Tonight's Sky

Tonight's Sky — Change location



Tonight's Sky — Select location

Tonight's Sky — Enter coordinates

° '
° '

Huygens begins its mission to Saturn moon surface

For more information, contact:
Matt Quandt
Assistant editor
(w) 262.796.8776 x.419
(cell) 414.719.0116

December 22, 2004
Huygens meets Titan
Despite inspection across the spectrum by the Cassini spacecraft, Saturn's moon Titan remains an enigma. In January 2005, the Huygens probe will give us an unprecedented view.
In this release:
Let the mission begin — Titan's hazy, dense atmosphere — Titan's wet surface? — Descent details — Fast facts about the mission — Links to public-domain images of Cassini and Huygens — Astronomy magazine's extensive Cassini coverage

Let the mission begin
WAUKESHA, WI — While children look to the sky Christmas Eve, hoping to catch a glimpse of Santa Claus, planetary scientists will be gazing at computer screens to monitor celestial goings-on. But these grown-ups won't be concerned with the progress of a red-suited man in a sleigh. Instead, they will be following the progress of a golden-colored spacecraft starting the final leg of its 7-year, 2.25-billion-mile (3.62 billion kilometer) journey.

If all goes according to schedule, NASA's Cassini spacecraft will release the European Space Agency's Huygens probe the evening of December 24. Cassini has been orbiting Saturn for the past 6 months, sending back marvelous photographs and other data about the planet, its rings, and its family of moons. The Huygens probe has been riding piggyback all along, waiting for its time to come. Its sole purpose is to execute a 2.5-hour dive through the thick, hazy atmosphere of Saturn's giant moon, Titan. If the mission is a success, scientists will get their first close look at the atmosphere and surface of this enigmatic moon.

Titan's hazy, dense atmosphere
Titan's atmosphere consists mostly of nitrogen — just like Earth's — with small amounts of methane, ethane, acetylene, and other hydrocarbons mixed in. The atmosphere is 10 times thicker and exerts a surface pressure 50-percent greater than Earth's. At Titan's surface temperature — about -290° Fahrenheit (-179° Celsius) — methane should condense out of the atmosphere and "rain" down. Some scientists think lakes of liquid hydrocarbons might exist on Titan.

Titan's wet surface?
The surface could be shaped by hydrocarbon rain and flowing rivers, and the shorelines of any lakes could be carved by tides. Titan's environment — preserved in the deep freeze of the outer solar system — reminds many scientists of what the very young Earth might have been like and could provide important clues to understanding the chemical processes that led to life.

Descent details
When Huygens separates from Cassini at 9 P.M. EST December 24, it will pull away at less than 1 mile per hour. The separation maneuver will also impart a spin of 7 revolutions per minute to Huygens to ensure its stability on the 3-week journey to Titan. The only instrument on Huygens that will operate during the trip is a system of alarm clocks designed to wake the spacecraft a few hours before it hits the atmosphere's fringe the morning of January 14, 2005.

During Huygens' first 3 minutes inside the atmosphere, friction will slow the spacecraft from 11,200 miles per hour (18,025 km/h) to 870 miles per hour (1,400 km/h) and raise the temperature of the heat shield to more than 3,000° F (1,650° C). Robotic controls then will release a series of parachutes to slow the spacecraft further and expose science instruments to the atmosphere.

Four instruments will study the atmosphere's temperature, pressure, density, wind speed, and composition during the expected 2.5-hour-long descent. Shortly before Huygens reaches Titan's surface, a camera will photograph the area around the landing site. (A lamp will turn on just before touchdown to augment the weak sunlight, which is 1,000 times dimmer than at Earth's surface.)

Huygens should hit the surface at about 10 miles per hour (16 km/h). Huygens' batteries should survive for another 30 minutes. A suite of instruments will determine the physical properties of the surface — whether the probe lands on solid ground or in a hydrocarbon lake. All the information will be sent to the Cassini orbiter, which will relay the precious information to Earth.

Fast facts about the mission:
  • "Huygens" — named for Dutch astronomer Christiaan Huygens, who discovered Titan in 1655

  • "Cassini" — named for Italian-French astronomer Giovanni Cassini, who, between 1671 and 1684, discovered four of Saturn's moons and spotted several ring features

  • Diameter of Titan — 3,200 miles (5,150 km), about 1.5 times the size of Earth's Moon

  • Titan's distance from Saturn — 760,000 miles (1.22 million km), about 3 times as far as our Moon from Earth

  • Titan's period of revolution around Saturn — 15.95 days

  • Temperature at Titan's surface — -290° Fahrenheit (-179° Celsius)

  • Composition of Titan's atmosphere — 95 percent nitrogen with traces of methane, ethane, acetylene, and other hydrocarbons

  • Distance traveled by Cassini and Huygens since launch, October 15, 1997 — 2.25 billion miles (3.62 billion kilometers)

  • Diameter of Huygens spacecraft — 8.9 feet (2.7 meters)

  • Weight of Huygens spacecraft — 700 pounds (318 kilograms)

  • Speed of Huygens on arrival at Titan — 11,200 mph (18,025 km/h)

  • Speed at landing — 10 mph (16 km/h)

  • Number of scientific instruments on Huygens — six, although each has multiple experiments

  • Expected number of images from Huygens — 1,100

  • Links to public-domain images of Cassini and Huygens
    ****Copy and paste links, if they don't work directly****
    These links show Huygens being jettisoned from Cassini:

    The following show Huygens on or near Titan's surface:

    Astronomy magazine's extensive Cassini coverage
    In-depth information on this landmark mission can be found in "Journey to Saturn," an 8-page feature in the January 2004 Astronomy magazine. The article includes a graphical summary of Cassini's long journey; images of Saturn's atmosphere; top 10 (projected) Cassini mission highlights; information on the spacecraft namesakes: Giovanni Cassini and Christiaan Huygens; a summary of Huygens' instruments — with a full-color illustration of Huygens' descent; and, an overview of Saturn's medium-size moons. For a copy of this issue, please contact Matt Quandt: or 262.796.8776 x.419.

    Astronomy magazine and will keep you abreast of the latest findings from both Cassini and the Huygens probe.


    Read and share your comments on this article
    Comment on this article
    Want to leave a comment?
    Only registered members of are allowed to comment on this article. Registration is FREE and only takes a couple minutes.

    Login or Register now.


    Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter.


    Click here to receive a FREE e-Guide exclusively from Astronomy magazine.

    Find us on Facebook