Topic: Late September Astronomy Bulletin

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THE STARLINK INCIDENT

Spaceweather.com

A minor geomagnetic storm is supposed to be minor. That's why even experts were surprised on Feb. 4, 2022, when dozens of Starlink satellites started falling out of the sky. A weak CME had hit Earth's magnetic field, and the resulting G1-class (minor) storm was bringing them down. How could this happen? Although it was only 'minor,' the storm pumped almost 1200 gigawatts of energy into Earth's atmosphere. This extra energy heated Earth's upper atmosphere and sharply increased aerodynamic drag on the satellites. SpaceX launched the satellites from Cape Canaveral on Feb. 3, 2022. Forty-nine (49) Starlinks were crowded inside the Falcon 9 rocket; less than a quarter would survive. As was SpaceX's practice at the time, the satellites were deployed at an altitude of 210 km--their first stop en route to an operational altitude near 600 km. In the satellite business, 210 km is considered to be low, barely above the atmosphere. SpaceX starts there in case any satellite malfunctions after launch. From 210 km, a "bad sat" can be easily de-orbited. A little too easily, as it turns out. Using a physics-based computer model named "TIEGCM," researchers simulated conditions during the storm. As geomagnetic energy heated Earth's atmosphere, the air density at 210 km increased globally by 20% with "hot spots" as high as 60%. This movie shows what happened:

Starlink dodged the worst spots. The satellites did not hit any of the 60% regions. But that didn't save them. The weaker 20% enhancements were enough to bring down 38 out of 49 satellites. To prevent a repeat, SpaceX has started launching to 320 km instead of 210 km. Earth's atmosphere has to reach that much higher to drag the satellites back during a geomagnetic storm. Since the change, more than 1200 additional Starlink satellites have been launched on 24 rockets without incident. There's still danger, though. Air density at 320 km is an order of magnitude less (compared to 210 km), but it's not completely safe. During an extreme geomagnetic storm, density could increase from 200% to 800% even at these higher altitudes. Extreme storms may be in the offing. Young Solar Cycle 25 is just getting started. The profusion of minor storms we are observing today will intensify in the years ahead especially as we approach Solar Max around 2025.

MOXIE PRODUCES OXYGEN ON MARS

Massachusetts Institute of Technology

On the red and dusty surface of Mars, nearly 100 million miles from Earth, an instrument the size of a lunchbox is proving it can reliably do the work of a small tree. The MIT-led Mars Oxygen In-Situ Resource Utilization Experiment, or MOXIE, has been successfully making oxygen from the Red Planet's carbon-dioxide-rich atmosphere since February 2021, when it touched down on the Martian surface as part of NASA's Perseverance rover mission. Researchers report that, by the end of 2021, MOXIE was able to produce oxygen on seven experimental runs, in a variety of atmospheric conditions, including during the day and night, and through different Martian seasons. In each run, the instrument reached its target of producing six grams of oxygen per hour -- about the rate of a modest tree on Earth. Researchers envision that a scaled-up version of MOXIE could be sent to Mars ahead of a human mission, to continuously produce oxygen at the rate of several hundred trees. At that capacity, the system should generate enough oxygen to both sustain humans once they arrive, and fuel a rocket for returning astronauts back to Earth. The current version of MOXIE is small by design, in order to fit aboard the Perseverance rover, and is built to run for short periods, starting up and shutting down with each run, depending on the rover's exploration schedule and mission responsibilities. In contrast, a full-scale oxygen factory would include larger units that would ideally run continuously. Despite the necessary compromises in MOXIE's current design, the instrument has shown it can reliably and efficiently convert Mars' atmosphere into pure oxygen. It does so by first drawing the Martian air in through a filter that cleans it of contaminants. The air is then pressurized, and sent through the Solid OXide Electrolyzer (SOXE), an instrument developed and built by OxEon Energy, that electrochemically splits the carbon dioxide-rich air into oxygen ions and carbon monoxide. The oxygen ions are then isolated and recombined to form breathable, molecular oxygen, or O2, which MOXIE then measures for quantity and purity before releasing it harmlessly back into the air, along with carbon monoxide and other atmospheric gases. Since the rover's landing in February 2021, MOXIE engineers have started up the instrument seven times throughout the Martian year, each time taking a few hours to warm up, then another hour to make oxygen before powering back down. Each run was scheduled for a different time of day or night, and in different seasons, to see whether MOXIE could accommodate shifts in the planet's atmospheric conditions. As MOXIE continues to churn out oxygen on Mars, engineers plan to push its capacity, and increase its production, particularly in the Martian spring, when atmospheric density and carbon dioxide levels are high. They will also monitor the system for signs of wear and tear. As MOXIE is just one experiment among several aboard the Perseverance rover, it cannot run continuously as a full-scale system would. Instead, the instrument must start up and shut down with each run -- a thermal stress that can degrade the system over time. If MOXIE can operate successfully despite repeatedly turning on and off, this would suggest that a full-scale system, designed to run continuously, could do so for thousands of hours.

SATURN’S RINGS AND TILT COULD BE REMNANT OF ANCIENT MOON

Massachusetts Institute of Technology

Swirling around the planet's equator, the rings of Saturn are a dead giveaway that the planet is spinning at a tilt. The belted giant rotates at a 26.7-degree angle relative to the plane in which it orbits the Sun. Astronomers have long suspected that this tilt comes from gravitational interactions with its neighbour Neptune, as Saturn's tilt precesses, like a spinning top, at nearly the same rate as the orbit of Neptune. But a new modelling study by astronomers at MIT and elsewhere has found that, while the two planets may have once been in sync, Saturn has since escaped Neptune's pull. What was responsible for this planetary realignment? The team has one meticulously tested hypothesis: a missing moon The team proposes that Saturn, which today hosts 83 moons, once harboured at least one more, an extra satellite that they name Chrysalis. Together with its siblings, the researchers suggest, Chrysalis orbited Saturn for several billion years, pulling and tugging on the planet in a way that kept its tilt, or "obliquity," in resonance with Neptune. But around 160 million years ago, the team estimates, Chrysalis became unstable and came too close to its planet in a grazing encounter that pulled the satellite apart. The loss of the moon was enough to remove Saturn from Neptune's grasp and leave it with the present-day tilt. What's more, the researchers surmise, while most of Chrysalis' shattered body may have made impact with Saturn, a fraction of its fragments could have remained suspended in orbit, eventually breaking into small icy chunks to form the planet's signature rings. The missing satellite, therefore, could explain two longstanding mysteries: Saturn's present-day tilt and the age of its rings, which were previously estimated to be about 100 million years old -- much younger than the planet itself. In the early 2000s, scientists put forward the idea that Saturn's tilted axis is a result of the planet being trapped in a resonance, or gravitational association, with Neptune. But observations taken by NASA's Cassini spacecraft, which orbited Saturn from 2004 to 2017, put a new twist on the problem. Scientists found that Titan, Saturn's largest satellite, was migrating away from Saturn at a faster clip than expected, at a rate of about 11 centimetres per year. Titan's fast migration, and its gravitational pull, led scientists to conclude that the moon was likely responsible for tilting and keeping Saturn in resonance with Neptune.

But this explanation hinges on one major unknown: Saturn's moment of inertia, which is how mass is distributed in the planet's interior. Saturn's tilt could behave differently, depending on whether matter is more concentrated at its core or toward the surface. In their new study, the team looked to pin down Saturn's moment of inertia using some of the last observations taken by Cassini in its "Grand Finale," a phase of the mission during which the spacecraft made an extremely close approach to precisely map the gravitational field around the entire planet. The gravitational field can be used to determine the distribution of mass in the planet. The team modelled the interior of Saturn and identified a distribution of mass that matched the gravitational field that Cassini observed. Surprisingly, they found that this newly identified moment of inertia placed Saturn close to, but just outside the resonance with Neptune. The planets may have once been in sync, but are no longer. The team first carried out simulations to evolve the orbital dynamics of Saturn and its moons backward in time, to see whether any natural instabilities among the existing satellites could have influenced the planet's tilt. This search came up empty. So, the researchers reexamined the mathematical equations that describe a planet's precession, which is how a planet's axis of rotation changes over time. One term in this equation has contributions from all the satellites. The team reasoned that if one satellite were removed from this sum, it could affect the planet's precession. The question was, how massive would that satellite have to be, and what dynamics would it have to undergo to take Saturn out of Neptune's resonance? Colleagues ran simulations to determine the properties of a satellite, such as its mass and orbital radius, and the orbital dynamics that would be required to knock Saturn out of the resonance. They conclude that Saturn's present tilt is the result of the resonance with Neptune and that the loss of the satellite, Chrysalis, which was about the size of Iapetus, Saturn's third-largest moon, allowed it to escape the resonance. Sometime between 200 and 100 million years ago, Chrysalis entered a chaotic orbital zone, experienced a number of close encounters with Iapetus and Titan, and eventually came too close to Saturn, in a grazing encounter that ripped the satellite to bits, leaving a small fraction to circle the planet as a debris-strewn ring. The loss of Chrysalis, they found, explains Saturn's precession, and its present-day tilt, as well as the late formation of its rings.

WATER WORLDS MORE COMMON THAN EXPECTED

University of Chicago

Water is the one thing all life on Earth needs, and the cycle of rain to river to ocean to rain is an essential part of what keeps our planet's climate stable and hospitable. When scientists talk about where to search for signs of life throughout the galaxy, planets with water are always at the top of the list. A new study suggests that many more planets may have large amounts of water than previously thought -- as much as half water and half rock. The catch? All that water is probably embedded in the rock, rather than flowing as oceans or rivers on the surface. Thanks to better telescope instruments, scientists are finding signs of more and more planets in distant solar systems. A larger sample size helps scientists identify demographic patterns -- similar to how looking at the population of an entire town can reveal trends that are hard to see at an individual level. Astronomers at the Institute of Astrophysics of the Canary Islands and the University of La Laguna, decided to take a population-level look at a group of planets that are seen around a type of star called an M-dwarf. These stars are the most common stars we see around us in the galaxy, and scientists have catalogued dozens of planets around them so far. But because stars are so much brighter than their planets, we cannot see the actual planets themselves. Instead, scientists detect faint signs of the planets' effects on their stars -- the shadow created when a planet crosses in front of its star, or the tiny tug on a star's motion as a planet orbits. That means many questions remain about what these planets actually look like. The two different ways to discover planets each give you different information’ By catching the shadow created when a planet crosses in front of its star, scientists can find the diameter of the planet. By measuring the tiny gravitational pull that a planet exerts on a star, scientists can find its mass.

By combining the two measurements, scientists can get a sense of the makeup of the planet. Perhaps it's a big-but-airy planet made mostly out of gas like Jupiter, or a small, dense, rocky planet like Earth. These analyses had been done for individual planets, but much more rarely for the entire known population of such planets in the Milky Way galaxy. As the scientists looked at the numbers -- 43 planets in all -- they saw a surprising picture emerging. The densities of a large percentage of the planets suggested that they were too light for their size to be made up of pure rock. Instead, these planets are probably something like half rock and half water, or another lighter molecule. Imagine the difference between picking up a bowling ball and a soccer ball: they're roughly the same size, but one is made up of much lighter material. It may be tempting to imagine these planets like something out of Kevin Costner's Waterworld: entirely covered in deep oceans. However, these planets are so close to their suns that any water on the surface would exist in a supercritical gaseous phase, which would enlarge their radius. But we don't see that in the samples which suggests the water is not in the form of surface ocean. Instead, the water could exist mixed into the rock or in pockets below the surface. Those conditions would be similar to Jupiter's moon Europa, which is thought to have liquid water underground. The finding matches a theory of exoplanet formation that had fallen out of favour in the past few years, which suggested that many planets form farther out in their solar systems and migrate inward over time. Imagine clumps of rock and ice forming together in the cold conditions far from a star, and then being pulled slowly inward by the star's gravity.

BULGES IN MILKY WAY BAR

National Institutes of Natural Sciences

Astronomy is revealing the structure of the Milky Way Galaxy in which we live in increasing detail. We know that it is a disk galaxy, with two- or four- armed spirals, with a straight bar in the middle connecting the spirals. Now, we also know that the inner part of the bar has a "peanut-shaped bulge," places where the bar is thicker, sticking out above and below the mid plane of the Milky Way Galaxy and a "nuclear bulge," which is disky and located in the central part of the Milky Way. Some other galaxies, but not all, exhibit similar two-type bulges. The Astronomical Observatory of Japan (NAOJ) simulated one possible scenario for a Milky-Way-like galaxy on "ATERUI II" at NAOJ, the world's most powerful supercomputer dedicated to astronomy. The team's simulation is the most complete and accurate to date, including not only the stars in the galaxy, but also the gas. It also incorporates the birth of new stars from the gas and the deaths of stars as supernovae. The formation of a bar helps to channel gas into the central part of the galaxy, where it triggers the formation of new stars. So it might be reasonable to assume that the nuclear bugle in the galaxy is created from new stars born there. But the simulations show that there are almost no new stars in the bar outside the nuclear bulge, because the bar is so effective at channeling gas towards the centre. This means that pigging-out on gas is not the reason that a peanut-shaped bulge develops in the bar. Instead, the team finds that gravitational interactions can drive some of the stars into orbits which take them above and below the mid plane.

The most exciting part is that the simulation provides a testable scenario. Because the peanut-shaped bulge acquires no new stars, all of its stars must predate the formation of the bar. At the same time, the bar channels gas to the central region where it creates many new stars. So almost all of the stars in the nuclear bulge will have been born after the bar formed. This means that the stars in the peanut-shaped bulge will be older than the stars in the nuclear bulge, with a clear break between the ages. This break corresponds to the time when the bar formed. Data from the European Space Agency's Gaia probe and Japan's future JASMINE satellite will allow us to determine the motions and ages of the stars and test this scenario. If astronomers can detect a difference between the ages of the stars in peanut-shaped and nuclear bulges, it will not only prove that overeating is not to blame for the peanut-shaped bulge, it will tell us the age of the bar in the Milky Way Galaxy.

WHY MATTER AND NOT ANTIMATTER DOMINATES THE UNIVERSE

University of California - Riverside

Early in its history, shortly after the Big Bang, the Universe was filled with equal amounts of matter and "antimatter" -- particles that are matter counterparts but with opposite charge. But then, as space expanded, the Universe cooled. Today's Universe is full of galaxies and stars which are made of matter. Where did the antimatter go, and how did matter come to dominate the Universe? This cosmic origin of matter continues to puzzle scientists. Physicists have now opened a new pathway for probing the cosmic origin of matter by invoking the "cosmological collider." High energy colliders, such as the Large Hadron Collider, have been built to produce very heavy subatomic elementary particles that may reveal new physics. But some new physics, such as that explaining dark matter and the origin of matter, can involve much heavier particles, requiring much higher energy than what a human-made collider can provide. It turns out the early cosmos could have served as such a super-collider. It is widely believed that cosmic inflation, an era when the Universe expanded at an exponentially accelerating rate, preceded the Big Bang. Microscopic structures created by energetic events during inflation became stretched as the Universe expanded, resulting in regions of varying density in an otherwise homogeneous Universe. Subsequently, these microscopic structures seeded the large-scale structure of our Universe, manifested today as the distribution of galaxies across the sky. New subatomic particle physics may be revealed by studying the imprint of the cosmological collider in the cosmos' contents today, such as galaxies and the cosmic microwave background. By applying the physics of the cosmological collider and using precision data for measuring the structure of our Universe from upcoming experiments such as SPHEREx and 21 cm line tomography, the mystery of the cosmic origin of matter may be unravelled. Physicists propose testing leptogenesis, a well-known mechanism that explains the origin of the baryon -- visible gas and stars -- asymmetry in our Universe. Had the Universe begun with equal amounts of matter and antimatter, they would have annihilated each other into photon radiation, leaving nothing. Since matter far exceeds antimatter today, asymmetry is required to explain the imbalance. The new work proposes to test leptogenesis by decoding the detailed statistical properties of the spatial distribution of objects in the cosmic structure observed today, reminiscent of the microscopic physics during cosmic inflation. The cosmological collider effect, the researchers argue, enables the production of the super-heavy right-handed neutrino during the inflationary epoch.

DARK ENERGY PROBED BY TESTING GRAVITY

NASA

The Universe is expanding at an accelerating rate, and scientists don’t know why. This phenomenon seems to contradict everything researchers understand about gravity’s effect on the cosmos: It’s as if you threw an apple in the air and it continued upward, faster and faster. The cause of the acceleration, dubbed dark energy, remains a mystery. A new study from the international Dark Energy Survey, using the Victor M. Blanco 4-meter Telescope in Chile, marks the latest effort to determine whether this is all simply a misunderstanding: that expectations for how gravity works at the scale of the entire Universe are flawed or incomplete. This potential misunderstanding might help scientists explain dark energy. But the study – one of the most precise tests yet of Albert Einstein’s theory of gravity at cosmic scales – finds that the current understanding still appears to be correct. More than a century ago, Albert Einstein developed his Theory of General Relativity to describe gravity, and so far it has accurately predicted everything from the orbit of Mercury to the existence of black holes. But if this theory can’t explain dark energy, some scientists have argued, then maybe they need to modify some of its equations or add new components.

To find out if that’s the case, members of the Dark Energy Survey looked for evidence that gravity’s strength has varied throughout the universe’s history or over cosmic distances. A positive finding would indicate that Einstein’s theory is incomplete, which might help explain the universe’s accelerating expansion. They also examined data from other telescopes in addition to Blanco, including the ESA (European Space Agency) Planck satellite, and reached the same conclusion. The study finds Einstein’s theory still works. So no explanation for dark energy yet. But this research will feed into two upcoming missions: ESA’s Euclid mission, slated for launch no earlier than 2023, which has contributions from NASA; and NASA’s Nancy Grace Roman Space Telescope, targeted for launch no later than May 2027. Both telescopes will search for changes in the strength of gravity over time or distance.

WEBB Mid-Infrared Instrument Operations

NASA

The James Webb Space Telescope’s Mid-Infrared Instrument (MIRI) has four observing modes. On Aug. 24, a mechanism that supports one of these modes, known as medium-resolution spectroscopy (MRS), exhibited what appears to be increased friction during setup for a science observation. This mechanism is a grating wheel that allows scientists to select between short, medium, and longer wavelengths when making observations using the MRS mode. Following preliminary health checks and investigations into the issue, an anomaly review board was convened Sept. 6 to assess the best path forward. The Webb team has paused in scheduling observations using this particular observing mode while they continue to analyze its behaviour and are currently developing strategies to resume MRS observations as soon as possible. The observatory is in good health, and MIRI’s other three observing modes – imaging, low-resolution spectroscopy, and coronagraphy – are operating normally and remain available for science observations.