27 Jul 2016

Loneliest Young Star Seen by NASA’s Spitzer and WISE space telescopes

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Alone on the cosmic road, far from any known celestial object, a young, independent star is going through a tremendous growth spurt.

The unusual object, called CX330, was first detected as a source of X-ray light in 2009 by NASA's Chandra X-Ray Observatory while it was surveying the bulge in the central region of the Milky Way. Further observations indicated that this object was emitting optical light as well. With only these clues, scientists had no idea what this object was.

But when Chris Britt, postdoctoral researcher at Texas Tech University in Lubbock, and colleagues were examining infrared images of the same area taken with NASA's Wide-field Infrared Survey Explorer (WISE), they realized this object has a lot of warm dust around it, which must have been heated by an outburst.

Comparing WISE data from 2010 with Spitzer Space Telescope data from 2007, researchers determined that CX330 is likely a young star that had been out bursting for several years. In fact, in that three-year period its brightness had increased by a few hundred times.

Astronomers looked at data about the object from a variety of other observatories, including the ground-based SOAR, Magellan, and Gemini telescopes. They also used the large telescope surveys VVV and the OGLE-IV to measure the intensity of light emitted from CX330. By combining all of these different perspectives on the object, a clearer picture emerged.

"We tried various interpretations for it, and the only one that makes sense is that this rapidly growing young star is forming in the middle of nowhere," said Britt, lead author of a study on CX330 recently published in the Monthly Notices of the Royal Astronomical Society.

The lone star's behaviour has similarities to FU Orionis, a young out bursting star that had an initial three-month outburst in 1936-7. But CX330 is more compact, hotter and likely more massive than the FU Orionis-like objects known. The more isolated star launches faster "jets," or outflows of material that slam into the gas and dust around it.

"The disk has probably heated to the point where the gas in the disk has become ionized, leading to a rapid increase in how fast the material falls onto the star," said Thomas Maccarone, study co-author and associate professor at Texas Tech.

Most puzzling to astronomers, FU Orionis and the rare objects like it -- there are only about 10 of them -- are located in star-forming regions. Young stars usually form and feed from their surrounding gas and dust-rich regions in star-forming clouds. By contrast, the region of star formation closest to CX330 is over a thousand light-years away.

"CX330 is both more intense and more isolated than any of these young out bursting objects that we've ever seen," said Joel Green, study co-author and researcher at the Space Telescope Science Institute in Baltimore. "This could be the tip of the iceberg -- these objects may be everywhere."

In fact, it is possible that all stars go through this dramatic stage of development in their youth, but that the outbursts are too short in cosmological time for humans to observe many of them.

How did CX330 become so isolated? One idea is that it may have been born in a star-forming region, but was ejected into its present lonely pocket of the galaxy. But this is unlikely, astronomers say. Because CX330 is in a youthful phase of its development -- likely less than 1 million years old -- and is still eating its surrounding disk, it must have formed near its present location in the sky.

"If it had migrated from a star-forming region, it couldn't get there in its lifetime without stripping its disk away entirely," Britt said.

CX330 may also help scientists study the way stars form under different circumstances. One scenario is that stars form through turbulence. In this "hierarchical" model, a critical density of gas in a cloud causes the cloud to gravitationally collapse into a star. A different model, called "competitive accretion," suggests that stars begin as low-mass cores that fight over the mass of material left in the cloud. CX330 more naturally fits into the first scenario, as the turbulent circumstances would theoretically allow for a lone star to form.

It is still possible that other intermediate- to low-mass stars are in the immediate vicinity of CX330, but have not been detected yet.

When CX330 was last viewed in August 2015, it was still out bursting. Astronomers plan to continue studying the object, including with future telescopes that could view it in other wavelengths of light.

Outbursts from a young star change the chemistry of the star's disk, from which planets may eventually form. If the phenomenon is common, that means that planets, including our own, may carry the chemical signatures of an ancient disk of gas and dust scarred by stellar outbursts.

But as CX330 is continuing to devour its disk with increasing voracity, astronomers do not expect that planets are forming in its system.

"If it's truly a massive star, its lifetime is short and violent, and I wouldn't recommend being a planet around it," Green said. "You could experience some pretty intense heat for a few centuries."

The Chandra X-ray satellite Finds Evidence for Violent Stellar Merger

Coordinates (J2000) RA 15h 52m 03.27s | Dec +27° 36' 09.30" Constellation Corona Borealis

coGamma-ray bursts, or GRBs, are some of the most violent and energetic events in the Universe. Although these events are the most luminous explosions in the universe, a new study using NASA's Chandra X-ray Observatory, NASA's Swift satellite and other telescopes suggests that scientists may be missing a majority of these powerful cosmic detonations.

Astronomers think that some GRBs are the product of the collision and merger of two neutron stars or a neutron star and a black hole. The new research gives the best evidence to date that such collisions will generate a very narrow beam, or jet, of gamma rays. If such a narrow jet is not pointed toward Earth, the GRB produced by the collision will not be detected.

Collisions between two neutron stars or a neutron star and black hole are expected to be strong sources of gravitational waves that could be detected whether or not the jet is pointed towards the Earth. Therefore, this result has important implications for the number of events that will be detectable by the Laser Interferometry Gravitational-Wave Observatory (LIGO) and other gravitational wave observatories.

On September 3, 2014, NASA's Swift observatory picked up a GRB - dubbed GRB 140903A due to the date it was detected. Scientists used optical observations with the Gemini Observatory telescope in Hawaii to determine that GRB 140903A was located in a galaxy about 3.9 billion light years away, relatively nearby for a GRB.

Chandra Finds Evidence for Violent Stellar Merger

The large panel in the graphic is an illustration showing the aftermath of a neutron star merger, including the generation of a GRB. In the center is a compact object - either a black hole or a massive neutron star - and in red is a disk of material left over from the merger, containing material falling towards the compact object. Energy from this infalling material drives the GRB jet shown in yellow. In orange is a wind of particles blowing away from the disk and in blue is material ejected from the compact object and expanding at very high speeds of about one tenth the speed of light.

The image on the left of the two smaller panels shows an optical view from the Discovery Channel Telescope (DCT) with GRB 140903A in the middle of the square and a close-up X-ray view from Chandra on the right. The bright star in the optical image is unrelated to the GRB.

The gamma-ray blast lasted less than two seconds. This placed it into the "short GRB" category, which astronomers think are the output from neutron star-neutron star or black hole-neutron star collisions eventually forming either a black hole or a neutron star with a strong magnetic field. (The scientific consensus is that GRBs that last longer than two seconds result from the collapse of a massive star.)

About three weeks after the Swift discovery of GRB 140903A, a team of researchers led by Eleonora Troja of the University of Maryland, College Park (UMD), observed the aftermath of the GRB in X-rays with Chandra. Chandra observations of how the X-ray emission from this GRB decreases over time provide important information about the properties of the jet.

Specifically, the researchers found that the jet is beamed into an angle of only about five degrees based on the X-ray observations, plus optical observations with the Gemini Observatory and the DCT and radio observations with the National Science Foundation's Karl G. Jansky Very Large Array. This is roughly equivalent to a circle with the diameter of your three middle fingers held at arms length. This means that astronomers are detecting only about 0.4% of this type of GRB when it goes off, since in most cases the jet will not be pointed directly at us.

Previous studies by other astronomers had suggested that these mergers could produce narrow jets. However, the evidence in those cases was not as strong because the rapid decline in light was not observed at multiple wavelengths, allowing for explanations not involving jets.

Several pieces of evidence link this event to the merger of two neutron stars, or between a neutron star and black hole. These include the properties of the gamma ray emission, the old age and the low rate of stars forming in the GRB's host galaxy and the lack of a bright supernova. In some previous cases strong evidence for this connection was not found.

New studies have suggested that such mergers could be the production site of elements heavier than iron, such as gold. Therefore, the rate of these events is also important to estimate the total amount of heavy elements produced by these mergers and compare it with the amounts observed in the Milky Way galaxy.

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.

Magnetic reconnection on the Sun caught in the act

When two magnetic field lines connect and form a new one that “short-circuits” the magnetic field, one speaks of magnetic reconnection. These events can release large amounts of energy and play an important role in heating the upper layers of the solar atmosphere where they frequently occur. The direct observation of this phenomenon is difficult as reconnections occur on short time scales. Besides this, the structures that need to be observed are very small. An international team of researchers with participation from the Max Planck Institute for Solar System Research (MPS) now succeeded in in observing such a reconnection directly and in detail. With their results which appear today in the journal “Nature Physics” they confirm theoretical calculations.

Magnetic fields play a crucial role everywhere in the universe, be it during the formation of the first structures in the early universe, during star formation, or in activity cycles of the Sun and other stars. Often magnetic fields are visualized as strings connecting poles of opposite magnetic polarities. However, unlike strings magnetic field lines can reconnect and through this reconfigure the magnetic structure. This phenomenon is termed magnetic reconnection. During such a reconnection significant amounts of magnetic energy are converted into other forms of energy, e.g. into kinetic energy through particle acceleration of internal energy through heating. Theoretical models predict how magnetic reconnections should proceed in detail. However, a confirmation of the theory via observations proves to be difficult. Now a direct observation was made for the first time.

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Temperature enhancements (shown as red and yellow colours) of the plasmids in the X-type reconnection region. The dashed and dotted lines indicate the location of the magnetic field lines forming the X-shaped reconnection regions. In the red regions the temperature rises to several million degrees. L2 and L3 point out the location of pre-existing coronal structures that eventually recombine. The field-of-view of the region corresponds to a side length of 90.000 km. The small regions with high temperatures near the green or red arrows have diameters of about 3000 km, I.e. they are bigger than Europe.

Image: Key Laboratory of Solar Activity/NAO, Chinese Academy of Sciences

 

 

 

Through the release of energy magnetic reconnection is one of the key mechanisms for the heating of the outermost layer of the solar atmosphere, the so-called corona. For reasons not entirely understood, this layer is more than a million degrees hot, much hotter than layers below. To the naked eye the corona is only visible during a total solar eclipse. In the extreme ultraviolet it can be observed at all times with adequate instruments, for example with the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory (SDO).

It was images taken by this satellite, together with magnetic field measurements provided by the Helioseismic and Magnetic Imager (HMI) – also on board SDO - that the researchers have analysed for their study. They found a particularly important variety of magnetic reconnection, the so-called X-type reconnection. In this variety, the field lines are arranged in an X-like shape for a short time.

"We see here a clear example of X-type reconnection on the Sun with all the details predicted by theory" says Hardi Peter from MPS. He worked on the interpretation of the data relating them to theory, and is particularly intrigued by the clearly visible plasmids. These are pockets that are isolated from their surroundings by the magnetic fields. "The magnetic field lines have the form of an X with an elongated line at the crossing of the X. Here we can see small islands of magnetic field where we see an enhanced temperature, just as theory predicts". While observers looked for these roundish enhancements of temperature, it was rare that hints for these were found and never with this clarity.

This observation confirms that hot plasmids play an important role in magnetic reconnections in the solar atmosphere. It also opens new aspects in the interpretation of other phenomena on the Sun. For example they support the theory according to which spectroscopic signatures in the smallest, unresolved structures could also be caused by plasmids.

The Sun’s hidden magnetic field during grand minimum

The Sun has an 11-year cycle that involves, among other things, the occurrence and disappearance of sunspots as well as strong changes in the global magnetic field of the Sun. A study conducted by the ReSoLVE Centre of Excellence at Aalto University in Finland with participation of the Max Planck Institute for Solar System Research (MPS) in Göttingen now investigated the mechanisms underlying these long-term variations in solar activity. The research team lead by Maarit Käpylä ran a global computer model of the Sun on Finland’s most powerful super computer over a period of six months. Their results surprisingly show that the Sun's magnetic field during a grand minimum is in fact at maximum. At the same time, they created the world’s longest numerical simulation that produces a solar-like dynamo solution complete with its long-term variation.

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The most striking result of the study which was published in the May issue of the journal "Astronomy & Astrophysics" relates to the Sun’s silent periods known as grand minima, of which the Maunder Minimum is perhaps the best known. During this minimum which occurred between the years 1650 and 1700 astronomers could barely detect any sunspots despite their dedicated observing efforts. At the same time, the climate changed, and the Little Ice Age is known to have occurred in Europe, North America and China. The solar magnetic field was thought to wither during such grand minima and be so weak as not being capable of generating sunspots or other activity. The study now shows that in fact, the magnetic field was at its maximum during the Maunder Minimum.

‘The phenomena that occur in the Sun – including the cycle – change with time, so the behaviour need to be investigated over a long time span. Short-term variation is not interesting for the purposes of studying the space climate, for example,’ says Maarit Käpylä, who is the head of the DYNAMO team in the ReSoLVE (Research on SOlar Long-term Variability and Effects) Centre of Excellence and also conducts astroinformatics or computational astrophysics and data-analysis at the Department of Computer Science at Aalto University.

For their study the researchers used computer codes to simulate the processes taking place in our Sun. With their computation they created the world’s longest numerical simulation that produces a solar-like dynamo solution complete with its long-term variation. 'The increasing computer power enables us to model the Sun and its magnetic evolution in great detail. We hope that in a few years our models can answer the long standing question why we have an 11-years cycle.' says co-author Jörn Warnecke who is a Marie-Curie fellow at the MPS. Unlike observations the simulations allow to study not only the surface but provide a three-dimensional representation of the magnetically active part of the Sun.

'Thus far, we have only been able to examine what is visible on the solar surface, but simulations enable us to see below the surface. During the Maunder Minimum, the magnetic field sinks to the bottom of the convection zone and is very strong there,’ says Käpylä.

The outer layer of the Sun, the convection zone, is like a boiling kettle with its moving and heat-transferring bubbles. This not only generates a magnetic field, but also makes the entire area turbulent and extremely challenging to model. ‘The Sun as such is impossible to replicate on present-day computers – or those of the near future – due to its strong turbulence. And indeed we are not claiming that this modelling would really be the Sun. Instead, it is a 3D construction of various solar phenomena by means of which the star that runs our space climate can be better understood,’ Käpylä explains.

Maarit Käpylä will start as an independent group leader at the MPS in June 2016. From September onwards her newly formed group will conduct research on solar and stellar magnetic activity. This involves 3D numerical simulation using high performance computing modelling the Sun and other stars as well as the observation of solar-like stars to determine the properties of their magnetic cycles. The operations of the Aalto DYNAMO team  will continue under Käpylä’s direction, and both the German and the Finnish teams will focus on even larger simulations using graphical processing units.

All Sun type stars rotate in the same way

standard_fullOur Sun is an ordinary star. It is 186,000 miles in diameter, and is an incandescent ball of mainly hydrogen gas. It does not rotate as a sold body, at the equator the rotation period is about 25 earth days.

The Sun is a G-type main-sequence star (G2V) based on spectral class and is informally referred to as a yellow dwarf, making it yellowish in colour. It has a regular sunspot cycle of 11 years (we are presently edging towards sunspot minimum). Up until now astronomers did not know for certain whether others stars like the Sun had a similar rotation period.

Dr. Martin Bo Nielsen  of the International Max Planck Research School for Solar System Science, has for the first time been able to narrow in his thesis how much the rotation inside sun like stars changed. The change in rotation inside the sun is regarded as one of the principal mechanisms that drive the magnetic activity of the sun. Dr. Nielsen used current data from NASA’s Kepler satellite over several years. He determined the surface rotation by the movement of star spots and measured the rotation in deeper layers by studying vibrations inside the stars. By combining both methods, he succeeded for the first time to determine an upper limit on the change in rotation in depth and latitude of five sun-like stars.

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Indeed the rotation period matched that of the Sun, which is significant. We now know that most sun type stars behave in a similar way, which helps astronomers in the hunt for Earth like habitable planets.

The thesis was supervised by Prof. Dr. Laurent Gizon from the Institute of Astrophysics of the University of Göttingen and Dr. Hannah Schunker from Göttingen Max Planck Institute for Solar System Research.

Kontaktadressen:
Zur Absolventenfeier:
Veronika Lemburg
Georg-August-Universität Göttingen
Fakultät für Physik – Studiendekanat
E-Mail: veronika.lemburg@phys.uni-goettingen.de

Sky Diary August 2016

Aug 15 11pm N HemAug 15 11pm S Hem

 

 

 

 

 

 

 

 

 

 

 

 

 

NORTHERN HEMISPHERE AUGUST 15TH AT 23:00 UT ---- SOUTHERN HEMISPHERE AUGUST 15TH AT 23:00 UT
Click on all images to enlarge


MARS Aug 2016During August the nights are steadily getting longer. Here in the UK sunset on 1 August is at 7:48pm UT and at the end of the month the sun sets an hour earlier. In the southern hemisphere at latitude -30° the sunsets at 5:28pm on 1 August and 5:44pm at the end of the month. The time difference is due to the Earth’s axial tilt of 23½°; it is summer in the northern hemisphere so the North Pole is pointing sunwards, and the South Pole is pointing away from the Sun.

From mid month the planet Venus shining at Mag -3.9 becomes visible in the western sky after sunset. Its elongation from the sun increases from 16° to 23° during the month. Its phase is almost full, while is angular size is about 10.4 arc seconds. There are two nice photo opportunities to look forward to this month. Venus is 1.1°N of Regulus on 5 August and just 0.07°N of Jupiter on the 27th when it will be nice to see both planets close together. Incidentally, the NASA JUNO probe will passing close to Jupiter on 27th making its first science observation.

The planet Mars lies in the constellation of Scorpius during August, and is slowly fading from Mag -0.7 to -0.3. The planets small angular size is also decreasing, and this will be 11.6 arc seconds mid month so that a moderate size telescope will be needed to observe the planet. Mars is 1.8° N of Antares on 24 August and 4 ° S of Saturn on 25th August.

The planet Jupiter shining at -1.7 is visible through out August, and continues to be a lovely sight in small telescopes. There will be an occultation of Jupiter by the Moon at 04 h UT on 6th August, which will be visible from: South East Asia, Papua New Guinea, NW Australia, and Pacific Islands.

The planet Saturn shining at Mag +0.3 is visible throughout the night. It will be 12°S of the Moon on 12 August.

The planet Uranus shining at Mag 5.8 lies in the middle of Pisces (The fishes). On Aug 1st RA 01h 31m 42s DEC +8° 55’ 04” & Aug 15th RA 01h 31m 19s DEC +8° 52’ 28”

The planet Neptune shining at Mag 7.8 lies next to the star Lambda-Aquarii. On Aug 1st Mag +7.8 RA 22h 52m 56s DEC -8° 03’ 54.8”

SKY DIARY [All times are UT : Universal Time]

02 21h : New Moon 18 09h ; Full Moon
04 06h : Venus 4 deg N of the Moon 19 12h : Neptune 1.1 deg S of Moon (Occultation)
04 22h : Mercury 0.6 deg N of the Moon 20 12h : Pallas at opposition
05 09h : Venus 1.1 deg N of Regulus 22 10h : Uranus 3 deg S of the Moon
06 04h :Jupiter 0.2 deg N of Moon (Occultation) 24 04h : Mars 1.8 deg N of Antares
10 00h : Moon at apogee 25 04h : Last Quarter
10 18h : First Quarter 25 17h : Aldebaran 0.2 deg S of Moon (Occultation)
11 22h : Mars 8 deg S of the Moon 25 18h : Mars 4 deg S of the Moon
12 12h : Saturn 4 deg S of the Moon 27 05h : Mercury 5 deg S of Venus
13 18h : Saturn stationary 27 22h : Venus 0.07 deg N of Jupiter
16 21h : Mercury greatest Elong E (27 degrees) 30 01h : Mercury stationary

Moons phases

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26 Jul 2016

The 28 inch telescope return’s to Greenwich

FOURTY FIVE years ago the 28 inch refractor telescope was returned to the the Royal Greenwich Observatory from Herstmonceux, after a period of safe keeping.

The telescope was originally housed at the Royal Greenwich Observatory up until the start of World War 2, then the telescope was stored in a safe place. Just as well because a bomb fell nearby damaging the telescope dome it was housed in. Following the last war the move to Herstmonceux was planned because Greenwich Park had become unsuitable a site for observations. The onion dome was taken down and the 28 inch was set up at a new dome at Herstmonceux castle.

Sir Patrick Moore was on hand to see the 28 inch return to the Royal Greenwich Observatory on 23 October 1971, and he made a Sky at Night program about it that was broadcast that December. These exclusive images are from Patrick Moore’s photo archive.

This month I went along to meet the Curator of the Royal Greenwich Observatory, Dr Louise Devoy, to see the magnificent 28 inch refractor in its onion shape dome, and learn about the other equatorial telescopes that was housed at the observatory; you can see my program on 29 July ….

Richard Pearson F.R.A.S.

25 Jul 2016

Our New YouTube Channel is up & running

I have now set up a new YouTube site for all of my Astronomy programs, a one stop shop for everyone to enjoy watching FREE educational programs on various topics relating to Astronomy & Space.

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Here you will also find 6 dedicated playlist that will allow you to spend an evening watching some of the best Astronomy programs while the skies outside are cloudy or it’s raining, and you just wish to pass the time.

Astronomy & Space 2016: All of the programs that have been broadcast since January of this year. My new program for August ‘Equatorial telescopes at the Royal Greenwich Observatory’ can also bee found here.

Astronomy & Space 2015: All of season two programs of Astronomy & Space

Astronomy & Space 2014: All of season one programs of Astronomy & Space

History of Astronomy: A channel dedicated to various aspects of the history of Astronomy

The Stars: Guides to the Winter, Spring, Summer & Autumn constellations. Stars of the far south, Supernovae and gravitational waves, along with a look at the oldest stars and the origin of the Universe.

The planets: The Sun, Moon, and planets of our Solar System.

18 Jul 2016

NASA release New image of Zadeni crater on Ceres taken by the DAWN spacecraft

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With an extended mission NASA’s DAWN spacecraft is still in orbit around Ceres, the largest of the minor planets. This moody scene on Ceres, above right, is located within Zadeni Crater, named for the ancient Georgian god of bountiful harvest. Zadeni is approximately 76 miles (120 kilometres) in diameter. Dawn took this image on June 15, 2016, from its low-altitude mapping orbit, at a distance of about 240 miles (385 kilometres) above the surface. The image resolution is 120 feet (35 meters) per pixel.

The image on the left is of the same crater taken at a greater height above the surface. For more information about the Dawn mission, visit http://dawn.jpl.nasa.gov.

Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

13 Jul 2016

Outburst Brings Water Snow Line Into View

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The constellation of Orion is in the news for the second time this week.

The Atacama Large radio telescope Array (ALMA) has made the first ever resolved observation of a water snow line within a protoplanetary disc. This line marks where the temperature in the disc surrounding a young star drops sufficiently low for snow to form. A dramatic increase in the brightness of the young star V883 Orionis flash heated the inner portion of the disc, pushing the water snow line out to a far greater distance than is normal for a protostar, and making it possible to observe it for the first time. The results are published in the journal Nature on 14 July 2016.

Young stars are often surrounded by dense, rotating discs of gas and dust, known as protoplanetary discs, from which planets are born. The heat from a typical young solar-type star means that the water within a protoplanetary disc is gaseous up to distances of around 3 au from the star [280 m miles] — less than 3 times the average distance between the Earth and the Sun. Further out, due to the extremely low pressure, the water molecules transition directly from a gaseous state to form a patina of ice on dust grains and other particles. The region in the protoplanetary disc where water transitions between the gas and solid phases is known as the water snow line.

Shifting water snowline in V883 OrionisBut the star V883 Orionis is unusual. A dramatic increase in its brightness has pushed the water snow line out to a distance of around 40 au (about 6 billion kilometres or roughly the size of the orbit of the dwarf planet Pluto in our Solar System). This huge increase, combined with the resolution of ALMA at long baselines, has allowed a team led by Lucas Cieza (Millennium ALMA Disk Nucleus and Universidad Diego Portales, Santiago, Chile) to make the first ever resolved observations of a water snow line in a protoplanetary disc.

The sudden brightening that V883 Orionis experienced is an example of what occurs when large amounts of material from the disc surrounding a young star fall onto its surface. V883 Orionis is only 30% more massive than the Sun, but thanks to the outburst it is experiencing, it is currently a staggering 400 times more luminous — and much hotter.

The star V883 Orionis in the constellation of OrionLead author Lucas Cieza explains: “The ALMA observations came as a surprise to us. Our observations were designed to look for disc fragmentation leading to planet formation. We saw none of that; instead, we found what looks like a ring at 40 au. This illustrates well the transformational power of ALMA, which delivers exciting results even if they are not the ones we were looking for.”

The bizarre idea of snow orbiting in space is fundamental to planet formation. The presence of water ice regulates the efficiency of the coagulation of dust grains — the first step in planet formation. Within the snow line, where water is vaporised, smaller, rocky planets like our own are believed to form. Outside the water snow line, the presence of water ice allows the rapid formation of cosmic snowballs, which eventually go on to form massive gaseous planets such as Jupiter.

The discovery that these outbursts may blast the water snow line to about 10 times its typical radius is very significant for the development of good planetary formation models. Such outbursts are believed to be a stage in the evolution of most planetary systems, so this may be the first observation of a common occurrence. In that case, this observation from ALMA could contribute significantly to a better understanding of how planets throughout the Universe formed and evolved.

The Earth in Space

Running Time: 40 minutes

Acknowledgements: The European Space Agency, The European Southern Observatory, NASA/Goddard, and Tom Pickett.

On 18 June 2015 British astronaut Tim Peake safely returned home after spending the last 6 months on board the International Space Station. Tim has had a unique vantage point to see the Earth from space, so now seems a good time to mark the occasion by taking a look at our planet in more detail.

In August our program comes from The Royal Greenwich Observatory. We will be joined by special guest Dr. Louise Devoy who is the curator of instruments there. She will be showing us the magnificent 28 inch refractor telescope, and describing the scopes’ fascinating history.

Richard Pearson F.R.A.S.

Astronomers study the inside of rotating Black Holes

PIA20697_fig1

This artist's impression depicts the accretion disc surrounding a black hole, in which the inner region of the disc precesses. "Precession" means that the orbit of material surrounding the black hole changes orientation around the central object.

Ashampoo_Snap_2016.07.13_12h09m26s_001_The European Space Agency's orbiting X-ray observatory, XMM-Newton, has proved the existence of a "gravitational vortex" around a black hole. The discovery, aided by NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) mission, solves a mystery that has eluded astronomers for more than 30 years, and will allow them to map the behaviour of matter very close to black holes. It could also open the door to future investigations of Albert Einstein's general relativity.

Matter falling into a black hole heats up as it plunges to its doom. Before it passes into the black hole and is lost from view forever, it can reach millions of degrees. At that temperature it shines X-rays into space.

In the 1980s, pioneering astronomers using early X-ray telescopes discovered that the X-rays coming from stellar-mass black holes in our galaxy flicker. The changes follow a set pattern. When the flickering begins, the dimming and re-brightening can take 10 seconds to complete. As the days, weeks and then months progress, the period shortens until the oscillation takes place 10 times every second. Then, the flickering suddenly stops altogether.

The phenomenon was dubbed the Quasi Periodic Oscillation (QPO). "It was immediately recognized to be something fascinating because it is coming from something very close to a black hole," said Adam Ingram, University of Amsterdam, the Netherlands, who began working to understand QPOs for his doctoral thesis in 2009.

During the 1990s, astronomers had begun to suspect that the QPOs were associated with a gravitational effect predicted by Einstein's general relativity: that a spinning object will create a kind of gravitational vortex.

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"It is a bit like twisting a spoon in honey. Imagine that the honey is space and anything embedded in the honey will be "dragged" around by the twisting spoon," explained Ingram.  "In reality, this means that anything orbiting a spinning object will have its motion affected." In the case of an inclined orbit, it will "precess." This means that the whole orbit will change orientation around the central object. The time for the orbit to return to its initial condition is known as a precession cycle.

In 2004, NASA launched Gravity Probe B to measure this so-called Lens-Thirring effect around Earth. After painstaking analysis, scientists confirmed that the spacecraft would turn through a complete precession cycle once every 33 million years.

Around a black hole, however, the effect would be much more noticeable because of the stronger gravitational field. The precession cycle would take just a matter of seconds or less to complete. This is so close to the periods of the QPOs that astronomers began to suspect a link.

Ingram began working on the problem by looking at what happened in the flat disc of matter surrounding a black hole. Known as an accretion disc, it is the place where material gradually spirals inwards towards the black hole. Scientists had already suggested that, close to the black hole, the flat accretion disc puffs up into a hot plasma, in which electrons are stripped from their host atoms. Termed the hot inner flow, it shrinks in size over weeks and months as it is eaten by the black hole. Together with colleagues, Ingram published a paper in 2009 suggesting that the QPO is driven by the Lens-Thirring precession of this hot flow. This is because the smaller the inner flow becomes, the closer to the black hole it would approach and so the faster its Lens-Thirring precession cycle would be. The question was: how to prove it?

"We have spent a lot of time trying to find smoking gun evidence for this behaviour," said Ingram.

The answer is that the inner flow is releasing high-energy radiation that strikes the matter in the surrounding accretion disc, making the iron atoms in the disc shine like a fluorescent light tube. The iron releases X-rays of a single wavelength -- referred to as "a spectral line."

Because the accretion disc is rotating, the iron line has its wavelength distorted by the Doppler effect. Line emission from the approaching side of the disc is squashed -- blue shifted -- and line emission from the receding disc material is stretched -- red shifted. If the inner flow really is precessing, it will sometimes shine on the approaching disc material and sometimes on the receding material, making the line wobble back and forth over the course of a precession cycle.

Seeing this wobbling is where XMM-Newton came in. Ingram and colleagues from Amsterdam, Cambridge, Southampton and Tokyo applied for a long-duration observation that would allow them to watch the QPO repeatedly. They chose black hole H 1743-322, which was exhibiting a four-second QPO at the time. They watched it for 260,000 seconds with XMM-Newton. They also observed it for 70,000 seconds with NASA's NuSTAR X-ray observatory.

"The high-energy capability of NuSTAR was very important," Ingram said. "NuSTAR confirmed the wobbling of the iron line, and additionally saw a feature in the spectrum called a 'reflection hump' that added evidence for precession."

After a rigorous analysis process of adding all the observational data together, they saw that the iron line was wobbling in accordance with the predictions of general relativity. "We are directly measuring the motion of matter in a strong gravitational field near to a black hole," says Ingram.

This is the first time that the Lens-Thirring effect has been measured in a strong gravitational field. The technique will allow astronomers to map matter in the inner regions of accretion discs around black holes. It also hints at a powerful new tool with which to test general relativity.

Einstein's theory is largely untested in such strong gravitational fields. So if astronomers can understand the physics of the matter that is flowing into the black hole, they can use it to test the predictions of general relativity as never before - but only if the movement of the matter in the accretion disc can be completely understood.

"If you can get to the bottom of the astrophysics, then you can really test the general relativity," says Ingram. A deviation from the predictions of general relativity would be welcomed by a lot of astronomers and physicists. It would be a concrete signal that a deeper theory of gravity exists.

Larger X-ray telescopes in the future could help in the search because they are more powerful and could more efficiently collect X-rays. This would allow astronomers to investigate the QPO phenomenon in more detail. But for now, astronomers can be content with having seen Einstein's gravity at play around a black hole.

"This is a major breakthrough since the study combines information about the timing and energy of X-ray photons to settle the 30-year debate around the origin of QPOs. The photon-collecting capability of XMM-Newton was instrumental in this work," said Norbert Schartel, ESA Project Scientist for XMM-Newton.

12 Jul 2016

Astronomers Look deep inside the Orion Nebula

Very Large Telescope infrared images reveal an unexpected horde of
Low-mass stars, Brown dwarfs, and Planetary-mass-objects

A deep infrared view of the Orion Nebula from HAWK-I

Ashampoo_Snap_2016.07.12_00h21m38s_002_An international team has made use of the power of the HAWK-I infrared instrument on ESO’s Very Large Telescope (VLT) in Chile to produce the deepest and most comprehensive view of the Orion Nebula to date. Not only has this led to an image of spectacular beauty, but it has revealed a great abundance of faint brown dwarfs and isolated planetary-mass objects. The very presence of these low-mass bodies provides an exciting insight into the history of star formation within the nebula itself.

The famous Orion Nebula spans about 24 light-years within the constellation of Orion, and is visible from Earth with the naked eye, as a fuzzy patch in Orion’s sword. Some nebulae, like Orion, are strongly illuminated by ultraviolet radiation from the many hot stars born within them, such that the gas is ionised and glows brightly.

The relative proximity of the Orion Nebula makes it an ideal test bed to better understand the process and history of star formation, and to determine how many stars of different masses form.

potw1239aAccounting for the contamination of background stars and galaxies, the team found that Orion Nebula Cloud’s Initial Mass Function is bimodal with distinct peaks at about 0.25 and 0:025M separated by a pronounced dip at the hydrogen burning limit (0.08M ), with a depth of about a factor 2–3 below the log-normal distribution. Apart from 920 low mass stars (M < 1:4M ) the IMF contains 760 brown dwarf candidates and 160 isolated planetary mass object candidates with M > 0:005M , hence about ten times more sub-stellar candidates than known before. The sub-stellar IMF peak at 0.025M could be caused by Brown Dwarfs and Isolated Planetary Mass Objects which have been ejected from multiple systems during the early star-formation process or from circumstellar disks.

Amelia Bayo (Universidad de Valparaíso, Valparaíso, Chile; Max-Planck Institute für Astronomie, Königstuhl, Germany), a co-author of the new paper and member of the research team, explains why this is important: "Understanding how many low-mass objects are found in the Orion Nebula is very important to constrain current theories of star formation. We now realise that the way these very low-mass objects form depends on their environment."

This new image has caused excitement because it reveals a unexpected wealth of very-low-mass objects, which in turn suggests that the Orion Nebula may be forming proportionally far more low-mass objects than closer and less active star formation regions.

Highlights from a new infrared image of the Orion NebulaAstronomers count up how many objects of different masses form in regions like the Orion Nebula to try to understand the star-formation process. Before this research the greatest number of objects were found with masses of about one quarter that of our Sun. The discovery of a plethora of new objects with masses far lower than this in the Orion Nebula has now created a second maximum at a much lower mass in the distribution of star counts.

These observations also hint tantalisingly that the number of planet-sized objects might be far greater than previously thought. Whilst the technology to readily observe these objects does not exist yet, ESO’s future European Extremely Large Telescope (E-ELT), scheduled to begin operations in 2024, is designed to pursue this as one of its goals.

Lead scientist Holger Drass (Astronomisches Institute, Ruhr-Universität Bochum, Bochum, Germany; Pontificia Universidad Católica de Chile, Santiago, Chile) enthuses: “Our result feels to me like a glimpse into a new era of planet and star formation science. The huge number of free-floating planets at our current observational limit is giving me hope that we will discover a wealth of smaller Earth-sized planets with the E-ELT.

Chilean FIDEOS instrument begins operations on the ESO 1-metre telescope

ESO 1-metre telescope

The new FIDEOS (Fiber Dual Echelle Optical Spectrograph) instrument has made its first observations — known as  first light — collecting its first scientific data and confirming its successful operation. FIDEOS is operating on the ESO 1-metre telescope at La Silla in Chile, the first telescope to be installed on the site back in 1966. It is one of the telescopes no longer run directly by ESO, and is now operated by the Universidad Católica del Norte (UCN), having been refurbished by the Centro de Astro Ingeniería de la Universidad Católica de Chile (AIUC).

Ashampoo_Snap_2016.07.12_00h21m38s_002_ann16046bFIDEOS, which was designed and assembled by a team from the AIUC, is a high-resolution spectrograph that is optimised for determining radial velocities of stars to high precision, thereby identifying candidate exoplanets. A star that is orbited by an exoplanet is made to “wobble” by the gravitational effect of the exoplanet’s mass as it orbits around its host star. Very precise measurements of the radial velocities of stars can therefore indicate the presence of exoplanets. FIDEOS will use this method in its primary role as an exoplanet hunter, achieving high stability and the expectation of obtaining extremely high precision measurements.

Significantly, this is the first time that an instrument installed at an international observatory such as La Silla has been produced entirely by a Chilean institute. The project was funded by FONDEF (Fondo de Fomento al Desarrollo Científico y Tecnológico) at CONICYT (Comisión Nacional de Investigación Científica y Tecnológica).

11 Jul 2016

Project scientists release new Comet 67P images

The_comet_s_two_lobes

The methods used by Rosetta scientists to determine that Comet 67P/Churyumov–Gerasimenko’s shape arises from two separately forming comets.

Ashampoo_Snap_2016.07.13_12h09m26s_001_Left: high-resolution OSIRIS images were used to visually identify over 100 terraces (green) or strata – parallel layers of material (red dashed lines) – in exposed cliff walls and pits all over the comet surface (top: Hathor and surrounding regions on comet’s small lobe; bottom: Seth region on comet’s large lobe).

Middle: a 3D shape model was used to determine the directions in which the terraces/strata are sloping and to visualise how they extend into the subsurface. The strata ‘planes’ are shown superimposed on the shape model (left panel) and alone (right panel) and show the planes coherently oriented all around the comet, in two separate bounding envelopes (scale bar indicates angular deviation between plane and local gravity vector).

Right: local gravity vectors visualised on the comet shape model perpendicular to the terrace/strata planes further realise the independent nature of the two lobes.

Layers_on_the_comet_s_surface

A selection of high-resolution OSIRIS images used to identify patterns in Comet 67P/Churyumov–Gerasimenko’s extensive layering.

Top left: main terraces (green) and exposed layers (red dashed lines) seen in the Seth region on the comet’s large lobe. The terraces become more inclined towards the comet neck region. The close-up shows terraces in two locations (thin white and yellow arrows) together with examples of parallel lineaments (large white arrows) that define a continuous stratification.

Bottom left: outline of exposed layers (red dashed lines) primarily in the Imhotep and Ash region on the comet’s large lobe. The terraces in Ash change their dip direction from that in Seth to very slightly dip towards Imhotep. Some layers are also indicated on the comet’s small lobe in the background. The close-up shows the details of the parallel layers in a section along the Imhotep-Ash boundary.

Top right: main layers (red dashed lines) and cross-cutting fractures (blue dashed lines) in the Hathor cliff face on the comet’s small lobe. No abrupt change in the orientation of the layers is seen between Hathor and Ma’at. The close-up shows stratification in an alcove at the Hathor-Anuket boundary, providing a view of the Anuket inner structure, which appears to extend under Ma’at. Terraces on Anuket (white arrows) are seen in different orientations to neighbouring regions. Taken together, this reinforces the idea that Hathor represents the inner comet structure that has been exposed, with Anuket as the remnant.

Bottom right: layers (white dashed lines) at the boundary of Anubis and Seth on the comet’s large lobe. This continuous scarp suggests the thickness of the Seth region is about 150 m. The three arrow heads point to a terrace margin in Anubis and the single white arrow points to a terrace in the adjacent Atum region.

Comet_cliffs

  • This striking view of Comet 67P/Churyumov–Gerasimenko reveals portions of both comet lobes, with dramatic shadows on the 'neck' region between them. It was taken by Rosetta’s navigation camera (NavCam) on 30 June 2016, from a distance of 25.8 km, and measures about 2.3 km across.
  • Since reaching the comet on 6 August 2014, Rosetta has extensively mapped its surface. The comet nucleus has a curious shape consisting of two lobes that are often referred to as the 'head' and the 'body'.

    Depicted in the lower right part of the image is the region Hathor, a very intriguing portion of the comet head, named after the ancient Egyptian deity of love, music and beauty. In this region, the head declines steeply towards the neck and body of the comet.

    This view shows a good fraction of the 900-m high cliff that forms Hathor, with marked linear features crossing the region from left to right. Perpendicular to these, additional streaks and even small terraces can be seen.

    Beyond the cliff of Hathor, on the right, are hints of the Ma'at region, named after the ancient Egyptian goddess of truth and balance.

    In the upper right corner, smoother patches of the large comet lobe, or body, are visible, covered in dust and boulders. The large lobe casts its shadow on the comet's neck, which separates the two lobes and is hidden from view in this image.

  • Copyright ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; M. Massironi et al

Jabbah | a lovely multiple double star in Scorpius

606218main_pia14881-43_fullJabbah is the name of the bright star right of centre, surrounded by a red coloured dust cloud. The Arabic name means "the forehead of the scorpion."

Mag +4.0
Right ascension 16h 11m 59.7s 
Declination −19° 27' 39

It is at least a quintuple star, probably a septuplet, consisting of two close groups that are separated by 41 arc seconds. The brighter group, Nu Scorpii A and B, is split by 1.3" and composed of spectral type B2 sub giants. The fainter pair, Nu Scorpii C and D, are spectral type B8 and B9 main sequence dwarfs split by 2.4". Nu Scorpii A is itself a semi-detached spectroscopic binary, having a fainter B-type companion separated by approximately 0.3 mas.

This view from NASA's Wide-field Infrared Survey Explorer, or WISE, takes in an area of the sky in the constellation of Scorpius surrounding Jabbah, which is larger than a grid of eight by eight full moons.

Though Jabbah appears to be a single star, it is actually a whole system of stars (possibly as many as seven), each of which is many times more massive, larger, hotter and more luminous than the sun. The Jabbah system is located about 440 light-years away from us and lights up a giant cloud of dust and gas near it. The cloud near Jabbah is designated IC 4592, and the portion farthest away to the far left in the image is IC 4601.

The other bright stars in this image are mostly part of the "Upper Scorpius Association" and were probably once all born in the same cluster about 5 million years ago. These stars are all moving apart as the cluster ages, and are probably no longer bound to each other by gravity.

Scorpio

Another star of interest in the image is 9 Scorpii, located in the lower right corner with the bright red dust cloud primarily on one side of it. 9 Scorpii is another very massive star that is probably a member of the Upper Scorpius Association. It is also moving through space at an enormous speed of 1,000 kilometres per second (224,000 miles per hour). With such a speed, the star may be a runaway star once in a system with a more massive member that exploded as a supernova and sent 9 Scorpii zooming through space. The red cloud near it may be a bow shock in front of it similar to the stars called Alpha Cam and Zeta Oph.

This image was made from observations by all four infrared detectors aboard WISE. Blue and cyan (blue-green) represent infrared light at wavelengths of 3.4 and 4.6 microns, which is primarily from stars, the hottest objects pictured. Green and red represent light at 12 and 22 microns, which is primarily from warm dust.

Image credit: NASA/JPL-Caltech/UCLA

10 Jul 2016

Where on Mars Does Carbon Dioxide Frost Form Often?

PIA20758

ON MARS the Autumn Equinox was on 4 July, so day & night are about equal over the planet while the autumn season has just begun

Water on Mars H2O is associated with the polar ice caps which is also the place to find Carbon Dioxide ice, so it comes as no surprise these latest finding confirm. What is fascinating is that there are high levels of C0over the volcanic Tharsis area, which is a vast volcanic plateau cantered near the equator in the western hemisphere of Mars. The region is home to the largest volcanoes in the Solar System, including the three enormous shield volcanoes Arsia Mons, Pavonis Mons, and Ascraeus Mons, which are collectively known as the Tharsis Montes.

There are also high levels of Carbon Dioxide in the Valles Marineris, which is a system of canyons that runs along the Martian surface east of the Tharsis region. 2,500 miles long, 120 miles wide and up to 23,000 feet deep.

This map shows the frequency of carbon dioxide frost's presence at sunrise on Mars, as a percentage of days year-round. Carbon dioxide ice more often covers the ground at night in some mid-latitude regions than in polar regions, where it is generally absent for much of summer and Autumn.

Colour coding is based on data from the Mars Climate Sounder instrument on NASA's Mars Reconnaissance Orbiter. A colour-key bar below the map shows how colours correspond to frequencies. Yellow indicates high frequencies, identifying areas where carbon dioxide ice is present on the ground at night during most of the year. Blue identifies areas where it is rarely present; red is intermediate. Areas without colour coding are regions where carbon dioxide frost is not detected at any time of year.

The areas with highest frequency of overnight carbon dioxide frost correspond to regions with surfaces of loose dust, which do not retain heat well, compared to rockier areas. Those areas also have some of the highest mid-afternoon temperatures on the planet. The dust surface heats up and cools off rapidly.

Six science instruments on the Mars Reconnaissance Orbiter have been examining Mars since 2006. NASA's Jet Propulsion Laboratory, a division of the Caltech in Pasadena, California, manages the mission for NASA's Science Mission Directorate in Washington and built the Mars Climate Sounder. Lockheed Martin Space Systems of Denver built the orbiter and operates it in collaboration with JPL.

 
Image Credit: NASA/JPL-Caltech

8 Jul 2016

Globular cluster M2 in Aquarius likely ‘formed inside a dwarf galaxy’

Messier-30-NGC-7099-991x1024THE BRIGHT Mag +6.2 globular cluster Messier 2 lies in the constellation of Aquarius at Right ascension 21h 33m 27.02s Declination –00° 49′ 23.7″ and is a favourite among Astrophotographers as it is relatively easy to photograph.

Ashampoo_Snap_2016.07.08_02h32m45s_003_A team of astronomers led by P.B. Kuzma from the Research School of Astronomy and Astrophysics, Australian National University, Canberra, Australia, have now studied M2 in great detail, and conclude that M2 likely formed inside a dwarf galaxy that was later accreted into the Milky Way halo and destroyed.

“We have searched the region surrounding the Milky Way globular cluster M2 for the presence of low surface brightness substructures, using deep wide field imaging mosaics from MegaCam and DECam. We use the observed colour magnitude diagram to identify likely cluster members across the respective fields of view, and that a composite radial surface density profile indicates substantial extra-tidal populations extending well beyond the literature value for the tidal radius of 12:50 arc minutes. These remote M2 populations entirely ll our 0.8 x 0.8 degree MegaCam mosaic, and it is only with a 13 square degree mosaic from DECam that we are able to identify a diffuse, extended envelope surrounding the cluster to a radial distance of at least 60 arc minutes ( 210 pc), five times larger than the nominal tidal radius. Our two-dimensional density map reveals the envelope to be mildly elliptical, with e = 0:11 0:06 and the major axis oriented at a position angle of = 69 degrees east of north. There is no evidence for a distinct stellar stream or tidal tails, although we identify a small but statistically significant over-density of M2 stars beyond the apparent edge of the envelope, that follows a potential axis extending from north-east to south-west in broad agreement with the orientation of the envelope.

Ashampoo_Snap_2016.07.08_01h36m29s_002_

The nature and origin of the diffuse envelope surrounding M2 is not well understood. One possibility is that this structure is due to the dynamical evolution of the cluster, although how external factors such as tidal shocking might give rise to such an envelope, as opposed to the distinct tidal tails observed around disrupting globular clusters and seen in numerical simulations, is not clear. Numerous globular clusters have been found with power-law extended without tidal tails, though none of these studies have a found an envelope to the size of, or exhibiting a profile a shallow as, M2. An alternative scenario is that M2 was originally formed in a dwarf galaxy that was later accreted into the Milky Way halo and destroyed { in this case the envelope might constitute the final remaining vestiges of the host. A similar structure has been observed to surround the globular cluster NGC 1851, and simulations of this system have shown that the nucleus of a dwarf galaxy can possess a halo-like structure surrounding the dense core long after the majority of the original dwarf and its dark matter halo have been stripped away and lost. In this context it is intriguing that M2 is a member of a small group of massive Milky Way globular clusters (also including NGC 1851) observed to exhibit internal dispersions in both iron abundance and s-process elements. Deeper imaging of the region around M2, together with spectroscopic velocity and abundance measurements of stars in the envelope, will be required to understand the origin of this structure with greater certainty.”

Article:  P. B. Kuzma, G. S. Da Costa, A. D. Mackey, and T. A. Roderick:  The Outer Envelopes of Globular Clusters. I. NGC 7089 (M2) MNRAS stw1561 doi:10.1093/mnras/stw1561 first published online July 1, 2016

NEW images of Ceres from NASA’s DAWN spacecraft

PIA20825 3DThis image shows the limb of Ceres from above an equatorial region east of Kirnis Crater. The scene is cantered at approximately 10 degrees north latitude, 284 degrees east longitude.

NASA's Dawn spacecraft took this image on June 13, 2016, from its low-altitude mapping orbit, at a distance of about 240 miles (385 kilometres) above the surface. The image resolution is 120 feet (35 meters) per pixel.

THE WHITE SPOT

The brightest area on Ceres, located in the mysterious Occator Crater, has the highest concentration of carbonate minerals ever seen outside Earth, according to a new study from scientists on NASA's Dawn mission. The study, published online in the journal Nature, is one of two new papers about the makeup of Ceres.

"This is the first time we see this kind of material elsewhere in the solar system in such a large amount," said Maria Cristina De Sanctis, lead author and principal investigator of Dawn's visible and infrared mapping spectrometer. De Sanctis is based at the National Institute of Astrophysics, Rome.

At about 80 million years old, Occator is considered a young crater. It is 57 miles (92 kilometres) wide, with a central pit about 6 miles (10 kilometres) wide. A dome structure at the centre, covered in highly reflective material, has radial and concentric fractures on and around it.

De Sanctis' study finds that the dominant mineral of this bright area is sodium carbonate, a kind of salt found on Earth in hydrothermal environments. This material appears to have come from inside Ceres, because an impacting asteroid could not have delivered it. The upwelling of this material suggests that temperatures inside Ceres are warmer than previously believed. Impact of an asteroid on Ceres may have helped bring this material up from below, but researchers think an internal process played a role as well.

More intriguingly, the results suggest that liquid water may have existed beneath the surface of Ceres in recent geological time. The salts could be remnants of an ocean, or localized bodies of water, that reached the surface and then froze millions of years ago.

"The minerals we have found at the Occator central bright area require alteration by water," De Sanctis said. "Carbonates support the idea that Ceres had interior hydrothermal activity, which pushed these materials to the surface within Occator."

PIA20694_hires 3D2The spacecraft's visible and infrared mapping spectrometer examines how various wavelengths of sunlight are reflected by the surface of Ceres. This allows scientists to identify minerals that are likely producing those signals. The new results come from the infrared mapping component, which examines Ceres in wavelengths of light too long for the eye to see.

Last year, in a Nature study, De Sanctis' team reported that the surface of Ceres contains ammoniated phyllosilicates, or clays containing ammonia. Because ammonia is abundant in the outer solar system, this finding introduced the idea that Ceres may have formed near the orbit of Neptune and migrated inward. Alternatively, Ceres may have formed closer to its current position between Mars and Jupiter, but with material accumulated from the outer solar system.

The new results also find ammonia-bearing salts -- ammonium chloride and/or ammonium bicarbonate -- in Occator Crater. The carbonate finding further reinforces Ceres' connection with icy worlds in the outer solar system. Ammonia, in addition to sodium carbonate and sodium bicarbonate found at Occator, has been detected in the plumes of Enceladus, an icy moon of Saturn known for its geysers erupting from fissures in its surface. Such materials make Ceres interesting for the study of astrobiology.

"We will need to research whether Ceres' many other bright areas also contain these carbonates," De Sanctis said.

A separate Nature study in 2015 by scientists with the Dawn framing camera team hypothesized that the bright areas contain a different kind of salt: magnesium sulphate. But the new findings suggest sodium carbonate is the more likely constituent.

"It's amazing how much we have been able to learn about Ceres' interior from Dawn's observations of chemical and geophysical properties. We expect more such discoveries as we mine this treasure trove of data," said Carol Raymond, deputy principal investigator for the Dawn mission, based at NASA's Jet Propulsion Laboratory, Pasadena, California.

Dawn science team members have also published a new study about the makeup of the outer layer of Ceres in Nature Geoscience, based on images from Dawn's framing camera. This study, led by Michael Bland of the U.S. Geological Survey, Flagstaff, Arizona, finds that most of Ceres' largest craters are more than 1 mile (2 kilometres) deep relative to surrounding terrain, meaning they have not deformed much over billions of years. These significant depths suggest that Ceres' subsurface is no more than 40 percent ice by volume, and the rest may be a mixture of rock and low-density materials such as salts or chemical compounds called clathrates. The appearance of a few shallow craters suggests that there could be variations in ice and rock content in the subsurface.