Skip navigation

Tag Archives: Titan

Adapted from an article by Kenneth Chang published in The New York Times, September 14, 2017:

NASA’s Cassini spacecraft, the intrepid robotic explorer of Saturn’s magnificent beauty, has finally ended its 20-year journey. By design, the probe vanished into Saturn’s atmosphere, disintegrating moments after its final signal slipped away into the background noise of the Solar System. Until the end, new measurements streamed one billion miles back to Earth, preceded by the spacecraft’s last picture show of dazzling sights from around the Sun’s sixth planet.

15cassini-beforeplunge-jumbo

Credit: Credit NASA/JPL-Caltech/Space Science Institute

 

The mission for Cassini, in orbit since 2004, stretched far beyond the original four-year plan, sending back multitudes of striking photographs, solving some mysteries and upending prevailing notions about the Solar System with completely unexpected discoveries.

Even at the end, 20 years after launch, Cassini and its instruments remained in good working shape. The plutonium power source was still generating electricity. But there was not enough propellant fuel left to safely send Cassini anywhere except into Saturn.

In the very last phase of the mission, Cassini dove through the gap between Saturn and the planet’s innermost ring. This provided new, sharp views of the rings and allowed the craft to probe the planet’s interior, as another NASA’s Juno spacecraft is doing at Jupiter.

Links: read the full article; also NYT’s ‘100 Images from Cassini’ feature.

Advertisements

An article in New Scientist summarizes work by Michael Wong at Caltech, published in the journal Icarus, about how Titan keeps its surface methane liquid.

Saturn’s largest moon may once have been a giant snowball. Titan is already a frigid moon made mostly of ice. But methane gas in its atmosphere keeps the surface just warm enough for a scattering of lakes filled with liquid hydrocarbons. Scientists have puzzled over Titan’s atmospheric methane because the molecule is easily broken down by sunlight. Calculations suggest that all the methane Titan seems to possess should have been used up within tens of millions of years – a blip in the moon’s roughly 4-billion-year lifetime.

Adding to the mystery, the methane breakdown creates other compounds that rain over the surface, helping to fill the lakes. If used-up methane was replaced, this process would happen constantly, so Titan should be covered not by lakes, but by a global ocean hundreds of metres deep.

Michael Wong at Caltech says snowballs may be the missing piece. Scientists suspect Earth went through a snowball phase about 2 billion years ago, when the planet became covered in ice. A similar event could have taken place on Titan, says Wong. Methane levels may rise and fall if the gas is periodically released from inside the moon. If at some point the methane dropped by a factor of 100, temperatures would fall, and surface liquids would freeze over. A different mix of compounds would also be produced in the atmosphere. So this cold snap would mean the moon’s surface should host lots of compounds called nitriles, which would be solid rather than creating an ocean.

The New Horizons mission to Pluto could offer early clues. Like Titan, Pluto has an atmosphere that is mostly nitrogen with some methane. Pluto’s atmosphere is much thinner and colder, but the physics are similar enough that examining its composition could boost the snowball model.

Links: the New Scientist report; Icarus article.

A newly released image of Titan, Saturn’s largest moon reveals details of seas or lakes near its northern pole.

Credit: NASA/JPL-Caltech/U. Arizona/U. Idaho

The false-color mosaic, made from infrared data collected by NASA’s Cassini spacecraft, reveals the differences in the composition of surface materials around these hydrocarbon lakes. Titan is the only other place in the Solar System that we know has stable liquid on its surface – but its lakes are made of liquid ethane and methane rather than liquid water. While there is one large lake and a few smaller ones near Titan’s south pole, almost all of Titan’s lakes appear near the moon’s north pole.

The image data suggest parts of Titan’s lakes and seas may have evaporated and left behind the Titan equivalent of Earth’s salt flats. They appear orange in this image against the greenish backdrop of Titan’s typical bedrock of water ice.

Launched in 1997, Cassini has been exploring the Saturn system since 2004. A full Saturn year is 30 years, and Cassini has been able to observe nearly a third of a Saturn year. In that time, Saturn and its moons have seen the seasons change from northern winter to northern summer.
Links: press release from Cassini imaging team; annotated image from NASA’s Cassini mission homepage.