Where is the search for extraterrestrial life up to?
Updated
Despite the headlines, no alleged signals from ET have ever been confirmed. Yet far from being put off their search, scientists are stepping it up.
For decades scientists have been searching for evidence of life beyond Earth — intelligent or otherwise — using an array of methods.
"If you are talking about life in the solar system, like life on Mars, or maybe Saturn's moon Titan, or maybe one of Jupiter's moons like Europa, then you just send a rocket and look for it," said Seth Shostak, of the Search for Extraterrestrial Intelligence (SETI) Institute in Mountain View, California.
There could be microbial life in all of these places, Dr Shostak said, "but you have to look hard, probably underneath the surfaces of these planets and moons".
As for finding life around other stars, scientists have to use really big telescopes to scan distant planets for chemicals — like oxygen, methane and water vapour.
The challenge is that these kinds of molecular tracers for life could also indicate geological events.
Scientists are still trying to pin down the exact chemical signature that would really prove life and not just the existence of volcanoes, Dr Shostak said.
Other chemicals like ammonia, carbon and amino acids could also be signs of life.
Meanwhile, the SETI Institute and others are focusing on another technique: looking for potential communication signals from ET.
"You just do what Jodie Foster did in the movie Contact and eavesdrop on radio signals," Dr Shostak explained.
Optical laser transmissions as well as narrow-band radio signals are possible signs of intelligent life out there.
But again it is hard to be sure where a signal really comes from, especially when you can't pick it up more than once.
False alarms and hoaxes
Take the recent report that the giant Russian RATAN-600 radio telescope had picked up a signal while scanning a star called HD164595, in the constellation Hercules, the year before.
"I've no doubt the signal was there, but the question was: is it ET, or just some satellite that's just wheeling overhead and producing some radio emission that they picked up?" Dr Shostak said.
He used SETI's Allen Telescope Array in northern California, to zoom in on the star system.
"We didn't find anything, the guys at the University of California Berkeley using their big telescope in West Virginia didn't find anything. The Russians looked in this direction, I think 39 times, and only found this signal once," Dr Shostak said.
So, this looks very much like another false alarm — just like the claim last year that a giant alien engineering project had been set up on a planet orbiting a star called KIC 8462852.
At least it wasn't a hoax like the claim, by an amateur UK radio astronomer in 1998, that he had found radio signals coming from a system of two dwarf stars in the constellation Pegasus.
The best candidate for an alien radio transmission remains the so-called WOW! signal, detected in 1977 by Ohio University's Big Ear radio telescope, Dr Shostak said.
The signal has not been heard again since so remains unconfirmed.
Scientists step up the search
Despite the lack of definitive evidence so far, the search for extraterrestrial life continues, and indeed scientists are stepping up the search.
The European Space Agency's ExoMars program is concentrating on Mars. An orbiter launched in March this year aims to examine the Martian atmosphere and a follow-up mission, featuring a rover vehicle, has a launch date of 2020.
Looking outside our solar system is NASA's Kepler space observatory, which lifted off in 2009. It has found thousands of planets, including dozens that could possibly support life.
The number of planets has increased substantially over the past few years thanks to faster data processing.
Meanwhile, the James Webb Space Telescope, planned for launch in 2018, will investigate the potential for extraterrestrial life by "sniffing" the atmospheric chemistry of Earth-like planets around other stars.
Back on Earth, the world's biggest single dish radio telescope, the 500-metre Aperture Spherical Radio Telescope (FAST), began operating in south-western China last month.
Construction of the Square Kilometre Array (SKA), a giant multi radio telescope — made up of thousands of dishes and up to 1 million antennas — is also due to start in 2018.
If it goes ahead, Australia will host more than 500 stations, each containing about 250 individual antennas.
As part of a key science program, called Cradle of Life, SKA will focus on searching for carbon-containing chemicals in planetary atmospheres, while also trying to detect radio emissions from extraterrestrial civilisations.
Parkes Observatory moves to centre stage
Meanwhile, the biggest-ever search for intelligent alien life ramps up this month when Parkes Observatory joins Green Bank Observatory in West Virginia in the $100 million Breakthrough Listen initiative.
The project picks up fainter radio signals and covers 10 times more sky than previous hunts for alien life.
Data is being analysed by computers belonging to volunteers of the citizen science project SETI@home.
About 10 million people around the world have downloaded the free SETI@home software.
While some scientists are sceptical about finding life on other planets, Dr Shostak said it was only a matter of time.
He plans to buy everyone he knows a flat white coffee if SETI doesn't find ET "within the next two decades".
"I might be wrong about that, and I may have to buy a lot of flat whites, but that's my estimate of how long it will take," he said.
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Topics: science-and-technology, space-exploration, planets-and-asteroids
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