{"id":14691,"date":"2017-04-24T18:35:44","date_gmt":"2017-04-24T10:35:44","guid":{"rendered":"https:\/\/wp-productionenv-bjg9h2g2bgg5b8aa.southeastasia-01.azurewebsites.net\/news\/cassini-sails-by-saturns-moon-titan-for-last-time\/"},"modified":"2017-04-24T18:35:44","modified_gmt":"2017-04-24T10:35:44","slug":"cassini-sails-by-saturns-moon-titan-for-last-time","status":"publish","type":"post","link":"https:\/\/starpath.global\/news\/cassini-sails-by-saturns-moon-titan-for-last-time\/","title":{"rendered":"Cassini sails by Saturn\u2019s moon Titan for last time"},"content":{"rendered":"
\"\"
Cassini flew by Saturn\u2019s moon Titan on Saturday for the mission\u2019s final close encounter with the Earth-like moon.<\/figcaption><\/figure>\n

NASA\u2019s Cassini spacecraft sped by the moon Titan on Saturday, using the hazy world\u2019s gravity to slingshot the probe on a trailblazing trajectory to explore the region between Saturn\u2019s hydrogen-helium atmosphere and the planet\u2019s famous rings for the first time.<\/p>\n

Closing out an era of discovery that gave scientists their first glimpses of Titan\u2019s seas, weather patterns and rippling sand dunes, Cassini sailed around 608 miles (979 kilometers) above the moon at 0608 GMT (2:08 a.m. EDT) Saturday.<\/p>\n

The encounter served a dual purpose: Gather the mission\u2019s final bits of close-up data on Titan, and reshape Cassini\u2019s orbit to make the first passage inside Saturn\u2019s rings.<\/p>\n

Saturday\u2019s flyby was be the last time scientists will capture detailed observations of Titan for at least a decade, and perhaps much longer. Cassini\u2019s scientific sensors planned to gather information on Titan\u2019s lakes and seas, study the moon\u2019s atmosphere, probe the interaction between Titan\u2019s ionosphere and Saturn\u2019s magnetic field, and take a sequence of pictures.<\/p>\n

\u201cCassini\u2019s up-close exploration of Titan is now behind us, but the rich volume of data the spacecraft has collected will fuel scientific study for decades to come,\u201d said Linda Spilker, the mission project scientist at the Jet Propulsion Laboratory in Pasadena, California.<\/p>\n

Researchers will spend the coming weeks and months analyzing data from Saturday\u2019s flyby, which sent Cassini past Titan at a relative speed of about 13,000 mph (21,000 kilometers per hour).<\/p>\n

Before Cassini arrived at Saturn in 2004, scientists knew little about Titan. The moon\u2019s surface was hidden under an orange atmosphere rich in nitrogen, and NASA\u2019s Voyager probes could not see through Titan\u2019s hazy veneer when they flew by Saturn in 1980 and 1981.<\/p>\n

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This unprocessed image of Saturn\u2019s moon Titan was captured by NASA\u2019s Cassini spacecraft during its final close flyby of the hazy, planet-sized moon on April 21, 2017. Credit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>\n

Cassini ushered in more than a decade of Titan exploration when it braked into orbit around Saturn on July 1, 2004. The plutonium-powered spacecraft made 127 flybys of Titan, peering through the moon\u2019s clouds with radar to scan the moon\u2019s landscape, finding seas, lakes and streams of liquid methane and ethane.<\/p>\n

Scientists say the radar images, which are generated by bouncing radar beams off Titan\u2019s surface, helped create topographic maps of about a quarter of the moon, revealing complex river systems and liquid-filled depressions fed by rainfall, mountains and craters, and sand dunes resembling those on Earth.<\/p>\n

Titan\u2019s surface temperature is a frigid minus 292 degrees Fahrenheit (minus 180 degrees Celsius), much too cold for liquid water. But Titan, the only moon in the solar system with a dense atmosphere, experiences day\/night cycles and seasons remarkably similar to Earth, with fluctuations in rainfall, cloud patterns and temperatures.<\/p>\n

Cassini also found that Titan apparently hides an underground ocean of salty liquid water and ammonia.<\/p>\n

A day on Titan, about the size of Mercury, lasts about 16 days, the same period of time it takes the moon to complete one orbit of Saturn. Titan is tidally locked to its parent planet, with the same face of the moon always turned to Saturn.<\/p>\n

Titan\u2019s seasons change as Saturn orbits the sun every 29 years, exposing the moon\u2019s northern and southern hemispheres to more sunlight along the way, driving the moon\u2019s weather patterns and moisture cycles.<\/p>\n

Cassini\u2019s brush with Titan on Saturday \u2014 the 127th targeted Titan flyby of the mission \u2014 was the last time the craft will come so close to Titan, and scientists aimed to gather data on the moon\u2019s reservoirs of liquid hydrocarbons. Cassini\u2019s Italian-developed Ku-band radar bounced signals off a swath of Titan\u2019s north polar region during the flyby, extending the coverage of the moon\u2019s topographic maps.<\/p>\n

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These images from the Radar instrument aboard NASA\u2019s Cassini spacecraft show the evolution of a transient feature in the large hydrocarbon sea named Ligeia Mare on Saturn\u2019s moon Titan. Analysis by Cassini scientists indicates that the bright features, informally known as the \u201cmagic island,\u201d are a phenomenon that changes over time. Cassini\u2019s flyby of Titan on Saturday was the last chance to unravel the mystery behind the magic island in Ligeia Mare. Credit: NASA\/JPL-Caltech\/ASI\/Cornell<\/figcaption><\/figure>\n

Scientists were eager to use the radar data for the first \u2014 and last \u2014 time to study the composition and depth of some of Titan\u2019s small lakes.<\/p>\n

The radar beams also passed over a feature scientists have dubbed a \u201cmagic island\u201d in Ligeia Mare, one of Titan\u2019s large hydrocarbon seas. Images from Cassini\u2019s radar have revealed at least two locations in different seas that appear to change over time, with bright reflections visible in some returns and not there in others.<\/p>\n

Scientists believe the \u201cmagic islands\u201d are most likely caused by waves, and members of the Cassini team have developed models that could estimate wind speeds at Titan\u2019s surface based on radar imagery of the magic islands.<\/p>\n

\u201cCoupling these models to the brightness of the observed specular reflections (allow us) to potentially use Cassini as an anemometer, similar to the way we use weather satellites here on Earth,\u201d said Alex Hayes, a professor of astronomy at Cornell University who studies Titan\u2019s lakes and seas.<\/p>\n

Hayes said winds on Titan, which has an atmospheric pressure around one-and-a-half times that of Earth, might average around 1 to 3 mph.<\/p>\n

Researchers will spend the coming weeks crunching the radar data to see if the instrument detected any waves during Saturday\u2019s encounter.<\/p>\n

\u201cI\u2019m not sure if we\u2019ll see the magic island, but I think we have a better chance to see waves now than we have in any other flyby, statistically, so I\u2019d say the chances are higher than they\u2019ve been in the past,\u201d Hayes said March 20 in a presentation at the Lunar and Planetary Science Conference near Houston.<\/p>\n

Other observations planned during Saturday\u2019s flyby were focused on ions and neutral gas lingering in the uppermost layers of Titan\u2019s atmosphere, a tail of particles streaming behind Titan generated from the moon\u2019s interaction with Saturn\u2019s magnetic field, and an array of images from Cassini\u2019s optical camera.<\/p>\n

Saturday marked the conclusion of Cassini\u2019s exploration of Titan, but the mission still has nearly five months left to go.<\/p>\n

With a gravitational nudge from Titan, Cassini is now heading for its first passage between Saturn and its rings, ready to fly through a region that was long thought too hazardous to traverse.<\/p>\n

The trajectory will take Cassini through the 1,500-mile (2,400-kilometer) gap between Saturn and the inner perimeter of the D ring, a dark band of icy grains that is the closest ring to the planet\u2019s yellow-gold cloud tops.<\/p>\n

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The blue arcs represent Cassini\u2019s orbits through Saturn\u2019s ring gap. Credit: NASA\/JPL-Caltech<\/figcaption><\/figure>\n

Cassini will make the trip inside the rings around 0900 GMT (5 a.m. EDT) Wednesday, flying with its 13-foot-diameter (4-meter) dish-shaped high-gain antenna in the so-called \u201cram\u201d position facing in the craft\u2019s direction of travel.<\/p>\n

The probe will hide behind the antenna, shielding Cassini\u2019s control computers and science instruments from any icy debris that might be hiding in the ring gap as it races through it at a relative speed of 76,000 mph (122,000 kilometers per hour).\u201d<\/p>\n

\u201cAt those speeds, even a tiny piece could do damage to our science instruments,\u201d said Joan Stupik, a Cassini guidance and control engineer at JPL. \u201cSo we use our high-gain antenna as a shield to protect the rest of the spacecraft.\u201d<\/p>\n

The Cassini project, first conceived in the 1980s, has cost nearly $3.3 billion from start to finish. Cassini launched in October 1997 from Cape Canaveral aboard a Titan 4 rocket, flew by Venus and Jupiter, and reached Saturn in July 2004, becoming the first space probe to slip into orbit there.<\/p>\n

The orbiter dropped a European probe named Huygens to land on the surface of Titan, Saturn\u2019s largest moon, in January 2005. Since then, Cassini has circled Saturn more than 260 times, collecting detailed imagery of Saturn\u2019s atmosphere and mysterious hexagonal polar vortex, explored its rings in minute detail, and observed 49 of Saturn\u2019s 62 known moons with close and long-range flybys.<\/p>\n

Cassini was originally scheduled to collect data for four years after arriving in orbit around Saturn, but NASA extended the mission as the probe discovered that the planet and its moons demanded further study.<\/p>\n

\u201cIn many ways, the grand finale for Cassini is like a brand new mission,\u201d Spilker said earlier this year. \u201cWe\u2019re going to probe Saturn\u2019s interior, measure the magnetic field, look for the magnetic dynamo, and try and figure out why is there is so little, or perhaps no, tilt between the magnetic field axis and the spin axis of Saturn. What\u2019s going on there?\u201d<\/p>\n

NASA considered steering the Pioneer 11 flyby probe through a gap between two parts of Saturn\u2019s rings in 1979. The agency again thought about guiding the Voyager probes through the so-called Cassini Division in the rings in the 1980s, but managers opted for a farther flyby out of safety concerns.<\/p>\n

\u201cThis is not without risk,\u201d said Earl Maize, Cassini\u2019s project manager at JPL. \u201cYou can see the dust kind of extending and slowly disappearing into the black.<\/p>\n

\"\"
Saturn\u2019s rings obscure part of Titan\u2019s colorful visage in this image from NASA\u2019s Cassini spacecraft from 2012. Credit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>\n

\u201cWe\u2019re going to stay as far away from the visible dust as we can, and we\u2019re using our very best models of the rings that we\u2019ve been developing,\u201d Maize said. \u201cWe have the best ring experts in the world to extrapolate into the region we can\u2019t see in order to determine if we can be safe.\u201d<\/p>\n

Navigators at JPL have kept Cassini right on course throughout its tour of Saturn, zipping by moons with remarkable precision and mapping out the probe\u2019s trajectory years in advance.<\/p>\n

\u201cOur concern is not our accuracy, but have we modeled that system correctly? For a couple of those orbits, the ring plane crossing is kind of flirting with the edge of where we think it\u2019s safe,\u201d Maize said.<\/p>\n

Cassini will fly through the gap at slightly different locations on each orbit. On four passages from May through July, the spacecraft will be closer to the D ring, and engineers will pivot Cassini to again put its antenna in the ram position on those orbits.<\/p>\n

\u201cThere is a possibility, and it\u2019s higher than we normally accept, of dust collision,\u201d he said. \u201cWe\u2019re going to try to be careful, but at the same time there is that possibility.\u201d<\/p>\n

Ground controllers will not know if Cassini survived the first ring gap passage until around 0705 GMT (3:05 a.m. EDT) Thursday, when radio signals from the spacecraft should reach Earth. Cassini will be out of radio contact with the ground team for about a day after zooming by Saturn while its instruments take measurements.<\/p>\n

Cassini\u2019s will make 22 runs through the ring gap before a plunge into Saturn\u2019s atmosphere Sept. 15 destroys the craft in a crushing finale intended to ensure it never crashes into one of the planet\u2019s moons, such as Titan or Enceladus, that scientists believe might support microbial life.<\/p>\n

Scientists will use the up-close orbits to measure the mass of Saturn\u2019s rings for the first time, inspect the planet\u2019s atmosphere, and derive Saturn\u2019s interior structure by studying its gravity field.<\/p>\n

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This view from NASA\u2019s Cassini spacecraft shows planet Earth as a point of light between the icy rings of Saturn on April 13. Credit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>\n

\u201cOne of the things we can do with the rings is, in the grand finale orbits, for the first time address the question of the origin and the age of the rings,\u201d Spilker said. \u201cWe\u2019ll do this by measuring the mass of the rings very accurately.<\/p>\n

\u201cIf the rings are a lot more massive than we expect, perhaps they\u2019re old, as old as Saturn itself, and they\u2019ve been massive enough to survive the micrometeoroid bombardment and erosion and leave us with the rings we see today,\u201d she said. \u201cNow, on the other hand, if the rings are less massive, perhaps they\u2019re very young, maybe forming as little as 100 million years ago. Maybe a comet or a moon got too close, got torn apart by Saturn\u2019s gravity and we have the rings that we see today.\u201d<\/p>\n

The Cassini spacecraft, though otherwise healthy, is running on its last few pounds of propellant. That means the clock is ticking until Cassini will no longer be controllable.<\/p>\n

There are no more missions to Saturn planned by NASA or any other space agency, although scientists are expected to submit proposals this week for a spacecraft that could launch in the mid-2020s to explore Titan and Enceladus, two of Saturn\u2019s moons considered by researchers to be top candidates for life elsewhere in the solar system.<\/p>\n

But Saturday\u2019s swing by Titan committed Cassini to its fate, and the craft will naturally fall into Saturn in September even if it runs out of fuel or fails.<\/p>\n

\u201cWith this flyby we\u2019re committed to the grand finale,\u201d Maize said. \u201cThe spacecraft is now on a ballistic path, so that even if we were to forgo future small course adjustments using thrusters, we would still enter Saturn\u2019s atmosphere on Sept. 15 no matter what.\u201d<\/p>\n

Email the author.<\/i><\/b><\/p>\n

Follow Stephen Clark on Twitter: @StephenClark1.<\/strong><\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

Cassini flew by Saturn\u2019s moon Titan on Saturday for the mission\u2019s final close encounter with the Earth-like moon. NASA\u2019s Cassini spacecraft sped by the moon Titan on Saturday, using the hazy world\u2019s gravity to slingshot the probe on a trailblazing trajectory to explore the region between Saturn\u2019s hydrogen-helium atmosphere and the planet\u2019s famous rings for […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":"","_links_to":"","_links_to_target":""},"categories":[2],"tags":[2394,1183,1561,1562,2396],"class_list":["post-14691","post","type-post","status-publish","format-standard","hentry","category-news","tag-cassini","tag-jet-propulsion-laboratory","tag-planetary-science","tag-saturn","tag-titan"],"acf":[],"_links":{"self":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/14691"}],"collection":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/comments?post=14691"}],"version-history":[{"count":0,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/14691\/revisions"}],"wp:attachment":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media?parent=14691"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/categories?post=14691"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/tags?post=14691"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}