As well as receiving signals from outer space, radio telescopes such as Arecibo can also broadcast signals to the entire galaxy and beyond. In 1974, radio waves beamed from the Arecibo telescope carried a message deep into space. The message consisted of 1679 pulses that, when arranged into a grid 23 columns wide and 73 rows tall. The message was aimed at a dense ball of stars called M 13, which is so far away from Earth that it could take up to 50,000 years for a possible reply.
Serendip uses the world’s largest radio telescope to scan a fair fraction of the celestial sphere. This means it samples many billions of Milky Way stars and many thousands of background galaxies. No one star gets as deep a scrutiny as Project Phoenix provided, but the number of stars being scanned is immense.
No real-time followup yet. This is a problem for piggyback SETI, partly because weak signals from beyond several hundred light-years should fade in and out of audibility, on a timescale of minutes, due to “interstellar scintillation” caused by the thin gas between the stars. Therefore several repeat observations of each point on the sky will probably be needed to catch a single repeat of a continuous weak signal. And, of course, if the aliens turn their transmitter elsewhere (or off) before a dedicated follow-up is scheduled, the chance to confirm a signal disappears.
Astronomers have detected nearly 2,000 alien planets to date. As that number continues to rise, so too does the prospect of finding intelligent extraterrestrial life. In terms of the search for extraterrestrial intelligence (SETI), it may no longer be a matter of answering the “are we alone” question, some scientists say. Rather, just how crowded is the universe?
And if ET is out there, it may be possible to reach out with direct “radio waving” to potentially habitable exoplanets. This form of cosmic cryptography, called “Active SETI,” involves no longer merely listening for a signal but purposefully broadcasting to, and perhaps establishing contact with, other starfolk.
Active SETI sounds like science fiction, but some astronomers are discussing it seriously today. The idea is, as it has been in the past, a controversial, hot-button issue, with some researchers wary of sending signals out to touch base with intelligent aliens.