Titan (astronomy) - Titan (astronomy) [Electronic resources] نسخه متنی

Titan (astronomy)

I INTRODUCTION

Titan (astronomy), largest moon of the planet Saturn. Titan is spherical, measuring about 5,150 km (about 3,200 mi) in diameter, larger than the planets Mercury and Pluto. It the second-largest moon in the solar system, after Jupiter's moon Ganymede. Saturn's first moon to be discovered, Titan was found in 1655 by Dutch astronomer Christiaan Huygens. The moon is named after the Titans, a family of giants in Greek mythology.

II ORBIT

Titan orbits Saturn at a distance of about 1.22 million km (about 759,000 mi), completing an orbit about once every 16 Earth days. Like Earth's Moon, Titan is tidally locked, meaning that Titan rotates once in the same amount of time that it completes an orbit around Saturn. This rate of rotation keeps one side of Titan facing toward the planet at all times. Titan's orbit parallels Saturn's equator and is nearly circular.

III OBSERVATION AND EXPLORATION

Titan appears as a featureless orange ball when observed with optical telescopes. The United States Voyager probes took pictures of Titan as they flew past Saturn in 1980 and 1981, but they were unable to see surface details because of the moon's hazy atmosphere. The Hubble Space Telescope and the Infrared Space Observatory (ISO) satellite of the European Space Agency (ESA) looked at Titan in the infrared range but could only make out minimal surface and atmospheric details.

Most of our knowledge of Titan comes from the Cassini spacecraft and the Huygens probe that Cassini carried to Titan. Cassini began studying Saturn and its moons when it arrived in 2004, and Huygens touched down on the Titan's surface early in 2005. The Cassini-Huygens mission was a joint effort between the National Aeronautics and Space Administration (NASA), the ESA, and Italy's space agency.

IV ATMOSPHERE

Titan's atmosphere appears as a nearly featureless orange haze. It is 60 percent denser than Earth's atmosphere. Nitrogen is the dominant component of Titan's atmosphere (about 94 percent), with the balance made up of methane, ethane, hydrogen cyanide, carbon dioxide, water vapor, and other chemicals. Most of these components seem to be well mixed in the atmosphere, but astronomers have been able to detect discrete clouds of methane.

Titan's atmosphere is thought to be quite similar to Earth's early atmosphere, before life began. Titan's atmosphere stretches much farther from its surface, however, because of the moon's low gravity. Cassini has revealed multiple layers of haze higher than 400 km (250 mi) above the moon's surface. The majority of Earth's atmosphere lies within 16 km (10 mi) of the surface.

V SURFACE

Observation of Titan has revealed a geologically young surface sculpted by liquid and almost devoid of impact craters. With a surface temperature of about -180C (about -290F), Titan is much too cold for this liquid to be water. Scientists think that the chemical methane, which is liquid at low temperatures, rains on the surface and flows in rivers, acting in much the same way that water does on Earth. Spacecraft have revealed bright elevated regions that may be continents and drainage channels leading to dark featureless lowlands or seas. One raised area named Xanadu is the size of Australia. Pictures of Titan's surface taken by the Huygens probe reveal rounded “rocks” that may actually be chunks of water ice. The rocks are sitting on what looks like a flood plain and may have been rounded by flowing liquid methane.

Titan is Saturn's densest moon. Planetary scientists theorize that Titan has a rocky core about 3,400 km (about 2,100 mi) in diameter, surrounded by ice. The core is probably partly molten.

Saturn's Moon Titan

Titan is the largest moon of Saturn, larger even than the planets Mercury and Pluto. Its thick orange atmosphere, full of organic chemicals, hides the surface in this photo. Layers of haze float hundreds of kilometers above the ground.

Space Science Institute/NASA/JPL