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IBEX spacecraft set to map the final frontier

Probe will catch atoms from the edge of our Solar System's protective bubble.

IBEX will map the boundaries of the Solar System. Credit: NASA

A NASA mission to study our Solar System's final frontier is due to launch this weekend. The Interstellar Boundary Explorer (IBEX) will catch energetic particles streaming from the termination shock - the zone where the solar wind that blows from the Sun suddenly slows down as it slams into the thin, cold gas of interstellar space.

The outward pressure of the solar wind, made mostly of protons and electrons, carves out a protective bubble around the Solar System called the heliosphere, which helps to deflect most of the potentially life-threatening forms of radiation coming from elsewhere in our Galaxy.

Astronomers got their first data about this sheath when the deep-space probe Voyager 1 slammed into the termination shock in 2004. Its sibling craft Voyager 2 banged into a different point of the boundary in 2007. Their data showed that the heliosphere, which lies roughly 100 times as far from the Sun as does Earth, is dented at various points, says Edward Stone of the California Institute of Technology in Pasadena, the chief scientist for Voyager 1.

IBEX gives us a chance to look at how our Solar System's bubble fits in as a tiny piece of the entire Galaxy. David McComas , Southwest Research Institute in San Antonio, Texas

IBEX will map the variation in the boundary's distance from the Sun, and hopefully reveal what processes cause those indentations. The craft, which is the size of a bus tyre, will ride into the sky in the belly of an L1011 jet on Sunday 19 October. The plane will then release a Pegasus rocket to take IBEX to around 200 kilometres from Earth, before the probe boosts itself into its final Earth orbit 322,000 kilometres away. Its mission is slated to last for two years.

Atom catchers

IBEX is built to collect energetic neutral atoms (ENAs) – many of which are formed when positive ions in the solar wind, travelling at hundreds of kilometres per second along magnetic field lines emanating from the Sun, hit neutral atoms of interstellar material and wrest electrons from them. Once the fast-moving particles are neutralized they no longer feel the effect of the magnetic field, and some slingshot back towards the Sun.

IBEX will be carried into space in a Pegasus rocket. Credit: NASA

The probe captures these ENAs in two ways. They can bounce off a smooth diamond surface, picking up a negative charge before hitting the IBEX-Lo detector; or pass through a thin carbon foil that strips electrons from the ENAs, making positive ions that are picked up by the IBEX-Hi detector. In both cases, the instruments note the particles' mass, their energy, and where they came from. The craft will rotate slowly so that during the mission's first six months, each instrument can scan the entire sky to create a three-dimensional map of the heliosphere, which will be updated and refined as the mission progresses.

David McComas of the Southwest Research Institute in San Antonio, Texas, and IBEX's principal investigator, says that the mission should also provide clues about the processes that deflect the DNA-damaging galactic cosmic rays — valuable information for creating safe manned missions to the Moon and Mars. IBEX also comes with a relatively cheap price tag of about US$165 million, he notes.

"IBEX gives us a chance to look at how our Solar System's bubble fits in as a tiny piece of the entire Galaxy," he says.

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Voyager streaming through the heliosphere

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NASA’s IBEX website

IBEX PI David J. McComas’ website

IBEX animation page

ENA tutorial page

Detailed mission profile

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Yeager, A. IBEX spacecraft set to map the final frontier. Nature (2008). https://doi.org/10.1038/news.2008.1177

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