Two moons for the price of one

IN THIS RELEASE: TITAN FLYBY – ENCELADUS FLYBY – FAST FACTS ABOUT TITAN AND ENCELADUS – SUPPLEMENTAL INFORMATION – AVAILABLE IMAGES

WAUKESHA, WI – The Cassini spacecraft – in orbit around Saturn since June 30, 2004 – passes close to two of the ringed planet’s most intriguing moons this week. On the morning of February 15, Cassini swoops within 980 miles (1,580 kilometers) of Titan, a moon revealed just last month to have drainage channels and intermittent lakes of liquid methane. Two days later – February 17 – Cassini flies 730 miles (1,175 km) above Enceladus, an icy world whose surface shows signs of geologic activity.

TITAN FLYBY
To many people, the flyby of Titan may seem superfluous. After all, Cassini sent the Huygens probe all the way to the surface of Titan January 14. Scientists got their first close-up looks of the moon’s surface and saw convincing evidence that liquid methane rains out of Titan’s thick atmosphere and helps shape the ground below. Yet Huygens saw only a tiny part of Titan. With a diameter of 3,200 miles (5,150 km) – bigger than both Mercury or Pluto – Titan likely possesses other wonders elsewhere on its surface.

Cassini will turn its full complement of instruments to Titan during the flyby. Perhaps most interesting, the spacecraft’s radar will target the same area as the optical and infrared cameras. This marks the first time in the mission all three instruments will be studying the same region. Cassini will fly past Titan more than 40 times in the next 4 years as scientists try to build a complete picture of the moon’s atmosphere and surface.

ENCELADUS FLYBY
Two days after the Titan encounter, Cassini will rush past Enceladus. Although Enceladus has a surface area only 1 percent as big as Titan’s, scientists are eager to learn more about it. Enceladus has the brightest surface known in the solar system, reflecting nearly 100 percent of the sunlight that hits. Planetary scientists think the surface is covered with pure water ice.

Even more intriguing, images taken by the Voyager 2 spacecraft in 1981 show large swaths of the surface lack impact craters, while neighboring regions sport sinuous mountain ridges that rise a mile or so above their surroundings. Because meteorites continue to pelt the outer solar system, some geologic process must be erasing the impact craters. Many scientists suspect tidal interactions with other moons warm the interior of Enceladus, driving a form of icy volcanism that covers part of the moon’s surface. Cassini will come 100 times closer than Voyager 2 did, so the best images returned should be 100 times sharper.

Cassini will send data from the Titan and Enceladus flybys back this week, and scientists will begin the often-arduous process of deciphering what they mean. Astronomy magazine and Astronomy.com will keep you abreast of the latest findings.

FAST FACTS ABOUT TITAN AND ENCELADUS: