Water Production by Comet 103P/Hartley 2 Observed with the SWAN Instrument on the SOHO Spacecraft

Global water production rates were determined from the Lyα emission of hydrogen around comet 103P/Hartley 2, observed with the SWAN (Solar Wind Anisotropies) all-sky camera on the SOHO spacecraft from 2010 September 14 through December 12. This time period included the November 4 flyby by the EPOXI spacecraft. Water production was three times lower than during the 1997 apparition also measured by SWAN. In 2010, it increased by a factor of ~2.5 within one day on September 30 with a similar corresponding drop between November 24 and 30. The total surface area of sublimating water within ±20 days of perihelion was ~0.5 km2, about half of the mean cross section of the nucleus. Outside this period it was ~0.2 km2. The peak value was 90%, implying a significant water production by released nucleus icy fragments.