Month: May 2019

Explosions Of Universe’s First Stars Spewed Powerful Jets

Several hundred million years after the Big Bang, the very first stars flared into the universe as massively bright accumulations of hydrogen and helium gas. Within the cores of these first stars, extreme, thermonuclear reactions forged the first heavier elements, including carbon, iron, and zinc.

These first stars were likely immense, short-lived fireballs, and scientists have assumed that they exploded as similarly spherical supernovae.

But now astronomers at MIT and elsewhere have found that these first stars may have blown apart in a more powerful, asymmetric fashion, spewing forth jets that were violent enough to eject heavy elements into neighboring galaxies. These elements ultimately served as seeds for the second generation of stars, some of which can still be observed today.

In a paper published today in the Astrophysical Journal, the researchers report a strong abundance of zinc in HE 1327-2326, an ancient, surviving star that is among the universe’s second generation of stars. They believe the star could only have acquired such a large amount of zinc after an asymmetric explosion of one of the very first stars had enriched its birth gas cloud.

“When a star explodes, some proportion of that star gets sucked into a black hole like a vacuum cleaner,” says Anna Frebel, an associate professor of physics at MIT and a member of MIT’s Kavli Institute for Astrophysics and Space Research. “Only when you have some kind of mechanism, like a jet that can yank out material, can you observe that material later in a next-generation star. And we believe that’s exactly what could have happened here.”

“This is the first observational evidence that such an asymmetric supernova took place in the early universe,” adds MIT postdoc Rana Ezzeddine, the study’s lead author. “This changes our understanding of how the first stars exploded.”

“A sprinkle of elements”

HE 1327-2326 was discovered by Frebel in 2005. At the time, the star was the most metal-poor star ever observed, meaning that it had extremely low concentrations of elements heavier than hydrogen and helium — an indication that it formed as part of the second generation of stars, at a time when most of the universe’s heavy element content had yet to be forged.

“The first stars were so massive that they had to explode almost immediately,” Frebel says. “The smaller stars that formed as the second generation are still available today, and they preserve the early material left behind by these first stars. Our star has just a sprinkle of elements heavier than hydrogen and helium, so we know it must have formed as part of the second generation of stars.”

In May of 2016, the team was able to observe the star which orbits close to Earth, just 5,000 light years away. The researchers won time on NASA’s Hubble Space Telescope over two weeks, and recorded the starlight over multiple orbits. They used an instrument aboard the telescope, the Cosmic Origins Spectrograph, to measure the minute abundances of various elements within the star.

The spectrograph is designed with high precision to pick up faint ultraviolet light. Some of those wavelength are absorbed by certain elements, such as zinc. The researchers made a list of heavy elements that they suspected might be within such an ancient star, that they planned to look for in the UV data, including silicon, iron, phosophorous, and zinc.

“I remember getting the data, and seeing this zinc line pop out, and we couldn’t believe it, so we redid the analysis again and again,” Ezzeddine recalls. “We found that, no matter how we measured it, we got this really strong abundance of zinc.”

A star channel opens

Frebel and Ezzeddine then contacted their collaborators in Japan, who specialize in developing simulations of supernovae and the secondary stars that form in their aftermath. The researchers ran over 10,000 simulations of supernovae, each with different explosion energies, configurations, and other parameters. They found that while most of the spherical supernova simulations were able to produce a secondary star with the elemental compositions the researchers observed in HE 1327-2326, none of them reproduced the zinc signal.

As it turns out, the only simulation that could explain the star’s makeup, including its high abundance of zinc, was one of an aspherical, jet-ejecting supernova of a first star. Such a supernova would have been extremely explosive, with a power equivalent to about a nonillion times (that’s 10 with 30 zeroes after it) that of a hydrogen bomb.

“We found this first supernova was much more energetic than people have thought before, about five to 10 times more,” Ezzeddine says. “In fact, the previous idea of the existence of a dimmer supernova to explain the second-generation stars may soon need to be retired.”

The team’s results may shift scientists’ understanding of reionization, a pivotal period during which the gas in the universe morphed from being completely neutral, to ionized — a state that made it possible for galaxies to take shape.

“People thought from early observations that the first stars were not so bright or energetic, and so when they exploded, they wouldn’t participate much in reionizing the universe,” Frebel says. “We’re in some sense rectifying this picture and showing, maybe the first stars had enough oomph when they exploded, and maybe now they are strong contenders for contributing to reionization, and for wreaking havoc in their own little dwarf galaxies.”

These first supernovae could have also been powerful enough to shoot heavy elements into neighboring “virgin galaxies” that had yet to form any stars of their own.

“Once you have some heavy elements in a hydrogen and helium gas, you have a much easier time forming stars, especially little ones,” Frebel says. “The working hypothesis is, maybe second generation stars of this kind formed in these polluted virgin systems, and not in the same system as the supernova explosion itself, which is always what we had assumed, without thinking in any other way. So this is opening up a new channel for early star formation.”

A New Filter To Better Map The Dark Universe

The earliest known light in our universe, known as the cosmic microwave background, was emitted about 380,000 years after the Big Bang. The patterning of this relic light holds many important clues to the development and distribution of large-scale structures such as galaxies and galaxy clusters.

Distortions in the cosmic microwave background (CMB), caused by a phenomenon known as lensing, can further illuminate the structure of the universe and can even tell us things about the mysterious, unseen universe — including dark energy, which makes up about 68 percent of the universe and accounts for its accelerating expansion, and dark matter, which accounts for about 27 percent of the universe.

Set a stemmed wine glass on a surface, and you can see how lensing effects can simultaneously magnify, squeeze, and stretch the view of the surface beneath it. In lensing of the CMB, gravity effects from large objects like galaxies and galaxy clusters bend the CMB light in different ways. These lensing effects can be subtle (known as weak lensing) for distant and small galaxies, and computer programs can identify them because they disrupt the regular CMB patterning.

There are some known issues with the accuracy of lensing measurements, though, and particularly with temperature-based measurements of the CMB and associated lensing effects.

While lensing can be a powerful tool for studying the invisible universe, and could even potentially help us sort out the properties of ghostly subatomic particles like neutrinos, the universe is an inherently messy place.

And like bugs on a car’s windshield during a long drive, the gas and dust swirling in other galaxies, among other factors, can obscure our view and lead to faulty readings of the CMB lensing.

There are some filtering tools that help researchers to limit or mask some of these effects, but these known obstructions continue to be a major problem in the many studies that rely on temperature-based measurements.

The effects of this interference with temperature-based CMB studies can lead to erroneous lensing measurements, said Emmanuel Schaan, a postdoctoral researcher and Owen Chamberlain Postdoctoral Fellow in the Physics Division at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).

“You can be wrong and not know it,” Schaan said. “The existing methods don’t work perfectly — they are really limiting.”

To address this problem, Schaan teamed up with Simone Ferraro, a Divisional Fellow in Berkeley Lab’s Physics Division, to develop a way to improve the clarity and accuracy of CMB lensing measurements by separately accounting for different types of lensing effects.

“Lensing can magnify or demagnify things. It also distorts them along a certain axis so they are stretched in one direction,” Schaan said.

The researchers found that a certain lensing signature called shearing, which causes this stretching in one direction, seems largely immune to the foreground “noise” effects that otherwise interfere with the CMB lensing data. The lensing effect known as magnification, meanwhile, is prone to errors introduced by foreground noise. Their study, published May 8 in the journal Physical Review Letters, notes a “dramatic reduction” in this error margin when focusing solely on shearing effects.

The sources of the lensing, which are large objects that stand between us and the CMB light, are typically galaxy groups and clusters that have a roughly spherical profile in temperature maps, Ferraro noted, and the latest study found that the emission of various forms of light from these “foreground” objects only appears to mimic the magnification effects in lensing but not the shear effects.

“So we said, ‘Let’s rely only on the shear and we’ll be immune to foreground effects,'” Ferraro said. “When you have many of these galaxies that are mostly spherical, and you average them, they only contaminate the magnification part of the measurement. For shear, all of the errors are basically gone.”

He added, “It reduces the noise, allowing us to get better maps. And we’re more certain that these maps are correct,” even when the measurements involve very distant galaxies as foreground lensing objects.

The new method could benefit a range of sky-surveying experiments, the study notes, including the POLARBEAR-2 and Simons Array experiments, which have Berkeley Lab and UC Berkeley participants; the Advanced Atacama Cosmology Telescope (AdvACT) project; and the South Pole Telescope — 3G camera (SPT-3G). It could also aid the Simons Observatory and the proposed next-generation, multilocation CMB experiment known as CMB-S4 — Berkeley Lab scientists are involved in the planning for both of these efforts.

The method could also enhance the science yield from future galaxy surveys like the Berkeley Lab-led Dark Energy Spectroscopic Instrument (DESI) project under construction near Tucson, Arizona, and the Large Synoptic Survey Telescope (LSST) project under construction in Chile, through joint analyses of data from these sky surveys and the CMB lensing data.

Increasingly large datasets from astrophysics experiments have led to more coordination in comparing data across experiments to provide more meaningful results. “These days, the synergies between CMB and galaxy surveys are a big deal,” Ferraro said.

In this study, researchers relied on simulated full-sky CMB data. They used resources at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC) to test their method on each of the four different foreground sources of noise, which include infrared, radiofrequency, thermal, and electron-interaction effects that can contaminate CMB lensing measurements.

The study notes that cosmic infrared background noise, and noise from the interaction of CMB light particles (photons) with high-energy electrons have been the most problematic sources to address using standard filtering tools in CMB measurements. Some existing and future CMB experiments seek to lessen these effects by taking precise measurements of the polarization, or orientation, of the CMB light signature rather than its temperature.

“We couldn’t have done this project without a computing cluster like NERSC,” Schaan said. NERSC has also proved useful in serving up other universe simulations to help prepare for upcoming experiments like DESI.

The method developed by Schaan and Ferraro is already being implemented in the analysis of current experiments’ data. One possible application is to develop more detailed visualizations of dark matter filaments and nodes that appear to connect matter in the universe via a complex and changing cosmic web.

What A Dying Star’s Ashes Tell Us About The Birth Of Our Solar System

A grain of dust forged in the death throes of a long-gone star was discovered by a team of researchers led by the University of Arizona.

The discovery challenges some of the current theories about how dying stars seed the universe with raw materials for the formation of planets and, ultimately, the precursor molecules of life.

Tucked inside a chondritic meteorite collected in Antarctica, the tiny speck represents actual stardust, most likely hurled into space by an exploding star before our own sun existed. Although such grains are believed to provide important raw materials contributing to the mix from which the sun and our planets formed, they rarely survive the turmoil that goes with the birth of a solar system.

“As actual dust from stars, such presolar grains give us insight into the building blocks from which our solar system formed,” said Pierre Haenecour, lead author of the paper, which is scheduled for advance online publication on Nature Astronomy’s website on Apr. 29. “They also provide us with a direct snapshot of the conditions in a star at the time when this grain was formed.”

Dubbed LAP-149, the dust grain represents the only known assemblage of graphite and silicate grains that can be traced to a specific type of stellar explosion called a nova. Remarkably, it survived the journey through interstellar space and traveled to the region that would become our solar system some 4.5 billion years ago, perhaps earlier, where it became embedded in a primitive meteorite.

Novae are binary star systems in which a core remnant of a star, called a white dwarf, is on its way to fading out of the universe, while its companion is either a low-mass main sequence star or a red giant. The white dwarf then begins syphoning material off its bloated companion. Once it accretes enough new stellar material, the white dwarf re-ignites in periodic outbursts violent enough to forge new chemical elements from the stellar fuel and spew them deep into space, where they can travel to new stellar systems and become incorporated in their raw materials.

Since shortly after the Big Bang, when the universe consisted of only hydrogen, helium and traces of lithium, stellar explosions have contributed to the chemical enrichment of the cosmos, resulting in the plethora of elements we see today.

Taking advantage of sophisticated ion and electron microscopy facilities at the UA’s Lunar and Planetary Laboratory, a research team led by Haenecour analyzed the microbe-sized dust grain down to the atomic level. The tiny messenger from outer space turned out to be truly alien — highly enriched in a carbon isotope called 13C.

“The carbon isotopic compositions in anything we have ever sampled that came from any planet or body in our solar system varies typically by a factor on the order of 50,” said Haenecour, who will join the Lunar and Planetary Laboratory as an assistant professor in the fall. “The 13C we found in LAP-149 is enriched more than 50,000-fold. These results provide further laboratory evidence that both carbon- and oxygen-rich grains from novae contributed to the building blocks of our solar system.”

Although their parent stars no longer exist, the isotopic and chemical compositions and microstructure of individual stardust grains identified in meteorites provide unique constraints on dust formation and thermodynamic conditions in stellar outflows, the authors wrote.

Detailed analysis revealed even more unexpected secrets: Unlike similar dust grains thought to have been forged in dying stars, LAP-149 is the first known grain consisting of graphite that contains an oxygen-rich silicate inclusion.

“Our find provides us with a glimpse into a process we could never witness on Earth,” Haenecour added. “It tells us about how dust grains form and move around inside as they are expelled by the nova. We now know that carbonaceous and silicate dust grains can form in the same nova ejecta, and they get transported across chemically distinct clumps of dust within the ejecta, something that was predicted by models of novae but never found in a specimen.”

Unfortunately, LAP-149 does not contain enough atoms to determine its exact age, so researchers hope to find similar, larger specimens in the future.

“If we could date these objects someday, we could get a better idea of what our galaxy looked like in our region and what triggered the formation of the solar system,” said Tom Zega, scientific director of the UA’s Kuiper Materials Imaging and Characterization Facility and associate professor in the Lunar and Planetary Laboratory and UA Department of Materials Science and Engineering. “Perhaps we owe our existence to a nearby supernova explosion, compressing clouds of gas and dust with its shockwave, igniting stars and creating stellar nurseries, similar to what we see in Hubble’s famous ‘Pillars of Creation’ picture.”

The meteorite containing the speck of stardust is one of the most pristine meteorites in the Lunar and Planetary Laboratory’s collection. Classified as a carbonaceous chondrite, it is believed to be analogous to the material on Bennu, the target asteroid of the UA-led OSIRIS-REx mission. By taking a sample of Bennu and bringing it back to Earth, the OSIRIS-REx mission team hopes to provide scientists with material that has seen little, if any, alteration since the formation of our solar system.

Until then, researchers depend on rare finds like LAP-149, which survived being blasted from an exploding star, caught in a collapsing cloud of gas and dust that would become our solar system and baked into an asteroid before falling to the earth.

“It’s remarkable when you think about all the ways along the way that should have killed this grain,” Zega said.

Two Neutron Stars Collided Near The Solar System Billions Of Years Ago

Astrophysicists Szabolcs Marka at Columbia University and Imre Bartos at the University of Florida, have identified a violent collision of two neutron stars 4.6 billion years ago as the likely source of some of the most coveted matter on Earth.

This single cosmic event, close to our solar system, gave birth to 0.3 percent of the Earth’s heaviest elements, including gold, platinum and uranium, according to a new paper appearing in the May 2 issue of Nature.

“This means that in each of us we would find an eyelash worth of these elements, mostly in the form of iodine, which is essential to life,” Bartos said. “A wedding ring, which expresses a deep human connection, is also a connection to our cosmic past predating humanity and the formation of Earth itself, with about 10 milligrams of it likely having formed 4.6 billion years ago.”

“Meteorites forged in the early solar system carry the traces of radioactive isotopes,” said Bartos, who received his Ph.D. at Columbia.

“As these isotopes decay they act as clocks that can be used to reconstruct the time they were created,” Marka said.

To arrive at their conclusion, Bartos and Marka compared the composition of meteorites to numerical simulations of the Milky Way. They found that a single neutron-star collision could have occurred about 100 million years before the formation of Earth, in our own neighborhood, about 1000 light years from the gas cloud that eventually formed the Solar System.

The Milky Way galaxy itself is 100,000 light years in diameter, or 100 times the distance of this cosmic event from the cradle of Earth. “If a comparable event happened today at a similar distance from the Solar System, the ensuing radiation could outshine the entire night sky,” Marka said.

The researchers believe that their study provides insight into a uniquely consequential event in our history. “It sheds bright light on the processes involved in the origin and composition of our solar system, and will initiate a new type of quest within disciplines, such as chemistry, biology and geology, to solve the cosmic puzzle,” Bartos said.

“Our results address a fundamental quest of humanity: Where did we come from and where are we going? It is very difficult to describe the tremendous emotions we felt when realized what we had found and what it means for the future as we search for an explanation of our place in the universe, ” Marka said.

Telescopes In Space For Even Sharper Images Of Black Holes

Astronomers have just managed to take the first image of a black hole, and now the next challenge facing them is how to take even sharper images, so that Einstein’s Theory of General Relativity can be tested. Radboud University astronomers, along with the European Space Agency (ESA) and others, are putting forward a concept for achieving this by launching radio telescopes into space. They publish their plans in the scientific journal Astronomy & Astrophysics.

The idea is to place two or three satellites in circular orbit around the Earth to observe black holes. The concept goes by the name Event Horizon Imager (EHI). In their new study, the scientists present simulations of what images of the black hole Sagittarius A* would look if they were taken by satellites like these.

More than five times as sharp

“There are lots of advantages to using satellites instead of permanent radio telescopes on Earth, as with the Event Horizon Telescope (EHT),” says Freek Roelofs, a PhD candidate at Radboud University and the lead author of the article. “In space, you can make observations at higher radio frequencies, because the frequencies from Earth are filtered out by the atmosphere. The distances between the telescopes in space are also larger. This allows us to take a big step forward. We would be able to take images with a resolution more than five times what is possible with the EHT.”

Sharper images of a black hole will lead to better information that could be used to test Einstein’s Theory of General Relativity in greater detail. “The fact that the satellites are moving round the Earth makes for considerable advantages,” Radio Astronomy Professor Heino Falcke says. “With them, you can take near perfect images to see the real details of black holes. If small deviations from Einstein’s theory occur, we should be able to see them.”

The EHI will also be able to image about five additional black holes that are smaller than the black holes that the EHT is currently focussing on. The latter are Sagittarius A* at the centre of our Milky Way and M87* at the centre of Messier 87, a massive galaxy in the Virgo Cluster.

Technological challenges

The researchers have simulated what they would be able to see with different versions of the technology under different circumstances. For this they made use of models of plasma behaviour around the black hole and the resulting radiation. “The simulations look promising from a scientific aspect, but there are difficulties to overcome at a technical level,” Roelofs says.

The astronomers collaborated with scientists from ESA/ESTEC to investigate the technical feasibility of the project. “The concept demands that you must be able to ascertain the position and speed of the satellites very accurately,” according to Volodymyr Kudriashov, a researcher at the Radboud Radio Lab who also works at ESA/ESTEC. “But we really believe that the project is feasible.”

Consideration also has to be given to how the satellites exchange data. “With the EHT, hard drives with data are transported to the processing centre by airplane. That’s of course not possible in space.” In this concept, the satellites will exchange data via a laser link, with the data being partially processed on board before being sent back to Earth for further analysis. “There are already laser links in space,” Kudriashov notes.

Hybrid system

The idea is that the satellites will initially function independently of the EHT telescopes. But consideration is also being given to a hybrid system, with the orbiting telescopes combined with the ones on Earth. Falcke: “Using a hybrid like this could provide the possibility of creating moving images of a black hole, and you might be able to observe even more and also weaker sources.”

The research is part of the BlackHoleCam project, which is an ERC Synergy Grant awarded in 2013 to a team of European astrophysicists to image, measure and understand black holes. BlackHoleCam is an active partner of the Event Horizon Telescope collaboration.

At Least 15 Dead As Cyclone Fani Moves Toward Bangladesh

Dhaka, Bangladesh — A mammoth preparation exercise that included the evacuation of more than 1 million people appears to have spared India a devastating death toll from Cyclone Fani, one of the biggest storms in decades. However, the full extent of the damage was yet to be known, officials said Saturday.

The cyclone packed winds of 155 miles per hour when it made landfall in eastern Odisha state on Friday, equivalent in strength to a Category 4 hurricane, said Mohammad Heidarzadei, an expert on cyclones at Brunel University of London.

As of late Saturday, India’s National Disaster Response Force director S.N. Pradhan said three people had been killed, though the storm smashed thatched-roof huts, uprooted trees and power lines, ripped the roof off a medical college and sprayed the emptied coastline with debris. “The precautions that have been taken should be continued,” Pradhan said.

Officials cautioned that the death toll could rise as communications were restored.

Fani crossed over India’s West Bengal state and moved northeast toward Bangladesh on Saturday, weakening from a severe cyclonic storm to a cyclonic storm.

At least a dozen people had been confirmed killed in Bangladesh as the cyclone hovered over the country’s southwestern coast early Saturday, delivering battering rain storms. Lightning killed at least six people, local newspapers and TV reported. However, the death toll had not increased by Saturday afternoon, suggesting effective preparedness in Bangladesh as well.

Bad weather from the storm system was projected to affect around 100 million people in South Asia, from India’s distant Andaman Islands to Mount Everest in Nepal.

The relatively low casualty count demonstrates much improved disaster readiness in India since 1999, when a “super” cyclone killed around 10,000 people and devastated large parts of Odisha.

“In the event of such a major calamity like this — where Odisha was hit by close to a super-cyclone — instead of being a tragedy of humongous proportion, we are in the process of restoring critical infrastructure. That is the transformation that Odisha has had,” the state’s top government official, Naveen Patnaik, said in a statement.

India’s disaster response agency said authorities were working “on war footing” to restore power and communications, and clear roads of debris. Widespread power outages, damaged water supplies and roads blocked by fallen trees and power lines made transport around the affected area difficult, officials said.

Pravat Ranjan Mohapatra, the deputy relief commissioner at Odisha’s emergency center, said his phone line and internet were down for most of Saturday.

“Earlier we were not able to connect with authorities for infrastructure damage, how many houses are damaged or how many people have died or were injured,” he said.

According to the Press Trust of India, one victim was a teenager killed by a falling tree in the district of Puri, a popular tourist area in Odisha. Another woman was killed while fetching water when she was struck by flying debris loosened from a concrete structure. Another woman, age 65, died after a suspected heart attack at a cyclone shelter, PTI reported.

Water Found In Samples From Asteroid Itokawa

Two cosmochemists at Arizona State University have made the first-ever measurements of water contained in samples from the surface of an asteroid. The samples came from asteroid Itokawa and were collected by the Japanese space probe Hayabusa.

The team’s findings suggest that impacts early in Earth’s history by similar asteroids could have delivered as much as half of our planet’s ocean water.

“We found the samples we examined were enriched in water compared to the average for inner solar system objects,” says Ziliang Jin. A postdoctoral scholar in ASU’s School of Earth and Space Exploration, he is the lead author on the paper published May 1 in Science Advances reporting the results. His co-author is Maitrayee Bose, assistant professor in the School.

“It was a privilege that the Japanese space agency JAXA was willing to share five particles from Itokawa with a U.S. investigator,” Bose says. “It also reflects well on our School.”

The team’s idea of looking for water in the Itokawa samples came as a surprise for the Hayabusa project.

“Until we proposed it, no one thought to look for water,” says Bose. “I’m happy to report that our hunch paid off.”

In two of the five particles, the team identified the mineral pyroxene. In terrestrial samples, pyroxenes have water in their crystal structure. Bose and Jin suspected that the Itokawa particles might also have traces of water, but they wanted to know exactly how much. Itokawa has had a rough history involving heating, multiple impacts, shocks, and fragmentation. These would raise the temperature of the minerals and drive off water.

To study the samples, each about half the thickness of a human hair, the team used ASU’s Nanoscale Secondary Ion Mass Spectrometer (NanoSIMS), which can measure such tiny mineral grains with great sensitivity.

The NanoSIMS measurements revealed the samples were unexpectedly rich in water. They also suggest that even nominally dry asteroids such as Itokawa may in fact harbor more water than scientists have assumed.

Fragmented world

Itokawa is a peanut-shaped asteroid about 1,800 feet long and 700 to 1,000 feet wide. It circles the Sun every 18 months at an average distance of 1.3 times the Earth-Sun distance. Part of Itokawa’s path brings it inside Earth’s orbit and at farthest, it sweeps out a little beyond that of Mars.

Based on Itokawa’s spectrum in Earth-based telescopes, planetary scientists place it in the S class. This links it with the stony meteorites, which are thought to be fragments from S-type asteroids broken off in collisions.

“S-type asteroids are one of the most common objects in the asteroid belt,” says Bose. “They originally formed at a distance from the Sun of one-third to three times Earth’s distance.” She adds that although they are small, these asteroids have kept whatever water and other volatile materials they formed with.

In structure, Itokawa resembles a pair of rubble piles crunched together. It has two main lobes, each studded with boulders but having different overall densities, while between the lobes is a narrower section.

Jin and Bose point out that today’s Itokawa is the remnant of a parent body at least 12 miles wide that at some point was heated between 1,000 and 1,500 degrees Fahrenheit. The parent body suffered several large shocks from impacts, with one final shattering event that broke it apart. In the aftermath two of the fragments merged and formed today’s Itokawa, which reached its current size and shape about 8 million years ago.

“The particles we analyzed came from a part of Itokawa called the Muses Sea,” says Bose. “It’s an area on the asteroid that’s smooth and dust-covered.”

Jin adds, “Although the samples were collected at the surface, we don’t know where these grains were in the original parent body. But our best guess is that they were buried more than 100 meters deep within it.”

He adds that despite the catastrophic breakup of the parent body, and the sample grains being exposed to radiation and impacts by micrometeorites at the surface, the minerals still show evidence of water that has not been lost to space.

In addition, says Jin, “The minerals have hydrogen isotopic compositions that are indistinguishable from Earth.”

Bose explains, “This means S-type asteroids and the parent bodies of ordinary chondrites are likely a critical source of water and several other elements for the terrestrial planets.”

She adds, “And we can say this only because of in-situ isotopic measurements on returned samples of asteroid regolith — their surface dust and rocks.

“That makes these asteroids high-priority targets for exploration.”

Scouting for samples

Bose notes that she is building a clean-lab facility at ASU, which along with the NanoSIMS (partially funded by National Science Foundation) would be the first such facility at a public university capable of analyzing dust grains from other solar system bodies.

Another Japanese mission, Hayabusa 2, is currently at an asteroid named Ryugu, where it will collect samples, bringing them back to Earth in December 2020. The director of ASU’s Center for Meteorite Studies, professor Meenakshi Wadhwa, is a member of the Initial Analysis team for Chemistry for the Hayabusa 2 mission.

ASU is also on board NASA’s OSIRIS-REx sample-return mission, which is orbiting a near-Earth asteroid named Bennu. Among other instruments, the spacecraft carries the OSIRIS-REx Thermal Emission Spectrometer (OTES), designed by ASU Regents’ Professor Philip Christensen and built at the School. OSIRIS-REx is scheduled to collect samples from Bennu in summer 2020 and bring them back to Earth in September 2023.

For planetary scientists and cosmochemists who are drawing a picture of how the solar system formed, asteroids are a great resource. As leftover building blocks for the planetary system, they vary greatly among themselves while preserving materials from early in solar system history.

Says Bose, “Sample-return missions are mandatory if we really want to do an in-depth study of planetary objects.”

And she adds, “The Hayabusa mission to Itokawa has expanded our knowledge of the volatile contents of the bodies that helped form Earth. It would not be surprising if a similar mechanism of water production is common for rocky exoplanets around other stars.”