Thirty-two years into its mission and 8.4 million miles from Earth, Voyager 2 will soon enter the Local Fluff, an interstellar cloud of hydrogen and helium measuring thirty lightyears across. And, according to Voyager's measurements, the fluff is surprisingly magnetic.

The Local Fluff, more properly known as the Local Interstellar Cloud, is a wispy band of particles through which our solar system is slowly moving. The solar system entered the cloud anywhere between 44,000 to 150,000 years ago, and scientists estimate we will not leave it for another 10,000 to 20,000 years. Although it's not technically part of the solar system, the Local Fluff is the last distinct region Voyagers 1 and 2 will pass through before they leave the heliosheath and enter interstellar space.


A recent article from Discovery News charts the recent developments in the exploration of this interstellar cloud. Astronomers had hoped the Voyager probes might be able to shed some light on the Local Fluff's existence, as by all rights it shouldn't exist:

Approximately 10 million years ago, a supernova cluster detonated nearby, generating a huge bubble of million-degree gas. Researchers have been very confused as to why the Local Fluff remains intact; it should have been blown away by the ferocious supernovae exhaust long ago.

It would be like expecting a wisp of cigarette smoke to retain its structure in the middle of a tornado; some kind of force would need to be surrounding (or intertwined through) the smoke helping it resist being dispersed. In the case of the wispy Local Fluff, a magnetic field may be helping.

Although scientists had not seriously considered the possibility of magnetized interstellar clouds, the theory does essentially explain all the current problems with the existence of such clouds. This appears to be the rare case where new astronomical data actually answers a cosmic question instead of raising five new ones:

"Voyager data show that the Fluff is much more strongly magnetized than anyone had previously suspected — between 4 and 5 microgauss," said Merav Opher, a NASA Heliophysics Guest Investigator from George Mason University and lead author of research published in Nature on Dec. 24. "This magnetic field can provide the extra pressure required to resist destruction."
However, the Voyagers aren't inside the Fluff yet, how can they measure the cloud's magnetic field strength? By measuring the size of the heliosphere (which is maintained by the outward magnetic pressure of the sun's magnetic field), the probes have been able to deduce how much inward magnetic pressure is pushing down on the heliosphere. This inward pressure is being caused by the Local Fluff, so its magnetic field can be indirectly measured.


Although the current data obviously only applies to the Local Interstellar Cloud, Opher suspects other clouds elsewhere in the galaxy are similarly magnetized. This potentially means that our solar system has passed through other magnetized clouds in its past, or will again in its future as it orbits the center of the galaxy. This magnetization can affect the size of the heliosphere that encircles the solar system.

The potentially serious effect of a decrease in the heliosphere's size is an increase in bombardment by cosmic rays. A particularly magnetized cloud might allow an unusual amount of cosmic rays to enter the inner solar systems. This could affect the Earth's atmosphere, and it could greatly increase the risk of space exploration to astronauts who would be unprotected from the bombardment of these rays.


[Discovery News]

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