NASA's Pluto probe has woken up and is on its way to slipping out of the sun's protective bubble and into true interstellar space. NASA says New Horizons recently woke up from a 321-day hibernation, its longest yet, and is in good health and ready to start transmitting data. The spacecraft, currently about 5.9 billion miles from Earth and cruising through the Kuiper Belt, has been alternately hibernating and waking as it pushes toward the edge of the heliosphere—a vast, comet-shaped zone sculpted by the sun's charged-particle wind, Gizmodo reports. That bubble shields the solar system from high-energy galactic radiation, and its outer limits remain fuzzy.
Two new studies from Southwest Research Institute scientists, published in the Astrophysical Journal and Advances in Space Research, try to pin down when New Horizons will hit the first big boundary, known as the termination shock, where the solar wind abruptly slows as it meets interstellar wind. Their estimate: sometime between 2029 and 2040, depending on how the heliosphere swells and shrinks with the sun's 11-year activity cycle—wide enough that the craft could cross the boundary more than once. It's possible that the spacecraft "could cross the boundary more than once as the heliosphere continues to expand and contract," says researcher Jonathan Gasser.
Only Voyagers 1 and 2 have gone beyond this region before, and they didn't have scientific instruments as sophisticated as those on New Horizon. The Voyager spacecraft were launched in 1977 and New Horizons began its journey in 2006. For scientists, New Horizons' data could refine where the sun's influence truly ends and help inform any future attempt at an intentional interstellar mission.
- "The data from the termination shock encounter will be a treasure trove for space physicists worldwide who are eager to understand how this vast boundary works," New Horizons project scientist tells Space.com. "All these discoveries from pioneering missions like Voyager and New Horizons teach us how little we know about what lies beyond."
- NASA says New Horizons's exploration of the area is the latest step in a mission that included a "flyby of Jupiter in February 2007 that included stunning views of the gas giant and its moons; the first exploration through the Pluto system in July 2015; the first exploration of a Kuiper Belt object, Arrokoth, in January 2019, and unique studies of the Sun's outer heliosphere and dozens of additional Kuiper Belt objects since then."
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