Topic: Early October Astronomy Bulletin

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SCHOOL BUS SIZED ASTEROID SAFELY FLIES PAST EARTH
NASA

A small near-Earth asteroid (or NEA) briefly visited Earth's neighbourhood on Thursday, Sept. 24, zooming past at a distance of about 22,000 kilometres above our planet's surface. The asteroid will made its close approach below the ring of geostationary satellites orbiting about 36,000 kilometres away from Earth. Based on its brightness, scientists estimate that 2020 SW is roughly 5 to 10 metres wide - or about the size of a small school bus. Although it was not on an impact trajectory with Earth, if it were, the space rock would almost certainly break up high in the atmosphere, becoming a bright meteor known as a fireball. There are a large number of tiny asteroids like this one, and several of them approach our planet as close as this several times every yea. In fact, asteroids of this size impact our atmosphere at an average rate of about once every year or two. After asteroid 2020 SW was discovered on Sept. 18 by the NASA-funded Catalina Sky Survey in Arizona, follow-up observations confirmed its orbital trajectory with high precision, ruling out any chance of impact. In 2005, Congress assigned NASA the goal of finding 90% of the near-Earth asteroids that are about 140 metres or larger in size.  These larger asteroids pose a much greater threat if they were to impact, and they can be detected much farther away from Earth, because they're simply much brighter than the small ones. It is thought that there are over 100 million small asteroids like 2020 SW, but they are hard to discover unless they get very close to Earth. The detection capabilities of NASA's asteroid surveys are continually improving, and we should now expect to find asteroids of this size a couple days before they come near our planet.


COMET HAS ITS OWN NORTHERN LIGHTS
NASA/Jet Propulsion Laboratory

Data from NASA instruments aboard the ESA (European Space Agency) Rosetta mission have helped reveal that comet 67P/Churyumov-Gerasimenko has its own far-ultraviolet aurora. It is the first time such electromagnetic emissions in the far-ultraviolet have been documented on a celestial object other than a planet or moon. On Earth, aurora (also known as the northern or southern lights) are generated when electrically charged particles speeding from the Sun hit the upper atmosphere to create colourful shimmers of green, white, and red. Elsewhere in the solar system, Jupiter and some of its moons -- as well as Saturn, Uranus, Neptune, and even Mars -- have all exhibited their own version of northern lights. But the phenomena had yet to be documented in comets. Rosetta is space exploration's most travelled and accomplished comet hunter. Launched in 2004, it orbited comet 67P/Churyumov -Gerasimenko (67P/C-G) from Aug. 2014 until its dramatic end-of-mission comet landing in Sept. 2016. The data for this most recent study is on what mission scientists initially interpreted as "dayglow," a process caused by photons of light interacting with the envelope of gas -- known as the coma -- that radiates from, and surrounds, the comet's nucleus. But new analysis of the data paints a very different picture. The data indicate 67P/C-G's emissions are actually auroral in nature.  Electrons streaming out in the solar wind -- the stream of charged particles flowing out from the Sun -- interact with the gas in the comet's coma, breaking apart water and other molecules. The resulting atoms give off a distinctive far-ultraviolet light. Invisible to the naked eye, far-ultraviolet has the shortest wavelengths of radiation in the ultraviolet spectrum. Exploring the emission of 67P/C-G will enable scientists to learn how the particles in the solar wind change over time, something that is crucial for understanding space weather throughout the solar system. By providing better information on how the Sun's radiation affects the space environment they must travel through, such information could ultimately can help protect satellites and spacecraft, as well as astronauts traveling to the Moon and Mars.


RADIATION LEVELS ON THE MOON
Kiel University

In the coming years and decades, various nations want to explore the Moon, and plan to send astronauts there again for this purpose. But on our inhospitable satellite, space radiation poses a significant risk. The Apollo astronauts carried so-called dosimeters with them, which performed rudimentary measurements of the total radiation exposure during their entire expedition to the Moon and back again. Now Chinese and German scientists report for the first time on time-resolved
measurements of the radiation on the Moon. The measurements show an equivalent dose rate of about 60 microsieverts per hour. In comparison, on a long-haul flight from Frankfurt to New York, it is about 5 to 10 times lower, and on the ground well over 200 times lower. Since astronauts would be on the Moon for much longer than passengers flying to New York and back, this represents considerable exposure for humans. Humans are not really made to withstand space radiation. However, astronauts can and should shield themselves as far as possible during longer stays on the Moon, for example by covering their habitat with a thick layer of lunar soil. During long-term stays on the Moon, the astronauts' risk of getting cancer and other diseases could thus be reduced. The measurements were taken on board the Chinese lunar lander Chang'e-4, which landed on the far side of the Moon on 3 January 2019. The data from the device and the lander is transmitted back to Earth via the relay satellite Queqiao, which is located behind the Moon. The data obtained also has some relevance with respect to future interplanetary missions. Since the Moon has neither a protective magnetic field nor an atmosphere, the radiation field on the surface of the Moon is similar to that in interplanetary space, apart from the shielding by the Moon itself.


THREE BURIED LAKES ON MARS
Nature Astronomy

Two years ago, planetary scientists reported the discovery of a large saltwater lake under the ice at Mars’s south pole, a finding that was met with excitement and some scepticism. Now, researchers have confirmed the presence of that lake — and found three more. The discovery was made using radar data from the European Space Agency’s Mars-orbiting spacecraft, called Mars Express. It follows the detection of a single subsurface lake in the same region in 2018 — which, if confirmed, would be the first body of liquid water ever detected on the red planet and a possible habitat for life. But that finding was based on just 29 observations made from 2012 to 2015, and many researchers said they needed more evidence to support the claim. The latest study used a broader data set comprising 134 observations from 2012 to 2019. The team used a radar instrument on Mars Express called the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) to probe the planet’s southern polar region. MARSIS sends out radio waves that bounce off layers of material in the planet’s surface and subsurface. The way the signal is reflected back indicates the kind of material that is present at a particular location — rock, ice or water, for example. A similar method is used to identify subsurface glacial lakes on Earth. The team detected some areas of high reflectivity that they say indicate bodies of liquid water trapped under more than one kilometre of Martian ice. The lakes are spread over about 75,000 square kilometres — an area roughly one-fifth the size of Germany. The largest, central lake measures 30 kilometres across, and is surrounded by 3 smaller lakes, each a few kilometres wide.

On the surface of Mars, the low pressure that results from the planet’s lack of a substantial atmosphere makes liquid water impossible. But scientists have long thought that there could be water trapped under Mars’s surface, perhaps a remnant of when the planet once had seas and lakes billions of years ago. If such reservoirs exist, they could be potential habitats for Martian life. On Earth, life is able to survive in subglacial lakes in places such as Antarctica. But the amount of salt present could pose problems. It’s thought that any underground lakes on Mars must have a reasonably high salt content for the water to remain liquid. Although this far beneath the surface there might be a small amount of heat from the interior of Mars, this alone would not be enough to melt the ice into water. “From a thermal point of view, it has to be salty. Lakes with a salt content that is about 5 times that of sea-water can support life, but as the concentration approaches 20 times that of sea-water, life is no longer present. The presence of the Martian lakes themselves is also still debated. After the 2018 discovery, researchers raised concerns such as the lack of an adequate heat source to turn the ice into water. And, although the latest finding supports the 2018 observation and involves much more data, not everyone is convinced that the identified regions are liquid water. A Chinese mission that is on its way to Mars might offer one way to check the claims. The Tianwen-1 mission will enter orbit in February 2021, and as well as deploying a rover onto the surface, the orbiter will carry a suite of scientific instruments. These include radar equipment that could be used to make similar observations


MARS ROVER WILL USE X-RAYS TO HUNT FOSSILS
NASA

NASA's Mars 2020 Perseverance rover has a challenging road ahead: After having to make it through the harrowing entry, descent, and landing phase of the mission on Feb. 18, 2021, it will begin searching for traces of microscopic life from billions of years back. That's why it's packing PIXL, a precision X-ray device powered by artificial intelligence (AI). Short for Planetary Instrument for X-ray Lithochemistry, PIXL is a lunchbox-size instrument located on the end of Perseverance's 2-metre -long robotic arm. The rover's most important samples will be collected by a coring drill on the end of the arm, then stashed in metal tubes that Perseverance will deposit on the surface for return to Earth by a future mission. Nearly every mission that has successfully landed on Mars, from the Viking landers to the Curiosity rover, has included an X-ray fluorescence spectrometer of some kind. One major way
PIXL differs from its predecessors is in its ability to scan rock using a powerful, finely-focused X-ray beam to discover where - and in what quantity - chemicals are distributed across the surface. PIXL's X-ray beam is so narrow that it can pinpoint features as small as a grain of salt. Rock textures will be an essential clue when deciding which samples are worth returning to Earth. On our planet, distinctively warped rocks called stromatolites were made from ancient layers of bacteria, and they are just one example of fossilized ancient life that scientists will be looking for.


SECOND ALIGNMENT PLANE OF SOLAR SYSTEM
National Institutes of Natural Sciences

A study of comet motions indicates that the Solar System has a second alignment plane. Analytical investigation of the orbits of long-period comets shows that the aphelia of the comets, the point where they are farthest from the Sun, tend to fall close to either the well-known ecliptic plane where the planets reside or a newly discovered "empty ecliptic." This has important implications for models of how
comets originally formed in the Solar System. In the Solar System, the planets and most other bodies move in roughly the same orbital plane, known as the ecliptic, but there are exceptions such as comets. Comets, especially long-period comets taking tens-of-thousands of years to complete each orbit, are not confined to the area near the ecliptic; they are seen coming and going in various directions. Models of Solar System formation suggest that even long-period comets originally formed near the ecliptic and were later scattered into the orbits observed today through gravitational interactions, most notably with the gas giant planets. But even with planetary scattering, the comet's aphelion, the point where it is farthest from the Sun, should remain near the ecliptic. Other, external forces are needed to explain the observed distribution. The Solar System does not exist in isolation; the gravitational field of the Milky Way Galaxy in which the Solar System resides also exerts a small but non-negligible influence. Scientists studied the effects of the Galactic gravity on long-period comets through analytical investigation of the equations governing orbital motion. She showed that when the Galactic gravity is taken into account, the aphelia of long-period comets tend to collect around two planes. First the well-known ecliptic, but also a second "empty ecliptic." The ecliptic is inclined with respect to the disk of the Milky Way by about 60 degrees.

The empty ecliptic is also inclined by 60 degrees, but in the opposite direction. Researchers are calling this the "empty ecliptic" based on mathematical nomenclature and because initially it contains no objects, only later being populated with scattered comets. Comparing the analytical and computational results to the data for long-period comets listed in NASA's JPL Small Body Database showed that the distribution has two peaks, near the ecliptic and empty ecliptic as predicted. This is a strong indication that the formation models are correct and long-period comets formed on the ecliptic. However, the sharp peaks are not exactly at the ecliptic or empty ecliptic planes, but near them. An investigation of the distribution of observed small bodies has to include many factors. Detailed examination of the distribution of long-period comets will be our future work. The all-sky survey project known as the Legacy Survey of Space and Time (LSST) will provide valuable information for this study.


GALAXY WITH ULTRAVIOLET LUMINOSITY COMPARABLE TO QUASAR
Instituto de Astrofísica de Canarias

The galaxy, called BOSS-EUVLG1, has a red-shift of 2.47. This is a measure of the reddening of the light coming from the galaxy, and can be used to find its distance: the further away the galaxy, the greater the value. For BOSS-EUVLG1, the value of 2.47 means that the galaxy has been observed when the universe was some 2000 million years old, around 20% of its present age. The large values of redshift and luminosity of BOSS-EUVLG1 caused it to be classified previously in the BOSS (Baryon Oscillation Spectroscopic Survey) project as a quasar. However, from the observations made with the OSIRIS and EMIR instruments on the GTC, and with the millimeter-wave telescope ALMA, the researchers have shown that it is not a quasar, but in fact a galaxy with extreme, exceptional properties. The study revealed that the high luminosity of BOSS-EUVLG1 in the ultraviolet and in Lyman-alpha emission is due to the large number of young, massive stars in the galaxy.  This high luminosity, well above the range for other galaxies, gave rise to its initial identification as a quasar. However, in quasars, the high luminosity is due to the activity around the supermassive black holes in their nuclei and not to star formation.  The rate of star formation in this galaxy is very high, around 1000 solar masses per year, which is about 1000 times higher than that in the Milky Way, although the
galaxy is 30 times smaller. This rate of star formation is comparable only to the most luminous infrared galaxies known, but the absence of dust in BOSS-EUVLG1 allows its ultraviolet and visible emission to reach us with hardly any attenuation.

The results of the study suggest that BOSS-EUVLG1 is an example of the initial phases of the formation of massive galaxies. In spite of its high luminosity and star formation rate, its low metallicity shows that the galaxy has hardly had time to enrich its interstellar medium with dust and newly formed metals. Nevertheless, astronomers believe the galaxy will evolve toward a dustier phase, similar to the infrared galaxies. Also, its high luminosity in the UV will last only a few hundred million years, a very short period in the evolution of a galaxy. This would explain why other galaxies similar to BOSS-EUVLG1 have not been discovered. BOSS-EUVLG1 was discovered via the analysis of a half-million spectra of galaxies and quasars in the BOSS project of the Sloan Digital Sky Survey (SDSS) and observations with large telescopes such as the GTC and ALMA.


PRECISE MEASUREMENT OF MATTER IN UNIVERSE
University of California - Riverside

A top goal in cosmology is to precisely measure the total amount of matter in the Universe, a daunting exercise for even the most mathematically proficient. A team of astronomers has determined that matter makes up 31% of the total amount of matter and energy in the Universe, with the remainder consisting of dark energy. To put that amount of matter in context, if all the matter in the Universe were spread out evenly across space, it would correspond to an average mass density equal to only
about six hydrogen atoms per cubic meter. However, since we know 80% of matter is actually dark matter, in reality, most of this matter consists not of hydrogen atoms but rather of a type of matter which cosmologists don't yet understand. One well-proven technique for determining the total amount of matter in the Universe is to compare the observed number and mass of galaxy clusters per unit volume with predictions from numerical simulations. Because present-day galaxy clusters have formed from matter that has collapsed over billions of years under its own gravity, the number of clusters observed at the present time is very sensitive to cosmological conditions and, in particular, the total amount of matter. A higher percentage of matter would result in more clusters. The 'Goldilocks' challenge for the team was to measure the number of clusters and then determine which answer was 'just right.' But it is difficult to measure the mass of any galaxy cluster accurately because most of the matter is dark so we can't see it with telescopes. To overcome this difficulty, the team of astronomers first developed "GalWeight," a cosmological tool to measure the mass of a galaxy cluster using the orbits of its member galaxies.  The researchers then applied their tool to observations from the Sloan Digital Sky Survey (SDSS) to create "GalWCat19," a publicly available catalogue of galaxy clusters. Finally, they compared the number of clusters in their new catalogue with simulations to determine the total amount of matter in the Universe.

The team succeeded in making one of the most precise measurements ever made using the galaxy cluster technique. Moreover, this is the first use of the galaxy orbit technique which has obtained a value in agreement with those obtained by teams who used noncluster techniques such as cosmic microwave background anisotropies, baryon acoustic oscillations, Type Ia supernovae, or gravitational lensing. A huge advantage of using the GalWeight galaxy orbit technique was that the team was able to determine a mass for each cluster individually rather than rely on more indirect, statistical methods. By combining their measurement with those from the other teams that used different techniques, the scientists were able to determine a best combined value, concluding that matter makes up 31.5±1.3% of the total amount of matter and energy in the Universe.