That is an easy one… there are NINE. Er, EIGHT… Er, hang on I am going to have to count them.
#1: Vulcan… sorry, what?Vulcan is a tricky one. It appears in the 1966 debut story for Mr Dr Pat, "The Power of the Daleks (it is static electricity, yum yum)". It is the site of a struggling human colony who have made a discovery in the mercury swamps (guess what they've found). Travel to Vulcan is by rocket ship and it's all very "Dan Dare" which suggests that it might be part of colonising the Solar System, rather than anything interstellar. And the one that has always been the clincher is the DATE – the story has long been rumoured to be set in 2020, which is soooooo very early that it HAS to be a planet in the Solar System, although this date actually isn't mentioned in the TV show, it comes from the RadioTimes, so it could be questionable.
The idea of another planet closer in to the Sun than Mercury comes from the Nineteenth Century when more and more accurate measures were being taken of the orbits of the planets, and they were found to be very slightly WRONG compared to the predictions make by Mr Sir Isaac's Theory of Gravitation. The error in the prediction of Uranus' orbit led to the discovery of Neptune, and in turn the error in Neptune's orbit led to people looking for a "Planet X" further out – and eventually the discovery of Pluto in 1930 (which actually WASN'T the answer because it is not big enough; the real answer was that they had overestimated the masses of Uranus and Neptune, something we now know better thanks to the Voyager missions). At the same time, the errors in Mercury's orbit led people to guess there might be another small planet near to the Sun.
However, then along came Mr Professor Albert and said "E=MC2" among other stuff and his General Theory of Relativity showed that the Sun was BENDING the space around it and THAT was what was throwing off Mercury's orbit.
So, the jury is out on Vulcan.
#2 MercuryYup, familiar with that one – it is (now) the smallest of the "eight" planets officially recognised by the International Astronomers' board of space tourism.
#3 VenusHome planet of the Venusians (well, durr!), a people who practiced Karate and Aikido, or at least the local equivalents.
Apparently they had more that the usual number of arms and legs, and definitely more than three eyes if we are to believe Dr Who's claim that "Klokleda partha menin klatch" is a Venusian lullaby meaning "Close your eyes my darling; well three of them at least". On the other fluffy foot, Ms Professor Bernice Summerfield says that this is, in fact, one of the bawdiest ditties in the known universe.
Sadly the Venusians became extinct at some point billions of years ago. More about these unfortunate people is discovered in the Missing Adventure "Venusian Lullaby".
The planet is inhabited again – probably colonised by humans – by the "space year" 17,000 when it is attacked by the Daleks.
#4 Luna (aka The Moon)In the Doctor Who scheme of thing, the Moon is a "rogue planet" that comes barrelling into orbit in order to frighten the Silurians (aka Eocenes aka Earth Reptiles etc) into packing up their civilisation and hiding in bunkers for millions of years.
Actually, the Moon is rather similar to Mercury, if a little bit smaller, and if you are asking "where did this rogue come FROM?" you might conjecture that it was Mercury's TWIN – and stranger things have happened in this Solar System – before something or someone decided to start messing around with the arrangements of the constellation. (Remember, in Doctor Who, "constellation" appears to mean planetary system.)
Of course this would not be the first time that someone has blown the Moon out of orbit…
#5 EarthMostly Harmless
#6 MondasHome Planet (mark one) of the Cybermen.
Earth's so-called "twin planet" and it is VERY twin if the images that survive from "The Tenth Planet" have it right – it's identical to Earth (but upside-down). This is so AMAZINGLY improbable that it probably means it is artificial. Or the Earth is. One of them, anyway. This suggests the intervention of The Dæmons, since they tend to go in for experimental science on a planetary scale and we know that they have been here, with one planet being maintained as a "control" while the other is the experiment.
Or possibly it's been commissioned by the MICE.
The idea of a twin Earth was a favourite of the scientific romances (and, let's be fair, even Gerry Anderson was giving it a go as late on as the 1960s). The idea being that a planet could be in orbit at Lagrange 3 i.e. exactly opposite on the far side of the Sun and we would never see it, what with the Sun being in the way.
The usual assumption for Earth and Mondas, though, is the two planets orbiting a common barycentre, so that one can be seen from the other like a really BIG moon.
For some reason, Mondas goes out of its orbit and "drifts to the edge of space". Being an unpowered planet (at least on the way out) this suggests that the "edge of space" means the edges of the Solar System five trillion kilometres away.
The temptation to tie in Mondas going out of orbit with the arrival of the Moon in some sort of INTERPLANETARY BILLIARDS is almost irresistible.
It would open up several intriguing possibilities: did the Silurians and the early Pre-Cyber Mondasians know about each other? And did any of the Mondasians try evacuating to Earth? Is it possible that humans are their descendents and NOT native to Earth after all?
For counting purposes, getting blown to pieces in 1986 may disqualify it.
#7 MarsHome planet of the Ice Warriors. And possibly at least one earlier species, according to Dr Who in "Image of the Fendahl". Civilisations on Mars seem to have a habit of being obliterated.
Assuming that the native Martians DID die out first, and that the Ice Warriors arrived from somewhere else, the question has to be where? And the obvious answer looks like being Earth (again). Great big bipedal reptiles, who does THAT sound like? Is it in fact the case that we are seeing a THIRD cousin of the Silurians, this time with an adaptation for COLD in the way the Sea Devils have an adaptation for WATER? Perhaps as the Moon bore down on the planet, and the main bulk of their race were going into hibernation, a breakaway faction took off in rockets for the relative safety of Mars.
If they aren't the original natives, then who were? The answer again is obvious: they must have been the insect-like creatures seen in "Quatermass and the Pit", what with Professor Quatermass and the British Rocket Group apparently existing in the Doctor Who universe. They, of course, wiped themselves out in a frenzy of ethnic cleansing… or were they driven to it?
#8 ThanatosHome planet of the Fendahl.
The planet was devastated by the Fendahl before it transmitted itself to Mars in the form of (probably) a skull. The Time Lords, trying to trap it, time looped the planet, but the Fendahl was already gone.
Interestingly, the Fendahl is a gestalt entity consisting of a core and twelve supporting Fendahleen – essentially it has thirteen lives. You would have to expect that the Fendahl is a literally lethal mutation of a naturally evolved gestalt species – that is, the Death Eater is a single individual, not one of a species, and it wiped out all other life on the planet, before going on to Mars and then starting work on Earth. The Fendahleen creatures resemble giant caterpillars or insect larvae and this is also suggestive of a mutation arresting a natural cycle of pupa and rebirth into an adult form (a dozen butterfly-like "Fendahlira" perhaps).
It would be total speculation to wonder just who might have come along and stolen the ability of an individual to undergo twelve rebirths, and what that might have done to the individual from whom they stole it. Though it might give them an even more important reason for Time Looping the evidence.
The novel "The Taking of Planet Five" (ironic, muchly, in this counting scheme) has Time Lords from the future Time War try to break open the Time Loop in order to release the Fendahl Predator – what they call a memeovore, meaning that it eats ideas! – to use as a weapon against their Enemy (cough cough the Daleks). Actually this is a scheme within a scheme, and the Predator is actually turned loose on the conceptual entities known as Celestis (formerly the Celestial Intervention Agency). Since they are literally made of ideas, this destroys them rather a lot.
Of course, there shouldn't actually BE a Fendahl Predator on Thanatos, because the Fendahl isn't actually THERE to be predated.
(Strictly speaking, planets are named after Roman Gods, and Thanatos is Greek, but the Roman equivalent would be Mors, and that would be confusing with Mars just next door.)
The asteroid belt is said to be the remains of Thanatos from when the planet broke up, though this is not true, because there just isn't enough mass in all the asteroids – even the really big ones like Ceres – to add up to a planet.
People used to think that there OUGHT to be a planet there because it would satisfy a nice GEOMETRIC PROGRESSION in the distances from the sun to each planet: Earth is about 125 million kilometres from the Sun; Mars is roughly two-hundred-and-fifty million kilometres; spot the gap; Jupiter is a billion kilometres; and Saturn is two billion kilometres away.
Nowadays, though, we think that they are just "left over bits".
#9 JupiterLargest planet of the Solar System, with over sixty moons counted to date.
Or twelve, if you are in the mid-1970s and/or mid-2870s, according to "Revenge of the Cybermen".
The BBC novel "To the Slaughter" tries to explain this numerical embarrassment by having a concept artists and solar decorator blow up the supernumerous satellites in an act of cosmic Feng Shui. You can tell that it was time to have a new series on the telly, can't you.
The atmosphere of Jupiter is said to be a battleground between two alien viruses in the novel "Fear Itself". This may or may not be supposed to be an origin for the Virus found in space in between Jupiter and Saturn in "The Invisible Enemy", which shares many features with the Fear virus, and eventually gets blown up on Saturn's largest moon, Titan.
#10 The Tenth PlanetA really cool shop in Barking, East London.
#10 VogaThe "Planet of Gold". Home planet of the Vogans.
Another "rogue planet" this one, apparently disappearing from wherever it started off in the universe during the Cyberwars and reappearing in "Revenge of the Cybermen" as a "thirteenth" moon of Jupiter.
Voga was the source of the gold used against the Cybermen in the Cyberwars. We later infer that the Cyberwars took place in the Twenty-Sixth Century as the story "Earthshock" takes place then and sees the Cybermen trying to prevent the formation of an alliance against them. At the end of the wars, the Cybermen staged a last attack on Voga and presumably blasted it across space to arrive here.
"Revenge of the Cybermen" is thought to take place in the late Twenty-Ninth or early Thirtieth Centuries based on Dr Who's assessment of Space Station Nerva's architecture when he first arrived (although at a MUCH later point in time) with Harry and Sarah in "The Ark in Space".
Actually, Voga might STILL not count as a "planet" because it is in orbit around Jupiter, thus making it a satellite.
#11 SaturnRuns rings round other planets.
#12 UranusParent planet of the moon Sycorax, possibly home of the, er, Sycorax.
This would in fact lead to a slight temporal anomaly, since the moon is named after a character, the mother of Caliban, in Shakespeare's play "The Tempest", and – at least implicitly – Shakespeare gets the idea for that from Dr Who mentioning the Sycorax to him, based on the Sycorax that he's already seen, who are named for the character who's name he's just suggested. Er, if you see what I mean.
A much LARGER moon is Oberon, suggested in several New Adventures to be the headquarters of the Order of Adjudicators, seen in "Colony in Space" and many New Adventures, perhaps most importantly "Lucifer Rising" and "Original Sin". It is heavily implied that the Adjudicators eventually turn into the Knights of the Grand Order of Oberon, as represented by excommunicated example Orcini in "Revelation of the Daleks".
Apparently, when Mr Mavic Chen tells the Daleks that the only place in the galaxy where you can mine Taranium in large enough quantities to power a Time Destructor is "one of the dead worlds of the solar system", everyone thinks he means Uranus. Given that he is already one of the CAMPEST space villains in history, it is probably wise that he did NOT say to the Daleks: "the Taranium can only be found on…"!
#13 NeptuneEven when Pluto WAS a planet, its irregular orbit would sometimes make Neptune the outermost of the Solar System. So far.
#14 PlutoBecause Pluto IS a planet in the Doctor Who universe, because Dr Who says so, and even visits it in "The Sun Makers".
Or if not…
#14 CassiusAlso in "The Sun Makers", Dr Who refers to the discovery of Cassius making Pluto no longer the outermost planet of the Solar System. The Battle of Cassius is mentioned by the late Mr Craig Hinton as crucial to the relief of Earth after the Dalek Invasion and occupation in 2157.
#14 ErisDiscovered in 2003 and named after the goddess of strife because all the fuss caused by its discovery resulted in Pluto being demoted from planet status, what with Eris actually being slightly larger. And, unlike Pluto, does not appear to be part of the Kuiper Belt.
Early reports had the planet named as "Xena", a play on the old Planet X and after the character played on telly by Lucy Lawless. Apparently Eris has a moon called Dysnomia. Dysnomia was the daughter of Eris and goddess of Lawless-ness. This is the sort of thing that is considered FUNNY in astronomical circles.
But, let's face it, it ought to be…
#14 TelosHome planet of the Cryons; home planet (mark two) of the Cybermen.
The reference in "The Invasion" to Mr Dr Pat being known to the Cybermen from "Planet 14" has long led to speculation about this "missing" adventure.
As mentioned above, it never seemed likely that the Cybermen's planet of Mondas developed interstellar capabilities and so its wanderings probably only took it within reach of local planets. The Cybermen have always been the most rubbish of Dr Who's arch enemies – while the Daleks and the Sontarans may conquer galaxies, the Cybermen almost always have trouble staying alive long enough to perish from exposure to one of their many allergies (radiation, gravity, nail varnish, emotions, gold etc.).
If the plan to build a great big engine and power Mondas back into Earth orbit wasn't working out, then a chance encounter with a distant Solar planet just as Mondas was trundling off into Interstellar Space may have seemed like a last chance to escape for some of the already converted Cyber-Mondasians.
Although Dr Who visits Telos twice – in "Tomb of the Cybermen" and "Attack of the Cybermen" – we do not find out for sure where it lies. You can assume that it's in another Solar System if you like. The rocket ship that gets Professor Parry and his team of doomed archaeologists there looks a bit Flash Gordon, but then we're back to the same argument as Vulcan being in-system.
Incidentally, Mr Tat has an interesting theory about the TIMING of "Attack of the Cybermen", pointing out that it does not make a lot of sense of "Attack" to be set on Telos in the FUTURE; and might it be contemporary with their actions on Earth, i.e. 1985. (Basically, if Commander Lytton can communicate though TIME then why would he choose to talk to the Cybermen and the Cryons, when he could dial up the Daleks and ask for a time tunnel home. OK, maybe they WERE trying to kill him last time but, hey, that could be worked out!) Just because the Cybermen HAVE a (stolen) Time Machine (two, with the Doctor's TARDIS) doesn't mean that they have time-travelled to get from Telos to Earth.
But unfortunately the Cyber-leader refers to the Cyber-Controller being "damaged" in the events of "Tomb" which definitely has to be in the future.
Anyway, how many planets is that? I have LOST COUNT!