The life and death of a Saturnian probe
The Cassini spacecraft has entered thefinal year of its epic mission to explore the Saturnian system. JoinNew Atlas as we take a look at a selection of the spacecraft's manyscientific achievements, and how the probe will ultimately meet itsdramatic end in September 2017.
The planning, fabrication, andoperation of the Cassini spacecraft, which was led by NASA, ESA, andthe Italian space agency, the Agenzia Spaziale Italiana (ASI), was atruly international endeavor, representing the work of over 5,000individuals hailing from a total of 17 countries.
When launched in October 1997 atop aTitan IVB/Centaur rocket, Cassini carried a suite of nine scientificinstruments that would allow the probe to execute an ambitious four-year primary mission to explore the Saturnian system. As it forgedthe 2.2 billion mile journey across the solar system to rendezvouswith Saturn and her moons, Cassini was not entirely without company.
Much like Rosetta carried Philae, Cassini was tasked with thesafe passage of the Huygens lander, whose objective was to descend tothe surface of Saturn's largest moon, Titan. The lander had beendesigned to harvest as much data as possible regarding the nature ofthe inhospitable moon during its two-hour descent period, and for ashort time after setting down on the surface of the alien world.
However, beforeCassini could drop off its passenger, the probe's handlers had toorchestrate a complex ballet across the Solar System in order todeliver the robotic explorers to their objective. The cosmic roadtrip saw Cassini undertake two flybys of Venus and one of Earth,before spending six months exploring Jupiter and her moons.
This pit stopafforded Cassini the perfect opportunity to test out its instrumentsbefore capitalizing on the gas giant's gravitational influence toslingshot itself onwards to its ultimate mission objective, Saturn.
Exploring a gas giant
Cassini finallyarrived in orbit around Saturn on June 30, 2004. Huygens would haveto wait a further five months to be cut loose. Upon finallydescending to the surface of Titan on January 14, 2005, Huygens revealedit to have a surprisingly Earth-like terrain, albeit blemished with hydrocarbon lakes. A recent study based on data harvested by the robotic duosuggests that this inhospitable world may be capable of hostingnon-water based life.
The Cassini probehas now been exploring Saturn for more than 12 years, and hasrevolutionized our knowledge of how gas giants tick. The probe hasallowed us a greater understanding of the complex processes thatdrive the storms raging across the surface of the chaotic world including the vast,dark expanse of Saturn's south polar storm.
Cassini datasuggests that Saturn's polar storms are generated and sustained by amultitude of smaller storms scattered across the surface of the gasgiant, which work to divert air to the polar regions. A greaterunderstanding of Saturn's storms could allow future astronomers todivine whether distant exoplanets host polar cyclones of their ownsimply by observing the overall storm intensity spread across aplanet's surface.
Scientists at NASAare exploring the potential of using probes known as windbots to explore Saturn's upper cloud layer. The concept mission suggestsusing lightweight probes that would harvest the turbulence presentin the upper atmosphere of a gas giant, and supply this energy to apropulsion system. This would allow the probe to harvest energy evenwhile operating on the night side of a gas giant.
Many planets inour solar system boast weak ring systems of their own, yet none caneven come close to comparing to the majesty of Saturn's adornment.Even through a weak telescope, they are striking to behold, andthrough the eyes of the Cassini spacecraft, they are simplybreathtaking.
Observations madeby the veteran probe have revolutionized our understanding ofSaturn's rings. It is thought that the ring system was once muchlarger than it is today, and that much of the material contained inthe early rings coalesced to form some of the gas giant's many moons.
In April 2013, theCassini spacecraft was lucky enough to see this process in action as it observed the formation of a new moon. The spacecraft detected disturbances in the edge ofSaturn's A ring, created by the weak gravitational influence of thenewly formed satellite, which has since been named Peggy.
It is possiblethat, as Cassini moves closer to the A ring (here's a good primer on how Saturn's rings are named) prior to the end of itsmission, the probe may be able to image Peggy directly, and that thisnewest addition may well be the final moon to be created bySaturn's depleted rings.
InFebruary 2016 Cassini made history once more by becoming the firstspacecraft to measure the weight of one of Saturn's rings. This wasachieved by observing the light from distant stars as it passedthrough Saturn's B ring.
Itwas discovered that the B ring was much lighter than earlierestimates had suggested. Saturn's rings are thought to owe aproportion of their mass to dust from meteorites and other sources.Since the B ring weighs less than predicted, it is possible that it has not been around longenough to accrue the expected amount of dust. This led astronomers tohypothesize that the B ring may have formed a few hundredmillion years ago, rather than the few billion years that hadpreviously been hypothesized.
The moons of Saturn
Saturn plays hostto dozens of moons that display an astounding range of diversity. Theorbital paths of a number of these satellites, known as shepherdmoons, are thought to be responsible for creating visible divisionsin Saturn's rings.
Others,such as Hyperion boast bizarre traits, such as a surface density solow that collisions with asteroids simply compress the surface,rather than impacting it, creating a sponge-like porous appearance.
Repeated closeproximity passes between Cassini and a number of these satelliteshave allowed scientists to gain a greater understanding of thesurprising levels of diversity on display in our solar system. One ofCassini's key targets for observation, the Saturnian moon Enceladus,represents one of the most likely breeding grounds for life outsideof Earth's atmosphere.
In 2005, Cassinidiscovered the first evidence of icy plumes rising from "tigerstripe" vents marking Enceladus' south polar region. It has beenhypothesized that the material thrown out in the geyser eruptions wasdrawn from a subsurface ocean with the potential to play host tomicrobial life.
Datacollected by Cassini suggeststhat tidal forces generated by Saturn's gravitational pull are thedriving force behind the eruptions.
In October 2015,Cassini made its final dive through Enceladus' plumes at a distanceof only 30 mi (49 km) above the moon's south pole, harvesting datathat would help scientists to analyze the composition of thesatellite's subsurface ocean. NASA is so intrigued with Enceladusthat a mission concept has received funding under the agency's NIAC program to examine the feasibility of using a Russian nesting doll-like spacecraft and lander to plumb thedepths of one of the moon's tiger stripe vents.
These are but afew examples of how Cassini has advanced our understanding of theSaturnian system. The final stage of Cassini's mission will be knownas the "Grand Finale," and will see the probe draw closer toSaturn and her rings than ever before, providing an unprecedentedopportunity to gather data on the workings of the gas giant, whileproviding stunning high-resolution imagery.
Prior to the onset of the Grand Finale,Cassini will undertake a series of orbits in close proximity toSaturn's, F-ring. This phase of the endgame, which is set to begin on30. Nov. 2016, will see Cassini undertake 20 week-long orbits that take the spacecraft towithin 4,850 miles (7,800 km) of the centre of Saturn's F-ring.
"During the F-ring orbits weexpect to see the rings, along with the small moons and otherstructures embedded in them, as never before," states LindaSpilker, Cassini project scientist at NASA's Jet PropulsionLaboratory, Pasadena, California. "The last time we got thisclose to the rings was during arrival at Saturn in 2004, and we sawonly their backlit side. Now we have dozens of opportunities toexamine their structure at extremely high resolution on both sides."
Following the F-ring orbits, Cassini'smission team plans to use thegravitational influence of Titan tomanipulate the probe's orbit to send the spacecraft between the gasgiant's surface and its innermost ring.
Cassini isexpected to dive between Saturn's uppermost cloud layer and closestring, a gap of only 1,500 miles (2,400 km), a total of 22 times,beginning on April 27, 2017. The spacecraft's proximity to the planetand her rings during this Grand Finale will allow it to map Saturn'smagnetic and gravitational fields to a precision never beforeachieved. Cassini will also provide new insights as to thecomposition of Saturn's atmosphere, and make detailed measurementsregarding the weight of the gas giant's rings.
Cassini'sincredible journey is set to come to an end on September 13, 2017, withthe spacecraft plunging into Saturn's atmosphere. Unlike the Huygenslander, Cassini will never hit solid ground, instead burning up dueto the friction created between the fast moving spacecraft and thedense layers of atmospheric cloud.
The agedspacecraft will provide one final gift as it plunges to its demise,transmitting atmospheric data right up until the signal is lost
Already, there isa countdown clock running in NASA JPL's mission control roomkeeping track of the days, hours and minutes left before Cassini'sfinal embrace with Saturn, and we have a strong feeling that when it ticks tozero, there won't be a dry eye in the room.
Scroll down to view a time lapse video displaying four days on Saturn, courtesy of NASA.