Posted on by Anne Minard

New Image: VLT Captures Tumult of Starbirth

Credit: ESO

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Newborn stars spew material into the surrounding gas and dust, creating a surreal landscape of glowing arcs, blobs and streaks — and ESO’s Very Large Telescope (VLT) has caught some of them on candid camera. This new image, released today, hails from NGC 6729, a nearby star-forming region in the constellation Corona Australis.

Star formation in the constellation of Corona Australis. Courtesy of ESO

The stellar nursery NGC 6729 (RA 19h 01m 54.1s; dec -36° 57′ 12″)  is part of one of the closest stellar nurseries to Earth and therefore one of the best studied. The new VLT image gives a close-up view of a section of this strange and fascinating region.

The data were selected from the ESO archive by Sergey Stepanenko of the Ukraine, as part of the Hidden Treasures competition. The 2010 competition gave amateur astronomers the chance to search through ESO’s astronomical archives, hoping to find a well-hidden gem that needed polishing by the entrants. Participants vied for prizes, including a free trip to see the VLT in Chile for the overall winner. Stepanenko’s picture of NGC 6729 was ranked third.

Stars form deep within molecular clouds and the earliest stages of their development cannot be seen in visible-light telescopes because they kick out so much dust. Although very young stars at the upper left of the image cannot be seen directly, the havoc they have wreaked on their surroundings dominates the picture. High-speed jets of material that travel away from the baby stars at velocities as high as one million kilometers per hour are slamming into the surrounding gas and creating shock waves. The shocks cause the gas to shine and create the strangely-colored glowing arcs and blobs known as Herbig–Haro objects.

The astronomers George Herbig and Guillermo Haro were not the first to see one of the objects that now bear their names, but they were the first to study the spectra of these strange objects in detail. They realized that they were not just clumps of gas and dust that reflected light, or glowed under the influence of the ultraviolet light from young stars — but were a new class of objects associated with ejected material in star-forming regions.

Credit: ESO

In this view, the Herbig–Haro objects form two lines marking out the probable directions of ejected material. One stretches from the upper left to the lower center, ending in the bright, circular group of glowing blobs and arcs at the lower center. The other starts near the left upper edge of the picture and extends towards the center right. The peculiar sabre-shaped bright feature at the upper left is probably mostly due to starlight being reflected from dust and is not a Herbig–Haro object.

The enhanced-color picture was created from images taken using the VLT’s FORS1 instrument. Images were taken through two different filters that isolate the light coming from glowing hydrogen (shown as orange) and glowing ionized sulphur (shown as blue). The different colors in different parts of this violent star formation region reflect different conditions — for example where ionized sulphur is glowing brightly (blue features) the velocities of the colliding material are relatively low — and help astronomers to unravel what is going on in this dramatic scene.

Source: ESO press release. The paper, from the Astrophysical Journal, is available here.

Posted on by Anne Minard

Touching the Tarantula: Hubble Gets in Close

Credit: NASA, ESA

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Hubble has edged in close to the Tarantula Nebula, peering into its bright center of ionized gases, dust and still-forming stars. The Tarantula is already a go-to celestial marvel, because its hydrogen-fueled young stars shine with such intense ultraviolet light that they ionize and redden the surrounding gas — making the nebula visible without a telescope for Earth-bound observers 170,000 light-years away. The new image may make this popular beacon, in our neighboring galaxy the Large Magellanic Cloud, even more famous.

 

Credit: NASA, ESA

The wispy arms of the Tarantula Nebula (RA 05h 38m 38s dec -69° 05.7?) were originally thought to resemble spindly spider legs, giving the nebula its unusual name. The part of the nebula visible in the new image is criss-crossed with tendrils of dust and gas churned up by recent supernovae. These remnants include NGC 2060, visible above and to the left of the center of the image, which contains the brightest known pulsar.

The tarantula’s bite goes beyond NGC 2060. Near the edge of the nebula, outside the frame, below and to the right, lie the remains of supernova SN 1987a, the closest supernova to Earth to be observed since the invention of telescopes in the 17th century. Hubble and other telescopes have been returning to spy on this stellar explosion regularly since it blew up in 1987, and each subsequent visit shows an expanding shockwave lighting up the gas around the star, creating a pearl necklace of glowing pockets of gas around the remains of the star. SN 1987a is visible in wide field images of the nebula, such as that taken by the MPG/ESO 2.2-meter telescope.

A compact and extremely bright star cluster called RMC 136 lies above and to the left of this field of view, providing much of the radiation that powers the multi-coloured glow. Until recently, astronomers debated whether the source of the intense light was a tightly bound cluster of stars, or perhaps an unknown type of super-star thousands of times bigger than the sun. It is only in the last 20 years, with the fine detail revealed by Hubble and the latest generation of ground-based telescopes, that astronomers have been able to conclusively prove that it is, indeed, a star cluster.

But even if the Tarantula Nebula doesn’t contain this hypothetical super-star, it still hosts some extreme phenomena, making it a popular target for telescopes. Within the bright star cluster lies star RMC 136a1, which was recently found to be the heaviest ever discovered: the star’s mass when it was born was around 300 times that of the sun. This heavyweight is challenging astronomers’ theories of star formation, smashing through the upper limit they thought existed on star mass.

Source: ESA press release at the Hubble site. See also previous releases on the Large Magellanic Cloud and RMC 136.

Posted on by Anne Minard

Bullseye: MESSENGER Gears Up For First-Ever Mercury Orbit

Planned footprint for the first image to be acquired from a spacecraft orbiting Mercury, on March 29, including a portion of Mercury's surface not previously seen by spacecraft. Over the subsequent six hours, MESSENGER will acquire 364 images in total before beginning to downlink the data to Earth. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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When MESSENGER streaked into the early morning sky over Cape Canaveral on Aug. 3, 2004, very little was known about Mercury.

That could soon change. This week, MESSENGER — which stands for MErcury Surface, Space ENvironment, GEochemistry and Ranging — will make history when it becomes the first spacecraft to orbit Mercury.

At 8:45 p.m. EDT on Thursday, MESSENGER will execute a 15-minute maneuver that will place it into orbit around Mercury, kicking off a year-long science campaign to understand the innermost planet. The craft will fly around Mercury 730 times in the first year, and may be extended for another year after that.

No spacecraft had approached Mercury since the Mariner 10 space probe performed three fly-by maneuvers over the course of 1974 and 1975, imaging the planet’s surface. However, Mariner 10 sent back photos of only one side of the planet, leaving the other shrouded in mystery.

The MESSENGER mission — led by NASA, the Applied Physics Laboratory at Johns Hopkins University and the Carnegie Institution — is an effort to study the geologic history, magnetic field, surface composition and other mysteries of the planet. The findings are expected to broaden our understanding of rocky planets, more and more of which are being discovered in other solar systems. One of the most compelling enigmas surrounds Mercury’s magnetic field. At a diameter only slightly larger than that of the moon (about 4,800 kilometers or 2,983 miles), Mercury should have solidified to the core. However, the presence of a magnetic field suggests the planet’s insides are partially molten.

During its journey toward Mercury, MESSENGER passed the planet several times, filling in the imaging gaps left by Mariner 10. Now, the entire planet with the exception of about five percent has been observed. MESSENGER will focus its cameras on getting the best possible images of the remaining portions, mostly in the polar regions.

The in-flight preparations for this historic injection maneuver began on Feb. 8, when several heaters on the spacecraft were configured to condition the bi-propellant used during the maneuver. Starting on March 8, antennas from each of the three Deep Space Network (DSN) ground stations began a round-the-clock vigil, allowing flight control engineers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., to monitor MESSENGER on its final approach to Mercury. Also that day, the spacecraft began executing the last cruise command sequence of the mission.  The command load executed until today. Now, the command sequence containing the orbit-insertion burn has begun.

APL is hosting a live webcast about the orbit insertion maneuver starting at 7:55 p.m. EDT on Thursday, March 17.

For those of you living near Johns Hopkins, APL and The Planetary Society will co-host a public lecture in APL’s Kossiakoff Center, featuring MESSENGER Project Scientist Ralph L. McNutt, Jr. The lecture will begin at 8 p.m. on Thursday. RSVP online.

Check Universe Today late on Thursday for coverage of the orbit insertion, with input from related talks at the Laboratory for Space Physics (LASP) in Boulder, Colorado. Meanwhile, for more information, check out NASA’s MESSENGER mission website.

Sources: NASA’s MESSENGER mission website and a press release from the University of Arizona.

Posted on by Anne Minard

Did Mars’ Missing Carbon Go Underground in a Wetter Age?

Image credit: NASA/JPL-Caltech/Arizona State Univ. North is toward the top of the image, which is centered at 14 degrees south latitude, 304.4 degrees west longitude.

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A close look at the Wisconsin-sized Huygens Crater, above, in Mars’ southern highlands gave NASA and Arizona State University scientists some clues to announce this week as to a possible source of the carbon that’s mysteriously missing from the red planet’s thin atmosphere.

It might be buried underground.

The impact that formed the crater lifted material from far underground and piled some of it at the crater’s rim, where, at about 10 o’clock on the photo, an unnamed crater later exposed rocks containing carbonate minerals. The minerals were identified by observations with the mineral-mapping Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on NASA’s Mars Reconnaissance Orbiter.

Carbon dioxide makes up nearly all of today’s Martian air and likely was most of a thicker early atmosphere, too. In today’s thin, cold atmosphere, liquid water quickly freezes or boils away.

Carbonates found in rocks elsewhere on Mars, from orbit and by NASA’s Spirit rover, are rich in magnesium. Those could form from reactions of volcanic deposits with moisture, said James Wray of Cornell University in Ithaca, N.Y. “The broader compositional range we’re seeing that includes iron-rich and calcium-rich carbonates couldn’t form as easily from just a little bit of water reacting with igneous rocks. Calcium carbonate is what you typically find on Earth’s ocean and lake floors.”

He said the carbonates at Huygens and Leighton “fit what would be expected from atmospheric carbon dioxide interacting with ancient bodies of water on Mars.” Key additional evidence would be to find similar deposits in other Martian regions. A hunting guide for that search is the CRISM low-resolution mapping, which has covered about three-fourths of the planet and revealed clay-mineral deposits at thousands of locations.

“A dramatic change in atmospheric density remains one of the most intriguing possibilities about early Mars,” added Mars Reconnaissance Orbiter Project Scientist Richard Zurek, of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Increasing evidence for liquid water on the surface of ancient Mars for extended periods continues to suggest that the atmosphere used to be much thicker.”

Credit: NASA/JPL-Caltech/Univ. of Arizona

The HiRISE image above covers an area about 460 meters (1,500 feet) across in which carbonate minerals have been identified. It combines information collected separately in red, blue-green, and near-infrared wavelengths. It’s from HiRISE observation ESP_012897_168, made on April 27, 2009, and centered at 11.6 degrees south latitude, 51.9 degrees east longitude.

“We’re looking at a pretty lucky location in terms of exposing something that was deep beneath the surface,” Wray said. He reported the latest carbonate findings on Tuesday at the Lunar and Planetary Science Conference near Houston.

Observations in CRISM’s high-resolution mode show spectral characteristics of calcium or iron carbonate at this site. Detections of clay minerals in lower-resolution mapping mode by CRISM had prompted closer examination with the spectrometer, and the carbonates are found near the clay minerals. Both types of minerals typically form in wet environments.

The occurrence of this type of carbonate in association with the largest impact features suggests that it was buried by a few kilometers (or miles) of younger rocks, possibly including volcanic flows and fragmented material ejected from other, nearby impacts.

The new findings reinforce a report by other researchers five months ago identifying the same types of carbonate and clay minerals from CRISM observation of a site about 1,000 kilometers (600 miles) away. At that site, a meteor impact has exposed rocks from deep underground, inside Leighton crater. In their report of that discovery, Joseph Michalski of the Planetary Science Institute in Tucson, Ariz., and Paul Niles of NASA Johnson Space Center in Houston, proposed that the carbonates at Leighton “might be only a small part of a much more extensive ancient sedimentary record that has been buried by volcanic resurfacing and impact ejecta.”

NASA will launch the Mars Atmosphere and Volatile Evolution Mission (MAVEN) in 2013 to investigate processes that could have stripped the gas from the top of the atmosphere into interplanetary space. Meanwhile, CRISM and other instruments now in orbit continue to look for evidence that some of the carbon dioxide in that ancient atmosphere was removed, in the presence of liquid water, by formation of carbonate minerals now buried far beneath the present surface.

Source: NASA news release. See also NASA’s Mars Reconnaissance Orbiter page.

Posted on by Anne Minard

Grieving Glory — And Will The Taurus XL Fly Again?

Orbital Sciences Taurus rocket. Credit: NASA

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Last week’s loss of the $420 million Glory satellite has sent NASA into an intensive investigation to find out why two climate change missions in a row — flying aboard the same type of rocket — crashed due to what apparently was a similar technical glitch. Orbital Sciences out of Dulles, Va. is the company that designed the Taurus XL rocket that hosted both Glory and the Orbiting Carbon Satellite that crashed in 2009. They insisted last week that they’ll bounce back with the Taurus. But they may not be bouncing back on a NASA mission. Joy Bretthauer, NASA’s Glory program executive, acknowledged that the Orbiting Carbon Observatory 2, which will launch in 2013, is contracted to fly on none other than a Taurus XL. That may not stand, she said: “The bottom line is NASA will not fly in a launch vehicle that we do not have confidence in.”

Meanwhile, scores of researchers who poured their hearts into the mission are working to cope with the loss. Greg Kopp, the Boulder, Colorado-based principal investigator on the Total Irradiance Monitor that was supposed to fly aboard Glory, gave a thorough debriefing about his experience for the radio program Colorado Matters, on Colorado Public Radio out of Denver. It airs today.

Rich Straka, deputy general manager for operations for the Orbital Sciences launch systems group,  said during a NASA press briefing that the problem with both launches had to do with a protective covering called a clamshell fairing, held onto the vehicle with frangible, or breakable, joints meant to explosively fracture when commanded to do so.

“The fairing is then in two halves and there are piston pushers that push the fairing off,” Straka explained.

But in neither launch — the OCO in 2009 or Glory last week — did the fairing come off the rocket. In both cases, it stayed put and weighed the satellite down, preventing its flight toward orbit.

“We went into this flight confident that we had nailed the fairing issue,” said Ron Grabe, executive vice president and general manager of Orbital Sciences’ launch systems group. “We went so far as to completely change out the initiation system to a system that we use on one of our other vehicles, and in the intervening years that system flew successfully three times.”

Specifically, the company had previously used a hot gas system to drive the pistons that would push the fairing halves apart. But they traced the OCO launch loss to an initiation failure in the hot gas system. Orbital Sciences redesigned the Taurus XL rocket to use a cold gas system, starting with a pressurized bottle of nitrogen, just like the one in use on their Minotaur rocket.

NASA’s Bretthauer said she and others in the agency are heavy-hearted, but also baffled that their review of the OCO failure didn’t rule out the same mishap for Glory.

“We really thought we had it right,” she said. “We obviously never would have launched if we had not strongly believed the OCO failure had been mitigated.”

Kopp, a solar physicist at CU Bouder’s Laboratory for Atmospheric and Space Physics (LASP), said Bretthauer herself has asked a key question during early meetings to investigate the Glory failure: If a thorough investigation by both NASA and Orbital Sciences missed a key problem, how can we trust the process the second time around?

Meanwhile, Kopp and others are regrouping to see how much of Glory’s science can be salvaged. His instrument, the TIM, was supposed to continue an ongoing measure of the sun’s energy reaching Earth, to try to better understand the sun’s role in climate change. For now, older instruments like SORCE are carrying the torch. And it’s possible that development of missions currently in the pipeline — like the Joint Polar Satellite System (JPSS), a collaboration between NASA and NOAA — might be sped up to fill in the gaps.

More information: See also NASA’s Glory and OCO pages, a previous story about the Glory mission, and two stories about the OCO crash in 2009, here and here. This story is cross-posted at anneminard.com.

Posted on by Anne Minard

‘Armada of Telescopes’ Captures Most Distant Galaxy Cluster Ever Seen

Hubble infrared image showing CL J1449+0856, the most distant mature cluster of galaxies found. Color data was added from ESO’s Very Large Telescope and the NAOJ’s Subaru Telescope. Credit: NASA, ESA, R. Gobat (Laboratoire AIM-Paris-Saclay, CEA/DSM-CNRS–)

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The galaxies above are among the oldest objects astronomers have ever laid eyes — er, telescopes — on, formed when the Universe was less than a quarter of its current age. In a new study out in the journal Astronomy & Astrophysics, a team of researchers has announced that they’ve used a fleet of the world’s most powerful telescopes to measure the distance from here to there.

And things look awfully familiar.

“The surprising thing is that when we look closely at this galaxy cluster it doesn’t look young — many of the galaxies have settled down and don’t resemble the usual star-forming galaxies seen in the early Universe,” said lead author Raphael Gobat of Université Paris Diderot in France.

The Very Large Telescope (VLT) at ESO's Cerro Paranal observing site in the Atacama Desert of Chile, consisting of four Unit Telescopes with main mirrors 8.2-m in diameter and four movable 1.8-m diameter Auxiliary Telescopes. The telescopes can work together, in groups of two or three, to form a giant interferometer, allowing astronomers to see details up to 25 times finer than with the individual telescopes. Credit: Iztok Boncina/ESO

Clusters of galaxies are the largest structures in the Universe that are held together by gravity. Astronomers expect these clusters to grow over time so that massive clusters would be rare in the early Universe. Although even more distant clusters have been seen, they appear to be young clusters in the process of formation, not settled mature systems.

The international team of astronomers used the powerful VIMOS and FORS2 instruments on ESO’s Very Large Telescope (VLT) to measure the distances to some of the blobs in a curious patch of very faint red objects first observed with the Spitzer space telescope. This grouping, named CL J1449+0856  for its position in the sky, had all the hallmarks of being a very remote cluster of galaxies. The results showed that we are indeed seeing a galaxy cluster as it was when the Universe was about three billion years old.

Once the team knew the distance to this very rare object, they looked carefully at the component galaxies using both Hubble and ground-based telescopes, including the VLT. They found evidence suggesting that most of the galaxies in the cluster were not forming stars, but were composed of stars that were already about one billion years old. This makes the cluster a mature object, similar in mass to the Virgo Cluster, the nearest rich galaxy cluster to the Milky Way.

Further evidence that this is a mature cluster comes from observations of X-rays coming from CL J1449+0856 made with ESA’s XMM-Newton space observatory. The cluster is giving off X-rays that must be coming from a very hot cloud of tenuous gas filling the space between the galaxies and concentrated towards the center of the cluster. This is another sign of a mature galaxy cluster, held firmly together by its own gravity, as very young clusters have not had time to trap hot gas in this way.

As Gobat concludes, “These new results support the idea that mature clusters existed when the Universe was less than one quarter of its current age. Such clusters are expected to be very rare according to current theory, and we have been very lucky to spot one. But if further observations find many more then this may mean that our understanding of the early Universe needs to be revised.”

Source: ESO press release. The research appears in a paper, “A mature cluster with X-ray emission at z = 2.07,” by R. Gobat et al., published in the journal Astronomy & Astrophysics. (see also arxiv). Lead author’s affiliation page: Université Paris Diderot.

Posted on by Anne Minard

New Look at Messier 82 Reveals Superwind Source, Young Star Clusters

False color mosaic showing the Subaru COMICS image (red), a Hubble Space Telescope near-infrared image of stars (green) and a Chandra satellite X-ray image (blue) dominated by extremely hot gas and black holes. Credit: JAXA

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Messier 82’s galactic windstorms emanate from many young star clusters, rather than any single source, say astronomers who released this new image today.

The international team of scientists, led by Poshak Gandhi of the Japan Aerospace Exporation Agency (JAXA), has used the Subaru Telescope to produce a new view of M 82 at infrared wavelengths that are 20 times longer than those visible to the human eye.

M 82 (09h 55m 52.2s, +69° 40′ 47″) is located close to the ladle of the Big Dipper in the constellation Ursa Major and is the nearest starburst galaxy, at a distance of about 11 million light years from Earth.

The combination of Subaru Telescope’s large 8.2 m primary mirror and its Cooled Mid-Infrared Camera and Spectrometer (COMICS) allowed the team to obtain a sharp, magnified view of the inner area of the galaxy.

Images of M 82. The bottom image from Subaru shows the superwind crossing the disk structure. Courtesy of JAXA.

Previous observations of M 82 with infrared telescopes, including the middle and bottom image in the three-part series, have found a very strong wind emanating from it — a ‘superwind’ that is composed of dusty gas and extends over many hundreds of thousands of light years. This high-powered windstorm ejects material from the galaxy at a speed of about a half a million miles per hour, sweeping it up from the central regions and depositing it far and wide over the galaxy and beyond. The contents of this material are seeds for solar systems like our own, and perhaps for life itself. The dusty superwind glows brightly in the infrared, because billions of bright, newly-formed stars heat it up.

With the new Subaru image, scientists have gained insight about the sources of the superwind.

“The wind is found to originate from multiple ejection sites spread over hundreds of light years rather than emanating from any single cluster of new stars. We can now distinguish ‘pillars’ of fast gas, and even a structure resembling the surface of a ‘bubble’ about 450 light years wide,” Gandhi explained.

COMICS has detectors particularly adept at indicating the presence of warm dust, which it found was more than 100 degrees hotter than the bulk of material filling the rest of the galaxy. The widespread, continuous flow of energy from young stars into the galactic expanse keeps the dust hot.

Further insights from the Subaru image emerge when it’s combined with previous images from Hubble and Chandra. Their integration produces a beautiful mosaic, represented in the lead image, that provides the first opportunity to isolate M 82’s infrared properties. Supported by these data, scientists can study the broad spectrum of radiation of different kinds of objects spread over the galaxy’s plane, including supernovae, star clusters, and black holes.

Many questions remain, such as how many more stars the galaxy contains — many could still be obscured by the dust of star formation — and whether or not M 82 hosts an actively growing supermassive black hole.

The results are reported in the article “Diffraction-limited Subaru imaging of M82: sharp mid-infrared view of the starburst core” by P. Gandhi, N. Isobe, M. Birkinshaw, D.M. Worrall, I. Sakon, K. Iwasawa & A. Bamba, in the Publications of the Astronomical Society of Japan, v. 63 (2011), in press.

Source: Subaru press release

Posted on by Anne Minard

‘Climate Change Satellite’ Fails to Reach Orbit, Crashes in Ocean

Credit: NASA

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NASA’s Glory mission launched from Vandenberg Air Force Base in California Friday at 5:09:45 a.m. EST failed to reach orbit. Telemetry indicated the fairing, the protective shell atop the Taurus XL rocket, did not separate as expected about three minutes after launch. The failure represents a $420 million loss for NASA, and the loss of two important investigations related to climate change: ongoing data collection to monitor the sun’s energy reaching Earth, and a study of how aerosols move through Earth’s atmosphere and may influence climate.

This is the second time a Taurus XL rocket has failed to separate. NASA’s $273 million Orbiting Carbon Observatory crashed into the ocean in February 2009 due to a similar mishap. After that failure, Orbital Sciences redesigned the system. It has worked three times since on the company’s Minotaur rocket.

Source: NASA press release. Also see a previous story about the mission.

Posted on by Anne Minard

Solar System’s Story Revealed in a Pea

False-color compositional x-ray image of the rim and margin of a ~4.6 billion-year-old calcium aluminum refractory inclusion (CAI) from the Allende carbonaceous chondrite. Credit: Erick Ramon and Justin Simon

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Feast your eyes on some of the solar system’s earliest materials: the pink core comprises melilite, spinel and perovskite. The multi-colored rim contains hibonite, perovskite, spinel, melilite/sodalite, pyroxene, and olivine. This close-up reveals part of a pea-sized chunk of meteorite, a calcium-aluminum rich inclusion, formed when the planets in our solar system were still dust grains swirling around the sun — and it can tell an early part of the story about what happened next.

Pieces of the Allende meteorite, the largest carbonaceous chondrite ever found on Earth. Estimated to have been the size of a car, it broke up as it fell through the atmosphere in 1969, showering the ground in Chichuahua, Mexico, with hundreds of pieces, many collected for subsequent study. Credit: NASA

Meteorites have puzzled space scientists for more than 100 years because they contain minerals that could only form in cold environments, as well as minerals that have been altered by hot environments. Carbonaceous chondrites, in particular, contain millimeter-sized chondrules and up to centimeter-sized calcium-aluminum-rich inclusions, like the one shown above, that were once heated to the melting point and later welded together with cold space dust.

“These primitive meteorites are like time capsules, containing the most primitive materials in our solar system,” said Justin Simon, an astromaterials researcher at NASA’s Johnson Space Center in Houston, who led the new study. “CAIs are some of the most interesting meteorite components. They recorded the history of the solar system before any of the planets formed, and were the first solids to condense out of the gaseous nebula surrounding our protosun.”

For the new paper, which appears in Science today, Simon and his colleagues performed a micro-probe analysis to measure oxygen isotope variations in micrometer-scale layers of the core and outer layers of the ancient grain, estimated to be 4.57 billion years old.

All of these calcium-aluminum-rich inclusions, or CAIs, are thought to have originated near the protosun, which enriched the nebular gas with the isotope oxygen-16. In the inclusion analyzed for the new study, the abundance of oxygen-16 was found to decrease outward from the center of the core, suggesting that it formed in the inner solar system, where oxygen-16 was more abundant, but later moved farther from the sun and lost oxygen-16 to the surrounding 16O-poor gas.

Credit: Justin Simon/NASA

Simon and his colleagues propose that initial rim formation could have occurred as inclusions fell back into the midplane of the disk, indicated by the dashed path A above; as they migrated outward within the plane of the disk, shown as path B; and/ or as they entered high density waves (i.e., shockwaves). Shockwaves would be a reasonable source for the implied 16O-poor gas, increased dust abundance and thermal heating. The first mineral layer outside the core had more oxygen-16, implying that the grain had subsequently returned to the inner solar system. Outer rim layers had varying isotope compositions, but in general indicate that they also formed closer to the sun, and/or in regions where they had lower exposure to the 16O-poor gas from which the terrestrial planets formed.

The researchers interpret these findings as evidence that dust grains traveled over large distances as the swirling protoplanetary nebula condensed into planets. The single dust grain they studied appears to have formed in the hot environment of the sun, may have been thrown out of the plane of the solar system to fall back into the asteroid belt, and eventually recirculated back to the sun.

This odyssey is consistent with some theories about how dust grains formed in the early protoplanetary nebula, or propylid, eventually seeding the formation of planets.

Perhaps the most popular theory explaining the composition of chrondrules and CAIs is the so-called X-wind theory propounded by former UC Berkeley astronomer Frank Shu. Shu depicted the early protoplanetary disk as a washing machine, with the sun’s powerful magnetic fields churning the gas and dust and tossing dust grains formed near the sun out of the disk.

Once expelled from the disk, the grains were pushed outward to fall like rain into the outer solar system. These grains, both flash-heated chondrules and slowly heated CAIs, were eventually incorporated along with unheated dust into asteroids and planets.

“There are problems with the details of this model, but it is a useful framework for trying to understand how material originally formed near the sun can end up out in the asteroid belt,” said coauthor Ian Hutcheon, deputy director of Lawrence Livermore National Laboratory’s Glenn T. Seaborg Institute.

In terms of today’s planets, the grain probably formed within the orbit of Mercury, moved outward through the region of planet formation to the asteroid belt between Mars and Jupiter, and then traveled back toward the sun again.

“It may have followed a trajectory similar to that suggested in the X-wind model,” Hutcheon said. “Though after the dust grain went out to the asteroid belt or beyond, it had to find its way back in. That’s something the X-wind model doesn’t talk about at all.”

Simon plans to crack open and probe other CAIs to determine whether this particular CAI (referred to as A37) is unique or typical.

Source: Science and a press release from the University of California at Berkeley.

Posted on by Anne Minard

New Study: Sun’s Deep Physics Explain Sunspot-Free Days

Image credit: NASA/Goddard/SDO-AIA/JAXA/Hinode-XRT; Artistic rendering: Cygnus-Kolkata/William T. Bridgman; Conceptualization and simulation data: Dibyendu Nandy, Andres Munoz-Jaramillo and Petrus C.H. Martens.

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The long lull in sunspots at the end of Solar Cycle 23 wasn’t just fodder for global cooling predictions — it gave solar physicists plenty to study. And a new computer analysis may have come up with a fairly simple explanation for the sun’s odd quiet. Lead author Dibyendu Nandy, of the Indian Institute of Science Education and Research in Kolkata, and his colleagues report in Nature today that the long string of sunspot-free days between solar cycles 23 and 24 may directly correlate with the speed of north-south flow of plasma toward the sun’s equator. Their collage, above, shows magnetic fields in the interior of the Sun simulated using a solar dynamo model (center) and the observed solar corona at two different phases of solar activity: A quiescent phase during the recent, unusually long minimum, at right, and a comparatively active phase following the minimum, at left.

This visible-light photograph, taken in 2008 by NASA's Solar and Heliospheric Observatory (SOHO) spacecraft, shows the Sun's face free of sunspots. Credit: NASA/SOHO

The sun’s magnetic activity varies periodically, exhibiting an ~11-year cycle that can be monitored by observing the frequency and location of sunspots. Sunspots are strongly magnetized regions generated by the sun’s internal magnetic field and are the seats of solar storms that generate beautiful auroras but also pose hazards to satellites, navigation technologies like GPS and communications infrastructures.

Towards the end of solar cycle 23, which peaked in 2001 and wound down in 2008, the Sun’s activity entered a prolonged minimum, characterized by a very weak polar magnetic field and an unusually large number of days without sunspots: 780 days between 2008 and 2010. In a typical solar minimum, the sun goes spot-free for about 300 days, making the last minimum the longest since 1913.

The study authors conducted magnetic dynamo simulations of 210 sunspot cycles spanning some 2,000 years while varying the speed of the solar internal meridional (north-south) plasma flow. The sun’s plasma flows much like Earth’s ocean currents: rising at the equator, streaming toward the poles, then sinking and flowing back to the equator. At a typical speed of 40 miles per hour, it takes about 11 years to make one loop.

Nandy and his colleagues discovered that the Sun’s plasma rivers speed up and slow down like a malfunctioning conveyor belt, probably due to complicated feedback between the plasma flow and solar magnetic fields.

“It’s like a production line – a slowdown puts distance between the end of the last solar cycle and the start of the new one,” said study co-author Andres Munoz-Jaramillo, a visiting research fellow at the Harvard-Smithsonian Center for Astrophysics.

Specifically, the authors write, a fast meridional flow in the first half of a cycle, followed by a slower flow in the second half, leads to a deep sunspot minimum — and can reproduce the observed characteristics of the cycle 23 minimum.

Nandy and his colleagues say continued solar observations will be key to confirming and elaborating on the modeling results.

“We anticipate that NASA’s recently launched Solar Dynamics Observatory will provide more precise constraints on the structure of the plasma flows deep in the solar interior, which could be useful for complementing these simulations,” they write.

Source: Nature and the Harvard-Smithsonian Center for Astrophysics.