Titan is an unusual object in our solar system. It has more in common with Earth and Venus than it does with moons. Titan sports a rocky surface and a thick atmosphere. Rainfall, rivers and seas cover the moon’s surface.
Scientists at UCL have spotted another Earth-like feature. Polar winds.
“Data from CAPS proved a few years ago that the top of Titan’s atmosphere is losing about seven tonnes of hydrocarbons and nitriles every day, but didn’t explain why this was happening. Our new study provides evidence for why this is happening,” said study lead Andrew Coates.
CAPS is the Cassini Plasma Spectrometer onboard the Cassini spacecraft.
Hydrocarbons are molecules that are made up of methane, which Titan has a lot of.
Coates and his team found that Titan’s atmospheric loss is caused by a polar wind. This polar wind is powered by the Sun’s interaction with Titan’s upper atmosphere.
“Although Titan is ten times further from the Sun than Earth is, its upper atmosphere is still bathed in light,” says Coates. “When the light hits molecules in Titan’s ionosphere, it ejects negatively charged electrons out of the hydrocarbon and nitrile molecules, leaving a positively charged particle behind. These electrons, known as photoelectrons, have a very specific energy of 24.1 electronvolts, which means they can be traced by the CAPS instrument, and easily distinguished from other electrons, as they propagate through the surrounding magnetic field.”
The magnetic field Coates is describing isn’t Titan’s. Not all of Titan’s features are Earth-like. One of them is its lack of a magnetic field. But, Saturn’s magnetic field picks up the slack by covering Titan.
During nearly two dozen flybys of Titan’s ‘magnetic field,’ Cassini measured noticeable quantities of photoelectrons. The scientists found the photoelectrons created an electrical field. And, this electrical field was strong enough to pull hydrocarbon particles from the sunlit portion of Titan’s atmosphere.
The same effect is also observed on Earth as polar wind. Since Earth has its own magnetic field, particles escape where the magnetic field is open – at the poles. Titan’s lack of magnetic field means this phenomenon can happen over a wider area.
Right now, scientists know ‘polar wind’ is unique to Earth and now Titan. Similar particle escapes are likely happening on Mars and Venus, but scientists haven’t been able to confirm.
Cassini and Titan
Cassini has moved on to Saturn’s other moons, but exploring Titan was one of the mission’s highlights.
From the Sun’s reflection off a hydrocarbon lake. (image captured in near-infrared)
To a massive vortex.
To spying Titan’s lakes through its hazy atmosphere.
Cassini has captured incredible images of Saturn’s largest moon.
The Cassini mission is nearing its end. Later this year, Cassini will exit Saturn’s equatorial plane and set up for its final year. During the final stage of its mission, Cassini will repeatedly dive through the space between Saturn and its rings. You think the images we’ve seen have been incredible? Just wait until next year. Cassini will blow us away.
Image credits: NASA