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Cassini snaps at Titan's surface
|October 27, 2004
| The Cassini spacecraft has sent back images of Saturn's moon Titan giving scientists the closest views yet of the mysterious satellite.
The hazy shots were beamed back to a Nasa antenna based in Madrid, Spain, on Wednesday, at 0225 BST.
The probe went within 1,200km (746 miles) of the moon, 300 times closer than its first flyby in July.
The first images were the clearest yet of the moon's surface, and scientists said they expected better images later.
What we've got is a very primitive atmosphere that has been preserved for 4.6 billion years. Titan gives us the chance for cosmic time travel
Toby Owens, Nasa JPL
In pictures: Cassini's Titan flyby
Attempts to view Titan's icy surface have so far been frustrated by a thick, orange haze that shrouds the moon. But scientists had hoped Tuesday's pass would be close enough for Cassini's instruments to penetrate the satellite's dense smog.
"This is history in the making. We will never be this innocent, or this ignorant, again. In a matter of hours, the Solar System will become a very much smaller place," said Cassini imaging team leader Dr Carolyn Porco.
The Cassini team say they have mountains of data to pore over in the weeks ahead. Although the flyby had happened at 1745 BST, scientists at Nasa's Jet Propulsion Laboratory in Pasadena, California, had to wait nine hours until data was sent back.
"It's very exciting because Titan has such a thick atmosphere. It will be exciting to find out what's on the surface," said Cassini project manager Peter Poon.
Titan, received on 26 October (AP Photo/NASA, JPL, Space Science Institute)
Titan is thought to have oceans of liquid methane and ethane on its frozen surface
Later this year, the piggybacked Huygens probe will be released from Cassini and enter Titan's atmosphere.
It will transmit data during its parachute-assisted descent, and carry out science tasks on the surface - if it survives.
But this week's visit could answer some key questions about this unexplored world. In particular, it could help settle a vigorous debate about the nature of Titan's freezing surface, which some scientists think might harbour oceans of liquid methane and ethane.
One theory is that the dark patches seen in the images represent solid continental landmasses, while the lighter areas are oceans of liquid methane and ethane.
Click here to see a comparison of Saturn's largest moons
Whole new world
In order to settle this debate, Cassini is using its cameras, an instrument called the Visual Infrared Mapping Spectrometer (Vims) and its imaging radar to penetrate the moon's thick haze.
The probe's cameras took high-resolution images of Titan, helping to map Huygens' landing site. Cameras have also been taking photos every 15 minutes on the approach. These will be compiled into a movie to show cloud movements in Titan's atmosphere.
Vims will investigate atmospheric phenomena and geological features on Titan while Cassini's imaging radar, which has never been used to gather data about Titan, will build up topographical maps.
CASSINI'S KEY PARTS
1. Antennas enabling communication with Earth
2. Boom carrying instrument to measure magnetic fields
3. Two cameras will take 300,000 pictures of the planet
4. Infra-red spectrometer analyses Saturn's temperature and composition
5. Radioisotope thermoelectric generators supply 750W of power
6. Cassini has two engines - one is a back-up
7. Thrusters used for small changes of direction or speed
8. Huygens probe will land on Saturn's largest moon, Titan
9. Plasma spectrometer measures charged particles and solar winds
These instruments should help reveal whether Huygens will touch down on a sea or river of liquid hydrocarbon, on organic sludge, or on solid ice.
In addition to this, mass spectrometers will analyse the composition of Titan's atmosphere during the pass.
Conditions on Titan - which is the second biggest moon in the Solar System - are thought to be very similar to those on Earth 4.6 billion years ago. Temperatures rarely venture above -179C (-290F) and the atmosphere is dominated by nitrogen and carbon-based compounds.
So mission scientists think the moon might have something to teach us about the conditions that were necessary for the origin of life on our planet.
"What we've got is a very primitive atmosphere that has been preserved for 4.6 billion years. Titan gives us the chance for cosmic time travel," said Toby Owens, principal scientist at JPL in Pasadena, California.
Cassini's flyby - one of 45 planned for its tour of Saturn - is expected to give a taster of what Huygens can expect when it enters the Titan's atmosphere.
Cassini entered into orbit around Saturn in July, on its four-year mission to explore the ringed planet and its moons. It is a cooperative project between Nasa, the European Space Agency (Esa) and the Italian Space Agency
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