Topic: Mid May Astronomy Bulletin

[Clive]

SCIENTISTS EXPLAIN POLE’S MAGNETIC WANDERINGS
BBC Science

European scientists think they can now describe with confidence what's driving the drift of the North Magnetic Pole. It's shifted in recent years away from Canada towards Siberia. And this rapid movement has required more frequent updates to navigation systems, including those that operate the mapping functions in smartphones. The behaviour is explained by the competition of two magnetic "blobs" on the edge of the Earth's outer core. Changes in the flow of molten material in the planet's interior have altered the strength of the above regions of negative magnetic flux. This change in the pattern of flow has weakened the patch under Canada and ever so slightly increased the strength of the patch under Siberia.  This is why the North Pole has left its historic position over the Canadian Arctic and crossed over the International Date Line. Northern Russia is winning the 'tug of war', if you like. Earth has three poles at the top of the planet. A geographic pole which is where the planet's rotation axis intersects the surface. The geomagnetic pole is the location which best fits a classic dipole (its position alters little). And then there is the North Magnetic, or dip, Pole, which is where field lines are perpendicular to the surface. It is this third pole that has been doing all the movement. When first identified by explorer James Clark Ross in the 1830s, it was in Canada's Nunavut territory. Back then it didn't wander very far, very fast. But in the 1990s, it took off, racing to ever higher latitudes and crossing the date line in late 2017. In the process, it came to within just a few hundred kilometres of the geographic pole.

Using data from satellites that have measured the evolving shape of Earth's magnetic field over the past 20 years, scientists have attempted to model the North Magnetic Pole's wanderings. Two years ago when they first presented their ideas at the American Geophysical Union meeting in Washington DC, they suggested there might be a connection with a westward-accelerating jet of molten material in the outer core. But the models were a complex fit and the team has now revised its assessment to align with a different flow regime. The jet is tied to quite high northern latitudes and the alteration in the flow in the outer core that's responsible for the change in the position of the pole is actually further south. The team's latest modelling indicates the pole will continue to move towards Russia but will in time begin to slow. At top speed, it's been making 50-60km a year. Whether or not it will move back again in the future is anyone's guess. The pole's recent race across the top of the world prompted the US National Geophysical Data Center and the British Geological Survey to issue an early update to the World Magnetic Model last year.  This model is a representation of Earth's magnetic field across the entire globe. It is incorporated into all navigation devices, including modern smartphones, to correct for any local compass errors.


ASTEROID ZIPS VERY CLOSE TO EARTH
ESA

A reasonably small 4-8 metre asteroid recently flew by Earth, passing close to satellites orbiting in the geostationary ring at a distance of about 42,735 km from Earth’s centre and only about 1200 km from the nearest satellite. After the initial discovery, observers around the world rapidly set their eyes on the ‘new’ space rock, determining it would safely pass our planet in one of the closest flybys ever recorded. While the asteroid, now named 2020 HS7, came close to the geostationary ring, it passed ‘under’ the nearest satellite and posed no major risk as their orbits did not intersect. Observers around the world quickly joined the effort to find out more about this unknown asteroid. Only 50 minutes after the initial Pan-STARRS report was released, the Xingming Observatory in China obtained the first follow-up ‘astrometry’ — data on its position, motion, and brightness.

With this data, it became clear that the object was not going to collide with the Earth, but it was heading towards a very close fly-by the following day, roughly at the distance of Earth’s geostationary ring. At just a few metres in size, the asteroid would not have caused any significant threat if it had been on a collision course, as it would likely have burned up in Earth’s atmosphere. Subsequent observations obtained by additional ESA collaborators and many other observatories worldwide determined that the flyby of the asteroid, now named 2020 HS7, ranks among the 50 closest ever recorded. Interestingly, the fly-by happened only 15 hours before the closest approach of (52768) 1998 OR2, a much larger kilometre-sized object that attracted the attention of the worldwide media. However, this latter object approached our planet at a distance 16 times farther than the Moon while 2020 HS7 came significantly closer to us, representing a more significant event for the astronomical community.


COMET SWAN TO GRACE OUR SKIES
NASA/Goddard Space Flight Center

In late May and early June, we may be able to glimpse Comet SWAN. The comet is currently faintly visible to the unaided eye in the Southern Hemisphere just before sunrise -- providing skywatchers with a relatively rare glimpse of a comet bright enough to be seen without a telescope. But Comet SWAN's initial discovery was made not from the ground, but via an instrument on board ESA (the European Space Agency) and NASA's Solar and Heliospheric Observatory, or SOHO, satellite. The new comet was first spotted in April 2020, by an amateur astronomer using data from a SOHO instrument called Solar Wind Anisotropies, or SWAN.  SWAN maps the constantly outflowing solar wind in interplanetary space by focusing on a particular wavelength of ultraviolet light emitted by hydrogen atoms. The new comet -- officially classified C/2020 F8 (SWAN) but nicknamed Comet SWAN -- was discovered in the images because it's releasing huge amounts of water, about 1.3 tons per second. As water is made of hydrogen and oxygen, this release made Comet SWAN visible to SOHO's instruments.

Comet SWAN is the 3,932nd comet discovered using data from SOHO. Almost all of the nearly 4,000 discoveries have been made using data from SOHO's coronagraph, an instrument that blocks out the Sun's bright face using a metal disk to reveal the comparatively faint outer atmosphere, the corona. This is only the 12th comet discovered with the SWAN instrument since SOHO's launch in 1995. Comet SWAN made its closest approach to Earth on May 13, at a distance of about 53 million miles. Comet SWAN's closest approach to the Sun, called perihelion, will happen on May 27. Though it can be very difficult to predict the behaviour of comets that make such close approaches to the Sun, scientists are hopeful that Comet SWAN will remain bright enough to be seen as it continues its journey. It will be an early morning object for us in the UK as it passes low in the eastern sky, potentially reaching a magnitude of about +3.5.


4-BILLION-YEAR-OLD ORGANIC MOLECULES IN MARTIAN METEORITES
Tokyo Institute of Technology

A research team has found nitrogen-bearing organic material in carbonate minerals in a Martian meteorite. This organic material has most likely been preserved for 4 billion years since Mars' Noachian age. Because carbonate minerals typically precipitate from the groundwater, this finding suggests a wet and organic-rich early Mars, which could have been habitable and favourable for life to start. For decades, scientists have tried to understand whether there are organic compounds on Mars and if so, what their source is. Although recent studies from rover-based Mars exploration have detected strong evidence for Martian organics, little is known about where they came from, how old they are, how widely distributed and preserved they may be, or what their possible relationship with biochemical activity could be.  Martian meteorites are pieces of Mars' surface that were themselves blasted into space by meteor impacts, and which ultimately landed on Earth. They provide important insights into Martian history. One meteorite in particular, named Allan Hills (ALH) 84001, named for the region in Antarctica it was found in 1984, is especially important. It contains orange-coloured carbonate minerals, which precipitated from salty liquid water on Mars' near-surface 4 billion years ago. As these minerals record Mars' early aqueous environment, many studies have tried to understand their unique chemistry and whether they might provide evidence for ancient life on Mars. However, previous analyses suffered from contamination with terrestrial material from Antarctic snow and ice, making it difficult to say how much of the organic material in the meteorite were truly Martian. In addition to carbon, nitrogen (N) is an essential element for terrestrial life and a useful tracer for planetary system
evolution. However, due to previous technical limitations, nitrogen had not yet been measured in ALH84001.

This new research conducted by the joint ELSI-JAXA team used state-of-the-art analytical techniques to study the nitrogen content of the ALH84001 carbonates, and the team is now confident they have found the first solid evidence for 4-billion-year-old Martian organics containing nitrogen. Terrestrial contamination is a serious problem for studies of extraterrestrial materials. To avoid such contamination, the team developed new techniques to prepare the samples with. For example, they used silver tape in an ELSI clean lab to pluck off the tiny carbonate grains, which are about the width of a human hair, from the host meteorite. The team then prepared these grains further to remove possible surface contaminants with a scanning electron microscope-focused ion beam instrument at JAXA. They also used a technique called Nitrogen K-edge micro X-ray Absorption Near Edge Structure (μ-XANES) spectroscopy, which allowed them to detect nitrogen present in very small amounts and to determine what chemical form that nitrogen was in. Control samples from nearby igneous minerals gave no detectable nitrogen, showing the organic molecules were only in the carbonate. After the careful contamination checks, the team determined the detected organics were most likely truly Martian.  They also determined the contribution of nitrogen in the form of nitrate, one of the strong oxidants on current Mars, was insignificant, suggesting the early Mars probably did not contain strong oxidants, and as scientists have suspected, it was less-oxidizing than it is today.

Mars' present surface is too harsh for most organics to survive. However, scientists predict that organic compounds could be preserved in near-surface settings for billions of years. This seems to be the case for the nitrogen-bearing organic compounds the team found in the ALH84001 carbonates, which appear to have been trapped in the minerals 4 billion years ago and preserved for long periods before finally being delivered to Earth. The team agrees that there are many important open questions, such as where did these nitrogen-containing organics come from? There are two main possibilities: either they came from outside Mars, or they formed on Mars. Early in the Solar System's history, Mars was likely showered with significant amounts of organic matter, for example from carbon-rich meteorites, comets and dust particles. Some of them may have dissolved in the brine and been trapped inside the carbonates." The research team lead, Koike adds that alternatively, chemical reactions on early Mars may have produced the N-bearing organics on-site. Either way, they say, these findings show there was organic nitrogen on Mars before it became the red planet we know today; early Mars may have been more 'Earth-like', less oxidising, wetter, and organic-rich.


DEEPEST PROBE INTO JUPITER’S ATMOSPHERE
NASA/Goddard Space Flight Center

Researchers are combining multiwavelength observations from Hubble and Gemini with close-up views from Juno's orbit about Jupiter, gaining new insights into turbulent weather on this distant world. Jupiter's constant storms are gigantic compared to those on Earth, with thunderheads reaching 40 miles from base to top -- five times taller than typical thunderheads on Earth -- and powerful lightning flashes up to three times more energetic than Earth's largest "superbolts." Like lightning on Earth, Jupiter's lightning bolts act like radio transmitters, sending out radio waves as well as visible light when they flash across the sky. Every 53 days, Juno races low over the storm systems detecting radio signals known as "sferics"  and "whistlers," which can then be used to map lightning even on the day side of the planet or from deep clouds where flashes are not otherwise visible. Coinciding with each pass, Hubble and Gemini watch from afar, capturing high-resolution global views of the planet that are key to interpreting Juno's close-up observations. Juno's microwave radiometer probes deep into the planet's atmosphere by detecting high-frequency radio waves that can penetrate through the thick cloud layers. The data from Hubble and Gemini can tell us how thick the clouds are and how deep we are seeing into the clouds. By mapping lightning flashes detected by Juno onto optical images captured of the planet by Hubble and thermal infrared images captured at the same time by Gemini, the research team has been able to show that lightning outbreaks are associated with a three-way combination of cloud structures: deep clouds made of water, large convective towers caused by upwelling of moist air -- essentially Jovian thunderheads -- and clear regions presumably caused by downwelling of drier air outside the convective towers. The Hubble data show the height of the thick clouds in the convective towers, as well as the depth of deep water clouds. The Gemini data clearly reveal the clearings in the high-level clouds where it is possible to get a glimpse down to the deep water clouds.

It’s thought that lightning is common in a type of turbulent area known as folded filamentary regions, which suggests that moist convection is occurring in them. These cyclonic vortices could be internal energy smokestacks, helping release internal energy through convection. It doesn't happen everywhere, but something about these cyclones seems to facilitate convection. The ability to correlate lightning with deep water clouds also gives researchers another tool for estimating the amount of water in Jupiter's atmosphere, which is important for understanding how Jupiter and the other gas and ice giants formed, and therefore how the solar system as a whole formed. While much has been gleaned about Jupiter from previous space missions, many of the details -- including how much water is in the deep atmosphere, exactly how heat flows from the interior and what causes certain colours and patterns in the clouds -- remain a mystery. The combined result provides insight into the dynamics and three-dimensional structure of the atmosphere. With Hubble and Gemini observing Jupiter more frequently during the Juno mission, scientists are also able to study short-term changes and short-lived features like those in the Great Red Spot. Images from Juno as well as previous
missions to Jupiter revealed dark features within the Great Red Spot that appear, disappear and change shape over time. It was not clear from individual images whether these are caused by some mysterious dark-coloured material within the high cloud layer, or if they are instead holes in the high clouds -- windows into a deeper, darker layer below. Now, with the ability to compare visible-light images from Hubble with thermal infrared images from Gemini captured within hours of each other, it is possible to answer the question. Regions that are dark in visible light are very bright in infrared, indicating that they are, in fact, holes in the cloud layer. In cloud-free regions, heat from Jupiter's interior that is emitted in the form of infrared light -- otherwise blocked by high-level clouds -- is free to escape into space and therefore appears bright in Gemini images.


RARE IMAGES OF PLANET-FORMING STAR DISKS
KU Leuven

An international team of astronomers has captured fifteen images of the inner rims of planet-forming disks located hundreds of light years away. These disks of dust and gas, similar in shape to a music record, form around young stars. The images shed new light on how planetary systems are formed. To understand how planetary systems, including our own, take shape, you have to study their origins. Planet-forming or protoplanetary disks are formed in unison with the star they surround. The dust grains in the disks can grow into larger bodies, which eventually lead to the formation of planets. Rocky planets like the Earth are believed to form in the inner regions of protoplanetary disks, less than five astronomical units (five times the Earth-Sun distance) from the star around which the disk has formed. Before this new study, several pictures of these disks had been taken with the largest single-mirror telescopes, but these cannot capture their finest details. The team created  the images at the European Southern Observatory (ESO) in Chile by using a technique called infrared interferometry. Using ESO's PIONIER instrument, they combined the light collected by four telescopes at the Very Large Telescope observatory to capture the disks in detail. However, this technique does not deliver
an image of the observed source. The details of the disks needed to be recovered with a mathematical reconstruction technique. This technique is similar to how the first image of a black hole was captured.

Some findings immediately stand out from the images. Some spots are brighter or less bright. This hints at processes that can lead to planet formation. For example: there could be instabilities in the disk that can lead to vortices where the disk accumulates grains of space dust that can grow and evolve into a planet. The team will do additional research to identify what might lie behind these irregularities. It will also do new observations to get even more detail and to directly witness planet formation in the regions within the disks that lie close to the star. Additionally, a team has started to study 11 disks around other, older types of stars also surrounded by disks of dust, since it is thought these might also sprout planets.


CLOSEST BLACK HOLE TO EARTH
ESO

A team of astronomers has discovered a black hole lying just 1000 light-years from Earth. The black hole is closer to our Solar System than any other found to date and forms part of a triple system that can be seen with the naked eye. The team found evidence for the invisible object by tracking its two companion stars using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. They say this system could just be the tip of the iceberg, as many more similar black holes could be found in the future. The team originally observed the system, called HR 6819, as part of a study of double-star systems. However, as they analysed their observations, they were stunned when they revealed a third, previously undiscovered body in HR 6819: a black hole. The observations with the FEROS spectrograph on the MPG/ESO 2.2-metre telescope at La Silla showed that one of the two visible stars orbits an unseen object every 40 days, while the second star is at a large distance from this inner pair. The hidden black hole in HR 6819 is one of the very first stellar-mass black holes found that do not interact violently with their environment and, therefore, appear truly black. But the team could spot its presence and calculate its mass by studying the orbit of the star in the inner pair. An invisible object with a mass at least 4 times that of the Sun can only be a black hole.  Astronomers have spotted only a couple of dozen black holes in our galaxy to date, nearly all of which strongly interact with their environment and make their presence known by releasing powerful X-rays in this interaction. But scientists estimate that, over the Milky Way’s lifetime, many more stars collapsed into black holes as they ended their lives. The discovery of a silent, invisible black hole in HR 6819 provides clues about where the many hidden black holes in the Milky Way might be. There must be hundreds of millions of black holes out there, but we know about only very few. Knowing what to look for should put us in a better position to find them.

Already, astronomers believe their discovery could shine some light on a second system. They realised that another system, called LB-1, may also be such a triple, though they would need more observations to say for sure. LB-1 is a bit further away from Earth but still pretty close in astronomical terms, so that means that probably many more of these systems exist. By finding and studying them we can learn a lot about the formation and evolution of those rare stars that begin their lives with more than about 8 times the mass of the Sun and end them in a supernova explosion that leaves behind a black hole. The discoveries of these triple systems with an inner pair and a distant star could also provide clues about the violent cosmic mergers that release gravitational waves powerful enough to be detected on Earth. Some astronomers believe that the mergers can happen in systems with a similar configuration to HR 6819 or LB-1, but where the inner pair is made up of two black holes or of a black hole and a neutron star. The distant outer object can gravitationally impact the inner pair in such a way that it triggers a merger and the release of gravitational waves. Although HR 6819 and LB-1 have only one black hole and no neutron stars, these systems could help scientists understand how stellar collisions can happen in triple star systems.


FRB SIGNAL FROM OUR GALAXY
University of Toronto

A radio signal coming from a source within the Milky Way has been detected by astronomers. The signal is a fast radio burst (FRB), bright radio bursts that last milliseconds and appear to come from deep space. Because they are short-lived, they were often only identified in satellite data after the signal was recorded. Finding where they came from and what produced them has been largely a mystery. The first FRBs were discovered over a decade ago. Since then, scientists have been
trying to work out what is causing them. Suggestions have included cataclysmic events, such as the collision of two neutron stars or a collapsing black hole. But these hypotheses were questioned when a repeating FRB was uncovered. A black hole can only collapse once, because when the FRB repeated scientists realized either there must be another explanation, or more than one source can produce these bursts.

Over recent years, an international group of scientists has come together to solve the mystery of FRBs. The collaboration has led to the discovery of more FRBs, with researchers using the findings to home in on more of their locations across the Universe. For example, earlier this year, one team was able to trace on FRB to an "odd" V-shaped star-forming region in a huge spiral galaxy half a billion light years away. Until now, however, none appeared to have come from our own galaxy. The latest discovery announced the detection of a bright radio burst coming from the active magneter known as SGR 1935+2154. This is a type of neutron star, the collapsed core of a massive star that is thought to have an extremely powerful magnetic field.


HOW THE UNIVERSE GOT ITS STRUCTURE
Carnegie Institution for Science

The Universe is full of billions of galaxies -- but their distribution across space is far from uniform. Why do we see so much structure in the Universe today and how did it all form and grow? A 10-year survey of tens of thousands of galaxies made using the Magellan Baade Telescope at Las Campanas Observatory in Chile provided a new approach to answering this fundamental mystery. The Carnegie-Spitzer-IMACS Redshift Survey was designed to study the relationship between galaxy growth and the surrounding environment over the last 9 billion years, when modern galaxies' appearances were defined. The first galaxies were formed a few hundred million years after the Big Bang, which started the Universe as a hot, murky soup of extremely energetic particles. As this material expanded outward from the initial explosion, it cooled, and the particles coalesced into neutral hydrogen gas. Some patches were denser than others and, eventually, their gravity overcame the Universe's outward trajectory and the material collapsed inward, forming the first clumps of structure in the cosmos. The density differences that allowed for structures both large and small to form in some places and not in others have been a longstanding topic of fascination. But until now, astronomers' abilities to model how structure grew in the Universe over the last 13 billion years faced mathematical limitations.

So, astronomers either used mathematical approximations -- which compromised the accuracy of their models -- or large computer simulations that numerically model all the interactions between galaxies, but not all the interactions occurring between all of the particles, which was considered too complicated. A key goal of the survey was to count up the mass present in stars found in an enormous selection of distant galaxies and then use this information to formulate a new approach to understanding how structure formed in the Universe. The research demonstrated for the first time that the growth of individual proto-structures can be calculated and then averaged over all of space. Doing this revealed that denser clumps grew faster, and less-dense clumps grew more slowly. They were then able to work backward and determine the original distributions and growth rates of the fluctuations in density, which would eventually become the large-scale structures that determined the distributions of galaxies we see today. In essence, their work provided a simple, yet accurate, description of why and how density fluctuations grow the way they do in the real Universe, as well as in the computational-based work that underpins our understanding of the Universe's infancy.