Radio Astronomy and SETI Jenny Bailey G 0
Radio Astronomy and SETI Jenny Bailey G 0 VQH Bernie Wright G 4 HJW Introduction History of Radio Astronomy SETI Practical Radio Astronomy Practical SETI Questions
Is there anyone out there ? The Drake Equation : Where N = The number of civilisations trying to contact us R = The average rate of Star Formation fp = The fraction of stars that are suitable for planet formation ne = Number of Earth-like planets fl = Fraction of Earth-like planets where life develops fi = Fraction of Earth-like planets where life has intelligence fc = Fraction of intelligent species who want to communicate L = Lifetime of a civilisation
Where Should we look l Frequency Radio - The ‘Water Hole’ Optical Gravity Waves The next big discovery l Polarisation Circular, linear, modulated ? l Direction Targeted search All-Sky survey l Radio Leakage Intentional messages RF leakage l Modulation Narrow band signals - preferably pure CW.
The ‘Water Hole’
SETI Projects l Arecibo/Jodrell l Project Argus l SETI@Home l Optical SETI Bank
How far can we hear ? Distant civilisation wants to signal us. Tx : Assume 1 GW into a 300 m dish at 1420 MHz. Rx : Assume Project Argus station as receiver - 4 m dish. Ga. As. FET LNA 10 Hz channels.
What signal should we look for ? l. A signal with Doppler shift would indicate non-terrestrial. CW signal to get attention A CW beacon would stand out from Galactic noise Can be seen with low bandwidth receiver l. A modulated signal This will spread the signal over a wide bandwidth and make the signal hard to detect
Should we Transmit A signal was sent from the Arecibo Telescope to celebrate its commissioning. This was controversial because : – The message was very USA-centric. It was argued that any message should be agreed by all nations. – We should not attract attention to our planet, we might invite BAD aliens.
How do we search ? l We need to look at as much Bandwidth as possible l The receiver must have a narrow Bandwidth to enhance the sensitivity Use an ex-PMR FM radio modified to product detect - creating a 25 KHz wide SSB receiver Synthesise narrow receive filters using PC running FFT software to chop the receiver bandwidth into many 10 Hz channels. Average each 10 Hz channel over a few seconds to improve receiver sensitivity
Signal Verification A signal from a distant star will have the following characteristics : l The signal will come and go with the response of the receiving aerial l The signal will have Doppler shift corresponding to the Earth’s spin and rotation around the sun.
- Slides: 10