{"id":14251,"date":"2017-10-19T18:08:36","date_gmt":"2017-10-19T10:08:36","guid":{"rendered":"https:\/\/wp-productionenv-bjg9h2g2bgg5b8aa.southeastasia-01.azurewebsites.net\/news\/cassini-results-still-keeping-scientists-busy\/"},"modified":"2017-10-19T18:08:36","modified_gmt":"2017-10-19T10:08:36","slug":"cassini-results-still-keeping-scientists-busy","status":"publish","type":"post","link":"https:\/\/starpath.global\/news\/cassini-results-still-keeping-scientists-busy\/","title":{"rendered":"Cassini results still keeping scientists busy"},"content":{"rendered":"
\"\"
Cassini took this image of Saturn in April 2016 from a distance of approximately 1.9 million miles (3 million kilometers). Credit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>\n

Scientists examining data from the Cassini mission\u2019s final months reported this week unexpected measurements of Saturn\u2019s gravity field and outer atmosphere, suggesting they may have to revisit theories about the planet\u2019s rings and the forces that generate magnetic fields.<\/p>\n

Presenting an update at the American Astronomical Society\u2019s Division for Planetary Sciences meeting in Provo, Utah, researchers said Monday that NASA\u2019s Cassini spacecraft yielded unforeseen results as it repeatedly looped between Saturn and its rings during the final four months of the nearly 20-year mission.<\/p>\n

\u201cWe\u2019ve been analyzing the grand finale data, and there are lots of surprises,\u201d said Linda Spilker, Cassini\u2019s project scientist at NASA\u2019s Jet Propulsion Laboratory. \u201cSaturn, its rings, and the region in between are not what we expected.\u201d<\/p>\n

Thirteen years since it braked into orbit around Saturn, Cassini made 22 passes through the gap between planet and its rings between late April and Sept. 15. Ground controllers intentionally guided the plutonium-powered probe toward a destructive dive into the planet\u2019s hydrogen atmosphere last month.<\/p>\n

Scientists devised Cassini\u2019s final act to collect new measurements of Saturn\u2019s atmosphere, and gather data on the planet\u2019s gravity and magnetic fields, which they expected to provide insights about the inner structure of Saturn, including the size and nature of its core.<\/p>\n

Michele Dougherty, a researcher from Imperial College London, said Cassini\u2019s instruments helped refine estimates of the tilt of Saturn\u2019s magnetic field, revealing it to be closely aligned with the planet\u2019s rotation axis.<\/p>\n

\u201cThe real surprise is turning out to be the fact that the tilt between the rotation axis of the planet and the dipole axis is really small,\u201d Dougherty said.<\/p>\n

Scientists knew the rotation and magnetic field axes were in tight alignment, predicting before Cassini\u2019s newest measurements that they were separated by less than 0.6 degrees. Now they estimate the tilt is less than 0.06 degrees.<\/p>\n

Magnetic fields on Earth and Jupiter are produced by dynamos deep inside the planets, where conducting fluid under heavy pressure generates an electric current, helping propagate a field that extends outside the planets\u2019 atmospheres, creating a magnetic bubble responsible for producing auroras and shielding from solar and cosmic radiation.<\/p>\n

\"\"
This illustration shows the interior of Saturn, including its core of heavy elements (orange), liquid metallic hydrogen layer (grey), and gaseous molecular hydrogen envelope (brown). The planet\u2019s magnetic field is thought to originate from the top of the metallic hydrogen layer. Credit: NASA\/JPL-Caltech<\/figcaption><\/figure>\n

Earth\u2019s dynamo uses liquid iron to generate its magnetic field. Dynamos inside gas giants like Jupiter and Saturn are believed to rely on hydrogen compressed under the force of several million atmospheres and stripped of their electrons, making it behave like a metal.<\/p>\n

Conventional thought on dynamos inside Earth and Jupiter suggest they require a tilt between the rotation and magnetic field axes. Earth\u2019s dipole is oriented around 11.5 degrees from its rotation axis, and Jupiter\u2019s differs by about 10 degrees.<\/p>\n

Mathematical models indicate a planet\u2019s magnetic field would wither if the axes were aligned, dying within around 100 million years instead of persisting through the solar system\u2019s 4.5-billion-year history.<\/p>\n

\u201cThe fact that we haven\u2019t been able to measure this tilt yet \u2014 we know that it\u2019s really very small \u2014 points to the fact that there\u2019s much more sophisticated dynamics taking place inside Saturn than we thought,\u201d Dougherty said.<\/p>\n

Once they complete their detective work, Dougherty said scientists will have a better idea of the size of Saturn\u2019s core, and the source of the magnetic field.<\/p>\n

\u201cMy understanding is that we\u2019re going to change our minds about planetary dynamos,\u201d she said.<\/p>\n

Cassini\u2019s magnetic field measurements during the mission\u2019s grand finale orbits were four times more sensitive than before, Dougherty said.<\/p>\n

\u201cBy getting inside the rings \u2026 we were away from the currents being generated by the rings \u2014 currents being generated in the environment around Saturn \u2014 (and) it is allowing us to focus on the signal coming from the interior.\u201d<\/p>\n

The data will also help scientists sort out the rotation rate of planet\u2019s interior, telling them the exact length of a day on Saturn. The best estimate today suggests a Saturn day lasts around 10.8 hours.<\/p>\n

Cassini\u2019s ion and neutral mass spectrometer sampled Saturn\u2019s atmosphere as the spacecraft barreled inside the rings. The atmosphere\u2019s tenuous outer layers extend out almost to the rings, and Cassini discovered molecules raining down from the rings onto Saturn.<\/p>\n

\"\"
This natural color composite is one of the highest-resolution color images of any part of Saturn\u2019s rings, to date, showing a portion of the inner-central part of the planet\u2019s B Ring. Cassini\u2019s narrow-angle camera took images to produce this composite on July 6, 2017. Credit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>\n

Scientists expected to find evidence of ring material in Cassini\u2019s first-ever direct measurements of the atmosphere, but the spacecraft detected unexpectedly high levels of methane.<\/p>\n

They predicted most of the molecules to be water because that makes up the bulk of the particles in the rings.<\/p>\n

Methane should not persist in Saturn\u2019s rings or in the planet\u2019s outer atmosphere, said Mark Perry, an associate scientist on the ion and neutral mass spectrometer team.<\/p>\n

\u201cWhat we\u2019re seeing are things that come from the rings, and methane is highly volatile,\u201d Perry said. \u201cEven if it\u2019s in the rings, it shouldn\u2019t last very long, and none of the models \u2014 none of the analyses \u2014 predicted methane, let alone in this abundance.\u201d<\/p>\n

Cassini also found the expected water molecules in the outer atmosphere, but the methane was a surprise.<\/p>\n

\u201cWe think the water is there,\u201d Perry said. \u201cWhat we can\u2019t explain is why it is not much more than anything else. That\u2019s the confusing part.\u201d<\/p>\n

Cassini\u2019s narrow-angle imaging camera obtained close-up views of intricate structures inside Saturn\u2019s rings during the mission\u2019s final months. One new mosaic recorded by Cassini in May shows the rings emerging from behind Saturn\u2019s hazy limbs, with the rings\u2019 shadows projected on the planet\u2019s atmosphere.<\/p>\n

Before it zipped through Saturn\u2019s ring gap, Cassini was on a trajectory that grazed the outer edge of the rings on each orbit.<\/p>\n

The spacecraft took pictures of features dubbed propellers \u2014 wakes created by tiny moons that would have otherwise gone undetected. The moonlets embedded inside Saturn\u2019s rings leave a distinguishing mark, disturbing nearby particles as they sail around the planet.<\/p>\n

\u201cThese are important because this is a window into planetary formation processes,\u201d said Matthew Tiscareno of the SETI Institute. \u201cWhat happens when big solar systems are forming is that you start to get the seed of a planet, but it\u2019s embedded in a disk. So the disk is affecting the embedded mass, but the embedded mass is also affecting the disk, and we want to know more about what happens in both directions, and propellers give us a window into that.\u201d<\/p>\n

\"\"
This view from NASA\u2019s Cassini spacecraft shows Cassini\u2019s best image of the propeller feature known informally as Bleriot. The propeller is named after Louis Bleriot, the French engineer and aviator who in 1909 was the first person to fly across the English Channel. Credit: NASA\/JPL-Caltech\/Space Science Institute<\/figcaption><\/figure>\n

Tiscareno said scientists identified propellers with two classes of moonlets \u2014 some a few hundred meters in size and some around a kilometer (0.6 miles) across.<\/p>\n

One primary objective of Cassini\u2019s grand finale was to determine the mass, age and origin of Saturn\u2019s rings.<\/p>\n

Cassini\u2019s position close to Saturn in the last few months allowed the probe\u2019s instruments to sort out the difference between the pull of gravity from the planet and the rings.<\/p>\n

If the rings are more massive, scientists think they could be old, perhaps as old as Saturn itself. A result indicating less massive rings would point to a more recent origin, perhaps when a moon or comet got too close to Saturn and was ripped apart.<\/p>\n

The initial results suggest the rings are slightly less massive than expected, Spilker said, but uncertainty remains in the measurements. Scientists still must calculate the strength of Saturn\u2019s gravity field from data downlinked from Cassini and remove the effect of atmospheric drag from the measurements.<\/p>\n

\u201cOnce we resolve Saturn\u2019s gravity field, we\u2019ll have a better handle then on the mass of the rings,\u201d Spilker said.<\/p>\n

A new study based on Cassini data shows that the gravitational pull from several of Saturn\u2019s moons combine to keep Saturn\u2019s rings from spreading out and disappearing.<\/p>\n

Scientists thought the small moon Janus single-handedly kept the rings in check, but measurements of the masses of Saturn\u2019s moons and detailed images of waves in the rings led to a conclusion that seven moons \u2014 Pan, Atlas, Prometheus, Pandora, Janus, Epimetheus and Mimas \u2014 work together to keep the outer A ring from extending farther from Saturn.<\/p>\n

Radwan Tajeddine of Cornell University led the study investigating the relationship between Saturn\u2019s moons and rings.<\/p>\n

\u201cIf these moons weren\u2019t working together, then the A ring would have spread out over hundreds of millions of years, and the A ring would be gone,\u201d Spilker said.<\/p>\n

Meanwhile, engineers have assessed how the Cassini spacecraft behaved in its final moments plunging into Saturn\u2019s atmosphere.<\/p>\n

\"\"
Artist\u2019s concept of the Cassini spacecraft entering Saturn\u2019s atmosphere. Credit: NASA\/JPL-Caltech<\/figcaption><\/figure>\n

Launched 20 years ago this week, Cassini was traveling through the rarefied outer layers of Saturn\u2019s atmosphere as it beamed back its last data to Earth, speeding through gas with about the same density that as encountered by the International Space Station as it soars 250 miles (400 kilometers) above Earth, according a NASA press release.<\/p>\n

But Cassini was moving four-and-a-half times faster than the space station, multiplying the aerodynamic forces, officials said.<\/p>\n

Cassini encountered Saturn\u2019s atmosphere as it reached a point around 1,200 miles (3,600 kilometers) above the cloud tops. Atmospheric particles began pushing on Cassini\u2019s 36-foot-long (11-meter) magnetometer boom.<\/p>\n

The spacecraft fired thrusters to damp its rotation, using its jets for longer and more frequent pulses as it fell deeper into the atmosphere, according to NASA.<\/p>\n

\u201cWith its thrusters firing almost continuously, the spacecraft held its own for 91 seconds against Saturn\u2019s atmosphere \u2014 the thrusters reaching 100 percent of their capacity during the last 20 seconds or so before the signal was lost,\u201d officials wrote in a press release. \u201cThe final eight seconds of data show that Cassini started to slowly tip over backward.\u201d<\/p>\n

Engineers programmed Cassini to broadcast science data and telemetry in real-time during its final moments, rather than storing the information on recorders for later playback.<\/p>\n

Tracking antennas on Earth lost lock with Cassini\u2019s dish-shaped antenna as the spacecraft turned away. A radio carrier signal continued streaming down from the probe for 24 more seconds, then it went silent.<\/p>\n

\u201cGiven that Cassini wasn\u2019t designed to fly into a planetary atmosphere, it\u2019s remarkable that the spacecraft held on as long as it did, allowing its science instruments to send back data to the last second,\u201d said Earl Maize, Cassini project manager at JPL. \u201cIt was a solidly built craft, and it did everything we asked of it.\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 took this image of Saturn in April 2016 from a distance of approximately 1.9 million miles (3 million kilometers). Credit: NASA\/JPL-Caltech\/Space Science Institute Scientists examining data from the Cassini mission\u2019s final months reported this week unexpected measurements of Saturn\u2019s gravity field and outer atmosphere, suggesting they may have to revisit theories about the planet\u2019s […]<\/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":[2394,3147,1183,1561,2993,1562],"class_list":["post-14251","post","type-post","status-publish","format-standard","hentry","category-news","tag-cassini","tag-dynamo","tag-jet-propulsion-laboratory","tag-planetary-science","tag-rings","tag-saturn"],"acf":[],"_links":{"self":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/14251"}],"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=14251"}],"version-history":[{"count":0,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/14251\/revisions"}],"wp:attachment":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media?parent=14251"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/categories?post=14251"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/tags?post=14251"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}