths and second, it emits less radiation at all wavelengths.

This turns out to be extremely useful. When a radio astronomer looks at a particular location of the sky and exclaims that it has a noise temperature of 1500 K, he/she isn't declaring how hot the body (nebulae, etc) really is, but is providing a measurement of the strength of the radiation from the source at the observed frequency. For example, radiation from an extra solar body may be heated from a nearby source such as a star. If this body is radiating at a temperature of 500 K, it exhibits the same emissions across all frequencies that a local test source does. The calculated noise figure will be the same across all frequencies. (Note: this does not take into account other sources of radiation such as synchrotron radiation).

A problem for radio astronomers is that not only the observed source emits thermal radiation; the local environment (ground, atmosphere, etc) and the equipment (antenna, amplifiers, cables, receiver, etc) being used to make the measurements also emit thermal radiation. To accurately observe and measure the distant sources, the radio astronomer must subtract all of the local environment and detection equipment noise additions.

Back in 1963, Arno Penzias and Robert Wilson were working with a horn antenna trying to obtain the high efficiency possible for the Telstar project. This antenna was also going to be used for radio astronomy at a later date. They pointed it to a quiet part of the sky and took measurements. When they subtracted all of the known sources of noise, they found approximately 3 K left over. They worked very diligently to eliminate/describe this noise source and were unable to. This mysterious source of noise seemed to be there no matter where they pointed the antenna. What they had discovered was the microwave background produced from the Big Bang. This 3 (closer to 2.7) K microwave background originated approximately 300,000 years after the Big Bang itself had occurred. It has been determined that when these signals originated, the universe had already cooled down to around 3000 K.

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