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On Sunday, a small space probe with a big mission took off from Earth in a flawless launch, setting off on a two-year assignment to map the edge of our solar system. The Interstellar Boundary Explorer soared into space aboard an Orbital Space Sciences Pegasus rocket that fired as planned at 12:48 p.m. CDT, moments after dropping from the belly of a modified airliner that flew across the South Pacific near Kwajalein Atoll [San Antonio Express-News].

The $169 million NASA probe will settle into a long, elliptical orbit around Earth that takes it beyond the interference of our planet’s magnetosphere, and almost as far as the moon. From there the IBEX will record the impacts of particles that are formed at the edge of our solar system’s protected space, a region known as the heliosphere. The solar wind, a stream of charged particles spewing from the sun at 1 million miles per hour, carves out a protective bubble around the solar system. This bubble … shields against most dangerous cosmic radiation that would otherwise interfere with human spaceflight [AP]. At the edge of the heliosphere, the solar wind slows down as it slams into interstellar space; IBEX will observe the particles created in this “termination shock” to chart the solar system’s perimeter.

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On October 19, NASA will launch the small Interstellar Boundary Explorer (IBEX) into orbit on a mission to map the turbulent edge of our solar system, where the solar wind slams into interstellar space. While it won’t actually travel beyond all the planets to investigate the solar system’s far reaches, the coffee table-sized spacecraft must escape the area where Earth’s magnetic field reigns, which could interfere with its measurements. The $169 million observatory is due to climb 200,000 miles (322,000 kilometers) above Earth and settle into orbit there for a mission of at least two years. For comparison, the moon orbits about 240,000 miles (385,000 km) from Earth [SPACE.com].

The edge of the solar system is currently being explored directly by the Voyager 1 and Voyager 2 spacecrafts; both Voyagers launched 31 years ago and recently passed the point where the solar wind is slowed by interactions with the interstellar plasma, a point known as the termination shock. These crafts “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,” said [IBEX researcher David] Mc­Co­mas [World Science].

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The solar wind, a steady stream of charged subatomic particles that stream out from the sun at a speed of one million miles per hour, has dwindled to its weakest state since recording began, researchers say. While researchers already knew that solar winds fluctuate in 11-year cycles, the current doldrums trump the declines seen over the past 50 years. “We know that the sun has been this cool before, this inactive before,” said [physicist] Nancy Crooker…. “But that was prior to the Space Age, so we didn’t have actual physical measurements until now” [SPACE.com].

The data was collected by the first solar explorer, the Ulysses probe, which was launched in 1990 as a joint venture between NASA and the European Space Agency. The 17-year-old space probe, which circles the sun from a distance of about 337 million miles, has been studying the environment above and below the poles of the sun. It is just months away from shutting down because of freezing fuel [AP].

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Nobody expected to take it this far. When NASA launched two probes named Voyager 1 and Voyager 2 in the summer of 1977, scientists hoped the probes would get as far as Saturn during their five-year mission. Instead, the nuclear-powered explorers are still sending data home over 30 years after their launch, and are currently pushing through the boundary of our solar system into interstellar space.

A collection of five papers in tomorrow’s issue of the journal Nature [subscription required] analyze the data sent back from Voyager 2 as it reached a turbulent frontier known as the termination shock. The sun is constantly spewing out particles in all directions; as these particles move through the solar system, they are known as the solar wind. This wind pushes back against the interstellar plasma that exists throughout the galaxy. At the end of the solar system, the solar wind finally begins to lose out and its speed drops below the speed of sound (relative to the interstellar medium), resulting in a roughly spherical shell known as the termination shock front [Nobel Intent blog, Ars Technica].

Voyager 1 passed through the shock in a different region several years ago but vexed scientists by failing to send back data during that crucial transition. That made Voyager 2’s observations all the more critical. NASA says the probe encountered the termination shock over August 31 and September 1 of last year, and surprised researchers by crossing the boundary several times. The multiple crossings indicate that “the shock is not the steady structure that is predicted by the simplest theory,” says Len Burlaga of NASA’s Goddard Space Flight Center in Greenbelt, Md. “It is like a wave approaching a beach, that grows, breaks, dissipates, and then re-forms closer to shore” [Science News].

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