Space Sunday: distant stars, sounds on Mars, a return and a rocket

The Artemis 1 Space Launch System (SLS) rocket stands on its mobile launch platform at Kennedy Space Centre’s Pad 39B, where it is undergoing a full wet dress rehearsal ahead of its launch later this year – see later in this article for more. Credit: NASA

The Furthest Star

My previous Space Sunday update ended with a note that NASA would be making an announcement at the end of March 2022 concerning a new discovery by the Hubble Space Telescope (HST) that could have repercussions for the James Webb Space Telescope (JWST), once it commences its scientific mission. Announced on March 30th, that discovery was revealed to be the imaging of the most distant individual star from Earth yet discovered. So distant, in fact, that it has taken the light from it 12.9 billion years to reach us. By contrast, the next oldest individual star we have detected using Hubble was born when the universe was already some 4 billion years old, taking 9 billion years to reach us.

Christened  Eärendel, the Old English term for “morning star” (and, as Tolkien fans like me will know, was the name initially given to the half-human, half-elven navigator, prior to Tolkien changing the name of that character to Earendil), the star was discovered as a part of a HST programme called RELICS -the REionisation LensIng Cluster Survey, intended to capture to light from really far distant objects born not long after the Big Bang.

To do this, RELICS employs the phenomenon of gravitational lensing, whereby the mass of a huge object such as a galaxy or cluster of galaxies bend and focuses the light coming from objects far beyond them, allowing us to see them as magnified, arc-like objects. In this case, a cluster of galaxies called WHL0137-08 was found to be lensing the light of a galaxy far beyond them, drawing the collected light of that galaxy out into a slender crescent Hubble could see and which astronomers nicknamed the Sunrise Arc.

The red arc of the Sunrise Arc galaxy, and within it, the single point of light of Eärendel. Credit: NASA, ESA, Brian Welch (JHU), Dan Coe (STScI)

For the most part, the Sunrise Arc is blurred and instinct, like sunlight diffracted by the ripples on the surface of a swimming pool cast blurred clouds of light on the bottom of the pool. However, by coincidence, at the time the images of the Arc were recorded, Eärendel appeared directly on, or extremely close to, a curve in space-time that provided maximum brightening, allowing its light to stand out as an individual point within the blurriness of the Sunrise Arc – just like some rays of light can strike the surface of a swimming pool at precisely the right moment to avoid diffraction by the surface ripples and form pinpoints of light on the bottom of the pool rather than being blurred.

Initially it was thought that the star might in fact be a cluster, rather than a lone star, but careful analysis of Eärendel ‘s red shift has swayed astronomers towards believing it is most likely just the one star (although the potential for it to be a binary system hasn’t been entirely ruled out) of enormous size at least 50 times the mass of the Sun and correspondingly enormous luminosity.

Such is Eärendel age, that it at the time its light departed it, the star was likely only made up of primordial hydrogen and helium following the Big Bang. This makes it a prime target for study by JWST – which thanks to is infra-red capability can pick out more information about a target object than HST -, as doing so could reveal more about the state of the early universe and early stellar development.

However, such is the nature of things that – whilst referring to the star in the present tense, it’s important to note that it is very likely that while the most distant individual star observed by HST, Eärendel is not the oldest star yet found; in fact, it probably no longer exists. This is because such supermassive stars tend to burn through their available fuel stocks in mere millions of years, rather than billions. It’s therefore very likely that at some point when the light captured by Hubble was still making its way towards us, Eärendel either violently exploded into a supernova, or collapsed into a black hole – something we’ll only know for sure a few million years into our future.

The Nature of Sound on Mars

We’re all familiar with the concept of the speed of sound. Here on Earth and at sea level, with the temperature at 20ºC, sound travels at 343 metres per second (m/s). However, that is not an absolute; it varies according to the relative atmospheric temperature and density. At altitudes up to 20 km, the speed of sound slowly declines due to the thinning of the atmosphere; however, above 20 km, whilst the atmosphere continues to thin, its temperature actually increases, making it more excitable, and so the speed of sound increases once more.

Much the same was thought to be true on Mars, where the relatively thin atmospheric density close to the surface of the planet was thought to limit sound waves to around an average of 240 m/s (again, allowing for variations in temperature).  However, what no-one expected was that the speed of sound would vary according to frequency – but that is what the Mars 2020 mission has revealed.

An international team of scientists reached this conclusion after analysing recordings made by one of two microphones mounted on the Perseverance rover. The SuperCam microphone mounted at the top of the rover’s mast is somewhat directional in nature in that turning / tilting the SuperCam unit allows the microphone to be pointed directly at sound sources, allowing it to record them with a good level of fidelity.

The Mars 2020 rover’s SuperCam system with the “directional” microphone highlighted. Credit: NASA/JPL

This is been done a number of time during the rover’s mission. For example, the camera has been pointed towards the Ingenuity Mars helicopter, allowing it to directly record the low-frequency beating of the helicopter’s rotors. It is also naturally pointing at rockets targeted for “zapping” by SuperCam’s laser. It has also been able to listen to tools and equipment operating at the end of the rover’s robot arm. All of these sounds have now been collectively analysed, and scientist have been surprised to find that while lower frequency sounds – such as the beating of Ingenuity’s rotors – travel at the expected Martian average of 240 m/s, sounds at frequencies greater then 240 Hertz, such as the higher-pitched click-click-clicking of the SuperCam laser actually travel around 10 m/s faster – the first time this has ever been observed.

The cause for this unusual difference is thought to be the result of the Martian atmosphere being largely carbon-dioxide. In studying the tenuous Martian atmosphere, scientists have discovered during the day, the heat of the Sun, deflected as it is by the surface of the planet, generates an unusual turbulence in the first 10 km of atmosphere above the planet. This turbulence has an unusual impact on the carbon dioxide that isn’t seen in Earth’s denser atmosphere: it allows higher frequency sounds to excite the carbon dioxide molecules a lot more than low-frequency sounds, allowing such higher frequencies to be more rapidly transmitted through the atmospheric medium.

Because this effect happens almost smack in the middle of the bandwidth of sounds audible to the human ear, it means that if we were able to stand out in the open on Mars and listen to something like a symphony being played a few 10 of metres away, rather than hearing all the notes collectively as we would on Earth, we’d hear the higher notes a second or so ahead of the lower notes, resulting in a discordant mess. However, a more practical outcome of this discovery is that engineers believe that by listening to the different frequencies within the sounds made by various pieces of audible equipment on the rover, they could potentially identify if that part of the rover is experiencing issues, and thus be forewarned that action might be required well before a potential failure occurs.

Astronaut Vande Hei Back on Earth with Cosmonaut Colleagues

NASA’s Mark Vande Hei returned to Earth from the International Space Station (ISS) on Wednesday, March 30th, a couple of days later than originally scheduled, but without any of the drama promised by Roscosmos chief Dmitry Rogozin. Earth in the month, and in response to international sanctions against Russia in the wake of its invasion of Ukraine, Rogozin had issued a (slightly unhinged) threat to leave Vande Hei “abandoned” on the ISS when Soyuz MS-19, the vehicle he was due to return to Earth aboard at the end of the month, departed the station.

Despite being hyped by some media outlets, Rogozin’s threat never merited serious consideration; but even if even it had proved to be true, Vande Hei would hardly have been “abandoned” or without the means to return to Earth. However, MS-19 departed the ISS with Vande Hei aboard as expected, together with cosmonauts  Pyotr Dubrov and Anton Shkaplerov. Prior to their departure, Shkaplerov voiced a shared sentiment among the ISS crew during a live television transmission before he and his crewmates began their preparations for departure.

People have problem on Earth. On orbit … we are one crew. The space station is a symbol of friendship and cooperation and … future of exploration of space.

– Cosmonaut Anton Shkaplerov

Mark Vande Hei gives a thumbs-up after his (US) record-breaking 355 days aboard the ISS and return to Earth on Soyuz MS-19. Credit: NASA/Bill Ingalls

Following his return to Earth as the US record holder for the longest time spent aboard the ISS – a total of 355 days – 55-year-old Vande Hei revealed that the situation in Ukraine was not in any way a divisive subject on the station, with Russians and Americans working in partnership throughout the current tensions.

Landing on the Kazakh steppes in winds strong enough to roll the capsule on its side before the parachutes settled, the Soyuz vehicle was met by a joint Russian-US team, and following medical checks at the landing site the crew were flown by helicopter to Karaganda, a city in Kazakhstan. From there, the US team transferred to a NASA jet for a flight back to the Johnson Space Centre, Texas, arriving on March 31st, with Vande Hei repeating he was looking forward to enjoying coffee with his wife and spending time outdoors after his “24/7 indoor job” of the past year.

Artemis 1 Wet Dress Rehearsal

The Wet Dress Rehearsal (WDR) for NASA’s Artemis 1 Space Launch System rocket has been underway at Kennedy Space Centre, Florida, over the weekend, and has not been without incident or a touch of drama.

Having been at KSC’s Pad 39B since its roll-out from the Vehicle Assembly Building (VAB) on March 17th, the huge rocket – the first of its kind – has been undergoing various tests ahead of the WDR, and the pad itself has undergone the installation of the flame deflectors beneath the mobile launch platform – something that required a vehicle to be in position on the pad in order to ensure their correct alignment.

The full countdown for the WDR commenced on Friday, April 1st, and will continue down through until 9 seconds before launch – the point at which the four main liquid-fuelled engines would be spun-up and ignited. However, on Saturday, April 2nd, drama came in the form of four lightning strikes at the launch pad.

The first three were relatively low power events according to NASA, but the fourth was much more powerful – although it didn’t strike the rocket itself. Instead, it was caught by the lightning protection system ranged around the pad as series of three towers ranged around the launch pad specifically designed to attract lightning, and which had been recently enhanced to provide better protection for SLS launches.

One of the strikes last night was the strongest we have seen since we installed the new lightning protection system. It hit the catenary wire that runs between the 3 towers. System performed extremely well & kept SLS and Orion safe. Glad we enhanced protection since Shuttle!

– Jeremy Parsons, NASA’s deputy manager of the Exploration Ground Systems

The moment of the strike was caught on the 24/7 livestream of WDR activities, although such was the camera angle of the recording, it was mistakenly believed by some observers that that lightning actually struck the launch platform’s umbilical support tower. While neither this strike or the initial three “low power” strikes halted the WDR countdown, a series of checks where run in parallel to the WDR monitoring to ensure none of the rocket’s electrical and power systems had been adversely affected.

However, a more serious problem occurred on the morning of Sunday, April 3rd, when shortly before propellant loading was due to commencing at 11:20 UTC, a pressurisation issue was detected within the fuel feeds of the launch support system. This prompted a 6-hour hold on the WDR schedule while teams at the pad attempted to correct the issue.

Then, when the problem had been thought to be rectified, a further issue was detected with the primary and secondary fans also in the cryo feed system, preventing it from maintaining the correct positive pressure. When it became clear this problem would require a lot longer to correct, the decision was taken at 16:06 UTC  to suspend the WDR for the day, and to hopefully resume with propellent loading on the rocket on Monday, April 4th.

In the meantime, in anticipation of the Artemis 1 WDR being extended, NASA, SpaceX and Axiom space had earlier in the week agreed that the planned launch of the private Axiom / SpaceX AX-1 mission to the ISS aboard a Crew Dragon vehicle would be delayed until no earlier than Wednesday, April 6th, 2022, and the planned NASA Crew 4 mission to the ISS, also using a Crew Dragon vehicle from Kennedy Space Centre’s Pad 39A will not launch before April 20th.