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About 2.6 million years ago, an oddly bright light arrived in the prehistoric sky and lingered there for weeks or months. It was a supernova some 150 light years away from Earth. Within a few hundred years, long after the strange light in the sky had dwindled, a tsunami of cosmic energy from that same shattering star explosion could have reached our planet and pummeled the atmosphere, touching off climate change and triggering mass extinctions of large ocean animals, including a shark species that was the size of a school bus.

A nearby supernova remnant [Credit: NASA]

The effects of such a supernova -- and possibly more than one -- on large ocean life are detailed in a paper just published in Astrobiology.

"I've been doing research like this for about 15 years, and always in the past it's been based on what we know generally about the universe -- that these supernovae should have affected Earth at some time or another," said lead author Adrian Melott, professor emeritus of physics & astronomy at the University of Kansas. "This time, it's different. We have evidence of nearby events at a specific time. We know about how far away they were, so we can actually compute how that would have affected the Earth and compare it to what we know about what happened at that time -- it's much more specific."

Melott said recent papers revealing ancient seabed deposits of iron-60 isotopes provided the "slam-dunk" evidence of the timing and distance of supernovae.

"As far back as the mid-1990s, people said, 'Hey, look for iron-60. It's a telltale because there's no other way for it to get to Earth but from a supernova.' Because iron-60 is radioactive, if it was formed with the Earth it would be long gone by now. So, it had to have been rained down on us. There's some debate about whether there was only one supernova really nearby or a whole chain of them. I kind of favor a combo of the two -- a big chain with one that was unusually powerful and close. If you look at iron-60 residue, there's a huge spike 2.6 million years ago, but there's excess scattered clear back 10 million years."

Melott's co-authors were Franciole Marinho of Universidade Federal de Sao Carlos in Brazil and Laura Paulucci of Universidade Federal do ABC, also in Brazil.

According to the team, other evidence for a series of supernovae is found in the very architecture of the local universe.

"We have the Local Bubble in the interstellar medium," Melott said. "We're right on its edge. It's a giant region about 300 light years long. It's basically very hot, very low-density gas -- nearly all the gas clouds have been swept out of it. The best way to manufacture a bubble like that is a whole bunch of supernovae blows it bigger and bigger, and that seems to fit well with idea of a chain. When we do calculations, they're based on the idea that one supernova that goes off, and its energy sweeps by Earth, and it's over. But with the Local Bubble, the cosmic rays kind of bounce off the sides, and the cosmic-ray bath would last 10,000 to 100,000 years. This way, you could imagine a whole series of these things feeding more and more cosmic rays into the Local Bubble and giving us cosmic rays for millions of years."

Muons showering Earth may have spelled curtains for Megalodon, a school-bus-sized shark, 2.6 million years ago [Credit: Karen Carr]

Whether or not there was one supernova or a series of them, the supernova energy that spread layers of iron-60 all over the world also caused penetrating particles called muons to shower Earth, causing cancers and mutations -- especially to larger animals.

"The best description of a muon would be a very heavy electron - but a muon is a couple hundred times more massive than an electron," Melott said. "They're very penetrating. Even normally, there are lots of them passing through us. Nearly all of them pass through harmlessly, yet about one-fifth of our radiation dose comes by muons. But when this wave of cosmic rays hits, multiply those muons by a few hundred. Only a small faction of them will interact in any way, but when the number is so large and their energy so high, you get increased mutations and cancer -- these would be the main biological effects. We estimated the cancer rate would go up about 50 percent for something the size of a human -- and the bigger you are, the worse it is. For an elephant or a whale, the radiation dose goes way up."

A supernova 2.6 million years ago may be related to a marine megafaunal extinction at the Pliocene-Pleistocene boundary where 36 percent of the genera were estimated to become extinct. The extinction was concentrated in coastal waters, where larger organisms would catch a greater radiation dose from the muons.

According to the authors of the new paper, damage from muons would extend down hundreds of yards into ocean waters, becoming less severe at greater depths: "High energy muons can reach deeper in the oceans being the more relevant agent of biological damage as depth increases," they write.

Indeed, a famously large and fierce marine animal inhabiting shallower waters may have been doomed by the supernova radiation.

"One of the extinctions that happened 2.6 million years ago was Megalodon," Melott said. "Imagine the Great White Shark in 'Jaws,' which was enormous -- and that's Megalodon, but it was about the size of a school bus. They just disappeared about that time. So, we can speculate it might have something to do with the muons. Basically, the bigger the creature is the bigger the increase in radiation would have been."

The KU researcher said the evidence of a supernova, or series of them, is "another puzzle piece" to clarify the possible reasons for the Pliocene-Pleistocene boundary extinction.

"There really hasn't been any good explanation for the marine megafaunal extinction," Melott said. "This could be one. It's this paradigm change -- we know something happened and when it happened, so for the first time we can really dig in and look for things in a definite way. We now can get really definite about what the effects of radiation would be in a way that wasn't possible before."

Source: University of Kansas [December 11, 2018]

New work from the Carnegie Supernova Project provides the best-yet calibrations for using type Ia supernovae to measure cosmic distances, which has implications for our understanding of how fast the universe is expanding and the role dark energy may play in driving this process. Led by Carnegie astronomer Chris Burns, the team's findings are published in The Astrophysical Journal.

An artist's conception of what's called the cosmic distance ladder -- a series of celestial objects, including type Ia supernovae that have known distances and can be used to calculate the rate at which the universe is expanding [Credit: NASA/JPL-Caltech]

Type Ia supernovae are fantastically bright stellar phenomena. They are violent explosions of a white dwarf--the crystalline remnant of a star that has exhausted its nuclear fuel--which is part of a binary system with another star.

In addition to being exciting to observe in their own right, type Ia supernovae are also a vital tool that astronomers use as a kind of cosmic mile marker to infer the distances of celestial objects.

While the precise details of the explosion are still unknown, it is believed that they are triggered when the white dwarf approaches a critical mass, so the brightness of the phenomenon is predictable from the energy of the explosion. The difference between the predicted brightness and the brightness observed from Earth tells us the distance to the supernova.

Astronomers employ these precise distance measurements, along with the speed at which their host galaxies are receding, to determine the rate at which the universe is expanding. Thanks to the finite speed of light, not only can we measure how quickly the universe is expanding right now, but by looking farther and farther out into space, we see further back in time and can measure how fast the universe was expanding in the distant past. This led to the astonishing discovery in the late-1990s that the universe's expansion is currently speeding up due to the repulsive effect of a mysterious "dark" energy. Improving the distance estimates made using type Ia supernovae will help astronomers better understand the role that dark energy plays in this cosmic expansion.

"Beginning with its namesake, Edwin Hubble, Carnegie astronomers have a long history of working on the Hubble constant, including vital contributions to our understanding of the universe's expansion made by Alan Sandage and Wendy Freedman," said Observatories Director John Mulchaey.

This is an artist's conception shows a type Ia supernova exploding [Credit: ESO]

However, the speed at which the brightness of type Ia supernova explosions fade away is not uniform. In 1993, Carnegie astronomer Mark Phillips showed that the explosions that take longer to fade away are intrinsically brighter than those that fade away quickly. This correlation, which is commonly referred to as the Phillips relation, allowed a group of astronomers in Chile, includingPhillips and Texas A&M astronomer Nicholas Suntzeff, to develop type Ia supernovae into a precise tool for measuring the expansion of the universe.

Studying the supernovae using the near-infrared part of the spectrum was crucial to this finding. The light from these explosions must travel through cosmic dust to reach our telescopes, and these fine-grained interstellar particles obscure light on the blue end of the spectrum more than they do light from the red end of the spectrum in the same manner as smoke from a forest fire makes everything appear redder. This can trick astronomers into thinking that a supernova is farther away than it is. But working in the infrared allows astronomers to peer more clearly through this dusty veil.

"One of the Carnegie Supernova Project's primary goals has been to provide a reliable, high-quality sample of supernovae and dependable methods for inferring their distances," said lead author Burns.

"The quality of this data allows us to better correct our measurements to account for the dimming effect of cosmic dust" added Mark Phillips, an astronomer at Carnegie's Las Campanas Observatory in Chile and a co-author on the paper.

The calibration of these mile markers is crucially important, because there are disagreements between different methods for determining the universe's expansion rate. The Hubble constant can independently be estimated using the glow of background radiation left over from the Big Bang. This cosmic microwave background radiation has been measured with exquisite detail by the Planck satellite, and it gives astronomers a more slowly expanding universe than when measured using type Ia supernovae.

"This discrepancy could herald new physics, but only if it's real," Burns explained. "So, we need our type Ia supernova measurements to be as accurate as possible, but also to identify and quantify all sources of error."

Source: Carnegie Institution for Science [December 11, 2018]

Researchers have created tiny droplets of the ultra-hot matter that once filled the early universe, forming three distinct shapes and sizes: circles, ellipses and triangles.

Visualization of expanding drops of quark gluon plasmas in three geometric shapes [Credit: Javier Orjuela Koop]

The study, published in Nature Physics, stems from the work of an international team of scientists and focuses on a liquid-like state of matter called a quark gluon plasma. Physicists believe that this matter filled the entire universe during the first few microseconds after the Big Bang when the universe was still too hot for particles to come together to make atoms.

CU Boulder Professor Jamie Nagle and colleagues on an experiment known as PHENIX used a massive collider at Brookhaven National Laboratory in Upton, New York, to recreate that plasma. In a series of tests, the researchers smashed packets of protons and neutrons in different combinations into much bigger atomic nuclei.

They discovered that, by carefully controlling conditions, they could generate droplets of quark gluon plasma that expanded to form three different geometric patterns.

"Our experimental result has brought us much closer to answering the question of what is the smallest amount of early universe matter that can exist," Nagle said.

Researchers from CU Boulder and Vanderbilt University lead the data analysis efforts for the PHENIX experiment.

Scientists first started studying such matter at Brookhaven's Relativistic Heavy Ion Collider (RHIC) in 2000. They crashed together the heavy nuclei of gold atoms, generating temperatures of trillions of degrees Celsius. In the resulting boil, quarks and gluons, the subatomic particles that make up all protons and neutrons, broke free from their atomic chains and flowed almost freely.

Graphic showing how atomic collisions between different starting ingredients expand over time to produce plasmas in distinct shapes. The top collision was generated by slamming a single proton into a gold atom; the middle from a collision between a deuteron and a gold atom; and the bottom from a collision between helium-3 and a gold atom [Credit: PHENIX, Nature 2018]

Several years later, another group of researchers reported that they seemed to have created a quark gluon plasma not by slamming together two atoms, but by crashing together just two protons.

That was surprising because most scientists assumed that lone protons could not deliver enough energy to make anything that could flow like a fluid.

Nagle and his colleagues devised a way to test those results in 2014: If such tiny droplets behaved like liquid, then they should hold their shape.

As he explained, "Imagine that you have two droplets that are expanding into a vacuum. If the two droplets are really close together, then as they're expanding out, they run into each other and push against each other, and that's what creates this pattern."

In other words, if you toss two stones into a pond close together, the ripples from those impacts will flow into each other, forming a pattern that resembles an ellipse. The same could be true if you smashed a proton-neutron pair, called a deuteron, into something bigger, Nagle and Romatschke reasoned. Likewise, a proton-proton-neutron trio, also known as a helium-3 atom, might expand out into something akin to a triangle.

And that's exactly what the PHENIX experiment found: collisions of deuterons formed short-lasting ellipses, helium-3 atoms formed triangles and a single proton exploded in the shape of a circle.

The results, the researchers said, could help theorists better understand how the universe's original quark gluon plasma cooled over milliseconds, giving birth to the first atoms in existence.

The new study includes co-authors from 65 institutions. Co-authors from CU Boulder include postdoctoral researchers Ron Belmont and Darren McGlinchey and graduate student Javier Orjeula-Koop, all in physics.

Author: Daniel Strain | Source: University of Colorado at Boulder [December 10, 2018]

From August through early December, the OSIRIS-REx spacecraft aimed three of its science instruments toward Bennu and began making the mission's first observations of the asteroid. During this period, the spacecraft traveled the last 1.4 million miles (2.2 million km) of its outbound journey to arrive at a spot 12 miles (19 km) from Bennu on Dec. 3. The science obtained from these initial observations confirmed many of the mission team's ground-based observations of Bennu and revealed several new surprises.

This mosaic image of asteroid Bennu is composed of 12 PolyCam images collected on Dec. 2 by the OSIRIS-REx spacecraft from a range of 15 miles (24 km) [Credit: NASA/Goddard/University of Arizona]

Team members of the mission, which is led by the University of Arizona, presented the results at the Annual Fall Meeting of the American Geophysical Union, or AGU, in Washington, D.C. on Dec. 10.

In a key finding for the mission's science investigation, data obtained from the spacecraft's two spectrometers, the OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) and the OSIRIS-REx Thermal Emissions Spectrometer (OTES), reveal the presence of molecules that contain oxygen and hydrogen atoms bonded together, known as "hydroxyls." The team suspects that these hydroxyl groups exist globally across the asteroid in water-bearing clay minerals, meaning that at some point, the rocky material interacted with water. While Bennu itself is too small to have ever hosted liquid water, the finding does indicate that liquid water was present at some time on Bennu's parent body, a much larger asteroid.

"This finding may provide an important link between what we think happened in space with asteroids like Bennu and what we see in the meteorites that scientists study in the lab," said Ellen Howell, senior research scientist at the UA's Lunar and Planetary Laboratory (LPL) and a member of the mission's spectral analysis group. "It is very exciting to see these hydrated minerals distributed across Bennu's surface, because it suggests they are an intrinsic part of Bennu's composition, not just sprinkled on its surface by an impactor."

"The presence of hydrated minerals across the asteroid confirms that Bennu, a remnant from early in the formation of the solar system, is an excellent specimen for the OSIRIS-REx mission to study the composition of primitive volatiles and organics," said Amy Simon, OVIRS Deputy Instrument Scientist at NASA Goddard Space Flight Center.

Additionally, data obtained from the OSIRIS-REx Camera Suite (OCAMS) corroborate ground-based radar observations of Bennu and confirm that the original model -- developed in 2013 by OSIRIS-REx Science Team Chief Michael Nolan, now based at LPL, and collaborators -- closely predicted the asteroid's actual shape. Bennu's diameter, rotation rate, inclination and overall shape presented almost exactly as projected.

Soon after the asteroid later named Bennu was discovered in 1999, Nolan's group used the Arecibo Observatory in Puerto Rico to gather clues about its size, shape and rotation by bouncing radar waves off of it during one of its close approaches to Earth, about five times the distance between Earth and the moon.

"Radar observations don't give us any information about colors or brightness of the object, so it is really interesting to see the asteroid up close through the eyes of OSIRIS-REx," Nolan said. "As we are getting more details, we are figuring out where the craters and boulders are, and we were very pleasantly surprised that virtually every little bump we saw in our radar image back then is actually really there."

The mission team used this ground-based Bennu model when designing the OSIRIS-REx mission. The accuracy of the model means that the mission, spacecraft, and planned observations were appropriately designed for the tasks ahead at Bennu.

One outlier from the predicted shape model is the size of the large boulder near Bennu's south pole. The ground-based shape model calculated this boulder to be at least 33 feet (10 meters) in height. Preliminary calculations from OCAMS observations show that the boulder is closer to 164 feet (50 meters) in height, with a width of approximately 180 feet (55 meters).

As expected, the initial assessment of Bennu's regolith indicates that the surface of Bennu is a mix of very rocky, boulder-filled regions and a few relatively smooth regions that lack boulders. However, the quantity of boulders on the surface is higher than was expected. The team will make further observations at closer ranges to more accurately assess where a sample can be taken on Bennu for later return to Earth.

"Our initial data show that the team picked the right asteroid as the target of the OSIRIS-REx mission. We have not discovered any insurmountable issues at Bennu so far," said Dante Lauretta, OSIRIS-REx principal investigator and professor of planetary science and cosmochemistry at LPL. "The spacecraft is healthy and the science instruments are working better than required. It is time now for our adventure to begin."

"What used to be science fiction is now a reality," said UA President Robert C. Robbins. "Our work at Bennu brings us a step closer to the possibility of asteroids providing astronauts on future missions into the solar system with resources like fuel and water."

The mission is currently performing a preliminary survey of the asteroid, flying the spacecraft in passes over Bennu's north pole, equator and south pole at ranges as close as 4.4 miles (7 km) to better determine the asteroid's mass. This survey also provides the first opportunity for the OSIRIS-REx Laser Altimeter (OLA), an instrument contributed by the Canadian Space Agency, to make observations now that the spacecraft is in proximity to Bennu. The spacecraft's first orbital insertion is scheduled for Dec. 31, and OSIRIS-REx will remain in orbit until mid-February 2019, when the mission transitions into the next survey phase. During this first orbital phase, the spacecraft will orbit the asteroid at a range of 0.9 miles (1.4 km) to 1.24 miles (2 km) from the center of Bennu -- setting two new records for the smallest body ever orbited by a spacecraft and the closest orbit of a planetary body by any spacecraft.

Author: Erin Morton and Daniel Stolte | Source: University of Arizona [December 10, 2018]

A team led by Southwest Research Institute has concluded that the surface of dwarf planet Ceres is rich in organic matter. Data from NASA's Dawn spacecraft indicate that Ceres's surface may contain several times the concentration of carbon than is present in the most carbon-rich, primitive meteorites found on Earth.

NASA's Dawn spacecraft captured this 12.5-mile-across close-up of the central peak of the 99-mile-wide Urvara impact crater on Ceres. The remarkable 6,500-foot central ridge is made from materials uplifted from depth,  arising from terrains enriched with products of rock-water interactions, such as carbonates [Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA]

"Ceres is like a chemical factory," said SwRI's Dr. Simone Marchi, a principal scientist who was the lead author of research published in Nature Astronomy. "Among inner solar system bodies, Ceres' has a unique mineralogy, which appears to contain up to 20 percent carbon by mass in its near surface. Our analysis shows that carbon-rich compounds are intimately mixed with products of rock-water interactions, such as clays."

Ceres is believed to have originated about 4.6 billion years ago at the dawn of our solar system. Dawn data previously revealed the presence of water and other volatiles, such as ammonium derived from ammonia, and now a high concentration of carbon. This chemistry suggests Ceres formed in a cold environment, perhaps outside the orbit of Jupiter. An ensuing shakeup in the orbits of the large planets would have pushed Ceres to its current location in the main asteroid belt, between the orbits of Mars and Jupiter.

"With these findings, Ceres has gained a pivotal role in assessing the origin, evolution and distribution of organic species across the inner solar system," Marchi said. "One has to wonder about how this world may have driven organic chemistry pathways, and how these processes may have affected the make-up of larger planets like the Earth."

SwRI scientists constructed a possible schematic path for the evolution of Ceres' upper crust. The figure shows  the presence of carbonaceous chondrite-like materials (black) mixed with products of aqueous alteration such as phyllosilicates, carbonates and magnetite (green) and organics (orange). Shaded blue regions indicate water, and blue lines represent conduits for water migration. Organics may have formed in place during aqueous alteration or could have been concentrated by fluids ascending to the upper crust, resulting in the inferred higher-than-chondritic carbon concentration on Ceres' surface. Over time, the surface gets homogenized by mixing due to collisions and other processes [Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA]

Geophysical, compositional and collisional models based on Dawn data revealed that Ceres' partially differentiated interior has been altered by fluid processes. Dawn's Visible and Infrared Mapping Spectrometer has shown that the overall low albedo of Ceres'' surface is a combination of rock-water interaction products such as phyllosilicates and carbonates and a significant amount of spectrally neutral darkening agents, such as an iron oxide called magnetite.

Because Dawn's Gamma Ray and Neutron Detector limits magnetite to only a few percent by mass, the data point to the presence of an additional darkening agent, probably amorphous carbon, a carbon-rich organic material. Interestingly, specific organic compounds have also been detected near a 31-mile-wide impact crater named Ernutet, giving further support to the widespread presence of organics in Ceres' shallow subsurface.

The new study also finds that 50-60 percent of Ceres' upper crust may have a composition similar to primitive carbonaceous chondrite meteorites. This material is compatible with contamination from infalling carbonaceous asteroids, a possibility supported by Ceres' battered surface.

"Our results imply that either Ceres' accreted ultra-carbon-rich materials or that carbon was concentrated in its crust," said said Marchi. "Both potential scenarios are important, because Ceres' mineralogical composition indicates a global-scale event of rock-water alteration, which could provide conditions favorable to organic chemistry."

Source: Southwest Research Institute [December 10, 2018]

Andrés Muñoz-Jaramillo of Southwest Research Institute and José Manuel Vaquero of the University of Extremadura have developed a new technique for looking at historic solar data to distinguish trustworthy observations from those that should be used with care. This work is critical to understanding the Sun's past and future as well as whether solar activity plays a role in climate change.

A team led by SwRI integrated a sunspot drawing made by Hevelius in 1644 (top) with images from NASA's Solar Dynamics Observatory to illustrate how widely varying telescopes and observation techniques can affect data. The team integrated data from 700 observations to assess the reliability of historical data, to better understand the history of solar activity [Credit: NASA/SDO/SwRI]

"Scientists have been monitoring solar activity since Galileo made the first drawings in 1612 by counting sunspots and groups of sunspots," said SwRI's Dr. Andrés Muñoz-Jaramillo, a senior research scientist who is first author of a paper in Nature Astronomy outlining the research. "However, putting all observations in perspective is quite challenging due to wide-ranging observation techniques and telescope magnifications used. We see much more now and our understanding of what we see changes the way we count spots."

The team created a technique that takes all historic data gathered and digitized thus far and combines them visually, to provide a complete picture of the data we have and where are we missing information. Roughly every 11 years, the magnetic structure and activity of the Sun cycle between periods known as solar minimum and solar maximum. During solar maximum, the Sun emits high levels of solar radiation, ejects large amounts solar material and displays large numbers of intense sunspots, flares and other phenomena. During solar minimum, this activity is muted. Changes on the Sun cause effects in space, in the atmosphere and on Earth's surface.

The Sun also experiences century-long variations, including periods of abnormally low solar activity called grand minima. Maunder Minimum refers to a 70-year period between 1645 and 1715 when observations revealed thousands of days without sunspots. The term was the title of a 1976 paper that first identified these longer cycles, named for a husband-wife team of solar astronomers from the late 17th century. In contrast, modern observations typically record hundreds of days without sunspots over similar periods of time.

"Scientists are investigating whether Maunder Minimum could serve as archetype of a grand minimum in magnetic activity for the Sun and other stars," Muñoz said. However, data prior to, during and after the Maunder Minimum, is less reliable and lacks the precision and coverage of today's measurements. Recent reevaluations of sunspot observations have yielded a conflicted view on the evolution of solar activity over the last 400 years.

"Due to our lack coverage we don't know if the Sun took decades to recover from the Maunder Minimum to the levels of solar activity we see today, or if it was quick as if a switch had been turned on," Muñoz said. "There is currently a team of experts from all over the world working hard to find the best way of combining these data. In the meantime, one has to be very careful when using historic sunspot data to study potential links between the Sun and changes in terrestrial climate, given that these effects would be complex and subtle. Our work uses historical data to provide context to users of these estimates that may not be aware of their limitations."

Source: Southwest Research Institute [December 10, 2018]

For the second time in history, a human-made object has reached the space between the stars. NASA's Voyager 2 probe now has exited the heliosphere -- the protective bubble of particles and magnetic fields created by the Sun.

This illustration shows the position of NASA’s Voyager 1 and Voyager 2 probes, outside of the heliosphere, a protective bubble created by the Sun that extends well past the orbit of Pluto [Credit: NASA/JPL-Caltech]

Members of NASA's Voyager team will discuss the findings at a news conference at 11 a.m. EST (8 a.m. PST) today at the meeting of the American Geophysical Union (AGU) in Washington. The news conference will stream live on the agency's website.

Comparing data from different instruments aboard the trailblazing spacecraft, mission scientists determined the probe crossed the outer edge of the heliosphere on Nov. 5. This boundary, called the heliopause, is where the tenuous, hot solar wind meets the cold, dense interstellar medium. Its twin, Voyager 1, crossed this boundary in 2012, but Voyager 2 carries a working instrument that will provide first-of-its-kind observations of the nature of this gateway into interstellar space.

Voyager 2 now is slightly more than 11 billion miles (18 billion kilometers) from Earth. Mission operators still can communicate with Voyager 2 as it enters this new phase of its journey, but information -- moving at the speed of light -- takes about 16.5 hours to travel from the spacecraft to Earth. By comparison, light traveling from the Sun takes about eight minutes to reach Earth.

The most compelling evidence of Voyager 2's exit from the heliosphere came from its onboard Plasma Science Experiment (PLS), an instrument that stopped working on Voyager 1 in 1980, long before that probe crossed the heliopause. Until recently, the space surrounding Voyager 2 was filled predominantly with plasma flowing out from our Sun. This outflow, called the solar wind, creates a bubble -- the heliosphere -- that envelopes the planets in our solar system. The PLS uses the electrical current of the plasma to detect the speed, density, temperature, pressure and flux of the solar wind. The PLS aboard Voyager 2 observed a steep decline in the speed of the solar wind particles on Nov. 5. Since that date, the plasma instrument has observed no solar wind flow in the environment around Voyager 2, which makes mission scientists confident the probe has left the heliosphere.


"Working on Voyager makes me feel like an explorer, because everything we're seeing is new," said John Richardson, principal investigator for the PLS instrument and a principal research scientist at the Massachusetts Institute of Technology in Cambridge. "Even though Voyager 1 crossed the heliopause in 2012, it did so at a different place and a different time, and without the PLS data. So we're still seeing things that no one has seen before."

In addition to the plasma data, Voyager's science team members have seen evidence from three other onboard instruments -- the cosmic ray subsystem, the low energy charged particle instrument and the magnetometer -- that is consistent with the conclusion that Voyager 2 has crossed the heliopause. Voyager's team members are eager to continue to study the data from these other onboard instruments to get a clearer picture of the environment through which Voyager 2 is traveling.

"There is still a lot to learn about the region of interstellar space immediately beyond the heliopause," said Ed Stone, Voyager project scientist based at Caltech in Pasadena, California.

Together, the two Voyagers provide a detailed glimpse of how our heliosphere interacts with the constant interstellar wind flowing from beyond. Their observations complement data from NASA's Interstellar Boundary Explorer (IBEX), a mission that is remotely sensing that boundary. NASA also is preparing an additional mission -- the upcoming Interstellar Mapping and Acceleration Probe (IMAP), due to launch in 2024 -- to capitalize on the Voyagers' observations.

At the end of 2018, the cosmic ray subsystem aboard NASA's Voyager 2 spacecraft provided evidence that Voyager 2 had left the heliosphere. There were steep drops in the rate of heliospheric particles that hit the instrument's radiation detector, and significant increases in the rate of cosmic rays [Credit: NASA/JPL-Caltech/GSFC]

"Voyager has a very special place for us in our heliophysics fleet," said Nicola Fox, director of the Heliophysics Division at NASA Headquarters. "Our studies start at the Sun and extend out to everything the solar wind touches. To have the Voyagers sending back information about the edge of the Sun's influence gives us an unprecedented glimpse of truly uncharted territory."

While the probes have left the heliosphere, Voyager 1 and Voyager 2 have not yet left the solar system, and won't be leaving anytime soon. The boundary of the solar system is considered to be beyond the outer edge of the Oort Cloud, a collection of small objects that are still under the influence of the Sun's gravity. The width of the Oort Cloud is not known precisely, but it is estimated to begin at about 1,000 astronomical units (AU) from the Sun and to extend to about 100,000 AU. One AU is the distance from the Sun to Earth. It will take about 300 years for Voyager 2 to reach the inner edge of the Oort Cloud and possibly 30,000 years to fly beyond it.

The Voyager probes are powered using heat from the decay of radioactive material, contained in a device called a radioisotope thermal generator (RTG). The power output of the RTGs diminishes by about four watts per year, which means that various parts of the Voyagers, including the cameras on both spacecraft, have been turned off over time to manage power.

"I think we're all happy and relieved that the Voyager probes have both operated long enough to make it past this milestone," said Suzanne Dodd, Voyager project manager at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "This is what we've all been waiting for. Now we're looking forward to what we'll be able to learn from having both probes outside the heliopause."

The set of graphs on the left illustrates the drop in electrical current detected in three directions by Voyager 2's plasma science experiment (PLS) to background levels. They are among the key pieces of data that show that Voyager 2 entered interstellar space in November 2018 [Credit: NASA/JPL-Caltech/MIT]

Voyager 2 launched in 1977, 16 days before Voyager 1, and both have traveled well beyond their original destinations. The spacecraft were built to last five years and conduct close-up studies of Jupiter and Saturn. However, as the mission continued, additional flybys of the two outermost giant planets, Uranus and Neptune, proved possible. As the spacecraft flew across the solar system, remote-control reprogramming was used to endow the Voyagers with greater capabilities than they possessed when they left Earth. Their two-planet mission became a four-planet mission. Their five-year lifespans have stretched to 41 years, making Voyager 2 NASA's longest running mission.

The Voyager story has impacted not only generations of current and future scientists and engineers, but also Earth's culture, including film, art and music. Each spacecraft carries a Golden Record of Earth sounds, pictures and messages. Since the spacecraft could last billions of years, these circular time capsules could one day be the only traces of human civilization.

Voyager's mission controllers communicate with the probes using NASA's Deep Space Network (DSN), a global system for communicating with interplanetary spacecraft. The DSN consists of three clusters of antennas inGoldstone, California; Madrid, Spain; and Canberra, Australia.

Author: Dwayne Brown / Karen Fox | Source: NASA/Jet Propulsion Laboratory [December 10, 2018]

"Super-Earths" and Neptune-sized planets could be forming around young stars in much greater numbers than scientists thought, new research by an international team of astronomers suggests.

The Taurus Molecular Cloud, pictured here by ESA's Herschel Space Observatory, is a star-forming region about 450  light-years away. The image frame covers roughly 14 by 16 light-years and shows the glow of cosmic dust in the interstellar  material that pervades the cloud, revealing an intricate pattern of filaments dotted with a few compact, bright cores -- the seeds of future stars [Credit: ESA/Herschel/PACS, SPIRE/Gould Belt survey Key Programme/Palmeirim et al. 2013]

Observing a sampling of young stars in a star-forming region in the constellation Taurus, researchers found many of them to be surrounded by structures that can best be explained as traces created by invisible, young planets in the making. The research, published in the Astrophysical Journal, helps scientists better understand how our own solar system came to be.

Some 4.6 billion years ago, our solar system was a roiling, billowing swirl of gas and dust surrounding our newborn sun. At the early stages, this so-called protoplanetary disk had no discernable features, but soon, parts of it began to coalesce into clumps of matter - the future planets. As they picked up new material along their trip around the sun, they grew and started to plow patterns of gaps and rings into the disk from which they formed. Over time, the dusty disk gave way to the relatively orderly arrangement we know today, consisting of planets, moons, asteroids and the occasional comet.

Scientists base this scenario of how our solar system came to be on observations of protoplanetary disks around other stars that are young enough to currently be in the process of birthing planets. Using the Atacama Large Millimeter Array, or ALMA, comprising 45 radio antennas in Chile's Atacama Desert, the team performed a survey of young stars in the Taurus star-forming region, a vast cloud of gas and dust located a modest 450 light-years from Earth. When the researchers imaged 32 stars surrounded by protoplanetary disks, they found that 12 of them - 40 percent - have rings and gaps, structures that according to the team's measurements and calculations can be best explained by the presence of nascent planets.

"This is fascinating because it is the first time that exoplanet statistics, which suggest that super-Earths and Neptunes are the most common type of planets, coincide with observations of protoplanetary disks," said the paper's lead author, Feng Long, a doctoral student at the Kavli Institute for Astronomy and Astrophysics at Peking University in Bejing, China.

Until recently, protoplanetary disks were believed to be smooth, like pancake-like objects. The results from this study show that some disks are more like doughnuts with holes, but even more often appear as a series of rings. The rings are likely carved by planets that are otherwise invisible to us. Credit: Feng Long

While some protoplanetary disks appear as uniform, pancake-like objects lacking any features or patterns, concentric bright rings separated by gaps have been observed, but since previous surveys have focused on the brightest of these objects because they are easier to find, it was unclear how common disks with ring and gap structures really are in the universe. This study presents the results of the first unbiased survey in that the target disks were selected independently of their brightness - in other words, the researchers did not know whether any of their targets had ring structures when they selected them for the survey.

"Most previous observations had been targeted to detect the presence of very massive planets, which we know are rare, that had carved out large inner holes or gaps in bright disks," said the paper's second author Paola Pinilla, a NASA Hubble Fellow at the University of Arizona's Steward Observatory. "While massive planets had been inferred in some of these bright disks, little had been known about the fainter disks."

The team, which also includes Nathan Hendler and Ilaria Pascucci at the UA's Lunar and Planetary Laboratory, measured the properties of rings and gaps observed with ALMA and analyzed the data to evaluate possible mechanisms that could cause the observed rings and gaps. While these structures may be carved by planets, previous research has suggested that they may also be created by other effects. In one commonly suggested scenario, so-called ice lines caused by changes in the chemistry of the dust particles across the disc in response to the distance to the host star and its magnetic field create pressure variations across the disk. These effects can create variations in the disk, manifesting as rings and gaps.

The researchers performed analyses to test these alternative explanations and could not establish any correlations between stellar properties and the patterns of gaps and rings they observed.

"We can therefore rule out the commonly proposed idea of ice lines causing the rings and gaps," Pinilla said. "Our findings leave nascent planets as the most likely cause of the patterns we observed, although some other processes may also be at work."

Since detecting the individual planets directly is impossible because of the overwhelming brightness of the host star, the team performed calculations to get an idea of the kinds of planets that might be forming in the Taurus star-forming region. According to the findings, Neptune-sized gas planets or so-called super-Earths - terrestrial planets of up to 20 Earth masses - should be the most common. Only two of the observed disks could potentially harbor behemoths rivaling Jupiter, the largest planet in the solar system.

"Since most of the current exoplanet surveys can't penetrate the thick dust of protoplanetary disks, all exoplanets, with one exception, have been detected in more evolved systems where a disk is no longer present," Pinilla said.

Going forward, the research group plans to move ALMA's antennas farther apart, which should increase the array's resolution to around five astronomical units (one AU equals the average distance between the Earth and the sun), and to make the antennas sensitive to other frequencies that are sensitive to other types of dust.

"Our results are an exciting step in understanding this key phase of planet formation," Long said, "and by making these adjustments, we are hoping to better understand the origins of the rings and gaps."

Source: University of Arizona [December 06, 2018]

Although helium is a rare element on Earth, it is ubiquitous in the Universe. It is, after hydrogen, the main component of stars and gaseous giant planets. Despite its abundance, helium was only detected recently in the atmosphere of a gaseous giant by an international team including astronomers from the University of Geneva (UNIGE), Switzerland. The team, this time led by Genevan researchers, has observed in detail and for the first time how this gas escapes from the overheated atmosphere of an exoplanet, literally inflated with helium. The results are published in Science.

Evaporation of atmopheric helium on the giant exoplanet WASP-69b [Credit: Gabriel Perez Diaz, SMM (IAC)]

Helium is the second most abundant element in the Universe. Predicted since 2000 as one of the best possible tracers of the atmospheres of exoplanets, these planets orbiting around other stars than the Sun, it took astronomers 18 years to actually detect it. It was hard to spot due to the very peculiar observational signature of helium, located in the infrared, out of range for most of the instruments used previously.

The discovery occurred earlier this year, thanks to Hubble Space Telescope observations, which proved difficult to interpret. Team members from UNIGE, members of the National Centre for Competence in Research PlanetS, had the idea of pointing another telescope equipped with a brand-new instrument -- a spectrograph called Carmenes.

Detecting colours of planets with Carmenes

A spectrograph decomposes the light of a star into its component colours, like a rainbow. The "resolution" of a spectrograph is a measure indicating the number of colours that can be revealed. While the human eye cannot distinguish any colour beyond red without an adapted camera, the infrared eye of Hubble is capable of identifying hundreds of colours there. This proved sufficient to identify the coloured signature of helium. The instrument Carmenes, installed on the 4-metre telescope at the observatory of Calar Alto in Andalusia, Spain, is capable to identify more than 100'000 colours in the infrared!


This high spectral resolution allowed the team to observe the position and speed of helium atoms in the upper atmosphere of a gaseous Neptune-size exoplanet, 4 times larger than the Earth. Located in the Cygnus (the Swan) constellation, 124 light-years from home, HAT-P-11b is a "warm Neptune" (a decent 550°C!), twenty times closer to its star than the Earth from the Sun.

"We suspected that this proximity with the star could impact the atmosphere of this exoplanet" says Romain Allart, PhD student at UNIGE and first author of the study. "The new observations are so precise that the exoplanet atmosphere is undoubtedly inflated by the stellar radiation and escapes to space," he adds.

A planet inflated with helium

These observations are supported by numerical simulation, led by Vincent Bourrier, co-author of the study and member of the European project FOUR ACES. Thanks to the simulation, it is possible to track the trajectory of helium atoms: "helium is blown away from the day side of the planet to its night side at over 10'000 km/h," Vincent Bourrier explains. "Because it is such a light gas, it escapes easily from the attraction of the planet and forms an extended cloud all around it." This gives HAT-P-11b the shape of a helium-inflated balloon.

This result opens a new window to observe the extreme atmospheric conditions prevailing in the hottest exoplanets. The Carmenes observations demonstrate that such studies, long thought feasible only from space, can be achieved with greater precision by ground-based telescopes equipped with the right kind of instruments. "These are exciting times for the search of atmospheric signatures in exoplanets," says Christophe Lovis, senior lecturer at UNIGE and co-author of the study.

In fact, UNIGE astronomers are also heavily involved in the design and exploitation of two new high-resolution infrared spectrographs, similar to Carmenes. One of them, called SPIRou, has just started an observational campaign from Hawaii, while the UNIGE Department of astronomy houses the first tests of the Near Infrared Planet Searcher (NIRPS), which will be installed in Chile at the end of 2019.

"This result will enhance the interest of the scientific community for these instruments. Their number and their geographical distribution will allow us to cover the entire sky, in search for evaporating exoplanets," concludes Lovis.

Source: Université de Genève [December 06, 2018]

The Earth formed relatively quickly from the cloud of dust and gas around the Sun, trapping water and gases in the planet's mantle, according to research published in the journal Nature. Apart from settling Earth's origins, the work could help in identifying extrasolar systems that could support habitable planets.

Artist's impression of a young star surrounded by a protoplanetary disk in which planets are forming. Based on measures of neon isotopes, UC Davis researchers conclude that the Earth formed relatively quickly from this cloud of dust and gas, collecting water, carbon and nitrogen in the deep Earth [Credit: European Southern Observatory]

Drawing on data from the depths of the Earth to deep space, University of California Davis Professor Sujoy Mukhopadhyay and postdoctoral researcher Curtis Williams used neon isotopes to show how the planet formed.

"We're trying to understand where and how the neon in Earth's mantle was acquired, which tells us how fast the planet formed and in what conditions," Williams said.

Neon is actually a stand-in for where gases such as water, carbon dioxide and nitrogen came from, Williams said. Unlike these compounds that are essential for life, neon is an inert noble gas, and it isn't influenced by chemical and biological processes.

"So neon keeps a memory of where it came from even after four and a half billion years," Mukhopadhyay said.

There are three competing ideas about how the Earth formed from a protoplanetary disk of dust and gas over four billion years ago and how water and other gases were delivered to the growing Earth. In the first, the planet grew relatively quickly over two to five million years and captured gas from the nebula, the swirling cloud of dust and gas surrounding the young Sun. The second theory suggests dust particles formed and were irradiated by the Sun for some time before condensing into miniature objects called planetesimals that were subsequently delivered to the growing planet. In the third option, the Earth formed relatively slowly and gases were delivered by carbonaceous chondrite meteorites that are rich in water, carbon and nitrogen.

These different models have consequences for what the early Earth was like, Mukhopadhyay said. If the Earth formed quickly out of the solar nebula, it would have had a lot of hydrogen gas at or near the surface. But if the Earth formed from carbonaceous chondrites, its hydrogen would have come in the more oxidized form, water.

Neon from ocean floor to deep space

To figure out which of the three competing ideas on planet formation and delivery of gases were correct, Williams and Mukhopadhyay accurately measured the ratios of neon isotopes that were trapped in the Earth's mantle when the planet formed. Neon has three isotopes, neon-20, 21 and 22. All three are stable and non-radioactive, but neon-21 is formed by radioactive decay of uranium. So the amounts of neon-20 and 22 in the Earth have been stable since the planet formed and will remain so forever, but neon-21 slowly accumulates over time. The three scenarios for Earth's formation are predicted to have different ratios of neon-20 to neon-22.

The closest they could get to the mantle was to look at rocks called pillow basalts on the ocean floor. These glassy rocks are the remains of flows from deep in the Earth that spilled out and cooled in the ocean, later to be collected by a drilling expedition led by the University of Rhode Island, which makes its collection available to other scientists.

The gases are found in tiny bubbles within the basalt. Using a press, Williams cracked basalt chips in a sealed chamber, allowing the gases to flow into a sensitive mass spectrometer.

Now for the space part. Previous researchers established the neon isotope ratio for the "solar nebula" (early rapid formation) model with data from the Genesis mission, which captured particles of the solar wind. Data for the "irradiated particles" model came from analyses of lunar soils and of meteorites. Finally, carbonaceous chondrite meteorites provided data for the "late accretion" model.

Minimum size for a habitable planet

The isotope ratios they found were well above those for the "irradiated particles" or "late accretion" models, Williams said, and support rapid early formation.

"This is a clear indication that there is nebular neon in the deep mantle," Williams said.

Neon, remember, is a marker for those other volatile compounds. Hydrogen, water, carbon dioxide and nitrogen would have been condensing into the Earth at the same time -- all ingredients that, as far as we know, go into making up a habitable planet.

The results imply that to absorb these vital compounds, a planet must reach a certain size -- the size of Mars or a little larger -- before the solar nebula dissipates. Observations of other solar systems show that this takes about two to three million years, Williams said.

Does the same process happen around other stars? Observations from the Atacama Large Millimeter Array, or ALMA, observatory in Chile suggest that it does, the researchers said.

ALMA uses an array of 66 radiotelescopes working as a single instrument to image dust and gas in the universe. It can see the planet-forming disks of dust and gas around some nearby stars. In some cases, there are dark bands in those disks where dust has been depleted.

"There are a couple of ways dust could be depleted from the disk, and one of them is that they are forming planets," Williams said.

"We can observe planet formation in a gas disk in other solar systems, and there is a similar record of our own solar system preserved in Earth's interior," Mukhopadhyay said. "This might be a common way for planets to form elsewhere."

Source: UC Davis [December 05, 2018]

Scientists at the University of Oxford may have solved one of the biggest questions in modern physics, with a new paper unifying dark matter and dark energy into a single phenomenon: a fluid which possesses 'negative mass." If you were to push a negative mass, it would accelerate towards you. This astonishing new theory may also prove right a prediction that Einstein made 100 years ago.

3D illustration of the dark matter explosion and creation of the universe with billions of cosmic atoms, flying meteors, a lot of of light elements, and halos of new stars [Credit: Shutterstock]

Our current, widely recognised model of the Universe, called LambdaCDM, tells us nothing about what dark matter and dark energy are like physically. We only know about them because of the gravitational effects they have on other, observable matter.

This new model, published in Astronomy and Astrophysics, by Dr. Jamie Farnes from the Oxford e-Research Centre, Department of Engineering Science, offers a new explanation. Dr. Farnes says: "We now think that both dark matter and dark energy can be unified into a fluid which possesses a type of 'negative gravity," repelling all other material around them. Although this matter is peculiar to us, it suggests that our cosmos is symmetrical in both positive and negative qualities."

The existence of negative matter had previously been ruled out as it was thought this material would become less dense as the Universe expands, which runs contrary to our observations that show dark energy does not thin out over time. However, Dr. Farnes' research applies a 'creation tensor," which allows for negative masses to be continuously created. It demonstrates that when more and more negative masses are continually bursting into existence, this negative mass fluid does not dilute during the expansion of the cosmos. In fact, the fluid appears to be identical to dark energy.

Dr. Farnes's theory also provides the first correct predictions of the behaviour of dark matter halos. Most galaxies are rotating so rapidly they should be tearing themselves apart, which suggests that an invisible 'halo' of dark matter must be holding them together. The new research features a computer simulation of the properties of negative mass, which predicts the formation of dark matter halos just like the ones inferred by observations using modern radio telescopes.

Albert Einstein provided the first hint of the dark universe exactly 100 years ago, when he discovered a parameter in his equations known as the 'cosmological constant," which we now know to be synonymous with dark energy. Einstein famously called the cosmological constant his 'biggest blunder," although modern astrophysical observations prove that it is a real phenomenon. In notes dating back to 1918, Einstein described his cosmological constant, writing that 'a modification of the theory is required such that "empty space" takes the role of gravitating negative masses which are distributed all over the interstellar space." It is therefore possible that Einstein himself predicted a negative-mass-filled universe.

Dr. Farnes says: "Previous approaches to combining dark energy and dark matter have attempted to modify Einstein's theory of general relativity, which has turned out to be incredibly challenging. This new approach takes two old ideas that are known to be compatible with Einstein's theory—negative masses and matter creation—and combines them together.

"The outcome seems rather beautiful: dark energy and dark matter can be unified into a single substance, with both effects being simply explainable as positive mass matter surfing on a sea of negative masses."

Proof of Dr. Farnes's theory will come from tests performed with a cutting-edge radio telescope known as the Square Kilometre Array (SKA), an international endeavour to build the world's largest telescope in which the University of Oxford is collaborating.

Dr. Farnes adds: "There are still many theoretical issues and computational simulations to work through, and LambdaCDM has a nearly 30 year head start, but I'm looking forward to seeing whether this new extended version of LambdaCDM can accurately match other observational evidence of our cosmology. If real, it would suggest that the missing 95% of the cosmos had an aesthetic solution: we had forgotten to include a simple minus sign."

Source: University of Oxford [December 05, 2018]

A study led by Texas Tech University shows that supersoft X-ray emissions can come from accretion as well as nuclear fusion.

Credit: NASA/CXC/M.Weiss

For decades, astronomers and astrophysicists have used a specific type of supernova to measure the expansion of the universe. But a recent discovery led by Texas Tech University may turn that notion on its head.

Supersoft X-ray emission – a very strong level of the weakest X-rays – has long been considered a result of nuclear fusion on the surface of a white dwarf, a small, very dense star. But a new detection of supersoft emissions that are clearly not powered by fusion is showing scientists that fusion is not the only way such emissions occur, according to a study published in the journal Nature Astronomy.

The event, ASASSN16-oh, was first noticed as a transient in the Small Magellanic Cloud by the All-Sky Automated Survey. Additional observations from NASA's Swift Observatory and the Chandra X-ray Observatory helped to verify the finding.

"In the past, the supersoft sources have all been associated with nuclear fusion on the surface of white dwarfs," said lead author Tom Maccarone, a professor in the Texas Tech Department of Physics & Astronomy. "As a white dwarf captures material from a companion star, the material piles up on the surface and becomes hot, and, eventually nuclear fusion takes place, much like in a hydrogen bomb.

"But this emission is coming from a region smaller than the surface of the white dwarf, and we have strong arguments against any kind of explosion having taken place on the white dwarf. Specifically, there are no broad emission lines in the X-ray or optical spectra, so there cannot have been any kind of strong wind generated. In some cases, nuclear fusion can be steady on the surface of a white dwarf, but it cannot start immediately as steady fusion. There must be an explosion of some kind when the fusion starts."

The source of these emissions, then, is thought to be accretion – the process of accumulating matter – not fusion. The scientists believe the system consists of a highly evolved red giant star and a white dwarf with an extremely large disk of emission around it. The rate of inflow of matter through the disk is unstable, and when the material starts flowing more quickly, the brightness of the system shoots upward.

"What we're seeing here is a transient episode of supersoft emission, but without any of the signs that we associate with nuclear fusion," Maccarone said. "If a nova took place, we would expect to see material flowing away from the white dwarf. Here we don't. Instead, what we are seeing is hot emission from the disk that is transporting the material from the companion star to the white dwarf. The transfer of mass is happening at a higher rate than in any system we've caught in the past."

So what this finding shows is that there are two ways by which supersoft emission can be made: nuclear fusion and accretion.

"I am excited by this result," Maccarone said. "It was a totally new phenomenon, and any time one finds one of those, it's exciting."

As exciting as this finding is on its own, perhaps the most important part is that it may change how astrophysicists measure the expansion of the universe. These objects were thought to be one of the main ways by which white dwarfs grow in mass and eventually explode as Type Ia supernovae.

"These systems also are the way we measure the expansion of the universe," Maccarone said. "To measure that expansion more accurately than we do now, we need to understand the origin of the Type Ia supernovae. This finding – that there's a new way to make supersoft sources – will cause us to re-think our approach to matching up the populations of these objects with the rates of the supernovae."

Author: Glenys Young | Source: Texas Tech University [December 04, 2018]