New study finds evidence of changing seasons, rain on Titan's north pole

January 16, 2019, American Geophysical Union
New research provides evidence of rainfall on the north pole of Titan, the largest of Saturn’s moons, shown here. The rainfall would be the first indication of the start of a summer season in the moon’s northern hemisphere, according to the researchers. Credit: NASA/JPL/University of Arizona. 

An image from the international Cassini spacecraft provides evidence of rainfall on the north pole of Titan, the largest of Saturn's moons. The rainfall would be the first indication of the start of a summer season in the moon's northern hemisphere.

"The whole Titan community has been looking forward to seeing clouds and rains on Titan's north pole, indicating the start of the northern summer, but despite what the climate models had predicted, we weren't even seeing any clouds," said Rajani Dhingra, a in physics at the University of Idaho in Moscow, and lead author of the new study accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union. "People called it the curious case of missing clouds."

Dhingra and her colleagues identified a reflective feature near Titan's north pole on an image taken June 7, 2016, by Cassini's near-infrared instrument, the Visual and Infrared Mapping Spectrometer. The reflective feature covered approximately 46,332 square miles, roughly half the size of the Great Lakes, and did not appear on images from previous and subsequent Cassini passes.

Analyses of the short-term reflective feature suggested it likely resulted from sunlight reflecting off a wet surface. The study attributes the reflection to a methane event, followed by a probable period of evaporation.

Titan’s north pole as seen by the Cassini Visual and Infrared Mapping Spectrometer. The orange box shows the “wet sidewalk” region, what analyses suggests is evidence of changing seasons and rain on Titan’s north pole. The blue box shows the expanded region in the bottom panel. Bottom Panel: Pictured is an expanded view of Titan’s north pole. Dark blue arrows mark clouds. Red arrows mark the mirror-like reflection from a lake called Xolotlan Lacus. Pink arrows mark the “wet sidewalk”region. The black dot marks the actual north pole of Titan. Light blue arrows mark the edges of the largest north polar sea, Kraken Mare. Credit: NASA/JPL/University of Arizona/University of Idaho.
"It's like looking at a sunlit wet sidewalk," Dhingra said.

This represents the first observations of summer rainfall on the moon's northern hemisphere. If compared to Earth's yearly cycle of four seasons, a season on Titan lasts seven Earth years. Cassini arrived at Titan during the southern summer and observed clouds and rainfall in the southern hemisphere. Climate models of Titan predicted similar weather would occur in the northern hemisphere in the years leading up to the northern solstice in 2017. But, by 2016, the expected cloud cover in the northern had not appeared. This observation may help scientists gain a more complete understanding of Titan's seasons.

"We want our model predictions to match our observations. This rainfall detection proves Cassini's climate follows the theoretical we know of," Dhingra said. "Summer is happening. It was delayed, but it's happening. We will have to figure out what caused the delay, though."

Additional analyses suggest the methane rain fell across a relatively pebble-like surface, Dhingra said. A rougher surface generates an amorphous pattern as the liquid settles in crevasses and gullies, while liquid falling on a smooth would puddle in a relatively circular pattern.

Dhingra is using the wet sidewalk effect to search for additional rain events on Titan as part of her research.

Explore further: Cassini's final view of Titan's northern lakes and seas

More information: Rajani D. Dhingra et al, Observational evidence for summer rainfall at Titan's north pole, Geophysical Research Letters (2019). DOI: 10.1029/2018GL080943

Related Stories

Cassini's final view of Titan's northern lakes and seas

September 13, 2018

During NASA's Cassini mission's final distant encounter with Saturn's giant moon Titan, the spacecraft captured the enigmatic moon's north polar landscape of lakes and seas, which are filled with liquid methane and ethane.

Watching summer clouds on Titan

November 7, 2016

NASA's Cassini spacecraft watched clouds of methane moving across the far northern regions of Saturn's largest moon, Titan, on Oct. 29 and 30, 2016.

Cassini tracks clouds developing over a Titan sea

August 12, 2014

(Phys.org) —NASA's Cassini spacecraft recently captured images of clouds moving across the northern hydrocarbon seas of Saturn's moon Titan. This renewed weather activity, considered overdue by researchers, could finally ...

Cassini gazes at veiled Titan

September 23, 2010

(PhysOrg.com) -- NASA's Cassini spacecraft will swing high over Saturn's moon Titan on Friday, Sept. 24, taking a long, sustained look at the hazy moon. At closest approach, Cassini will fly within 8,175 kilometers (5,080 ...

Cassini sees dramatic seasonal changes on Titan

October 21, 2016

As southern winter solstice approaches in the Saturn system, NASA's Cassini spacecraft has been revealing dramatic seasonal changes in the atmospheric temperature and composition of Saturn's largest moon, Titan.

Recommended for you

Light-based production of drug-discovery molecules

February 18, 2019

Photoelectrochemical (PEC) cells are widely studied for the conversion of solar energy into chemical fuels. They use photocathodes and photoanodes to "split" water into hydrogen and oxygen respectively. PEC cells can work ...

6 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

smartist
3 / 5 (2) Jan 16, 2019
Why can't you guys post images with larger resolution? I click to enlarge and it gets smaller!
SkyLight
5 / 5 (2) Jan 17, 2019
I clicked on both, and they both got bigger. You need to activate the embiggerator in your computer !
wduckss
1 / 5 (1) Jan 17, 2019
Change paradigm (now we have summer and winter time) and acceptance of evidence from my article.
https://www.svemi...ml#Titan "What are the lakes on Titan made of?"
Basins of liquid were discovered in the northern and southern polar areas,
which are much colder than average, according to the general principles of temperature arrangement on an object, due to the different influence of tidal forces on the equator and the poles of an object.
Methane changes into solid state of matter at the temperature of -182,5°C and ethane at the temperature of -182,8°C.
This has a certificate in a new measurement of the stratosphere at the south pole of Titan, which is 40 ° less than average temperatures.
http://phys.org/n...tan.html
FredJose
3 / 5 (4) Jan 18, 2019
One nagging question remains in the room like a large looming elephant:
Why does Titan still have any methane at all given the ongoing transformation from methane to ethane? Current estimates show that the methane should run out in another 10 million years. So just how much methane must have been on Titan originally for there to still be so much left after billions of years of existence? Where would such an absolutely ginormous amount of methane come from?

Secondly and seemingly totally unrelated - Enceladus has been spewing forth fresh ice in a geologic frenzy. Scientists have now firmly established (thanks to Cassini) that the geologic activity is evidence of heating going on inside the moon and that the heating is of 15.3 GW magnitude. This is much more than that which can possibly be produced by gravitational squeezing from Saturn only ( which causes about 1.GW of heating at most).
The question arises - how is it possible for such heating to continue over billions of years?
FredJose
2.3 / 5 (3) Jan 18, 2019
Another Titanic question is "Where is all the expected seas of Ethane from billions of years of activity?" There is none.
So as creationists have been saying for decades now - The solar system exhibits strong and clear evidence of being very, very young.
It's just the ungodly big bang belief system that creates all the old-age problems that require miracle upon miracle upon miracle to explain away. Literally.
wduckss
not rated yet Jan 18, 2019
It is not enough to notice the deficiencies. Answers should be sought. The temperature of -179 ° C determines the flow processes. Elements and compounds that are solid at 179 ° are not in play. Nitrogen and oxygen are gaseous. Methane is at the border but within the working zone (as water on Earth). At the equator and at the friction caused by tidal forces becomes liquid and gaseous. In the atmosphere, methane does not have much, because it removes it, low temperatures (below -182.5 is in solid state). We see that the temperatures are below -200 ° C (temperatures depend on summer and winter). At the poles of Titan nitrogen may be in the period between the summer and winter to be in a liquid state.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.