This time space fans we’re focusing on the remarkable achievements of the Cassini mission.
CASSINI’S GRAND FINALE
Its been a long 13 years for this old spacecraft. Its almost out of fuel so the science team in charge decided to make it do a few stunts on it way to its firey demise in Saturn’s atmosphere. Cassini has started to perform its heroic dives through the planet’s rings before its swansong on September 15. On April 22, Cassini completed its 127th and last flyby of Saturn’s huge moon, Titan. The carefully designed operation put the craft onto its final orbital trajectory: a series of 22 orbits, where it spirals in closer to Saturn and passing amongst the planet’s innermost rings and kiting through its outer atmosphere.
The first traversal of the rings happened on April 26. After continued dives through this unknown area, the Cassini mission will finish its voyage by collecting unique science to answer outstanding questions about the formation of Saturn and its satellites.
The Big Empty
“The region between the rings and Saturn is ‘the big empty,’ apparently,” said Cassini Project Manager Earl Maize of NASA’s Jet Propulsion Laboratory in Pasadena, California. “Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected.”
With 21 dives remaining, four of them will pass through the innermost areas of the rings which means that the Cassini’s main antenna has to be used as a shield for these orbits. If there was as much dust as previously thought, then the antenna would have to be utilised more often which would impact on what and which instruments it can use to take scientific measurements, so this is a bonus in that there are fewer hazards to the spacecraft, however perplexing.
A Voyage of Discoveries, From Titan…
Cassini-Huygens spacecraft embarked in 1997 on a seven year trek across the Solar System, finally reaching Saturn in July 2004. A few months later, ESA’s Huygens probe was launched from Cassini which arrived on Titan in 2005, which was at the time, the first landing in the outermost Solar System. The data gathered has greatly added to our comprehension of the Saturn system, plus of course its other moons and Saturn’s rings.
By combining the science collected by Huygens and other measurements collected by Cassini during its many flybys of the huge moon, some of the sectrets of this enigmatic moon began to emerge, particularly how its thick nitrogen atmosphere helps drive its weather and seasons, as well as the surface morphology and interior structure, which may include a subsurface liquid water ocean. Its surface is partly covered by lakes and rivers, much the the hydrology cycle on Earth, meaning rain and liquid resurfacing and erosion that bears some interesting similarities to our planet.
Its no idendtical however as there are important differences as the key component there is the primary solvent is not water, but methane, and its damn cold! Colder than anywhere here on Earth-180°C at the surface. During its 13 year mission, Cassini will have observed about half of Saturn’s long orbit. This takes around 29 years which is quite some time. This does mean that Cassini has seen two seasons on Titan, I wonder if it has more!
… To Enceladus
This little moon was a surprise to everyone! Cassini’s detection of plumes of water vapour and organic material spraying into space from its fractured surface near its South pole, the now famous ‘tiger stripes‘ of Enceladus. The chemically rich jets indicate that a sufsurface ocean of liquid water is very close under the ice, just a few kilometres below in face, which has been confirmed by gravity and rotation measurements.
Analysis of the latest data recieved from flybys of Enceladus using the Cassini Ion Neutral Mass Spectrometer also revealed molecular hydrogen in the plume. The presence of molecular hydrogen suggests that rock might be reacting with warm water on the seafloor of the moon’s subsurface ocean, much like chemical ‘mixing’ happens here . This hydrothermal activity could provide a chemical energy source for life. On Earth, non-photosynthetic extremophiles found near hydrothermal vents form the basis for parts of the deep-ocean food chain and may well have been responsible for the origin of life on Earth. This welcoming discovery about Enceladus could point to a similar potential for life in Enceladus’ underground ocean. When you factor in the other icy moons in the Solar system, the implications are very exciting!
Parting is Such Sweet Sorrow
After so many incredible discoveries and so much ground-breaking science, Cassini is almost spent. With so little fuel left to allow it to move its trajectory, the mission team has had to make the heartbreaking decision to end the spacecraft’s life by plunging it into Saturn’s atmosphere on September 15, 2017. In the process, Cassini will burn up, satisfying planetary protection requirements to avoid possible contamination of any moons of Saturn that could have conditions suitable for life.This firey end is not just a simple end however, no scientist in their right mind would waste the opportunity to gather as much data as possible before it dies . Much like when the Rosetta mission team crashed their craft into 67P/Churyumov–Gerasimenko for the same reason, they didn’t waste the opportunity to get the data.
These orbits will also give the chance to look closely at the material that makes up the rings and the general chemical and physical environment around Saturn. Using radio spectroscopy, Cassini will observe Saturn’s gravitational field as close as 3000 km from Saturn’s upper cloud layers. The current models on Saturn’s atmospheric and internal structure will be greatly improved and updated. Another hope is that the mass of the rings can be established with much greater accuracy. Ground stations operated by the ESA in Argentina and Australia will assist in receiving the radio spectroscopy information, giving a series of 22 tracking passes through its final few months.
These last orbits will also observe the planet’s magnetic field with the same close views. Observations in the past have shown that Saturn’s magnetic field is surprisingly less strong than expected, with its magnetic poles aligned with the planet’s rotation, unlike the Earth’s. The hope is that this new data collected by the Cassini instruments will give clues to comprehend why this happens and where its generated, gas giants are tricky customers like this! Its could be something in Saturn’s atmosphere has been obscuring its magnetic mysteries from Cassini until now.
As it crosses the plane of Saturn’s rings , Cassini’s Cosmic Dust Analyzer will directly measure the dust particle composition from various parts of the ring system, whereas the Ion Neutral Mass Spectrometer will sample the upper atmospheric layers of Saturn to examine the composition of molecules which escape from the planet’s atmosphere as well as any water based molecules that can originate from the rings.
“At last, we have now reached the final and most audacious phase of this pioneering mission, pushing the spacecraft once again into unexplored territory,” says Nicolas Altobelli, ESA Cassini project scientist. “We are looking forward to the flow of exciting new data that Cassini will send back in the coming months.”
I’m quite sure yours truly will shed a tear or two at the passing of this hugely sucessful mission. Thanks to the creativity and ingenuity of the combined NASA and ESA scientists, Cassini has far exceeded its original remit, and made incredible discoveries. So we most definitely need to take another look at Enceladus! See you next time spacefans.