"The appearance of this ice cloud goes against everything we know about the way clouds form on Titan," said Carrie Anderson, a CIRS co-investigator at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study.
The puzzling appearance of an ice cloud seemingly out of thin air has prompted NASA scientists to suggest that a different process than previously thought—possibly similar to one seen over Earth's poles—could be forming clouds on Saturn's moon Titan. Located in Titan's stratosphere, the cloud is made of a compound of carbon and nitrogen known as dicyanoacetylene (C4N2), an ingredient in the chemical cocktail that colors the giant moon's hazy, brownish-orange atmosphere.Decades ago, the infrared instrument on NASA's Voyager 1 spacecraft spotted an ice cloud just like this one on Titan. What has puzzled scientists ever since is this: they detected less than 1 percent of the dicyanoacetylene gas needed for the cloud to condense.
Recent observations from NASA's Cassini mission yielded a similar result. Using Cassini's composite infrared spectrometer, or CIRS—which can identify the spectral fingerprints of individual chemicals in the atmospheric brew—researchers found a large, high-altitude cloud made of the same frozen chemical. Yet, just as Voyager found, when it comes to the vapor form of this chemical, CIRS reported that Titan's stratosphere is as dry as a desert.
The typical process for forming clouds involves condensation. On Earth, we're familiar with the cycle of evaporation and condensation of water. The same kind of cycle takes place in Titan's troposphere—the weather-forming layer of Titan's atmosphere—but with methane instead of water.
A different condensation process takes place in the stratosphere—the region above the troposphere—at Titan's north and south winter poles. In this case, layers of clouds condense as the global circulation pattern forces warm gases downward at the pole. The gases then condense as they sink through cooler and cooler layers of the polar stratosphere.
Either way, a cloud forms when the air temperature and pressure are favorable for the vapor to condense into ice. The vapor and the ice reach a balance point—an equilibrium—that is determined by the air temperature and pressure. Because of this equilibrium, scientists can calculate the amount of vapor where ice is present.
This graphic illustrates how scientists think "solid state" chemistry may be taking place in ice particles that form clouds in the atmosphere of Saturn's moon Titan. Credit: NASA/JPL-Caltech/GSFC
"For clouds that condense, this equilibrium is mandatory, like the law of gravity," said Robert Samuelson, an emeritus scientist at Goddard and a co-author of the paper.
But the numbers don't compute for the cloud made from dicyanoacetylene. The scientists determined that they would need at least 100 times more vapor to form an ice cloud where the cloud top was observed by Cassini's CIRS.
One explanation suggested early on was that the vapor might be present, but Voyager's instrument wasn't sensitive enough in the critical wavelength range needed to detect it. But when CIRS also didn't find the vapor, Anderson and her Goddard and Caltech colleagues proposed an altogether different explanation. Instead of the cloud forming by condensation, they think the C4N2 ice forms because of reactions taking place on other kinds of ice particles. The researchers call this "solid-state chemistry," because the reactions involve the ice, or solid, form of the chemical.
The first step in the proposed process is the formation of ice particles made from the related chemical cyanoacetylene (HC3N). As these tiny bits of ice move downward through Titan's stratosphere, they get coated by hydrogen cyanide (HCN). At this stage, the ice particle has a core and a shell comprised of two different chemicals. Occasionally, a photon of ultraviolet light tunnels into the frozen shell and triggers a series of chemical reactions in the ice. These reactions could begin either in the core or within the shell. Both pathways can yield dicyanoacteylene ice and hydrogen as products.
The researchers got the idea of solid-state chemistry from the formation of clouds involved in ozone depletion high above Earth's poles. Although Earth's stratosphere has scant moisture, wispy nacreous clouds (also called polar stratospheric clouds) can form under the right conditions. In these clouds, chlorine-bearing chemicals that have entered the atmosphere as pollution stick to crystals of water ice, resulting in chemical reactions that release ozone-destroying chlorine molecules.
"It's very exciting to think that we may have found examples of similar solid-state chemical processes on both Titan and Earth," said Anderson.
The researchers suggest that, on Titan, the reactions occur inside the ice particles, sequestered from the atmosphere. In that case, dicyanoacetylene ice wouldn't make direct contact with the atmosphere, which would explain why the ice and the vapor forms are not in the expected equilibrium.
"The compositions of the polar stratospheres of Titan and Earth could not differ more," said Michael Flasar, CIRS principal investigator at Goddard. "It is amazing to see how well the underlying physics of both atmospheres has led to analogous cloud chemistry."
The Daily Galaxy via NASA
NASA will announce new findings about Jupiter's ocean-harboring moon Europa during a news conference at 2 p.m. EDT (1800 GMT) on Monday (Sept. 26). "Astronomers will present results from a unique Europa observation campaign that may be related to the presence of a subsurface ocean on Europa," NASA officials wrote in a media advisory Tuesday (Sept. 20).
In 2013, huge active plumes containing water vapor being released from the surface of Jupiter's moon Europa were discovered shooting up 1200 kilometers. This sensational find was made using the NASA/ESA Hubble Space Telescope. Europa has been a focus of extraterrestrial research for some time, as there were clear indications that it harbors a liquid vast ocean beneath its icy crust. The plumes were not sighted again, however. The involvement of Hubble raises the possibility that Europa's elusive plumes may finally have been spotted again.The new information comes via NASA's Hubble Space Telescope, agency officials said. We'll post the conference live at dailygalaxy.com via NASA TV
The participants in Monday's briefing are:
Paul Hertz, director of the Astrophysics Division at NASA Headquarters in Washington.
William Sparks, astronomer with the Space Telescope Science Institute in Baltimore.
Britney Schmidt, assistant professor at the School of Earth and Atmospheric Sciences at Georgia Institute of Technology in Atlanta.
Jennifer Wiseman, senior Hubble project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
VIEW MONDAY's CONFERENCE On NASA TV HERE
Astrobiologists regard Europa as one of the solar system's best bets to host alien life.
The existence of the plumes "is the kind of thing that could have a profound impact on how we explore Europa," Curt Niebur, outer planets program scientist at NASA headquarters, said during a NASA planetary sciences subcommittee meeting. "With an ocean that is tens of kilometers below the ice, most likely, if you can have a plume that's possibly bringing material from that ocean up to orbit, well, that's going to affect how you explore," Niebur added.
Lorenz Roth of the Southwest Research Institute in San Antonio, Texas and Joachim Saur of the University of Cologne used the Hubble to prove that there is water vapour erupting near its south pole. The water plumes are in comparison to earth geysers immensely large and reach heights of approximately 200 km. Europa has a circumference of 3200 kilometers, comparable in size with the Moon.
But new Hubble observations in January and February of this year showed no signs of the massive plumes. "It could be just the way that we use the auroral emissions coming from those plumes at the UV [ultraviolet] wavelengths of light that we use with Hubble," discovery team member Kurt Retherford, of the Southwest Research Institute in San Antonio, told Space.com. "These things depend on Jupiter's plasma environment," Retherford added. "Maybe there were just a lot of particles, atoms, getting excited by electrons and ions in Europa's atmosphere, more so than at other times, and [they] just lit up the plumes more than they usually do."
Retherford added that the plumes may sometimes simply be too small to see by the scientists who are relying on the Earth-orbiting Hubble to study the features on Europa, Retherford said. Another possibility Retherford noted is that the geysers don't exist, that the detection by Hubble, which was based primarily on observations the telescope made in December 2012, was an artifact or misinterpretation of some sort. "The best explanation still is plumes for that dataset, no doubt about it," he said
“Water is generally considered a basic prerequisite for life at least as we know it on earth,” said Lorenz Roth, who was in charge of analysing the 2013 Hubble observations and who has been working at the Southwest Research Institute in America. “For this reason, the discovery of a water vapour plumes on the moon Europa has increasingly become a focus of extraterrestrial research.” The plumes eject material from the surface which will make further investigations of the moon Jupiter much easier in the future.
“We have been advancing the search for water and water plumes with multiple Hubble campaigns,” says Joachim Saur. “However, it was only after a camera on the Hubble Space Telescope in one of the last Space Shuttle Missions was repaired that we were able to achieve enough sensitivity to observe the fountains.”
The water plumes could only be seen in the observations when Europe was in a position in its orbit where the moon was furthest away from Jupiter. That means that the activity of the fountain varies temporally. Europa's orbit is not quite circular but slightly elliptical. When Europa is furthest away from Jupiter in its orbit, the tidal forces cause the huge fractures in Europa's ice surface to widen from which presumably the vapour is released.
Similar plumes of water vapor were discovered by the Cassini spacecraft on the Saturnian moon Enceladus. The activities there are similar to those on Europa during its orbit around its mother planet.
The Daily Galaxy via NASA and uni-koeln.de and space.com
Image Credit: K. Retherford, Southwest Research Institute, NASA/ESA/K.
390
US one sheet for DRUMS ALONG THE MOHAWK (John Ford, USA, 1939)
Artist: uncredited
Poster source: Heritage Auctions
Photograph of the Stevens Family outside their home in Linn Creek, Missouri, ca. 1905 by an unidentified photographer. Silver and photographic gelatin on photographic paper
(Collection of the Smithsonian National Museum of African American History and Culture, Gift of Jackie Bryant Smith)
Clutching a revolver against his chest, an unidentified African American Union soldier stares out from an 1861-1865 Civil War tintype. Barack and Michelle Obama relax together on a sofa in their Chicago home in a 1996 black and white portrait taken by Mariana Cook. An African American mother smiles joyfully at her newborn baby in a 1952 photograph by Robert Gailbraith from the series “Reclaiming Midwives: Stills from All My Babies.” Breathtaking, tragic, solemn, overwhelming, exuberant are but a few of the adjectives that try but fail to capture the radiance and breadth of the some 30,000 photographs now in the permanent collection of the Smithsonian's National Museum of African American History and Culture.
Started by curators Michèle Gates Moresi and Jacquelyn Serwer, this remarkable collection has lately been growing with the added expertise of Aaron Bryant, one of NMAAHC's curators, and Rhea Combs, head of the museum's Stafford Center for African American Media Arts. “Michelle, Jackie, Rhea and I work as a team, acquiring photographs for the museum,” Bryant explains. Other curators, however, also collect images relevant to their particular interests.
Here Smithsonian Insider asks Bryant a few questions about what type of photos he looks for and how he acquires them for the African American History and Culture Museum.
Portrait of a couple on a motorcycle outside of Anderson Photo Service studio ca. 1960, by Rev. Henry Clay Anderson. Silver and photographic gelatin on acetate film (Collection of the Smithsonian National Museum of African American History and Culture)
Bryant: One way is to build relationships directly with photographers. Our job is to share history and preserve American legacies, and sharing and preserving the work of photographers who have documented our nation's culture and history is part of that.
Equally important, however, are the scores of donors who have reached out to the museum. You'd be surprised and touched by the number of people who have donated their collections, including family albums with images that extend as far back as the 19th century.
The provenance and personal stories behind certain images, as well as the donors' reasons for wanting to donate, are incredibly moving. People supporting NMAAHC's vision by helping to build the museum through donating family treasures has real value to us. Our collection is like a national family album of sorts, with thousands of different branches in the family tree, and each one is significant to telling a broader story. Our donors become an important part of a national history, and the sense that the museum is working with a community of people as part of a national family aligns with our mission.
We've also gotten certain photographs from collectors, auction houses, and galleries. They've been instrumental in helping us identify specific, hard to find images that are essential to stories we want to tell.
Autographed photograph of LeRoi Jones, Jan. 31, 1962 by Carl Van Vechten. Silver and photographic gelatin on photographic paper. (Collection of the Smithsonian National Museum of African American History and Culture)
Bryant: Yes. A photograph is actually an object in many ways. Just as museums are most interested in collecting original three-dimensional artifacts, we collect original photographs, negatives, digital negatives, or digital scans from negatives, depending on why and how the photo will be shared with the public. Antique and vintage photos and negatives, are different from the contemporary images that sometimes come to us as digital negatives from the photographer.
In addition to being an object, though, images are also archival documents. So we'd want to collect images as original archival material as well. Our collection of Robert Houston's images from his time at Resurrection City during the 1968 Poor People's Campaign is an example. In addition to the journal he kept at the time, we also have images he shot as a visual diary of his experiences with the poverty campaign. The collection includes vintage prints and slides. He made an earlier donation of high-resolution digital scans of negatives. As a museum operating in the 21st century, we recognize that the original might also include digital files from digital cameras or high-resolution scans of negatives, which helps to stabilize images.
Views of Thomasville and Vicinity: 44 Weighing Cotton ca. 1895 by photographer A. W. Möller. Unidentified women and men. Albumen and silver on paper mounted on cardboard. (Collection of the Smithsonian National Museum of African American History and Culture, Gift of Mr. and Mrs. Norman and Sandra Lindley)
Bryant: We're building a collection that reflects America's history, African American culture, and a history of photography. So in addition to covering people, places, events, subjects, and time periods, the collection is also an evolutionary survey of photographic processes and mediums that cover a spectrum of time periods. The collection ranges from 19th century daguerreotypes to digital images as recent as several months ago. In fact, we have cell phone images from Devin Allen as examples of a new photographic medium in art, social media, and photojournalism. Allen captured images of protests in Baltimore, which Time magazine and a number of other media outlets later published after they went viral online. Aperture recently published a few in its special issue “Vision & Justice,” which is getting lots of global attention in the field.
“Positive Reflections,” unidentified man, Oct. 16, 1995, by photographer Roderick Terry. Silver and photographic gelatin on photographic paper. (Collection of the Smithsonian National Museum of African American History and Culture, Gift of Roderick Terry)
Our collection also houses traditional mediums like gelatin silver prints, magic lantern slides, carte-de-visites, cabinet cards, ambrotypes, tintypes, negatives and transparencies, and a host of other examples of how photography has evolved from its early history in the 1800s to today.
We're also considering the evolution of artistic genres, from Pictorialism and the painterly kinds of images of late 19thcentury early modernism to contemporary art photography, straight photography, portraiture, and abstraction. We extend beyond the historicity of social documentary and photojournalism a bit to include traditional genres and interesting hybrids, where images are created through innovative and unexpected mediums. Since the museum also collects visual art, artistic genres in photography is something we will consider more as we move forward.
In this tintype an unidentified African American Union soldier with a moustache and beard, holds a pistol across his chest. His buttons and belt buckle are hand-colored in gold paint. The hand-coloring on the buckle reads “Z O”. Thermoplastic case with brass hinges and red velvet liner. (Collection of the National Museum of African American History and Culture)
My particular interests are in sociopolitical history, cultures of everyday life, and art photography. There are lots of photographers who create social documentary photography that's also considered art. Sometimes the purely social documentary images give us a lot of cultural and historical information.
Bryant: We've published four books focusing on the museum's photography collection and will soon publish a fifth. The first book was Through the African American Lens. In our second book, Civil Rights and the Promise of Equality, there is a photo by James H. Wallace taken in 1964 of students in Chapel Hill, N.C. participating in a July 4, protest against segregation. In looking at the image, we'd consider ways the photograph might document an American story from different perspectives, including African Americans. It's 1964. What was Chapel Hill like at that time? What was North Carolina as a cultural and ideological space like for people at that time? And what was the university like for students, as well as for the people working or living in the area?
Photograph of Senator Henry Hall Falkener and family ca. 1905. Unidentified photographer. Silver and photographic gelatin on photographic paper. (Collection of the Smithsonian National Museum of African American History and Culture, Gift of Margaret Falkener DeLorme, Waldo C. Falkener, Cameron S. Falkener and Gilbert E. DeLorme)
In North Carolina by 1963, Bob Jones was leading the emergence of one of the largest Klan groups in the country. The Klan had become notorious in North Carolina and the effects of their presence were felt generations later. So the Chapel Hill images have a certain context that goes beyond the two-dimensionality of the photograph.
No matter the period, it's the history surrounding the image that helps us tell American stories. African American perspectives can be the prism for interpreting the experience. Then there might be a broader contextualization in which the photo and the moment it captures is placed within a larger history. What led to that particular protest in Chapel Hill, for example, and how might the moment reflect 1964 America?
Bryant: The museum and its collection were built from scratch. We started without a collection or facility, but now we have a museum on the National Mall with roughly 30,000 images. We've collected to build a foundation for the photography collection, while hoping to add to the canons in various fields in a way that shifts cultural paradigms and historical narratives.
We also were aware that we were building a 21st century collection for a museum that would serve several generations. So while collecting to preserve a distant past, we also collect to reflect contemporary histories and issues as well. We built the collection with the idea that we are about the present and the future, as well as the past.
Untitled (photograph from the Film & Photo League Archive) by unidentified photographer, 1931 1936. Silver and photographic gelatin on photographic paper. (Collection of the Smithsonian National Museum of African American History and Culture)
Bryant: We recently accessioned photographs of Black Lives Matter protests in different cities, including Ferguson and Baltimore. This would be a case in which we accessioned images with history, the present, and the future in mind.
The photographs were taken by Zun Lee, Sheila Pree Bright, Jermaine Gibbs, and Devin Allen. Allen is the millennial sensation, whose images of unrest in Baltimore went viral on social media. Allen democratized photography in a way that impacted the field for future generations, using social media, rather than mainstream media, as a voice and platform. Jermaine Gibbs is a commercial photographer in Baltimore, who also captured images of the city's unrest. Zun Lee and Shelia Pree Bright have also gotten media attention in recent years as part of a new generation of socially conscious photographers. They are redefining traditions. Sheila is known for her series 1960NOW! and Plastic Bodies, while Zun has received recognition for his series of found Polaroids, Fade Resistance, as well as his Father Figure series. Acquisitions that involve contemporary social histories, while working with living photographers like these, are exciting.
However, another one of my favorite acquisitions was also one of my first acquisitions for the museum. Our chief curator, Jackie Serwer, and I met with a donor, Simone Durrah Logan, who wanted to donate her family photos from the 19th and early 20th century. They were a wedding gift from her dad. Most of the images were taken in Yankton, S.D.
Few people think about the history of African Americans in places like North and South Dakota during Reconstruction. When we think of African American history, we often think of the east coast, but African Americans were building communities and creating cultures all over the country. Simone's family images help us to create new narratives and perspectives and share stories about what attracted communities of African Americans out west following Emancipation.
Ambrotype of Frederick Douglass, 1855-1865, by an unidentified photographer. Collodion and silver on glass photographic plates, leather. (Collection of the Smithsonian National Museum of African American History and Culture)
Bryant: Images have power. As a form of language, visual data influences the way we create social meaning and share cultural knowledge. Seeing and then interpreting what we see is critical to our understanding the world from a particular lens or worldview.
Additionally, images have an ability to communicate beyond the power or necessity of words. It is true that a picture can be worth a thousand words, particularly in contemporary cultures that are visually driven. Images offer “thick descriptions” of people, events, places, and particular moments in time. It's why social media is so popular and instrumental in present-day cultures.
Images also offer first-person perspectives on historical events that help us see and understand from different points of view. Photographs allow us to immerse ourselves in the histories and moments caught in a camera's lens.
Photographs can be objects or works of art. They can be a form of archival texts that document time, or windows into different cultures and worlds from our past. I like to think that photographs can bear witness. They provide visual evidence of a culture as a testament to our nation's history.
The post Building a grand photography collection for the new African American museum appeared first on Smithsonian Insider.
1960 Czech poster for MOANA (Serge Arnoux, Bernard Gorki, Roger Lesage, Pierre Pasquier, France, 1959)
Designer: Daisy Mrazkova
Poster source: Posteritati
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