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Hot Times Ahead?
August 2, 2010   
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The Sun and the rest of the solar system are heading toward a cloud of interstellar matter that has a mind-boggling temperature of 1 million degrees Kelvin; the encounter may take place some 100 years from now, but this does not mean that life on Earth will be destroyed, according to scientists from the Polish Academy of Sciences’ Space Research Center in Warsaw.

The scientists published their theory in a peer-reviewed scientific journal entitled Astrophysical Journal Letters. Some experts say the theory may help explain the nature of the so-called Space Ribbon, a ring-shaped formation that cuts across the sky and was discovered by the American Interstellar Boundary Explorer (IBEX) probe last year.

The probe has provided data pointing to the existence of a baffling formation in the sky, a gigantic strip shaped like an open ring, experts say. The United States’ National Aeronautics and Space Administration (NASA) called the Space Ribbon one of the most important discoveries in space research in 2009. While all previous hypotheses involved phenomena on the boundaries of our solar system, the latest hypothesis provides a different explanation, says the Space Research Center’s Prof. Stanisław Grzędzielski.

Space Ribbon and a very hot cloud

“The Space Ribbon is there because the Sun is approaching the boundaries of a very hot cloud of interstellar matter,” Grzędzielski said.

The IBEX probe, launched into orbit by NASA in October 2008, is investigating the distribution of fluxes of energetic neutral atoms (ENAs). Such atoms are created when the protons of hot gas mix with the atoms of neutral gas and intercept electrons from the latter. ENAs have no electric charge and so they are indifferent to magnetic fields and thus travel along straight lines. Only slight amounts of such atoms reach the Earth’s region of the solar system. IBEX detectors record from several ENAs per second to one per hour. Prior to the IBEX launch, scientists expected that most ENAs would be coming from the direction in which our solar system travels. Nobody expected the data from the new satellite to reveal a gigantic, ring-shaped formation, according to Grzędzielski.

Over the past several months, six theories have been proposed to account for the origins of the Space Ribbon and all six refer to phenomena triggered by magnetic fields on the boundaries of, or close to, the heliosphere, Grzędzielski says. The heliosphere is a gigantic bubble of gas “blown” into the interstellar medium—the hydrogen and helium gas that permeates the galaxy—by the solar wind.

“If ENAs were created on the edge of the heliosphere, that would not be very far away, just several hundred astronomical units from the Sun,” says Andrzej Czechowski, Ph.D., from the Space Research Center. “Under our hypothesis, they are in fact created much farther than that.”

Local Bubble and other wonders

The Space Research Center scientists suppose that ENAs are the product of processes that occur on the border of two interstellar clouds: the cold Local Interstellar Cloud, which the Sun is currently traveling through and whose temperature is 6,000-7,000 K, and the very hot Local Bubble whose temperature reaches around 1 million K. The Local Interstellar Cloud is located inside the Local Bubble. The Local Bubble measures hundreds of light years across and is probably what remains of a sequence of supernova blasts. ENAs are created when high-energy protons in the bubble interact with the neutral hydrogen of the Local Interstellar Cloud.

“If our hypothesis is correct, then we are catching atoms that originate from an interstellar cloud that is different from ours,” said Maciej Bzowski, Ph.D., head of a Polish team taking part in the IBEX mission.

But since the creation of such ENAs is occurring throughout the entire boundary layer between the clouds, why do we see the Ribbon? According to Grzędzielski, “It’s a purely geometrical effect, which we observe because the Sun is presently just in the right place, within a thousand of astronomical units from the cloud boundary. If the cloud-cloud boundary is flat, or better slightly extruded towards the Sun, then it appears the thinnest towards the center of the Ribbon and thicker at the sides, right where we see the edge of the Ribbon. If we were farther away from the boundary, we would see no Ribbon, because all the ENAs would be reionized and dispersed in the intervening gas of the Local Cloud.”

A similar effect occurs in the atmosphere of the Earth, Grzędzielski says. The planet is wrapped in a coating layer of even thickness, but when an astronaut gazes at the Earth’s horizon from the International Space Station, the layer of gas appears to be much thicker there.

No reason to panic

Models developed at the Space Research Center suggest that, contrary to earlier theories, the border between the cold and hot clouds may lie not several light years from the Earth, but just 500-2,000 astronomical units away. This means that our solar system may enter an interstellar cloud of 1 million K as early as the next century, according to the Polish scientists.

But there is no reason to panic, they say. “The Sun frequently traverses various clouds of interstellar gas during its galactic journey,” says Grzędzielski. He adds that such clouds are of very low density—much lower than even the best vacuum obtained in laboratories. As a result of entering the hot cloud, the heliosphere may shrink and the amount of cosmic rays reaching the Earth could increase slightly. “Future generations will perhaps have to design electronic devices that will be a bit more resistant to cosmic rays,” Grzędzielski says.

The IBEX probe, fitted with two sensitive ENA detectors, is used to survey fluxes of ENAs reaching the Earth’s region from all directions. The IBEX has the size of a bus wheel and is traveling around the Earth in a highly eccentric elliptical orbit (15,000 by 300,000 kilometers), making a full circle in around eight days. The main phase of the IBEX mission will last two years, but it may be extended to better investigate the dynamics of processes which produce ENAs.
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