Topic: Late July Astronomy Bulletin

[Clive]

ROLE WATER PLAYED IN MOON’S FORMATION

Johns Hopkins University Applied Physics Laboratory

Using data collected over two decades ago, scientists from the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, have compiled the first complete map of hydrogen abundances on the Moon's surface. The map identifies two types of lunar materials containing enhanced hydrogen and corroborates previous ideas about lunar hydrogen and water, including findings that water likely played a role in the Moon's original magma-ocean formation and solidification. Researchers used orbital neutron data from the Lunar Prospector mission to build their map. The probe, which was deployed by NASA in 1998, orbited the Moon for a year and a half and sent back the first direct evidence of enhanced hydrogen at the lunar poles, before impacting the lunar surface. When a star explodes, it releases cosmic rays, or high-energy protons and neutrons that move through space at nearly the speed of light. When those cosmic rays come into contact with the surface of a planet, or a moon, they break apart atoms located on those bodies, sending protons and neutrons flying. Scientists are able to identify an element and determine where and how much of it exists by studying the motion of those protons and neutrons. The team calibrated the data to quantify the amount of hydrogen by the corresponding decrease of neutrons measured by the Neutron Spectrometer, one of five instruments mounted on Lunar Prospector to complete gravitational and compositional maps of the Moon.

The team's map confirms enhanced hydrogen in two types of lunar materials. The first, at the Aristarchus Plateau, is home to the Moon's largest pyroclastic deposit. These deposits are fragments of rock erupted from volcanoes, corroborating prior observations that hydrogen and/or water played a role in lunar magmatic events. The second is KREEP-type rocks. KREEP is an acronym for lunar lava rock that stands for potassium (K), rare earth elements (REE) and phosphorus (P). When the Moon originally formed, it's largely accepted that it was molten debris from a huge impact with Earth. As it cooled, minerals formed out of the melt, and KREEP is thought to be the last type of material to crystallize and harden. The new map not only completes the inventory of hydrogen on the Moon but could also lead to quantification of how much hydrogen and water was present in the Moon when it was born. In 2013, APL researchers also confirmed the presence of water ice at the poles on the planet Mercury using data from the neutron spectrometer on the APL-built MESSENGER spacecraft. These discoveries are important not only for understanding the solar system but also in planning future human exploration of the solar system.

WHAT DO MARS AND ICELAND HAVE IN COMMON?

Northern Arizona University

These days, not so much. But more than 4.5 billion years ago, it's possible the Red Planet had a crust comparable to Iceland today. This discovery, hidden in the oldest Martian fragments found on Earth, could provide information about our planet that was lost over billions of years of geological movement and could help explain why the Earth developed into a planet that sustains a broad diversity of life and Mars did not. These insights into Earth's past came out of a new study that details how they found the likely Martian origin of the 4.48-billion-year-old meteorite, informally named Black Beauty. Its origin is one of the oldest regions of Mars. The team searched for the location of origin of a Martian meteorite (officially named NWA -- Northwest Africa -- 7034 for where it was found on Earth). This meteorite, the chemistry of which indicates that Mars had volcanic activity to that found on Earth, recorded the first stage of Mars' evolution. Although it was ejected from the surface of Mars five to 10 million years ago after an asteroid impact, its source region and geological context has remained a mystery. This team studied chemical and physical properties of Black Beauty to pinpoint where it came from; they determined it was from Terra Cimmeria-Sirenum, one of the most ancient regions of Mars. It may have a surface similar to Earth's continents. Planetary bodies like Mars have impacts craters all over their surface, so finding the right one is challenging. In a previous study, The team developed a crater detection algorithm that uses high-resolution images of the surface of Mars to identify small impact craters, finding about 90 million as small as 50 metres in diameter. In this study, they were able to isolate the most plausible ejection site -- the Karratha crater that excavated ejecta of an older crater named Khujirt. The team's algorithm is adapted to detect impact craters constellating Mercury and the Moon, the other terrestrial bodies. This can be used to help unravel their geographical history and answer foundational questions regarding their formation and evolution. This work is a starting point to guide future investigations of the Solar System.



WHY JUPITER DOESN’T HAVE RINGS LIKE SATURN

University of California - Riverside

Because it's bigger, Jupiter ought to have larger, more spectacular rings than Saturn has. But new research shows Jupiter's massive moons prevent that vision from lighting up the night sky. To understand the reason Jupiter currently looks the way it does, astronomers ran a dynamic computer simulation accounting for the orbits of Jupiter's four main moons, as well as the orbit of the planet itself, and information about the time it takes for rings to form. Saturn's rings are largely made of ice, some of which may have come from comets, which are also largely made of ice. If moons are massive enough, their gravity can toss the ice out of a planet's orbit, or change the orbit of the ice enough so that it collides with the moons. All four giant planets in our solar system -- Saturn, Neptune, Uranus and also Jupiter -- do in fact have rings. However, both Neptune and Jupiter's rings are so flimsy they're difficult to view with traditional stargazing instruments. Coincidentally, some of the recent images from the newly commissioned James Webb Space Telescope included pictures of Jupiter, in which the faint rings are visible. Uranus has rings that are aren't as large but are more substantial than Saturn's. Going forward, Kane intends to run simulations of the conditions on Uranus to see what the lifetime of that planet's rings might be. Some astronomers believe Uranus is tipped over on its side as the result of a collision the planet had with another celestial body. Its rings could be the remains of that impact. Beyond their beauty, rings help astronomers understand the history of a planet, because they offer evidence of collisions with moons or comets that may have happened in the past. The shape and size of the rings, as well as the composition of the material, offers an indication about the type of event that formed them.

UNDEAD PLANETS

Royal Astronomical Society

The first ever exoplanets were discovered 30 years ago around a rapidly rotating star, called a pulsar. Now, astronomers have revealed that these planets may be incredibly rare. The processes that cause planets to form, and survive, around pulsars are currently unknown. A survey of 800 pulsars followed by the Jodrell Bank Observatory over the last 50 years has revealed that this first detected exoplanet system may be extraordinarily uncommon: less than 0.5% of all known pulsars could host Earth-mass planets. Pulsars are a type of neutron star, the densest stars in the Universe, born during powerful explosions at the end of a typical star's life. They are exceptionally stable, rapidly rotating, and have incredibly strong magnetic fields. Pulsars emit beams of bright radio emission from their magnetic poles that appear to pulse as the star rotates. In 1992, the first ever exoplanets were discovered orbiting a pulsar called PSR B1257+12. The planetary system is now known to host at least three planets similar in mass to the rocky planets in our Solar System. Since then, a handful of pulsars have been found to host planets. However, the extremely violent conditions surrounding the births and lives of pulsars make 'normal' planet formation unlikely, and many of these detected planets are exotic objects (such as planets made mostly of diamond) unlike those we know in our Solar System. A team of astronomers at the University of Manchester performed the largest search for planets orbiting pulsars to date. In particular, the team looked for signals that indicate the presence of planetary companions with masses up to 100 times that of the Earth, and orbital time periods between 20 days and 17 years. Of the 10 potential detections, the most promising is the system PSR J2007+3120 with the possibility of hosting at least two planets, with masses a few times bigger than the Earth, and orbital periods of 1.9 and ~3.6 years. The results of the work indicate no bias for particular planet masses or orbital periods in pulsar systems. However, the results do yield information of the shape of these planets' orbits: in contrast to the near-circular orbits found in our Solar System, these planets would orbit their stars on highly elliptical paths. This indicates that the formation process for pulsar-planet systems is vastly different than traditional star-planet systems.



PLANET COULD BE A "ROSETTA STONE" FOR FINDING ALIEN LIFE

Universe

The ultra-powerful James Webb Space Telescope will catch a glimpse of the enigmatic atmosphere of a terrestrial (Earth-sized) exoplanet known as Gliese 486 b, previously termed as a “Rosetta Stone” because it could unlock the secrets of habitable. Gliese 486 b is probably not habitable in itself, but will serve as a proving ground for planets that may be. We usually define "habitable" as a rocky world that could host liquid water on its surface, although the picture is … complicated. The odd behaviour of parent red dwarf stars like Gliese 486 — popular planet-seeking targets due to their relative small size and lack of stray light interfering with observations — might shoot out a lot of life-harming radiation, for a start. We also know little about the composition of rocky planet atmospheres like Gliese 486 b, although we can make educated guesses from models and from what we can observe in planets and moons in our own Solar System. Happily, however, Webb's high-resolution view gives us a serious chance at learning about the complex environment of this exoplanet. Perched at Lagrange Point 2, Webb has an 18-segment hexagonal mirror optimized for deep space operations. The huge mirror and lack of stray light will at last allow astronomers to probe the transient molecules of gas visible in a distant, tiny planet like Gliese 486 b.

Gliese 486 b is close enough to its parent star that investigators suspect one side is permanently facing its star. Gravitational interactions between the planet and the sun – similar to the Earth and the Moon – lock the planet into a synchronous rotation with the star during Gliese 486 b's orbit. Investigators will watch as the planet passes behind its parent star, from Earth's perspective. That will allow them the best view possible of the "dayside" of the star, as this spot will be shining for Webb to observe during some of this time. Gliese 486 b is a perfect target for such an observation as it is quite hot and orbits a relatively small star, which will make its light easier to distinguish from any stellar interference. If this testbed for atmospheric observations work, the implications are huge as Webb prepares for another 20 years of operations. Secondary eclipse techniques seem to fit the bill of efficient observing, from what the team can deduce, while still being scientifically effective. "The idea here is that a planet without an atmosphere will be relatively hot, because this planet is expected to have one hemisphere — the day side — that constantly faces the star. With no atmosphere, rocks would heat up to searing temperatures visible from afar. With an atmosphere, however, the planet's dayside would be much cooler — perhaps due to highly reflective clouds that reflect away starlight, or through circulating heat to the nightside. Deductions about the planet's atmosphere would thus be visible through temperature — above a certain threshold, there likely would be no atmosphere. Webb, happily, is optimized to look in the mid-infrared wavelengths needed to assess Gliese 486 b's atmosphere or lack thereof. Coupled with its high resolution, Webb would be able to deduce the spectra or "signatures" of different gases through the telescope's spectrometers, "to try and understand what the atmosphere is made of," Mansfield said.

That Gliese 486 b is rocky is not in dispute, as eclipse observations from NASA's Transiting Exoplanet Survey Satellite coupled with radial velocity measurements from ground telescopes show a mass within the range of a rocky planet. Webb, however, will finally be able to deduce more of the planet's nature — especially because most planets emit their light in mid-infrared at five to 14 microns, precisely where the telescope is optimized to see. Webb will also allow for a large span of wavelengths to be observed at one time, giving investigators the best chance possible of spotting the unique fingerprint a gas shows in its spectrum. If Gliese 486 b has an atmosphere at its close orbital distance, there might be hope for planets in the habitable region of stars that are also red dwarfs. Flaring dwarfs might strip gas from planets' atmosphere with their radiation, making it difficult for scientists to assess whether planets might be able to hold on to their atmospheres long enough for life to develop. Even if the atmosphere isn't apparent, it still will be an exciting find as scientists will be gazing directly at the surface of a small, rocky world from afar. In that case, we will have a chance to do exo-geology', and try and figure out what types of rock the surface of the planet is made of.

NEW METHOD TO DETECT EXOPLANETS

RAS

In recent years, a large number of exoplanets have been found around single ‘normal’ stars. New research shows that there may be exceptions to this trend. Researchers suggest a new way of detecting dim bodies, including planets, orbiting exotic binary stars known as Cataclysmic Variables (CVs). CVs are binary star systems in which the two stars are in extremely close proximity to each other; so close that the less massive object transfers mass to the more massive. CVs are typically formed of a small, cool type of star known as a red dwarf star, and a hot, dense star – a white dwarf. Red dwarf stars have a mass between 0.07 and 0.30 solar masses and a radius of around 20% of the Sun’s, while white dwarf stars have a typical mass of around 0.75 Solar masses and a very small radius similar to that of planet Earth. In the CV system, the transfer of matter from the small star forms an accretion disk around the compact, more massive star. The brightness of a CV system mainly comes from this disk, and overpowers the light coming from the two stars. A third dim body orbiting a CV can influence the mass transfer rate between the two stars, and hence the brightness of the entire system.  The method described in the new work is based on the change of brightness in the accretion disk due to perturbations of the third body that orbits around the inner two stars.

In their research, astronomers have estimated the mass and distance of a third body orbiting four different CVs using the changes in the brightness of each system. According to calculations carried out by the team, such brightness variations have very long periods in comparison to the orbital periods in the triple system. Two out of the four CVs appear to have bodies resembling planets in orbit around them. The work has proven that a third body can perturb a cataclysmic variable in such a way that can induce changes in brightness in the system. These perturbations can explain both the very long periods that have been observed - between 42 and 265 days- and the amplitude of those changes in brightness. Of the four systems studied, observations suggest that two of the four have objects of planetary mass in orbit around them. The scientists believe that this is a promising new technique for finding planets in orbit around binary star systems, adding to the thousands already found in the last three decades.

EXTREMELY BRIGHT ASTRONOMICAL EVENT IN DISTANT UNIVERSE

Kavli Institute for the Physics and Mathematics of the Universe

A team of astronomers has discovered a mysterious short-duration astronomical event, or transient, that is as bright as a superluminous supernova, but evolving much faster. The Universe is full of energetic transient phenomena, astronomical events that occur over a short period of time. For example, most massive stars end their lives by exploding spectacularly, known as a supernova, a major type of transients. In order to understand the origin of these transient phenomena, various time-domain surveys have been carried out in the past few decades. As more and more transients have been discovered, researchers began noticing some new transient types in recent years. To figure out the nature of various transient phenomena, an international transient survey project called "MUltiband Subaru Survey for Early-phase Supernovae" (MUSSES). By carrying out consecutive Subaru/HSC observations in December 2020, 20 fast-evolving transients have been discovered, and one of them, MUSSES2020J (AT 2020afay), caught the team’s attention. The data has stimulated intensive discussion about the origins of MUSSES2020J and a few other FBUTs, led by various researchers within the team. The theoretical investigation is still ongoing, but the team has so far narrowed down the possibilities to a few scenarios, most of which involve an active compact object -- either a black hole or a highly magnetized neutron star -- to power these extremely bright objects. There is almost no doubt that an active compact object is involved, and it is a main reason why these transients are so different from normal supernovae.

The remaining possibilities are an event where a star is tidally disrupted by a massive black hole, or a massive star collapse which is different from normal supernovae in a sense that it has probably left a highly active compact object like an accreting black hole. The very early-phase data provided for the first time for a class of FBUTs hints the existence of sub-relativistic outflow distinctly from a bulk of the slower ejecta, and this must be a key to solving the problem. We are currently checking the details of each model to robustly identify the origin of MUSSES2020J, with the strong constraint provided by this new observation. MUSSES2020J shows a similar light curve of AT 2018cow. The light curve of AT 2018cow is well-reproduced by the model of interaction between circumstellar matter and the ejecta of a pulsational pair-instability supernova (PPISN). The PPISN is the explosion of a very massive star which would collapse to form a black hole and eject the outer layer in a jet-like form. Therefore, it is possible that a similar PPISN model with a different amount of circumstellar matter can also explain the light curve of MUSSES2020J.

UNDERSTANDING THE LIFE CYCLE OF SUPERMASSIVE BLACK HOLES

Dartmouth College

Black holes with varying light signatures but that were thought to be the same objects being viewed from different angles are actually in different stages of the life cycle, according to a new study. The research on black holes known as "active galactic nuclei," or AGNs, says that it definitively shows the need to revise the widely used "unified model of AGN" that characterizes supermassive black holes as all having the same properties. Supermassive black holes are believed to reside at the centre of nearly all large galaxies, including the Milky Way. The objects devour galactic gas, dust and stars, and they can become heavier than small galaxies. For decades, researchers have been interested in the light signatures of active galactic nuclei, a type of supermassive black hole that is "accreting," or in a rapid growth stage. Beginning in the late 1980s, astronomers realized that light signatures coming from space ranging from radio wavelengths to X-rays could be attributed to AGNs. It was assumed that the objects usually had a doughnut-shaped ring -- or "torus" -- of gas and dust around them. The different brightness and colours associated with the objects were thought to be the result of the angle from which they were being observed and how much of the torus was obscuring the view. From this, the unified theory of AGNs became the prevalent understanding. The theory guides that if a black hole is being viewed through its torus, it should appear faint. If it is being viewed from below or above the ring, it should appear bright. According to the current study, however, the past research relied too heavily on data from the less obscured objects and skewed research results.

The new study focuses on how quickly black holes are feeding on space matter, or their accretion rates. The research found that the accretion rate does not depend upon the mass of a black hole, it varies significantly depending on how obscured it is by the gas and dust ring. The result shows that the amount of dust and gas surrounding an AGN is directly related to how much it is feeding, confirming that there are differences beyond orientation between different populations of AGNs. When a black hole is accreting at a high rate, the energy blows away dust and gas. As a result, it is more likely to be unobscured and appear brighter. Conversely, a less active AGN is surrounded by a denser torus and appears fainter. The study stems from a decade-long analysis of nearby AGNs detected by Swift-BAT, a high-energy NASA X-ray telescope. The telescope allows researchers to scan the local Universe to detect obscured and unobscured AGNs. The research is the result of an international scientific collaboration -- the BAT AGN Spectroscopic Survey (BASS) -- that has been working over a decade to collect and analyze optical/infrared spectroscopy for AGN observed by Swift BAT. According to the paper, by knowing a black hole's mass and how fast it is feeding, researchers can determine when most supermassive black holes underwent most of their growth, thus providing valuable information about the evolution of black holes and the Universe. Future research could include focusing on wavelengths that allow the team to search beyond the local Universe. In the nearer term, the team would like to understand what triggers AGNs to go into high accretion mode, and how long it takes rapidly accreting AGNs to transition from heavily obscured to unobscured.

WEBB FINDS GALAXY ONLY 233 MILLION YEARS AFTER BIG BANG

Ars Technica

Data from the Webb Space Telescope has only arrived into the hands of astronomers over the last few weeks, but they've been waiting for years for this, and apparently had analyses set to go. The result has been something like a race back in time, as new discoveries find objects that formed ever closer to the Big Bang that produced our Universe. Just recently, one of these searches turned up a galaxy that was present less than 400 million years after the Big Bang. This week, a new analysis has picked out a galaxy as it appeared only 233 million years after the Universe popped into existence. The discovery is a happy byproduct of work that was designed to answer a more general question: How many galaxies should we expect to see at different time points after the Big Bang? The e early Universe was opaque to light at any wavelengths that carry more energy than is needed to ionize hydrogen. That energy is in the UV portion of the spectrum, but the red shift caused by 13 billion years of an expanding Universe has shifted that cut-off point into the infrared portion of the spectrum. To find galaxies from this time, we have to look for objects that aren't visible at shorter infrared wavelengths (meaning that light was once above the hydrogen cut-off), but do appear at lower-energy wavelengths. The deeper into the infrared the boundary between invisible and visible is, the stronger the redshift, and the more distant the object is. The more distant the object, the closer in time it is to the Big Bang. Studies of these galaxies can tell us something about their individual properties. But identifying a large collection of early galaxies can help us determine how quickly they formed and identify any changes in galaxy dynamics that happened at a specific time in the Universe's past. This change over time in the frequency of visible objects is called a "luminosity function," and some work has been done to characterize the luminosity function of early galaxies. But the infrared wavelengths of the earliest galaxies are absorbed by Earth's atmosphere, and so have to be imaged from space.

The researchers used two data sources to reconstruct the galaxies' appearances at different points in time. One was produced by analyzing work done with a ground-based infrared telescope (the ESA's VISTA telescope) and the Spitzer space telescope, both of which imaged galaxies that were relatively older when they produced the light that's now reaching Earth—about 600 million years or more after the Big Bang. The other involved data generated by the Webb, including those data sets analyzed in the paper we reported on and an area imaged in the first public photo release. In all cases, the researchers searched for the same thing: objects that were present at longer infrared wavelengths but absent from shorter ones.  Overall, the team identified 55 distant galaxies, 44 of which had never been noted previously. Thirty-nine of these come from the Webb data, and that figure included the two ancient galaxies that were identified last week. The numbers aren't especially precise at higher redshifts, where they're based on just one or two galaxies. But overall, the trend suggests a gradual decline in visible objects out to within a few hundred million years of the Big Bang, with no sharp changes or cutoffs.

But the striking thing is that there is data for a galaxy at an extremely large redshift (z = 16.7 which  places it at less than 250 million years after the Big Bang. That distance is based partly on the fact that the first wavelength filter in which the object appears shows it to be very dim there, suggesting that it is faint at the wavelengths the filter lets through. That suggests that the light cutoff generated by hydrogen is near the edge of the filter's range.  Like the distant galaxies described last week, it also appears to have the equivalent of a billion Suns of material in the form of stars. The researchers estimate that it might have started star formation as early as 120 million years after the Big Bang, and had certainly done so by 220 million years.  The researchers are pretty confident that this new galaxy represents a real finding: "Having searched extensively, we are currently unable to find any plausible explanation for this object, other than a galaxy at a new redshift record." And by adding a second independent confirmation of the earlier galaxy finds, it greatly increases the confidence we have in those discoveries. All of which indicates the new telescope is delivering as promised, at least in terms of early galaxies. 

'UNCORRECTABLE' DAMAGE TO WEBB MIRROR

Live Science

Since launching on Dec. 25, 2021, NASA's James Webb Space Telescope (JWST) has been pelted by at least 19 tiny space rocks — including one large one that left noticeable damage on one of the telescope's 18 gold-plated mirrors. The impact — which likely occurred between May 23 and May 25 this year — left "uncorrectable" damage to a tiny portion of that mirror, the report says. However, this little dent doesn't seem to have inhibited the telescope's performance at all. In fact, the JWST's performance is exceeding expectations "almost all across the board." Tiny rocks known as micrometeoroids are an all-too-familiar threat to spacecraft in near-Earth orbit. The U.S. Space Surveillance Network keeps track of more than 23,000 pieces of orbital debris measuring larger than the size of a softball — however, the millions of nearby space chunks that are smaller than that are almost impossible to monitor. Instead, NASA and other space agencies plan for unavoidable impacts. So far, six micrometeoroids have left noticeable "deformities" on the JWST's mirrors, amounting to about one noticeable impact per month since the telescope launched. That's all within the realm of the expected. When building the JWST, engineers intentionally hit mirror samples with micrometeoroid-sized objects to test how such impacts would affect the telescope's performance. What was unexpected, however, was the size of the larger impactor that dented the C3 mirror. This space rock was seemingly larger than the team had prepared for, and researchers are now trying to assess the impact that further strikes like this could have on the JWST.