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October 13, 2019 at 4:47 pm #9927Anonymous
THE SOCIETY FOR POPULAR ASTRONOMY
Electronic News Bulletin No. 500 2019 October 13
Here is the latest round-up of news from the Society for Popular Astronomy. The SPA is arguably Britain's liveliest astronomical society, with members all over the world. We accept subscription payments online at our secure site and can take credit and debit cards. You can join or renew via a secure server or just see how much we have to offer by visiting
MARS INSIGHT LANDER PROBE
The Mars InSight lander, which is on a mission to explore the deep interior of Mars, has positioned its robotic arm to assist the spacecraft's self-hammering heat probe. Known as 'the mole', the probe has been unable to dig more than about 35 centimetres since it began burying itself into the ground on 2019 Feb. 28. The manoeuvre is in preparation for a tactic, to be tried
over several weeks, called “pinning”. Whether the extra pressure on the mole will compensate for the unique soil remains an unknown. Designed to burrow as much as 5 metres underground to record the amount of heat escaping from the planet's interior, the mole needs friction from surrounding soil in order to dig: without it, recoil from the self-hammering action causes it simply to bounce in place, which is what the mission team suspects is happening now. Removing the structure allowed the InSight team to get a better look at the hole that formed around the mole as it hammered. It's possible that the mole has hit a rock, but testing by DLR suggested that the issue was soil that clumps together rather than falling around the mole as it hammers. Sure enough, the arm's camera discovered that below the surface
appears to be 5 to 10 centimetres of duricrust, a kind of cemented soil thicker than anything encountered on other Mars missions and different from the soil the mole was designed for.
Using a scoop on the robotic arm, the team poked and pushed the soil seven times over the summer in an effort to collapse the hole. No such luck. It shouldn't take much force to collapse the hole, but the arm isn't pushing at full strength. The team placed HP3 as far from the lander as possible so that the spacecraft's shadow wouldn't influence the heat probe's temperature
readings. As a result, the arm, which wasn't intended to be used that way, has to stretch out and press at an angle, exerting much less force than if the mole were closer. Interplanetary rescue operations aren't new to NASA. The Mars Exploration Rover team helped save Spirit and Opportunity on more than one occasion. Coming up with workable solutions requires an extraordinary amount of patience and planning. JPL has a working replica of InSight to practise arm movements, and it has a working model of the heat probe as well.
TWENTY NEW MOONS OF SATURN DISCOVERED
Carnegie Institution for Science
A team of astronomers has found 20 new moons orbiting Saturn. They bring the ringed planet's total number of moons to 82, surpassing Jupiter, which has 79. The discovery was announced by the International Astronomical Union's Minor Planet Center. Each of the newly discovered moons is about five kilometres in diameter. Seventeen of them orbit the planet in a
retrograde direction, meaning their movement is opposite to the planet's rotation around its axis. The other three moons orbit in the prograde — the same direction as Saturn rotates. Two of the prograde moons are closer to the planet and take about two years to travel once around Saturn. The more-distant retrograde moons and one of the prograde moons each take more
than three years to complete an orbit. The outer moons of Saturn appear to be grouped into three different clusters in terms of the inclinations of the angles at which they are orbiting around the planet. Two of the newly discovered prograde moons fit into a group of outer moons with inclinations of about 46 degrees called the Inuit group, as they are named after Inuit mythology. Those moons may once have comprised a larger moon that was broken apart in the distant past. Likewise, the newly announced retrograde moons have similar inclinations to other previously known retrograde Saturnian moons, indicating that they also are likely to be fragments from a once-larger parent moon that was broken apart. The retrograde moons are in the Norse group, with names coming from Norse mythology. One of the newly discovered retrograde moons is the farthest known moon around Saturn. The other newly found prograde moon has an inclination near 36 degrees, which is similar to the other known grouping of inner prograde moons around Saturn called the Gallic group. But the new moon orbits much farther away from Saturn than any of the other prograde moons, indicating that it might have been pulled outwards over time or might not be associated with the more inner grouping of prograde moons. If a significant amount of gas or dust were present when a larger moon broke apart and created these clusters of smaller moon fragments, there would have been strong frictional interactions between the smaller moons and the gas and dust, causing them to spiral into the planet. The new moons were discovered using the Subaru telescope on Mauna Kea in Hawaii.
NEW ORGANIC COMPOUNDS FOUND ON ENCELADUS
New kinds of organic compounds, the ingredients of amino acids, have been detected in the plumes bursting from Saturn's moon Enceladus. The findings are the result of the ongoing deep dive into data from NASA's Cassini mission. Powerful hydrothermal vents eject material from Enceladus' core, which mixes with water from the moon's massive subsurface ocean before it is released into space as water vapour and ice grains. The newly discovered
molecules, condensed onto the ice grains, were determined to be nitrogen and oxygen-bearing compounds. On Earth, similar compounds are part of chemical reactions that produce amino acids, the building blocks of life. Hydrothermal vents on the ocean floor provide the energy that fuels the reactions. Scientists believe Enceladus' hydrothermal vents may operate in the same way, supplying energy that leads to the production of amino acids. Although the Cassini mission ended in September 2017, the data it provided will be mined for decades. The team used data from the spacecraft's Cosmic Dust Analyzer, or CDA, which detected ice grains emitted from Enceladus into Saturn's E ring. The scientists used the CDA's mass spectrometer measurements to determine the composition of organic material in the grains. The identified organics first dissolved in the ocean of Enceladus, then evaporated from the water surface before condensing and freezing onto ice grains inside the fractures in the moon's crust, scientists found. Blown into space with the rising plume emitted through those fractures, the ice grains were then analyzed by Cassini's CDA. The new findings complement the team's discovery last year of large, insoluble complex organic molecules believed to float on the surface of Enceladus' ocean. The team went deeper with this recent work to find the ingredients, dissolved in the ocean, that are needed for the hydrothermal processes that would spur amino acid formation.
A PLANET THAT SHOULD NOT EXIST
University of Bern
The red dwarf GJ 3512 is located 30 light-years from us. Although the star is only about a tenth of the mass of the Sun, it possesses a giant planet — an unexpected observation. Astronomers say there should only be planets the size of the Earth or somewhat more massive Super-Earths in orbit around it. GJ 3512b, however, is a giant planet with a mass about half as big as that of Jupiter, and thus at least one order of magnitude more massive than the planets predicted by theoretical models for such small stars. The planet was detected by a Spanish-German research consortium called CARMENES, which has set itself the goal of discovering planets around the smallest stars. For this purpose, the consortium built a new instrument, which was installed at the Calar Alto Observatory at 2100 m altitude in southern Spain. Observations with that infrared spectrograph showed that the small star regularly moved towards and away from us — a phenomenon triggered by a companion which had to be particularly massive in this case. Because this discovery was so unexpected, the consortium contacted, among others, the research group of Mordasini, one of the world's leading experts in the theory of planet formation, to discuss plausible formation scenarios for the
giant exoplanet. Our model of the formation and evolution of planets
predicts that around small stars a large number of small planets will be
The star Trappist-1 is comparable to GJ 3512 and has seven planets with masses roughly equal to or even less than the mass of the Earth. In this case, the calculations of the Bern model agree well with the observation. Not so with GJ 3512. The model predicts that there should be no giant planets around such stars. One possible explanation for the failure of
current theory could be the mechanism underlying the model, known as core accretion. Planets are formed by the gradual growth of small bodies into ever larger masses. The experts call this a “bottom-up process”. Maybe the giant planet GJ 3512b was formed by a fundamentally different mechanism, a so-called gravitational collapse. A part of the gas disk in which the planets are formed collapses directly under its own gravitational force. But even that explanation poses problems. Why hasn't the planet continued to grow and migrate closer to the star in this case? One would expect both if the gas disk had enough mass to become unstable under its gravity. The planet GJ 3512b is therefore an important discovery that may improve our understanding of how planets form around such stars.
CENTRE OF MILKY WAY 'RECENTLY' EXPLODED
ARC Centre of Excellence for All Sky Astrophysics in 3D (ASTRO 3D)
A titanic, expanding beam of energy sprang from close to the supermassive black hole in the centre of the Milky Way just 3.5 million years ago, sending a cone-shaped burst of radiation through both poles of the Galaxy and out into deep space. The phenomenon, known as a Seyfert flare, created two enormous 'ionisation cones' that sliced through the Milky Way —
beginning with a relatively small diameter close to the black hole, and expanding vastly as they left the Galaxy. So powerful was the flare that it impacted on the Magellanic Stream — a long trail of gas extending from nearby dwarf galaxies called the Large and Small Magellanic Clouds. The Magellanic Stream lies at an average 200,000 light years from the Milky Way.
The explosion was too huge, says the Australian-US research team, to have been triggered by anything other than nuclear activity associated with the black hole, known as Sagittarius A, or Sgr A*, which is about 4.2 million times as massive than the Sun. Using data gathered by the Hubble Space Telescope, the researchers calculated that the massive explosion took place
little more than three million years ago. In Galactic terms, that is astonishingly recent. On Earth at that point, the asteroid that triggered the extinction of the dinosaurs was already 63 million years in the past, and humanity's ancient ancestors, the Australopithecines, were afoot in
Africa. The blast, the researchers estimate, lasted for perhaps 300,000 years — an extremely short period in galactic terms. The flare event that occurred three million years ago was so powerful that it had consequences on the surroundings of our Galaxy. We are the witness to the awakening of the sleeping beauty. The latest work firms up SgrA* as prime suspect, but, the researchers concede, there is still a lot more work to be done. How black holes evolve, influence and interact with galaxies, they conclude, “is an outstanding problem in astrophysics”.
VIOLENT HISTORY OF ANDROMEDA
Australian National University
Astronomers have pieced together the cannibalistic past of our neighbouring large galaxy Andromeda, which has now set its sights on the Milky Way as its next main course. The galactic detective work found that Andromeda has eaten several smaller galaxies, probably within the last few billion years, with left-overs found in large streams of stars. Researchers have found very faint traces of more small galaxies that Andromeda absorbed even earlier, perhaps as far back as 10 billion years when it was first forming. The Milky Way is on a collision course with Andromeda in about four billion years. So knowing what kind of a monster our galaxy is up against is useful in anticipating the Milky Way's ultimate fate. Andromeda has a much bigger and more complex stellar halo than the Milky Way, which indicates that it has cannibalised many more galaxies, possibly larger ones. The signs of ancient merging are written in the stars orbiting Andromeda, with the team studying dense groups of stars, known as globular clusters, to reveal the timings. By tracing the faint remains of these smaller galaxies with embedded star clusters, we've been able to recreate the way Andromeda drew
them in and ultimately enveloped them at the different times. The discovery presents several new mysteries, with the two bouts of galactic feeding coming from completely different directions. More surprising is the discovery that the direction of the ancient feeding is the same as the bizarre 'plane of satellites', an unexpected alignment of dwarf galaxies orbiting Andromeda. The researchers were part of a team that previously discovered such planes were fragile and rapidly destroyed by Andromeda's gravity within a few billion years. This deepens the mystery as the plane must be young, but it appears to be aligned with ancient feeding of dwarf galaxies.
ENIGMATIC RADIO BURST
Using one cosmic mystery to probe another, astronomers analysed the signal from a fast radio burst to shed light on the diffuse gas in the halo of a massive galaxy. In 2018 November the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope pinpointed a fast radio burst, named FRB 181112. Follow-up observations with ESO's Very Large Telescope (VLT) and other telescopes revealed that the radio pulses have passed through the halo
of a massive galaxy on their way towards the Earth. This finding allowed astronomers to analyse the radio signal for clues about the nature of the halo gas. Astronomers still don't know what causes fast radio bursts and only recently have been able to trace some of these very short, very bright radio signals back to the galaxies in which they originated. A galactic
halo contains both dark and ordinary (baryonic) matter that is primarily in the form of a hot ionised gas. While the luminous part of a massive galaxy might be around 30 000 light-years across, its roughly spherical halo is ten times larger in diameter. Halo gas fuels star formation as it falls towards the centre of the galaxy, while other processes, such as supernova
explosions, can eject material out of the star-forming regions and into the galactic halo.
One reason astronomers want to study the halo gas is to understand better those ejection processes which can shut down star formation. The signal of FRB 181112 was comprised of a few pulses, each lasting less than 40 microseconds (10 000 times shorter than the blink of an eye). The short duration of the pulses puts an upper limit on the density of the halo gas
because passage through a denser medium would broaden the duration of the radio signal. The researchers calculated that the density of the halo gas must be less than 0.1 atoms per cubic centimetre (equivalent to several hundred atoms in a volume the size of a child's balloon). The study found no evidence of cold turbulent clouds or small dense clumps of cool halo gas. The fast radio burst signal also yielded information about the magnetic field in the halo, which is very weak — a billion times weaker than that of a refrigerator magnet. At this point, with results from only one galactic halo, the researchers cannot say whether the low density and low magnetic field strength they measured are unusual or if previous studies of galactic halos have overestimated those properties. Astronomers expect that ASKAP and other radio telescopes will use fast radio bursts to study many more galactic halos and resolve their properties.
THREE BLACK HOLES ON COLLISION COURSE
Astronomers have discovered three giant black holes within a titanic collision of three galaxies. The unusual system was captured by several observatories, including three NASA space telescopes. The system is known as SDSS J084905. 51+111447.2 (SDSS J0849+1114 for short) and is located a billion light-years from Earth. To uncover this rare black hole trifecta, researchers needed to combine data from telescopes both on the ground and in
space. First, the Sloan Digital Sky Survey (SDSS) telescope, which scans large swaths of the sky in optical light from New Mexico, imaged SDSS J0849+1114. With the help of citizen scientists participating in a project called Galaxy Zoo, it was then tagged as a system of colliding galaxies. Then, data from NASA's Wide-field Infrared Survey Explorer (WISE) mission – managed by NASA's Jet Propulsion Laboratory — revealed that the system was
glowing intensely in infrared light during a phase in the galaxy merger when more than one of the black holes is expected to be feeding rapidly. To follow up on these clues, astronomers then turned to Chandra and the Large Binocular Telescope (LBT) in Arizona. The Chandra data revealed X-ray sources — a telltale sign of material being consumed by the black holes —
at the bright centres of each galaxy in the merger, exactly where scientists expect supermassive black holes to reside. Chandra and NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) — managed by JPL as well — also found evidence for large amounts of gas and dust around one of the black holes, typical of a merging black-hole system.
Meanwhile, optical light data from SDSS and LBT showed characteristic spectral signatures of material being consumed by the three supermassive black holes. One reason it is difficult to find a triplet of supermassive black holes is that they are likely to be shrouded in gas and dust, blocking much of their light. The infrared images from WISE, the infrared spectra from LBT and the X-ray images from Chandra bypass this issue, because infrared and X-ray light pierce clouds of gas much more easily than optical light. Three supermassive black holes merging behave differently from just a pair. When there are three such black holes interacting, a pair should merge into a larger black hole much faster than if the two were alone. This may be a solution to a theoretical conundrum called the 'final parsec problem', in which two supermassive black holes can approach to within a few light-years of each other but would need some extra pull inwards to merge because of the excess energy they carry in their orbits. The influence of a third black hole, as in SDSS J084 9+1114, could finally bring them together. Computer simulations have shown that 16% of pairs of supermassive black holes in colliding galaxies will have interacted with a third supermassive black hole before they merge. Such mergers will produce ripples through spacetime called gravitational waves. These waves will have lower frequencies than the National Science Foundation's Laser Interferometer Gravitational-Wave Observatory (LIGO) and European Virgo gravitational-wave detector can detect. However, they may be detectable with radio observations of pulsars, as well as future space observatories, such as ESA's Laser Interferometer Space Antenna (LISA), which will detect black holes up to one million solar masses.
Bulletin compiled by Clive Down
(c) 2019 The Society for Popular Astronomy
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