Research Interests

I have worked on the solar environment, which includes the galactic gas in the Sun vicinity, the interaction between our star and the interstellar medium it is moving through, and the confinement of the expanding solar wind by this medium to form the heliosphere. We have identified the local interstellar cloud surrounding the Sun, using nearby star spectroscopy, and shown that its temperature and motion are identical to those of the interstellar helium flow within the heliosphere, establishing a "bridge" between the solar system and the galactic environment. Using remote sensing observations of the interstellar gas, we have shown that some interstellar species are modified upon entry in the heliosphere, in particular neutral hydrogen is decelerated and heated. This allows us to determine the ionized fraction of the ambient interstellar gas as well as the size of our heliosphere. We have also derived some characteristics of the interaction processes between the solar wind and the inflowing interstellar gas, such as the decrease of hydrogen ionization above the solar poles. We have recently measured a huge increase of helium ionization within the earth orbit with rising solar activity; this phenomenon, due to solar wind electron impact, influences the fluxes of energetic helium ions. Because the local interstellar medium properties result from the history of our "galactic corner", we have studied the interstellar medium at larger scale. Ground and space observing programs have resulted in the detection of the group of nearby interstellar clouds, and, more recently, in the first computed maps of the Local Interstellar Cavity, a 100 parsecs volume filled by hot gas, a "remnant" of stellar explosions. We can trace back and forth in time the trajectory of our Sun in this cavity and in the embedded nearby interstellar clouds.

Membership Type

International Member

Election Year


Primary Section

Section 16: Geophysics

Secondary Section

Section 12: Astronomy