In Depth: Titan's turbulence surprises scientists

Nov 30, 2005
Huygens probe descending through Titan's atmosphere

Strong turbulence in the upper atmosphere, a second ionospheric layer and possible lightning were among the surprises found by the Huygens Atmospheric Structure Instrument (HASI) during the descent to Titan’s surface.

Above: Huygens probe descending through Titan's atmosphere.

HASI provided measurements from an altitude of 1400 km down to the surface of the physical characteristics of the atmosphere and surface, such as temperature and density profiles, electrical conductivity, and surface structure. The Huygens SSP made measurements just above and on the surface of Titan.

High-altitude atmospheric structure had been inferred from earlier solar occultation measurements by Voyager, but the middle atmosphere (200–600 km) was not well determined, although telescopic observations indicated a complex vertical structure.

Very little was known about the surface of Titan because it is hidden by a thick 'haze' - initial speculation was that the surface was covered by a deep hydrocarbon ocean, but infrared and radar measurements showed definite albedo contrasts —possibly consistent with lakes, but not with a global ocean.

Earlier observations showed that the surface pressure on Titan was comparable to that on Earth, and that methane formed a plausible counterpart to terrestrial water for cloud and rain formation. There was also speculation on the possibility of lightning occurring in Titan’s atmosphere that could affect the chemical composition of the atmosphere.

The HASI instrument's accelerometers recorded the signature of the probe impact.

The HASI instrument's accelerometers recorded the signature of the probe impact. Credits: ESA /ASI/UPD/OU (background: ESA/NASA/UofA)

HASI found that in the upper part of the atmosphere, the temperature and density were both higher than expected. The temperature structure shows strong wave-like variations of 10-20 K about a mean of about 170 K. This, together with other evidence, indicates that Titan’s atmosphere has many different layers.

Models of Titan's ionosphere predicted that galactic cosmic rays would produce an ionospheric layer with a maximum concentration of electrons between 70 and 90 km altitude. HASI also surprised the Huygens team by finding a second lower ionospheric layer, between 140 km and 40 km, with electrical conductivity peaking near 60 km.

HASI may also have seen the signature of lightning. Several electrical field impulse events were observed during the descent, caused by possible lightning activity in the spherical waveguide formed by the surface of Titan and the inner boundary of its ionosphere.

The vertical resolution of the temperature measurement was sufficient to resolve the structure of the planetary boundary layer. This boundary layer had a thickness of about 300 m at the place and time of landing. The surface temperature was accurately measured at 93.65±0.25 K and the pressure 1467±1 hPa (very close to measurements made earlier by Voyager, about 95K and 1400 hPa).

Source: ESA

Explore further: SDO captures images of two mid-level flares

add to favorites email to friend print save as pdf

Related Stories

Key to longevity of imperial Roman monuments

Dec 16, 2014

No visit to Rome is complete without a visit to the Pantheon, Trajan's Markets, the Colosseum, or the other spectacular examples of ancient Roman concrete monuments that have stood the test of time and the ...

Recommended for you

SDO captures images of two mid-level flares

Dec 19, 2014

The sun emitted a mid-level flare on Dec. 18, 2014, at 4:58 p.m. EST. NASA's Solar Dynamics Observatory, which watches the sun constantly, captured an image of the event. Solar flares are powerful bursts ...

Why is Venus so horrible?

Dec 19, 2014

Venus sucks. Seriously, it's the worst. The global temperature is as hot as an oven, the atmospheric pressure is 90 times Earth, and it rains sulfuric acid. Every part of the surface of Venus would kill you ...

Image: Christmas wrapping the Sentinel-3A antenna

Dec 19, 2014

The moment a team of technicians, gowned like hospital surgeons, wraps the Sentinel-3A radar altimeter in multilayer insulation to protect it from the temperature extremes found in Earth orbit.

Video: Flying over Becquerel

Dec 19, 2014

This latest release from the camera on ESA's Mars Express is a simulated flight over the Becquerel crater, showing large-scale deposits of sedimentary material.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.