News from Saturn
Amazing discoveries continue to pour in from Cassini, now within its second extended mission since arriving at Saturn in 2004. The spacecraft is back to nominal operations after a 3-week safing event caused by a single-bit error in the onboard computer (JPL). The recovery came just in time for another major flyby of Enceladus.
- Enceladus eruptions: The geysers of Enceladus continue to erupt out the south pole. The parallel cracks, dubbed “tiger stripes,” from which the eruptions occur, are longer and more complex than originally thought. This comes from new data taken November 30 during the 12th flyby at 45,000 altitude at closest approach – the last good look at the south pole in sunlight. This was E12: the twelfth targeted encounter with Enceladus. JPL and the Cassini Imaging Team released images of the bright jets shooting gas and dust outward at supersonic speeds. Particles reaching escape velocity create the E-ring around Saturn; others fall back onto the moon and brighten its surface.
Live Science reminded its readers that the heat energy per unit area coming out of this small icy moon, “once thought to be cold and geologically dead,” is five times that in Yellowstone. That’s heat, of course, not temperature, since the Composite Infrared Spectrometer (CIRS) measured highest temperatures of 190 Kelvin (-120° F), cold enough to be intolerable to humans. Live Science remarked, “While that sounds cold, it is actually quite warm for this icy moon around Saturn.” Temperatures at other regions of Enceladus are typically around 80 Kelvin (-315° F) and as low as 33 K (-400° F) at the north pole. Yellowstone obviously has scalding hot temperatures localized to its geysers and hot springs, but overall, Enceladus’ geysers emit more heat energy per unit area – an astonishing discovery for a small icy moon separated from significant external heat sources.
Earlier flybys had measured temperatures of 170K. Scientists are trying to understand if the new high of 190K represents increased activity along the fissure observed in the greatest detail, named Damascus Sulcus. More likely, it results from the higher resolution possible on this flyby by the CIRS instrument, allowing it to focus in on the inner regions of the channel. The observations also revealed forks at the end of two cracks where heat emission continues past the main channel, and an isolated warm spot not associated with a tiger stripe (see JPL story and image). Space.com, PhysOrg and Science Daily all reported the story.
- Hyperion pox: The geometry of the Enceladus flyby allowed Cassini to make another non-targeted flyby of Hyperion from about 72,000km. Since the pock-marked potato-shaped moon has a chaotic rotation, engineers cannot predict what side will face the camera. The best image was posted by JPL and SpaceRef; on YouTube, someone colorized 61 of the images and made them into a video sequence.
- Saturn hex: Atmospheric scientists have modeled in the lab how the mysterious hexagon at Saturn’s north pole might remain stable as a standing wave; see abstract on Icarus.1 The shape was first observed 30 years ago by the Voyagers and continues unabated to this day. “Why the jet stream takes the characteristic six-sided shape and how it is stably maintained across multiple Saturnian seasons are yet to be explained,” they said. They came up with a model and simulation that partly fits the observations; “However, our results also show that a vortex street model of the Hexagon cannot reproduce the observed propagation speed unless the zonal jet’s speed is modified beyond the uncertainties in the observed zonal wind speed, which suggests that a vortex street model of the Hexagon and the observed zonal wind profile may not be mutually compatible.” It remains a work in progress.
- Rhea gas: Last month Cassini scientists were surprised to find a tenuous atmosphere at Rhea composed of oxygen and carbon dioxide. Though 5 trillion times less dense than Earth’s atmosphere, it is 100 times more dense than the exospheres of Mercury and Earth’s moon, according to Science Daily. Scientists believe the oxygen comes from bombardment of the surface by Saturn’s magnetic field, causing decomposition of surface ice; “The source of the carbon dioxide is less certain.” “The new results suggest that active, complex chemistry involving oxygen may be quite common throughout the solar system and even our universe,” said lead author Ben Teolis of Southwest Research Institute; but it’s not quite clear how he connected the dots with his next statement: “Such chemistry could be a prerequisite for life.” Rhea is not exactly a lively place, as he well knows: “All evidence from Cassini indicates that Rhea is too cold and devoid of the liquid water necessary for life as we know it.” Life as we don’t know it is purely imaginary at this point.
- Dione donut: The Cassini site released a photo of Dione from its Oct. 17 non-targeted flyby, showing off the donut-shaped crater Erelus with a central peak 75 miles across. Cassini keeps a public diary of its activities on the Significant Events page.
One of the coolest educational tools ever produced by JPL, Eyes on the Solar System was recently released by NASA. Take the Getting Started tutorials first; then, you can command your own tour of the solar system from any angle, and watch the planets and moons in motion at any speed. Current spacecraft are included, too; you can ride along with Cassini, EPOXI, MESSENGER, Rosetta, DAWN, Stardust, all the Earth orbiters, and even Voyagers 1 and 2, and see the action from their vantage points. The looks of the planets and moons and the orbits of spacecraft are all informed by actual photographs of the objects and orbital tour plans, allowing you to watch both past and future encounters. “Eyes” is the brainchild of JPL animator Kevin Hussey, a pioneer of scientific visualization, and his team, who also produced a similarly dazzling tool Eyes on the Earth 3D. Watch the Demonstration video to see all the things one can learn about our home planet.
1. Morales-Juberias, Sayanagi, Dowling and Ingersoll, “Emergence of Polar-Jet Polygons from Jet Instabilities in a Saturn Model,” Icarus, article in press.
Warning: Eyes on the Solar System and Eyes on the Earth 3D can be addicting! Get your kids off the blood-and-gun video games and introduce them to these real-world visualization tools. Reality can be so much more interesting than fiction. These websites have the potential to inspire the next generation of space navigators, planetary scientists and aeronautical engineers, and are fascinating interactive adventures for everyone.
None of the Enceladus articles talked about how this little moon could be putting out so much energy for 4.5 billion years. That’s because they don’t have a clue. The geysers remain exciting, but not as wildly improbable, without the Law of the Misdeeds and Perversions, which cannot be altered, known as the A.S.S. (age of the solar system).