An egregious fallacy

In London, and indeed other big cities, pavement cyclists are a regular and unpleasant fact of life for pedestrians. For the avoidance of any doubt, by ‘pavement cyclist’ I do not mean cyclists using a shared space; I do not mean young children accompanied by a parent; and I can turn a blind eye to tourists doing walking pace on Boris bikes. No, to be clear, I mean aggressive, healthy young men, usually wearing full cycling kit, who choose to ride on the pavement even when roads are quiet or – as was often the case during lock-down – entirely free of traffic.

In common with most people, I’d rather not have a cyclist hurtle past me, barely a foot away, on the pavement. Especially now, in the middle of a pandemic and social distancing. I also take a dim view of the foul and abusive language and/or threatening behaviour that usually follows any attempt to remonstrate with these individuals.

One might imagine the response of responsible cyclists to this issue would be to roundly condemn such behaviour, but nothing could be further from the case. On forums or social media sites like Twitter the response ranges from indifference to intolerance. As night follows day, the argument is trotted out that pedestrians are more at risk from cars than they are from cyclists using the pavement or ignoring red lights. Cars, we are told, are the ‘real problem’ and pavement cycling isn’t even open to discussion.

That this is blatant “whataboutery” isn’t even the most serious flaw in this line of reasoning.

It is entirely true that more pedestrians are killed or injured by cars than by cyclists. This is a matter of elementary physics: a car has far more kinetic energy than a cyclist. Most cyclist-on-pedestrian collisions result in nothing more than a few bruises. The small number of deaths mostly involve head injuries arising from being knocked to the ground. But – and it’s a big BUT – the lifetime risk of being killed or seriously injured by a car are also small. The real issue is not death or serious injury.

Albeit the consequences are usually less serious, you are far more likely to be hit by a cyclist than by a car. I have lived in London since the 1970s and I cannot recall more than two, maybe three close calls as a pedestrian involving a car. By contrast, barely a week goes by without a pavement cyclist skimming past me at close quarters and particularly alarming incidents occur every few months on average. Quite often these near misses are only the beginning of the unpleasantness as these louts rarely take kindly to anybody challenging them.

Most people do not want to be hit by a pavement cyclist, even if no serious injury results.
Most people don’t want to have to jump out of the way of a pavement cyclist, even if no collision results.
Most people don’t want to be subjected to foul-mouthed abuse or threatening behaviour.
But above all, most people don’t want to be told that this is not the ‘real problem’.

To put it bluntly, this sort of appalling behaviour is an urban blight and the ‘real problem’ argument is an egregious fallacy.

Yet even supposedly responsible cycling organisations refuse to take the problem seriously.  A high profile incident a few years ago drew the usual Pravda-like response from the London Cycling Campaign. Elsewhere, on social media and discussion fora, complaints about inconsiderate cycling are met with the party line, or howled down if anybody exposes it for the specious nonsense that it is. Many platforms now no longer allow cycling threads because of the inability of this minority to engage in adult conversation.

About two years ago, an anonymous article appeared in the Guardian by an individual who identified as a keen cyclist but not – as he put it – a Cyclist with a big C. He was very critical of the attitude of Cyclists, and was sufficiently worried about possible repercussions that he had written anonymously. That in itself is cause for concern.

If the cycling community want the sympathy of non-cycling public – not an unreasonable thing to want – then they are going the wrong way about it. An intolerance of criticism not out of place in Pyongyang only fuels Daily Mail reader prejudices against cyclists in general.

The crescent phase of Venus

It’s not the greatest photograph you’ll ever see of Venus, but it’s the first I’ve managed to take that clearly shows the crescent phase. The Sun had just set and the sky was still very bright. The crescent was just discernible through a pair of 7×50 binoculars. Against a darker sky the dazzling brightness of Venus makes it difficult to make out the phase. I then decided to have a go with my Canon 530 zoom. Again, I have previously been unable to capture the phase against a darker sky. The 530 is a rather basic camera, and the lack of a viewfinder made it difficult to locate Venus. Eventually, I succeeded and photographed Venus against the still bright sky. I took eight images, six of which were of reasonable quality.Crescent Venus - 19 May 2020

What is a planet revisited

On 24 August 2006, the 26th General Assembly of the International Astronomical Union in Prague came up with one of the most controversial rulings in the history of astronomy:

The IAU therefore resolves that planets and other bodies, except satellites, in our Solar System be defined into three distinct categories in the following way:

A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

All other objects, except satellites, orbiting the Sun shall be referred to collectively as “Small Solar System Bodies”.

The three glaring questions arising were (1) what is meant by “cleared the neighbourhood around its orbit” since nearly all the recognised planets, including Jupiter and Earth, share their orbit with other bodies (2) what of planets orbiting stars other than the Sun, which by 2006 had already been detected in large numbers (3) why was a definition of a planet needed at all?

The last of these is the easiest to answer: the Pluto question. The status of Pluto, the smallest and outermost planet, had been questioned for some time. Pluto was discovered by American astronomer Clyde Tombaugh in 1930 after a search for an undiscovered planet that was supposedly affecting the orbit of Uranus. Similar considerations had led to the discovery of Neptune in 1846, but subsequent observations suggested that the picture was incomplete, and that more than one planet was involved. But instead of another planet the size of Neptune or Uranus, Pluto appeared to be no larger than Earth. Even this turned out to be a gross overestimate, and by the 1980s Pluto had been determined to be considerably smaller than the Moon. Its diameter is now known to be 2376.6 km (1467.8 miles) and its mass about 18 percent that of the Moon. It was far too small to have any significant affect on the orbit of Uranus. In the event, it was eventually discovered that Neptune was more massive than had been believed, and there was no need for a second planet. That Pluto should have happened to be close to where the supposed planet lay was a pure coincidence. Furthermore, Pluto is in an eccentric orbit ranging from 50 astronomical units (au) at aphelion to 30 au at perihelion, when it is closer to the Sun than Neptune. The orbital inclination to the ecliptic is 17.6 degrees. For comparison, the orbital inclination of Mercury is 7 degrees, and no other planet has an inclination greater than 2.5 degrees.

By the 1990s, it was becoming clear that Pluto was merely the largest denizen of a region known as the Kuiper Belt (more accurately the Edgeworth-Kuiper belt), extending from the orbit of Neptune at 30 au from the Sun to around 50 au from the Sun. The region is populated by icy trans-Neptunian objects (TNOs) left over from the formation of the Solar System. It was first conjectured to exist by Irish astronomer Kenneth Edgeworth in 1943 and by Dutch astronomer Gerald Kuiper in 1951. Kuiper suggested that periodically, one of these objects entered the inner Solar System to become a comet.

However, it was not until 1992 that the first Kuiper Belt object was located. It was given the provisional designation of 1992 QB1. The respectably-sized 200 km (125 mile) diameter body lies just outside the orbit of Pluto. Its discoverers wanted to name it ‘Smiley’ after John le Carré’s fictional intelligence officer, but the name had already been allocated to an asteroid to honour the American astronomer Charles Smiley. QB1 remained unnamed until 2018, when it received the name 15760 Albion (the mythological name for Britain, now associated with several football teams). Other discoveries soon followed, and over a two thousand Kuiper Belt objects are now known. These are thought to be no more than a fraction of the total.

Kuiper Belt objects fall into two main classes: ‘classical’ objects with orbits of fairly low eccentricity; and ‘resonant’ objects that are in ‘orbital resonance’ with Neptune, that is to say their orbital period and that of Neptune can be expressed as a simple numerical ratio. For example, an object in a 2:3 resonance will complete two orbits of the Sun while Neptune is completing three. The resonant objects are in rather more eccentric orbits than the classical objects, and it is believed that they were perturbed into their present orbits by Neptune as it migrated outwards from the Sun during the early history of the Solar System.

Astronomers began to take the view that Pluto was nothing more than a Kuiper Belt object in a 2:3 orbital resonance with Neptune, along with around 200 other objects. To be sure, Pluto was much larger than these other object, but that didn’t necessarily make it a planet. Neptune’s major moon Triton almost certainly started life as a Kuiper Belt object. Triton’s orbit around Neptune is retrograde, i.e. in the opposite direction to that of Neptune and indeed the majority of Solar System bodies. Retrograde satellites cannot have formed from the primordial solar nebula alongside their parent bodies and must therefore have been captured from elsewhere.  Most are small, but at 2,707 km (1,682 miles) in diameter, Triton is rather larger than Pluto.

The debate over Pluto’s status was not without precedent. On the first day of the nineteenth century Italian astronomer Giuseppe Piazzi found a star-like object that moved from hour to hour. Piazzi, who was compiling a star catalogue, thought he had discovered a comet, but soon began to suspect it might be a new planet. In the weeks that followed he observed it 24 times, but before he could complete his observations he was taken ill. By the time he had recovered, the object had disappeared into the evening twilight. However, the German mathematician Carl Friedrich Gauss was able to calculate an orbit from Piazzi’s interrupted observations and on New Year’s Eve 1801, the object was recovered by German astronomer Heinrich Olbers. The object was named Ceres after the Roman goddess of agriculture, and it was at once recognised as a new planet between the orbits of Mars and Jupiter. Three more objects were soon found, and named Pallas, Juno, and Vesta. All were recognised as planets for several decades, but then six more were discovered in the 1840s, and thereafter discoveries came in thick and fast. The four new ‘planets’ were eventually downgraded to asteroids – even Ceres, which at 960 km (597 miles) in diameter was twice the size of any of the others.

Although early Kuiper Belt discoveries were all far smaller than Pluto, after 2000 much larger objects began to turn up, including Haumea, Makemake, Varuna, Quaoar, Orcus, and Sedna. These new objects were all named for mythological names associated with creation in various traditions. Though they were still rather smaller than Pluto, all were comparable in size to Ceres or larger. It was speculated that even larger objects might be found – and so it proved.

At the time of its discovery, Sedna was the most distant Solar System object ever observed, lying at a distance of three times that of Neptune from the Sun – but it is in a highly eccentric orbit and actually spends most of its 11,400 year orbital period at even greater distances. At perihelion, it is 76 astronomical units from the Sun, but the aphelion distance is a staggering 937 astronomical units.  At that distance, even travelling at the speed of light, it would take more than five days to get there. Even when close to perihelion, Sedna lies well outside the main Kuiper Belt and its motion against the starry background is very slow. Its discovery led a team at Mount Palomar to recalibrate their image-searching software, to see if any similar objects had simply been ignored because they were moving too slowly against the background stars to be picked up. Also, given that Sedna just happened to be close to perihelion, it was likely that there were similar objects at other, further, points of their orbits.

Sure enough, on 5 January 2005, an object was discovered on plates taken some 15 months earlier (in fact ‘precovery’ images going back to 1954 would later be found not only of it but also Quaoar and Varuna). The Palomar team nicknamed the new body ‘Xena’ after the fictional TV character. Like Sedna, Xena was located beyond the main Kuiper Belt. The orbit was again highly eccentric, with a perihelion of 38 astronomical units and aphelion of 98 astronomical units, but unlike Sedna, Xena was fairly close to aphelion. The orbit was steeply inclined at 44 degrees, far more so even than Pluto. Xena was probably perturbed into its present orbit by Neptune, and it is referred to as a ‘scattered disk object’. The team then found themselves caught between the conflicting needs of best practice and priority. An announcement was not made immediately because more observations were required to permit more accurate determinations of the object’s size. Against that were fears that another team might beat them to an announcement. On 29 July 2005, the Palomar team finally went public, by which time they suspected that Xena was slightly larger than Pluto. A few months after the announcement, Xena was found to have a moon, enabling its mass to be determined. Regardless of its diameter (it eventually turned out to be fractionally smaller than Pluto), Xena was 27 percent more massive than Pluto, bringing to a head the whole debate on the latter’s status as a planet. It was obvious that if Pluto was a planet, then a more massive object like Xena had to be also. Conversely, if Xena wasn’t a planet, then neither was Pluto.

Even before the discovery of Xena, the International Astronomical Union had set up a committee to consider possible definitions of a planet. On 16 August 2006, a draft proposal was published at the IAU’s Prague conference. It stated: “A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet.” This concise and readily testable definition of a planet would have recognised Xena as a planet and retained Pluto’s status. Under this proposal, Ceres, the only asteroid large enough to qualify, stood to regain the planetary status it had lost a century and half earlier. In addition, it was proposed to elevate Pluto’s major moon Charon to planetary rank. At 1207 km (750 miles) in diameter, Charon is very large in comparison to Pluto, with 11.6 percent its mass. The two are 19,571 km (12,161 miles) apart centre to centre, but crucially Charon is not in orbit around Pluto; instead the two rotate around a common centre of gravity with a period of 6.4 days. The two are tidally locked, meaning that on either, from one hemisphere, the other hangs motionless in the sky while from the other hemisphere it is never seen at all. The Pluto-Charon system would be considered a binary planet, the only such entity in the Solar System. Had the 16 August proposal been accepted, the Solar System’s Premier League would have retained Pluto, regained Ceres, and gained Xena and Charon.

Perhaps the latter was too much for some. How could Charon be a planet when much larger moons,  including our own, were not? At all events, the 16 August proposal was rejected, and the proposal of 24 August adopted instead. Pluto’s 66-year membership of the top-flight was over, and Ceres’s hopes for a return were dashed. Wannabe Xena, having failed to gain a seat at the top table, was given the official name Eris a few days later, and the moon was named Dysnomia. Eris is the Greek goddess of discord and Dysnomia means ‘lawless’, an oblique reference to Lucy Lawless, who played Xena in the TV series. All three were given the confusing designation of ‘dwarf planet’ – with the proviso that a ‘dwarf planet’ isn’t actually a planet. It is not only confusing, it is ungrammatical. An adjective describes a noun, it doesn’t completely change its meaning. A dwarf star is still a star; a dwarf hippopotamus is still a hippopotamus, not a horse or a tiger. But, apparently, a dwarf planet is not a planet. Ditto an exoplanet, since the definition of a planet required it to orbit the Sun. At least it could be argued that ‘exoplanet’ is a noun in its own right, albeit the meaning is ‘external planet’.

It was noted that only about only four percent of the International Astronomical Union’s membership had voted on the resolution, and that most of these were not planetary scientists. Many attendees at the conference had already left before the vote was taken.

The most troubling aspect of the definition was the phrase meant by “cleared the neighbourhood around its orbit”. Jupiter shares its orbit with two clusters of asteroids known as the Trojans at its Lagrange points, with one group (‘the Greeks’) leading by 60 degrees and the other group (‘the Trojans’) trailing by 60 degrees. The asteroids have names taken from the two sides in the Trojan War, but the term ‘trojan’ is now used for any asteroid in a similar relationship with other planets. Neptune, Uranus, Mars, and Earth also have trojan asteroids.

The term ‘gravitationally dominant’ is often used in ‘explainers’ of orbit clearing. Trojan asteroids and the Kuiper Belt objects in orbital resonance with Neptune have all been marshalled into their current orbits by a gravitationally dominant planet. However, the term does not form part of the 2006 definition. But even if we incorporate gravitational dominance into the definition, a planet will still be partially defined in terms of its location, which raises a problem. In 1949, Kuiper estimated the diameter of Pluto to be 10,300 km (6,400 miles), only slightly smaller than Earth. If that figure had turned out to be correct, Pluto would still not be a planet on the new definition, despite being larger than Mars or Mercury.

While accepting that the IAU was under pressure to define a planet, the question must still be asked: do we actually need a formal definition for a word that once simply referred to bright star-like objects that, unlike the fixed stars, moved over a period of time? The word ‘continent’ lacks a formal definition, yet most would list the continents as Europe, Asia, Africa, North America, South America, Australia, and Antarctica. Similarly, Sir Patrick Moore came up with the common-sense definition that Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune are planets and everything else isn’t. He was long of the opinion that Pluto was not a planet, but just as some would combine Europe and Asia into Eurasia, or the Americas into a single continent, we could add Pluto and Eris nee Xena if we wished.

While the promotion of Charon might have been the last straw for some, a major concern was that the 16 August proposal opened up the way to planethood for objects the size of Ceres, of which there are many in the Kuiper Belt. Haumea, Makemake, Varuna, Quaoar, Gonggong (discovered in 2007), and Sedna are larger than Ceres, and Orcus is only slightly smaller. Nor is Ceres the lower limit: the asteroid Hygiea, the Saturnian moons Enceladus and Mimas, and the Uranian moon Miranda are all around half the diameter of Ceres, but they are spherical and under the 24 August ruling the moons would qualify as dwarf planets if they orbited the Sun.

However,  matters are not entirely clear-cut. The asteroids Vesta and Pallas are larger than any of these four bodies, and the Neptunian moon Proteus is larger than Mimas – yet all are irregular in shape. The Ceres/Orcus-Mimas size range also includes 67 known trans-Neptunian objects and the moons Dysnomia (Eris I) and Vanth (Orcus I).

Currently, in addition to Pluto, Eris, and Ceres, Haumea and Makemake are officially recognised as dwarf planets. Varuna, Quaoar, Gonggong, Sedna, Orcus, and Hygiea are probably dwarf planets, as are at least some of the trans-Neptunian objects intermediate between Ceres/Orcus and Mimas. If we were to adopt the 16 August proposal, the Solar System would comprise at least 14, probably 20, and potentially as many as 88 planets (including Charon).

Is 88 ‘too many’? Generations of schoolchildren have been able to name the eight (previously nine) planets of the Solar System. Even seasoned astronomers would struggle to remember 88, the majority of which do not even yet have names. But is that a reason? How many chemists could name all 118 currently known chemical elements; how many geographers could name all the 193 members of the United Nations?

I now intend to go even further than the 16 August proposal, which proposed to elevate Charon to planethood, even though it is only the twelfth largest moon in the Solar System. Two of these moons – Ganymede and Titan – are larger, albeit less massive, than Mercury. If we accept that location cannot be a determinant of whether something is or isn’t a planet, then being a moon should not disbar it. Indeed, planetary scientists often refer to Ganymede, Titan, and other large moons as planets. The seven large moons, in order of size, are Ganymede, Titan, Callisto, Io, the Moon, Europa, and Triton. In addition, there are eleven medium-sized spherical moons: Rhea, Tethys, Dione, Enceladus, and Mimas (Saturn), Ariel, Umbriel, Titania, Oberon, and Miranda (Uranus), and Charon (Pluto). This adds a further 17 planets to the roster, not counting Charon which has already been included.

At a conservative estimate, that would give us a fifty-planet Solar System. Again, just as chemical elements are grouped in accordance with the periodic table, so planets can be categorised by type. Traditionally, planets were divided between rocky Earth-type planets (Mercury, Venus, Earth, Mars) and gas giants (Jupiter, Saturn, Uranus, Neptune), but Uranus and Neptune are now classed as ice giants, composed predominantly of methane, ammonia, and water rather than hydrogen and helium. The ‘new’ planets are of many types, including:

Silicate (rocky) surface and mantle, metal core e.g. the Moon
Icy surface, silicate mantle, metal core e.g. Ganymede
Icy surface, icy mantle, silicate and metal core, e.g. Triton
Icy surface, icy mantle, silicate core, e.g. Titan
Icy surface, icy mantle, icy core e.g. Mimas

Some of the icy moons are believed to have deep subsurface oceans, including Europa, Ganymede, and Enceladus.

The IAU has no plans to revisit its definition of a planet, but nobody is under any obligation to abide by it. Pluto’s demotion was especially unpopular in Clyde Tombaugh’s home state of Illinois. The Illinois Senate passed the following resolution:

RESOLVED, BY THE SENATE OF THE NINETY-SIXTH GENERAL ASSEMBLY OF THE STATE OF ILLINOIS, that as Pluto passes overhead through Illinois’ night skies, that it be reestablished with full planetary status, and that March 13, 2009 be declared “Pluto Day” in the State of Illinois in honor of the date its discovery was announced in 1930.

 

Phobos and Deimos

They have likewise discovered two lesser stars, or satellites, which revolve around Mars, whereof the innermost is distant from the centre of the primary exactly three of his diameters, and the outermost five: the former revolves in the space of ten hours, and the latter in twenty-one and a half.”

So wrote Jonathon Swift in Gulliver’s Travels when Gulliver travels on from Lilliput to floating island of Laputa, a land inhabited by mathematicians and astronomers. Swift was writing in 1726, a century and a half before the two small Martian moons were actually discovered.

Swift’s description is surprisingly accurate. The innermost moon, Phobos, orbits at a mean distance of 9,376 km (2.76 Mars radii) from the Martian centre; the outermost, Deimos, orbits at a mean distance of 23,463 km (6.92 Mars radii) from the Martian centre. The orbital period of Phobos is 7 hrs 39 mins; that of Deimos is 30 hrs 18 min.

Inevitably, there has been speculation that Swift learned about the moons from visiting Martians. In fact, there is nothing particularly mysterious about the ‘discovery’. At the time, Jupiter was known to have four moons; Earth has one, and Mars could therefore have two. Any Martian moons had to be small and close to the planet, or they would already have been observed. Swift would have used Kepler’s laws of planetary motion to calculate the orbital periods. Voltaire, writing in 1752, also mentions two Martian moons. It is presumed that he was influenced by Swift.

The actual discovery came in August 1877. Asaph Hall was an astronomer at the United States National Observatory in Washington, DC. In 1875, he was put in charge of the Observatory’s 26-inch (66 cm) refracting telescope, then the largest refractor in the world (it would be surpassed by the 28-inch refractor at the Royal Greenwich Observatory in 1893). In 1877, Mars made a close approach to Earth, and Hall’s wife, mathematician Angeline Stickney, encouraged him to look for Martian moons. Hall himself had believed that the chance of finding any moons was so small that without Angeline’s encouragement he might have given up.

On 12 August, Hall sighted Deimos, but soon lost it due to fog rising from the Potomac River. Not until the 17th were weather condition again favourable, and he recovered Deimos on the other side of Mars to where he had first seen it. On the 18th, while waiting for Deimos to come into view, he found Phobos. Further observations confirmed the existence of the two satellites, and the discovery was  announced by the USNO Superintendent, Admiral John Rogers the next day.

Hall named the moons Phobos (fear) and Deimos (terror) at the suggestion of Henry Madan, Science Master of Eton. Madan was inspired by Book XV of Homer’s Iliad in which Ares summons Fear and Fright.

Phobos has an apparent magnitude of +11.80 and Deimos +12.45, within the range of a good amateur telescope of 25 cm (10 inch) or more.

Although by no means the smallest moons in the Solar System, Phobos and Deimos are tiny. Phobos measures 27 x 22 x 18 km (17 x 14 x 11 miles) mean diameter 22.2 km (13.8 miles) and its mass is 1.08×1016 kg, and Deimos is 15 x 12 x 11 km (9 x 7.5 x 7 miles) mean diameter 12.6 km (7.8 miles) and a mass of 2.0×1015 kg.  The surface gravity of Phobos is 0.0057 ms-2 or 5.8 x 10-4 times that of Earth and the escape velocity is 11.39 ms-1 or 41 km/hr (25 mph); for Deimos the surface gravity is 0.0030 ms-2 or 3.0 x 10-4 times that of Earth and the escape velocity is 5.56 ms-1 or 20 km/hr (12.5 mph). A high jump athlete could just about jump into space from Deimos, though not from Phobos.

Phobos orbits just  6,000 km (3,700 miles) above the Martian surface, closer to its primary than any other Solar System body, and it is only slightly further from Mars than London is from New York. It is so close to Mars that it is not visible south of 70.4°S or north of 70.4°N. The orbital period is far shorter than the Martian day of 24 hrs 37 mins, so as seen from the surface of Mars it rises in the west, moves across the sky in 4 hours and 15 minutes, and sets in the east.

The orbit of Phobos is decaying at a rate of 1.8 cm per year, meaning that it will eventually collide with Mars or be pulled apart by tidal forces. This could happen in 30 to 50 million years from now. In 1958, the Russian astrophysicist Iosif Samuilovich Shklovsky suggested that based on the braking effect of the Martian upper atmosphere and the observed rate of orbital decay, Phobos would have to be hollow – possibly a sphere with a diameter of 16 km (10 miles) but a thickness of only 6 cm (2.5 inch). The suggestion that Phobos was an alien space station cropped up in the science fiction of the time, for example Mission to the Heart Stars, by James Blish. Shklovsky was assuming a decay rate of 5 cm per years, which was later shown to be an overestimate. In fact, purely tidal effects can account for the orbital decay; because Phobos is orbiting faster than Mars rotates, these effects are pulling it down rather than pushing it further away, as is the case for Deimos. Both moons are tidally locked, keeping the same face to Mars at all times.

Phobos is heavily cratered. The largest crater, the 9 km (5.6 mile) diameter Stickney, is named for Asaph Hall’s wife Angeline Stickney. The crater takes up a substantial portion of the surface area of Phobos, and the impact that created it must have nearly shattered the moon. Hall has had to make do with a much smaller crater. Two other features, Laputa Regio and Lagado Planitia are named after places in Gulliver’s Travels. The surface also bears many grooves and streaks, typically less than 30 meters (98 ft) deep, 100 to 200 meters (330 to 660 ft) wide, and up to 20 km (12 miles) in length. The grooves were once thought to have been caused by the impact that formed Stickney, but they appear to be of different ages. One possibility is that they are ‘stretch marks’ caused by the tidal deformation of Phobos, but these are too weak to deform a solid body. The suggestion, therefore, is that Phobos is a ‘rubble pile’ surrounded by a layer of powdery regolith (loose material) about 100 m (330 ft) deep. If so, it will break up when it falls to within a distance of 2.1 Mars radii (6,800 km; 4,225 miles) of the centre at which point its feeble gravity will be overwhelmed by that of Mars. At all events, the density of Phobos is too low for it to be composed of solid rock.

Deimos is less heavily cratered than Phobos. Only two features have been given names: the craters Swift and Voltaire.

Phobos and Deimos both appear to be composed of C-type rock, similar to blackish carbonaceous chondrite asteroids. The traditional view is that they are captured asteroids, but the low eccentricity and inclination of their orbits argues against this. One possibility is that they were formed from ejecta produced a large asteroid collided with Mars.

Very little was known about the physical condition of either satellite prior to the space age. The first photographs were taken by the Mariner 7 fly-by probe in August 1969; two years later the first closeups were obtained by the Mariner 9 orbiter. The satellites have been extensively photographed since. Both have also been photographed by rovers on the Martian surface. Due to its low orbital inclination, Phobos regularly causes annular eclipses of the Sun, but as its apparent diameter from the Martian surface is only a third that of the moon, it is too small to cause a total eclipse. The eclipses last around thirty seconds.

No successful landings have yet been made on either, although the Russians have made two attempts to land probes on Phobos. Phobos 1 and Phobos 2 were launched in 1988. Phobos 1 was lost en route to Mars after a technician accidentally shut down the probe’s attitude thrusters. Phobos 2 reached Mars orbit successfully, and it returned images of both Mars and Phobos. It was then supposed to approach to within 50 m of Phobos and deploy a pair of landers, but during this phase a computer malfunction caused the probe to lose contact with Earth.

In November 2011, the Russians tried again. Fobos-Grunt (‘Phobos Ground’) was supposed to be a sample-return mission, but the spacecraft failed to leave orbit and eventually fell back to Earth. Since the failure of this mission, there have been a number of proposals for a sample return mission to Phobos, but none are likely to launch in the next few years.

Many proposals for human exploration of Mars call for landings on Phobos and Deimos as a first stage.  Human missions to the Martian moons would result in the development and operation of new technologies, many of which would be required for an eventual landing on Mars, but without the attendant complexities and risks.

Thunderbirds – the date controversy

Like many boys (and girls) in the 1960s, I was an avid fan of Gerry Anderson’s science-fiction ‘Supermarionation’ TV shows. The decade was spanned by Supercar, Fireball XL5, Stingray, Thunderbirds, Captain Scarlet & the Mysterons, and Joe 90. With the exception of the last, all found their way into the legendary boy’s magazine TV 21. Girls had Lady Penelope, featuring the eponymous Thunderbirds London Agent. Joe 90 was briefly given his own magazine, but it was eventually merged with TV 21.

A question that has exercised enthusiasts for decades is, in what year was Thunderbirds set? It is commonly assumed to have been set a hundred years in the future (i.e. in the 2060s), as were Fireball XL5, Stingray, and Captain Scarlet. Indeed, TV 21 presented all four strips as if they were current events being reported in a 2060s newspaper. But is this assumption correct?

The only series to formally establish a date was Captain Scarlet where the opening sequence informs viewers that the year is 2068 AD. In Fireball XL5, the date is established through dialogue on several occasions as being 2062. The Stingray episode The Lighthouse Dwellers establishes the year as 2065 when a dedication plaque reveals that the newly-decommissioned Arago Rock Lighthouse was in use from 1890 to 2065.

With Thunderbirds, though, matters are rather less clear cut. On several occasions during the show’s run, we are shown mocked-up newspapers where a date can just be made out – dates include 1964, 1965, 2007, and 2065. The mock-ups have news item relating to the episode pasted over an otherwise standard 1960s newspaper. Some news items of the day (for example the approach of the bright comet Ikeya–Seki of 1965) can be recognised. The first time this device was used, obviously nobody bothered to amend the date. The dates are actually difficult to see without freeze-framing, which of course was unavailable in the 1960s. Possibly it was realised that a keen-eyed viewer might notice, so dates were subsequently altered.

The only date seen in clear sight is a calendar in the very last episode to be shown, Give or take a million, which aired on Boxing Day 1966. The calendar is dated 2026. On the face of it, this is no more and no less tenuous than the Arago Rock Lighthouse dedication plaque, which is the sole indication of a date given during the entire run of Stingray. The question is, can Give or take a million be classed as a proper Thunderbirds episode? The series was just six episodes into its second season when it was abruptly cancelled after ITC boss Lew Grade failed to obtain a deal with TV networks in the United States. Give or Take a million was a Christmas show rather than a regular episode. It did not feature a rescue and the plot revolved around Brains’ snow-making machine and a kid from a children’s hospital spending Christmas on Tracy Island. To provide something vaguely resembling excitement, after a failed bank heist two crooks take shelter in a rocket that is to be used to deliver toys to the children’s hospital. On Tracy Island, the kid is shown with some (actual) Thunderbirds toys – but given the Tracys’ aversion to their machines being photographed, such toys could not have existed in the world of the TV series. As such, the canonicity of this episode is suspect, but it has started a 2065 vs 2026 debate that continues to this day.

The 2065 camp will point to Zero-X, the spacecraft featured in the movie Thunderbirds are go that went on to appear in the first episode of Captain Scarlet & the Mysterons. Zero-X, which was also given its own strip in TV 21, is the only example of a continuity between two different Anderson shows, and it implies that Thunderbirds and Captain Scarlet are set in the same universe (even if the other shows were not). Captain Scarlet, as we have seen, is set in the 2060s therefore, it is argues, so must Thunderbirds. The Anderson enthusiast blog Security Hazard makes the point “...unless the Zero-X program has been running, unaltered, for over 40 years that pretty much shuts down any thought of Thunderbirds taking place in 2026.” But given that the Zero-X project was “the most costly yet devised by man” it is entirely possible that Zero-X spacecraft could still be in service after 40 years. US Navy aircraft carriers such as the Forrestal and Kittyhawk classes remained in service for fifty years. The Boeing B-52 Stratofortress first flew in 1952 and is still in service – indeed it could remain so into the 2050s. Even the Space Shuttle was in use for thirty years.

I will now argue that both dates are wrong, and that Thunderbirds probably takes place no later than the 1990s. In the first episode, Trapped in the Sky, it is established that former astronaut Jeff Tracy was one of the first men to land on the Moon. The episode aired four years before the first actual Moon landing, but Project Apollo was well advanced by this time and a landing was planned for before the end of the decade.

Even if we ignore that reality, in the Captain Scarlet episode Lunaville 7 it is stated that humans first landed on the Moon in the 1970s (remember that Captain Scarlet and Thunderbirds are set in the same universe). So Jeff’s Moon landing must have taken place around that time. Jeff is now in his fifties, and assuming that he was in his thirties as an astronaut, then some twenty years have passed since the first Moon landings. Notably, the first attempts are being made to reach Mars (the Martian Space Probe featured in Day of Disaster and Zero-X) and there is also a crewed sample-return mission to the Sun (Sunprobe). In the 1960s, it would have seemed likely that such efforts would follow about twenty years after reaching the Moon.

Even the 2026 timeline would put the early Moon landings in the 2000s, and the 2065 timeline would delay them to the 2040s. It is difficult to believe that Gerry Anderson believed that a Moon landing lay so far in the future; also, even at the glacial speed of post-Apollo crewed spaceflight programs, humans should reach Mars well before the 2060s.

The Rise and Fall of TV 21

The 1960s will be remembered for many things, and if you were a boy at that time there is a good chance that you will remember it for Gerry Anderson as well as for the Beatles. Beginning early in 1961 with Supercar (1961-62), Gerry Anderson and his production company AP Films released a series of science-fiction themed ‘Supermarionation’ TV shows that included Fireball XL5 (1962-63), Stingray (1964-65), Thunderbirds (1965-66), Captain Scarlet and the Mysterons (1967-68), and Joe 90 (1968-69). AP Films comprised Gerry and Sylvia Anderson, cameraman Arthur Provis, production designer Reg Hill, and producer John Reed. Provis left the partnership, but the company retained its name until 1965 when it was renamed Century 21 Productions.

Fifty-five years ago today, on 23 January 1965, the London-based publisher City Magazines launched TV Century 21, a quality boy’s magazine with a unique marketing hook. Priced at 7d (old pence), it ran comic strips based on Fireball XL5 and Stingray, presented as if they were current events in a 2060s newspaper. Every edition would have a newspaper-style front page, promoting one or both strips. The publication date would be given as one hundred years in the future, beginning with Universe Edition 1 Dateline 23 January 2065. The magazine featured Lady Penelope and The Daleks as its other lead strips. Thunderbirds would not launch until September that year, so readers would probably have been unaware that Penelope was another Anderson character. The Daleks presented the early history of Dr Who’s arch enemies several years before a rather different history was revealed in the TV serial Genesis of the Daleks. The Doctor did not appear in the TV 21 strip. Supercar was not part of the canon and ran as a comedy strip for 51 episodes. The canon also included Dateline 2065, a ‘news roundup’ with snippets of news from around the universe.

The line-up at launch also included the non-canon strips Burke’s Law and My Favourite Martian. The former was soon dropped to make way for two more ‘humour’ strips: The Munsters and Get Smart. Many non-fiction articles appeared over the course of the magazine’s run. These included The World We Share (wild animal of the week, starting with the grizzly bear), and Oceans of Mystery (underwater exploration).

The Truth about Space provides a fascinating insight into what was known about the other planets of the Solar System in the mid-1960s, at a time when space probes had visited only the Moon, Mars, and Venus. The long-standing view that Mercury always kept the same side facing the Sun had recently been disproved and a ‘sensational new theory’ (and long-forgotten) had been proposed that it was an escaped moon of Venus.  This was presumably a re-use of a 1950s theory that Pluto was an escaped moon of Neptune. Pluto was then thought to be moonless and comparable in size to Earth.

The column also featured articles about the US space program and a ‘spaceman portrait gallery. Usually, these were household names like first American in space Alan Shepard and spacewalkers Alexei Leonov and Ed White. However, issue 29 (7 August 1966) featured the backup pilot for an upcoming Gemini mission, a 34-year-old former Navy pilot by the name of Neil Armstrong.

TV 21 also cashed in on the then current spy craze. Like other children’s magazines of the time, it featured a letters page – but with a difference. The Contact 21 page invited readers to become secret agents with the Universal Secret Service (USS), a secret organisation headed up by Special Agent Twenty-One aka Brent Cleever. Starting in Universe Edition 21, Twenty-One got his own strip, set 20 years before the main timeline, in the 2040s. Then an active field agent, he reported to Air Marshal Zodiac (father of Fireball XL5‘s Steve Zodiac), code-named ‘S’. This strip did much to establish the TV 21 canon, with stories expanding on how the ‘Anderverse’ came to be.

All the major planets in the Solar System have been terraformed and colonised, with the exception of Neptune. Earth has a World Government, based at Unity City in Bermuda and a World President named Nikita Bandranaik. In addition to the World Space Patrol from Fireball XL5 and the World Aquanaut Security Patrol from Stingray, the World Government fields a World Army, a World Navy, and a World Air Force. The USS is headquartered in a toy factory on the outskirts of the city of Kahra, Mars.

Nearly every country on Earth is a member of the World Government; the Eastern European state of Bereznik is a notable exception. In one of his early adventures, Special Agent Twenty-One helps a group of rebels to overthrow the right-wing military government in Britain. The rebel leader proudly proclaims that “Now we’re masters of our own country” and Britain subsequently joins the World Government. Remember, this story ran fifty years before the Brexit vote.

Special Agent Twenty-One’s main adversaries are Bereznik and a terrorist group known as the Solar Organisation for Revenge and Murder (SOFRAM). In another percipient story, Twenty-One determines to wipe out SOFRAM, and launches a war on terror that proves to be no more successful than that launched by George W. Bush after 9/11. Other recurring characters were the Astrans, aliens resembling large jelly-beans that maintained an at-times uneasy alliance with the Solar Empire.

The magazine was edited by Alan Fennell, who had written many of the episodes of Fireball XL5 and Stingray. The stories were illustrated by many of the leading comic artists of the day, including Vicente Alcazar, Frank Bellamy, John Cooper, Gerry Embleton, Ron Embleton, Richard E. Jennings, Mike Noble, Ron Turner, and Keith Watson.

TV 21 was an immediate success, not least of all because Fireball XL5 and Stingray slotted neatly into its carefully constructed universe. But Thunderbirds was not such a good fit. In the Thunderbirds universe, there were no colonies on the other planets of the Solar System and attempts were still being made to reach Mars. Possibly this explains the delay before Thunderbirds made its appearance in TV 21. The series began running on the ITN network in September 1965, but it did not make it onto the pages of TV 21 until January 1966. At the same time, Lady Penelope was given her own magazine.

One solution to the continuity problem might have been to avoid stories involving the spacecraft Thunderbird 3. Throughout the entire run of the television series, it only featured in three rescues and only one of these – Sunprobe – involved it venturing beyond Earth orbit. However, the writers of TV 21 adopted the opposite approach. In common with the other Thunderbird machines, Thunderbird 3 was portrayed as being far in advance of anything else in existence, including the World Space Patrol’s XL class ships, and undertaking missions that the World Space Patrol could not.

Many of the stories featured crossovers: for example, in one episode of Stingray, the Hood joined forces with Titan.

A problem for the publishers of TV 21 was that by late 1966, an increasing portion of the magazine’s target audience were now too young to remember Fireball XL5, or even Stingray. In the meantime, the Thunderbirds television series had been cancelled six episodes into its second season after ITC boss Lew Grade failed to obtain a deal with TV networks in the United States. The last episode, Give or Take a Million, aired on Boxing Day 1966. This meant it would be nine months before the next Anderson series aired.

To inject new blood into the magazine, the canon but non-Anderson strip Catch or Kill was introduced in October 1966, then from 21 January 1967 the Zero-X spacecraft featured in the movie Thunderbirds are Go was given its own strip. This caused even more problems with the continuity. In the movie, Zero-X made the first landing on Mars; its missions in TV 21 took it back to Mars, then Jupiter, Saturn, the asteroid belt, Mercury, and Uranus – all of which were portrayed as either uninhabited or inhabited by aliens.  Mercury was portrayed as having one side permanently facing the Sun, more than two years after this view had been disproved and reported by The Truth About Space. After exploring the Solar System, Zero-X was upgraded for interstellar travel. In what was the only ever crossover between two Anderson television shows, Zero-X later went on to appear in the first episode of Captain Scarlet and the Mysterons.

In mid-1967, another new strip, Front Page, was launched about the newspaper TV 21 in the year 2067. The main purpose of the strip was to introduce the upcoming Anderson series Captain Scarlet and the Mysterons, which debuted on ITN on 29 September 1967; when TV 21 reporter Pete Tracker investigates the secretive Spectrum organisation, it results in TV 21 being given exclusive rights to cover their missions. Captain Scarlet and the Mysterons launched as a TV 21 strip just days after it began its television run. At the same time, the Universal Secret Service was dumped in favour of Spectrum: the Contact 21 page gave way to Shades of Spectrum as readers were enrolled as Spectrum ‘Shades’ rather than USS secret agents. The magazine dropped ‘Century’ from its masthead to become simply TV 21, the name by which it had in any case long been known. The Spectrum logo was added to the masthead and ‘front page stories’ almost always promoted the current Captain Scarlet story. Two months later, the ‘newspaper’ concept was abandoned altogether, with Captain Scarlet moving to the front page from issue 155, published on 6 January 1968. Fireball XL5 was downgraded to black-and-white, it briefly became a text story, and then it was dropped altogether. Stingray was replaced by an interminable story, also now in black-and-white, about Troy Tempest’s attempts to clear his name after being falsely accused of shooting down a World Air Force jet.

This new format proved unpopular with readers and after issue 213 the newspaper format returned, along with a masthead reading “First with the Space and Spy News”. But it failed to halt the decline. The problem, ultimately, was that the later Anderson shows could not readily be accommodated into the ‘Anderverse’ established by the earlier ones. Rebooting the magazine with Captain Scarlet and Zero-X produced a far less coherent universe than the original; one that never captured readers’ imagination in the same way.

From issue 192, TV 21 merged with TV Tornado to become TV 21 and TV Tornado and in September 1969, from issue 242, it merged with Joe 90: Top Secret to become TV 21 and Joe 90. The issue number was reset to 1 and the price – unchanged at 7d  since the beginning – now went up to 8d. The most recent Supermarionation show, Joe 90, had been given its own magazine, but was merged into its parent after just 38 issues. The merger brought with it strips based on such non-Anderson shows as Star Trek and Land of the Giants. By now, in an attempt to compete with football-themed magazines, more football-related material had been introduced including Super League, a strip about Manchester Eagles FC (a thinly disguised Manchester United) in the 2060s. The only Anderson strips to survive the merger were Thunderbirds and Joe 90, both now in black and white. After 37 issues, the title reverted to TV 21 and the Joe 90 strip ended. One issue later, the Thunderbirds strip ended, ending any connection with the Anderson universe. The front page was taken over by Star Trek.

One feature that remained constant throughout these years was the Corgi Model Club news, which promoted Corgi die-cast models (to actually join, it was necessary to purchase a model).

After 105 issues, in September 1971, TV 21 was merged into Valiant and as the junior partner in the merged publication, it effectively eased to exist. The TV 21 name was retained until April 1974, when it was finally dropped.

Could things have been different? Even before the last Anderson connection was cut, TV 21 had lost pretty well everything that had made it unique. The decline really begun with Captain Scarlet/Spectrum reboot, and that was forced upon them. TV 21‘s continuing success depended upon fresh Anderson shows that could be incorporated into the Fireball XL5/Stingray/Special Agent 21 canon – but the converse might also have been true.

While Captain Scarlet and the Mysterons was another hit (albeit much darker in tone than the earlier shows), Joe 90 was less successful than the earlier Supermarionation shows (it wasn’t helped by at least one network running it against the BBC’s Dr Who). Its successor, the spy-themed Secret Service, was cancelled after just thirteen episodes. Two Thunderbirds feature films were made, Thunderbirds are Go and Thunderbird 6. Neither was a box-office hit. After this, Gerry Anderson switched to live-action productions: the feature film Doppelganger, and the TV series UFO and Space 1999. Both retain a cult following, but UFO confused networks who couldn’t work out whether it was aimed at children or adults. Space 1999 was an ambitious attempt at a British version of Star Trek, but it was not a success and it was cancelled mid-way through its second season. Anderson had always wanted to work with live-action rather than puppets – but suppose he’d persisted with the latter?

Thunderbirds was cancelled because Lew Grade could not sell an hour-long show to the US networks. Supposing that instead of making a brand-new show (Captain Scarlet and the Mysterons) Grade and Anderson had repackaged Thunderbirds as a half-hour show? Most of the first-season stories could have been compressed into half an hour by omitting extended launch sequences & various subplots. Episodes could have featured crossovers into the worlds of the World Space Patrol and the World Aquanaut Security Patrol with special guest appearances by Fireball XL5 and Stingray. When the time came to finally retire Thunderbirds, care could then have been taken to devise a show that could be accommodated within the TV 21 canon. There is absolutely no reason why Supermarionation and TV 21 could not have lasted until well into the 1970s.

TV 21′s peak lasted for less than three years, yet it is remembered as landmark in the history of children’s magazines. The Supermarionation strips have been reprinted on numerous occasions over the last half century. The combination of exciting story lines and spectacular artwork allowed fans to enjoy the Anderson shows when they were not being shown on television in an era before DVDs, VHS, and when most television sets were still black-and-white. Many of the stories are held in the same regard as the best of the television episodes.