A remarkable measurement is that of the variation with altitude, below 140 km height, of the abundance ratio between methane and nitrogen. Constant in the stratosphere of Titan, this ratio starts to grow in the troposphere below 32 km altitude up to 8 km, where it becomes constant until the surface. This behavior suggests that methane is saturated at 8 km, altitude where it could condense and form fog. A remarkable phenomenon was observed on the surface. Two minutes after the impact, the abundance ratio of methane increased abruptly by 40% (Figure 4). This is correlated with the increase in the inlet temperature of the GCMS (marked "inlet") whose radiation heats the surface (initially at -179°C) which thus degasses. The temperature of the inlet climbs up until 85°C. Other species degassed (Figure 4) : ethane, carbon dioxide, and most probably other hydrocarbons including benzene. It could be the index of the presence on the surface of much more complex organic compounds, responsible for the color of the dark material observed by DISR.
The data collected "in situ" by HASI are essential to the calibration of the measures carried out from the other instruments of the Huygens probe and constitute the "ground truth" for the observations carried out from the Cassini instruments, thus contributing in meaningful way to the Titan global knowledge.
References
- Tomasko et al. 2005 : Rain, winds and haze during the Huygens probe’s descent to Titan’s surface. Niemann et al. 2005 : The abundances of constituents of Titan’s atmosphere from the GCMS instrument on the Huygens probe. Fulchignoni et al. 2005 : In situ measurements of the physical characteristics of Titan’s environment. Nature (publications en ligne le 30 novembre, sur papier le 8 décembre)
Contact DISR
Bruno Bézard (Observatoire de Paris, LESIA) HASI & SSP
Marcello Fulchignoni (Observatoire de Paris, LESIA) GCMS
Daniel Gautier (Observatoire de Paris, LESIA)