Miércoles 5 de Septiembre de 2007, Ip nº 206

Vibrations on the Sun may 'shake' the Earth
Por David Shiga

What do dropped mobile phone calls, mysterious signals in undersea communications cables, and tiny tremors on the Earth have in common? They are all caused by vibrations on the Sun, according to one team of scientists. But other researchers question the claim, arguing that the pulsations may never escape the Sun's surface in the first place.

Churning motions inside the Sun produce various kinds of waves, including sound waves called p-modes and another type of wave called g-modes. G-modes arise when pockets of material rising up from deep within the Sun get pulled downwards again by gravity, leading to a wave motion similar to the rise and fall of waves on the surface of the ocean.

Both types of waves vibrate very slowly. The p-modes vibrate with periods of a few minutes, while the periods of g-modes are even longer, lasting tens of minutes or even several hours.

In the mid-1990s, a team led by engineer and statistician David J Thomson of Queen's University in Kingston, Ontario, Canada, reported seeing fluctuations in the solar wind – a stream of charged particles from the Sun – with periods in the same range as p-modes and g-modes. The data came from observations by the Ulysses spacecraft, which launched into space in 1990 to study the Sun. The researchers suggested that the solar vibrations were somehow imprinting onto the solar wind to produce the regular fluctuations.

Now, Thomson's team says it has evidence that these modes not only travel through space in the solar wind, but also influence natural phenomena and human technologies on Earth.

Dropped calls

Voltages on undersea communications cables experience, for example, unexplained fluctuations with periods characteristic of p-modes, they say. Also, seismic measurements of the Earth show very long periods in the range of g-modes. And the number of dropped mobile phone calls seems to fluctuate regularly with periods that tie them to solar vibrations, too.

"We can't think of anything else that generates that kind of frequency and is this stable," Thomson says, pointing out that the Ulysses spacecraft data suggests the oscillations persist at the same frequencies for years.

But how would vibrations imprinted on the solar wind produce these effects?

Geomagnetic storms caused by solar activity are widely acknowledged to have effects on power lines, so it seems possible that they may also affect undersea cables (see Unique double solar punch strikes Earth). How the fluctuations would affect mobile phone signals, however, is unclear.

'Extremely unlikely'

As for shaking the Earth, Thomson ventures that magnetic materials within the planet, such as nickel, could respond to the solar wind fluctuations. "It's a really odd kind of phenomenon," he told New Scientist. "It's not a very violent shaking, but it is measurable."

Other scientists are very sceptical that the fluctuations could affect things on Earth. "It seems extremely unlikely to me," says David Hathaway, a solar physicist at NASA's Marshall Space Flight Center in Huntsville, Alabama, US.

For one thing, some studies have found that the vibrations may not be able to escape from the Sun at all. Theory predicts that the g-modes in particular should be extremely weak by the time they rise to the Sun's surface and that they will not have any effect on the solar wind.

But Thomson counters that magnetic field lines that penetrate the visible surface of the Sun could help channel the g-modes into space: "You could, in fact, radiate a fair amount of energy."

'Profound implications'

Then, assuming the g-modes and p-modes could get off the Sun's surface, many scientists say such regular disturbances would be wiped out by the chaotic solar wind long before they could be observed on Earth. Thomson, however, claims that recent computer simulations have shown that the vibrations can indeed survive the turbulent solar wind.

Hathaway readily acknowledges that fluctuations in the solar wind can cause currents in wires on Earth. "But I'm sceptical that g-modes are the things that are producing them," he says.

Peter Riley at Science Applications International Corporation in San Diego, California, US, who has studied the fluctuations, agrees. Still, he says it would be exciting if Thomson's claims were true, since the g-modes, which come from deep within the Sun, would provide a unique perspective on our host star.

"If it turns out that they're right, then there are definitely some very profound implications of this work," he told New Scientist. "It would almost be a direct probe into the interior of the Sun."

  21/08/2007. New Scientist Magazine.