Category: Space Sunday

The subject of water on Mars has been a topic of scientific debate and speculation for well over 100 years. Since the earliest reliable observations of Mars via telescope, it had been thought that water ice and water vapour existed on the planet and in its atmosphere as a result of the seeing the polar ice caps (although we now know the major stakeholder in these is carbon dioxide) and cloud formations.

However, the idea that Mars was still subject to liquid water flowing across its surface in our modern era became popularised in the late 1800s. In  1877, respective Italian Astronomer  Giovanni  Schiaparelli – already noted for his observations of Mars in which he correctly identified and named multiple visible surface features – used the Great Opposition of 1877 (when Mars and Earth were both on the same side of the Sun relative to one another and Earth was effectively “overtaking” Mars in their respective orbits, thus bringing the two into “close” proximity to one another) to carry out further observations. During these he noted the presence of multiple canali  on Mars.

Canali is an innocent term, meaning “channel”, and Schiaparelli simply used this term to differentiate what he thought is saw from other features he observed. But in English-speaking newspapers it was later translated as canals, evocative of artificial and intelligent construction. This resulted in wealthy Bostonian businessman Percival Lowell, following his return to the United States in the early 1890s to establish an observatory in Flagstaff, Arizona, specifically (initially at least) so he could observe these “canals” for himself.

Over the course of 15 years (1893-1908), Lowell saw his canals, which grew into a globe-spanning network and led to the publication of three books (Mars (1895), Mars and Its Canals (1906), and Mars As the Abode of Life (1908 – an original copy of which I actually own!) in which he expounded his theory that Mars had a network of canals built by an ancient civilisation in a last-ditch effort to carry liquid water from the planet’s poles to their equatorial and temperature cities as the planet increasingly became more desert-like.

Lowell stuck to this belief throughout his observations in spite of increasing scientific evidence that Mars was likely incapable of supporting liquid water on its surface and observations from other observatories with larger telescopes than his which could not find any evidence of “canals”, and that at least some of what he was seeing was actually (as Schiaparelli had believed) lines of demarcation between different elevations / terrains.

As a result of this belief, Lowell has become regarded as a bit of a crackpot  – which is a same, as he led a remarkable life with multiple achievements as a traveller, diplomat, writer and armchair scientist, and did gain recognition in his lifetime for his work – He was elected a Fellow of the American Academy of Arts and Sciences in 1892 and then to the American Philosophical Society in 1897, whilst the volume of work he carried out as an astronomer outside of his theories about Mars saw him receive the Prix Jules Janssen, the highest award of the Société Astronomique de France, in 1904.

This volume of work include daytime studies of Venus and the search for “planet X”, a planetary body believed (and still believed by some) to be orbiting the Sun far out beyond the orbit of Neptune. In fact, the Lowell Observatory became a centre for this work, for which it was rewarded in 1930 when Clyde Tombaugh located Pluto using the observatory’s telescopes and equipment.

Of course, whilst liquid water does not exist on the surface of Mars today and hasn’t for billions of years, we have found plenty of evidence for its past presence on the planet’s surface.

In my previous Space Sunday article, for example, I wrote about the Great Lake of Mars, Lake Eridania, whilst both the Mars Science Laboratory Curiosity and Mars 2020 rover Perseverance have literally been following the evidence for free flowing water in both of the locations on Mars they are exploring. Prior to them, the Mars Exploration Rovers Spirit and Opportunity both uncovered evidence of past liquid water on Mars, as have orbital vehicles from NASA, Europe and other nations. But the two big questions have always been – where did it go, and where did it come from?

In terms of where it went, the most common theories are that the water either evaporated and was lost to space along with Mars’ vanishing atmosphere relatively early in the planet’s life or retreated down into the Martian crust where it froze out into icy “reservoirs”. The first is likely for a certain volume of water, whilst subterranean tracts of water ice have been located not too far under the surface of Mars. However, the latter cannot possibly account for the amount of water believed to have existed on the surface of Mars in its early history, not could simple evaporation account for the disappearance of to greater majority of it. So where did the rest go? And where did it come from originally?

Well, in a new report published this month a team of scientists believe they have the answer, and it lay within data obtained by NASA’s InSight (INterior exploration using Seismic Investigations, Geodesy and Heat Transport) lander.

This ambitious craft landed on Mars in 2018, with the mission running from November of that year through until the end of December 2022. In particular, the lander carried with it two unique instruments it deployed onto the Martian surface using a robot arm. One of these was the French-lead Seismic Experiment for Interior Structure (SEIS), designed to measure marsquakes and other internal activity on Mars and things like the response to meteorite impacts, in order to better understand the planet’s internal structure. The data continues to be studied, and has revealed much about the planet’s internal structure and its history.

Most recently, a US team from the Scripps Institution of Oceanography at the University of California, San Diego and the University of California, Berkeley, have been reviewing the SEIS findings specifically to try to answer the question of where the water went. In particular, they have been using mathematical models employed here on Earth to locate aquifers and oil and gas fields deep underground. By adjusting the models so they provided results consistent what is largely known about the Martian crust down to a depth of several kilometres below the surface, they ran a series of passes on data gathered from deeper and deep within the planet’s crust, In particular, the came across two interesting results. The first indicated that while deposits of water ice do exist below the surface of Mars, and less than 5 km from the surface, they are likely to be far less commonplace than had been thought. The second result they took note of was consistent with those indicative of layers of water-saturated igneous rock deep within the Earth’s crust.

Most interestingly, the results of the SEIS data modelled suggest this deep layer of rock and water – laying some 11.5 to 20 km below the surface of Mars could be widespread across the planet to the extent that it could contain more water than would have been required to fill the oceans and seas of ancient Mars.

Taken together, these result indicate that while the theories about water on Mars being lost to space or frozen into subsurface ice are still valid, the vast majority of the water most likely retreated deep down into the planet, possibly returning to the reserves from which it might have originally burst forth to flood parts of Mars during the planet’s late Noachain / early Hesperian period of extreme volcanic activity.

One intriguing question that arises from this work is related to the potential for Mars to have harboured life, and what happened to it as the water vanished. if the modelling in the study is correct, and the water did retreat deep under the surface of Mars and form aquifers and pools with the rocks there, did any ancient microbial life gone with it, and if so – might it have survived? The pressure and temperatures at the depth which the water appears to reside would keep it both liquid and warm and provide energy, as would mineral deposited within the rock; so the question is not without merit.

Establishing that there is a big reservoir of liquid water provides some window into what the climate was like or could be like. And water is necessary for life as we know it. I don’t see why [the underground reservoir] is not a habitable environment. It’s certainly true on Earth — deep, deep mines host life, the bottom of the ocean hosts life. We haven’t found any evidence for life on Mars, but at least we have identified a place that should, in principle, be able to sustain life.

– Michael Manga, Professor of Earth and Planetary Science, UC Berkeley

But the is a question that’s unlikely be to answered any time soon. Determining if the environment is at the very least amenable to life, much less actually finding evidence for life within it – or even simply reaching any of the water deposits –is going to be pretty much impossible for a good while yet. Current deep drilling techniques here on Earth for extracting oil and gas only go down to around 2 km; getting that sort of equipment to Mars and enabling it to dill down at least 11-12 km will pretty much remain the stuff of dreams for a good while to come.

 JUICE to Swing by the Moon and Earth

The European Jupiter Icy Moons Explorer (JUICE) mission will be making a first-of-its kind fly-by of the Moon and Earth this week, the first in more than 5 gravity assist manoeuvres the vehicle will make (excluding those made while orbiting Jupiter) during its mission to study the icy moons on the Jovian system.

Such manoeuvres are often used with space missions and for a variety of reasons. With JUICE, it means the craft could be flown into space using a medium-lift launch vehicle and make (and albeit relatively sedate) flight to Jupiter, involving a total of three fly-bys of Earth and one of Venus to accelerate it to a peak velocity of 2.7 km per second using the minimum of fuel and then slingshot it out to a point in space where it will intercept the Jovian system, and they use further flybys of the planet and its Moons to both slow itself down into orbit around them and then adjust its course so it can study the icy moons of Jupiter – Ganymede, Callisto, and Europa.

This first fly-by comes 16 months since the launch of the vehicle, and will be the very first Earth gravity assist which also employs the Moon as a critical component. On August 19th, Juice will as around the Moon at a distance of just 700 km (reaching the altitude at 21:16 UTC), using the Moon’s gravity to swung it onto a trajectory that will see it pass by Earth just over 24 hours later, passing over north-eastern Asia and the Pacific at an altitude of just 6,807 km on the morning of August 20th (local time) before heading back out to loop around the Sun. After this it will get a further gravity assist from Venus in August 2025 and then two more from Earth (without the Moon helping) in 2026 and 2029, that latter of which will  slingshot the vehicle on it way to rendezvous with Jupiter and its moons.

On August 15th, Juice briefly caused a stir when it was mistaken as a near-Earth object (NEO) on a potential collision course with Earth. At 27 metres across, most of which is some 85 square metres of solar arrays, Juice is a strong reflector of sunlight, and this briefly confused systems at the ATLAS Sky Survey, Hawai’i, which attempts to locate, identify and track potentially threatening NEOs. However, the system’s confusion was quickly identified as actually being the Juice spacecraft and the alert corrected.

This was actually the second time an ESA deep-space vehicle has been mistaken as a hazardous NEO; in November 2007, and as it approached Earth for a flyby, Europe’s Rosettta mission spacecraft  – also with a large span of solar arrays – was also briefly mis-identified as a NEO on a possible collision course with Earth. On that occasion, it was mis-identified by a human observer, and further manual checking was required before it was confirmed the object being tracked was actually the Rosetta spacecraft and not of any threat to Earth.

Following its arrival at the Jovian system, Juice will spend 1259 days orbiting the system, the majority of which will be in Jupiter-centric orbits that will allow it to study Ganymede, Callisto and Europa, with numerous gravity-assists of both Ganymede and Callisto used to alter its trajectory and velocity, allowing it to study them from different orbital inclinations and also to dip down into the inner Jovian system to study Europa.

However, the final 284 days of the time (from early 2035) will be spent in a dedicated orbit around Ganymede, allowing the spacecraft to complete some 6 months of dedicated studies of the moon once it has settled into a 500 km circular orbit around Ganymede. By the end of 2035, the spacecraft is expected to have expended the last of its 3 tonnes of manoeuvring propellants, bringing the mission to an end. without the ability to manoeuvre, Juice is expected to quickly fall victim to further Jupiter gravitational perturbations and crash into Ganymede within weeks of running out of propellants.

Twenty-five years ago, on July 23rd, 1999, the Chandra X-Ray Observatory was launched aboard the Space Shuttle Columbia as a part of STS-93. At the time of its launch, it was the third of NASA’s four Great Observatories, the other three being the Hubble space Telescope (HST), launched in 1990; the Compton Gamma Ray Observatory (1991–2000) and the Spitzer Space Telescope launched after Chandra, in 2003 and operating through until 2020.

Originally called the Advanced X-ray Astrophysics Facility (AXAF), Chandra can trace its history back to the mid-1970s. Originally intended for operations in an orbit similar to that of Hubble, thus making its servicing and upgrade possible using the space shuttle, the observatory went through various design changes during the 1980s and 1990s, with its overall mission being redefined in 1992. This saw Chandra have four of it planned 12 mirrors eliminated from the telescope, together with two of the six planned science payloads. To compensate for this, the telescope’s mission was revised so that it could be placed in an orbit well above Earth and well clear of the planet’s radiation belts, allowing it to have a clearer view of deep space.

Renamed in 1998 in honour of Nobel Prize-winning astrophysicist Subrahmanyan Chandrasekhar, Chandra was deployed from Columbia’s payload the same day as it launched, attached to a 2-stage Boeing  Inertial upper Stage (IUS) space launch system. Together, they represented the heaviest payload ever carried to orbit by the shuttle system, massing 22.75 tonnes.

Once the shuttle had moved to a safe distance, the IUS first stage fired for 125 seconds, boosting Chandra away from Earth (and beyond any capacity for it to be upgraded or serviced), followed by a 117-second burn of the IUS upper stage motor. The later placed Chandra into a geocentric orbit with a perigee some 14,307.9 km from Earth and an apogee of 134,527.6 km, roughly one-third of the way to the Moon.

Following a short period of commissioning, Chandra started returning data to Earth within a month of launch, and has continued to do so almost without interruption through to 2024 – although its primary mission period was placed at a conservative 5 years. Through this time, only one system on board has suffered significant damage, but it is still operational alongside the other science instruments, and only one significant glitch – lasting three days in October 2018 – when the observatory entered a safe mode as a result of a short-term issue with one of the gyroscopes used for pointing it at targets and holding it steady during observations. All science functions were fully restored once the issue had been resolved.

Over the years, Chandra’s import and discoveries have tended to be overshadowed by Hubble and, more recently, the James Webb Space Telescope (JWST). These have included the first observations of a “mid-sized” black hole, claimed to be the “missing link” between stellar-sized black holes and the super massive black holes found at the centres of galaxies; making one of the most accurate measurements of the Hubble constant; observing the most massive X-ray flare yet recorded from the super massive black hole Sagittarius A* (pronounced “Sagittarius A star”) at the centre of our galaxy; and making possibly the first observation of an object (possibly an asteroid) crossing the black hole’s event horizon; and also making potentially the first indirect observations of an exoplanet in another galaxy.

In additional to all of this, Chandra has supported Hubble in making significant observations of the planet and dwarf planets and moons in our own solar system, and also like Hubble, has benefitted the work of early career researchers, helping them to become established in the fields of astronomy, astrophysics and space science.

To mark Chandra’s 25th anniversary, NASA has issued a wallpaper featuring 25 of Chandra’s most stunning images captured in the X-ray wavelengths. The official announcement of the images can be found on the Chandra website, and the images are previewed in the video below, as well as being available for download as a wallpaper mosaic for computers.

Sadly, the celebration is a potentially bitter-sweet affair. Currently, Chandra has the ability to remain operational for at least another decade – possibly long enough to see the European Space Agency launch what might be seen as its successor, the Advanced Telescope for High-ENergy Astrophysics (Athena), which is due to be launched sometime in the early-to-mid 2030s. Unfortunately, this is may not now be the case; Chandra could cease operations within the next 12 months.

The reason for this is that NASA’s space science budget is being tightly squeezed, largely as a result of the rising costs associated with Project Artemis and returning humans to the surface of the Moon. In 2024, the space science budget had been due to get a US $500 million boost. Instead, Congress actually cut it by that amount. For 2025, Congress is looking to cut NASA’s space science directorate’s budget by almost US $1 billion.

As a result NASA has been looking at programmes to cut – and Chandra has been one to top the lists, with NASA management suggesting its US $67 million budget could be cut by 40%. The reaction to this was swift, with those managing Chandra both from within and without NASA pointing out that a cut that large would effectively end Chandra’s science mission forthwith. Thus, in an attempt to find some middle ground that would allow both Chandra and Hubble to continued to be operated, various ideas were put forward as to how Chandra’s costs could be reduced and / or how both the Chandra and Hubble science missions could be redefined, in order to allow both to continue for the next few years.

In response to this efforts, NASA authorised an Operations Paradigm Change Review (OPCR) to look at all of the suggested options and make a determination on their viability to reduce costs. The findings of this review were presented on the very day of the 25th anniversary of Chandra’s launch, during a meeting of the Astrophysics Advisory Committee, or APAC, the body, chartered to provide advice to NASA’s astrophysics programme. And the news was not good.

Having reviewed all the options weighted the costs and saving, the OPCR has essentially concluded that while they believe Chandra could be operated a a budget smaller than its present allocation, it would still require funding beyond what the new science directorate budget can afford – at least not without putting programmes and missions outside of it and Hubble at risk. Therefore, it may not be feasible for Chandra to continue from 2025 onwards.

The OPCR findings drew some frustration from APAC members, in part because APAC was itself excluded from any involvement in the OPCR process and was not given the opportunity to review the report ahead of the announcement. In response, OPCR members stated the review had to be handled on a short-term turn-around so that if a way forward could be identified and which offered a reasonable compromise on costs, it had to be published rapidly, so as to allow NASA and the agencies responsible for both Chandra and Hubble (the Chandra X-Ray Centre and Space Telescope Science Institute) to assess the overall feasibility ahead of staff layoffs across both programmes that are due to commence in September 2024.

The report does not automatically seal Shandra’s fate, options may yet arise where it is allowed to continue – such as through the support of one or both of the houses in Congress – but right now, it does make Chandra’s future appear to be grim.

SpaceX Resumes Starlink Flights with Falcon 9; Announces Dragon Splashdowns to Move back to US West Coast

In my previous Space Sunday article, I noted that SpaceX Falcon 9 flights were suspended pending the results of a Federal Aviation Administration (FAA) Mishap Investigation relating to the loss of a Falcon 9 upper stage and its Starlink payload during a July 11th/12th launch.

On July 25th, SpaceX announced the root cause of the loss had been traced to fatigue causing a a crack in a redundant “sense line” in the upper stage, resulting in “excessive cooling” of engine components, causing the rocket motor to fail. A near-term fix – removing the redundant line – has been identified pending a more in-depth fix, and this has been enough for the FAA to clear Falcon 9 to resume commercial launches. As a result, on July 27th, a Falcon 9 lifted-off from Kennedy Space Centre’s Launch Complex 39A, carrying 23 of the company’s own Starlink satellites.

Whilst successful, the flight does not mean Falcon 9 flights to the International Space Station will necessarily immediately resume. NASA still plans for a “rigorous certification” of Falcon 9 and the software associated with the sensor to which the sense line had been connected, once SpaceX has completed all modifications to the upper stage of the vehicle. As such, the agency is not committing to going ahead with the launch of the 4-person Crew 9 mission to the ISS, due to lift-off on August 18th, 2024. However, whether this also means the planned launch of an automated Cygnus resupply vehicle to the station due on August 3rd remains on hold, is unclear; NASA’s had previously indicated all Falcon 9 flights to the ISS would be suspended pending re-certification, but following the July 27th launch, the agency specifically only mentioned the Crew 9 flight.

In a separate press release, SpaceX has indicated it will be switching Dragon splashdowns to off the west coast of the United States from 2025 onwards, rather than bringing them down off the Florida coast.

The decision is in the wake of significant pieces of debris from the Dragon vehicle’s trunk (effectively the power and propulsion “service module”) surviving re-entry into the denser atmosphere to fall to ground in places as wide apart as Australia, North Carolina and Saskatchewan. The change means that from 2025, instead of being used in the initial de-orbit burn and and then jettisoned from the Dragon capsule, which then performs its own final de-orbit burn, leaving the trunk to decay in its orbit and later re-enter the atmosphere a burn up, dragon vehicles will remain attached to the trunk throughout both de-orbit burns, with the trunk being jettisoned just before both reach the re-enter interface.

This means the the capsule and trunk will come down over the Pacific Ocean, rather than passing over the North American continent, with any trunk debris surviving its re-entry hitting the water somewhat up-range from where the capsule will splash down under parachutes.

Boeing Starliner Remains at ISS Amidst More Media Alarmism

The past week saw NASA provide an update on the Boeing Starliner situation, in which the CST-100 Calypso remains docked at the International Space Station, where it has been for some 50 days, despite the first planned crewed flight of the vehicle only being intended to last some 6 days in total following its launch in early June 2024.

As noted previously in these pages, issues occurred during the vehicle flight to the ISS, when it suffered a series of thruster failures – an issue that has been dogging the Starliner programme for some time. While the vehicle, carrying astronauts Barry “Butch” Wilmore and Sunita “Suni” Williams managed to safely docked with the ISS, its return has been repeatedly delayed leading to highly inaccurate references in the media and on social media to the idea that Wilmore and Williams are somehow “stranded” in space.

This is far from the case, again as I noted as recently as June 30th (see: Space Sunday: of samples and sheltering); the delays have been purely to allow Boeing and NASA to conduct further comparative tests between systems on the ground and those aboard the Starliner docked at the ISS to better understand precisely where the issue lies. These tests are necessary inasmuch as the service module of the vehicle – which is home to the problematic thruster systems –will not be returning to Earth, but will burn-up in the atmosphere when Calypso does eventually make its return. Ergo, keeping it in space and carrying out these tests is the only means of verifying the findings of on-going Earthside investigations.

With further tests taking place over the weekend of July 27th/28th, both NASA and Boeing believe they are honing into on the root cause. Starliner has four clusters of thrusters gathered around the outside of the service module. These clusters, comprising a mix of four larger orbital manoeuvring and attitude control (OMAC) thrusters and smaller reaction control system (RCS) thrusters (28 in total, of which only one has completely failed) are housed in protective units call “doghouses”. Both the OMACs and RCS units are required during flight operations, often firing in sequence.

What appears to be happening is that under orbital conditions, pulse-firing the RCS thrusters (a rapid series of short, sharp burst of firing) immediately following the use of the OMACs thrusters in a doghouse can cause the temperatures inside the unit to rise well above anticipated levels. This causes the helium purge valves to leak, causing problems.

Because of this, engineers, together with Wilmore and Williams, have been looking to make operational changes to how the OMCS and RCS system are used – such as by reducing the number of pulses the RCS makes when fired, or by reducing the number of times OMACs and RCS need to be fired either individually or in sequence, thus preventing the temperature spikes within the doghouse units.

During the update, NASA clearly stated that if the July 27th/28th tests yield good results, then an agency-level review on clearing Starliner for a return to Earth could take place within a week of the test results being confirmed. However, this still didn’t stop some media continuing to report Wilmore and Williams as continuing to be “stuck” or “stranded” in orbit, because drama maketh the headline.

What is a “Planet”? This might sound like a catch question, but in fact it has been the cause for debate for almost two decades at least, and its roots go back as far as – wait for it – 1801.

Up until the start of the 21st century, everyone was reasonably comfortable with the idea of what a planet was: we’d discovered a total of nine making their way around our star over the previous centuries, including the somewhat oddball Pluto. The general (and informal) agreement was that a “planet” was that of a large, roundly spheroid / round object moving in an orbit around the Sun.

Then, in 1801 Ceres was discovered. Whilst tiny by comparison to the like of our Moon, it was nevertheless almost circular in shape and bumbling around the Sun in its own orbit. Hence, many argued, it was a planet – that in fact it was the so-called “missing planet” believed to exist between Mars and Jupiter. However, by 1851 the discovery of yet more bodies within this region of space had pushed the total number of “planets” in the solar system to 23; the eight large planets of Mercury through Neptune, and all these “little” planets, many of which weren’t entirely circular in shape (but others, like Juno, Vesta and Pallas) came pretty close. It was also clear the number was liable to keep on growing.

Thus, astronomers started cataloguing these smaller bodies in their own right and, effectively, the idea of the asteroid belt was born, with Ceres becoming the first asteroid within the belt to be discovered. Problem solved; not even Clyde Tombaugh’s discovery of Pluto in 1930 didn’t upset this approach too much, nor the definition of “satellite / moon”. But then in 1978, someone had to go and find Pluto’s Moon Charon, a body so large, it broke the traditional view of a “moon”, coming close to being a twin planet to Pluto. Then, in 2005, Eris was discovered, and the wheels really started coming off the wagon.

Whilst two other relatively large, “planet-like” Kuiper Belt bodies had been discovered orbiting the Sun – Quaoar (2002) and Sedna (2004) – prior to Eris, they were comparatively small and easy to lump into the “asteroid” container alongside Ceres. But Eris turned out to be around the size of Pluto, and more massive; so, either it was a planet (and was actually referenced the “tenth planet” of the solar system immediately following its discovery) – or Pluto wasn’t a planet. Cue astronomical bun fight.

The fight between classifying Eris as a planet or downgrading Pluto to “not a planet” became quite heated relatively quickly, prompting much debate within the International Astronomical Union (IAU) which wrestled mightily with the question of how all the various celestial bodies in the solar system should be formally classified – starting with was should be meant by “planet”.   In the end, and possibly fearful of the sudden blossoming of planetary bodies within the Kuiper Belt following the discovery of Eris, as had been seen 200 years ago with the asteroid belt following the discovery of Ceres, in 2006 the IAU settled on the side of downgrading Pluto’s status from “planet” to “dwarf” planet.

In doing so, the organisation also sought to ratify the term “planet”, eventually settling on three criteria, published under what id now referred to as Resolution 5B, as found within GA26-5-6. Clause 1 of which holds:

A planet is a celestial body that:

• is in orbit around the Sun;
• has sufficient mass so as to assume hydrostatic equilibrium (aka “a round shape”);
• has “cleared the neighbourhood” around its orbit.

The decision caused (and still causes) a lot of emotional upset where Pluto is concerned, and this masked a potentially bigger issue with Resolution 5B-1: be defining a planet and a “celestial body orbiting the Sun”, it immediately excluded the term being formally used with regards to planets orbiting other stars.

Oops.

In fairness, while astronomers have been locating exoplanets since 1992, by the time the IAU arrived at their definition in 2006 the number discovered was measured in the handful, so considering them didn’t really factor into the IAU’s thinking. Since then, of course, things have changed dramatically: we’re fast approaching 6,000 planets known to be orbiting other stars.

Again, being fair to the IAU, they did try to address the issue of exoplanets (the term simply means planet outside the solar system, rather than having any meaningful definition) in 2018. However, the effort never got beyond the “working” phase. In fact, the 2018 discussions revealed that even when applied to just the solar system, Resolution 5B-1 was pretty woolly and unquantifiable; something better was needed. Things weren’t much better by the time of the next IAU General Assembly in 2021.

Potentially, the best way to offer a properly unquantifiable definition for planets wherever they might be found, do this is via mathematical modelling, removing any subjectivity from how both the term and planets are defined.

This is precisely what a team from the USA and Canada has attempted to do. AS they note in their study, published in The Planetary Science Journal, they sought to break down the the potential taxonomy of planetary bodies – both solar and extra-solar – in terms of critical physical characteristics: mass, density, etc., local dynamical dominance within their orbits, the bodies they orbit (single stars, brown dwarfs, binary systems, etc.). Using mathematical models to quantify these measures, they have been able to show that celestial bodies tend to fall in to distinct clusters, and this has enabled them to develop a far more quantifiable definition of the term “planet”, thus:

A planet is a celestial body that:

a.       Orbits one or more stars, brown dwarfs or stellar remnants and
b.       Is more massive than 10²³ kg and
c.       Is less massive than 13 Jupiter masses (2.5 x 10²⁶ kg)

This definition is due to be presented at the 32nd IAU General Assembly being held in Cape Town, South Africa in August. If adopted, it will establish a meaningful framework by which planets, dwarf planets and natural satellites – wherever they might be found – can be quantitatively defined in  manner that could objectively, rather than subjectively, help shape our understanding of the universe and our place in it.

VIPER Cancelled

On July 17th, NASA announced it has cancelled its Volatiles Investigating Polar Exploration Rover (VIPER) mission due to cost increases and schedule delays.

Roughly the size of a golf cart (1.4m x 1.4m x 2m), VIPER was a relatively lost-cost (in the overall scheme of things) rover charged with an ambitious mission: to carry out extensive prospecting the permanently shadowed areas of the Moon’s South Polar Region, seeking resources and mapping the distribution and concentration of water ice. However, the project has been repeatedly hit by delays and increasing costs, both with the rover (built by NASA) and its Griffin lander vehicle, supplied by commercial space company Astrobotic Technology Inc., and which was due to fly with additional payloads to the rover.

In 2022, these delays resulted in the mission being pushed back to a late 2024 launch date from a planned 2023 date. This was then further pushed back to September 2025. At the time this decision was made, the overall cost for the rover had risen from US $250 million to US $433.5 million and would likely exceed US $450 million by the 2025 launch date. More recently, a review found that whilst the rover is largely completely, it has yet to undergo environmental testing and still lacked proper ground support systems, noting that delays with either of these could quickly eliminate any chance of meeting the 2025 launch date and push the costs up even further.

At the same time, the cost to NASA for the development of the Griffin lander has risen by over 30% (from some US $200 million to US $323 million). These are likely to rise even further as a result of NASA’s requested additional testing of the lander in the wake of the January failure with Astrobiotic’s smaller Peregrine One lunar lander, test which could have also impacted the lander’s readiness for a 2025 launch.

The problem here is that the VIPER mission can only be launched at certain times in order to capitalise on favourable lighting conditions in its proposed landing zone; any delay beyond November 2025 for mission launch would therefore mean the mission could not take place until the second half of 2026. As a result, overall costs for the mission could be nudging US $1 billion by the time it is launched. Given NASA’s overall science budget for 2025 has already been tightly constrained by Congress, this was seen as unacceptable by the review board, as it potentially meant putting other missions at risk. Ergo, the decision was made to cancel VIPER.

That said, the Griffin lander flight to the Moon will still go ahead with NASA support, allowing it to fly its planned commercial payloads, together with a payload simulator replacing the rover. In addition, NASA is also seeking to get the rover to the Moon by offering it to any USA company and / or any of NASA’s international partners willing to fly it to the Moon at their own cost. If no such offers are received by August 1st, 2024, then the rover will be dissembled and its science instruments and other components put aside for use with other missions.

NASA Confirms Use of SpaceX for ISS Deorbit Whilst Suspending  Falcon 9 Station  Launches

On July 17th, 2024, NASA supplied further information on the planned use of SpaceX hardware to de-orbit the International Space Station (ISS) when it reached its end of life in 2030, whilst simultaneously effectively suspending SpaceX launches to the space station pending its own review of Falcon 9 following the recent loss of a Falcon 9 upper stage and its payload.

NASA originally awarded the contract for the United States Deorbit Vehicle (USDV) – the vehicle that will physically de-orbit the ISS – was awarded to SpaceX on June 26th, 2024 with little in the way of specifics, other than NASA aimed to obtain the vehicle for no more than US $843 million. In the more recent statement, NASA confirmed that SpaceX will provide NASA with an “enhanced” version of their Dragon vehicle, comprising a standard capsule with a lengthened “trunk” (the service module providing propulsion and power) equipped with a total of 46 Draco motors and 16 tonnes of propellants.

Under NASA’s plans, the USDV will be launched prior to the final crew departing. At this point, the station’s orbit will be allowed to naturally decay to around 330 km, at which point the last crew will depart. The station’s orbit will then be allowed to decay for a further six months prior to the USDV being used to orient the ISS for re-entry in a manner that will see much of the station burn-up in the atmosphere, and what survives falling into the south Pacific.

The contract awarded to SpaceX is for the Dragon vehicle only, not for its launch or operation; on completion, the vehicle will be handed over to NASA to operate. However, given the 30-tonne mass of the USDV and the fact it is a Dragon vehicle makes the SpaceX Falcon Heavy a strong contender as a potential launch vehicle (unless superseded by the company’s Starship / Super Heavy combination by the time USDV is ready for launch).

In the meantime, NASA has suspended all Falcon 9 launches to the ISS pending their own reauthorisation review in the wake of the July 11th loss of a Falcon 9 upper stage and its payload of Starlink satellites.

That loss is already under investigation on behalf of the US Federal Aviation Administration, however, on July 17th, NASA confirmed it will carry out its own review once the FAA’s work in concluded, although preparations for upcoming flights – notably a launch of a Cygnus resupply vehicle via Falcon 9 due on August 3rd and the launch of the Crew 9 rotation due later in August – will continue.

The suspension of operations is normal when a launch vehicle utilised by the space agency is involved, and NASA made it clear that none of the crew currently on the ISS are in danger or at risk of running out of supplies.

SpaceX has sought to limit the impact of the FAA investigation citing that given the fault occurred in the vehicle’s upper stage and when it was entering orbit, it posed no threat to public safety and so other launches should not be discriminated against as a result. However, NASA has indicated that even if the FAA agreed with SpaceX and allowed Falcon 9 launches to continue during the mishap investigation, the NASA suspension of operations would remain in place until such time as its own review has been completed.

Crew safety and mission assurance are top priorities for NASA. SpaceX has kept the agency informed as it works closely with the Federal Aviation Administration throughout the investigation, including the implementation of any corrective actions necessary ahead of future agency missions. NASA and its partners also will implement the standard flight readiness review process to ensure we fly our crew missions as safely as possible.

NASA statement on ISS-related Falcon 9 launches in the wake of the July 11 loss of a Falcon 9 upper stage