Study Reveals One Of Universe’s Secret Ingredients For Life

A new study led by ANU has investigated the nature of a cosmic phenomenon that slows down star formation, which helps to ensure the universe is a place where life can emerge.

Lead researcher Dr. Roland Crocker from the ANU Research School of Astronomy and Astrophysics said the research team studied a particular way stars provide a counter-pressure to gravity that slows down the star-formation process.

“If star formation happened rapidly, all stars would be bound together in massive clusters, where the intense radiation and supernova explosions would likely sterilise all the planetary systems, preventing the emergence of life,” he said.

“The conditions in these massive star clusters would possibly even prevent planets from forming in the first place.”

The study found that ultraviolet and optical light from young and massive stars spreads out into the gas from which the stars have recently formed and hits cosmic dust, which then scatters infrared light that acts effectively as a kind of pressure that pushes against gravity.

“The phenomenon we studied occurs in galaxies and star clusters where there’s a lot of dusty gas that is forming heaps of stars relatively quickly,” Dr. Crocker said.

“In galaxies forming stars more slowly—such as the Milky Way—other processes are slowing things down. The Milky Way forms two new stars every year, on average.”

Other galaxies in our vicinity and elsewhere in the universe continuously form new stars at a relatively slow and steady rate.

Dr. Crocker said the study’s mathematical findings indicated the phenomenon set an upper limit on how quickly stars can form in a galaxy or giant gas cloud.

“This and other forms of feedback help to keep the universe alive and vibrant,” he said.

“We are investigating other ways stars might feed back into their environment to slow down the overall rate of star formation.”

Professor Mark Krumholz and Dr Dougal Mackey from the ANU Research School of Astronomy and Astrophysics, Professor Todd Thompson from Ohio State University in the United States and Associate Professor Holger Baumgardt at the University of Queensland contributed to the study, which was published in the Monthly Notices of the Royal Astronomical Society.

Ultra-Hot Gas Around Remnants Of Sun-Like Stars

Solving a decades-old mystery, an international team of astronomers have discovered an extremely hot magnetosphere around a white dwarf, a remnant of a star like our Sun. The work was led by Dr Nicole Reindl, Research Fellow of the Royal Commission 1851, based at the University of Leicester, and is published today (7 November) in the journal Monthly Notices of the Royal Astronomical Society.

White dwarfs are the final stage in the lives of stars like our Sun. At the end of their lives, these stars eject their outer atmospheres, leaving behind a hot, compact and dense core that cools over billions of years. The temperature on their surfaces is typically around 100,000 degrees Celsius (in comparison the surface of the Sun is 5500 degrees).

Some white dwarfs though challenge scientists, as they show evidence for highly ionised metals. In astronomy ‘metals’ describe every element heavier than helium, and high ionisation here means that all but one of the outer electrons usually in their atoms have been stripped away. That process needs a temperature of 1 million degrees Celsius, so far higher than the surface of even the hottest white dwarf stars.

Reindl’s team used the 3.5-metre Calar Alto telescope in Spain to discover and observe a white dwarf in the direction of the constellation of Triangulum, catalogued as GALEXJ014636.8+323615, located 1200 light years from the Sun. Analysing the light from the white dwarf with a technique known as spectroscopy, where the light is dispersed into its constituent colours, revealed the signatures of highly ionised metals. Intriguingly these varied over a period of six hours — the same time it takes for the white dwarf to rotate.

Reindl and her team conclude that the magnetic field around the star — the magnetosphere — traps material flowing from its surface. Shocks within the magnetosphere heat the material dramatically, stripping almost all the electrons from the metal atoms.

“It’s like a doughnut made up of ultra-hot material that surrounds the already very hot star” explains Reindl.

“The axis of the magnetic field of the white dwarf is tilted from its rotational axis. This means that the amount of shock-heated material we see varies as the star rotates.

‘After decades of finding more and more of these obscure stars without having a clue where these highly ionised metals come from,” she continues, “our shock-heated magnetosphere model finally explains their origin.”

Magnetospheres are found around other types of stars, but this is the first report of one around a white dwarf. The discovery might have far-reaching consequences. “We simply didn’t take this into account,” admits Reindl. “Ignoring their magnetospheres could mean measurements of other basic properties of white dwarfs are wrong, like their temperatures and masses.”

It may be that a quarter of white dwarfs go through a stage of trapping and super-heating material. Reindl and her team now plan to model them in detail and to extend their research by studying more of these fascinating objects.

Astronomers Find Pairs Of Black Holes At The Centers Of Merging Galaxies

For the first time, a team of astronomers has observed several pairs of galaxies in the final stages of merging together into single, larger galaxies. Peering through thick walls of gas and dust surrounding the merging galaxies’ messy cores, the research team captured pairs of supermassive black holes — each of which once occupied the center of one of the two original smaller galaxies — drawing closer together before they coalescence into one giant black hole.

Led by University of Maryland alumnus Michael Koss (M.S. ’07, Ph.D. ’11, astronomy), a research scientist at Eureka Scientific, Inc., with contributions from UMD astronomers, the team surveyed hundreds of nearby galaxies using imagery from the W.M. Keck Observatory in Hawaii and NASA’s Hubble Space Telescope. The Hubble observations represent more than 20 years’ worth of images from the telescope’s lengthy archive. The team described their findings in a research paper published on November 8, 2018, in the journal Nature.

“Seeing the pairs of merging galaxy nuclei associated with these huge black holes so close together was pretty amazing,” Koss said. “In our study, we see two galaxy nuclei right when the images were taken. You can’t argue with it; it’s a very ‘clean’ result, which doesn’t rely on interpretation.”

The high-resolution images also provide a close-up preview of a phenomenon that astronomers suspect was more common in the early universe, when galaxy mergers were more frequent. When the black holes finally do collide, they will unleash powerful energy in the form of gravitational waves — ripples in space-time recently detected for the first time by the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors.

The images also presage what will likely happen in a few billion years, when our Milky Way galaxy merges with the neighboring Andromeda galaxy. Both galaxies host supermassive black holes at their center, which will eventually smash together and merge into one larger black hole.

The team was inspired by a Hubble image of two interacting galaxies collectively called NGC 6240, which later served as a prototype for the study. The team first searched for visually obscured, active black holes by sifting through 10 years’ worth of X-ray data from the Burst Alert Telescope (BAT) aboard NASA’s Neil Gehrels Swift Observatory.

“The advantage to using Swift’s BAT is that it observes high-energy, ‘hard’ X-rays,” said study co-author Richard Mushotzky, a professor of astronomy at UMD and a fellow of the Joint Space-Science Institute (JSI). “These X-rays penetrate through the thick clouds of dust and gas that surround active galaxies, allowing the BAT to see things that are literally invisible in other wavelengths.”

The researchers then combed through the Hubble archive, zeroing in on the merging galaxies they spotted in the X-ray data. They then used the Keck telescope’s super-sharp, near-infrared vision to observe a larger sample of the X-ray-producing black holes not found in the Hubble archive.

The team targeted galaxies located an average of 330 million light-years from Earth — relatively close by in cosmic terms. Many of the galaxies are similar in size to the Milky Way and Andromeda galaxies. In total, the team analyzed 96 galaxies observed with the Keck telescope and 385 galaxies from the Hubble archive.

Their results suggest that more than 17 percent of these galaxies host a pair of black holes at their center, which are locked in the late stages of spiraling ever closer together before merging into a single, ultra-massive black hole. The researchers were surprised to find such a high fraction of late-stage mergers, because most simulations suggest that black hole pairs spend very little time in this phase.

To check their results, the researchers compared the survey galaxies with a control group of 176 other galaxies from the Hubble archive that lack actively growing black holes. In this group, only about one percent of the surveyed galaxies were suspected to host pairs of black holes in the later stages of merging together.

This last step helped the researchers confirm that the luminous galactic cores found in their census of dusty interacting galaxies are indeed a signature of rapidly-growing black hole pairs headed for a collision. According to the researchers, this finding is consistent with theoretical predictions, but until now, had not been verified by direct observations.

“People had conducted studies to look for these close interacting black holes before, but what really enabled this particular study were the X-rays that can break through the cocoon of dust,” explained Koss. “We also looked a bit farther in the universe so that we could survey a larger volume of space, giving us a greater chance of finding more luminous, rapidly-growing black holes.”

It is not easy to find galactic nuclei so close together. Most prior observations of merging galaxies have caught the coalescing black holes at earlier stages, when they were about 10 times farther away. The late stage of the merger process is so elusive because the interacting galaxies are encased in dense dust and gas, requiring very high-resolution observations that can see through the clouds and pinpoint the two merging nuclei.

“Computer simulations of galaxy smashups show us that black holes grow fastest during the final stages of mergers, near the time when the black holes interact, and that’s what we have found in our survey,” said Laura Blecha, an assistant professor of physics at the University of Florida and a co-author of the study. Blecha was a JSI Prize Postdoctoral Fellow in the UMD Department of Astronomy prior to joining UF’s faculty in 2017. “The fact that black holes grow faster and faster as mergers progress tells us galaxy encounters are really important for our understanding of how these objects got to be so monstrously big.”

Future infrared telescopes such as NASA’s highly anticipated James Webb Space Telescope (JWST), slated for launch in 2021, will provide an even better view of mergers in dusty, heavily obscured galaxies. For nearby black hole pairs, JWST should also be capable of measuring the masses, growth rates and other physical parameters for each black hole.

“There might be other objects that we missed. Even with Hubble, many nearby galaxies at low redshift cannot be resolved — the two nuclei just merge into one,” said study co-author Sylvain Veilleux, a professor of astronomy at UMD and a JSI Fellow. “With JWST’s higher angular resolution and sensitivity to the infrared, which can pass through the dusty cores of these galaxies, searches for these nearby objects should be easy to do. Also with JWST, we will be able to push toward larger distances, to see objects at higher redshift. With these observations, we can begin to explore the fraction of objects that are merging in the youngest, most distant regions of the universe — which should be fairly frequent.”

Kin Of Gravitational Wave Source Discovered

On October 16, 2017, an international group of astronomers and physicists excitedly reported the first simultaneous detection of light and gravitational waves from the same source — a merger of two neutron stars. Now, a team that includes several University of Maryland astronomers has identified a direct relative of that historic event.

The newly described object, named GRB150101B, was reported as a gamma-ray burst localized by NASA’s Neil Gehrels Swift Observatory in 2015. Follow-up observations by NASA’s Chandra X-ray Observatory, the Hubble Space Telescope (HST) and the Discovery Channel Telescope (DCT) suggest that GRB150101B shares remarkable similarities with the neutron star merger, named GW170817, discovered by the Laser Interferometer Gravitational-wave Observatory (LIGO) and observed by multiple light-gathering telescopes in 2017.

A new study suggests that these two separate objects may, in fact, be directly related. The results were published on October 16, 2018 in the journal Nature Communications.

“It’s a big step to go from one detected object to two,” said study lead author Eleonora Troja, an associate research scientist in the UMD Department of Astronomy with a joint appointment at NASA’s Goddard Space Flight Center. “Our discovery tells us that events like GW170817 and GRB150101B could represent a whole new class of erupting objects that turn on and off — and might actually be relatively common.”

Troja and her colleagues suspect that both GRB150101B and GW170817 were produced by the same type of event: a merger of two neutron stars. These catastrophic coalescences each generated a narrow jet, or beam, of high-energy particles. The jets each produced a short, intense gamma-ray burst (GRB) — a powerful flash that lasts only a few seconds. GW170817 also created ripples in space-time called gravitational waves, suggesting that this might be a common feature of neutron star mergers.

The apparent match between GRB150101B and GW170817 is striking: both produced an unusually faint and short-lived gamma ray burst and both were a source of bright, blue optical light and long-lasting X-ray emission. The host galaxies are also remarkably similar, based on HST and DCT observations. Both are bright elliptical galaxies with a population of stars a few billion years old that display no evidence of new star formation.

“We have a case of cosmic look-alikes,” said study co-author Geoffrey Ryan, a postdoctoral researcher in the UMD Department of Astronomy and a fellow of the Joint Space-Science Institute. “They look the same, act the same and come from similar neighborhoods, so the simplest explanation is that they are from the same family of objects.”

In the cases of both GRB150101B and GW170817, the explosion was likely viewed “off-axis,” that is, with the jet not pointing directly towards Earth. So far, these events are the only two off-axis short GRBs that astronomers have identified.

The optical emission from GRB150101B is largely in the blue portion of the spectrum, providing an important clue that this event is another kilonova, as seen in GW170817. A kilonova is a luminous flash of radioactive light that produces large quantities of important elements like silver, gold, platinum and uranium.

While there are many commonalities between GRB150101B and GW170817, there are two very important differences. One is their location: GW170817 is relatively close, at about 130 million light years from Earth, while GRB150101B lies about 1.7 billion light years away.

The second important difference is that, unlike GW170817, gravitational wave data does not exist for GRB150101B. Without this information, the team cannot calculate the masses of the two objects that merged. It is possible that the event resulted from the merger of a black hole and a neutron star, rather than two neutron stars.

“Surely it’s only a matter of time before another event like GW170817 will provide both gravitational wave data and electromagnetic imagery. If the next such observation reveals a merger between a neutron star and a black hole, that would be truly groundbreaking,” said study co-author Alexander Kutyrev, an associate research scientist in the UMD Department of Astronomy with a joint appointment at NASA’s Goddard Space Flight Center. “Our latest observations give us renewed hope that we’ll see such an event before too long.”

It is possible that a few mergers like the ones seen in GW170817 and GRB150101B have been detected previously, but were not properly identified using complementary observations in different wavelengths of light, according to the researchers. Without such detections — in particular, at longer wavelengths such as X-rays or optical light — it is very difficult to determine the precise location of events that produce gamma-ray bursts.

In the case of GRB150101B, astronomers first thought that the event might coincide with an X-ray source detected by Swift in the center of the galaxy. The most likely explanation for such a source would be a supermassive black hole devouring gas and dust. However, follow-up observations with Chandra placed the event further away from the center of the host galaxy.

According to the researchers, even if LIGO had been operational in early 2015, it would very likely not have detected gravitational waves from GRB150101B because of the event’s greater distance from Earth. All the same, every new event observed with both LIGO and multiple light-gathering telescopes will add important new pieces to the puzzle.

“Every new observation helps us learn better how to identify kilonovae with spectral fingerprints: silver creates a blue color, whereas gold and platinum add a shade of red, for example,” Troja added. “We’ve been able identify this kilonova without gravitational wave data, so maybe in the future, we’ll even be able to do this without directly observing a gamma-ray burst.”

Giant Planets Around Young Star Raise Questions About How Planets Form

Researchers have identified a young star with four Jupiter and Saturn-sized planets in orbit around it, the first time that so many massive planets have been detected in such a young system. The system has also set a new record for the most extreme range of orbits yet observed: the outermost planet is more than a thousand times further from the star than the innermost one, which raises interesting questions about how such a system might have formed.

The star is just two million years old — a ‘toddler’ in astronomical terms — and is surrounded by a huge disc of dust and ice. This disc, known as a protoplanetary disc, is where the planets, moons, asteroids and other astronomical objects in stellar systems form.

The star was already known to be remarkable because it contains the first so-called hot Jupiter — a massive planet orbiting very close to its parent star — to have been discovered around such a young star. Although hot Jupiters were the first type of exoplanet to be discovered, their existence has long puzzled astronomers because they are often thought to be too close to their parent stars to have formed in situ.

Now, a team of researchers led by the University of Cambridge have used the Atacama Large Millimeter/submillimeter Array (ALMA) to search for planetary ‘siblings’ to this infant hot Jupiter. Their image revealed three distinct gaps in the disc, which, according to their theoretical modelling, were most likely caused by three additional gas giant planets also orbiting the young star. Their results are reported in The Astrophysical Journal Letters.

The star, CI Tau, is located about 500 light years away in a highly-productive stellar ‘nursery’ region of the galaxy. Its four planets differ greatly in their orbits: the closest (the hot Jupiter) is within the equivalent of the orbit of Mercury, while the farthest orbits at a distance more than three times greater than that of Neptune. The two outer planets are about the mass of Saturn, while the two inner planets are respectively around one and 10 times the mass of Jupiter.

The discovery raises many questions for astronomers. Around 1% of stars host hot Jupiters, but most of the known hot Jupiters are hundreds of times older than CI Tau. “It is currently impossible to say whether the extreme planetary architecture seen in CI Tau is common in hot Jupiter systems because the way that these sibling planets were detected — through their effect on the protoplanetary disc — would not work in older systems which no longer have a protoplanetary disc,” said Professor Cathie Clarke from Cambridge’s Institute of Astronomy, the study’s first author.

According to the researchers, it is also unclear whether the sibling planets played a role in driving the innermost planet into its ultra-close orbit, and whether this is a mechanism that works in making hot Jupiters in general. And a further mystery is how the outer two planets formed at all.

“Planet formation models tend to focus on being able to make the types of planets that have been observed already, so new discoveries don’t necessarily fit the models,” said Clarke. “Saturn mass planets are supposed to form by first accumulating a solid core and then pulling in a layer of gas on top, but these processes are supposed to be very slow at large distances from the star. Most models will struggle to make planets of this mass at this distance.”

The task ahead will be to study this puzzling system at multiple wavelengths to get more clues about the properties of the disc and its planets. In the meantime, ALMA — the first telescope with the capability of imaging planets in the making — will likely throw out further surprises in other systems, re-shaping our picture of how planetary systems form.

The research has been supported by the European Research Council.

When Is A Nova Not A Nova? When A White Dwarf And A Brown Dwarf Collide

Researchers from Keele University and an international team of astronomers have reported for the first time that a white dwarf and a brown dwarf collided in a ‘blaze of glory’ that was witnessed on Earth in 1670.

Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the astronomers found evidence that a white dwarf (the remains of a sun-like star at the end of its life) and a brown dwarf (a failed star without sufficient mass to sustain thermonuclear fusion) collided in a short-lived blaze of glory that was witnessed on Earth in 1670 as Nova Cygni—”a new star below the head of the Swan.” It appeared abruptly as a star as bright as those in the plough, that gradually faded, reappeared, and finally disappeared from view.

Modern astronomers studying the remains of this cosmic event initially thought it was triggered by the merging of two main-sequence stars on the same evolutionary path as our sun. This nova was long referred to as “Nova Vulpeculae 1670,” and later became known as CK Vulpeculae. However, we now know that CK Vulpeculae was not what we would today describe as a nova, but was, in fact, the merger of two stars—a white dwarf and a brown dwarf.

By studying the debris from this explosion, which today appears as dual rings of dust and gas resembling an hourglass with a compact central object, the research team concluded that a brown dwarf merged with a white dwarf. Professor Nye Evans, Professor of Astrophysics at Keele University and co-author on the in the Monthly Notices of the Royal Astronomical Society, explains, “CK Vulpeculae has in the past been regarded as the oldest ‘old nova.’ However, the observations of CK Vulpeculae I have made over the years using telescopes on the ground and in space convinced me that this was no nova. Everyone knew what it wasn’t—but nobody knew what it was. But a stellar merger of some sort seemed the best bet. With our ALMA observations of the exquisite dusty hourglass and the warped disc, plus the presence of lithium and peculiar isotope abundances, the puzzle fit together: In 1670, a brown dwarf star was shredded and dumped on the surface of a white dwarf star, leading to the 1670 eruption and the hourglass we see today.”

The team of European, American and South African astronomers used the Atacama Large Millimeter/submillimeter Array to examine the remains of the merger and reported some interesting findings. By studying the light from two more distant stars as they shine through the dusty remains of the merger, the researchers were able to detect the telltale signature of the element lithium, which is easily destroyed in stellar interiors.

Dr. Stewart Eyres, deputy dean of the Faculty of Computing, Engineering and Science at the University of South Wales and lead author on the paper, says, “The material in the hourglass contains the element lithium, normally easily destroyed in stellar interiors. The presence of lithium, together with unusual isotopic ratios of the elements C, N, O, indicate that an astronomically small amount of material, in the form of a brown dwarf star, crashed onto the surface of a white dwarf in 1670, leading to thermonuclear burning, an eruption that led to the brightening seen by the Carthusian monk Anthelme and the astronomer Hevelius, and in the hourglass we see today.”

Professor Albert Zijlstra, from The University of Manchester’s School of Physics & Astronomy, co-author of the study, says, “Stellar collisions are the most violent events in the universe. Most attention is given to collisions between neutrons stars, or between two white dwarfs—which can produce a supernova—and star-planet collisions. But it is very rare to actually see a collision, and where we believe one occurred, it is difficult to know what kind of stars collided. The collision here is a new one, not previously considered or ever seen before. This is an extremely exciting discovery.”

Professor Sumner Starrfield, Regents’ Professor of Astrophysics at Arizona State University says, “The white dwarf would have been about 10 times more massive than the brown dwarf, so as the brown dwarf spiraled into the white dwarf it would have been ripped apart by the intense tidal forces exerted by the white dwarf. When these two objects collided, they spilled out a cocktail of molecules and unusual element isotopes. These organic molecules, which we could detected with ALMA, expanded measurably into the surrounding environment, providing compelling evidence of the true origin of this blast. This is the first time such an event has been conclusively identified. Intriguingly, the hourglass is also rich in organic molecules such as formaldehyde (H2CO), methanol (CH3OH) and methanamide (NH2CHO). These molecules would not survive in an environment undergoing nuclear fusion and must have been produced in the debris from the explosion. This lends further support to the conclusion that a brown dwarf met its demise in a star-on-star collision with a white dwarf.”

Since most star systems in the Milky Way are binary, stellar collisions are not that rare, the astronomers note. Professor Starrfield says, “Such collisions are probably not rare, and this material will eventually become part of a new planetary system, implying that they may already contain the building-blocks of organic molecules as they are forming.”

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First Results From Cassini’s Final Mission Phase Show Protons Of Extreme Energies Between The Planet And Its Dense Rings

Approximately one year ago, a spectacular dive into Saturn ended NASA’s Cassini mission—and with it a unique, 13-year research expedition to the Saturnian system. In the mission’s last five months, the probe entered uncharted territory again: Twenty-two times, it plunged into the almost unexplored region between the planet Saturn and its innermost ring, the D ring. On Friday, 5 October 2018, the journal Science is releasing six articles describing first results from this mission phase.

In one of these papers, a research team led by the Max Planck Institute for Solar System Research in Germany and the Applied Physics Laboratory of Johns Hopkins University in the U.S. reports on the unique proton radiation belts formed in close proximity to the planet. Due to presence of the dense A, B, and C rings, this area is almost completely decoupled from the main radiation belt and the rest of the magnetosphere, which extend farther outward.

When the space probe Cassini swung into its first orbit around Saturn and its rings on July 1, 2004, the Magnetospheric Imaging Instrument (MIMI) particle detector suite, including Low Energy Magnetospheric Measurement System (LEMMS), developed and built under the leadership of MPS, caught a brief glimpse of the region between the planet and the innermost D ring. The measurements indicated that a population of charged particles may be present, but its exact composition and properties remained obscure. In the following years, MIMI-LEMMS investigated the particles that are trapped by Saturn’s strong magnetic field outside its rings, forming its main radiation belt that consists of high-energy protons and electrons. The proton radiation belt extends more than 285,000 kilometers into space and is strongly influenced by Saturn’s numerous moons, which segment it into five sectors. “Only 13 years later, shortly before the end of the mission, we were given the opportunity to follow up on our very first measurements at Saturn and see if an additional radiation belt sector co-exists with the D ring and the upper atmosphere of the planet,” explains Elias Roussos, scientist at the Max Planck Institute for Solar Systems lead author of the current study.

The 13-year-long test of patience has now paid off. In their current Science article, the scientists paint a comprehensive picture of the protons surrounding Saturn in close proximity. Two articles in the journal Geophysical Research Letters elaborate these findings.

Similar to the main proton belt of Saturn, the protons that populate the region close to the planet are generated by incident galactic cosmic radiation. When cosmic radiation interacts with material in Saturn’s atmosphere or in its dense rings, it triggers a chain of reactions generating high-energy protons that are subsequently trapped by the planet’s magnetic field.

Saturn’s magnetic field is more than 10 times stronger near the planet than it is in the main radiation belts. That makes trapping so efficient that protons can remain for years in the same magnetic field line. That forces them to interact continuously with the D ring and the Saturnian atmosphere and gradually lose their full energy. But with the densities of the tenuous D ring unknown, it was unclear how fast this energy loss develops and whether a radiation belt could be maintained. Theoretical modeling indicated that one viable scenario might be MIMI measuring nothing but noise.

That fortunately did not happen – at least for protons. LEMMS measurements revealed a stable accumulation of energetic protons that extends from the atmosphere of Saturn and all across the D ring. The energy that many of these protons have is extreme: more than 10 times higher than what LEMMS was designed to measure. “We had to dig out old mechanical drawings of the instrument and construct new models of it to understand how it would measure in such an extreme environment,” Roussos adds.

“Outward of the D ring, Saturn’s A, B and C rings are significantly denser and dustier, forming an effective 62,000-kilometer barrier for the trapping of charged particles,” Roussos continues. That meant that the outer edge of the D ring was as far as this new proton belt could extend – and LEMMS measurements confirmed that. “This creates a radiation belt that is completely isolated from the rest of the magnetosphere,” says MPS scientist Dr. Norbert Krupp, Principal Investigator of the MIMI-LEMMS team and co-author of the study in Science.

This region is unique in the solar system. It offers the possibility to examine a radiation belt in laboratory-like conditions, as its protons are created by a very stable process, guided and controlled by Saturn’s strong magnetic field. In Saturn’s main radiation belt and in the radiation belts of Earth and Jupiter, these conditions are different—and much more complicated. At Earth, for example, a variable influx of high-energy particles from the sun can have a strong influence on the radiation belt structure.

Equally valuable is the new information that LEMMS adds about the D ring system, which is too faint to study by imaging alone. This ring contains a total of three narrow ringlets, all brighter than the rest of the ring and named as D68, D72 and D73. While the intensity of protons was reduced by ringlets D68 and D73, ringlet D72 lying between them does not appear to have an effect. “Even though the D72 and D68 ringlets are similarly bright, LEMMS measurements show us that they must actually be very different,” says Roussos.

MIMI measurements also revealed a secondary, lower-energy proton radiation belt at an altitude below several thousand kilometers. This belt forms occasionally when fast neutral hydrogen atoms created in Saturn’s magnetosphere get trapped near the planet when they impact its atmosphere and become charged. “The presence of this lower-altitude belt shows that some minimal information by Saturn’s variable, distant magnetosphere can be transmitted across the planet’s dense rings,” Krupp adds.

In the 13 years the MIMI/LEMMS instrument spent at Saturn, it conducted one of the most comprehensive investigations of a planetary radiation belt other than that of the Earth and even helped to discover unknown rings. A summary of these and further discoveries can be found in the book Saturn in the 21st Century, which is published by Cambridge University Press this month. Dr. Norbert Krupp from the MPS is among its four editors.