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Voyager 1 and 2: first measurements of neutral hydrogen ultraviolet emission from the Milky Way

Launched in 1977, the two spacecrafts Voyager 1 and 2 are moving out of the solar system and are penetrating in the ambient interstellar gas. From more than fifteen billions of kilometers from the Earth, they continue to transmit new data. An international team, led by Rosine Lallement (GEPI/ Observatoire de Paris), and including scientists from CNRS and Institut Pierre Simon-Laplace has detected for the first time the ultraviolet (Lyman-α) light from hydrogen atoms in the Milky Way. From closer to the Sun this emission is completely masked by a radiation at the same wavelength, but of solar origin.

For more information see the Paris-Observatory website

The paper Voyager Measurements of Hydrogen Lyman-α Diffuse Emission from the Milky Way (Lallement, Quémerais, Bertaux, Sandel & Izmodenov) is published in Science.

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Illustration of the measurements. Voyager 1 and 2, at the periphery of the heliosphere, move out from the intense local radiation and detect Lyman-α radiation from star-forming region in the Milky Way (here shown in Hα light)