Rain and dewdrops on titan based on in situ imaging

Erich Karkoschka, Martin G Tomasko

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

The Descent Imager/Spectral Radiometer (DISR) of the Huygens probe was in an excellent position to view aspects of rain as it descended through Titan's atmosphere. Rain may play an important part of the methane cycle on Titan, similar to the water cycle on Earth, but rain has only been indirectly inferred in previous studies. DISR detected two dark atmospheric layers at 11 and 21 km altitude, which can be explained by a local increase in aerosol size by about 5-10%. These size variations are far smaller than those in rain clouds, where droplets grow some 1000-fold. No image revealed a rainbow, which implies that the optical depth of raindrops was less than ∼ 0.0002 / km. This upper limit excludes rain and constrains drizzle to extremely small rates of less than 0.0001 mm/h. However, a constant drizzle of that rate over several years would clear the troposphere of aerosols faster than it can be replenished by stratospheric aerosols. Hence, either the average yearly drizzle rate near the equator was even less (< 0.1   mm / yr), or the observed aerosols came from somewhere else. The implied dry environment is consistent with ground-based imaging showing a lack of low-latitude clouds during the years before the Huygens descent. Features imaged on Titan's surface after landing, which might be interpreted as raindrop splashes, were not real, except for one case. This feature was a dewdrop falling from the outermost baffle of the DISR instrument. It can be explained by warm, methane-moist air rising along the bottom of the probe and condensing onto the cold baffle.

Original languageEnglish (US)
Pages (from-to)442-448
Number of pages7
JournalIcarus
Volume199
Issue number2
DOIs
StatePublished - Feb 2009

Fingerprint

Titan
rain
descent
drizzle
aerosols
radiometers
radiometer
raindrops
baffles
raindrop
aerosol
methane
Huygens probe
probe
Titan atmosphere
hydrological cycle
rainbows
condensing
landing
cloud droplet

Keywords

  • Titan

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Rain and dewdrops on titan based on in situ imaging. / Karkoschka, Erich; Tomasko, Martin G.

In: Icarus, Vol. 199, No. 2, 02.2009, p. 442-448.

Research output: Contribution to journalArticle

Karkoschka, Erich ; Tomasko, Martin G. / Rain and dewdrops on titan based on in situ imaging. In: Icarus. 2009 ; Vol. 199, No. 2. pp. 442-448.
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