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NASA's IBEX to sniff interstellar boundary

Looking beyond the termination shock

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NASA's Interstellar Boundary Explorer, aka IBEX, will on 19 October lift off from Kwajalein Atoll in the Marshall Islands on a mission to probe the interstellar boundary beyond our heliosphere's termination shock1 - a region where "the hot solar wind slams into the cold expanse of space", as NASA nicely puts it.

From an altitude of roughly 200,000 miles (322,00km) at apogee, and beyond interference from the Earth's magnetosphere, IBEX will focus its two single-pixel “cameras” on Energetic Neutral Atoms (ENAs)2 to capture "images of processes taking place at the farthest reaches of the solar system".

Artist's impression of the IBEX spacecraft. Pic: NASA

IBEX principal investigator, David J. McComas, explained: "The interstellar boundary regions are critical because they shield us from the vast majority of dangerous galactic cosmic rays, which otherwise would penetrate into Earth's orbit and make human spaceflight much more dangerous."

Indeed, as we recently reported, the Ulysses spacecraft has indicated "the solar wind's global pressure is the lowest we have seen since the beginning of the space age", leading to "an excellent chance the heliosphere will diminish in size and strength".

Ed Smith, NASA's Ulysses project scientist, said: "If that occurs, more galactic cosmic rays will make it into the inner part of our solar system."

McComas noted that venerable spacecraft Voyager 1 and Voyager 2 have already left the inner solar system and "are making fascinating observations of the local conditions at two points beyond the termination shock that show totally unexpected results and challenge many of our notions about this important region".

However, much remains to be discovered. IBEX will spend the first six months of its nominal two-year mission mapping the entire sky to "reveal the global structure of the heliosheath [see note 1, below] and termination shock for the first time".

IBEX mounted in its Pegasus launch vehicle. Pic: NASA

Before getting down to the task in hand, IBEX will be carried aloft to an altitude of around 130 miles (210km) by a Pegasus rocket (see pic, above) dropped from under an L-1011 aircraft. It'll then fire up its own solid rocket motor to travel out to its final working orbit.

NASA's main IBEX mission page is here, and the agency has a factsheet here (pdf). ®

Notes

1The termination shock is the point in the heliosphere where the solar wind is slowed to subsonic speeds (relative to the emitting star) by interaction with the interstellar medium. Beyond it lie the heliosheath, "a vast expanse of turbulent gas and twisting magnetic fields", and the heliopause, where the wind's particles are no longer energetic enough to advance against rival particles from other stars.

2The two cameras (IBEX-Lo IBEX-Hi) measure ENAs with energies of 10 eV to 2 keV and 300 eV to 6 keV, respectively.

Bootnote

NASA explains that IBEX is "23 inches high x 38 inches across (eightsided shape, like a STOP sign)", or "about the size of a bus tire". Come on, chaps, those are not accepted standards.

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Latest Comments

@stizzleswick

Thanks for that. I'd wondered about that one from earlier, voyager-related articles mentioning the termination shock. I'd never got round to looking it up myself though.

Have an oakleaf and cluster to go with that boffin icon.

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Cosmic Rays

"The interstellar boundary regions are critical because they shield us from the vast majority of dangerous galactic cosmic rays, which otherwise would penetrate into Earth's orbit and make human spaceflight much more dangerous."

Which is a GOOD thing.

Because it means that any human being crossing the heliopause will be subject to rapid vapourisation by a relentless barrage of pi-mesons.

Which means that the human vermin are confined by their weak biology to their own solar system.

This of course makes your Lizard Alliance overlords very happy, not to mention rather relieved.

Mine's the one with "I, for one..." printed on the back, ta.

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@AC re: subsonic

Space is not entirely a vacuum, only a medium well approximation of one. Deep space is full of matter (mostly thinly distributed hydrogen with traces of Helium and a few other elements).

In astronomical terms, the speed of sound is defined as that speed at which a stream of particles (e.g. the solar wind) is so fast it cannot simply displace matter it encounters on its way, but impacts fast enough to create a shock wave (e.g., the heliosphere's termination shock). That is the point in the heliosphere at which the solar wind is just strong enough to completely displace the interstellar medium. Outside the termination shock, interstellar medium and solar wind can intermingle, because the solar wind is no longer fast enough to completely displace the interstellar medium. Inside the termination shock, we don't get much interstellar medium, because the solar wind is still supersonic.

Hope this helped...

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