mercredi 13 décembre 2017

Two tales of one galaxy, Gaia's view of our galactic neighbours












ESA - Gaia Mission patch.

13 December 2017

Measuring the positions and motions of more than a billion stars, ESA's Gaia mission will refine our knowledge about our place in the Universe, providing the best ever star chart of our Milky Way and its neighbouring galaxies.


Image above: Gaia's view of the Large Magellanic Cloud. Click here for details and larger versions of the image. Image Credits: ESA/Gaia/DPAC.

One of the nearest galaxies to our Galaxy is the Large Magellanic Cloud (LMC), located around 166 000 light-years away and visible to the naked eye at intermediate and southern latitudes.

With a mass roughly equivalent to ten billion times the mass of our Sun – about one tenth of the Milky Way – the LMC is home to an intense star-forming activity, forming stars five time faster than in our Galaxy. Different aspects of the galaxy's stellar population are depicted in these two images, based on data collected by the Gaia satellite during its first 14 months of operations.

The view on the left, compiled by mapping the total density of stars detected by Gaia in each pixel of the image, shows the large-scale distribution of stars in the LMC, delineating the extent of the spiral arms. The image is peppered with bright dots – these are faint clusters of stars.

A series of diagonal stripes, visible along the central thick structure, or bar, are an artefact caused by Gaia's scanning procedure. These will gradually decrease as more data are gathered throughout the lifetime of the mission.

On the right, a different image provides a complementary view that reveals other aspects of this galaxy and its stars. Created by mapping the total amount of radiation, or flux, recorded per pixel by Gaia, this image is dominated by the brightest, most massive stars, which greatly outshine their fainter, lower-mass counterparts. In this view, the bar of the LMC is more clearly delineated, alongside individual regions of star formation like the sparkling 30 Doradus, visible just above the centre of the galaxy.

The images below, also obtained using data from the first 14 months of Gaia science operations, depict two nearby spiral galaxies: Andromeda (also known as M31), which is slightly more massive than the Milky Way and, at roughly 2.5 million light-years away, the largest galaxy in our vicinity; and its neighbour, the Triangulum galaxy (also known as M33) home to some fifty billion stars and located about 2.8 million light-years away.


Image above: Gaia's view of the Andromeda galaxy. Image Credits: ESA/Gaia/DPAC.

As in the case of the LMC, the image on the left is based on the total density of stars, and shows where stars of all types are located, while the image on the right is based on the flux and mainly depicts the bright end of the stellar population of each galaxy, tracing out the regions of most intense star formation.


Image above: Gaia's view of the Triangulum galaxy.  Credits: ESA/Gaia/DPAC.

The first batch of Gaia data, released in 2016 and based on 14 months of science operations, contained the position and brightness of more than one billion stars. Most of these stars are located in the Milky Way, but a good fraction are extragalactic, with around ten million belonging to the LMC.

For all these stars and more, the second release of Gaia data – planned for April 2018 – will also contain measurements of their parallax, which quantifies a star's distance from us, and of their motion across the sky. Astronomers are eagerly awaiting this unprecedented data set to delve into the present and past mysteries of our Galaxy and its neighbours.

By analysing the motions of individual stars in external galaxies like the LMC, Andromeda, or Triangulum, it will be possible to learn more about the overall rotation of stars within these galaxies, as well as the orbit of the galaxies themselves in the swarm they are part of, known as the Local Group.

In the case of the LMC, a team of astronomers have already attempted to do so by using a subset of data from the first Gaia release, the Tycho–Gaia Astrometric Solution (TGAS), for which parallaxes and proper motions had also been provided by combining the new data with those from ESA's first astrometry mission, Hipparcos. In the TGAS data set, consisting of two million stars, they identified 29 stars in the LMC with good measurements of proper motions and used them to estimate the rotation of the galaxy, providing a taster of the studies that will become possible with future releases of Gaia data.

Gaia. Image Credit: ESA

Observations of the LMC and its neighbour, the Small Magellanic Cloud (SMC), with Gaia are extremely important also for studying variable stars like Cepheids and RR Lyrae. These stars can be used as indicators of cosmic distances in galaxies beyond our own as long as they are first calibrated in a 'local' laboratory, such as the LMC and SMC, where it is possible to obtain a more direct estimate of their distance using parallax determined with Gaia.

Astronomers in the Gaia Data Processing and Analysis Consortium, or DPAC, tested this method on hundreds of LMC variable stars from the TGAS sample as part of the validation of the data from the first release. Their results, which are promising even though preliminary, are an exciting example of the rich scientific harvest that will be possible with future releases of the data that are being gathered by Gaia.

Related links:

ESA Gaia: http://sci.esa.int/gaia/

Gaia Data Processing and Analysis Consortium (DPAC): https://www.cosmos.esa.int/web/gaia/dpac

Images (mentioned), Text, Credit: European Space Agency (ESA).

Greetings, Orbiter.ch

Stellar Nursery Blooms into View












ESO - European Southern Observatory logo.

13 December 2017

Stellar Nursery Blooms into View

The OmegaCAM camera on ESO’s VLT Survey Telescope has captured this glittering view of the stellar nursery called Sharpless 29. Many astronomical phenomena can be seen in this giant image, including cosmic dust and gas clouds that reflect, absorb, and re-emit the light of hot young stars within the nebula.

The region of sky pictured is listed in the Sharpless catalogue of H II regions: interstellar clouds of ionised gas, rife with star formation. Also known as Sh 2-29, Sharpless 29 is located about 5500 light-years away in the constellation of Sagittarius (The Archer), next door to the larger Lagoon Nebula. It contains many astronomical wonders, including the highly active star formation site of NGC 6559, the nebula at the centre of the image.

The star formation region NGC 6559 in the constellation of Sagittarius

This central nebula is Sharpless 29’s most striking feature. Though just a few light-years across, it showcases the havoc that stars can wreak when they form within an interstellar cloud. The hot young stars in this image are no more than two million years old and are blasting out streams of high-energy radiation. This energy heats up the surrounding dust and gas, while their stellar winds dramatically erode and sculpt their birthplace. In fact, the nebula contains a prominent cavity that was carved out by an energetic binary star system. This cavity is expanding, causing the interstellar material to pile up and create the reddish arc-shaped border.

When interstellar dust and gas are bombarded with ultraviolet light from hot young stars, the energy causes them to shine brilliantly. The diffuse red glow permeating this image comes from the emission of hydrogen gas, while the shimmering blue light is caused by reflection and scattering off small dust particles. As well as emission and reflection, absorption takes place in this region. Patches of dust block out the light as it travels towards us, preventing us from seeing the stars behind it, and smaller tendrils of dust create the dark filamentary structures within the clouds.

The rich surroundings of Sharpless 29

The rich and diverse environment of Sharpless 29 offers astronomers a smorgasbord of physical properties to study. The triggered formation of stars, the influence of the young stars upon dust and gas, and the disturbance of magnetic fields can all be observed and examined in this single area.

But young, massive stars live fast and die young. They will eventually explosively end their lives in a supernova, leaving behind rich debris of gas and dust. In tens of millions of years, this will be swept away and only an open cluster of stars will remain.

Zooming in on the star-forming region Sharpless 29

Sharpless 29 was observed with ESO’s OmegaCAM on the VLT Survey Telescope (VST) at Cerro Paranal in Chile. OmegaCAM produces images that cover an area of sky more than 300 times greater than the largest field of view imager of the NASA/ESA Hubble Space Telescope, and can observe over a wide range of wavelengths from the ultraviolet to the infrared. Its hallmark feature is its ability to capture the very red spectral line H-alpha, created when the electron inside a hydrogen atom loses energy, a prominent occurrence in a nebula like Sharpless 29.

Panning across the VST’s view of Sharpless 29

More information:

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and by Australia as a strategic partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.

Links:

Photos of OmegaCAM: http://www.eso.org/public/images/archive/search/?adv=&subject_name=OmegaCAM

Photos of VST: http://www.eso.org/public/images/archive/search/?adv=&subject_name=VLT%20Survey%20Telescope

VLT Survey Telescope (VST): http://www.eso.org/public/teles-instr/paranal-observatory/surveytelescopes/vst/

NASA/ESA Hubble Space Telescope: http://www.spacetelescope.org/

ESOcast 142 Light: Stellar Nursery Blooms into View (4K UHD): http://www.eso.org/public/videos/eso1740a/

Images, Videos, Text, Credits: ESO/Richard Hook//M. Kornmesser/IAU and Sky & Telescope.

Greetings, Orbiter.ch

Blue Origin - Crew Capsule 2.0 First Flight










Blue Origin logo.

13 December 2017

New Shepard flew again for the seventh time on Dec. 12, 2017, from Blue Origin’s West Texas Launch Site. Known as Mission 7 (M7), the mission featured the next-generation booster and the first flight of Crew Capsule 2.0.

Crew Capsule 2.0 First Flight

Crew Capsule 2.0 features large windows, measuring 2.4 feet wide, 3.6 feet tall. M7 also included 12 commercial, research and education payloads onboard.

Crew Capsule 2.0

Crew Capsule 2.0 reached an apogee of 322,405 feet AGL/326,075 feet MSL (98.27 kilometers AGL/99.39 kilometers MSL). The booster reached an apogee of 322,032 feet AGL/325,702 feet MSL (98.16 kilometers AGL/99.27 kilometers MSL).

For more information, visit: https://www.blueorigin.com/

Image, Video, Text, Credits: Blue Origin.

Best regards, Orbiter.ch

Giant storms cause palpitations in Saturn's atmospheric heartbeat












ESA - Cassini Mission to Saturn logo.

13 December 2017

Immense northern storms on Saturn can disturb atmospheric patterns at the planet's equator, finds the international Cassini mission. This effect is also seen in Earth's atmosphere, suggesting the two planets are more alike than previously thought.


Video above: Temperature changes at Saturn's equator: 2004-2016. Video Credits: ESA/NASA.

Despite their considerable differences, the atmospheres of Earth, Jupiter, and Saturn all display a remarkably similar phenomenon in their equatorial regions: vertical, cyclical, downwards-moving patterns of alternating temperatures and wind systems that repeat over a period of multiple years.

These patterns–known as the Quasi-Periodic Oscillation (QPO) on Saturn and the Quasi-Quadrennial Oscillation (QQO) on Jupiter, due to their similarities to Earth's so-called Quasi-Biennial Oscillation (QBO)–appear to be a defining characteristic of the middle layers of a planetary atmosphere.

Earth's QBO is regular and predictable, repeating every 28 months on average. However, it can be disrupted by events occurring at great distances from the equator of our planet–and a new study reveals that the same is true of Saturn's QPO.

"These oscillations can be thought of as a planet's heartbeat," says Leigh Fletcher of the University of Leicester, UK, lead author of the study (published in Nature Astronomy) and co-investigator of Cassini's Composite Infrared Spectrometer (CIRS). "Cassini spotted them on Saturn about a decade ago, and Earth-based observations have seen them on Jupiter, too. Although the atmospheres of the distant gas giants may appear startlingly different to our own, when we look closely we start to discover these familiar natural patterns."


Image above: VLT image of a giant anti-cyclone in Saturn's stratosphere on 20 July 2011. Credit: Image courtesy of Leigh N. Fletcher, University of Oxford, UK, and ESO.

Cassini observed Saturn from June 2004 until 15 September 2017 when the mission concluded by plunging into the gas planet's atmosphere. To better understand Saturn's QPO, Fletcher and colleagues studied data from Cassini's CIRS covering this entire time period.

"We looked at data of Saturn's 'heartbeat', which repeats roughly every 15 Earth years, and found a huge disturbance–a palpitation, to continue the metaphor–spanning 2011 to 2013, where the whole equatorial region cooled dramatically," adds co-author Sandrine Guerlet from Laboratoire de Météorologie Dynamique (LMD), France. "When we checked the timing, we realised this happened directly after the eruption of a giant storm that wrapped around Saturn's entire northern hemisphere. This suggests a link between the two events: we think that the wave activity associated with this huge storm headed towards the equator and disrupted the QPO, despite the storm raging tens of thousands of kilometres away!"

This storm was known as the Great Northern Storm. Such storms occur roughly once every Saturnian year, which is equivalent to 30 Earth years. The timing of the storm was thus serendipitous, allowing Cassini to observe it in detail from orbit around the ringed planet.


Image above: Saturn's Great Northern Storm of 2011. Image Credits: NASA/JPL-Caltech/Space Science Institute.

Although the influence of Saturnian storms was known to be substantial, this study suggests an even wider influence than expected, and confirms a connection between Saturn's QPO and remote, distinct events occurring elsewhere in the planet's atmosphere.

"We became especially excited when we compared this palpitation on Saturn to one observed in Earth's QBO in 2016: it was disturbed in a similar way by waves carrying momentum from Earth's northern hemisphere to the equator," adds Fletcher. "That disruption was unprecedented in over 60 years of monitoring the QBO–and yet we were lucky enough to capture a similar behaviour at work on Saturn with Cassini."

On Earth, this relationship between distant events in a planet's climate system is known as teleconnection. Meteorological patterns across the globe are known to be delicately linked together, and can affect one another quite significantly. A key example of this is the El Niño Southern Oscillation, which can influence temperatures and climate patterns across the Earth.


Images above: Saturn's Great Northern Storm in visible light. Image Credits: NASA/JPL-Caltech/Space Science Institute.

"It's remarkable to see this process occurring on another planet within our Solar System–especially one that's so vastly different to our own," says Nicolas Altobelli, ESA Project Scientist for the Cassini-Huygens mission.

"Cassini-Huygens may now have ended its mission, but there's still a wealth of data to explore, and a huge amount of valuable information to be gathered from the spacecraft's observations. As well as telling us more about Saturn, gas giant planets, and the Solar System in general, this study helps us better understand the Earth. This is one key driver of our research into other planets: to discover more about our own."

Notes for Editors:

The paper "Disruption of Saturn's quasi-periodic equatorial oscillation by the Great Northern Storm" by L. N. Fletcher et al. is published in the journal Nature Astronomy. doi:10.1038/s41550-017-0271-5. http://www.nature.com/articles/s41550-017-0271-5

The Principal Investigator of Cassini's Composite Infrared Spectrometer (CIRS) is Michael Flasar (NASA/GSFC, USA).

Cassini-Huygens is a cooperative project of NASA, ESA, and ASI, the Italian space agency.

More information on the mission can be found here: http://sci.esa.int/cassini-huygens

Images (mentioned), Video (mentioned), Text, Credits: ESA/Nicolas Altobelli/Laboratoire de Météorologie Dynamique (LMD)/Sandrine Guerlet/University of Leicester/Leigh Fletcher.

Best regards, Orbiter.ch

mardi 12 décembre 2017

Does New Horizons’ Next Target Have a Moon?












NASA - New Horizons Mission logo.

Dec. 12, 2017

Image Credits: NASA/JHUAPL/SwRI

Scientists were already excited to learn this summer that New Horizons’ next flyby target – a Kuiper Belt object a billion miles past Pluto -- might be either peanut-shaped or even two objects orbiting one another. Now new data hints that 2014 MU69 might have orbital company: a small moon.

That’s the latest theory coming from NASA’s New Horizons team, as it continues to analyze telescope data on the target of a New Year’s Day 2019 flyby. “We really won’t know what MU69 looks like until we fly past it, or even gain a full understanding of it until after the encounter,” said New Horizons science team member Marc Buie, of the Southwest Research Institute, Boulder, Colorado, who offered an update on the analysis of MU69 Monday at the American Geophysical Union Fall Meeting in New Orleans. “But even from afar, the more we examine it, the more interesting and amazing this little world becomes.”

The data that led to these hints at MU69’s nature were gathered over six weeks in June and July, when the team made three attempts to place telescopes in the narrow shadow of MU69 as it passed in front of a star. The most valuable recon came on July 17, when five telescopes deployed by the New Horizons team in Argentina were in the right place at the right time to catch this fleeting shadow — an event known as an occultation – and capture important data on MU69’s size, shape and orbit. That data raised the possibility that MU69 might be two like-sized objects, or what’s known as a binary.


Images above: On three occasions in June and July 2017, New Horizons mission team members attempted to track a small, distant Kuiper Belt object, 2014 MU69, as it passed in front of a star – an event known as an occultation. The colored lines mark the path of the star as seen from different telescopes on each day; the blank spaces on those lines indicate the few seconds when MU69 blocked the light from the star. Scientists are using these observations to craft a picture of MU69 and any companion bodies. Images Credits: NASA/JHUAPL/SwRI/James Tuttle Keane.

The prospect that MU69 might have a moon arose from data collected during a different occultation on July 10, by NASA's airborne Stratospheric Observatory for Infrared Astronomy (SOFIA). Focused on MU69’s expected location while flying over the Pacific Ocean, SOFIA detected what appeared to be a very short drop-out in the star’s light. Buie said further analysis of that data, including syncing it with MU69 orbit calculations provided by the European Space Agency’s Gaia mission, opens the possibility that the “blip” SOFIA detected could be another object around MU69.

“A binary with a smaller moon might also help explain the shifts we see in the position of MU69 during these various occultations,” Buie added. “It’s all very suggestive, but another step in our work to get a clear picture of MU69 before New Horizons flies by, just over a year from now.”

New Horizons probe. Image Credits: NASA/JHUAPL/SwRI

That flyby will be the most distant in the history of space exploration. Ancient Kuiper Belt object MU69, just discovered in 2014, is more than 4 billion miles (6.5 billion kilometers) from Earth. It appears to be no more than 20 miles (30 kilometers) long, or, if a binary, each about 9-12 miles (15-20 kilometers) in diameter. Like other objects in the Kuiper Belt, MU69 offers a close-up look at the remnants of the ancient planet-building process, small worlds that hold critical clues to the formation of the outer solar system.

“The occultation effort that Marc Buie and his team led for New Horizons has been invaluable in opening our eyes to the very real possibilities that MU69 is both a lot more complex than anyone suspected, and that it holds many surprises for us at flyby on New Year’s Eve and New Year’s Day, 2019,” added New Horizons Principal Investigator Alan Stern, also from Southwest Research Institute. “The allure of its exploration is becoming stronger and stronger as we learn more and more about it. It’s just fantastic!”

Related links:

NASA's airborne Stratospheric Observatory for Infrared Astronomy (SOFIA): https://www.nasa.gov/mission_pages/SOFIA/index.html

New Horizons: http://www.nasa.gov/mission_pages/newhorizons/main/index.html

Images (mentioned), Text, Credits: NASA/Bill Keeter.

Best regards, Orbiter.ch

Chandra Reveals the Elementary Nature of Cassiopeia A












NASA - Chandra X-ray Observatory patch.

December 12, 2017


Where do most of the elements essential for life on Earth come from? The answer: inside the furnaces of stars and the explosions that mark the end of some stars’ lives.

Astronomers have long studied exploded stars and their remains – known as “supernova remnants” – to better understand exactly how stars produce and then disseminate many of the elements observed on Earth, and in the cosmos at large.

Due to its unique evolutionary status, Cassiopeia A (Cas A) is one of the most intensely studied of these supernova remnants. A new image from NASA’s Chandra X-ray Observatory shows the location of different elements in the remains of the explosion: silicon (red), sulfur (yellow), calcium (green) and iron (purple). Each of these elements produces X-rays within narrow energy ranges, allowing maps of their location to be created. The blast wave from the explosion is seen as the blue outer ring.

X-ray telescopes such as Chandra are important to study supernova remnants and the elements they produce because these events generate extremely high temperatures – millions of degrees – even thousands of years after the explosion. This means that many supernova remnants, including Cas A, glow most strongly at X-ray wavelengths that are undetectable with other types of telescopes.


Chandra’s sharp X-ray vision allows astronomers to gather detailed information about the elements that objects like Cas A produce. For example, they are not only able to identify many of the elements that are present, but how much of each are being expelled into interstellar space. 



The Chandra data indicate that the supernova that produced Cas A has churned out prodigious amounts of key cosmic ingredients. Cas A has dispersed about 10,000 Earth masses worth of sulfur alone, and about 20,000 Earth masses of silicon. The iron in Cas A has the mass of about 70,000 times that of the Earth, and astronomers detect a whopping one million Earth masses worth of oxygen being ejected into space from Cas A, equivalent to about three times the mass of the sun. (Even though oxygen is the most abundant element in Cas A, its X-ray emission is spread across a wide range of energies and cannot be isolated in this image, unlike with the other elements that are shown.)



Astronomers have found other elements in Cas A in addition to the ones shown in this new Chandra image. Carbon, nitrogen, phosphorus and hydrogen have also been detected using various telescopes that observe different parts of the electromagnetic spectrum. Combined with the detection of oxygen, this means all of the elements needed to make DNA, the molecule that carries genetic information, are found in Cas A.



Oxygen is the most abundant element in the human body (about 65% by mass), calcium helps form and maintain healthy bones and teeth, and iron is a vital part of red blood cells that carry oxygen through the body. All of the oxygen in the Solar System comes from exploding massive stars. About half of the calcium and about 40% of the iron also come from these explosions, with the balance of these elements being supplied by explosions of smaller mass, white dwarf stars. 



While the exact date is not confirmed, many experts think that the stellar explosion that created Cas A occurred around the year 1680 in Earth’s timeframe. Astronomers estimate that the doomed star was about five times the mass of the Sun just before it exploded. The star is estimated to have started its life with a mass about 16 times that of the Sun, and lost roughly two-thirds of this mass in a vigorous wind blowing off the star several hundred thousand years before the explosion.



Chandra X-ray Observatory. Animation Credits: NASA/CXC

Earlier in its lifetime, the star began fusing hydrogen and helium in its core into heavier elements through the process known as “nucleosynthesis.” The energy made by the fusion of heavier and heavier elements balanced the star against the force of gravity. These reactions continued until they formed iron in the core of the star.  At this point, further nucleosynthesis would consume rather than produce energy, so gravity then caused the star to implode and form a dense stellar core known as a neutron star.

The exact means by which a massive explosion is produced after the implosion is complicated, and a subject of intense study, but eventually the infalling material outside the neutron star was transformed by further nuclear reactions as it was expelled outward by the supernova explosion.

Chandra has repeatedly observed Cas A since the telescope was launched into space in 1999. The different datasets have revealed new information about the neutron star in Cas A, the details of the explosion, and specifics of how the debris is ejected into space.



NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

Image Credits: NASA/CXC/SAO.

Read More from NASA's Chandra X-ray Observatory: http://chandra.harvard.edu/photo/2017/casa_life/

Formore Chandra images, multimedia and related materials, visit: http://www.nasa.gov/chandra

Chandra X-Ray Observatory: https://www.nasa.gov/mission_pages/chandra/main/index.html

Image (mentioned), Animation (mentioned), Text, Credits: NASA/Lee Mohon.

Greetings, Orbiter.ch

Bright Areas on Ceres Suggest Geologic Activity












NASA - Dawn Mission patch.

December 12, 2017

Occator Perspective View

Image above: The bright areas of Occator Crater -- Cerealia Facula in the center and Vinalia Faculae to the side -- are examples of bright material found on crater floors on Ceres. This is a simulated perspective view. Image Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA PSI.

If you could fly aboard NASA's Dawn spacecraft, the surface of dwarf planet Ceres would generally look quite dark, but with notable exceptions. These exceptions are the hundreds of bright areas that stand out in images Dawn has returned. Now, scientists have a better sense of how these reflective areas formed and changed over time -- processes indicative of an active, evolving world.

"The mysterious bright spots on Ceres, which have captivated both the Dawn science team and the public, reveal evidence of Ceres' past subsurface ocean, and indicate that, far from being a dead world, Ceres is surprisingly active. Geological processes created these bright areas and may still be changing the face of Ceres today," said Carol Raymond, deputy principal investigator of the Dawn mission, based at NASA's Jet Propulsion Laboratory in Pasadena, California. Raymond and colleagues presented the latest results about the bright areas at the American Geophysical Union meeting in New Orleans on Tuesday, Dec. 12.

Different Kinds of Bright Areas

Since Dawn arrived in orbit at Ceres in March 2015, scientists have located more than 300 bright areas on Ceres. A new study in the journal Icarus, led by Nathan Stein, a doctoral researcher at Caltech in Pasadena, California, divides Ceres' features into four categories.

The first group of bright spots contains the most reflective material on Ceres, which is found on crater floors. The most iconic examples are in Occator Crater, which hosts two prominent bright areas. Cerealia Facula, in the center of the crater, consists of bright material covering a 6-mile-wide (10-kilometer-wide) pit, within which sits a small dome. East of the center is a collection of slightly less reflective and more diffuse features called Vinalia Faculae. All the bright material in Occator Crater is made of salt-rich material, which was likely once mixed in water. Although Cerealia Facula is the brightest area on all of Ceres, it would resemble dirty snow to the human eye.

The Bright Stuff: New NASA Dawn Findings at Ceres

More commonly, in the second category, bright material is found on the rims of craters, streaking down toward the floors. Impacting bodies likely exposed bright material that was already in the subsurface or had formed in a previous impact event.

Separately, in the third category, bright material can be found in the material ejected when craters were formed.

The mountain Ahuna Mons gets its own fourth category -- the one instance on Ceres where bright material is unaffiliated with any impact crater. This likely cryovolcano, a volcano formed bythe gradual accumulation of thick, slowly flowing icy materials, has prominent bright streaks on its flanks.

Oxo Crater at LAMO

Image above: Oxo Crater is an example of bright material found on the rims of a crater on Ceres. Image Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI.

Over hundreds of millions of years, bright material has mixed with the dark material that forms the bulk of Ceres' surface, as well as debris ejected during impacts. That means billions of years ago, when Ceres experienced more impacts, the dwarf planet's surface likely would have been peppered with thousands of bright areas.

"Previous research has shown that the bright material is made of salts, and we think subsurface fluid activity transported it to the surface to form some of the bright spots," Stein said.

The Case of Occator

Why do the different bright areas of Occator seem so distinct from one another? Lynnae Quick, a planetary geologist at the Smithsonian Institution in Washington, has been delving into this question.

The leading explanation for what happened at Occator is that it could have had, at least in the recent past, a reservoir of salty water beneath it. Vinalia Faculae, the diffuse bright regions to the northeast of the crater's central dome, could have formed from a fluid driven to the surface by a small amount of gas, similar to champagne surging out of its bottle when the cork is removed.

Haulani Crater in Enhanced Color

Image above: Ahuna Mons, Ceres' unique tall mountain, hosts the only example of bright material on Ceres that is not associated with an impact. This is a simulated perspective view. Image Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

In the case of the Vinalia Faculae, the dissolved gas could have been a volatile substance such as water vapor, carbon dioxide, methane or ammonia. Volatile-rich salty water could have been brought close to Ceres' surface through fractures that connected to the briny reservoir beneath Occator. The lower pressure at Ceres' surface would have caused the fluid to boil off as a vapor. Where fractures reached the surface, this vapor could escape energetically, carrying with it ice and salt particles and depositing them on the surface.

Cerealia Facula must have formed in a somewhat different process, given that it is more elevated and brighter than Vinalia Faculae. The material at Cerealia may have been more like an icy lava, seeping up through the fractures and swelling into a dome. Intermittent phases of boiling, similar to what happened when Vinalia Faculae formed, may have occurred during this process, littering the surface with ice and salt particles that formed the Cerealia bright spot.

Ahuna Mons: Side View

Image above: Ahuna Mons, Ceres' unique tall mountain, hosts the only example of bright material on Ceres that is not associated with an impact. This is a simulated perspective view. Image Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

Quick's analyses do not depend on the initial impact that formed Occator. However, the current thinking among Dawn scientists is that when a large body slammed into Ceres, excavating the 57-mile-wide (92-kilometer-wide) crater, the impact may have also created fractures through which liquid later emerged.

"We also see fractures on other solar system bodies, such as Jupiter's icy moon Europa," Quick said. "The fractures on Europa are more widespread than the fractures we see at Occator. However, processes related to liquid reservoirs that might exist beneath Europa's cracks today could be used as a comparison for what may have happened at Occator in the past."

Map of Ceres' Bright Spots

Image above: This map from NASA's Dawn mission shows locations of bright material on dwarf planet Ceres. There are more than 300 bright areas, called "faculae," on Ceres. Image Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI/Caltech.

As Dawn continues the final phase of its mission, in which it will descend to lower altitudes than ever before, scientists will continue learning about the origins of the bright material on Ceres and what gave rise to the enigmatic features in Occator.

The Dawn mission is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team. For a complete list of mission participants, visit: https://dawn.jpl.nasa.gov/mission

More information about Dawn is available at the following sites:

https://www.nasa.gov/dawn

https://dawn.jpl.nasa.gov

Images (mentioned), Video, Text, Credits: NASA/JPL/Elizabeth Landau.

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