Dartmouth Events

Abstract: In this talk, I will discuss what we recently learned from the in-situ measurements from Voyager spacecrafts as well as the remote sensing of energetic neutral atoms from CASSINI, IBEX and Cassini about the heliosphere. The very shape of the heliosphere is being challenged by these measurements and models as well as the realization that the heliosphere influences the local interstellar medium to distances far larger than its own. The shape of the heliosphere has been explored and proposed since the classic works of 50’s and 60’s, etc. Part of the unknown is the pressure of the interstellar medium with respect to the pressure exerted by the solar wind. The standard picture of the heliosphere with a comet-shape like structure stems from the view that magnetic forces from the solar magnetic field are negligible and that the solar magnetic field is convected passively down the tail. We argued by contrast that the heliosphere has a “croissant”-like shape where the distance to the heliopause downtail is almost the same as towards the nose; we showed that this was caused by the magnetic tension of the solar magnetic field that plays a crucial role in organizing the solar wind in the heliosheath into two jet-like structures. Interstellar Boundary Explorer (IBEX) has been observing the heliosphere with maps of energetic neutral atoms (ENAs) from 1-6keV. In 2013, they presented ENA maps of the tail (McComas et al. 2013) that shows multi-lobe structure. However, the ENA images at energies of IBEX 1-6keV cannot probe down the tail beyond around 100AU due to depletion of high energy ions due to charge exchange. On the contrary INCA on board of CASSINI is taking ENA images of the heliosphere in energies 5-55keV where the long tail can be probed. Dialynas et al. 2017 had argued based on the fact that the signal from the nose and tail are same magnitude as well as the spectral shape the heliosphere is “tailess” –consistent with our proposed picture of the heliosphere (Opher et al. 2015; 2016; Drake et al. 2015).