And… the November newsletter.
Well, winter is nearly here with the end of summer time. Nights are drawing in, cloud guaranteed especially when there is some time-limited viewing opportunity or aurora likely! Such is astronomical viewing in Cumbria. All you can do is get out when it is clear and enjoy. This month’s sky notes give the usual details of what is visible, subject to me discovering them as I’m not very good at looking for unusual events like planets or comets aligning up with each other or interesting deep sky objects.
In addition, this month, there are some details of a comet, Comet Leonard C/2021 A1 which has the potential to become quite bright [here we go again?]. This particular long period comet has been around the Sun a few times, which tends to make them more predictable as most volatile materials will have vapourised in previous perihelia. Volatile materials in ‘new’ comets tend to cause sudden outbursts leading people to think it’ll be much brighter when it gets closer to the Sun and so they often disappointed when the volatiles then stop vaporising and the comet dims. Hopefully this comet will behave and not disappoint when it is closest to Earth on December 12th. It is quite well-placed in the early morning sky in early December but rattles low along the western horizon in the evenings. Fingers crossed.
Committee members required. David and I have worked hard to keep the the Society alive and active. We really need to keep the momentum and help the Society to grow. For this, we really need some more people on the committee. David and I are getting somewhat ‘burnt out’ so we do need help. Please think seriously about volunteering, and let us know at a meeting or by email if you can help.
Also, don’t forget, contributions to the newsletter from any member are most welcome. They could be stories, historical snippets or photographs.
Ian Bradley, on behalf of the EAS committee.
Thursday November 4th, 7pm Kendal Museum, or online on Zoom.
Speaker: Jack Ellerby Friends of the Lake District on “The Cumbria Dark Skies Project”.
No doubt will tell us about some of his successes to get a reduction of light pollution in the Lake District national park.
Moonwatch with Friends of the Lake District
Just a gentle reminder that the Society will be running a Moonwatch on the Kirbie Kendal School playing fields on Friday November 12th starting at 18:30 and expecting to finish by 21:00. There is plenty of parking in the school car park and overflow, if that is full, at the Leisure centre up Burton Road. This is the Society’s Dark Skies Cumbria Festival that is running from 6th – 14th November .
All welcome. Members of the public have been asked to book on the FLD website, but EAS members can just turn up – you might get asked a few questions by visitors!
Joint Societies Christmas Dinner
Don’t forget the joint north-west societies Christmas dinner. This usually includes the societies from Lancaster & Morecambe, Blackpool and Preston. Date: 16th December. Location: Garstang. There will be the usual after-dinner talk from Prof. Allan Chapman with the meal costing £30. If you are interested, please let the committee know by email with a deadline for monies collection of our December meeting.
Federation of Astronomical Societies (FAS)
You may be aware that the Society gets third party liability insurance through the FAS. In addition, they also produce quarterly newsletters which sometimes contain an interesting article. These are available online, so go and have a look.
Astronomy News – David Glass
Still lots of construction work going on at Boca Chica, Texas, including the installation of the catch arms (‘chopsticks’) on the Mechazilla tower. We posted a link to an animation of what these are for in a previous newsletter – these are key to the rapid turnaround of boosters and starships to get material and personnel into orbit and beyond. There were also two test fires of the Raptor engines on a starship, S20, on 21/10 after proof tests late in September.
These tests involved ignition of both the sea -level optimised and vacuum-optimised engines for use in space, and were separated by a relatively short interval (just over an hour). The sea-level engines are gimballed and have been seen in action already for landing starships. The scale of the engines is seriously impressive – imagine screamingly hot gas at an exit pressure of about 300 bar (4,400 psi) blasting out of them:
No specific date has been announced for an orbital flight involving S20, but it may not be too long a wait.
On 4/10, Blue Origin’s flight NS-18 took four new passengers to the edge of space and back. One of these was William Shatner (the original Captain James T. Kirk for non-Star Trek fans), who at 90 became the oldest person to go into space. See here.
You will notice that I’m not using the term “astronaut” – the IAU changed the definition and I’m not sure that these passengers qualify. The link contains a replay of the build-up, launch and landing – it starts at 2h 26min, but the launch is at 2h 23min.
The flight went smoothly, and they are always fascinating to watch. However, the flight was eclipsed by Shatner’s reaction when he got out of the capsule. They say that seeing the Earth from space changes people…and he was visibly overwhelmed by what he saw (zoom to 2h 43 min in the replay). Here’s an interview where he discussed what he experienced:
NASA Space Launch System (SLS)
Steady progress is being made towards getting the SLS ready for its first flight (Artemis 1), which could be in February 2022. On 22/10 the Orion crew capsule was stacked onto the SLS, which is another milestone:
This now allows the end-to-end testing of the fully integrated rocket, including a full countdown practice. The rocket can then be moved to the launch pad on its mobile launcher for a full “wet dress rehearsal” test where it is loaded with cryogenic propellants and unloaded. Click on image to enlarge.
James Webb Space Telescope
After a 16-day boat trip, the James Webb Space Telescope was unloaded at the Guiana space centre on 12/10 and is being made ready for launch sometime in December (on or around 18/12 is planned):
The launch will use an Ariane 5 rocket, and will get the JWST to the L2 Lagrange point behind the Moon where its position will be relatively stable (think of a weight on the end of a piece of string circling a central point – that’s how gravity will pull on the telescope). For a straightforward description of Lagrange points, take a look here.
16/12 saw the launch of Lucy, a spacecraft intended to explore the Trojan asteroids that occupy space along Jupiter’s orbital path (at Lagrange points!). it should visit eight trojans over a period of about 12 years. These Trojans are thought to be remnants of the material from the earliest days of the Solar system, and studying them will help to plug gaps in our knowledge of how the Solar system formed. For more details of this fascinating mission, take a look at lucy.swri.edu and check out the mission overview in particular.
Currently (29/10) there seems to be an issue with the unfurling of its solar arrays, which hopefully will be resolved soon. Apart from that the spacecraft is healthy.
Imaging the Far Side of Pluto
Astronomers are great at wringing out science from any viable data source. In this case, a team used an image from the LORRI camera on the New Horizons spacecraft to image the far side of Pluto, illuminated only by the very faint reflected light from Pluto’s companion Charon. After some intelligent processing of the data, they managed to detect a high-albedo (i.e. reflective) region in the Southern hemisphere which could be a patch of frozen nitrogen. However, the South polar region had lower albedo, which might point to interesting seasonal phenomena.
The preprint of the research paper on this study is available here.
…and a non-technical summary is here.
The formation of the Moon – Ian Bradley
There used to be three ideas of how the Moon formed: the fission theory where a large mass of the presumed rapidly spinning Earth tore off to form the Moon; the capture theory, where the Earth gravitationally captured a body that had formed elsewhere; the co-creation theory, where the earth and Moon both formed at the same time in a similar region of space.
One indication that the fission theory was correct is that the average density of the Moon was very similar to that of the outer layers of the Earth as would be expected if some of the Earth’s outer layers were ripped off. However, the Apollo rock samples had more refractory elements and less volatile elements than those of the Earth’s surface rocks. Volatile materials boil at relatively low temperatures (900°C) compared to refractory ones (>1400°C). This suggested that the Moon formed from material that was heated to a higher temperature than the Earth so that some of the volatile material boiled away.
However, the consensus now is that none of these three ideas is correct. At a conference in 1974, Donald Davis and William Hartmann proposed an impact hypothesis. It turns out in the subsequent discussion that another group (Cameron and Ward) were independently working on a similar idea. The idea was that the Moon formed some 4.5 billion years ago from an off-centre collision between the Earth and a Mars-sized body, later named Theia after a daughter of Earth goddess Gaia and the sky god Uranus in Greek mythology. Debris from the Earth’s surface spalled off from the collision forming the Moon with most of Theia being absorbed onto the Earth. This ‘graze and merge’ scenario would explain the lack of both volatiles and a lunar iron core, assuming the iron was already in the Earth’s core. It also explains why the Earth spin axis is tilted relative to the plane of the ecliptic. But it left several questions unanswered, not least that simulations rarely gave a Moon with an Earth-like composition and the collision speed had to be improbably low.
Now, new simulations reported in the Planetary Journal (Erik Asphaug et al 2021 Planet. Sci. J. 2 200.) suggest that with faster approach speeds, Earth and Theia do a ‘hit and run’ where they come into violent contact for a short time (30 minutes) before what’s left of Theia escapes. Material passes between the two objects which has time to mix as the surfaces are molten post impact. Crucially, having lost a lot of energy and hence slower, Theia frequently comes back to have another glancing collision with the Earth in typically 0.1–1 million years according to the simulations. This second collision can now be a ‘graze and merge’ scenario as Theia sometimes approaches with the previously improbably low speed. This neatly solves both the composition and speed issues.
The paper goes into a lot more detail on material transfer and mixing if you are interested. No doubt this new model will have some other issues too, but it is an interesting new take on an old model.
Disk spotted round an exoplanet – a moon forming region? – Ian Bradley
Whilst on the subject of moon formation. The Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile has found evidence of a possible moon-forming region surrounding a newly forming and recently-discovered exoplanet PDS70c. This orbits the young star PDS70, which is 370 light-years away. The observation, reported over the summer in The Astrophysical Journal Letters ( Myriam Benisty et al 2021 ApJL 916 L2), could lead to important insights into how moons and planets form and evolve within young star systems.
Discs of gas and dust often surround young stars with rings and gaps cleared out by newly forming planets. These planets can also acquire discs of their own, it is believed that moons can form in these discs with a similar effect, more gaps. So far, the process has not been directly observed.
ESO’s Very Large Telescope (VLT) first detected two exoplanets forming round PDS70 by direct infrared images of the system Since then, these giant Jupiter-like planets have been observed using a variety of other techniques. In particular observations in the hydrogen-alpha (Hα) emission wavelength, associated with ionised hydrogen, suggest given the Hα emission that the planets were still accreting material.
ALMA is a millimetre wave telescope that detects the emissions from cool dust grains. The new observations of PDS70 clearly show a disc surrounding the outermost exoplanet, PDS70c, with an outer radius no larger than 1.2 au. They calculate that the disc could contain anywhere between 0.7% and 3.1% of Earth’s mass – enough material to form up to three satellites with similar masses to Earth’s Moon. In addition, the material in PDS70c’s disc is well within the radius where it would be retained by the exoplanet – providing ideal conditions for a moon to form.
The innermost exoplanet, PDS70b, did not display any clear evidence for a circumplanetary disc which could mean that the planet has a far smaller radius within which orbiting material can be retained. Alternatively, PDS70c could have ‘hoovered’ up all the dust as its orbit is better placed within PDS70’s circumstellar disc
The astronomers hope that observations with ESO’s Extremely Large Telescope (ELT), currently under construction in Chile and become available in 2027, could provide direct high-resolution images of the system. This could be a unique opportunity to study the formation of planets and moons which ultimately could improve our understanding of how moons form around young gas-giant planets.
Possible planet detected in another galaxy! – Ian Bradley
There were reports in the archive late last year [ here] of the possible detection of an exo-galactic planet in M51 using the Chandra X-ray telescope. This work has now been published in the peer-reviewed journal Nature Astronomy which, sadly I think, is behind a paywall. Try it.here .
The observers measured the brightness of one of the strongest X-ray sources in M51, with the exciting title of M51-ULS-1. The source is an X-ray binary system, typically containing a compact object, a neutron star or black hole, pulling in gas from a closely orbiting companion star. The material near the neutron star or black hole becomes superheated and glows at X-ray wavelengths, producing a very compact, planetary sized, X-ray source.
The observers noted the detected signal drop to zero for about 3 hours whilst observing the source for 53 hours. They concluded a Saturn-sized planet orbiting the compact object transited the X-ray source. Because the source is so compact, the transit completely occulted the source, totally different to normal exoplanet transits where even a 1% reduction or less is typical. The researchers deduced an orbital distance of about twice the distance of Saturn from our Sun. Unfortunately, the orbital period is estimated to be about 70 years so the gold-standard of a repeat transition proving it is an orbiting exoplanet cannot be done.
The authors also considered whether the dip could be due to:
- Intrinsic variability – but no short duration on-off change of this type has ever been observed before and such a change would be a real challenge for theory
- Absorption by dust in the accretion disk surrounding the compact object – but the spectral signature expected from such an event is not seen in the data
So they are left with the conclusion that they have observed the first ever exo-galactic planetary transit. They go onto say that “the search for extroplanets, planets in orbits located outside the Milky Way, has now become a realistic and practical enterprise.”
Not only do we have exo-planets, we now have extroplanets!