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No Shock Ahead of the Sun
The boundary of the heliosphere is the region where the solar wind interacts with interstellar space, and it marks the edge of our solar system. Based on observations from NASA's Interstellar Boundary Explorer, McComas et al. (p. 1291, published online 10 May; see the Perspective by Redfield) determined values for local interstellar parameters—such as speed, direction, and temperature—and show that these and other recent constraints are not consistent with a bow shock ahead of the heliosphere, as previously believed.
Abstract
As the Sun moves through the local interstellar medium, its supersonic, ionized solar wind carves out a cavity called the heliosphere. Recent observations from the Interstellar Boundary Explorer (IBEX) spacecraft show that the relative motion of the Sun with respect to the interstellar medium is slower and in a somewhat different direction than previously thought. Here, we provide combined consensus values for this velocity vector and show that they have important implications for the global interstellar interaction. In particular, the velocity is almost certainly slower than the fast magnetosonic speed, with no bow shock forming ahead of the heliosphere, as was widely expected in the past.
