Having already revolutionized our understanding of the dwarf planet Pluto, NASA's New Horizons spacecraft is providing a rare look at the vast, seldom-visited region of space that is the outer solar system. New Horizons is currently cruising through deep space roughly 35 astronomical units out from the Sun. Prior to the spacecraft's July 14, 2015 encounter with Pluto, the spacecraft captured roughly three years worth of observational data detailing the characteristics of the all pervading solar winds known to emanate from our Sun.
The data was recorded by New Horizons' Solar Wind Around Pluto (SWAP) instrument, which remained active as the rest of the probe's instruments hibernated in preparation for the spacecraft's primary mission.
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In 2012, as New Horizons passed beyond the orbit of Uranus, the instrument began its vigil, observing the behavior of the solar particles that make up the solar wind as they made a 3 billion-mile pilgrimage to the orbit of Pluto.
The solar winds observed in the inner solar system exhibit relatively clear patterns. Larger well-defined formations in the winds are often created by coronal mass ejections, and the merging of faster and slower winds into larger "shocks." Subtler patterns are also evident, created by the spin of our Sun, and the varying strengths of solar winds emanating from different regions of the star's surface.
The data collected by the SWAP instrument is proving to be instrumental for filling in a blind spot in the observation of solar winds, and is pointing towards a breakdown in these intricate patterns as the solar winds travel into the outer solar system.
Whilst still detectable, the subtle patterns created by the spin of our Sun were relatively feeble, with the more imposing shocks in the solar wind observed in the inner solar system were noted to unpredictably merge into even larger features, or flatten out completely.
Beyond providing a rare influx of data regarding the unpredictable weakening of the Sun's influence in the outer reaches of our solar system, New Horizons detailed observations are also shedding light on a class of ion particles known as anomalous cosmic rays. It is believed that these energetic particles are created when interstellar particles become ionized by the solar winds. They have been known to travel four times the speed of the surrounding winds, and are thought to be an influential force in determining the boundary of the solar winds and interstellar space.
The weaker, final stages of anomalous cosmic rays have been observed by the Voyager spacecraft at the interstellar boundary, but closer to Earth the more youthful and energetic particles are believed to pose a radiation threat to astronauts operating outside of our planet's protective atmosphere.
A better understanding of the movement and evolution of the particles could allow scientists to develop protective measures to shield future spacecraft and even astronauts on long-duration missions to destinations such as Mars.