Microwave Instrument for the Rosetta Orbiter (MIRO) Provides First Peek at the Comet's Dark Side

MDL-produced devices on board the Microwave Instrument for the Rosetta Orbiter (MIRO) first detected water vapor from the coma of comet 67P/Churyumov-Gerasimenko in June 2014, when Rosetta was 350,000 km from the comet nucleus. At that distance, the nucleus was unresolved and the entire coma filled MIRO's field of view. Now that Rosetta has rendezvoused with the comet, MIRO has begun observations to map the nucleus and coma in great detail. Recently, the MIRO instrument has detected an increase in the rate of water vapor coming from the comet, confirming that the water vapor rate on the comet is not constant. Observing the comet's southern polar regions, researchers found significant differences between the data collected with MIRO's millimeter and sub-millimeter wavelength channels. These differences might point to the presence of large amounts of ice within the first few tens of centimeters below the surface of these regions.

The MIRO instrument is a small, lightweight spectrometer that can map the abundance, temperature and velocity of cometary water vapor and other molecules that the nucleus releases. It can also measure the temperature up to about one inch (three centimeters) below the surface of the comet's nucleus. One reason the subsurface temperature is important is that the observed gases likely come from sublimating ices beneath the surface. By combining information on the gas and the subsurface, MIRO is able to study this process in detail.

MDL provided the 557-GHz radiometer with subharmonic planar diode mixers and multipliers for the spectrometer.

RIGHT: The southern hemisphere of Comet 67P/Churyumov-Gerasimenko, in a NAVCAM image taken on 26 August 2015. CREDIT: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0. LEFT: Image of the southern polar regions of Comet 67P/C-G taken with Rosetta's OSIRIS imaging system. CREDIT: ESA/Rosetta/MPS for OSIRIS Team, MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA ESA/Rosetta/MPS for OSIRIS Team, MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.

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