Interstellar radio communication

PRESENTED BY:AKHIL SOHANS7 ECE BROLL NO:2

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• Transmission and reception of signals between planetary systems

• Planetary systems can be located in two different galaxies

• Low energy radio waves are used

• Low frequency radio waves penetrate earth’s atmosphere and pass through interstellar space

• Mainly used for finding ET’s(extraterrestrial intelligence) and also used in pulsar astronomy

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STARSHIPS• Two way communication• Should travel at speed of light• High downlink rate• Relativistic effect can hamper wave propagation

CIVILIZATIONS• Establishment of two way communication difficult• Composition of message prior to our/their

knowledge• Chance of impairments at thousands of light years

due to scattering effects

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ENERGY

• Energy factor critical in information transmission

• Propagation loss compensated by larger antennas or increasing transmit power

• Omnidirectional transmit antenna used

• Reducing transmission energy can be beneficial

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• Equation to estimate the number of civilizations currently communicating in our Galaxy

Ncivil = N* fp np fl fi fc fL

Where,

N* = the number of stars in the Milky Wayfp = the fraction of stars that have “habitable planets”np = the number of habitable planets per systemfl = the fraction of habitable planets where life evolvesfi = the fraction of life-planets that evolve intelligencefc = the fraction of civilizations that communicatefL = the fraction of the star’s life that the civilization exists

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• Range of frequencies with minimum background radio noise

• Frequency range from

1.42Ghz(emission of H atom) to

1.721Ghz(emission of OH molecule)

• Messages from civilizations may be

gathered from this frequency range

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• It is a directional radio antenna

• Differs from optical telescope as it uses radio frequency in electromagnetic spectrum

• Large parabolic dish antenna,used singly or in an array

• Isolated from populated areas

• Radio telescopes in array uses radio interferometry

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ARECIBO RADIO TELESCOPE

DELIBERATE SIGNALS

• Sent in hopes that another civilization will receive them

• Radio waves are used

• Frequencies between a few hundred Mhz and a few thousand Mhz are best

• ‘’Spin flip’’ transition frequency in H atom=1420 Mhz

in OH atom=1721 Mhz

• H and OH atoms radiate itself at this frequencies causing background noise

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ACCIDENTAL SIGNALS

• Used by civilizations for other purposes, but escapes into space inadvertandly

• TV and FM radio transmissions have been leaving earth since about 1940.

• They have made it a little over 60 ly in that time (reached 2500 stars)

• Effect of doppler shift due to earth’s rotation about sun

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• It may contain pictures or simple coded language

• Math can be used to transmit a picture(binary coding)

• Mathematics provide a universal language that any technological civilization would understand

• Pictures may depict the image of human race,DNA,radio telescope,location of earth in solar system,location of solar system in milky way galaxy,as per the ideas known to us

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• Usage of multiple images to indicate motion

• Increasing the resolution of the image

• Using better coding techniques after successfully exchanging the information

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LASER COMMUNICATION

• Signal tightly collimated –energy concentration single direction

• Visible light(LASER) easier to use than radio wave or microwave(MASER)

• Good for interstellar communication if location is accurately known

• Possibility of getting accidental signals are very low

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NEUTRINO

• Neutrino is a subatomic particle produced by cosmic rays in earth’s atmosphere

• Neutrino communication is advantageous as it has low probability of interacting with any other matter

• Apparatus sensitive to wide-range• Superkamiokande detector is used for neutrino

detection • Means of detecting neutrinos are relatively

insensitive with current technology

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SETI(Search for extraterrestrial intelligence)

• Started in the early 1970’s by NASA• With main aim as to identify intelligence from another

communicating civilization• Established SETI programs as NASA’s AMES and JPL• AMES-can do target searches• JPL-can do sky surveys• NASA funding from 1988-1993 • Since then scaled down versions have been privately

funded

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PROJECT OZMA

• Frank Drake in 1960 independently came up with the same conclusion.

• Used a 26m radio telescope at Green Bank, West Virginia• Searched for ETI for 2 weeks.

• Called it Project Ozma (L. Frank Baum’s Land of Oz - “very far away,difficult to reach, and populated by strange and exotic beings”)

• Looked at Tau Ceti and Epsilon Eridani (stars about same age as the sun)

• Looked for repeated series of patterned pulses or a series of prime numbers.

• Showed systematic searches are feasible and eventually led to a small SETI program at NASA in the 1970’s

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PROJECT PHOENIX• Started in 1995• Targeted search of local objects in the sky within 200

light years• Examining 1,000 nearby stars using the world’s largest

antennas• Monitors millions of radio channels simultaneously

between 1,000-3,000 MHz.• Looking for narrow band signals.• By mid-1999 had examined 50% of stars on its “hit list”• Listening done automatically• Two billion channels examined for each target star

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OPTICAL SETI at licks observatory• Communicating by visual signals (e.g., lasers).• Requires more energy to send signal (than radio).• Tends to absorbed by dust grains in interstellar space.• Could use short bursts of laser light, into a Morse

code.• Should be immune to “false positives” from Radio SETI.• looking for laser pulses (billionth of a second long).• new technology makes this search possible.• uses a telescope and three photomultipliers, built by

UC Santa Cruz undergrad physics major.• examined 300 stars and a few star clusters.

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Allen Telescope Array• Funding from Paul Allen and Nathan Myhrvold• Being constructed for SETI use and radio

astronomy.• Joint effort by SETI and UC Berkeley.• Built at Hat Creek Observatory north of Lassen

Peak.• Will expand Project Phoenix to 100,000-1,000,000

stars• Will cover 1,000-10,000 MHz• Will be 350 - 6.1m antennas, randomly placed in 1

km diameter area.

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• The distances involved imply large transmitted power and/or large antennas

• The costs can be mitigated by reducing the energy delivered to the receiver

• Requires an end-to-end communication system

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• en.wikipedia.org• D.G. Messerschmitt, ”Design for minimum

energy in starshipand interstellar communication”submitted to the Journal of the British Interplanetary Society (available at arxiv.org/abs/1402.1215).

• seti.org• astronomytoday.com• Rohlfs, K., & Wilson, T. L. (2004). Tools of

radio astronomy. Astronomy and astrophysics library. Berlin: Springer.

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