Topic: Early November Astronomy Bulletin

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IMPACT CRATER DISCOVERED IN SPAIN
EPSC

The first probable impact crater in Spain has been identified in the southern province of Almeria. While around 200 impact structures have been identified around the world, the study is the first to identify signs of an impact crater on the Iberian Peninsula. The discovery is the result of 15 years of research by an international team of scientists from the University of Almeria, the Astrobiology Center of Madrid, the University of Lund and the University of Copenhagen. Scientists believe that the impact event occurred around 8 million years ago. They have investigated numerous aspects of the geology, minerology, geochemistry and geomorphology of the region. The basins of Alhabia and Tabernas in the area are filled with sediments dating back between 5 and 23 million years, and they overlie older metamorphic rocks. Much of the impact structure is buried by more modern sediments, but erosion has exposed it and opened up the opportunity for studies. The crater itself is thought to be about 4 kilometres in diameter, and it is surrounded by a larger structure about 20 kilometres across, where the impact caused the sedimentary strata to collapse. Evidence for the impact crater includes several examples of ‘shocked’ quartz grains in breccia – a sedimentary rock type with large fragments cemented into a finer-grained matrix. The grains show signs of being deformed in the enormous pressures of the impact, which were between 10 and 30 gigapascals.


HEAVIEST ELEMENT YET DETECTED IN EXOPLANET
ESO

Astronomers have discovered the heaviest element ever found in an exoplanet atmosphere — barium. They were surprised to discover barium at high altitudes in the atmospheres of the ultra-hot gas giants WASP-76 b and WASP-121 b — two exoplanets, planets which orbit stars outside our Solar System. This unexpected discovery raises questions about what these exotic atmospheres may be like. WASP-76 b and WASP-121 b are no ordinary exoplanets. Both are known as ultra-hot Jupiters as they are comparable in size to Jupiter whilst having extremely high surface temperatures soaring above 1000°C. This is due to their close proximity to their host stars, which also means an orbit around each star takes only one to two days. This gives these planets rather exotic features; in WASP-76 b, for example, astronomers suspect it rains iron. But even so, the scientists were surprised to find barium, which is 2.5 times heavier than iron, in the upper atmospheres of WASP-76 b and WASP-121 b. The fact that barium was detected in the atmospheres of both of these ultra-hot Jupiters suggests that this category of planets might be even stranger than previously thought. Although we do occasionally see barium in our own skies, as the brilliant green colour in fireworks, the question for scientists is what natural process could cause this heavy element to be at such high altitudes in these exoplanets. “

Determining the composition of an exoplanet’s atmosphere requires very specialised equipment. The team used the ESPRESSO instrument on ESO’s VLT in Chile to analyse starlight that had been filtered through the atmospheres of WASP-76 b and WASP-121 b. This made it possible to clearly detect several elements in them, including barium. These new results show that we have only scratched the surface of the mysteries of exoplanets. With future instruments such as the high-resolution ArmazoNes high Dispersion Echelle Spectrograph (ANDES), which will operate on ESO’s upcoming Extremely Large Telescope (ELT), astronomers will be able to study the atmospheres of exoplanets large and small, including those of rocky planets similar to Earth, in much greater depth and to gather more clues as to the nature of these strange worlds.


STARS SOUND WARNING WHEN THEY ARE ABOUT TO GO SUPERNOVA
RAS

Astronomers have devised an ‘early warning’ system to sound the alert when a massive star is about to end its life in a supernova explosion. In this new study, researchers determined that massive stars (typically between 8 and 20 solar masses) in the last phase of their lives, the so-called ‘red supergiant’ phase, will suddenly become around a hundred times fainter in visible light in the last few months before they die. This dimming is caused by a sudden accumulation of material around the star, which obscures its light. Until now, it was not known how long it took the star to accrete this material. Now, for the first time, researchers have simulated how red supergiants might look when they are embedded within these pre-explosion 'cocoons'. Old telescope archives show that images do exist of stars that went on to explode around a year after the image was taken. The stars appear as normal in these images, meaning they cannot yet have built up the theoretical circumstellar cocoon. This suggests that the cocoon is assembled in less than a year, which is considered to be extremely fast. The dense material almost completely obscures the star, making it 100 times fainter in the visible part of the spectrum. This means that, the day before the star explodes, you likely wouldn't be able to see it was there. Until now, astronomers have only been able to get detailed observations of supernovae hours after they’ve already happened. With this early-warning system they can get ready to observe them real-time, to point the world’s best telescopes at the precursor stars, and watch them getting literally ripped apart in front of our eyes.


PLANETS ORBITING MOST COMMON STAR MAY BE UNINHABITABLE
University of California - Riverside

An Earth-like planet orbiting an M dwarf -- the most common type of star in the Universe -- appears to have no atmosphere at all. This discovery could cause a major shift in the search for life on other planets. Because M-dwarfs are so ubiquitous, this discovery means a large number of planets orbiting these stars may also lack atmospheres and therefore are unlikely to harbour living things. The work that led to the revelations about the no-atmosphere planet, named GJ 1252b, are detailed in the Astrophysical Journal Letters. This planet orbits its star twice during the course of a single day on Earth. It is slightly larger than Earth, and it is much closer to its star than Earth is to the Sun, making GJ 1252b intensely hot as well as inhospitable. Earth also loses some of its atmosphere over time because of the Sun, but volcanic emissions and other carbon cycling processes make the loss barely noticeable by helping replenish what is lost. However, in greater proximity to a star, a planet cannot keep replenishing the amount being lost. In our solar system, this is the fate of Mercury. It does have an atmosphere, but one that is extremely thin, made up of atoms blasted off its surface by the Sun. The extreme heat of the planet causes these atoms to escape into space. To determine that GJ 1252b lacks an atmosphere, astronomers measured infrared radiation from the planet as its light was obscured during a secondary eclipse. This type of eclipse occurs when a planet passes behind a star and the planet's light, as well as light reflected from its star, is blocked. The radiation revealed the planet's scorching daytime temperatures, estimated to reach 2,242 degrees Fahrenheit -- so hot that gold, silver, and copper would all melt on the planet. The heat, coupled with assumed low surface pressure, led the researchers to believe there's no atmosphere.

Even with a tremendous amount of carbon dioxide, which traps heat, the researchers concluded GJ 1252b would still not be able to hold on to an atmosphere. The planet could have 700 times more carbon than Earth has, and it still wouldn't have an atmosphere. It would build up initially, but then taper off and erode away. M dwarf stars tend to have more flares and activity than the Sun, further reducing the likelihood that planets closely surrounding them could hold on to their atmospheres. It's possible this planet's condition could be a bad sign for planets even further away from this type of star. This is something we'll learn from the James Webb Space Telescope, which will be looking at planets like these. There are 5,000 stars in Earth's solar neighbourhood, most of them M dwarfs. Even if planets orbiting them can be ruled out entirely, there are still roughly 1,000 stars similar to the Sun that could be habitable. If a planet is far enough away from an M dwarf, it could potentially retain an atmosphere. We cannot conclude yet that all rocky planets around these stars get reduced to Mercury's fate.


MILKY WAY RIPPLES CAUSED BY PASSING GALAXY
Lund University

Using data from the Gaia space telescope, researchers have shown that large parts of the Milky Way's outer disk vibrate. The ripples are caused by a dwarf galaxy, now seen in the constellation Sagittarius, that shook our galaxy as it passed by hundreds of millions of years ago. Our cosmic home, the Milky Way, contains between 100 and 400 billion stars. Astronomers believe that the galaxy was born 13.6 billion years ago, emerging from a rotating cloud of gas composed of hydrogen and helium. Over billions of years, the gas then collected in a rotating disk where the stars, such as our Sun, were formed. The team can see that these stars wobble and move up and down at different speeds. When the dwarf galaxy Sagittarius passed the Milky Way, it created wave motions in our galaxy, a little bit like when a stone is dropped into a pond. By using data from the European space telescope Gaia, the research team was able to study a much larger area of the Milky Way's disk than was previously possible. By measuring how strong the ripples are in different parts of the disc, the researchers have begun to piece together a complex puzzle, providing clues about Sagittarius' history and orbit around our home galaxy. At the moment, Sagittarius is slowly being torn apart, but 1-2 billion years ago it was significantly larger, probably around 20 percent of the mass of the Milky Way's disk. The researchers were surprised by how much of the Milky Way they could study using the data from Gaia. To date the telescope, which has been in operation since 2013, has measured the movement across the sky of approximately two billion stars and the movement towards or away from us of 33 million. With this new discovery, the Milky Way can be studied in the same way that geologists draw conclusions about the structure of the Earth from the seismic waves that travel through it. This type of "galactic seismology" will teach us a lot about our home galaxy and its evolution.


C0SMIC RAYS DRIVE GALAXY’S WINDS
National Radio Astronomy Observatory

Astronomers have discovered an important new clue about how galaxies put the brakes on vigorous episodes of star formation. Their new study of the neighbouring galaxy M33 indicates that fast-moving cosmic ray electrons can drive winds that blow away the gas needed to form new stars. Such winds are responsible for slowing the rate of star formation as galaxies evolve over time. However, shock waves from supernova explosions and energetic, black hole-powered jets of material coming from galactic cores have been considered the primary drivers of those winds. Cosmic rays were thought to be minor contributors, particularly in galaxies like M33 that have regions of prolific star formation. The team made detailed, multi-wavelength VLA observations of M33, a spiral galaxy nearly 3 million light-years away and part of the Local Group of galaxies that includes the Milky Way. They also used data from previous observations with the VLA, the Effelsberg radio telescope in Germany, and millimeter-wave, visible-light, and infrared telescopes. Stars much more massive than our Sun speed through their life cycles, ultimately exploding as supernovae. The explosive shock waves can accelerate particles to nearly the speed of light, creating cosmic rays. Enough of these cosmic rays can build pressure that drives winds carrying away the gas needed to continue forming stars. Based on their observations, the astronomers concluded that the numerous supernova explosions and supernova remnants in M33's giant complexes of prolific star formation made such cosmic ray-driven winds more likely. This means that cosmic rays probably are a more general cause of galactic winds, particularly at earlier times in the Universe's history, when star formation was happening at a much higher rate. This mechanism thus becomes a more important factor in understanding the evolution of galaxies over time.