All Systems ‘Green’ on St. Patrick’s Day

Todd J. Barber, Cassini lead propulsion engineer

Happy St. Patrick’s Day from Cassini and its flight team! Appropriately, all systems are “green” on the spacecraft as we prepare for a small Titan-51 approach maneuver on our formerly back-up thrusters. In my next column, I’ll cover the thruster swap itself, but (as always, it seems) I’m behind on the latest science plans and results. The last half of February was quite busy, scientifically, including infrared observations of Saturn’s E ring and G ring, ultraviolet prodding of Enceladus, and radiometry at Titan using radar. Even as we on Earth were busy preparing for a mid-March thruster swap, the spacecraft was dutifully executing a full suite of science activities nearly a billion miles away.

Perhaps envious of Cassini’s front-row seat, Earth-bound astronomers (and the Hubble Space Telescope) turned their gaze toward the ringed planet as well. With the impending change in Saturn’s season, not only are the rings moving towards temporary invisibility, the Saturnian moons are moving in line with Saturn as seen from Earth. This is largely because many of Saturn’s moons orbit the ringed giant near its equatorial plane, enabling thrilling occultations by Saturn or even transits, the visible migration of Saturnian moons across the disk of Saturn. In fact, February closed with a rare quadruple transit of the moons Enceladus, Titan, Mimas, and Dione. Ring plane crossings also enable the search for new satellites of Saturn, since the nearby glare of the rings is temporarily subdued.

Speaking of new moons, Cassini finally snagged proof of a dusty moonlet in Saturn’s G ring. This small body was long suspected but never-before seen, and it helps explain not only the presence of the G-ring itself but also the “clumpiness” of its ring arc. As fun as this job is day to day, it’s always a special day when we find a new moon of Saturn, even if it’s too small to image directly. Our sister spacecraft, Kepler, was recently launched to hunt down some bodies it can’t actually image directly, either. We wish this grand space telescope and its team all the best as they strive to hunt down the first Earth-like planets around distant stars.

A plethora of ring science observations closed out the month of February, utilizing many different science instruments. What a thrill it was for me recently to see Cassini movies of the perplexing ring spokes zipping around Saturn. It was truly a case of déjà vu, because I recall Voyager movies of the spokes nearly thirty years ago, an inspirational moment for a young rocket scientist wannabe. Analyzing the latest ring science data will take some time, so I’ll close with the latest from Titan. Another recent press release caught my eye for its sheer beauty and simplicity. A composite map of over 16,000 Titan sand dunes was released, based on data taken from about twenty radar images. Eat your heart out, Lawrence of Arabia! Titan dunes appear to be composed of hydrocarbon sand grains, very unlike the silica sand grains of Earth. Perhaps most surprisingly, the orientation and shape of the dunes suggest Titan’s winds generally blow east—exactly the opposite direction expected from previous models of Titan’s atmospheric circulation. These surprises, though sometimes humbling, always bring a smile—reminding us how much we still have to learn about the endlessly fascinating Saturnian system.