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What are the ‘blood trails’ on Saturn’s moon? Experts are stumped by mysterious arch-shaped red lines on Tethys' icy surface
- The Cassini probe spotted mysterious red lines on Tethys, several hundred miles long and only a few miles wide
- Scientists say they may be exposed ice with chemical impurities or the result of outgassing from inside Tethys
- Except for a few small craters on Saturn's moon Dione, reddish-tinted features are rare on other moons of Saturn
By Ellie Zolfagharifard For Dailymail.com
Cassini has spotted mysterious red lines, several hundred miles long, scratched across the surface of Saturn's icy moon Tethys.
The unexplained arc-shaped 'blood trails' are among the most unusual colour features on Saturn's moons to be revealed by the probe.
Astronomers are baffled by their presence, with some suggesting they may be exposed ice containing chemical impurities, or the result of outgassing from inside Tethys.
Unusual arc-shaped, reddish streaks cut across the surface of Saturn's ice-rich moon Tethys in this enhanced-color mosaic. The red streaks are narrow, curved lines on the moon's surface, only a few miles wide but several hundred miles long. The red streaks are among the most unusual color features on Saturn's moons to be revealed by Cassini's cameras
The colour images for this observation, taken in April, are the first to show large northern areas of Tethys under the lighting and viewing conditions needed to see the arcs clearly.
As the Saturn system moved into its northern hemisphere summer over the past few years, northern latitudes have become increasingly well illuminated.
As a result, the arcs - which are only a few miles wide - have become clearly visible for the first time.
'The red arcs really popped out when we saw the new images,' said Cassini participating scientist Paul Schenk of the Lunar and Planetary Institute in Houston.
This mosaic of Saturn's icy moon Tethys shows a range of features on the moon's trailing hemisphere. Tethys is tidally locked to Saturn, so the trailing hemisphere is the side of the moon that always faces opposite its direction of motion as it orbits the planet
With the expanded range of colors visible to Cassini's cameras, differences in materials and their textures become apparent that are subtle or unseen in natural color views. Here, the giant impact basin Odysseus on Saturn's moon Tethys stands out brightly from the rest of the illuminated icy crescent
SATURN'S ICY MOON TETHYS
- Tethys is a small moon 662 miles (1,066 km) in diameter that orbits 183,100 miles (294,660 km) from Saturn.
- This cold, airless and heavily scarred body is very similar to sister moons Dione and Rhea except that Tethys is not as heavily cratered.
- This may be because its proximity to Saturn causes more tidal warming, and that warming kept Tethys partially molten longer.
- Tethys' density is 0.97 times that of liquid water, which suggests that Tethys is composed almost entirely of water ice and a small amount of rock.
- The moon is tidally locked in phase with its parent planet - one side always faces toward Saturn.
- Tethys also has gravitationally locked two smaller moons into its own subsystem - Telesto and Calypso.
'It's surprising how extensive these features are.'
The origin of the features and their reddish colour is a mystery to Cassini scientists.
Possibilities being studied include ideas that the reddish material is ice filled with impurities or substances that have come to the surface from inside Tethys.
They could also be associated with features like fractures that are below the resolution of the available images.
Except for a few small craters on Saturn's moon Dione, reddish-tinted features are rare on other moons of Saturn.
Many reddish features do occur, however, on the geologically young surface of Jupiter's moon Europa.
'The red arcs must be geologically young because they cut across older features like impact craters, but we don't know their age in years.' said Paul Helfenstein, a Cassini imaging scientist.
'If the stain is only a thin, coloured veneer on the icy soil, exposure to the space environment at Tethys' surface might erase them on relatively short time scales.'
The Cassini team is currently planning follow-up observations of the features, at higher resolution, later this year.
'After 11 years in orbit, Cassini continues to make surprising discoveries,' said Linda Spilker, Cassini project scientist at Nasa's Jet Propulsion Laboratory in Pasadena, California.
'We are planning an even closer look at one of the Tethys red arcs in November to see if we can tease out the source and composition of these unusual markings.'
Tethys is a small moon 662 miles (1,066 km) in diameter that orbits 183,100 miles (294,660 km) from Saturn. This image shows terrain slightly farther to the southwest than images taken a couple of hours earlier
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