BBC News - 'No signal' from targeted ET hunt
1 June 2012 Last updated at 11:50 ET
'No signal' from targeted ET hunt
VLBA telescope, Hawaii Very long baseline interferometry results in an
effective antenna of many kilometres in size
The hunt for other intelligent civilisations has a new technique in its
arsenal, but its first use has turned up no signs of alien broadcasts.
Australian astronomers used "very long baseline interferometry" to
examine Gliese 581, a star known to host planets in its "habitable zone".
The hunt for aliens is fundamentally a vast numbers game, so the team's
result should come as no surprise.
Their report, posted online, will be published in the Astronomical Journal.
In recent years, interest in such targeted searches has begun to surge
as the hunt for planets outside the Solar System continues to find them
at every turn.
Astronomers currently estimate that every star in the night sky hosts,
on average, 1.6 planets - implying that there are billions of planets
out there yet to be confirmed.
But a number of stars have already been identified as playing host to
rocky planets at a distance not too hot and not too cold for liquid
water - the first proxy for amenability to life.
ET or AT&T?
Gliese 581, a red dwarf star about 20 light-years away, is a
particularly interesting candidate for the Search for Extraterrestrial
Intelligence, or Seti.
It has six planets, two of which are "super-Earths" likely to be in this
So astronomers at Curtin University's International Centre for Radio
Astronomy Research in Australia, put one of radio astronomy's
highest-resolution techniques to work, listening in to the star system.
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Very long baseline interferometry (VLBI) is the process of using several
or many telescopes that are distant from one another, carefully
combining their signals to make them effectively act as one large
telescope, peering intently at a tiny portion of the sky.
The team trained the Australian Long Baseline Array onto Gliese 581 for
eight hours, listening in on a range of radio frequencies.
The result was radio silence - but the team used their experience to
validate VLBI as a technique particularly suited to this kind of
Seth Shostak, principal astronomer at the Seti Institute in the US, said
that the approach's strength lies in the fraction of the sky it examines.
"It's like they're looking at the sky through a 6-foot-long cocktail
straw - a tiny bit of the sky, so they're only sensitive to signals that
are coming from right around that star system," he told BBC News.
That is useful not only for getting a high-resolution view, but for
excluding the signals from Earthly technologies that plague Seti efforts.
"Figuring out 'is this ET or AT&T?' isn't always easy, and VLBI gives
you a good way of discriminating, because if you find something from
that tiny, tiny dot on the sky you can say that's not one of our
satellites," Dr Shostak said.
He added that the team's negative result was not disheartening, because
the odds have it that the hunt for aliens, if it is ever to find them,
will require thousands or millions of observations of this kind.
"Consider the fact that you could've looked at the Earth for four
billion years with radio antennas - here was a planet that's clearly in
the habitable zone, has liquid oceans, and has an atmosphere - and yet
unless you had looked in the last 70 years and were close enough, you
wouldn't have found any intelligent life," he said.
"The fact that we look at one star system and don't find a signal
doesn't tell you that there's no intelligent life."