Small Planets and a Dubious Signal
Last week, two items concerning deep space intrigued me. One
of them, a “mysterious” signal from deep space, was touted as a
possible signal from an advanced civilization. The other was a
major step forward towards finding a planet capable of
supporting a civilization that might send such a signal.
On August 31, NASA announced the discovery of two new
planets orbiting stars other than our Sun. A few years ago, the
discovery of planets outside our solar system would have been
front-page news. However, well over a hundred such planets
have been found, and two more might be greeted with a yawn.
But these two planets are different – they’re small. At only 10 –
20 times larger than Earth, they’re roughly the size of the planet
Neptune. This might not seem small except for the fact that all
the known planets outside our own solar system have been
giants, roughly the size of Jupiter or larger. Jupiter is over 300
times the size of Earth.
Like Jupiter, those monstrous planets are gaseous and obviously
aren’t places where life as we know it could flourish. The new
Neptune-size planets aren’t great candidates for life either.
However, their size makes it possible that they could be rocky
and/or icy planets, a step towards being livable places. Both the
new planets are much closer to their stars than we are to the Sun
and have very short years, completing their orbits around their
suns in less than three days. If you lived there, you’d get to be a
thousand years old pretty quickly!
One of the new planets is special. It orbits the star 55 Cancri in
the constellation Cancer, 41 light years away. It’s special
because it joins three other planets orbiting 55 Cancri. This
makes 55 Cancri the only star other than our Sun known to have
a planetary system with at least four planets circulating around it.
While the new planet zips around 55 Cancri in a bit less than
three days, the outermost gaseous giant planet is at roughly the
same distance from 55 as Jupiter is from the Sun. It takes it
4,520 days to orbit 55. You can bet this is one planetary system
that will get lots of attention in years to come.
Turning to that mystery signal, it’s highly unlikely that it will be
anything significant but I found it interesting to read about the
science behind the signal’s detection and evaluation. A brief
Reuters news item posted on AOL News cited a report dated
September 1 by Eugenie Reich in New Scientist magazine (and
on its Web site) about a mystery radio signal from deep space.
The signal was picked up by the huge Arecibo radio telescope in
Puerto Rico. For many years, one of this telescope’s missions
has been its involvement in a search for extraterrestrial
intelligence, SETI. SETI has been listening in on the universe,
trying to detect any sign of a signal transmitted by another
If there indeed is such a signal, SETI has to pick it out of all the
noise, interference and natural radio emissions from space. For
six years, SETI has also enlisted the support of anyone willing to
join in the search by downloading on their computers SETI
software designed to sift through the plethora of data. This effort
is called SETI@home. When the computers are resting in the
screensaver mode, the software kicks in and analyzes data
supplied from the Arecibo telescope.
Over a year ago, the Arecibo telescope was pointed to regions in
the sky from which radio signals of interest had been detected on
previous occasions. After analyzing the data, all but one have
disappeared, according to the New Scientist Web site article.
That signal has been picked up on three separate occasions and is
at an interesting frequency, 1420 megahertz. This frequency
corresponds to one of the main frequencies at which hydrogen,
the most abundant element in the universe, emits and absorbs
energy. Astronomers believe this would be a logical frequency
for an advanced civilization to use to advertise its presence to the
Of course, if this signal were truly from another civilization, it
would be the biggest news story ever. However, the total time
the signal has been observed is less than a minute! Dan
Werthimer, of UC Berkeley and the chief scientist of
SETI@home, says that they’re not “jumping up and down” but
they plan to continue to observe the mystery signal. The New
Scientist article discusses other possible sources of the signal.
Could hackers either have modified the software to return a
spurious signal, somehow generate a signal bearing the hallmarks
of an alien transmission or resort to some other nefarious scheme
to dupe the scientists?
Another suggested possibility is that the telescope has to be
pointed to the same spot in the sky to get the signal. Could that
particular position of the telescope somehow reflect a signal from
the ground into the detectors or could it be that there’s a source
on the ground emitting this signal that only gets picked up in this
specific position? Or, is the signal originating from some
unknown stellar source hitherto undetected? Jocelyn Bell
Burnell is cited as pointing to her discovery of the pulsar, thanks
to an anomalous signal from deep space. (We discussed her
work in the column of 5/19/2004.)
An Unexpected Diversion: Writing a column can be a weird
experience. When I typed SETI@home, Microsoft Word
automatically colored it blue and underlined it, mistakenly
assuming it was a Web site address. In trying to de-underline it
and color the font black, I inadvertently clicked while a little
hand was showing. Suddenly I was online and was led to the
actual SETI home site. This in turn led me to The Planetary
Society Web site and two articles by Amir Alexander, one titled
“Reports of SETI@home Extraterrestrial Signal Highly
Exaggerated” is dated September 2, 2004. The title is essentially
a quote attributed to the above-mentioned SETI scientist, Dan
The other article dated May 17, 2004 by Alexander, “Pulses,
Triplets and Gaussians: Rescoring Reobservations”, describes in
detail the SETI search for and the “scoring” of candidate signals
for further observation and evaluation. There are literally
billions of points in the sky where unusual signals have been
detected. One criterion SETI uses to dismiss the vast majority of
these points is to look at those same spots in the sky again and
see if the signals are still there. If they aren’t, out they go.
SETI looks for pulses at a fixed frequency that stand out above
the noise and triplets, which are sets of three equally spaced
pulses. There are also steady celestial signals that aren’t pulses.
The Arecibo telescope sweeps the region of the sky where these
steady signals are found. As you would expect, the signal
becomes strongest at the center of the beam and dies out as the
telescope sweeps away from the center. If you plot the signal
strength, or power, during a sweep you therefore get a bell-
shaped curve, known in the trade as a “gaussian” curve.
The mystery signal is a gaussian. But there’s a problem. It drifts
in frequency. If the Arecibo telescope had been a few seconds
later it would have missed the signal. If I understand correctly, I
imagine it would be as if our New York radio station WOR
began broadcasting with a drifting frequency around its normal
710 on our radio dials. If we tuned in at the wrong time we’d
miss it! But wait a minute; our Earth is moving and so would
any planet harboring a civilization trying to reach us. This
means that as the distant planet and we rotate, the frequency will
shift due to the Doppler effect, just as the horn changes
frequency as an auto speeds by.
How clever would an advanced civilization be? Some at SETI
think they would purposely drift the transmitted frequency to
compensate for their planet’s motion so we would receive it as a
single frequency. Hey, if they’re that clever, I’m impressed!
The SETI software people can correct for our own Earth’s
motion and they look at these gaussian signals corrected and
uncorrected. The mystery signal that has caused all the
commotion is a corrected signal but it still drifts. Bottom line –
Werthimer doubts that this signal will prove to be “the real
thing” but they’ll keep watching for it.
Down here on Earth, as I write this, Frances has arrived in our
area of New Jersey with gobs of moisture. We were happy to
hear from a number of our Florida friends that they survived
Frances’ wrath with little or no damage. Let’s hope Ivan goes
somewhere else and in a weakened state.
Allen F. Bortrum