EARTH CAN MAKE ITS OWN AURORAS
Spaceweather.com
New results from NASA's THEMIS-ARTEMIS spacecraft show that a type of Northern Lights called "diffuse auroras" comes from our own planet--no solar storms required. Diffuse auroras spread across the sky in a dim green haze, sometimes rippling as if stirred by a spoon. They're not as flamboyant as auroras caused by solar storms. Nevertheless, they are important because they represent a whopping 75% of the energy input into Earth's upper atmosphere at night. Researchers have been struggling to understand them for decades. High above our planet's poles, beams of negatively-charged particles shoot upward into space, accelerated by electric fields in Earth's magnetosphere. Sounding rockets and satellites discovered the beams decades ago. It turns out they can power the diffuse auroras. The beams travel in great arcs through the space near Earth. As they go, they excite ripples in the magnetosphere called Electron Cyclotron Harmonic (ECH) waves. ECH waves, in turn, knock other electrons out of their orbits, forcing them to fall back down onto the atmosphere. This rain of secondary electrons powers the diffuse auroras. Earth's polar electron beams sometimes weaken but they never completely go away, not even during periods of low solar activity. This means Earth can make auroras without solar storms.
A NEW METEOR SHOWER
Spaceweather.com
For thousands of years, Comet 15P/Finlay has been dive-bombing Earth's orbit, leaving trails of dust on our planet's doorstep, yet, strangely, there has never been a meteor shower. Until now. On Sept. 27th, Earth hit a stream of debris from Comet Finlay, and a meteor shower was born. It's long overdue. Every 6 years, Finlay passes only 0.01 au from Earth's orbit. Somehow, we've dodged the debris. The debris was ejected by the comet in 2014 and 2015. In those years, something unexpected happened. Astronomers watching Finlay dive through the inner Solar System were surprised when the comet erupted--twice--more than quadrupling in brightness and producing massive jets of gas and dust. Somewhere between 100 million and a billion kilograms of material were ejected. If Earth grazes this material, a meteor storm could occur. Unfortunately for sky watchers, the best place to see it is in Antarctica. However, the timing also favours observers in parts of South America. The radiant of the shower is the southern constellation of Ara which means the meteor shower is known as the Arids.
INSIGHTS INTO METAL-RICH NEAR-EARTH ASTEROIDS
University of Arizona
Metal-rich near-Earth asteroids, or NEAs, are rare, but their presence provides the intriguing possibility that iron, nickel and cobalt could someday be mined for use on Earth or in Space. New research, published in the Planetary Science Journal, investigated two metal-rich asteroids in our own cosmic backyard to learn more about their origins, compositions and relationships with meteorites found on Earth. These metal-rich NEAs were thought to be created when the cores of developing planets were catastrophically destroyed early in the solar system's history, but little more is known about them. A team of scientists studied asteroids 1986 DA and 2016 ED85 and discovered that their spectral signatures are quite similar to asteroid 16 Psyche, the largest metal-rich body in the solar system. Psyche, located in the main asteroid belt between the orbits of Mars and Jupiter rather than near Earth, is the target of NASA's Psyche mission. Analysis shows that both NEAs have surfaces with 85% metal such as iron and nickel and 15% silicate material, which is basically rock. These asteroids are similar to some stony-iron meteorites such as mesosiderites found on Earth. Astronomers have been speculating as to what the surface of Psyche is made of for decades. By studying metal-rich NEAs that come close to the Earth, they hope to identify specific meteorites that resemble Psyche's surface.
The paper also explored the mining potential of 1986 DA and found that the amount of iron, nickel and cobalt that could be present on the asteroid would exceed the global reserves of these metals. Additionally, when an asteroid is catastrophically destroyed, it produces what is called an asteroid family -- a bunch of small asteroids that share similar compositions and orbital paths. The team used the compositions and orbits of asteroids 1986 DA and 2016 ED85 to identify four possible asteroid families in the outer region of the main asteroid belt, which is home to the largest reservoir of small bodies in the inner part of the solar system. This also happens to be the region where most of the largest known metallic asteroids including 16 Psyche reside. The team believe that these two 'mini Psyches' are probably fragments from a large metallic asteroid in the main belt, but not 16 Psyche itself. It's possible that some of the iron and stony-iron meteorites found on Earth could have also come from that region in the solar system too.
POSSIBLE DISCOVERY OF FIRST PLANET ORBITING THREE STARS
University of Nevada, Las Vegas
In a distant star system -- 1,300 light years away from Earth, astronomers may have identified the first known planet to orbit three stars. Unlike our solar system, which consists of a solitary star, it is believed that half of all star systems, like GW Ori where astronomers observed the novel phenomenon, consist of two or more stars that are gravitationally bound to each other. But no planet orbiting three stars -- a circumptriple orbit -- has ever been discovered. Possibly until now. Using observations from the Atacama Large Millimeter/submillimeter Array (ALMA) telescope, astronomers analyzed the three observed dust rings around the three stars, which are critical to forming planets. But they found a substantial, yet puzzling, gap in the circumtriple disc. The research team investigated different origins, including the possibility that the gap was created by gravitational torque from the three stars. But after constructing a comprehensive model of GW Ori, they found that the more likely, and fascinating, explanation for the space in the disc is the presence of one or more massive planets, Jupiter-like in nature. Gas giants are usually the first planets to form within a star system. Terrestrial planets like Earth and Mars follow. The planet itself cannot be seen, but the finding suggests that this is the first circumtriple planet ever discovered. Further observations from the ALMA telescope are expected in the coming months, which could provide direct evidence of the phenomenon.
RADIO SIGNALS FROM DISTANT STARS SUGGEST HIDDEN PLANETS
University of Queensland
Using the world's most powerful radio antenna, scientists have discovered stars unexpectedly blasting out radio waves, possibly indicating the existence of hidden planets. Astronomers at the University of Queensland have been searching for planets using the Low Frequency Array (LOFAR) situated in the Netherlands. They have discovered signals from 19 distant red dwarf stars, four of which are best explained by the existence of planets orbiting them. It’s long been known that the planets of our own solar system emit powerful radio waves as their magnetic fields interact with the solar wind, but radio signals from planets outside our solar system had yet to be picked up. This discovery is an important step for radio astronomy and could potentially lead to the discovery of planets throughout the galaxy. Previously, astronomers were only able to detect the very nearest stars in steady radio emission, and everything else in the radio sky was interstellar gas, or exotica such as black holes. Now, radio astronomers are able to see plain old stars when they make their observations, and with that information, we can search for any planets surrounding those stars. The team focused on red dwarf stars, which are much smaller than the Sun and known to have intense magnetic activity that drives stellar flares and radio emission. But some old, magnetically inactive stars also showed up, challenging conventional understanding. The team is confident these signals are coming from the magnetic connection of the stars and unseen orbiting planets, similar to the interaction between Jupiter and its moon, Io.
Our own Earth has aurorae, commonly recognised here as the northern and southern lights, that also emit powerful radio waves -- this is from the interaction of the planet's magnetic field with the solar wind. But in the case of aurorae from Jupiter, they're much stronger as its volcanic moon Io is blasting material out into space, filling Jupiter's environment with particles that drive unusually powerful aurorae. The model for this radio emission from our stars is a scaled-up version of Jupiter and Io, with a planet enveloped in the magnetic field of a star, feeding material into vast currents that similarly power bright aurorae. Astronomers can't be 100 per cent sure that the four stars thought to have planets are indeed planet hosts, but they can say that a planet-star interaction is the best explanation for what we're seeing. Follow-up observations have ruled out planets more massive than Earth, but there's nothing to say that a smaller planet wouldn't do this. The discoveries with LOFAR are just the beginning, but the telescope only has the capacity to monitor stars that are relatively nearby, up to 165 lightyears away. With Australia and South Africa's Square Kilometre Array radio telescope finally under construction, hopefully switching on in 2029, the team predict they will be able to see hundreds of relevant stars out to much greater distances. This work demonstrates that radio astronomy is on the cusp of revolutionising our understanding of planets outside our Solar System.
EXOPLANET MORE EXOTIC THAN ORIGINALLY THOUGHT
Cornell University
Considered an ultra-hot Jupiter -- a place where iron gets vaporized, condenses on the night side and then falls from the sky like rain -- the fiery, inferno-like WASP-76b exoplanet may be even more sizzling than scientists had realized. A team of scientists reports the discovery of ionized calcium on the planet -- suggesting an atmospheric temperature higher than previously thought, or strong upper atmosphere winds. The discovery was made in high-resolution spectra obtained with Gemini North near the summit of Mauna Kea in Hawaii. Hot Jupiters are named for their high temperatures, due to proximity to their stars. WASP-76b, discovered in 2016, is about 640 light-years from Earth, but so close to its F-type star, which is slightly hotter than the Sun, that the giant planet completes one orbit every 1.8 Earth days. The research results are the first of a multiyear, Cornell-led project, Exoplanets with Gemini Spectroscopy survey, or ExoGemS, that explores the diversity of planetary atmospheres. As astronomers do remote sensing of dozens of exoplanets, spanning a range of masses and temperatures, they will develop a more complete picture of the true diversity of alien worlds -- from those hot enough to harbour iron rain to others with more moderate climates, from those heftier than Jupiter to others not much bigger than the Earth. The group spotted a rare trio of spectral lines in highly sensitive observations of the exoplanet WASP-76b's atmosphere. The spectral signature of ionized calcium could indicate that the exoplanet has very strong upper atmosphere winds. Or the atmospheric temperature on the exoplanet is much higher than previously thought.
STRANGE RADIO WAVES FROM GALACTIC CENTRE
University of Sydney
Astronomers have discovered unusual signals coming from the direction of the Milky Way's centre. The radio waves fit no currently understood pattern of variable radio source and could suggest a new class of stellar object. The strangest property of this new signal is that it is has a very high polarisation. This means its light oscillates in only one direction, but that direction rotates with time. The brightness of the object also varies dramatically, by a factor of 100, and the signal switches on and off apparently at random. Astronomers have never seen anything like it. Many types of star emit variable light across the electromagnetic spectrum. With tremendous advances in radio astronomy, the study of variable or transient objects in radio waves is a huge field of study helping us to reveal the secrets of the Universe. Pulsars, supernovae, flaring stars and fast radio bursts are all types of astronomical objects whose brightness varies. At first it was thought it could be a pulsar -- a very dense type of spinning dead star -- or else a type of star that emits huge solar flares. But the signals from this new source don't match what we expect from these types of celestial objects. Looking towards the centre of the Galaxy, the team found ASKAP J173608.2-321635, named after its coordinates. This object was unique in that it started out invisible, became bright, faded away and then reappeared. This behaviour was extraordinary.
After detecting six radio signals from the source over nine months in 2020, the astronomers tried to find the object in visual light. They found nothing. They turned to the Parkes radio telescope and again failed to detect the source. Then they tried the more sensitive MeerKAT radio telescope in South Africa. Because the signal was intermittent, it was observed for 15 minutes every few weeks. Luckily, the signal returned, but the behaviour of the source was dramatically different -- the source disappeared in a single day, even though it had lasted for weeks in our previous ASKAP observations. However, this further discovery did not reveal much more about the secrets of this transient radio source. The information has some parallels with another emerging class of mysterious objects known as Galactic Centre Radio Transients, including one dubbed the 'cosmic burper. While the new object, ASKAP J173608.2-321635, does share some properties with GCRTs there are also differences. And researchers really understand those sources, anyway, so this adds to the mystery. The scientists plan to keep a close eye on the object to look for more clues as to what it might be.
IMMENSE SET OF MYSTERIOUS RADIO BURSTS
University of Nevada, Las Vegas
An international team of astronomers recently observed more than 1,650 fast radio bursts (FRBs) detected from one source in deep space, which amounts to the largest set -- by far -- of the mysterious phenomena ever recorded. The FRB’s were recorded over the course of 47 days in 2019. More than a decade after the discovery of FRBs, astronomers are still baffled by the origins of the millisecond-long, cosmic explosions that each produces the energy equivalent to the Sun's annual output. Since FRBs were first discovered in 2007, astronomers worldwide have turned to powerful radio telescopes like FAST to trace the bursts and to look for clues on where they come from and how they're produced. The source that powers most FRBs is widely believed to be magnetars, incredibly dense, city-sized neutron stars that possess the strongest magnetic fields in the Universe. And while scientists are gaining greater clarity on what produces FRBs, the exact location of where they occur is still a mystery. There are two active models for where FRBs come from. One could be that they come from magnetospheres, or within a magnetar's strong magnetic field. Another theory is that FRBs form from relativistic shocks outside the magnetosphere traveling the speed of light. Researchers expect that FAST will continue to systematically investigate a large number of repeating FRBs in the future.
BURST FROM MOST DISTANT GALAXY WAS SPACE DEBRIS
Physics .org
The cosmos is the stage for a variety of giant explosions. These include stellar flares, where stars suddenly release magnetic energy; and neutron star mergers, where two dense stars collide together. But one class of explosions outshines the rest: gamma ray bursts are the most energetic explosions seen in the Universe. Gamma rays are one of the most energetic forms of light, and gamma ray bursts release almost unimaginable quantities of them. First discovered during the cold war—by military satellites searching for the signs of nuclear tests in the upper atmosphere—gamma ray bursts are now thought to be caused by massive stars undergoing huge explosions when they run out of fuel. These events are rare, but so energetic they can be seen in galaxies many billions of light years away. Recently, astronomers thought they had seen evidence for one of these explosions from the most distant galaxy ever seen. But a recently published paper casts doubt on these claims, suggesting it might have been caused by a more mundane source much closer to home. No gamma ray bursts have been documented in our galaxy yet, which may not be a bad thing. A gamma ray burst pointed directly at the Earth would probably lead to a mass extinction event, and the end of civilisation as we know it. Undocumented events may in fact already have caused mass extinction events in Earth's history. By modelling the duration and brightness of the flash, they ruled out the possibility that it was a natural or human-made satellite close to home. They also ruled out a number of other astronomical explanations, and concluded that the most likely explanation was, indeed, a gamma ray burst.
What was so unique about this discovery was that the team pinpointed the direction of the event and found it was coming from the same area as a galaxy known as GN-z11, which just so happens to be the most distant and oldest galaxy we've yet discovered. Was this an incredible cosmic coincidence? Or was this a sign that gamma ray bursts were more common in the very early Universe, just 400 million years after the big bang? The latter conclusion would have big implications for our understanding of how stars and galaxies form in the early Universe, and led to a lot of excitement among astronomers. But unease about the conclusions of the group surfaced, with some arguing it was much more likely that the flash was from an object within our solar system, which could be a natural (such as a moon) or artificial satellite. In another paper, a different team suggested the most likely explanation was a reflection from a human-made satellite. The original authors followed up on these claims, doubling down on their gamma ray burst interpretation, but the chorus of doubters was only getting louder. Now, the controversy has taken another turn, with a new paper recently published in Nature. The authors of this paper suggest the purported gamma-ray burst was in fact a flash caused by a human-made satellite after all. The researchers used a public space-track website to search for possible human satellite interference in the direction and at the time of the flash detection.
Around the time that the original team were studying the sky, a Russian proton rocket reached low Earth orbit and released its upper stages (dubbed Breeze-M), which then became space junk, orbiting the Earth. By looking at the orbit of the space debris and matching with the observations taken in the original study, the new team found the flash could be simply explained by the upper stage falling past the part of the sky the telescope was observing. The proton rocket has been in operation since the 1960s, and it's not the only time one of its Breeze-M upper stages has been in the news. In 2013 an explosion scattered huge amounts of debris into near Earth orbit, and left NASA scrambling to assess whether it would pose a danger to the International Space Station. While this particular incident was perhaps particularly unlucky, with increasing amounts of junk in space, and the launching of large constellations of satellites by the private company SpaceX and others in the coming years, it highlights the increasing difficulties astronomers face observing from the Earth's surface. Better databases of satellites and space debris will help avoid these kinds of misidentifications. But the increasing light pollution from satellite constellations threatens the ability of telescopes on the ground to even see clearly enough to do world-leading science.
PUTIN SLASHES RUSSIA’S SPACE BUDGET
Ars Technica
Russia plans to slash funding for spaceflight activities during the coming three-year period, from 2022 to 2024. The cuts will come to about 16 percent annually. For 2022, the state budget for space activities will be set at 210 billion rubles ($2.9 billion), a cut of 40.3 billion rubles ($557 million) from the previous year. Similar cuts will follow in subsequent years. The most significant decreases will be in areas such as “manufacturing-technological activities" and "cosmodrome development." Funding for "scientific research and development" was zeroed out entirely. Publications say Russian President Vladimir Putin is unhappy with the performance of Russia's space program. At a space industry meeting on September 29, they report, Putin criticized the industry’s failure to fulfill directives on long-term goals in the space sphere. In 2020, for example, Roscosmos failed to hit 30 of the 83 stated goals of the national space program. Putin has reportedly told the Russian space corporation, Roscosmos, that it must increase the reliability of Russian rockets and "master" the next generation of launch vehicles. This directive has come in response to growing competition in the global space launch business, particularly from US-based SpaceX. But what does seem clear is that the Russian space program's future is bleak. Whereas China is rising with a space station of its own and ambitious new exploration plans and the US space industry is flourishing amid a rise in commercial activity, Russia is seeking to maintain a status quo of space vehicles developed decades ago. The country's space employees are already paid extremely low wages. Now, there will be fewer resources to invest in the future—a future into which Putin has charged Rogozin with leading Russia's space program. This cannot be a comfortable position for Dmitry Olegovich Rogozin.
Topic: Mid October Astronomy Bulletin (Read 3414 times)