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New Scientist
01 September 04

Mysterious signals from 1000 light years away

In February 2003, astronomers involved in the search for extraterrestrial
intelligence (SETI) pointed the massive radio telescope in Arecibo, Puerto
Rico, at around 200 sections of the sky.
The same telescope had previously detected unexplained radio signals at
least twice from each of these regions, and the astronomers were trying to
reconfirm the findings. The team has now finished analysing the data, and
all the signals seem to have disappeared. Except one, which has got
stronger.
This radio signal, now seen on three separate occasions, is an enigma. It
could be generated by a previously unknown astronomical phenomenon. Or it
could be something much more mundane, maybe an artefact of the telescope
itself.
But it also happens to be the best candidate yet for a contact by
intelligent aliens in the nearly six-year history of the SETI@home project,
which uses programs running as screensavers on millions of personal
computers worldwide to sift through signals picked up by the Arecibo
telescope.

Absorb and emit

"It's the most interesting signal from SETI@home," says Dan Werthimer, a
radio astronomer at the University of California, Berkeley (UCB) and the
chief scientist for SETI@home. "We're not jumping up and down, but we are
continuing to observe it."
Named SHGb02+14a, the signal has a frequency of about 1420 megahertz. This
happens to be one of the main frequencies at which hydrogen, the most common
element in the universe, readily absorbs and emits energy.
Some astronomers have argued that extraterrestrials trying to advertise
their presence would be likely to transmit at this frequency, and SETI
researchers conventionally scan this part of the radio spectrum.
SHGb02+14a seems to be coming from a point between the constellations Pisces
and Aries, where there is no obvious star or planetary system within 1000
light years. And the transmission is very weak.
"We are looking for something that screams out 'artificial'," says UCB
researcher Eric Korpela, who completed the analysis of the signal in April.
"This just doesn't do that, but it could be because it is distant."

Unknown signature

The telescope has only observed the signal for about a minute in total,
which is not long enough for astronomers to analyse it thoroughly. But,
Korpela thinks it unlikely SHGb02+14a is the result of any obvious radio
interference or noise, and it does not bear the signature of any known
astronomical object.
That does not mean that only aliens could have produced it. "It may be a
natural phenomenon of a previously undreamed-of kind like I stumbled over,"
says Jocelyn Bell Burnell of the University of Bath, UK.
It was Bell Burnell who in 1967 noticed a pulsed radio signal which the
research team at the time thought was from extraterrestrials but which
turned out to be the first ever sighting of a pulsar.
There are other oddities. For instance, the signal's frequency is drifting
by between eight to 37 hertz per second. "The signal is moving rapidly in
frequency and you would expect that to happen if you are looking at a
transmitter on a planet that's rotating very rapidly and where the
civilisation is not correcting the transmission for the motion of the
planet," Korpela says.
This does not, however, convince Paul Horowitz, a Harvard University
astronomer who looks for alien signals using optical telescopes. He points
out that the SETI@home software corrects for any drift in frequency.

Fishy and puzzling

The fact that the signal continues to drift after this correction is "fishy"
, he says. "If [the aliens] are so smart, they'll adjust their signal for
their planet's motion."
The relatively rapid drift of the signal is also puzzling for other reasons.
A planet would have to be rotating nearly 40 times faster than Earth to have
produced the observed drift; a transmitter on Earth would produce a signal
with a drift of about 1.5 hertz per second.
What is more, if telescopes are observing a signal that is drifting in
frequency, then each time they look for it they should most likely encounter
it at a slightly different frequency. But in the case of SHGb02+14a, every
observation has first been made at 1420 megahertz, before it starts
drifting. "It just boggles my mind," Korpela says.
The signal could be an artefact that, for some reason, always appears to be
coming from the same point in the sky. The Arecibo telescope has a fixed
dish reflector and scans the skies by changing the position of its receiver
relative to the dish.
When the receiver reaches a certain position, it might just be able to
reflect waves from the ground onto the dish and then back to itself, making
it seem as if the signal was coming from space.
"Perhaps there is an object on the ground near the telescope emitting at
about this frequency," Korpela says. This could be confirmed by using a
different telescope to listen for SHGb02+14a.

Possible fraud

There is also the possibility of fraud by someone hacking the SETI@home
software to make it return evidence for an extraterrestrial transmission.
However, SHGb02+14a was seen on two different occasions by different
SETI@home users, and those calculations were confirmed by others.
Then the signal was seen a third time by the SETI@home researchers. The
unusual characteristics of the signal also make it unlikely that someone is
playing a prank, Korpela says. "As I can't think of any way to make a signal
like this, I can't think of any way to fake it."
David Anderson, director of SETI@home, remains sceptical but curious about
the signal. "It's unlikely to be real but we will definitely be re-observing
it." Bell Burnell agrees that it is worth persisting with. "If they can see
it four, five or six times it really begins to get exciting," she says.
It is already exciting for IT engineers Oliver Voelker of Logpoint in
Nuremberg, Germany and Nate Collins of Farin and Associates in Madison,
Wisconsin, who found the signal.
Collins wonders how his bosses will react to company computers finding
aliens. "I might have to explain a little further about just how much I was
using [the computers]," he says.

Eugenie Samuel Reich

**
Intergalactic messages 'in a bottle' are best

Rather than transmitting radio messages, extraterrestrial civilisations
would find it far more efficient to send us a "message in a bottle" - some
kind of physical message inscribed on matter. And it could be waiting for us
in our own backyard.
That is the conclusion of a new analysis of interstellar communications by
Christopher Rose of Rutgers University in New Jersey and Gregory Wright, a
physicist with Antiope Associates also in New Jersey.
Assuming the aliens do not care how long it takes for their message to
arrive, beaming a radio signal that can be detected 10,000 light years away,
for instance, would take a million billion times as much energy as just
shooting out matter in which data is embedded. "If energy is what you care
about, it's tremendously more efficient to toss a rock," Rose says.
Radiation loses out to rocks over long distances because it spreads out as
it travels through space, diluting the signal below detection levels unless
the beam is extremely powerful to begin with.

Bottle throwing aliens

If aliens are using a transmitter the size of the dish that astronomers on
Earth use to look for their signal - the 305-metre radio telescope in
Arecibo, Puerto Rico, which is the largest single-dish telescope on Earth -
they would have to be closer than Saturn for the transmission to be more
energy efficient than just flinging a bottle at us.
If the Voyager space probes, which are now at the edge of the solar system,
were each carrying three DVDs' worth of data, they would be a more
energy-efficient way of sending information to someone 2000 light years away
than an Arecibo-to-Arecibo radio communication.
Also, once radio signals pass they are gone for ever. So aliens would have
to beam signals continuously, or other civilisations might blink and miss
them. Physical objects stay where they land.
Not everyone is convinced by Rose and Wright's analysis. "Their conclusion
is that we should be looking for the Encyclopaedia Galactica within the
Solar System," says Fred Walker, an astronomer at Stony Brook University in
New York who is interested in the search for extraterrestrial intelligence.
"I'm not sure I would expend any effort on this."
However, Don Yeoman at NASA's Jet Propulsion Laboratory in Pasadena,
California, who co-ordinates a project looking for asteroids on a collision
course with Earth, accepts that their project could conceivably spot such
alien objects. "It's not completely out of the question."

Journal reference: Nature (vol 431, p 47)

Jenny Hogan

**
Two new rocky 'super Earths' found

Two Neptune-sized planets have been discovered circling stars beyond our
Solar System, US astronomers reported on Tuesday. The discoveries, which
come less than a week after a similar announcement by European scientists,
hint at a vast new class of extrasolar planet.
The new planets are "middleweight" and may be rocky, in contrast to the
massive planets whose discovery is favoured by current observational
techniques. Most of the 135 known extrasolar planets have masses on a par
with Jupiter, a gas giant several hundred times the mass of Earth. But the
two new planets weigh in at around Neptune's mass, which is 17 times that of
Earth, and span about three times Earth's diameter.
"We can't quite see Earth-like planets yet, but we're seeing their big
brothers," says Paul Butler, an astronomer at the Carnegie Institution of
Washington in Washington, DC, who found one of the planets. He believes
lower mass planets may outnumber their heftier gas giant cousins.
The two new planets each orbit their host stars in less than three days, at
distances about 10 and 20 times closer than Mercury orbits the Sun. They
were both discovered by the gravitational "wobbles" they induced in their
stars, which lie less than 45 light-years away from Earth.

Quadruple system

Butler and his colleagues used the powerful Keck Observatory in Hawaii to
find a planet 20 times the mass of Earth around Gliese 436, a type of star
called an M dwarf. Relatively lightweight planets are easier to detect
around these stars, which themselves boast just half the mass of the Sun.
However, M dwarfs have not been studied extensively because they are faint -
only one other is known to host a planet - but they represent about 70% of
nearby stars. That suggests more than 20 billion M dwarfs may harbour
planetary systems in our galaxy alone, according to the team.
The new find may also signal a link between planetary masses and star types.
"Perhaps these small stars typically have smaller planets," Butler says.
The other planet was discovered circling a star called 55 Cancri, which
already has three known planets. The discovery of the new planet, using the
Hobby-Eberly Telescope in Texas, makes 55 Cancri the first quadruple
planetary system found beyond the Solar System.
It is also the smallest-mass planet yet confirmed, as Hubble Space Telescope
observations pinned down its mass at 18 times that of Earth. European
astronomers did announce finding a planet about 14 times the mass of Earth
on 25 August - but this discovery was not peer-reviewed, the US scientists
say, citing a slightly tense "but friendly" race to find new planets.

Steam atmosphere

The new planets' compositions are a mystery. But astronomers believe they
formed at large distances from the Sun, like Neptune. They would have begun
with rocky, icy cores and thick atmospheres and migrated inward.
"People have speculated that such planets could then become ocean worlds as
the ice melts," says Sara Seager, an astronomer at the Carnegie Institution
of Washington. If the planets wandered too close to the star for liquid
water to be stable, the planets "would instead have a massive steam
atmosphere", she told New Scientist.
Alan Boss, a theorist at Carnegie, suggests two other - less likely -
formation scenarios. The planets could be "gas midgets" that formed mostly
from gas at large distances, like Jupiter, but either never reached
Jupiter's size or somehow hemorrhaged their mass. Or they could have taken
shape at their present orbits, making them "super Earths" made almost
entirely of rock.

Maggie McKee