The landing of the Huygens probe on Saturn's moon Titan on 14 January has been hailed as a success, although the European Space Agency (ESA) has launched an investigation into the loss of one of two data channels, which halved the number of images returned during the descent and from the surface.
Released from NASA's Saturn orbiter Cassini, the Huygens probe descended through 160km (100 miles) of hazy atmosphere to a safe landing on frozen ground resembling wet sand of clay with a thin solid crust. The probe returned 474Mbits of data via Cassini over 3h 44min, including 1h 12min of data received from the surface of Titan before the orbiter dropped below the horizon.
Analysis of Titan's atmosphere revealed a uniform mix of methane and nitrogen in the stratosphere, with methane concentration in the troposphere increasing steadily down to the surface. Methane clouds at about 20km altitude and methane or ethane fog near the surface were detected. Sounds recorded during the descent revealed strong winds.
Images taken during the descent and on the surface reveal a landscape apparently shaped by erosion, with drainage channels, an apparent shoreline and pebble-shaped objects on the surface. The probe touched down at 4.5m/s, breaking through the thin crust.
Loss of the data channel affected the measurement of wind profiles during the descent, but using signals from the probe received by Earth-based radio telescopes, ESA planned to reconstruct the Huygens' trajectory to an accuracy of 1km to provide data on Titan's winds.
GRAHAM WARWICK / WASHINGTON DC