пятница, 1 марта 2019 г.

Ancient extinct sloth tooth in Belize tells story of creature’s last year

Some 27,000 years ago in central Belize, a giant sloth was thirsty. The region was arid, not like today’s steamy jungle. The Last Glacial Maximum had locked up much of Earth’s moisture in polar ice caps and glaciers. Water tables in the area were low.

Ancient extinct sloth tooth in Belize tells story of creature's last year
Researchers analyzed the orthodentin and the cementum in the sloth tooth. Pits mark locations
where samples were collected for analysis [Credit: Stanley Ambrose]

The sloth, a beast that stood up to 4 meters tall, eventually found water – in a deep sinkhole with steep walls down to the water. That is where it took its final drink. In 2014, divers found some of the sloth’s remains – parts of a tooth, humerus and femur – while searching for ancient Maya artifacts in the pool, in Cara Blanca, Belize.

Though partially fossilized, the tooth still held enough unaltered tissue for stable carbon and oxygen isotope analysis, which provided clues to what the sloth ate in the last year of its life. This, in turn, revealed much about the local climate and environment of the region at the time. The findings, reported in the journal Science Advances, will aid the study of similar fossils in the future, the researchers said.

“We began our study with the hopes of gaining a better understanding of the landscape within which large mammals went extinct and humans emerged in central Belize,” said University of Illinois graduate student Jean T. Larmon, who led the research with U. of I. anthropology professors Lisa Lucero and Stanley Ambrose. “In the process, we discovered which part of the tooth had best maintained its integrity for analysis. And we refined methods for studying similar specimens in the future.”

The new findings “add to the evidence that many factors, in addition to a changing climate, contributed to the extinction of megafauna in the Americas,” said Lucero, who studies the ancient Maya of central Belize. “One of those potential factors is the arrival of humans on the scene 12,000 to 13,000 years ago.”

Ancient extinct sloth tooth in Belize tells story of creature's last year
Part of an extinct giant sloth’s upper humerus recovered by divers during the 2014 excavations
[Credit: Lisa J. Lucero, VOPA]

The teeth of giant sloths like the one found in Belize, Eremotherium laurillardi, differ from those of other large mammals, like mammoths, that went extinct between 14,000 and 10,000 years ago, Larmon said.

“Giant sloth teeth have no enamel, the hard, outer layer of human and some animal teeth that can be analyzed to learn about their diet,” she said.

Other factors have limited scientists’ ability to study the teeth of ancient sloths. Most are fossilized, with minerals replacing much or all of the original tissue and bone.

By using cathodoluminescence microscopy, a technique that causes minerals to glow and can detect the extent of mineralization in fossils, the researchers discovered that one type of tooth tissue, the dense orthodentin, was largely intact.

Ancient extinct sloth tooth in Belize tells story of creature's last year
The ancient sloth, Eremotherium laurillardi, grew up to 4 meters in height
[Credit: Julie McMahon]

Larmon drilled 20 samples of orthodentin for isotopic analysis along the 10-centimeter-long tooth fragment, spanning more than a year of tooth growth.

“This allowed us to trace monthly and seasonal changes in the sloth’s diet and climate for the first time, and also to select the best part of the tooth for reliable radiocarbon dating,” Ambrose said.

The isotopic analysis revealed that the giant sloth lived through a long dry season, which lasted about seven months, sandwiched between two short rainy seasons. The analysis also revealed that the creature lived in a savanna, rather than a forest, and consumed a variety of plants that differed between wet and dry seasons.

“We were able to see that this huge, social creature was able to adapt rather readily to the dry climate, shifting its subsistence to relying upon what was more available or palatable,” Larmon said.

“This supports the idea that the sloths had a diverse diet,” Lucero said. “That helps explain why they were so widespread and why they lasted so long. It’s likely because they were highly adaptable.”

Source: University of Illinois at Urbana-Champaign [February 27, 2019]



A rare assemblage of sharks and rays from nearshore environments of Eocene Madagascar

Eocene-aged sediments of Madagascar contain a previously unknown fauna of sharks and rays, according to a study published in the open-access journal PLOS ONE by Karen Samonds of Northern Illinois University and colleagues. This newly-described fauna is the first report of sharks and rays of this age in Madagascar.

A rare assemblage of sharks and rays from nearshore environments of Eocene Madagascar
Eocene shark teeth from northwestern Madagascar
[Credit: Samonds et al, 2019]

The Mahajanga basin of northwestern Madagascar yields abundant fossil remains of terrestrial and marine ecosystems, but little is known about fossil sharks and rays during the Eocene Epoch, 55-34 million years ago, in this region. This is in contrast to the numerous shark and ray faunas known from other Eocene sites around the globe, and to shark and ray ecosystems known from older and younger sediments in the Mahajanga basin.
In this study, Samonds and colleagues collected isolated teeth, dental plates, and stingray spines from ancient coastal sediments of the Ampazony and Katsepy regions of the basin, dated to the middle to late Eocene. They identified at least 10 species of sharks and rays, including one new species, Carcharhinus underwoodi. This is the oldest named species of Carcharhinus, a genus that has been globally distributed for the past 35 million years but is known only rarely from the Eocene.

Aside from the new species, the fauna of Eocene Madagascar shares many species with Eocene ecosystems across North Africa, suggesting these animals were widespread in southern seas at that time. On the other hand, the Madagascar fauna is uniquely lacking in sandsharks and dominated by eagle rays, indicating a somewhat unusual ecosystem, unsurprising given Madagascar’s long history of isolation. The authors caution that this study provides an incomplete picture given that they collected only fossils larger than 2 millimeters. They recommend that future studies target smaller material for a more complete view of the ancient ecosystem.

Source: Public Library of Science [February 27, 2019]



Amoebae diversified at least 750 million years ago, far earlier than expected

Brazilian researchers have reconstructed the evolutionary history of amoebae and demonstrated that at the end of the Precambrian period, at least 750 million years ago, life on Earth was much more diverse than suggested by classic theory.

Amoebae diversified at least 750 million years ago, far earlier than expected
Reconstitution of Amoebozoa’s evolution shows significant Precambrian species diversity. This study changes the view
of how life evolved in the very remote past and deepens the understanding of current climate change
(a Thecamoebian protist of genus Cyclopixys) [Credit: Daniel Lahr (IBUSP)]

The study, which was supported by São Paulo Research Foundation – FAPESP, revealed eight new ancestral lineages of Thecamoebae, the largest group in Amoebozoa. Thecamoebians are known as testates because of their hard outer carapace or shell.

Interpretations of the evolution of Earth’s atmosphere and climate change are also affected by the discovery that amoebae are more diverse than previously thought.

In this study, published in the journal Current Biology, researchers affiliated with the University of São Paulo’s Bioscience Institute (IB-USP) in Brazil, in partnership with colleagues at the Mississippi State University in the United States, used innovative techniques to reconstruct the phylogenetic (evolutionary) tree of Thecamoeba, which belongs to the order Arcellinida.

The new phylogenetic tree was created using mathematical algorithms and the transcriptomes of 19 arcellinids found in nature today. The researchers also established the morphology and composition of the hypothetical ancestors of this group of amoebae and compared them with the fossil record.

The results showed that at least 750 million years ago, ancestors of the thecamoebians were already evolving. This finding indicates that the late Precambrian was more diverse than previously thought.

“We reached our conclusions using a combination of two major scientific areas – paleontology and phylogenetic systematics, the field within biology that reconstructs evolutionary history and studies the patterns of relationships among organisms. In this way, we were able to untangle one of the knots in evolutionary theory about life on the planet,” said Daniel Lahr, a professor at IB-USP and lead author of the article.

Reclassification of Amoebozoa

The researchers completely dismantled the previous classification of thecamoebians. “We succeeded in developing a robust structure and for the first time, discovered eight deep lineages [from 750 million years ago] of arcellinids about which nothing was known,” Lahr told.

The old thecamoebian classification was based on shell composition. “They were divided into agglutinate and organic. However, from our molecular reconstruction, we discovered that the classification is actually determined by shell shape rather than composition,” Lahr said.

The old classification, he added, had been questioned for several years, but more evidence was needed to demolish it. Previous genetic research has shown that the classification was unsustainable, but not enough data were available to justify a new classification.

“The scientific community suspected that the arcellinid testate amoebae had emerged and evolved sufficiently to diversify some 750 million years ago. We’ve now succeeded in demonstrating this hypothesis,” he said.

Past and future

According to Lahr, the study presents a different view of how microorganisms evolved on the planet. The late Precambrian was considered a period of low biotic diversity, with only a few species of bacteria and some protists.

Amoebae diversified at least 750 million years ago, far earlier than expected
Reconstitution of Amoebozoa’s evolution shows significant Precambrian species diversity. This study changes the view
of how life evolved in the very remote past and deepens the understanding of current climate change
(a Thecamoebian protist of genus Cyclopixys) [Credit: Daniel Lahr (IBUSP)]

“It was in this period 800 million years ago that the oceans became oxygenated. For a long time, oxygenation was assumed to have led to diversification of the eukaryotes, unicellular and multicellular organisms in which the cell’s nucleus is isolated by a membrane, culminating in the diversification of macroorganisms millions of years later in the Cambrian,” Lahr said.

The study published in Current Biology, he added, focuses on a detail of this question. “We show that diversification apparently already existed in the Precambrian and that it probably occurred at the same time as ocean oxygenation. What’s more, geophysicists are discovering that this process was slow and may have lasted 100 million years or so,” he said.

However, scientists do not know what pressure triggered this oxygenation. “Regardless of the cause, oxygenation eventually led to more niches, the eukaryotes diversified, and there was more competition for niches. One way to resolve the competition was for some lineages to become larger and hence multicellular,” Lahr said.

The study has also contributed to a better understanding of today’s climate change. “We began to understand in more depth how this microbial life affected the planet in several ways,” Lahr said. “The climate changed in fundamental ways during the period, which saw the occurrence of the Sturtian glaciation some 717 million years ago. This was one of the largest glaciation events ever.”

According to Lahr, these changes may have had biological origins. “By increasing the resolution of how life evolved in the very remote past, we can understand a little better how life affects the planet’s climate and even its geology. That will help us understand the climate changes we’re currently experiencing,” he said.

In rock

In addition to the discovery of greater diversity in the Precambrian, the study also innovates by reconstructing the morphology of the ancestors of thecamoebians to establish that the vase-shaped microfossils (VSMs) found in various parts of the world already existed in the Precambrian and even in the major ice ages that occurred during this era.

VSMs are presumed to be fossils of testate amoebae. They are unicellular and eukaryotic and have an external skeleton. Significant diversity of VSMs has been documented for the Neoproterozoic Era, which spanned between 1 billion and 541 million years ago, and was the terminal era of the Precambrian.

“The study constitutes a very different vision of how microorganisms evolved on the planet. Although the fossils do not contain genetic information, it is possible to obtain morphological and compositional information and to verify whether they are organic or silica-based. So it’s possible to compare their shape and chemical composition, which in this case are especially well preserved, with those of current thecamoebians reconstituted by big data,” said Luana Morais, a postdoctoral researcher with a scholarship from FAPESP and coauthor of the article.

Innovative techniques

In addition to the lack of DNA-containing fossils, the researchers faced another obstacle in reconstructing the phylogenetic tree: thecamoebians cannot be cultured in the laboratory, and genetic sequencing by conventional means is therefore ruled out.

The solution to this problem was to use the single-cell transcriptome technique to analyze phylogenetics (instead of gene expression, its normal application). “We sequenced whole transcriptomes of arcellinid amoebae using live samples,” Lahr explained. “This yielded several thousand genes and some 100,000 amino acid sites, or 100,000 datapoints giving us the phylogenetic tree, which had never been seen before.”

The researchers used transcriptome-based methodology to capture all messenger RNAs from each individual cell and convert them into a sequenceable complementary DNA library.

“Our research drew fundamentally on single-cell transcriptomics, in which our lab is one of the worldwide pioneers,” Lahr said. “It’s a revolutionary technique in this field because it enables us to find a single [unicellular] amoeba, isolate and clean it, and perform all the laboratory procedures to sequence the whole transcriptome.”

In this study, the researchers selected 250 genes to construct the phylogenetic tree. “It’s no good looking at only one cell when you’re studying gene expression, because the resolution will be insufficient,” Lahr said. “In an evolutionary study, however, this doesn’t matter. You need to obtain the sequence, not the number of times a gene is expressed. So it’s possible to use this technique, which was originally developed for tumor cells, and adapt it, with the advantage that an amoeba cell is much larger than a tumor cell.”

Before the technique was developed, only organisms grown in the laboratory could be sequenced. “It extends the range of my research in this field by enabling me to obtain genetic information from organisms I’ve only found once. It’s estimated that only 1% or less of all biodiversity is cultivable,” Lahr said.

Source: Fundação de Amparo à Pesquisa do Estado de São Paulo [February 28, 2019]



500-million-year old worm ‘superhighway’ discovered in Canada

Prehistoric worms populated the sea bed 500 million years ago–evidence that life was active in an environment thought uninhabitable until now, research by the University of Saskatchewan (USask) shows.

500-million-year old worm 'superhighway' discovered in Canada
Brian Pratt in the Burgess Shale [Credit: University of Saskatchewan]

The sea bed in the deep ocean during the Cambrian period was thought to have been inhospitable to animal life because it lacked enough oxygen to sustain it.

But research published in the scientific journal Geology reveals the existence of fossilized worm tunnels dating back to the Cambrian period¬¬ 270 million years before the evolution of dinosaurs.

The discovery, by USask professor Brian Pratt, suggests that animal life in the sediment at that time was more widespread than previously thought.

The worm tunnels–borrows where worms lived and munched through the sediment–are invisible to the naked eye. But Pratt “had a hunch” and sliced the rocks and scanned them to see whether they revealed signs of ancient life.

The rocks came from an area in the remote Mackenzie Mountains of the Northwest Territories in Canada which Pratt found 35 years ago.

Pratt then digitally enhanced images of the rock surfaces so he could examine them more closely. Only then did the hidden ‘superhighway’ of burrows made by several different sizes and types of prehistoric worm emerge in the rock.

Some were barely a millimetre in size and others as large as a finger. The smaller ones were probably made by simple polychaetes–or bristle worms–but one of the large forms was a predator that attacked unsuspecting arthropods and surface-dwelling worms.

500-million-year old worm 'superhighway' discovered in Canada
These are worm tunnels (labelled) visible in small section of rock
[Credit: Professor Brian Pratt, University of Saskatchewan]

Pratt said he was “surprised” by the unexpected discovery.

“For the first time, we saw evidence of large populations of worms living in the sediment – which was thought to be barren,” he said. “There were cryptic worm tunnels – burrows – in the mud on the continental shelf 500 million years ago, and more animals reworking, or bioturbating, the sea bed than anyone ever thought.”

Pratt, a geologist and paleontologist and Fellow of the Geological Society of America, found the tunnels in sedimentary rocks that are similar to the Burgess Shale, a famous fossil-bearing deposit in the Canadian Rockies.

The discovery may prompt a rethink of the level of oxygenation in ancient oceans and continental shelves.

The Cambrian period saw an explosion of life on Earth in the oceans and the development of multi-cellular organisms including prehistoric worms, clams, snails and ancestors of crabs and lobsters. Previously the seas had been inhabited by simple, single-celled microbes and algae.

It has always been assumed that the creatures in the Burgess Shale–known for the richness of its fossils–had been preserved so immaculately because the lack of oxygen at the bottom of the sea stopped decay, and because no animals lived in the mud to eat the carcasses.

Pratt’s discovery, with co-author Julien Kimmig, now of the University of Kansas, shows there was enough oxygen to sustain various kinds of worms in the sea bed.

“Serendipity is a common aspect to my kind of research,” Pratt said. “I found these unusual rocks quite by accident all those years ago. On a hunch I prepared a bunch of samples and when I enhanced the images I was genuinely surprised by what I found,” he said.

“This has a lot of implications which will now need to be investigated, not just in Cambrian shales but in younger rocks as well. People should try the same technique to see if it reveals signs of life in their samples.”

Source: University of Saskatchewan [February 28, 2019]



New findings shed light on origin of upright walking in human ancestors

The oldest distinguishing feature between humans and our ape cousins is our ability to walk on two legs – a trait known as bipedalism. Among mammals, only humans and our ancestors perform this atypical balancing act. New research led by a Case Western Reserve University School of Medicine professor of anatomy provides evidence for greater reliance on terrestrial bipedalism by a human ancestor than previously suggested in the ancient fossil record.

New findings shed light on origin of upright walking in human ancestors
Fossil hominin talus from site GWM67 (2005) at the time of its discovery
[Credit: Case Western Reserve University School of Medicine]

Scott W. Simpson, PhD, led an analysis of a 4.5 million-year-old fragmentary female skeleton of the human ancestor Ardipithecus ramidus that was discovered in the Gona Project study area in the Afar Regional State of Ethiopia.

The newly analyzed fossils document a greater, but far from perfect, adaptation to bipedalism in the Ar. ramidus ankle and hallux (big toe) than previously recognized. “Our research shows that while Ardipithecus was a lousy biped, she was somewhat better than we thought before,” said Simpson.

Fossils of this age are rare and represent a poorly known period of human evolution. By documenting more fully the function of the hip, ankle, and foot in Ardipithecus locomotion, Simpson’s analysis helps illuminate current understanding of the timing, context, and anatomical details of ancient upright walking.

Previous studies of other Ardipithecus fossils showed that it was capable of terrestrial bipedalism as well as being able to clamber in trees, but lacked the anatomical specializations seen in the Gona fossil examined by Simpson. The new analysis, published in the Journal of Human Evolution, thus points to a diversity of adaptations during the transition to how modern humans walk today. “The fact that Ardipithecus could both walk upright, albeit imperfectly, and scurry in trees marks it out as a pivotal transitional figure in our human lineage,” said Simpson.

Key to the adaptation of bipedality are changes in the lower limbs. For example, unlike monkeys and apes, the human big toe is parallel with the other toes, allowing the foot to function as a propulsive lever when walking. While Ardipithecus had an offset grasping big toe useful for climbing in trees, Simpson’s analysis shows that it also used its big toe to help propel it forward, demonstrating a mixed, transitional adaptation to terrestrial bipedalism.

Specifically, Simpson looked at the area of the joints between the arch of the foot and the big toe, enabling him to reconstruct the range of motion of the foot. While joint cartilage no longer remains for the Ardipithecus fossil, the surface of the bone has a characteristic texture which shows that it had once been covered by cartilage. “This evidence for cartilage shows that the big toe was used in a more human-like manner to push off,” said Simpson. “It is a foot in transition, one that shows primitive, tree-climbing physical characteristics but one that also features a more human-like use of the foot for upright walking.” Additionally, when chimpanzees stand, their knees are “outside” the ankle, i.e., they are bow-legged. When humans stand, the knees are directly above the ankle – which Simpson found was also true for the Ardipithecus fossil.

The Gona Project has conducted continuous field research since 1999. The study area is located in the Afar Depression portion of the eastern Africa rift and its fossil-rich deposits span the last 6.3 million years. Gona is best known as documenting the earliest evidence of the Oldowan stone tool technology. The first Ardipithecus ramidus fossils at Gona were discovered in 1999 and described in the journal Nature in 2005. Gona has also documented one of the earliest known human fossil ancestors – dated to 6.3 million years ago. The Gona Project is co-directed by Sileshi Semaw, PhD, a research scientist with the CENIEH research center in Burgos, Spain, and Michael Rogers, PhD, of Southern Connecticut State University. The geological and contextual research for the current research was led by Naomi Levin, PhD, of the University of Michigan, and Jay Quade, PhD, of the University of Arizona.

Source: Case Western Reserve University [February 28, 2019]



Researchers discover oldest tattoo tool in western North America

Washington State University archaeologists have discovered the oldest tattooing artifact in western North America.

Researchers discover oldest tattoo tool in western North America
Close up of a 2,000-year-old cactus spine tattoo tool discovered by WSU archaeologist
Andrew Gillreath-Brown [Credit: Bob Hubner/WSU]

With a handle of skunkbush and a cactus-spine business end, the tool was made around 2,000 years ago by the Ancestral Pueblo people of the Basketmaker II period in what is now southeastern Utah.

Andrew Gillreath-Brown, an anthropology PhD candidate, chanced upon the pen-sized instrument while taking an inventory of archaeological materials that had been sitting in storage for more than 40 years.

He is the lead author of a paper on the tattoo tool which was published in the Journal of Archaeological Science: Reports.

His discovery pushes back the earliest evidence of tattooing in western North America by more than a millennium and gives scientists a rare glimpse into the lives of a prehistoric people whose customs and culture have largely been forgotten.

“Tattooing by prehistoric people in the Southwest is not talked about much because there has not ever been any direct evidence to substantiate it,” Gillreath-Brown, 33, said. “This tattoo tool provides us information about past Southwestern culture we did not know before.”

Tattooing is an artform and mode of expression common to many indigenous cultures worldwide. However, little is known about when or why the practice began.

Researchers discover oldest tattoo tool in western North America
The 2,000-year-old cactus spine tattoo tool discovered by WSU archaeologist Andrew Gillreath-Brown
[Credit: Bob Hubner/WSU]

This is especially the case in places like the southwestern United States, where no tattoos have been identified on preserved human remains and there are no ancient written accounts of the practice.

Instead, archaeologists have relied on visual depictions in ancient artwork and the identification of tattoo implements to trace the origins of tattooing in the region.

Previously, bundled and hafted, or handled, cactus spine tattoo tools from Arizona and New Mexico provided the best archaeological examples of early tattoo implements from the Southwest. The earliest of these have been dated to between AD 1100-1280.

So when Gillreath-Brown came across a very similar looking implement from a site in Utah that is 1,000 years older, he knew he had found something special.

“When I first pulled it out of the museum box and realized what it might have been I got really excited,” said Gillreath-Brown, who himself wears a large sleeve tattoo of a turtle shell rattle, mastodon, water, and forest on his left arm.

The tool consists of a 3 ½ inch wooden skunkbush sumac handle bound at the end with split yucca leaves and holding two parallel cactus spines, stained black at their tips.

Researchers discover oldest tattoo tool in western North America
Close up of a 2,000-year-old cactus spine tattoo tool discovered by WSU archaeologist
Andrew Gillreath-Brown [Credit: Bob Hubner/WSU]

“The residue staining from tattoo pigments on the tip was what immediately piqued my interest as being possibly a tattoo tool,” Gillreath-Brown said.

Encouraged by Aaron Deter-Wolf, a friend and co-author of the study who had done ancient tattooing and edited several books on the subject, Gillreath-Brown analyzed the tips with a scanning electron microscope, X-ray florescence and energy dispersive ray spectroscopy. For good measure, he did several test tattoos using a replica on pig skin.

He saw the crystalline structure of pigment and determined it likely contained carbon, a common element in body painting and tattooing.

The find, said Gillreath-Brown, “has a great significance for understanding how people managed relationships and how status may have been marked on people in the past during a time when population densities were increasing in the Southwest.”

Author: Will Ferguson | Source: Washington State University [February 28, 2019]



NASA Scientists Show How Ingredients for Water Could Be Made on Surface of Moon, a...

NASA Goddard Space Flight Center logo.

March 1, 2019

When a stream of charged particles known as the solar wind careens onto the Moon’s surface at 450 kilometers per second (or nearly 1 million miles per hour), they enrich the Moon’s surface in ingredients that could make water, NASA scientists have found.

Using a computer program, scientists simulated the chemistry that unfolds when the solar wind pelts the Moon’s surface. As the Sun streams protons to the Moon, they found, those particles interact with electrons in the lunar surface, making hydrogen (H) atoms. These atoms then migrate through the surface and latch onto the abundant oxygen (O) atoms bound in the silica (SiO2) and other oxygen-bearing molecules that make up the lunar soil, or regolith. Together, hydrogen and oxygen make the molecule hydroxyl (OH), a component of water, or H2O.

Image above: Waxing gibbous Moon at 11 days old. Credit: Ernie Wright/NASA.

“We think of water as this special, magical compound,” said William M. Farrell, a plasma physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who helped develop the simulation. “But here’s what’s amazing: every rock has the potential to make water, especially after being irradiated by the solar wind.”

Understanding how much water — or its chemical components — is available on the Moon is critical to NASA’s goal of sending humans to establish a permanent presence there, said Orenthal James Tucker, a physicist at Goddard who spearheaded the simulation research.

“We’re trying to learn about the dynamics of transport of valuable resources like hydrogen around the lunar surface and throughout its exosphere, or very thin atmosphere, so we can know where to go to harvest those resources,” said Tucker, who recently described the simulation results in the journal JGR Planets.

Animation above: Credits: NASA/JoAnna Wendel.

Several spacecraft used infrared instruments that measure light emitted from the Moon to identify the chemistry of its surface. These include NASA’s Deep Impact spacecraft, which had numerous close encounters with the Earth-Moon system en route to comet 103P/Hartley 2; NASA’s Cassini spacecraft, which passed the Moon on its way to Saturn; and India’s Chandrayaan-1, which orbited the Moon a decade ago. All found evidence of water or its components (hydrogen or hydroxyl).

But how these atoms and compounds form on the Moon is still an open question. It’s possible that meteor impacts initiate the necessary chemical reactions, but many scientists believe that the solar wind is the primary driver.

Image above: The Sun releases a constant stream of particles and magnetic fields called the solar wind. This solar wind slams worlds across the solar system with particles and radiation — which can stream all the way to planetary surfaces unless thwarted by an atmosphere, magnetic field, or both. Here’s how these solar particles interact with a few select planets and other celestial bodies. Image Credits: NASA’s Goddard Space Flight Center/Mary Pat Hrybyk-Keith.

Tucker’s simulation, which traces the lifecycle of hydrogen atoms on the Moon, supports the solar wind idea.

“From previous research, we know how much hydrogen is coming in from the solar wind, we also know how much is in the Moon’s very thin atmosphere, and we have measurements of hydroxyl in the surface,” Tucker said. “What we’ve done now is figure out how these three inventories of hydrogen are physically intertwined.”

Showing how hydrogen atoms behave on the Moon helped resolve why spacecraft have found fluctuations in the amount of hydrogen in different regions of the Moon. Less hydrogen accumulates in warmer regions, like the Moon’s equator, because hydrogen atoms deposited there get energized by the Sun and quickly outgas from the surface into the exosphere, the team concluded. Conversely, more hydrogen appears to accumulate in the colder surface near the poles because there’s less Sun radiation and the outgassing is slowed.

Overall, Tucker’s simulation shows that as solar wind continually blasts the Moon’s surface, it breaks the bonds among atoms of silicon, iron and oxygen that make up the majority of the Moon’s soil. This leaves oxygen atoms with unsatisfied bonds. As hydrogen atoms flow through the Moon’s surface, they get temporarily trapped with the unhinged oxygen (longer in cold regions than in warm). They float from O to O before finally diffusing into the Moon’s atmosphere, and, ultimately, into space. “The whole process is like a chemical factory,” Farrell said.

A key ramification of the result, Farrell said, is that every exposed body of silica in space — from the Moon down to a small dust grain — has the potential to create hydroxyl and thus become a chemical factory for water.

Goddard physicist Rosemary Margaret Killen and Dana M. Hurley, planetary scientist at Johns Hopkins University in Baltimore, Maryland, contributed to the simulation research, which was funded by NASA’s Solar System Exploration Research Virtual Institute.

Related links:

Moon to Mars: https://www.nasa.gov/topics/moon-to-mars/

Earth’s Moon: http://www.nasa.gov/moon

Humans in Space: https://www.nasa.gov/topics/humans-in-space

Animation & Images (mentioned), Text, Credits: NASA/Svetlana Shekhtman/Goddard Space Flight Center, by Lonnie Shekhtman.

Greetings, Orbiter.chArchive link

Meteor Activity Outlook for March 2-8, 2019

This outstanding fireball was captured by Patryk Sadowski at 22:59 UTC on February 2, 2019, from Ballintoy, North Ireland. © Patryk Sadowski. For more reports on this particular fireball visit: https://fireball.amsmeteors.org/members/imo_view/event/2019/575

As seen from the northern hemisphere, March is the slowest month of the year for meteor activity. No major annual showers are active and only a few very weak minor showers produce activity this month. The sporadic rates are also near their annual minimum so there is not much to look forward to this month except for the evening fireballs that seem to peak this time of year as seen from the northern hemisphere. This could be due to the fact the Antapex radiant lies highest above the horizon this time of year during the evening hours. From the southern hemisphere, activity from the Centaurid complex begins to wane with only the weak activity visible from Norma and perhaps others nearby areas. At least southern sporadic rates are still strong to make the late summer viewing a bit more pleasurable.

During this period the moon will reach its new phase on Wednesday March 6th. At this time the moon will be located near the sun and will be invisible at night. This weekend the waning crescent moon will rise during the morning hours but will not interfere with meteor observing as long as you keep the moon out of your field of view. Hourly meteor rates for evening observers this week is near 3 as seen from mid-northern latitudes (45N) and 5 as seen from tropical southern locations (25S). For morning observers the estimated total hourly rates should be near 7 as seen from mid-northern latitudes and 12 from the southern tropics. The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity. Note that the hourly rates listed below are estimates as viewed from dark sky sites away from urban light sources. Observers viewing from urban areas will see less activity as only the brighter meteors will be visible from such locations.

The radiant (the area of the sky where meteors appear to shoot from) positions and rates listed below are exact for Saturday night/Sunday morning March 2/3 . These positions do not change greatly day to day so the listed coordinates may be used during this entire period. Most star atlases (available at science stores and planetariums) will provide maps with grid lines of the celestial coordinates so that you may find out exactly where these positions are located in the sky. A planisphere or computer planetarium program is also useful in showing the sky at any time of night on any date of the year. Activity from each radiant is best seen when it is positioned highest in the sky, either due north or south along the meridian, depending on your latitude. It must be remembered that meteor activity is rarely seen at the radiant position. Rather they shoot outwards from the radiant so it is best to center your field of view so that the radiant lies near the edge and not the center. Viewing there will allow you to easily trace the path of each meteor back to the radiant (if it is a shower member) or in another direction if it is a sporadic. Meteor activity is not seen from radiants that are located far below the horizon. The positions below are listed in a west to east manner in order of right ascension (celestial longitude). The positions listed first are located further west therefore are accessible earlier in the night while those listed further down the list rise later in the night.

Radiant Positions at 7:00pm Local Standard Time

Radiant Positions at 12:00am Local Standard Time

Radiant Positions at 5:00am Local Standard Time

These sources of meteoric activity are expected to be active this week.

The center of the large Anthelion (ANT) radiant is currently located at 11:40 (175) +02. This position lies on the  Leo/Virgo border, 2 degrees west of the 4th magnitude star known as Zavijava (beta Virginis) Due to the large size of this radiant, Anthelion activity may also appear from western Virgo and Sextans as well as Leo. This radiant is best placed near 0100 local standard time (LST), when it lies on the meridian and is located highest in the sky. Rates at this time should be near 2 per hour no matter your location. With an entry velocity of 30 km/sec., the average Anthelion meteor would be of slow velocity.

The February Mu Virginids (FMV) were discovered by Damir Šegon and the Croatian Meteor Network team based on studying SonotaCo and CMN observations (SonotaCo 2007-2011, CMN 2007-2010). These meteors are active from February 17 through March 5 with maximum activity occurring on February 26. The current radiant position lies near 17:04 (256) +00, which actually places it in central Ophiuchus, 5 degrees southwest of the 4th magnitude star known as sigma Ophiuchi). Rates are expected to be less than 1 per hour no matter your location. These meteors are best seen near 0500 LST when the radiant lies highest above the horizon. At 62 km/sec. the February Mu Virginids would produce mostly swift meteors.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately 5 sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near 2 per hour. As seen from the tropical southern latitudes (25S), morning rates would be near 10 per hour as seen from rural observing sites and 3 per hour during the evening hours. Locations between these two extremes would see activity between the listed figures.

RA (RA in Deg.) DEC Km/Sec Local Standard Time North-South
Anthelion (ANT) 11:40 (175) +02 30 01:00 2 – 2 II
February mu Virginids (FMV) Feb 26 17:04 (256) +00 62 07:00 <1 – <1 IV

Source link

NGC 3079: Galactic Bubbles Play Cosmic Pinball with Energetic Particles

NGC 3079

Credit X-ray: NASA/CXC/University of Michigan/J-T Li et al.; Optical: NASA/STScI 

We all know bubbles from soapy baths or sodas. These bubbles of everyday experience on Earth are up to a few inches across, and consist of a thin film of liquid enclosing a small volume of air or other gas. In space, however, there are very different bubbles — composed of a lighter gas inside a heavier one — and they can be huge.

The galaxy NGC 3079, located about 67 million light years from Earth, contains two “superbubbles” unlike anything here on our planet. A pair of balloon-like regions stretch out on opposite sides of the center of the galaxy: one is 4,900 light years across and the other is only slightly smaller, with a diameter of about 3,600 light years. For context, one light year is about 6 trillion miles, or 9 trillion kilometers.

The superbubbles in NGC 3079 give off light in the form of X-ray, optical and radio emission, making them detectable by NASA telescopes. In this composite image, X-ray data from NASA’s Chandra X-ray Observatory are shown in purple and optical data from NASA’s Hubble Space Telescope are shown in orange and blue. A labeled version of the X-ray image shows that the upper superbubble is clearly visible, along with hints of fainter emission from the lower superbubble.

 NGC 3079  (Labeled)

Credit: NASA/CXC/University of Michigan/J-T Li et al.

New observations from Chandra show that in NGC 3079 a cosmic particle accelerator is producing ultra-energetic particles in the rims of the superbubbles. These particles can be much more energetic than those created by Europe’s Large Hadron Collider (LHC), the world’s most powerful human-made particle accelerator.

The superbubbles in NGC 3079 provide evidence that they and structures like them may be the source of high-energy particles called “cosmic rays” that regularly bombard the Earth. Shock waves — akin to sonic booms caused by supersonic planes — associated with exploding stars can accelerate particles up to energies about 100 times larger than those generated in the LHC, but astronomers are uncertain about where even more energetic cosmic rays come from. This new result suggests superbubbles may be one source of these ultra-energetic cosmic rays.

The outer regions of the bubbles generate shock waves as they expand and collide with surrounding gas. Scientists think charged particles scatter or bounce off tangled magnetic fields in these shock waves, much like balls rebounding off bumpers in a pinball machine. When the particles cross the shock front they are accelerated, as if they received a kick from a pinball machine’s flipper. These energetic particles can escape and some may eventually strike the Earth’s atmosphere in the form of cosmic rays.

The amount of radio waves or X-rays at different wavelengths, or “spectra,” of one of the bubbles suggest that the source of the emission is electrons spiraling around magnetic field lines, and radiating by a process called synchrotron radiation. This is the first direct evidence of synchrotron radiation in high energy X-rays from a galaxy-sized superbubble, and it tells scientists about the maximum energies that the electrons have attained. It is not understood why synchrotron emission is detected from only one of the bubbles.

The radio and X-ray spectra, along with the location of the X-ray emission along the rims of the bubbles, imply that the particles responsible for the X-ray emission must have been accelerated in the shock waves there, because they would have lost too much energy while being transported from the center of the galaxy. 

NGC 3079’s superbubbles are younger cousins of “Fermi bubbles,” first located in the Milky Way galaxy in 2010. Astronomers think such superbubbles may form when processes associated with matter falling into a supermassive black hole in the center of galaxy, which leads to the release of enormous amounts of energy in the form of particles and magnetic fields. Superbubbles may also be sculpted by winds flowing from a large number of young, massive stars.

A paper describing these results was led by Jiangtao Li of the University of Michigan and appears in The Astrophysical Journal. It is also available online. 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.

Fast Facts for NGC 3079:

Scale: Image is 3.2 arcmin (about 62,000 light years) across.
Category: Normal Galaxies & Starburst Galaxies
Coordinates (J2000) : RA 10h 01m 57.8s | Dec +55° 40´ 47.2″
Constellation: Ursa Major
Observation Date: 4 observations: Mar 7, 2001; Dec 27, 2006; Jan 30, 2018; Feb 1, 2018
Observation Time: 35 hours 45 min (1 day 11 hours 45 minutes)
Obs. ID: 2038, 7851, 19307, 20947
Instrument: ACIS
References: Li, J-T. et al, 2019, ApJ, accepted. arXiv:1901.10536
Color Code X-ray: purple & pink; Optical: red & blue
Distance Estimate: About 67 million light years

Archive link

2019 March 1 A Charioteer’s Comet Image Credit &…

2019 March 1

A Charioteer’s Comet
Image Credit & Copyright: Rolando Ligustri (CARA Project, CAST)

Explanation: Still racing across planet Earth’s night skies, Comet Iwamoto (C/2018 Y1) shares this pretty telescopic field of view with stars and nebulae of northern constellation Auriga, the Charioteer. Captured on February 27, Iwamoto’s greenish coma and faint tail appear between a complex of reddish emission nebulae and open star cluster M36 (bottom right). The reddish emission is light from hydrogen gas ionized by ultraviolet radiation from hot stars near the region’s giant molecular cloud some 6,000 light-years distant. The greenish glow from the comet, less than 5 light-minutes away, is predominantly emission from diatomic carbon molecules fluorescing in sunlight. M36, one of Auriga’s more familiar star clusters, is also a background object far beyond the Solar System, about 4,000 light-years away. Comet Iwamoto passed closest to Earth on February 12 and is outward bound in a highly elliptical orbit that will carry it beyond the Kuiper belt. With an estimated orbital period of 1,317 years it should return to the inner Solar System in 3390 AD.

∞ Source: apod.nasa.gov/apod/ap190301.html

Crew Dragon Ready for its Debut Flight

SpaceX – COTS C-1 Mission patch.

February 28, 2019

SpaceX’s Crew Dragon spacecraft—designed to fly astronauts to the International Space Station from U.S. soil—is ready for its debut flight on the company’s Falcon 9 rocket. It is a first-of-its-kind test mission of a commercially-built and operated American spacecraft and rocket designed for humans.

The Demo-1 uncrewed flight test, targeted to launch March 2, will demonstrate the company’s ability to safely launch crew to the space station and return them home.

Image above: A SpaceX Falcon 9 rocket with the company’s Crew Dragon spacecraft onboard is seen as it is rolled to the launch pad at Launch Complex 39A as preparations continue for the Demo-1 mission, Feb. 28, 2019 at NASA’s Kennedy Space Center in Florida. Photo credits: NASA/Joel Kowsky.

“It’s time to fly the SpaceX Demo-1 mission,” said Steve Stich, NASA launch manager and deputy manager of NASA’s Commercial Crew Program. “This mission is an important step in returning human spaceflight to American soil. SpaceX and NASA teams are working side-by-side on this mission from start to finish as we have throughout this process. This flight test will inform the system design, operations and drive any changes that need to be made ahead of crew flights. We are ready to learn by flying.”

NASA and SpaceX are working together as public-private partnerships to build on the success of American companies already delivering cargo to the space station. Demo-1 is a critical step for NASA and SpaceX to demonstrate the ability to safely fly missions with NASA astronauts to the orbital laboratory.

“Demo-1 is our end-to-end flight test to ensure the spacecraft and systems operate as designed before we put crew on board,” said Benji Reed, SpaceX director of crew mission management.

On launch day, SpaceX will command Crew Dragon and Falcon 9’s launch from Kennedy Space Center’s historic Launch Control Center Firing Room 4, which oversaw the countdown and liftoff of the final 15 space shuttle missions. Falcon 9 is targeted to lift off at 2:49 a.m. from Launch Complex 39A at NASA’s Kennedy Space Center. Pad A was the launch site for 11 Apollo Saturn V missions, including Apollo 11, the first Moon landing, and 82 space shuttle missions, including STS-1, the first shuttle launch, and STS-135, the final shuttle mission.

Image above: At NASA Kennedy Space Center’s Launch Complex 39A, the crew access arm has been extended to the SpaceX Crew Dragon spacecraft on Jan. 3, 2019. Mounted atop the company’s Falcon 9 rocket, both will undergo checkouts prior to its liftoff for Demo-1, the inaugural flight of one of the spacecraft designed to take NASA astronauts to and from the International Space Station. NASA has worked with SpaceX and Boeing in developing Commercial Crew Program spacecraft to facilitate new human spaceflight systems launching from U.S. soil with the goal of safe, reliable and cost-effective access to low-Earth orbit destinations such as the space station. Image Credit: SpaceX.

“Demo-1 is a demonstration of the Falcon 9 rocket, Crew Dragon spacecraft, ground systems and overall operations – basically just about everything that needs to be operating and operating well before we want to put our astronauts on-board,” said Mike Lee, NASA mission manager for SpaceX’s Demo-1 flight test. “Our main goals are to validate as many aspects of the spacecraft’s systems as we can without a crew on-board, monitor its approach and docking to the space station, and then monitor the undocking, deorbit, entry and splashdown.”

As Crew Dragon ascends into space, SpaceX will command Crew Dragon from its mission control center in Hawthorne, California. NASA teams will monitor operations throughout the flight from Mission Control, Houston at the agency’s Johnson Space Center.

SpaceX will test the spacecraft’s autonomous systems’ ability to maneuver and dock with the space station. During Crew Dragon’s approach, on-orbit demonstrations will include rendezvous activities from a distance of up to 2.5 miles (4 km), known as far field, and activities within one mile (1.6 km), known as near field. As the spacecraft approaches the space station, it will demonstrate its automated control and maneuvering capabilities by intentionally reversing course and backing away from the station before the final docking sequence. During this flight, Crew Dragon will dock to the station’s Harmony module forward, fitted with the new international docking adapter installed during an August 2016 spacewalk, port last used during the final shuttle mission in 2011.

The docking phase, as well as the return and recovery of Crew Dragon, include many new first-time events that cannot be totally modeled on the ground and thus are critically important to understand the design and systems ability to support crew flights. Previous cargo Dragon vehicles have been attached to the space station after capture by the station’s robotic arm. The Crew Dragon will fly in all the way to dock using new sensor systems, new propulsion systems and docking mechanism to attach to station.

Image above: A SpaceX Falcon 9 rocket with the company’s Crew Dragon attached, rolls out of the company’s hangar at NASA Kennedy Space Center’s Launch Complex 39A on Jan. 3, 2019. The rocket will undergo checkouts prior to the liftoff of Demo-1, the inaugural flight of one of the spacecraft designed to take NASA astronauts to and from the International Space Station. Image Credit: SpaceX.

or Demo-1, Crew Dragon will carry about 400 pounds of crew supplies and equipment to the space station and return some critical research samples to Earth. Teams in the space station Mission Control Center at Johnson will monitor station crew members’ opening of the spacecraft hatch, enter Crew Dragon and unpack the capsule. The spacecraft will remain docked to the space station for about two weeks. Ultimately, on future missions, Crew Dragon will be able to stay docked to station for up to 210 days during NASA crew rotation missions.

After undocking from station, Crew Dragon will begin its descent to Earth. Additional spacecraft mission objectives will include a safe departure from the station followed by a deorbit burn and parachute deployment to slow the spacecraft before splashdown in the Atlantic Ocean off the Florida Space Coast. SpaceX’s recovery ship, Go Searcher, will retrieve Crew Dragon and transport it back to port.

NASA and SpaceX will use data from Demo-1 to further prepare for Demo-2, the crewed flight test that will carry NASA astronauts Bob Behnken and Doug Hurley to the International Space Station. NASA will validate the performance of SpaceX’s systems before putting crew on-board for the Demo-2 flight, currently targeted for July.

Commercial crew is working with both Boeing and SpaceX to design, build, test and operate safe, reliable and cost-effective human transportation systems to low-Earth orbit. Both companies are targeting to have flight tests with NASA astronauts in 2019, which will restore the nation’s human launch capability to and from the station.

NASA continues to work with Boeing as the company plans for the uncrewed flight test of its CST-100 Starliner spacecraft atop a United Launch Alliance Atlas V rocket, known as the Orbital Flight Test, targeted for NET April 2019. Boeing’s Crew Flight Test is targeted for NET August 2019.

NASA to Provide Coverage of SpaceX Commercial Crew Flight Test

Image above:his illustration depicts SpaceX’s Crew Dragon spacecraft and Falcon 9 rocket lifting off from historic Launch Complex 39A at NASA’s Kennedy Space Center in Florida. Image Credit: SpaceX.

NASA and SpaceX are targeting 2:49 a.m. EST Saturday, March 2, for the launch of the company’s uncrewed Demo-1 flight, which will be the first time a commercially built and operated American rocket and spacecraft designed for humans will launch to the space station. The launch, as well as other activities leading up to the launch, will air on NASA Television and the agency’s website: http://www.nasa.gov/live

Related links:

Commercial Space: http://www.nasa.gov/exploration/commercial/index.html

Commercial Crew: https://www.nasa.gov/exploration/commercial/crew/index.html

International Space Station (ISS): https://www.nasa.gov/mission_pages/station/main/index.html

Images (mentioned), Text, Credits: NASA/KSC/Linda Herridge.

Greetings, Orbiter.chArchive link

Rethinking everything we thought we knew about star clusters

ESA – Gaia Mission patch.

28 February 2019

ESA’s Gaia satellite is on a mission: to map and characterise more than one billion of the stars in the Milky Way. Many of these stars reside in complex, eye-catching clusters scattered throughout our Galaxy and, by studying these stellar groupings, Gaia is revealing much about the formation and evolution of stars in our cosmic home and surroundings.

Image above: Gaia’s view of the sky. Image Credits: ESA/Gaia/DPAC, CC BY-SA 3.0 IGO.

The Milky Way is full of stars. Our Galaxy contains over a hundred billion of them, from dwarf to giant, populating its crowded centre and its spiralling disc.

Many of these stars are thought to have formed in the same way: from huge clouds of cool, condensing molecular gas, which collapse under the influence of gravity and fragment to form groups of hundreds to thousands of stars, known as star clusters. Some of these clusters last thousands of millions of years, while others disperse rapidly, releasing their stellar residents into the Milky Way’s disc.

It is likely that also our Sun formed in a cluster some 4.5 billion years ago, and the quest for solar siblings – stars that were born in the same cluster as the Sun and then went on different paths – will provide important information on the birth of our parent star.

Despite our growing knowledge, many open questions remain. For instance, how many clusters exist, how many are currently being formed, how many are falling apart – and at what pace?

The incredible diversity of stars and their birth clusters is currently being explored by ESA’s Gaia satellite.

Launched in December 2013, Gaia aims to map the nearby cosmos and execute the most extensive census of stars ever performed, tracking the positions, motions, and properties of more than one billion stars in the Milky Way and its surroundings. So far, the mission has released two packages of data: Data Release 1 (DR1) on 14 September 2016, and Data Release 2 (DR2) on 25 April 2018.

Comparison between Gaias first and second data releases

Video above: Comparison between Gaia’s first (left) and second (right) data releases. Click here for details and large versions of the video. Video Credits: ESA/Gaia/DPAC, CC BY-SA 3.0 IGO.

“The first release was planned as more of a test release than a full database, and the second is still early days for Gaia,” says Carme Jordi of the University of Barcelona, Spain, a member of the Gaia Science Team. “Nonetheless, these datasets have already offered us unique insights into the stars within our Galaxy, and in particular into stellar clusters.”

Gaia DR1 contained the positions and brightnesses of 1.1 billion stars, and the parallaxes (a way of measuring distance) and proper motions (movement through the sky) for a subset of two million. Gaia DR2 raises these figures to nearly 1.7 billion stars in terms of positions and brightnesses, over 1.3 billion in terms of parallax and proper motion, and adds new data about stellar colours, line-of-sight velocities, surface temperatures, variability, radii, luminosities, and more.

With Gaia DR2, the mission has provided scientists with new tools to look at star clusters in the Sun’s neighbourhood and beyond.

New clusters unveiled

Alfred Castro-Ginard and colleagues used a statistical method on a subset of Gaia DR1 to discover 21 nearby clusters that had previously gone unnoticed, confirming their findings using the full DR2 data. So far, even if not unanimously, scientists had generally thought that all such clusters out to distances between 3200 and 6500 light-years from Earth had been identified – but this study suggests that there is still much to discover, even in our cosmic neck of the woods.

“It’s worth noting that this study only looked at a small part of the sky,” explains Jordi. “The discovery of new nearby clusters, which should be the easiest to detect, indicates that our knowledge of these clusters is really quite incomplete out to greater distances.”

Image above: Parallaxes in Gaia’s sky. Image Credits: ESA/Gaia/DPAC, CC BY-SA 3.0 IGO.

This finding was soon followed and supported by a different study, led by Tristan Cantat-Gaudin, which re-analysed every previously reported cluster, known and putative alike, using data from Gaia DR2. This research confirmed earlier detections of about 1200 clusters, and determined their average distance and overall motion.

The scientists also serendipitously discovered 60 new potential clusters, but also surprisingly discarded clusters that had previously been identified. The study revealed that many such clusters are actually overlapping groups consisting of more than one cluster, while others are just asterisms – apparent patterns or groupings of stars that are in fact tricks of perspective on the two-dimensional sky.

Another study by Cantat-Gaudin and collaborators focussed on a nearby stellar group known as Vela OB2, which is somewhat looser than an ordinary cluster. Gaia’s precision allowed the scientists to study stellar motions within Vela OB2 in great detail, revealing that it comprises multiple smaller clumps of stars and that the overall complex is expanding. They used the data to unravel the history of this stellar group, which is associated with a large, expanding nearby shell of gas known as the IRAS Vela Shell and thought to have originated in a supernova explosion: according to Gaia, the powerful event that triggered this shell also sparked the formation of Vela OB2’s stars over 10 million years ago.

“Gaia’s extraordinary data are allowing us to revisit our existing stellar census and confirm, discard, and discover clusters,” says Jordi, who is a co-author on all three studies. “This is invaluable in helping us to characterise the distribution of clusters throughout the Milky Way’s disc, and their height in relation to the Galactic plane.”

Tracing clusters across the Galaxy

On a broader Galactic scale, the new cluster counts that scientist have started to put together with Gaia seems to indicate that clusters sitting high above the plane of the Milky Way are old, and located further from our Galaxy’s centre.

“It seems there aren’t old clusters at high altitudes in the inner part of the Galactic disc, so they must have dissolved – just as our models predict,” explains Jordi.

Looking specifically at clusters in higher-altitude areas of our Galaxy’s disc by combining positions and motions on the sky from Gaia DR2 with line-of-sight velocities from a ground-based survey, Janez Kos and colleagues discarded the existence of four out of the five analysed clusters.

In a different study, Caroline Soubiran and colleagues used line-of-sight velocities from Gaia DR2 to explore the kinematics of 861 stellar clusters, and found them to follow the velocity distribution of field stars – stars that are not associated to any cluster – in the solar neighbourhood.

Precise data from Gaia DR2 also contributed to revealing the ongoing evaporation of the nearest cluster to the Sun, the Hyades, in two independent studies led by Stefan Meingast and Siegfried Röser, respectively. This cluster was found to boast two well-defined tidal tails containing hundreds of stars, each extending from the cluster’s core in a distinct ‘S’ shape.

The Hyades cluster

Video above: Flythrough the Gaia data, towards the Hyades cluster. Click here for details and large versions of the video. Video Credits: ESA/Gaia/DPAC, CC BY-SA 3.0 IGO.

“This unique finding opens a new window for studying how clusters, through their gradual demise under the influence of the Milky Way’s gravity, continuously feed the Galactic disc with stars,” says Jordi.

Clusters as stellar test-beds

Star clusters are not only tracers of how the disc of our Galaxy has evolved over time, but also excellent laboratories for studying stellar physics. With its unprecedented data, Gaia has started to reveal previously unseen details that have an impact on our understanding of the formation and evolution of stars.

By plotting the colour of stars against their brightness, astronomers have been using the so-called Hertzsprung-Russell (HR) diagram to study the evolution of stellar populations for over a century. In this diagram, most stars lie along a top-left to bottom-right diagonal line known as the ‘main sequence’ – which identifies stars in their prime, burning hydrogen fuel in their cores – while stars in later stages of their lives are found away from this sequence.

The Hertzsprung-Russell diagram

Video above: The Hertzsprung-Russell diagram. Click here for details and large versions of the video. Video Credits: ESA/Gaia/DPAC, CC BY-SA 3.0 IGO.

In clusters, which were historically thought to contain a single, simple population of stars that formed all at the same time, the position in the diagram where the main sequence ‘turns off’ was customarily used to estimate the age of that particular stellar population. However, in recent years, scientists had found evidence that clusters may comprise more than one population of stars, based on the observation of multiple turn-off points in their HR diagrams.

Gaia is now calling for a rethink of this phenomenon, as several studies based on its latest dataset seem to indicate how the multiple turn-off points can be explained without invoking several populations of stars, but rather by properly including the effects of the rotation of cluster stars on their predicted colours. For example, Anna Marino and colleagues conducted two studies using photometric data from Gaia DR2 to suggest that this is a common feature in Milky Way clusters, while Beomdu Lim and colleagues found a similar result by combining Gaia proper motions with ground-based spectroscopic observations of M11, also known as the ‘Wild Duck’ cluster. Similarly, Giacomo Cordoni and colleagues used a mix of stellar velocity, photometry, and proper motion data to confirm that rotational effects of stars can affect their estimated colours and lifespans.

Gaia. Animation Credit: ESA

This is certainly not the final word on stellar clusters, and many more studies will follow in coming years and clarify, reopen, and perhaps even deepen these intriguing topics. Like every great mission or experiment, Gaia is providing scientists with precise and plentiful data that are increasing our understanding of many astronomical problems, giving rise to new and more profound questions as our knowledge grows.

“Gaia is unique and revolutionising all fields of astrophysics, with this recent research on star clusters being a good example,” says Jos de Bruijne, Gaia deputy project scientist at ESA.

“The mission has given us precise measurements of how stars move through space and their distances from us… and it has done this for over one billion stars. We’ve never had anything like this database before, and it’s invaluable in helping us study our Galaxy.

“The recent star-cluster discoveries make this a hugely exciting area of research – especially as we have more Gaia data releases to look forward to in coming years.”

More information:

ESA’s Gaia satellite was launched in 2013 to create the most precise three-dimensional map of more than one billion stars in the Milky Way. The mission has released two lots of data so far: Gaia Data Release 1 on 14 September 2016, and Gaia Data Release 2 on 25 April 2018. More releases will follow in coming years.

Related links:

Gaia Data Release 1: http://sci.esa.int/gaia/58275-data-release-1/

Gaia Data Release 2: http://sci.esa.int/gaia/60243-data-release-2/

Hertzsprung-Russell (HR) diagram: http://sci.esa.int/gaia-stellar-family-portrait/

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

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

Greetings, Orbiter.chArchive link


Полет на параплане с обрыва на мысу Куяльницкого лимана, соленого озера. Экстремальный развлекательный полет проводится для любителей. ...