Widespread Morning Drizzle on Titan
Máté Ádámkovics,1,2*
Michael H. Wong,1
Conor Laver,1
Imke de Pater1,2
Precipitation is expected in Titan's atmosphere, yet it has
not been directly observed, and the geographical regions where
rain occurs are unknown. Here we present near-infrared spectra
from the Very Large Telescope and W. M. Keck Observatories that
reveal an enhancement of opacity in Titan's troposphere on the
morning side of the leading hemisphere. Retrieved extinction
profiles are consistent with condensed methane in clouds at
an altitude near 30 kilometers and concomitant methane drizzle
below. The moisture encompasses the equatorial region over Titan's
brightest continent, Xanadu. Diurnal temperature gradients that
cause variations in methane relative humidity, winds, and topography
may each be a contributing factor to the condensation mechanism.
The clouds and precipitation are optically thin at 2.0 micrometers,
and models of "subvisible" clouds suggest that the droplets
are 0.1 millimeter or larger.
2 Center for Integrative Planetary Science, University of California, Berkeley, CA 94611, USA.
* To whom correspondence should be addressed. E-mail: mate{at}berkeley.edu
