Space and astronomy news
And now we finish our trilogy of Saturnian astronomers and missions with a look at the Dutch astronomer and mathematician, Christiaan Huygens. It was Huygens who discovered Titan, and figured out what Saturn’s rings really are, so it makes sense that a probe landing on the surface of Titan was named after him.
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Last week we talked about the Italian astronomer Giovanni Cassini. This week we’ll talk about the mission that shares his name: NASA’s Cassini Spacecraft. This amazing mission is orbiting Saturn right now, sending back thousands of high resolution images of the ringed planet and its moons.
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It might be one of the weirdest-looking moons in the solar system: Saturn’s moon Hyperion looks like a giant sponge. Additionally, its eccentric orbit makes it subject to gravitational forces from Saturn, so it is just tumbling along, almost out of control. Just yesterday, August 25, 2011, the Cassini spacecraft made a relatively close flyby of Hyperion (24,000 km 15,000 miles away) and took some amazing images.
“Hyperion is a small moon … just 168 miles across (270 kilometers)… orbiting between Titan and Iapetus,” said Carolyn Porco in an email. Porco is the Cassini imaging team lead. “It has an irregular shape and surface appearance, and it rotates chaotically as it tumbles along in orbit, making it impossible to say just exactly what terrain we would image during this flyby.”
See some more of the shots below:
Scientists say this flyby’s closeness has likely allowed Cassini’s cameras to map new territory. At the very least, it will help scientists improve color measurements of the moon. It will also help them determine how the moon’s brightness changes as lighting and viewing conditions change, which can provide insight into the texture of the surface. The color measurements provide additional information about different materials on the moon’s deeply pitted surface.
The next closest pass of Hyperion is coming up again soon: Sept. 16, 2011, when it passes the tumbling moon at a distance of about 36,000 miles (58,000 kilometers).
See more raw images at the CICLOPS website.
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Titan is making news again, this time with Cassini images from 2010 showing a storm nearly as big as Texas. Jonathan Mitchell from UCLA and his research team have published their findings which help answer the question:
What could cause such large storms to develop on a freezing cold world?
For starters, the huge arrow isn’t a cosmic detour sign reminding us to “Attempt No Landings” on Jupiter’s moon Europa.
In the study by Mitchell and his team, a model of Titan’s global weather was created to understand how atmospheric waves affect weather patterns on Titan. During their research, the team discovered a “stenciling” effect that creates distinct cloud shapes, such as the arrow-shaped cloud shown in the Cassini image above.
“These atmospheric waves are somewhat like the natural, resonant vibration of a wine glass,” Mitchell said. “Individual clouds might ‘ring the bell,’ so to speak, and once the ringing starts, the clouds have to respond to that vibration.”
Titan is the only other body in the solar system (aside from Earth) known to have an active “liquid cycle”. Much like Titan’s warmer cousin Earth, the small moon has an atmosphere primarily composed of Nitrogen. Interestingly enough Titan’s atmosphere is roughly the same mass as Earth’s and has about 1.5 times the surface pressure. At the extremely low temperatures on Titan, hydrocarbons such as methane appear in liquid form, rather than the gaseous form found on Earth.
With an active liquid both on the surface and in the atmosphere of Titan, clouds form and create rain. In the case of Titan, the rain on the plain is mainly methane. Water on Titan is rock-hard, due to temperatures hovering around -200 c.
Studies of Titan show evidence of liquid runoff, rivers and lakes, further emphasizing Titan’s parallels to Earth. Researchers believe better understanding of Titan may offer clues to understanding Earth’s early atmosphere. In another parallel to earth, the weather patterns on Titan created by the atmospheric waves can create intense rainstorms, sometimes with more than 20 times Titan’s average seasonal rainfall. These intense storms may cause erosion patterns that help form the rivers seen on Titan’s surface. Mitchell described Titan’s climate as “all-tropics”, basically comparing the weather to what is usually found near Earth’s equator. Could these storms be Titan’s equivalent of monsoon season?
Mitchell stated “Titan is like Earth’s strange sibling — the only other rocky body in the solar system that currently experiences rain”. Mitchell also added, “In future work, we plan to extend our analysis to other Titan observations and make predictions of what clouds might be observed during the upcoming season”.
The research was published Aug. 14 in the online edition of the journal Nature Geoscience .
If you’d like to learn more about the Cassini mission, visit: http://saturn.jpl.nasa.gov/index.cfm
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The name “Xanadu” just sounds exotic and enticing, and given that this region on Titan is right next to Shangri-la, how can we not be intrigued by the latest radar image of this region taken by the Cassini spacecraft? While Titan itself is shrouded in mystery with its thick, hazy atmosphere, via radar, Cassini can peer through and has found three major surface features: dunes, craters and the enigmatic Xanadu, a bright continent-sized feature centered near the moon’s equator. At upper right is the crater Ksa, first seen by Cassini in 2006. The dark lines running among Xanadu and Ksa are linear dunes, similar to sand dunes on Earth in Egypt and Namibia. In addition to the dunes, look closely at Xanadu to see hills, rivers and valleys which scientists believe are carved in ice rather than solid ground, by liquid methane or ethane.
This image was taken by Cassini’s Titan Radar Mapper on June 21, 2011.
Source: JPL
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In this new image from the Cassini Imaging Team Saturn’s moon Titan looks a little out of focus compared to the sharp, cratered surface of Tethys, seen in the foreground. But that’s only because Titan’s hazy atmosphere makes the moon look blurry. Titan’s current atmosphere is thought to resemble Earth’s early atmosphere, so we could be looking at an analog of early Earth.
And so, the Cassini mission is sharpening our understanding of Saturn and all its moons, but it might help us understand our own planet, as well.
At just over 1,000 kilometers in diameter, Tethys is believed to be almost entirely comprised of water ice, based on density estimates. Titan, at just over 5,000 kilometers in diameter is notable for being the second largest moon in our solar system, as well as having an atmosphere 1 1/2 times thicker than Earth. Titan is also known to have an active “liquid cycle” made up of various hydrocarbons, making Titan the second body in the solar system to have stable liquid on its surface.
The camera view is aimed at the Saturn-facing side of Titan and at the area between the trailing hemisphere and anti-Saturn side of Tethys. Not shown in frame is Saturn, which would be far to the left, from the perspective shown in the image.
The image was acquired with Cassini’s narrow-angle camera, in green visible light, on July 14, 2011. At a distance of roughly 3 million kilometers, the image scale for Titan is 19 kilometers per pixel. With Tethys at a distance of about 2 million kilometers, the image scale is roughly 11 kilometers per pixel.
If you’d like to learn more about the extended Cassini “solstice” mission, you can read more at: http://saturn.jpl.nasa.gov/mission/introduction/
Source: Cassini Solstice Mission Images
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This stunning new Cassini image was captured on July 29, 2011, and shows a portion of Saturn’s rings along with several moons dotting the view. How many moons can you find, and can you name them?
See below for a color version of this image, put together by our own Jason Major!
Jason shares on his Flickr page the process of how he edited the image. As Jason says, it’s a moon flash mob!
See the Cassini Solstice Mission raw images page for a larger view.
Hat tip to Stu Atkinson
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It’s five hundred times bigger than any anything like it observed by the Cassini Mission in the last two years. It’s encompassing approximately 2 billion square miles (4 billion square kilometers) of Saturn’s surface. It’s releasing lightning bolts at a rate of ten per second and it’s happening ten times more frequently than other storms monitored since 2004. It’s so intense that’s it’s even visible in larger amateur telescopes. Just what is it? A Saturn Super Storm…
“Last December, a remarkable thing happened at Saturn. A massive, hissing, lightning-producing storm violently erupted in the northern mid-latitudes of Saturn’s atmosphere and grew to gargantuan proportions.” says Carolyn Porco. “By the end of January, it had wrapped itself entirely around the planet, developing an enormous degree of wavy, even sensuous, details, reminiscent of the clouds on Jupiter.”
Known as “Great White Spots”, these huge storms aren’t new to Saturn – they are common each Saturnian year. While they are common to the ringed planet’s northern summer, right now it’s northern spring. This makes the Saturn Super Storm an early – and unexpected – arrival.
“Prior to the planet’s August 2009 northern vernal equinox, when the sun was shining in the southern hemisphere, the location of all observed storm activity on Saturn was a band encircling the planet at 35 degrees south latitude that imaging scientists had dubbed `Storm Alley’. Well, to our great puzzlement, this new storm — now 500 times larger than any previously seen by Cassini at Saturn and 8 times the surface area of Earth — has erupted at 35 degrees /north/ latitude.” says Ms. Porco. “The shadow cast by Saturn’s rings has a strong seasonal effect, and it is possible that the switch to powerful storms now being located in the northern hemisphere is related to the change of seasons and the changing position of Saturn’s ring shadow. But why the obvious hemispheric symmetry in storm eruption exists is not yet known.”
NASA’s Cassini spacecraft was listening to the sounds of the storm, too. Much like our terrestrial lightning causes a static effect on an AM radio, Saturn creates a phenomena known as Saturn electrostatic discharges. Check out this audio file of the action!
“The storm is also a prodigious source of radio noise, which comes from lightning deep in the planet’s atmosphere. As on Earth, the lightning is produced in the water clouds, where falling rain and hail generate electricity. The mystery is why Saturn stores energy for decades and releases it all at once. This behavior is unlike that at Jupiter and Earth, which have numerous storms occurring at any one time.” explains Dr. Porco.
Violent, yes… But incredibly beautiful. This false color image reveals clouds at different altitudes as seen by the Cassini spacecraft from a distance of approximately 1.5 million miles (2.4 million kilometers). Blue represents high and semi-transparent. Yellow and white are optically thick at high altitudes. Green is intermediate, while red and brown are low altitude unobscured by high clouds. Last, but not least is dark blue – a thin haze with nothing but Saturn below it. Scientists theorize the lightning is formed at the base cloud layer where water ice is covered by crystallized ammonia.
“This storm is thrilling because it shows how shifting seasons and solar illumination can dramatically stir up the weather on Saturn,” said Georg Fischer, a radio and plasma wave science team member at the Austrian Academy of Sciences in Graz. “We have been observing storms on Saturn for almost seven years, so tracking a storm so different from the others has put us at the edge of our seats.”
Original Story Source: JPL / NASA News.
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Researchers on the Cassini mission team have identified large salt grains in the plumes emanating from Saturn’s icy satellite Enceladus, making an even stronger case for the existence of a salty liquid ocean beneath the moon’s frozen surface.
Cassini first discovered the jets of water ice particles in 2005; since then scientists have been trying to learn more about how they behave, what they are made of and – most importantly – where they are coming from. The running theory is that Enceladus has a liquid subsurface ocean of as-of-yet undetermined depth and volume, and pressure from the rock and ice layers above combined with heat from within force the water up through surface cracks near the moon’s south pole. When this water reaches the surface it instantly freezes, sending plumes of ice particles hundreds of miles into space.
Much of the ice ends up in orbit around Saturn, creating the hazy E ring in which Enceladus resides.
Although the discovery of the plumes initially came as a surprise, it’s the growing possibility of liquid water that’s really intriguing – especially that far out in the Solar System and on a little 504-km-wide moon barely the width of Arizona. What’s keeping Enceladus’ water from freezing as hard as rock? It could be tidal forces from Saturn, it could be internal heat from its core, a combination of both – or something else entirely… astronomers are still hard at work on this mystery.
Now, using data obtained from flybys in 2008 and 2009 during which Cassini flew directly through the plumes, researchers have found that the particles in the jets closest to the moon contain large sodium- and potassium-rich salt grains. This is the best evidence yet of the existence of liquid salt water inside Enceladus – a salty underground ocean.
“There currently is no plausible way to produce a steady outflow of salt-rich grains from solid ice across all the tiger stripes other than salt water under Enceladus’s icy surface.”
– Frank Postberg, Cassini team scientist, University of Heidelberg, Germany
If there indeed is a reservoir of liquid water, it must be pretty extensive since the numerous plumes are constantly spraying water vapor at a rate of 200 kg (400 pounds) every second – and at several times the speed of sound! The plumes are ejected from points within long, deep fissures that slash across Enceladus’ south pole, dubbed “tiger stripes”.
Recently the tiger stripe region has also been found to be emanating a surprising amount of heat, even further supporting a liquid water interior – as well as an internal source of energy. And where there’s liquid water, heat energy and organic chemicals – all of which seem to exist on Enceladus – there’s also a case for the existence of life.
“This finding is a crucial new piece of evidence showing that environmental conditions favorable to the emergence of life can be sustained on icy bodies orbiting gas giant planets.”
– Nicolas Altobelli, ESA project scientist for Cassini
Enceladus has intrigued scientists for many years, and every time Cassini takes a closer look some new bit of information is revealed… we can only imagine what other secrets this little world may hold. Thankfully Cassini is going strong and more than happy to keep on investigating!
“Without an orbiter like Cassini to fly close to Saturn and its moons — to taste salt and feel the bombardment of ice grains — scientists would never have known how interesting these outer solar system worlds are.”
– Linda Spilker, Cassini project scientist at JPL
The findings were published in this week’s issue of the journal Nature.
Read more in the NASA press release here.
Image credits: NASA / JPL / Space Science Institute
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Jason Major is a graphic designer, photo enthusiast and space blogger. Visit his website Lights in the Dark and follow him on Twitter @JPMajor or on Facebook for the most up-to-date astronomy awesomeness!
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On June 18, 2011, the Cassini spacecraft performed a flyby of Saturn’s moon Helene. Passing at a distance of 6,968 km (4,330 miles) it was Cassini’s second-closest flyby of the icy little moon.
The image above is a color composite made from raw images taken with Cassini’s red, green and blue visible light filters. There’s a bit of a blur because the moon shifted position in the frames slightly between images, but I think it captures some of the subtle color variations of lighting and surface composition very nicely!
At right is a 3D anaglyph view of Helene made by Patrick Rutherford from Cassini’s original raw images … if you have a pair of red/blue glasses, check it out!
Cassini passed from Helene’s night side to its sunlit side. This flyby will enable scientists to create a map of Helene so they can better understand the moon’s history and gully-like features seen on previous flybys.
(When Cassini acquired the images, it was oriented such that Helene’s north pole was facing downwards. I rotated the image above to reflect north as up.)
Helene orbits Saturn at the considerable distance of 234,505 miles (377,400 km). Irregularly-shaped, it measures 22 x 19 x 18.6 miles (36 x 32 x 30 km).
Helene is a “Trojan” moon of the much larger Dione – so called because it orbits Saturn within the path of Dione, 60º ahead of it. (Its little sister Trojan, 3-mile-wide Polydeuces, trails Dione at the rear 60º mark.) The Homeric term comes from the behavioral resemblance to the Trojan asteroids which orbit the Sun within Jupiter’s path…again, 60º in front and behind. These orbital positions are known as Lagrangian points (L4 and L5, respectively.)
Read more on the Cassini mission site here.
Images: NASA / JPL / Space Science Institute.