Doctor Who: 10 big questions after Praxeus

Starting with…

Why did Adam Lang's shuttle crash, and why were the aliens experimenting on him?

Though it initially appears that “automatic system failure” is what felled Adam Lang’s space capsule, Suki (Molly Harris) later reveals that her own crew lost control of their alien shuttle and crash-landed on Earth, which in turn sent out “pulses and energy from the bottom of the ocean… enough to down and frazzle a returning space capsule.”

So in addition to infecting Earth with Praxeus, the crash of Suki’s ship in turn brought down Adam’s capsule. There’s actually a clue to this just before we glimpse the beleaguered capsule for the first time, with the Doctor’s narration noting that planet Earth is connected “from the depths of the oceans to the edge of the atmosphere” – not just poetry, but a hint at what’s affecting Lang’s capsule.

Suki and her crew then decided to take advantage of Adam having crashed into the Indian Ocean, transporting him from the site of their own wreck to their secondary HQ in Hong Kong, where they used him as a guinea pig in their efforts to find a cure for Praxeus. Morgan Jeffery

How did Adam text Jake? (And if he didn't, who did?)

Early in the episode, Warren Brown’s ex-cop Jake receives a text from an unknown number, revealed to be from his estranged astronaut husband Adam (McNulty) shortly after he’s been declared missing.

The text soon takes Jake to Hong Kong, where he finds Adam hooked up to a mysterious machine… but how on Earth did he manage to send a text? Did he have a handy mobile phone in his spacesuit? Why was it from an unknown number? The episode never actually addresses this, so for now we’ll have to assume one of the mutated aliens experimenting on him had a good data plan. Huw Fullerton

Why didn't the aliens' life signals register?

"I scanned this building for life signals before I sent you here," the Doctor says, after Graham (Bradley Walsh), Yaz and Jake are attacked by aliens in Hong Kong. "So why didn't these register?"

She suggests that it could be their suits "blocking the scan" – pretty impressive stuff, suggesting these extra-terrestrials have access to tech that means they can hide even from Time Lords.

Then again, the TARDIS was able to detect "active alien tech" in Hong Kong – so why could these aliens hide their life signs but not the "very unusual energy patterns" coming from their machinery? Hmmm... MJ

Does the Doctor have two brains?

We’ve always known the Doctor has two hearts – well, except when William Hartnell kept mentioning that he only had one and we all made up some reasons for that – but does she have two of something else?

At one point during Praxeus, the ongoing mystery befuddles the Doctor so much that she refers to her cerebral matter in the plural, much to the concern of her companions. Clearly, another new twist to Doctor Who canon we’ll all need to get used to… HF

What are microplastics? Are they real?

The Doctor's 'lightbulb moment' sees her realise that Praxeus is "alien bacteria homing in on microplastics because humans are full of them."

"Humans have flooded this planet with plastics that can't be fully broken down – so much so that you're ingesting micro-particles whether you know it or not," she explained. "You're poisoning yourselves as well as your planet!"

Unfortunately, this is all true – microplastics (any plastic fragment less than 5mm in length) have flooded our natural ecosystems, coming from sources including cosmetics, clothing, plastic bags, water bottles, fishing nets and industrial processes.

Because plastics degrade slowly, sometimes over thousands of years, this increases the probability them being ingested and accumulated in the bodies and tissues of many organisms... including human beings. MJ

Who are the Autons?

At one point, the Doctor name-checks an old foe as a potential source of this plastic-based pathogen, but quickly dismisses them as it’s not their usual M.O. – and of course she’s talking about classic baddies The Autons, best known as living shop window dummies who caused havoc in Christopher Eccleston’s first Doctor Who episode Rose.

Essentially plastic automatons animated by the telepathic Nestene Consciousness, the Autons appeared a couple of times in the classic series facing Jon Pertwee’s Third Doctor, where they showed off their ability to manipulate other forms of plastic – including inflatable chairs, memorably – so it’s not surprising that the current Doctor briefly thought they could have been involved in controlling the plastic-stuffed birds. HF

Wait, did Amaru just die? And who was he anyway?

This episode was absolutely stuffed with supporting characters, but one has us particularly confused. While we learned that Suki was actually an alien scientist responsible for the Praxeus virus’ spread on Earth, it’s never explained whether her assistant Amaru (Thapelo Maropefela) is also of her species, or if not why she chose to hire a human being rather than using one of her own people. Also, how did she pay him?

Later, poor old Amaru ends up being killed by the pathogen-controlled birds, and no-one even seems to notice. An ignominious end to an impressively punctual man. HF

What are gyres?

Though Yaz (Mandip Gill) thinks she’s tracked the source of Praxeus to an alien colony, the Doctor later reveals that she and her friends have been transported “a long way beneath the Indian Ocean, beneath a gyre of plastic pollution”.

“[It’s] a naturally occurring hotspot where ocean currents trap pollution,” the Doctor explains. “There are five major gyres on Earth right now.”

When Suki’s ship crash-landed on Earth, Praxeus was released, irradiated and built “a world of pure Praxeus” from the plastic in the ocean. Sea birds then got infected, in turn spreading the pathogen to humans.

All of this is loosely based on real science – there are five major ocean gyres (or vortexes) on Earth, large systems of circulating currents, and one is beneath the Indian Ocean.

These gyres are known to collect pollutants – the 'garbage patch' (as it's known) in the Indian Ocean was discovered in 2010 and is made up of elevated levels of plastics, chemical sludge and other debris. Though no alien pathogens – at least as far as we know... MJ

What is the European space agency?

You might be tempted to dismiss British astronaut Adam Lang's ventures into space as pure sci-fi – but again, there's some basis in truth.

It's true that the UK government has never developed a manned spaceflight programme, with the first seven British astronauts launching with either the American or Soviet/Russian space programmes. But in 2015, Tim Peake became the first UK government funded astronaut to spend time on the International Space Station – albeit as part of a Russian spaceflight.

Established in 1975 and headquartered in Paris, the European Space Agency is also a very real thing, with the UK having committed to contribute £374 million per year over five years to the ESA in order to fund sending more British astronauts into space by 2024.

Maybe Adam Lang will be one of them... MJ

Why didn’t anybody talk about the new Doctor or anything that happened last week?

Look, they all had a lot on. The TARDIS team was rushing around the globe, solving a mystery, battling gas-masked foes and avoiding deadly birds. There was plenty to be thinking about.

But were they really too distracted to think about the Earth-shattering revelations of the previous episode? You know, the one where there was another Doctor that the current incarnation couldn’t remember? The information that truly shook the Doctor to her core forever?

Well, as it turns out a quick T-shirt switch and a change of scenery was all she needed to take a breather. By next week she’ll have some new trousers and won’t be able to point out Gallifrey on a map. HF

Doctor Who continues on Sundays at 7:10pm on BBC One