Are There Waves On Titan’s Ligeia Sea?

Titan’s Ligeia Mare, a sea of liquid ethane and methane 260 miles (420 km) across, is comparable to Lake Superior on Earth – with a difference. The “water” in Ligeia Sea is liquid ethane and methane. Credit: NASA

Cassini will soon make its next flyby of the planet’s largest moon Titan to look for waves on the surface of Ligeia Mare (lie-JEE-uh MAH-ray), a large sea of bitterly-cold liquid ethane in the moon’s north polar region.

Titan’s great distance from the sun ensures that the average temperature there hovers at -290 F (-179 C), cold enough for ethane and methane, which are gases here on Earth, to condense as liquids.

On May 23, the probe will cruise just 603 miles (970 km) above the lake and bounce radio waves off its surface to fathom its surface texture. No one’s sure if the liquid natural gas is thick and flat like molasses or more like lake water here on Earth. Will we someday find rapids, waterfalls? I’m hoping for some cool images of waves. Row, row, row your boat.

Watch as Saturn’s B-ring, the bright ring at upper right, expands and contracts. 39 images taken over 1 hour and 40 minutes were used to create the video.

Also on Cassini’s to-do list was the creation of a movie of Saturn’s bright B-ring in order to better understand how the planet’s moons shape its rings. In the video, you can see the ring expand and contract. Look closely and halfway through the movie you’ll also notice an arc of brighter material sweep by just within the ring’s edge. High-resolution pictures show vertical structures in the ring plane here towering up to 2.2 miles (3.5 km) high.

What you’re seeing are ring particles – made of water ice – hovering above the ring plane. As they stream past an invisible moonlet embedded in the B-ring, the moon’s gravity temporarily squeezes them together and lifts them up to form an orbiting arc. The moonlet – estimated at 1,000 feet (300 m) across, was found sometime later, betrayed by the shadow it cast when Saturn’s rings were “level” with the sun at its 2009 equinox.

A low-angle view of Saturn’s B-ring (foreground) made by Cassini. Watch as it swells outward and then shrinks inward.

In the second video, the low-angle perspective makes the expansion and contraction of the B-ring even easier to see. Scientists have found four separate, independent movements of ring particles that create the hula-hoop-like wobble.

The repeated pulls of the inner moon Mimas on B-ring particles as they orbit Saturn creates one of the swellings. The other three travel around the ring with different speeds and are caused when random motions of icy ring particles reinforce one another to create a wave that flows outward to the boundary of the B-ring. From there it’s reflected back to the inner part of the ring, which in turn reflects it out again like waves bouncing around in a bathtub. Repeated back-and-forth bounces cause sections of the B-ring to expand and contract to the tune of 120 miles (200 km).

Small pieces of ice. Amazing what they’re capable of when their random motions work in tandem. Even the 15,800 mile (25,500 km) B-ring must bow (and bend) to their will.


4 Responses

  1. BCstargazer

    Thanks for the timely entry. I caught myself exploring the last Titan radar images for hours (PIA16845- released last month. Seeing the drainage basins and rivers got me and some friends wonder about the possibility of “methane falls”. We even thought of a possible name for it: Niagara Magnus Cataractus. Now that would be my honeymoon destination 🙂

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