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Late August Astronomy Bulletin
« on: August 24, 2021, 22:39 »
MOON’S SUPPOSED MAGNETIC FIELD
University of Rochester

In 2024, a new age of space exploration will begin when NASA sends astronauts to the Moon as part of their Artemis mission, a follow-up to the Apollo missions of the 1960s and 1970s. Some of the biggest questions that scientists hope to explore include determining what resources are found in the Moon's soil and how those resources might be used to sustain life. Researchers report their findings on a major factor that influences the types of resources that may be found on the Moon: whether or not the Moon has had a long-lived magnetic shield at any point in its 4.53 billion-year history. The presence or absence of a shield matters because magnetic shields protect astronomical bodies from harmful solar radiation. And the team's findings contradict some longstanding assumptions. Earth's magnetic shield originates deep within the planet's core. There, swirling liquid iron generates electric currents, driving a phenomenon called the geodynamo, which produces the shield. The magnetic shield is invisible, but researchers have long recognized that it is vital for life on Earth's surface because it protects our planet from solar wind -- streams of radiation from the Sun. But has Earth's moon ever had a magnetic shield? While the Moon has no magnetic shield now, there has been debate over whether or not the Moon may have had a prolonged magnetic shield at some point in its history. Since the Apollo missions, there has been this idea that the Moon had a magnetic field that was as strong or even stronger than Earth's magnetic field at around 3.7 billion years ago. The belief that the Moon had a magnetic shield was based on an initial dataset from the 1970s that included analyses of samples collected during the Apollo missions. The analyses showed that the samples had magnetization, which researchers believed was caused by the presence of a geodynamo.

But a couple of factors have since given researchers pause. The core of the Moon is really small and it would be hard to actually drive that kind of magnetic field. Plus, the previous measurements that record a high magnetic field were not conducted using heating experiments. They used other techniques that may not accurately record the magnetic field. The team tested glass samples gathered on previous Apollo missions, but used CO2 lasers to heat the lunar samples for a short amount of time, a method that allowed them to avoid altering the samples. They then used highly sensitive superconducting magnetometers to more accurately measure the samples' magnetic signals. One of the issues with lunar samples has been that the magnetic carriers in them are quite susceptible to alteration. By heating with a laser, there is no evidence of alteration in our measurements, so we can avoid the problems people may have had in the past. The researchers determined that the magnetization in the samples could be the result of impacts from objects such as meteorites or comets -- not the result of magnetization from the presence of a magnetic shield. Other samples they analyzed had the potential to show strong magnetization in the presence of a magnetic field, but didn't show any magnetization, further indicating that the Moon has never had a prolonged magnetic shield. Without the protection of a magnetic shield, the Moon was susceptible to solar wind, which may have caused a variety of volatiles -- chemical elements and compounds that can be easily evaporated -- to become implanted in the lunar soil. These volatiles may include carbon, hydrogen, water, and helium 3, an isotope of helium that is not present in abundance on Earth. The research may help inform a new wave of lunar experiments based on data that will be gathered by the Artemis mission. Data from samples gathered during the mission will allow scientists and engineers to study the presence of volatiles and better determine if these materials can be extracted for human use. Helium 3, for instance, is currently used in medical imaging and cryogenics and is a possible future fuel source.


ROCKY PLANET HAS HALF THE MASS OF VENUS
ESO

A team of astronomers have used the European Southern Observatory's Very Large Telescope (ESO's VLT) in Chile to shed new light on planets around a nearby star, L 98-59, that resemble those in the inner Solar System. Amongst the findings are a planet with half the mass of Venus -- the lightest exoplanet ever to be measured using the radial velocity technique -- an ocean world, and a possible planet in the habitable zone. The results are an important step in the quest to find life on Earth-sized planets outside the Solar System. The detection of biosignatures on an exoplanet depends on the ability to study its atmosphere, but current telescopes are not large enough to achieve the resolution needed to do this for small, rocky planets. The newly studied planetary system, called L 98-59 after its star, is an attractive target for future observations of exoplanet atmospheres. Its orbits a star only 35 light-years away and has now been found to host rocky planets, like Earth or Venus, which are close enough to the star to be warm. With the contribution of ESO's VLT, the team was able to infer that three of the planets may contain water in their interiors or atmospheres. The two planets closest to the star in the L 98-59 system are probably dry, but might have small amounts of water, while up to 30% of the third planet's mass could be water, making it an ocean world. Furthermore, the team found "hidden" exoplanets that had not previously been spotted in this planetary system. They discovered a fourth planet and suspect there is a fifth, in a zone at the right distance from the star for liquid water to exist on its surface.

The team used the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) instrument on ESO's VLT to study L 98-59. The astronomers first spotted three of L 98-59's planets in 2019, using NASA's Transiting Exoplanet Survey Satellite (TESS). This satellite relies on a technique called the transit method -- where the dip in the light coming from the star caused by a planet passing in front of it is used to infer the properties of the planet -- to find the planets and measure their sizes. However, it was only with the addition of radial velocity measurements made with ESPRESSO and its predecessor, the High Accuracy Radial velocity Planet Searcher (HARPS) at the ESO La Silla 3.6-metre telescope, that the team were able to find extra planets and measure the masses and radii of the first three. The team hopes to continue to study the system with the forthcoming NASA/ESA/CSA James Webb Space Telescope (JWST) , while ESO's Extremely Large Telescope (ELT), under construction in the Chilean Atacama Desert and set to start observations in 2027, will also be ideal for studying these planets. "The HIRES instrument on the ELT may have the power to study the atmospheres of some of the planets in the L 98-59 system, thus complementing the JWST from the ground," says Zapatero Osorio.


FIZZING SODIUM COULD EXPLAIN ASTEROID’S ACTIVITY
NASA/JPL

As a comet zooms through the inner solar system, the Sun heats it, causing ices below the surface to vaporize into space. The venting vapoUr dislodges dust and rock, and the gas creates a bright tail that can extend millions of miles from the nucleus like an ethereal veil. Whereas comets contain lots of different ices, asteroids are mainly rock and not known for producing such majestic displays. But a new study examines how near-Earth asteroid Phaethon may in fact exhibit cometlike activity, despite lacking significant quantities of ice. Known to be the source of the annual Geminid meteor shower, the 5.8 kilometre-wide) asteroid brightens as it gets close to the Sun. Comets typically behave like this: When they heat up, their icy surfaces vaporize, causing them to become more active and brighten as the venting gases and dust scatter more sunlight. But what is causing Phaethon to brighten if not vaporizing ices? The culprit could be sodium. As the new study’s authors explain, Phaethon’s elongated, 524-day orbit takes the object well within the orbit of Mercury, during which time the Sun heats the asteroid’s surface up to about 750 degrees Celsius. With such a warm orbit, any water, carbon dioxide, or carbon monoxide ice near the asteroid’s surface would have been baked off long ago. But at that temperature, sodium may be fizzing from the asteroid’s rock and into space.

The team was inspired by observations of the Geminids. when meteoroids streak through Earth’s atmosphere as meteors, they disintegrate. But before they do, friction with the atmosphere causes the air surrounding the meteoroids to reach thousands of degrees, generating light. The colour of this light represents the elements they contain. Sodium, for example, creates an orange tinge. The Geminids are known to be low in sodium. Until now, it was assumed that these small pieces of rock somehow lost their sodium after leaving the asteroid. This new study suggests that the sodium may actually play a key role in ejecting the Geminid meteoroids from Phaethon’s surface. The researchers think that as the asteroid approaches the Sun, its sodium heats up and vaporizes. This process would have depleted the surface of sodium long ago, but sodium within the asteroid still heats up, vaporizes, and fizzes into space through cracks and fissures in Phaethon’s outermost crust. These jets would provide enough oomph to eject the rocky debris off its surface. So the fizzing sodium could explain not only the asteroid’s cometlike brightening, but also how the Geminid meteoroids would be ejected from the asteroid and why they contain little sodium. To find out if sodium turns to vapour and vents from an asteroid’s rock, the researchers tested samples of the Allende meteorite, which fell over Mexico in 1969, in a lab at JPL. The meteorite may have come from an asteroid comparable to Phaethon and belongs to a class of meteorites, called carbonaceous chondrites, that formed during the earliest days of the solar system. The researchers then heated chips of the meteorite to the highest temperature Phaethon would experience as it approaches the Sun. This temperature happens to be around the point that sodium escapes from its rocky components. The team simulated this heating effect over the course of a ‘day’ on Phaethon – its three-hour rotation period – and, on comparing the samples’ minerals before and after our lab tests, the sodium was lost, while the other elements were left behind. This suggests that the same may be happening on Phaethon and seems to agree with the results of the models. The new study supports a growing body of evidence that categorizing small objects in our solar system as “asteroids” and “comets” is oversimplified, depending not only on how much ice they contain, but also what elements vaporize at higher temperatures.


MISSION TO TITAN ANNOUNCES BIG GOALS
Cornell University

Among our solar system's many moons, Saturn's Titan stands out -- it's the only moon with a substantial atmosphere and liquid on the surface. It even has a weather system like Earth's, though it rains methane instead of water. Might it also host some kind of life? NASA's Dragonfly mission, which will send a rotorcraft relocatable lander to Titan's surface in the mid-2030s, will be the first mission to explore the surface of Titan, and it has big goals which include searching for chemical biosignatures; investigating the moon's active methane cycle; and exploring the prebiotic chemistry currently taking place in Titan's atmosphere and on its surface. Though Cassini has been orbiting Saturn for 13 years, the thick methane atmosphere on Titan made it impossible to reliably identify the materials on its surface. While Cassini's radar enabled scientists to penetrate the atmosphere and identify Earth-like morphologic structures, including dunes, lakes and mountains, the data could not reveal their composition. The Huygens probe, which landed on Titan in 2005, was designed to either float in a methane/ethane sea or land on a hard surface. Its science experiments were predominantly atmospheric, because they weren't sure it would survive the landing. Dragonfly will be the first mission to explore the surface of Titan and identify the detailed composition of its organic-rich surface.

Dragonfly will spend a full Titan day (equivalent to 16 Earth days) in one location conducting science experiments and observations, and then fly to a new location. The science team will need to make decisions about what the spacecraft will do next based on lessons from the previous location -- "which is exactly what the Mars rovers have been doing for decades. Titan's low gravity (around one-seventh of Earth's) and thick atmosphere (four times denser than Earth's) make it an ideal place for an aerial vehicle. Its relatively quiet atmosphere, with lighter winds than Earth, make it even better. Many of the prebiotic chemical compounds that formed on early Earth are also formed in Titan's atmosphere, and the team is eager to see how far down the road of prebiotic chemistry Titan has really gone. Titan's atmosphere might be a good analogue for what happened on early Earth. Dragonfly's search for chemical biosignatures will also be wide-ranging. In addition to examining Titan's habitability in general, they'll be investigating potential chemical biosignatures, past or present, from both water-based life to that which might use liquid hydrocarbons as a solvent, such as within its lakes, seas or aquifers.


NAKED EYE NOVA ERUPTION
Science

In the equatorial constellation of Ophiuchus, a star named RS Ophiuchi about 4,566 light-years away has had an epic eruption. This nova was so bright that the star is now visible to the naked eye, at a magnitude of around 4.8 – a whopping seven magnitudes brighter than its usual 12th magnitude dimness. Novae are rare enough to spot at the best of times, but what makes this occasion so special is the rarity of the star. RS Ophiuchi is what is known as a recurrent nova – a star that erupts periodically – and only 10 of these stars have ever been discovered in the Milky Way. RS Ophiuchi typically erupts every 15 years or so. Its last nova was in 2006, so the new burst is right on schedule, and was first reported on 8 August 2021 by Irish amateur astronomer Keith Geary. That detection was rapidly followed by reports of others around the world.

RS Ophiuchi is a binary star, a white dwarf in close orbit with a red giant. As the two whirl around each other, material – primarily hydrogen – is siphoned off the red giant by the smaller, denser white dwarf. This hydrogen accumulates on the white dwarf's surface, where it heats up. Periodically, the mass becomes so great that the pressure and temperature at the bottom of the layer is sufficient to trigger a thermonuclear explosion, violently expelling the excess material into space. This is the nova. According to spectroscopic observations of the star, the brightening is consistent with a nova – so violent that the material is being ejected into space at velocities around 2,600 kilometers per second. The Fermi Gamma Ray Telescope also detected a gamma-ray source at the time and location of the nova, confirming that an outburst was indeed taking place. If the white dwarf accumulates so much mass that it exceeds a critical mass threshold called the Chandrasekhar limit, it will become unstable and explode in a Type Ia supernova, which will spell the end of the binary. Generally, what will happen next based on previous observations of the star's novae is that RS Ophiuchi, after a rapid burst into brightness, will gradually fade over the next few weeks, and eventually from view.


BLACK HOLE SIZE REVEALED
University of Illinois

The feeding patterns of black holes offer insight into their size, researchers report. A new study revealed that the flickering in the brightness observed in actively feeding supermassive black holes is related to their mass. supermassive black holes are millions to billions of times more massive than the Sun and usually reside at the centre of massive galaxies. When dormant and not feeding on the gas and stars surrounding them, SMBHs emit very little light; the only way astronomers can detect them is through their gravitational influences on stars and gas in their vicinity. However, in the early Universe, when SMBHs were rapidly growing, they were actively feeding -- or accreting -- materials at intensive rates and emitting an enormous amount of radiation -- sometimes outshining the entire galaxy in which they reside, the researchers said. The new study uncovered a definitive relationship between the mass of actively feeding SMBHs and the characteristic timescale in the light-flickering pattern. The observed light from an accreting SMBH is not constant. Due to physical processes that are not yet understood, it displays a ubiquitous flickering over timescales ranging from hours to decades. "There have been many studies that explored possible relations of the observed flickering and the mass of the SMBH, but the results have been inconclusive and sometimes controversial. The team compiled a large data set of actively feeding SMBHs to study the variability pattern of flickering. They identified a characteristic timescale, over which the pattern changes, that tightly correlates with the mass of the SMBH. The researchers then compared the results with accreting white dwarfs, the remnants of stars like our Sun, and found that the same timescale-mass relation holds, even though white dwarfs are millions to billions times less massive than SMBHs.

The light flickers are random fluctuations in a black hole's feeding process, the researchers said. Astronomers can quantify this flickering pattern by measuring the power of the variability as a function of timescales. For accreting SMBHs, the variability pattern changes from short timescales to long timescales. This transition of variability pattern happens at a characteristic timescale that is longer for more massive black holes. The team compared black hole feeding to our eating or drinking activity by equating this transition to a human belch. Babies frequently burp while drinking milk, while adults can hold in the burp for a more extended amount of time. Black holes kind of do the same thing while feeding, they said. These results suggest that the processes driving the flickering during accretion are universal, whether the central object is a supermassive black hole or a much more lightweight white dwarf. Astrophysical black holes come in a broad spectrum of mass and size. In between the population of stellar-mass black holes, which weigh less than several tens of times the mass of the Sun, and SMBHs, there is a population of black holes called intermediate-mass black holes that weigh between about 100 and 100,000 times the mass of the Sun. IMBHs are expected to form in large numbers through the history of the Universe, and they may provide the seeds necessary to grow into SMBHs later. However, observationally this population of IMBHs is surprisingly elusive. There is only one indisputably confirmed IMBH that weighs about 150 times the mass of the Sun. But that IMBH was serendipitously discovered by the gravitational wave radiation from the coalescence of two less-massive black holes.


NEW FINDINGS ON GALAXY EVOLUTION
New York University

Galaxies eventually undergo a phase in which they lose most of their gas, which results in a change into their properties over the course of their evolution. Current models for galaxy evolution suggest this should eventually happen to all galaxies, including our own Milky Way. The evolution of galaxies is directly linked to the activity of their central supermassive blackhole (SMBH). However, the connection between the activity of SMBHs and the ejection of gas from the entire galaxy is poorly understood. Observational studies, including our research, are essential to clarify how the central SMBH can influence the evolution of its entire host galaxy and prove key theoretical concepts in the field of astrophysics. A new paper titled "The impact of low luminosity AGN on their host galaxies: A radio and optical investigation of the kpc-scale outflow in MaNGA 1-166919," has been published in Astronomical Journal. Its findings outline gas ejection mechanisms, outflow properties, and how they are related to the activity of the supermassive blackhole (SMBH) at the centre of the host galaxy. To that end, the paper presents a detailed optical and radio study of the MaNGA 1-166919 galaxy, which appears to have an Active Galactic Nucleus (AGN). Radio morphology shows two lobes (jets) emanating from the centre of the galaxy, a clear sign of AGN activity that could be driving the optical outflow. By measuring the outflow properties, the NYUAD researchers documented how the extent of the optical outflow matches the extent of radio emission. The paper adds to the growing body of UAE space research and activities. The UAE has sent an Emirati into space, a spacecraft around Mars and recently announced plans to send a robotic rover to the Moon in 2022, ahead of the ultimate goal to build a city on Mars by 2117. Emirati women are playing a key role in the research and development behind these projects. The Mars Hope probe science team is 80 percent female


‘BREAK’ IN MILKY WAY’S SPIRAL ARM
NASA

Scientists have spotted a previously unrecognized feature of our Milky Way galaxy: A contingent of young stars and star-forming gas clouds is sticking out of one of the Milky Way’s spiral arms like a splinter poking out from a plank of wood. Stretching some 3,000 light-years, this is the first major structure identified with an orientation so dramatically different than the arm’s.
Astronomers have a rough idea of the size and shape of the Milky Way’s arms, but much remains unknown: They can’t see the full structure of our home galaxy because Earth is inside it. It’s akin to standing in the middle of Trafalgar Square and trying to draw a map of London. To learn more, the authors of the new study focused on a nearby portion of one of the galaxy’s arms, called the Sagittarius Arm. Using NASA’s Spitzer Space Telescope prior to its retirement in January 2020, they sought out newborn stars, nestled in the gas and dust clouds where they form. Spitzer detects infrared light that can penetrate those clouds, while visible light (the kind human eyes can see) is blocked.

Young stars and nebulae are thought to align closely with the shape of the arms they reside in. To get a 3D view of the arm segment, the scientists used the latest data release from the ESA (European Space Agency) Gaia mission to measure the precise distances to the stars. The combined data revealed that the long, thin structure associated with the Sagittarius Arm is made of young stars moving at nearly the same velocity and in the same direction through space. A key property of spiral arms is how tightly they wind around a galaxy. This characteristic is measured by the arm’s pitch angle. A circle has a pitch angle of 0 degrees, and as the spiral becomes more open, the pitch angle increases. “Most models of the Milky Way suggest that the Sagittarius Arm forms a spiral that has a pitch angle of about 12 degrees, but the structure examined really stands out at an angle of nearly 60 degrees. Similar structures – sometimes called spurs or feathers – are commonly found jutting off the arms of other spiral galaxies. For decades scientists have wondered whether our Milky Way’s spiral arms are also dotted with these structures or if they are relatively smooth. The newly discovered feature contains four nebulae known for their breathtaking beauty: the Eagle Nebula , the Omega Nebula, the Trifid Nebula, and the Lagoon Nebula. In the 1950s, a team of astronomers made rough distance measurements to some of the stars in these nebulae and were able to infer the existence of the Sagittarius Arm. Their work provided some of the first evidence of our galaxy’s spiral structure. Distances are among the most difficult things to measure in astronomy measurements from Gaia that make the geometry of this new structure so apparent. n the new study, researchers also relied on a catalogue of more than a hundred thousand newborn stars discovered by Spitzer in a survey of the galaxy called the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). When the Gaia and Spitzer data were put together astronomers can see that there’s quite a bit of complexity in this region that just hasn’t been apparent before.



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