By Seth Shostak
SETI Institute
posted: 31 January 2008
06:39 am ET

Incredibly, it's been only a bit more than a century since Oliver Heaviside consolidated the work of several 19th century physicists into the four compact mathematical formulations known as Maxwell's Equations. You may gleefully recall them from sophomore physics.

Aside from their display by the rabidly nerdy on pretentious t-shirts, the formulae have a splendid utility: they describe all electromagnetic radiation — in particular, light and radio. In the short time since their discovery, we have been able to milk these elegant equations to build crude spark transmitters, and eventually to develop the diminutive cell phones that allow you to blithely ring up your pals while comfortably seated in restaurants and movie theaters. We have exploited Maxwell's Equations like an old-growth forest, and many technical types aver that we know all there is to know about them.

Not true. And the fact that it's untrue may affect our thinking about SETI.

Today's SETI experiments generally look for what are politely termed "narrow-band signals." In other words, the receivers at the back ends of our radio telescopes search wide swaths of the spectrum looking for a signal that's at one spot on the dial — a signal that's very constrained in frequency. By putting all the transmitted power into this small bandwidth, the aliens can ensure that their signal will stand out like Yao Ming at a Munchkin picnic.




That makes sense — at least if the aliens want only to help us find their signal. But they might have other priorities. In particular, the history of earthly communication suggests that there is an inexorable pressure to increase the bit rate of any transmission channel. A half-decade ago, most readers accessed this web site with a simple dial-up phone line. Today, you're more likely to have some sort of wide-band service, which is to say, you're inhaling Internet bits at least ten times quicker than before.

More generally, in 150 years, we've gone from telegraph wires, capable of a few bits per second, to optical fibers that are billions of times speedier. The idea of "more bandwidth" is so compelling, the phrase has entered the lexicon of everyday speech — even among those who couldn't tell a hertz from a hub nut. Communication technology is always driven to send more bits — more information — per second.

Now consider the plight of aliens wishing to get in touch. Because the separation between one civilization and another is likely to be at least hundreds — and maybe thousands — of light-years, any interstellar pinging is effectively one-way. Back and forth conversations will take too long. So perhaps the aliens will opt to send, not the easiest-to-find signal, but a signal that says it all — a signal bristling with information. If you're going to stuff a message into a bottle, why not use onion-skin paper and write small?

The straightforward way to get more information down a radio channel is, as everyone knows, by using greater bandwidth. Nearly once a week someone sends me an e-mail pointing this out, saying that SETI should be looking for wide-band signals, not narrow-band ones. But there's a problem here. While sending a wide-band, information-rich signal between nearby stars is perfectly practical (assuming you're willing to pay the power bill), once the distance exceeds a thousand light-years or so the billowing hot gas that permeates interstellar space begins to wreak havoc and destruction on the transmission. A process of "dispersion" occurs, which works to slow the broadcast — but it slows different frequencies by different amounts. The result is to distort a wide-bandwidth signal in much the way that a highly reverberant hall would distort the music from an orchestra. A narrow-band signal (the acoustical analog is a simple flute note) would not be adversely affected.

So it seems that there may be difficulties in sending certain kinds of complex radio signals over significant distances in the Galaxy. Interstellar correspondence could be restricted to mere postcards, which would be a disappointment to aliens interested in heavy-duty data distribution.

However, some Swedish physicists are pointing out a possible scheme for beating this rap. In careful analyses of some of the subtle properties of Maxwell's Equations, Bo Thide and Jan Bergman at the Swedish Institute of Space Physics in Uppsala have explored a property of radio waves called orbital angular momentum. You can think of this orbital momentum as a twisting of the wave's electric and magnetic fields — a twisting that would show up if you were measuring the wave with an array of antennas. The technical details are intricate, but suffice it to say that the Swedish scientists are noting another way to send information in a radio signal — even a narrow-band radio signal — by encoding it in the orbital angular momentum.

It's as if they've found "subspace channels," a là Star Trek. Hidden highways down which additional bits can be moved. And there's reason to think that these momentum channels might be impervious to the interstellar jumbling that afflicts the usual types of wide-band signals when sent over great distances.





So it may be that our search for narrow-band signals is actually a very good SETI strategy, and not just an obvious one. While such monotonic messages may seem to be elementary and devoid of much information, they could be laden with additional, hidden complexity.

The investigation of new transmission modes by Thide and Bergman hints that if we do find a signal from ET, we may wish to reconfigure our radio telescopes to look for encoding of the message via such subtle effects as orbital angular momentum. A simple signal may only be a cipher for a more complex message, and there may be more things in heaven and earth than even Maxwell had dreamt of …

By Jeanna Bryner
Staff Writer @ SPACE.com
posted: 05 February 2008
06:42 am ET

As if reaching out with a come-hither motion, a giant gas finger emanating from two neighboring galaxies has hooked into the starry disk of the Milky Way and is pulling all three galaxies closer.

This extremity of hydrogen gas is actually the pointy end of the so-called Leading Arm of gas that streams ahead of two irregular galaxies called the Large and Small Magellanic Clouds.

The fate of these nearby galaxies, which are impacted by the Milky Way's gravity, has been somewhat of a mystery. The new finger findings suggest that the Magellanic Clouds will eventually merge with the Milky Way rather than zooming past.

Located about 160,000 light-years from Earth, the Large Magellanic Cloud (LMC) is only one-twentieth the diameter of our galaxy and contains one-tenth as many stars. The Small Magellanic Cloud resides 200,000 light-years from Earth and is about 100 times smaller than the Milky Way.

"We're thrilled because we can determine exactly where this gas is plowing into the Milky Way," said research team leader Naomi McClure-Griffiths of CSIRO's Australia Telescope National Facility.

Called HVC306-2+230, the gas finger is gouging into our galaxy's starry disk about 70,000 light-years away from Earth. In the night sky, the contact point would be nearest the Southern Cross.

Until last year, astronomers thought the Magellanic Clouds had orbited our galaxy many times. This scenario held a gloomy outlook for the clouds, which were said to be doomed to be ripped apart and swallowed by the gravitational goliath.

But then new Hubble Space Telescope measurements revealed the clouds are paying our galaxy a one-time visit rather than being its lunch.

McClure-Griffiths' results, however, are more in line with the previous tale pegging the Milky Way and the Magellanic Clouds as long-time companions. McClure-Griffiths remarks that this isn't the final word and that both theories are still on the table.

By pointing out the spot of contact between the Leading Arm and our galactic disk, the recent study will help astronomers to predict where the clouds themselves will travel in the future.




"We think the Leading Arm is a tidal feature, gas pulled out of the Magellanic Clouds by the Milky Way's gravity," McClure-Griffiths said. "Where this gas goes, we'd expect the clouds to follow, at least approximately."

By Jeremy Hsu
Staff Writer @ SPACE.com
posted: 06 February 2008
06:43 am ET


New discoveries about magnetic field lines and the first-ever direct observation of their reconnection in space are offering hope that scientists will learn how to unlock fusion power as an energy source in the future.

"The reconnection processes in the [Earth's] magnetosphere and in fusion devices are the same animal," said James Drake, a University of Maryland physicist.




Space contains magnetic fields that direct the flow of plasma, an energetic fourth state of matter consisting of positive ions and electrons. The plasma particles normally follow the paths of the magnetic field lines like streams of cars following highways.

Magnetic reconnection can release that stored energy when two magnetic field lines bend towards each other and fuse to create new field lines. The effect is not unlike an earthquake forcibly realigning parallel highways into perpendicular routes and channeling cars along the newly created paths. Although some released plasma energy travels in a straight line — called a super-Alfvenic electron jet — other plasma particles fan out as though escaping the opening of a trumpet.

The effect not only fascinates astrophysicists but also frustrates efforts on Earth to create sustained energy sources through fusion. Experimental fusion reactors force atomic particles to fuse together and release energy as plasma. The plasma is contained within a "magnetic bottle," or a cage of magnetic field lines, so that the high plasma temperatures can maintain the fusion reaction.

However, magnetic reconnection can break the magnetic bottle and allow plasma to reach the colder walls of the reactor where fusion will not sustain itself.

Drake became interested in the topic when he looked at early fusion studies and realized how many theories at the time were "dead wrong" about magnetic reconnection. To learn more about the phenomenon, he had to look beyond Earth.

"I started realizing some of the best magnetic reconnection data is in space," Drake said.

During a sabbatical at the University of California-Berkeley, the theoretical physicist happened to work in the same office as Tai Phan, an observational physicist who was looking at magnetic field data from the European Space Agency's Cluster satellites.

"I was doing theory, Tai was doing data and we suddenly saw this correspondence," Drake marveled. "It was purely accidental."



The four Cluster satellites crossed through a turbulent plasma region just outside Earth's magnetic field in January 2003, when they happened to run into an area where magnetic reconnection had occurred. Physicists thought such areas, known as electron diffusion regions, were just over six miles long and so spacecraft would probably miss them in the vastness of space.

Instead, a new look at the Cluster data showed that the electron diffusion region measured 1,864 miles long — 300 times longer than early theoretical expectations and still four times longer than seen in the latest astrophysics simulations. That also marked the first ever direct observations of magnetic reconnection in space.

Although the basic physics behind magnetic reconnection remain a mystery, Cluster promises that future missions have a good chance of further examining the phenomenon. One example is NASA's Magnetospheric Multiscale mission, which will consist of four spacecraft that study why the plasma particles can become "unfrozen" or unstuck from the magnetic field lines they normally travel along. Magnetic reconnection is simply the most "dramatic" example of this, Drake said.

Such an energy release amounts to a conversion of magnetic energy into particle energy, which can occur in black hole jets and drives solar flares. Drake hopes to someday create a computer model that can accurately describe the conversion process — and if scientists can also apply some understanding towards improving fusion reactors, so much the better.

By Joe Rao
SPACE.com Skywatching Columnist
posted: 20 July 2007
12:55 am ET

On Aug. 28, skywatchers across much of North America can watch as the Moon crosses into the Earth's shadow and will undergo its second total eclipse in 2007.

West Coast viewers will get the best show.

Lunar eclipses occur when Earth gets between the sun and the moon, casting a shadow. The view is different from each location on the planet. Along the West Coast of Canada and the United States and in Alaska, the entire eclipse will be visible from start to finish before moonset in the early morning hours of that Tuesday. Hawaiians will see totality – when the moon is completely in Earth's shadow – high in their sky around midnight.

In eastern Asia and Australia, the event will occur on the same date but in the evening, since for this part of the world it will coincide with moonrise.

What will happen

The Moon will track across the southern portion of the Earth's shadow, and will be completely immersed for one-hour and 30 minutes, making this a much-longer than normal totality.

Because some of the sunlight that strikes our Earth is diffused and scattered by our atmosphere, its shadow is not completely dark; enough of this light reaches the Moon to give it an eerie coppery glow even when it's totally eclipsed. It is anticipated that during the upcoming total eclipse the Moon will glow brightest across its lower portion, while its upper part (closest to the center of the shadow) will appear a deep shade of brown or gray.

For easterners, the eclipse will begin around dawn and will still be in progress when the Sun rises and the Moon sets, two events that happen almost simultaneously on a lunar eclipse night.

For the Canadian Maritime Provinces the Moon sets before total eclipse begins; be on the watch for a thinning sliver of the Moon's edge going down just above the western horizon. Across the eastern United States and the Great Lakes States, the Moon sets during totality. In this region, depending on where you are located and just how clear your western sky is on eclipse morning, you might lose sight of the eclipsed Moon completely before it sets, since the twilight sky will still be quite bright and the full Moon will be shining 1/10,000 as bright as it normally would; otherwise, you'll be hunting for a dim ball.

Across the Nation's midsection, the Plains and Rocky Mountain States totality has already ended before moonset and the eclipse is partial as the moon emerges from the Earth's shadow.

The next total lunar eclipse is scheduled for Feb. 20-21, 2008 and will widely visible from North and South America, as well as Europe, Africa and eastern Asia.

By Joe Rao
SPACE.com Skywatching Columnist
posted: 20 July 2007
12:55 am ET

On Aug. 28, skywatchers across much of North America can watch as the Moon crosses into the Earth's shadow and will undergo its second total eclipse in 2007.

West Coast viewers will get the best show.

Lunar eclipses occur when Earth gets between the sun and the moon, casting a shadow. The view is different from each location on the planet. Along the West Coast of Canada and the United States and in Alaska, the entire eclipse will be visible from start to finish before moonset in the early morning hours of that Tuesday. Hawaiians will see totality – when the moon is completely in Earth's shadow – high in their sky around midnight.

In eastern Asia and Australia, the event will occur on the same date but in the evening, since for this part of the world it will coincide with moonrise.

What will happen

The Moon will track across the southern portion of the Earth's shadow, and will be completely immersed for one-hour and 30 minutes, making this a much-longer than normal totality.

Because some of the sunlight that strikes our Earth is diffused and scattered by our atmosphere, its shadow is not completely dark; enough of this light reaches the Moon to give it an eerie coppery glow even when it's totally eclipsed. It is anticipated that during the upcoming total eclipse the Moon will glow brightest across its lower portion, while its upper part (closest to the center of the shadow) will appear a deep shade of brown or gray.

For easterners, the eclipse will begin around dawn and will still be in progress when the Sun rises and the Moon sets, two events that happen almost simultaneously on a lunar eclipse night.

For the Canadian Maritime Provinces the Moon sets before total eclipse begins; be on the watch for a thinning sliver of the Moon's edge going down just above the western horizon. Across the eastern United States and the Great Lakes States, the Moon sets during totality. In this region, depending on where you are located and just how clear your western sky is on eclipse morning, you might lose sight of the eclipsed Moon completely before it sets, since the twilight sky will still be quite bright and the full Moon will be shining 1/10,000 as bright as it normally would; otherwise, you'll be hunting for a dim ball.

Across the Nation's midsection, the Plains and Rocky Mountain States totality has already ended before moonset and the eclipse is partial as the moon emerges from the Earth's shadow.

The next total lunar eclipse is scheduled for Feb. 20-21, 2008 and will widely visible from North and South America, as well as Europe, Africa and eastern Asia.

By Dave Mosher
Staff Writer @ SPACE.com
posted: 23 July 2007
06:46 am ET

There's a strange moon whizzing around Saturn that's shaped, oddly, like a walnut.

Now astronomers find that Iapetus got its nutty shape from a super-fast spin that was frozen into place early in the solar system's formation.

When the Cassini spacecraft snapped close-ups of Saturn's moons in 2005, it revealed a bulging waistline of rock along the equator of the now slowly spinning Iapetus. Astronomers think this characteristic shape persists because Iapetus was cryogenically frozen in time about 3 billion years ago, during the moon's "teen" years.

"Iapetus spun fast, froze young and left behind a body with lasting curves," said Julie Castillo, a Cassini scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

Unlike any other moon in the solar system, Iapetus (eye-APP-eh-tuss) has retained its immature figure. Running exactly along its midsection, a chain of mountains 808 miles (1,300 kilometers) long and 12 miles (19 kilometers) high adds to the moon's walnut-like appearance.

"You would expect a very fast-spinning moon to have this bulge but not a slow-spinning moon, because the bulge would have been much flatter," said Dennis Matson, another Cassini project scientist at JPL. However, Mason said, "we've modeled how Iapetus formed its big, spin-generated bulge and why its rotation slowed down to its present, nearly 80-day period."

Iapetus originally spun once every five to 16 hours, which was fast enough to buckle its surface at the equator, according to the new model detailed in an upcoming online edition of the journal Icarus.

Scientists think radioactive elements heated the moon's interior to permit the crust to stretch and buckle, yet quickly froze the moon into shape as fuel ran out.

"Iapetus' development literally stopped in its tracks," Castillo said of the 4.564 billion-year-old hunk of rock. In order to slow the young moon down its present once-per-80-days rotational speed, Castillo explained, "its interior had to be much warmer, close to the melting point for water ice."

The finding should help astronomers better understand how the planets and their moon systems formed in the early solar system.