Titan's pebbles 'seen' by Huygens radio

July 25, 2006
Titan's pebbles 'seen' by Huygens radio
This technical sketch illustrates the radio signals emitted by the Huygens probe from Titan's surface after touch down on 14 January 2005. The probe survived the impact and continued to transmit to the Cassini mothership, orbiting above. Part of that radio signal ‘leaked’ downwards and hit the surface of Titan before being reflected back up to Cassini. On its way up, it interfered with the direct beam. Thanks to this 'multipath' phenomena related to the Huygens radio signal, it has been possible to deduce that the surface swathe must be relatively flat and covered mostly in stones of around 5-10 centimetres in diameter. Credits: M. Pérez-Ayúcar/ESA

An unexpected radio reflection from the surface of Titan has allowed ESA scientists to deduce the average size of stones and pebbles close to the Huygens’ landing site. The technique could be used on other lander missions to analyse planetary surfaces for free.

When Huygens came to rest on the surface of Titan on 14 January 2005, it survived the impact and continued to transmit to the Cassini mothership, orbiting above. Part of that radio signal 'leaked' downwards and hit the surface of Titan before being reflected back up to Cassini. On its way up, it interfered with the direct beam.

As Miguel Pérez-Ayúcar, a member of the Huygens Team at ESA’s European Space Research and Technology Centre (ESTEC) in The Netherlands, and his colleagues watched the signal coming back, they were initially puzzled to see the power of the signal rising and falling in a repetitive manner.

“Huygens had not been designed to necessarily survive impact so we had never thought about what the signal would look like from the surface,” says Pérez. After making a joke that aliens must be dragging the craft along the surface, Pérez and the team began work at once to understand the signal.

Titan's pebbles 'seen' by Huygens radio
An artist's interpretation of the area surrounding the Huygens landing site based on images and data returned on 14 January 2005. Credits: ESA

The clue was the repetitive oscillation of the power. It made Pérez think about the interaction of the direct signal with that reflecting from the surface of Titan. As Cassini travelled away from the Huygens landing site, the angle between it and Huygens changed. This altered the way in which the interference between the reflected and direct beams was detected, perhaps causing the variation in power.

He began running computer models and saw that not only could he reproduce the received signal but also it was sensitive to the size of pebbles on the surface of Titan.

Cassini collected data for 71 minutes after Huygens landed. After that time, the spacecraft’s motion took it below the horizon as seen from Huygens' landing site. Until then, it soaked up radio signals that encoded information about a swathe of Titan’s surface from 1 metre to 2 kilometres to the west of the landed probe.

To accurately mirror the true signal, Pérez and his team discovered that the surface swathe must be relatively flat and covered mostly in stones of around 5-10 centimetres in diameter.

This unique result complements the data taken by the Descent Imager and Spectral Radiometer (DISR) instrument. When Huygens came to rest on the surface of Titan, DISR was pointing due south. Its images show stones and terrain in good agreement with the newly deduced western facing radio data. "This is a real bonus to the mission. It requires no special equipment, just the usual communications subsystem," says Pérez.

Now that the scientists have understood the process using the unexpected Huygens data, the technique could be implemented on future lander missions. "This experience can be inherited by any future lander," says Pérez, "All that will be needed is a few refinements and it will become a powerful technique."

By subtly altering the properties of the radio beam for instance, the radio transmitter and receiver can be optimised to help deduce the chemical composition of the planetary surface.

Source: ESA

Explore further: First measurement of Titan’s winds from Huygens

Related Stories

First measurement of Titan’s winds from Huygens

February 9, 2005

Using a global network of radio telescopes, scientists have measured the speed of the winds faced by Huygens during its descent through the atmosphere of Titan. This measurement could not be done from space because of a configuration ...

How the world watched Huygens

July 27, 2006

As Huygens parachuted to the surface of Titan in January 2005, a battery of telescopes around the world were watching or listening. The results of those observations are now being collected together and published for the ...

Scientists prepare for Huygens descent on Titan

January 4, 2005

University of Arizona scientists, working on one of the most stunning robotic space missions ever attempted, head for Germany next week. Their experiments ride on the Huygens probe to Saturn's giant moon, Titan, part of ...

Huygens Probe Successfully Detached to Begin Its Final Journey

December 25, 2004

The ESA's Huygens probe has successfully detached from NASA's Cassini orbiter early this morning to begin a 21-day journey to Saturn's moon Titan. NASA's Deep Space Network tracking stations in Madrid, Spain, and Goldstone, ...

Huygens lands on Titan!

January 14, 2005

Today, after its seven-year journey through the Solar System on board the Cassini spacecraft, ESA’s Huygens probe has successfully descended through the atmosphere of Titan, Saturn’s largest moon, and safely landed on ...

Recommended for you

Earth's days getting longer: study (Update)

December 7, 2016

Earth's days are getting longer but you're not likely to notice any time soon—it would take about 3.3 million years to gain just one minute, according to a study published on Wednesday.

Curiosity rover team examining new drill hiatus

December 6, 2016

NASA's Curiosity Mars rover is studying its surroundings and monitoring the environment, rather than driving or using its arm for science, while the rover team diagnoses an issue with a motor that moves the rover's drill.

Cassini makes first ring-grazing plunge

December 6, 2016

NASA's Saturn-orbiting Cassini spacecraft has made its first close dive past the outer edges of Saturn's rings since beginning its penultimate mission phase on Nov. 30.

Colliding galaxy clusters

December 5, 2016

Galaxy clusters contain a few to thousands of galaxies and are the largest bound structures in the universe. Most galaxies are members of a cluster. Our Milky Way, for example, is a member of the "Local Group," a set of about ...

New dwarf satellite galaxy of Messier 83 found

December 5, 2016

(Phys.org)—Astronomers have found a new dwarf satellite of Messier 83 (M83, also known as the Southern Pinwheel Galaxy) located some 85,000 light years from its host. This satellite galaxy was designated dw1335-29 and could ...

0 comments

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.