A new set of post-Cassini papers has to deal with observational facts: Saturn and its rings cannot last billions of years.Science Magazine just added to the growing body of post-Cassini literature analyzing 13 years’ worth of data gathered by the legendary Saturn orbiter. During the last 22 “high-dive” orbits in 2017, Cassini had unprecedented opportunities to sample the space between the rings and the planet. Here are some of the surprising findings being reported.Hsu et al, “In situ collection of dust grains falling from Saturn’s rings into its atmosphere” (Science). A “ring rain” of nanoparticles detected by the Cosmic Dust Analyzer (CDA) puts an upper limit of 400 million years on the rings.Mitchell et al, “Dust grains fall from Saturn’s D-ring into its equatorial upper atmosphere” (Science). Atmospheric drag is ejecting dust from the D-ring analogous to “sawdust ejected from a circular saw as it cuts through wood.” They believe the process “plays a role in slowing the fall of the dust through the atmosphere,” but sawdust does not normally evolve back into wood.Waite et al, “Chemical interactions between Saturn’s atmosphere and its rings” (Science). This paper, with co-author Jeff Cuzzi, a ringmaster most of his professional life, cannot support billion-year rings. Water is falling into the planet from the rings at a rate of up to 45,000 kilograms per second. Other compounds are also flowing off the rings into Saturn, as measured by the Ion and Neutral Mass Spectrometer (INMS). Here’s the team’s conclusion:The large mass of infalling material has implications for ring evolution, likely requiring transfer of material from the C ring to the D ring in a repeatable manner. The infalling material can affect the atmospheric chemistry and the carbon content of Saturn’s ionosphere and atmosphere.Cassini dives through the gap between the D Ring and Saturn during its Grand Finale before burning up in Saturn’s atmosphere on September 15, 2017.Here’s the operative quote about ages: not millions of years, but thousands?The mass of Saturn’s C ring is ~1018 kg, about 0.03 times the mass of Saturn’s moon Mimas. Therefore, if we use the mass influx inferred from the INMS measurements (4800 to 45,000 kg s–1), we calculate a lifetime of 700,000 to 7 million years for the C ring. Yet this only reflects today’s influx. The current influx is directly from the D ring rather than the C ring, which must be the ultimate supplier because the mass of the D ring [likely no more than 1% of the C ring mass] can maintain current loss rates for only 7000 to 66,000 years—a very short amount of time in terms of solar history. It is unclear whether the C ring can lose 1% of its mass into the D ring by viscous spreading over that time period.Although viscous spreading of the C ring is likely not the cause of mass transfer to the D ring, occasional transfer of ~1% of the mass of the C ring into the D ring region via a large ring-tilting event is feasible. These ring-tilting events involve a stream of planet-orbiting rubble crossing the ring plane somewhere in the C or D rings. The C ring provides the ultimate source, containing enough mass to last (at current influx rates) about 5% of the time that the rings themselves have existed (~200 million years). The D ring could be repopulated sporadically by large impact events such as those that tilted the D and C ring plane. Once enough small particles are brought into the D ring region, exospheric drag would quickly drain them into the planet, as observed by Cassini.Notice that keeping the rings old (“repopulated”) requires an appeal to the old-age standby explanation: impacts. The number of lucky impacts needed to keep the rings billions of years old, however, stretches credibility.Perry et al, “Material Flux From the Rings of Saturn Into Its Atmosphere” (Geophysical Research Letters). This team measured the flow of nanometer-sized particles from the rings that are swept up by Saturn’s atmosphere and dragged into the planet. The predicted flux was wrong, and had to be revised upward significantly. It’s “exciting” to be wrong by a factor of a hundred, isn’t it?Surprisingly, the flux is a hundred times larger than past predictions, and at least half of the material is hydrocarbon, which comprises less than 5% of the water ice‐dominated rings. Cassini’s data also show that the influx varies at least a factor of 4 and may be linked to clumps that appeared in 2015 on D68, the ringlet on the inner edge of the rings. These newly discovered particles and processes alter the evolutionary landscape of the rings and provide an exciting, rich field for future research aimed at understanding the origin and history of the rings.How This Came Across in the Popular PressLeah Crane, “Cassini revealed three big surprises before diving into Saturn” (New Scientist). Can Ms Crane bring herself to criticize planetary scientists who got things so wrong? On the subject of Saturn’s magnetic field, she comes close:The magnetic fields of planets in our solar system are all tilted to some extent – Neptune’s is off by a whopping 47 degrees. But Saturn’s magnetic field seems to be perfectly straight, and our current theories of how these fields are generated suggests that should be impossible.“If you don’t have a tilt, you would expect the magnetic field to start dying away, but as we got in really close with the Grand Finale orbits, we saw that it is not,” says Michele Dougherty at Imperial College London.Michele is a dignified and accomplished woman on the Cassini team, but she was wrong on this point. She was wrong on another point, too (as were all the Cassini scientists). Once again, they are excited about being wrong:Even the seemingly empty space between Saturn’s surface and its rings is more exciting than we thought. “There’s this connection between the rings and the upper atmosphere of Saturn that we just didn’t think would be there,” says Dougherty. “That was a complete surprise.”Crane goes on to compare the amount of infalling material (dust, ice and gas), measured to be about 45,000 kg (22,000 pounds) per second, this way:That’s the equivalent of about 1800 cars falling into Saturn every minute – such a downpour may mean that the rings are disappearing faster than we thought.A little math helps picture this. How much material should have been lost in Saturn’s assumed lifetime? 4.5 x 104 kg/s times 86,400 sec/day times 365 days/year times 4.5 x 109 years: if this has been going on for the age of the solar system, Saturn’s rings would have lost 24 x 1021 kg of material by now. In plain English, that’s a whopping 6,500 billion billion kilograms, or 4,800 million billion cars! That’s close to 240 times the entire mass of the rings. Is that credible?Groundbreaking Science Emerges from Ultra-Close Orbits of Saturn (Jet Propulsion Laboratory). Will JPL apologize for getting it so wrong? Don’t count on it. Scientists must always look good to the public, because they are the high priests of knowledge in our culture.Scientists can’t be blamed for things that could not be measured or detected before, obviously, but much of what was taught about Saturn and its rings for decades has just been tossed out the window. The press release mentions “surprise” four times. How about that magnetic field? Haven’t students of geophysics been taught that a dynamo in the core generates the field? That’s been falsified, at least in the case of Saturn; “That might mean that Saturn produces its magnetic field differently from the other planets in our solar system,” Crane said. Actually, it might mean that the theory for generating magnetic fields is wrong for all planets. Philosophers of science look askance at special pleading.That’s not the only mystery or surprise, either. The whole mission was a string of surprises:According to everything scientists know about how planetary magnetic fields are generated, Saturn should not have one. It’s a mystery that physicists will be working to solve….But scientists were surprised to see that others [particles] are dragged quickly into Saturn at the equator. And it’s all falling out of the rings faster than scientists thought — as much as 22,000 pounds (10,000 kilograms) of material per second.Scientists were surprised to see what the material looks like in the gap between the rings and Saturn’s atmosphere. They knew that the particles throughout the rings ranged from large to small. But the sampling in the gap showed mostly tiny, nanometer-sized particles, like smoke, suggesting that some yet-unknown process is grinding up particles….Indeed, says project scientist Linda Spilker, “Almost everything going on in that region turned out to be a surprise.” No shame, though; “the data is tremendously exciting.”Now what? “Many mysteries remain, as we put together pieces of the puzzle,” Spilker said. “Results from Cassini’s final orbits turned out to be more interesting than we could have imagined.”In all these surprises, mysteries, and falsifications, one thing is never called into question by secular planetary scientists: the assumed age of the solar system. That figure—the Law of the Misdeeds and Perversions—cannot be altered.Instead of hiding their heads in shame, they are excited about being way off. So what is the likely impact of the revised estimates? Saturn’s rings are young. Plug that into your story of “understanding the origin and history of the rings.” The ramifications are likely to ripple across the solar system, all the way to Earth. (Visited 575 times, 1 visits today)FacebookTwitterPinterestSave分享0
US President Barack Obama watches news coverage of the passing of Nelson Mandela in the Outer Oval Office on Thursday 5 December 2013. Obama and his wife Michelle, as well as former US presidents Jimmy Carter, Bill Clinton and George W Bush, will be among the global leaders attending the memorial service for Mandela on Tuesday 10 December.(Official White House photo by Pete Souza)MEDIA CONTACTS• Phumla WilliamsCabinet spokesperson and acting chief executive officerGovernment Communication and Information System+27 83 5010 139Over 70 global leaders – including four US presidents – as well as royalty and international celebrities are heading to South Africa for the week of mourning for Nelson Mandela, which will include a massive memorial service on Tuesday and an official state funeral on Sunday.Tomorrow, 10 December, over 80 000 people will gather at FNB Stadium in Johannesburg for the memorial service in honour of South Africa’s first democratically elected president. The stadium is where Mandela made his last major public appearance, at the final of the 2010 Fifa World Cup.The service will be a final chance for grieving South Africans to unite in a mass celebration of Mandela’s life ahead of the smaller, more formal state funeral at his home village of Qunu in the Eastern Cape on 15 December.While Tuesday’s memorial service will likely be one of the largest gatherings of global leaders in recent history, only a handful of dignitaries will attend Sunday’s state burial in Mandela’s ancestral home of Qunu in the Eastern Cape. “We’re trying to keep that to the family,” foreign ministry spokesperson Clayson Monyela told Talk Radio 702.“The world literally is coming to South Africa, and the large number of high profile guests arriving is unprecedented,” Monyela said.Minister in the Presidency Collins Chabane said international heads of state and royalty had started arriving in South Africa. Representatives from almost every global organisation will attend.“I don’t think it has ever happened before. All organisations of the world.” Chabane said. “We also have princes and princesses, kings and queens coming.”US President Barack Obama and his wife Michelle will be accompanied by three of his country’s former presidents: Jimmy Carter, George W Bush and Bill Clinton and their wives, as well as 26 congressmen.Thirteen presidents from Africa and 15 from the rest of the world have confirmed attendance. Presidents David Cameron of the UK, François Hollande of France, Joachim Gauck of Germany, Enrique Pena of Mexico and Mahmud Abbas of Palestine will be at the memorial service, as will UN secretary-general Ban Ki-moon and Brazilian president Dilma Rousseff, who will lead a delegation made up of four of her country’s former presidents. Britain’s Prince Charles will represent his mother, Queen Elizabeth, at the funeral in Qunu.African leaders who have confirmed are President Goodluck Jonathan of Nigeria, President Jakaya Kikwere of Tanzania, President Joseph Kabila of the DRC, President Hifikepunye Pohamba of Namibia, and President Macky Saul of Senegal.Talk show queen Oprah Winfrey and singer-activist Bono, as well as British billionaire Richard Branson and musician Peter Gabriel are expected to be among the celebrity mourners at FNB Stadium.‘A special place in the hearts of people’“The fact that international leaders are making their way to South Africa at such short notice reflects the special place president Nelson Mandela holds in the hearts of people around the globe,” Chabane said.“We are touched by the fact that many countries have declared periods of mourning, ordered that flags be flown at half-mast and draped or lit landmarks in the colours of the South African flag. We truly appreciate these gestures.”South Africans have held permanent day and night vigils outside Mandela’s Johannesburg home since his death on the night of 5 December. Sunday marked the formal start of a week of official mourning for the country’s greatest statesman.Before the funeral, Mandela’s body will lie in state for three days from Wednesday 11 December in the amphitheatre of the Union Buildings in Pretoria, where was sworn in as president in 1994.Every morning for three days, his coffin will be carried through the streets of the capital in a funeral cortege, to give as many people as possible the chance to pay their final respects.The official memorial service at FNB Stadium will start at 11am with gates opening to the public at 06h00.“Entry to the stadium will be in a first come, first served basis,” Chabane said. No private vehicles will be given access to the stadium, with people urged to make use of public transport, such as the Gautrain, Metrorail and Rea Vaya. Mourners can also attend satellite services at Ellis Park, Orlando and Dobsonville stadiums, where the events at FNB Stadium will be broadcast on giant screens.
Focal reducers are a cost effective way to eliminate most cropping on Blackmagic Cinema Cameras.Blackmagic Design cameras offer a lot of really awesome features that give filmmakers a huge bang for their buck…but one of those features comes at a cost, the infamous crop factor. A Gizmodo review of the Blackmagic Cinema Camera states:The camera’s Super-16mm sensor—smaller than micro four-thirds—means you have to re-assess your lens selection to account for the crop-factor. Not only will few lenses get you a super-wide angle shot, but depth of field will not be nearly as shallow as a full-frame camera like the Canon 5D series, or even APS-C sensor cameras like the Canon 7D or Sony FS100. To get around this crop factor companies like Orion and Meade have created adapters that reduce cropping. These focal reducers come in a variety of prices but the real question is, do they work?In the following video presented by Ruben Kremer we take a look at a .72x focal reducer on a Blackmagic Pocket Camera and see if it’s worth the money.Pretty impressive huh? As with most lens adapters there is an added risk of creating some chromatic aberrations but it seems like the focal reducer that Ruben used worked pretty well. You can check out this focus reducer from Roxen on eBay.Thanks for sharing Ruben!Do you use focal adapters? Share your thoughts in the comments below!