Moving out into the asteroid belt and farther still to the gas giants, NASA\u2019s Dawn, Juno, and Cassini missions churned away in orbit of their respective hosts \u2013 with Dawn continuing an up-close-and-personal investigation of the dwarf planet Ceres, Juno\u2019s fantastically accurate arrival at Jupiter but frustratingly crippled start to its science mission, and the beginning of the end for the Cassini mission that\u2019s set to end in September 2017.<\/p>\n<\/p>\n
Dawn \u2013 Revealing dwarf planet Ceres:<\/b><\/p>\n
Launched on 27 September 2007, Dawn became the first spacecraft to enter orbit of two completely different celestial bodies on 6 March 2015 when it slipped into orbit of the dwarf planet Ceres after first spending 14 months in orbit of the protoplanet Vesta.<\/p>\n
![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-21-at-13.46.23-350x269.png\")
This year, Dawn marked the first anniversary of its arrival at Ceres, and Dawn\u2019s deputy principal investigator, Carol Raymond, stated that \u201cCeres has defied our expectations and surprised us in many ways thanks to a year\u2019s worth of data from Dawn. We are hard at work on the mysteries the spacecraft has presented to us.\u201d<\/p>\n
Among Ceres\u2019 most enigmatic features is the mountain Ahuna Mons, which appeared as a small, bright-sided bump as seen by Dawn\u2019s camera as early as February 2015 from a distance of 46,000 km (29,000 mi) before the spacecraft entered orbit. <\/p>\n
As Dawn gradually lowered its orbital altitude over its first year, the shape of this mysterious feature came into focus.<\/p>\n
From afar, Ahuna Mons looked pyramid-shaped, but upon closer inspection, it is best described as a dome with smooth, steep walls.<\/p>\n
Space Shuttle (adsbygoogle = window.adsbygoogle || []).push({});<\/p>\n \u201cNo one expected a mountain on Ceres, especially one like Ahuna Mons,\u201d said Chris Russell, Dawn\u2019s principal investigator. \u201cWe still do not have a satisfactory model to explain how it formed.\u201d<\/p>\n But Ahuna Mons isn\u2019t the only feature on Ceres that interests scientists. <\/p>\n About 670 km (420 mi) northwest of Ahuna Mons is Occator Crater \u2013 which the Hubble Space Telescope revealed to have a prominent bright patch on its surface prior to Dawn\u2019s arrival.<\/p>\n Dawn\u2019s subsequent orbital observations have revealed that there are at least 10 bright spots in this crater alone, with the brightest area on Ceres located in the center of Occator. <\/p>\n \u201cDawn began mapping Ceres at its lowest altitude in December, but it wasn\u2019t until very recently that its orbital path allowed it to view Occator\u2019s brightest area,\u201d said Marc Rayman, Dawn\u2019s chief engineer and mission director.<\/p>\n In particular, Dawn\u2019s view of Haulani Crater, with a diameter of 34 km (21 mi), revealed evidence of landslides from its crater rim \u2013 indications that the crater is a relatively new formation.<\/p>\n \u201cHaulani perfectly displays the properties we would expect from a fresh impact into the surface of Ceres,\u201d said Martin Hoffmann, co-investigator on the Dawn framing camera team.<\/p>\n The crater\u2019s polygonal structure is also noteworthy as most craters on planetary bodies are nearly circular, but the unique straight edges of some Cerean craters, including Haulani, are due to pre-existing stress patterns and faults beneath the surface.<\/p>\n Moreover, another crater, Oxo, also presents a uniqueness in that its rim is slumped \u2013 indicating an area where material has dropped below the surface \u2013 and that its crater floor contains minerals observed nowhere else on Ceres\u2019 surface.<\/p>\n At the end of June, NASA announced findings that Occator\u2019s bright areas contain the highest concentration of carbonate minerals ever seen outside Earth.<\/p>\n \u201cThis is the first time we see this kind of material elsewhere in the solar system in such a large amount,\u201d said Maria Cristina De Sanctis, principal investigator of Dawn\u2019s visible and infrared mapping spectrometer. <\/p>\n Specifically, the dominant mineral of this bright area is sodium carbonate, a salt found on Earth in hydrothermal environments.<\/p>\n On Ceres, the material appears to have come from inside the dwarf planet, having been lifted to the surface by an impacting asteroid \u2013 which suggests that temperatures inside Ceres are warmer than previously believed. <\/p>\n More intriguingly, the results suggest that liquid water may have existed beneath the surface of Ceres in recent geologic time and that the salts could be remnants of an ocean, or localized bodies of water, that reached the surface and then froze millions of years ago.<\/p>\n This discovery announcement came just one day before Dawn completed its primary mission on 30 June.<\/p>\n At this time, Dawn had taken 69,000 images, completed 48,000 hours of ion engine thrusting, collected more than 132 GB of science data, completed 2,450 orbits of Vesta and Ceres, travelled 3.5 billion miles since launch, and explored two new worlds.<\/p>\n On 1 July, Dawn entered its extended mission, which will see the craft continue to operate in Ceres orbit into 2017 \u2013 at which point, due to its highly stable orbit of the dwarf planet, it will become a permanent artificial satellite of Ceres.<\/p>\n Presently, Ceres is covered in countless small, young craters, but none are larger than 280 km (175 mi) in diameter. To scientists, this is a rather large mystery given that the dwarf planet must have been hit by numerous large asteroids during its 4.5 billion-year lifetime.<\/p>\n \u201cWe concluded that a significant population of large craters on Ceres has been obliterated beyond recognition over geological time scales, which is likely the result of Ceres\u2019 peculiar composition and internal evolution,\u201d said Simone Marchi, a senior research scientist at the Southwest Research Institute. <\/p>\n Marchi and her colleagues modeled collisions of other bodies with Ceres since the dwarf planet\u2019s formation, and these models predicted that Ceres should have up to 10 to 15 craters larger than 400 km (250 mi) in diameter, and at least 40 craters larger than 100 km (60 mi) wide. <\/p>\n \u201cWhatever the process or processes were, this obliteration of large craters must have occurred over several hundred millions of years,\u201d Marchi said.<\/p>\n One potential reason for the lack of large craters could be related to Ceres\u2019 interior structure.<\/p>\n Specifically, since Ceres\u2019 upper layers contain ice and salts \u2013 which are less dense than rock \u2013 the topography could \u201crelax,\u201d or smooth out, more quickly if ice or salt dominates the subsurface composition. <\/p>\n Moreover, past hydrothermal activity, which may have influenced the rising of salts to the surface at Occator Crater could also have something to do with the erasure of craters. <\/p>\n However, its wasn\u2019t just Ceres\u2019 surface features that scientists learned more about this year. <\/p>\n In August, a careful study of minute changes in Dawn\u2019s orbit from the first year of its orbital mission helped scientists gain a better understanding of Ceres\u2019 gravity field \u2013 and therefore its internal composition.<\/p>\n \u201cThe data suggests that Ceres has a weak interior, and that water and other light materials partially separated from rock during a heating phase early in its history,\u201d said Ryan Park, supervisor of the solar system dynamics group at JPL.<\/p>\n Among the things confirmed about Ceres in this data return is that Ceres has hydrostatic equilibrium \u2013 meaning its interior is weak enough that its shape is governed by how the dwarf planet rotates. <\/p>\n Moreover, the data indicate that Ceres is differentiated \u2013 meaning it has compositionally distinct layers at different depths, with the densest layer at the core. <\/p>\n Scientists were also able to confirm that Ceres is much less dense than Earth, the Moon, Vesta, and other rocky bodies in our solar system. <\/p>\n The data also led scientists to conclude that Ceres\u2019 weak mantle can be pushed aside by the mass of mountains and other high topography in its outermost layer \u2013 as though the high-elevation areas \u201cfloat\u201d on the material below.<\/p>\n Overall, by combining this new information with previous data from Dawn about Ceres\u2019 surface composition, scientist are beginning to reconstruct Ceres\u2019 history \u2013 in which water must have been mobile in the ancient subsurface while the interior did not heat up to the temperatures at which silicates melt and a metallic core forms.<\/p>\n Dawn had been \u2013 for eight months \u2013 in its low-altitude science orbit, but due to its mission extension and limited supply of hydrazine for orientation operations, controllers decided to raise Dawn\u2019s orbit for its extended mission so that the hydrazine can be used more sparingly.<\/p>\n \u201cMost spacecraft wouldn\u2019t be able to change their orbital altitude so easily. But thanks to Dawn\u2019s uniquely capable ion propulsion system, we can maneuver the ship to get the greatest scientific return from the remaining mission,\u201d said Marc Rayman.<\/p>\n The orbit raising maneuver, which began from an altitude of 385 km (240 mi), will push Dawn to 1,460 km (910 mi) above Ceres\u2019 surface \u2013 just about the orbit in which Dawn first slid into orbit around the dwarf planet.<\/p>\n The surprising finding emerged after Dawn\u2019s Gamma Ray and Neutron Detector (GRaND) observed evidence that Ceres had accelerated electrons from the solar wind to very high energies over a period of six days. <\/p>\n In theory, the interaction between the solar wind\u2019s energetic particles and atmospheric molecules could explain the GRaND observations.<\/p>\n A temporary atmosphere would also be consistent with water vapor detections via the Herschel Space Observatory in 2012-2013.<\/p>\n The electrons that GRaND detected could have been produced by the solar wind hitting the water molecules that Herschel observed, but scientists are also looking into alternative explanations.<\/p>\n \u201cWe\u2019re very excited to follow up on this and the other discoveries about this fascinating world,\u201d Russell said.<\/p>\n Juno \u2013 Triumphant arrival, less than stellar start to science mission:<\/b><\/p>\n After a spot-on precision arrival at Jupiter on 5 July, the Juno spacecraft entered its long, highly elliptical 53.4-day initial polar orbit.<\/p>\n However, just a few days before this scheduled burn, controllers noticed a performance issue with a pair of valves that are part of Juno\u2019s fuel pressurization system.<\/p>\n At the time, Rick Nybakken, Juno project manager, said, \u201cTelemetry indicates that two helium check valves that play an important role in the firing of the spacecraft\u2019s main engine did not operate as expected during a command sequence. <\/p>\n \u201cThe valves should have opened in a few seconds, but it took several minutes.\u201d<\/p>\n Controllers subsequently delayed the planned orbit adjustment burn to allow time to study the issue.<\/p>\n For Juno, this meant more orbits of Jupiter in its longer orbit.<\/p>\n Currently, the spacecraft has completed just three close flybys of Jupiter \u2013 not counting the flyby that occurred on the night of its arrival.<\/p>\n The third flyby occurred on 11 December, with the fourth now slated for 2 February 2017.<\/p>\n For comparison, when the third flyby occurred on 11 December, Juno should have been gearing up for its fifth flyby.<\/p>\n Now, if controllers are unable or unwilling to perform the orbit adjustment burn, the effects on the science mission as well as the mission\u2019s planned duration are somewhat unknown.<\/p>\n What is known is that the amount and quality of science collected during a close flyby is not affected by the prolonged orbit \u2013 which has a much greater apojove than the standard science orbit would but a nearly identical perijove.<\/p>\n Moreover, Juno\u2019s mission is slated to only last until February 2018 \u2013 at which time it is anticipated that Juno will have to be deorbited into Jupiter\u2019s atmosphere due to system failures triggered by the intense radiation.<\/p>\n Additionally, Juno mission directives call for a minimum of 7 to 10 operational flybys of Jupiter to achieve minimum mission success. <\/p>\n Given the safe mode pre-approach profile flown in October, the first operational flyby did not occur until 11 December \u2013 though even this wasn\u2019t a fully operational flyby as a critical instrument, the Jovian Infrared Auroral Mapper (JIRAM), was not active due to the need to upload a software patch to allow Juno\u2019s software to process information from JIRAM.<\/p>\n At present, if Juno is forced to remain in its 53.4-day orbit and if it still needs to be purposefully disposed of into Jupiter\u2019s atmosphere in February 2018, the mission stands a high chance of not actually or just barely meeting minimum mission success criteria.<\/p>\n Cassini \u2013 19 years after launch, the intrepid little probe prepares for its Grand Finale exit:<\/b><\/p>\n For Cassini, 2016 began as the last 11 years have \u2013 dutifully looping around the majestic ringed planet Saturn.<\/p>\n Previous Cassini observations of Enceladus saw its polar eruptions spraying three times as much icy dust into space when the moon neared aposaturnium \u2013 farthest point in its elliptical orbit around Saturn.<\/p>\n But scientists hadn\u2019t had an opportunity to see if the gas part of the eruptions \u2013 which account for the majority of the plume\u2019s mass \u2013 also increased at this time.<\/p>\n They got that chance on 11 March\u2026 and the results were surprising.<\/p>\n During a carefully planned observation, Cassini set its gaze on Epsilon Orionis, and at the appointed time, Enceladus \u2013 roughly at aposaturnium \u2013 and its erupting plume glided in front of the star.<\/p>\n Since lots of extra icy dust appears at this point in Enceladus\u2019 orbit, scientists expected to measure a lot more gas in the plume.<\/p>\n But instead of the expected large increase in gas output, UVIS only saw a bump of 20% in the total amount of gas.<\/p>\n \u201cWe went after the most obvious explanation first, but the data told us we needed to look deeper,\u201d said Cassini scientist Candy Hansen.<\/p>\n This led Hansen and her colleagues to focus on one of Enceladus\u2019 ejecta-spewing jets that was discovered to be four times more active than anticipated \u2013 producing 8% of the occultation-observed plume\u2019s total gas instead of just 2% as predicted.<\/p>\n However, the new observations provide helpful insights on what could be going on with the underground plumbing \u2013 cracks and fissures through which water from the moon\u2019s potentially habitable subsurface ocean makes its way into space.<\/p>\n","protected":false},"excerpt":{"rendered":" Moving out into the asteroid belt and farther still to the gas giants, NASA\u2019s Dawn, Juno, and Cassini missions churned away in orbit of their respective hosts \u2013 with Dawn continuing an up-close-and-personal investigation of the dwarf planet Ceres, Juno\u2019s fantastically accurate arrival at Jupiter but frustratingly crippled start to its science mission, and the […]<\/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":[2394,2839,1929],"class_list":["post-38892","post","type-post","status-publish","format-standard","hentry","category-news","tag-cassini","tag-dawn","tag-juno"],"acf":[],"_links":{"self":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/38892"}],"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=38892"}],"version-history":[{"count":0,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/38892\/revisions"}],"wp:attachment":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media?parent=38892"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/categories?post=38892"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/tags?post=38892"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-21-at-13.45.27-350x346.png\")
Dawn\u2019s latest images of Ahuna Mons, taken 120 times closer than in February 2015, reveal a significant amount of bright material on some of the mountain\u2019s slopes, and less on others. <\/p>\n![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-21-at-13.48.14-350x289.png\")
By late-April, Dawn returned stunning new images from its low-altitude (385 km \u2013 240 mi) mapping orbit of the dwarf planet\u2019s numerous bright material craters. <\/p>\n![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-21-at-13.51.32-350x320.png\")
However, a big focused remained on Occator crater, and by mid-year, Dawn had finally returned enough information about it that scientists were gaining a better understanding of its composition.<\/p>\n![](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/03\/Screen-Shot-2016-03-05-at-13.00.58-e1482346466915-350x248.png\")
\u201cThe minerals we\u2019ve found at the Occator central bright area require alteration by water,\u201d De Sanctis said. \u201cCarbonates support the idea that Ceres had interior hydrothermal activity, which pushed these materials to the surface within Occator.\u201d<\/p>\n![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-22-at-09.14.22-350x217.png\")
By the end of July, Dawn had returned information that helped scientists start to answer the question of what happened to all of Ceres large impact craters. <\/p>\n![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-22-at-09.16.07-350x210.png\")
However, Dawn has shown that Ceres has only 16 craters larger than 100 km, and none larger than 280 km across.<\/p>\n![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-22-at-09.25.55-350x200.png\")
If Ceres had widespread cryovolcanic activity in the past, the ejected cryogenic materials could have flowed across the surface and possibly buried pre-existing large craters. <\/p>\n![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-22-at-09.33.43-350x216.png\")
This confirmation validated one of the reasons why the International Astronomical Union classified Ceres as a dwarf planet in 2006.<\/p>\n![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-22-at-09.27.19-350x266.png\")
Following this announcement, Dawn controllers began maneuvering the spacecraft into its higher, mission extension orbit in early September.<\/p>\n![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-22-at-09.36.02-350x215.png\")
Also in September, Dawn scientists released information on a possible detection of a temporary atmosphere around the dwarf planet.<\/p>\n![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-22-at-09.39.32-350x249.png\")
Originally, Juno was to complete two of these 53.4-day orbits before performing a perijove burn on 19 October that would have altered its orbit to the pre-mission determined 14-day science orbit.<\/p>\n![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-22-at-09.41.11-350x326.png\")
As of writing, controllers have still not determined a best way forward and are currently investigating the valves\u2019 potential link to similar failures on Akatsuki and an Intelsat satellite.<\/p>\n![](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-22-at-09.42.13-294x350.png\")
Nonetheless, NASA has been quiet on the effect the prolonged orbit might have on the science collected at other points in the orbit and the effect the prolonged exposure to Jupiter\u2019s harsh radiation field will have on the craft\u2019s instruments \u2013 which now receive just under 4 times the amount of radiation exposure between scientific close flybys of Jupiter. <\/p>\n![](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-22-at-09.48.49-e1482418208735-350x255.png\")
The first major event for Cassini this year was a carefully choreographed observation of Enceladus as it occulted \u2013 passed in front of, as viewed from a specific location \u2013 the star Epsilon Orionis, the central star in Orion\u2019s belt. <\/p>\n![](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-22-at-09.49.09-350x186.png\")
Cassini\u2019s Ultraviolet Imaging Spectrometer (UVIS) measured how water vapor in the plume dimmed Epsilon Orionis\u2019 ultraviolet light, thereby revealing how much gas the plume contained. <\/p>\n![](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/Screen-Shot-2016-12-22-at-09.48.55-350x214.png\")
Thus, the occultation observation revealed that at least some of the narrow jets that erupt from the moon\u2019s surface blast with increased fury when the moon is at aposaturnium \u2013 but why the gas in the plume was so much less than anticipated is still a mystery.<\/p>\n