The Heliosphere’s Interstellar Interaction: No Bow Shock

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. Observations from the Interstellar Boundary Explorer are not consistent with a bow shock ahead of the heliosphere. 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.

[1]  V. Izmodenov,et al.  Direction of the interstellar H atom inflow in the heliosphere : Role of the interstellar magnetic field , 2005 .

[2]  N. Schwadron,et al.  Physical Processes in the Outer Heliosphere , 2009 .

[3]  J. W. Hamilton,et al.  The IBEX-Lo Sensor , 2009 .

[4]  G. Zank,et al.  A Forecast of the Heliospheric Termination-Shock Position by Three-dimensional MHD Simulations , 2007 .

[5]  G. Crew,et al.  LOCAL INTERSTELLAR NEUTRAL HYDROGEN SAMPLED IN SITU BY IBEX , 2012, 1202.0485.

[6]  N. Pogorelov,et al.  Comparison of Interstellar Boundary Explorer Observations with 3D Global Heliospheric Models , 2009, Science.

[7]  W. Webber,et al.  An asymmetric solar wind termination shock , 2008, Nature.

[8]  M. Witte.  Kinetic parameters of interstellar neutral helium - Review of results obtained during one solar cycle with the Ulysses/GAS-instrument , 2004 .

[9]  G. Crew,et al.  PRECISION POINTING OF IBEX-Lo OBSERVATIONS , 2012 .

[10]  G. Zank,et al.  Interaction of the solar wind with the local interstellar medium: A multifluid approach , 1996 .

[11]  R. Vanderspek,et al.  SEPARATION OF THE INTERSTELLAR BOUNDARY EXPLORER RIBBON FROM GLOBALLY DISTRIBUTED ENERGETIC NEUTRAL ATOM FLUX , 2011 .

[12]  G. Crew,et al.  Direct Observations of Interstellar H, He, and O by the Interstellar Boundary Explorer , 2009, Science.

[13]  Jeffrey L. Linsky,et al.  The Structure of the Local Interstellar Medium. IV. Dynamics, Morphology, Physical Properties, and Implications of Cloud-Cloud Interactions , 2007, 0709.4480.

[14]  E. Möbius,et al.  IBEX observations of heliospheric energetic neutral atoms: Current understanding and future directions , 2011 .

[15]  E. Möbius,et al.  ESTIMATION OF THE NEON/OXYGEN ABUNDANCE RATIO AT THE HELIOSPHERIC TERMINATION SHOCK AND IN THE LOCAL INTERSTELLAR MEDIUM FROM IBEX OBSERVATIONS , 2012 .

[16]  N. Pogorelov,et al.  Probing Heliospheric Asymmetries with an MHD-Kinetic model , 2008, 0801.4167.

[17]  M. Dopita,et al.  DETECTION OF BROWN DWARF LIKE OBJECTS IN THE CORE OF NGC 3603 , 2011, 1101.4521.

[18]  M. Gruntman,et al.  IBEX—Interstellar Boundary Explorer , 2009 .

[19]  R. Vanderspek,et al.  INTERSTELLAR GAS FLOW PARAMETERS DERIVED FROM INTERSTELLAR BOUNDARY EXPLORER-Lo OBSERVATIONS IN 2009 AND 2010: ANALYTICAL ANALYSIS , 2012 .

[20]  T. V. van Kempen,et al.  DISENTANGLING THE ENVIRONMENT OF THE FU ORIONIS CANDIDATE HBC 722 WITH HERSCHEL , 2011, 1103.2156.

[21]  K. Gayley,et al.  One- versus Two-Shock Heliosphere: Constraining Models with Goddard High Resolution Spectrograph Lyα Spectra toward α Centauri , 1997 .

[22]  G. Crew,et al.  NEUTRAL INTERSTELLAR HELIUM PARAMETERS BASED ON IBEX-Lo OBSERVATIONS AND TEST PARTICLE CALCULATIONS , 2012, 1202.0415.

[23]  E. Parker.  THE STELLAR WIND REGIONS , 1961 .

[24]  M. Ruderman,et al.  Kinetic-Gasdynamic Modeling of the Heliospheric Interface , 2009 .

[25]  M. Gruntman,et al.  Global Observations of the Interstellar Interaction from the Interstellar Boundary Explorer (IBEX) , 2009, Science.

[26]  Christopher F. McKee,et al.  The identification of absorption redshift systems in quasar spectra. , 1975 .

[27]  V. Baranov,et al.  MODEL FOR THE INTERACTION OF THE SOLAR WIND WITH THE INTERSTELLAR MEDIUM. , 1971 .

[28]  N. Pogorelov,et al.  The Effects of a κ-Distribution in the Heliosheath on the Global Heliosphere and ENA Flux at 1 AU , 2008, 0803.2538.

[29]  E. Möbius,et al.  AN ANALYTICAL MODEL OF INTERSTELLAR GAS IN THE HELIOSPHERE TAILORED TO INTERSTELLAR BOUNDARY EXPLORER OBSERVATIONS , 2012 .

[30]  D. Mccomas,et al.  An explanation of the Voyager paradox: Particle acceleration at a blunt termination shock , 2006 .

[31]  Paulett C. Liewer,et al.  The Effects of a Local Interstellar Magnetic Field on Voyager 1 and 2 Observations , 2006, astro-ph/0603318.

[32]  H. Fahr,et al.  Theoretical aspects of energetic neutral atoms as messengers from distant plasma sites with emphasis on the heliosphere , 2007 .

[33]  R. Ratkiewicz,et al.  Orientation of the local interstellar magnetic field inferred from Voyagers' positions , 2008 .

[34]  J. Ashby.  References and Notes , 1999 .

[35]  E. Grün,et al.  The Galactic Environment of the Sun: Interstellar Material Inside and Outside of the Heliosphere , 2009 .

[36]  N. Pogorelov,et al.  Physics of the Solar Wind–Local Interstellar Medium Interaction: Role of Magnetic Fields , 2009 .