We went out by a path that led through a big clump of flickering starflowers and then into Batwing. A whole bunch of Batwing grownups and newhairs were in their clearing banging away at a giant redlantern tree with their blackglass axes, working in the pink light of its flowers.

We walked round the edge of their clearing to Family Fence, dragged away the branches at the opening, and went out into open forest. No more shelters and campfires ahead of us now: nothing but shining trees.

Hmmmph, hmmmph, hmmmph, went the trees. Hmmmmmm, went forest. We walked for a waking under the light of the treelanterns, slashing down whatever birds and bats and fruit we could get as we went along, and finally stopped to rest at the big lump of rock called Lava Blob. Old Roger handed us out a gritty little seedcake each, made of ground-up starflower seeds, so we could have something in our bellies, and then we settled down with our backs against the rock, so we didn’t have to worry about leopards sneaking up behind us. There were lots of yellowlantern trees round there, which we didn’t get so much back in Family, and also yellow animals called hoppers that came bouncing out of forest on their back legs and wrung their four hands together while they looked at us with their big flat eyes and went Peep peep peep. But hoppers were no good to eat and their skins were no use either, so we just chucked stones at them to make them go away and let us sleep in peace.

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When we woke up, Starry Swirl was still bright bright in sky. We ate a bit of dry cake and off we went again, under redlanterns and whitelanterns and spiketrees, with flutterbyes darting and glittering all round us and bats chasing the flutterbyes and trees going hmmph, hmmph, hmmph like always, until it all blurred together into that hmmmmmmmmm that was the background of our lives.

After a few miles we came to a small pool full of shiny wavyweed and all us newhairs took off our wraps and dived into the warm water for crabfish and oysters to eat. All the boys watched Tina Spiketree diving in, and they all thought how graceful she was with her long legs, and how smooth her skin was, and how much they wanted to slip with her. But when she came up she swam straight to me, and gave me a dying oyster with the bright pink light still shining out of it.

“You know what they say about oysters, don’t you, John?” she said.

Tom’s neck, she was pretty pretty, the prettiest in whole of Family. And she knew it well well.

In another couple of hours we reached the place where Peckham Hills began to rise up out of forest of Circle Valley, and started to climb up through them by Monkey Path, which isn’t really a path, but just a way we know through the trees. The trees carried on up the slopes – redlanterns and whitelanterns and scalding hot spiketrees – and there were flickering starflowers growing beneath them, just like in the rest of forest. Streams ran through them down from darkness and ice, heading towards Greatpool, still cold cold but already bright and glittering with life. And small creatures called monkeys jumped from tree to tree. They had little thin bodies, and six long arms with a hand on the end of each. Handsome Fox shot one with an arrow, and was pleased pleased with himself, even though they were all bones and sinews and only give a mouthful of meat, because they move fast and are hard to aim at with those big blotches on their skin that flash on and off as they swing among the lanternflowers.

As we climbed up it got colder. The starflowers disappeared, the trees became smaller, and there weren’t any monkeys any more, only the occasional smallbuck darting away through the trees. And then the trees stopped and we came out from the top edge of forest onto bare ground. Pretty soon, when we’d climbed above the height of those last few little trees, we could see whole of Circle Valley spread out below us – whole of Eden that we knew, with thousands and thousands of lanterns shining all the way from where we stood on Peckham Hills to Dark shadow of Blue Mountains away in the distance, and from Rockies over the left, with the red glow of Mount Snellins smouldering in middle, to the deep darkness over to our right that was Alps. And above all of it the huge spiral of Starry Swirl was still shining down.

Of course, with no trees to give off light with their lanternflowers or to warm the air with their trunks, it was dark dark up there – you could only just barely make things out in the starlight and the light from the edge of forest – and it was cold cold, specially on our feet. But us newhairs dared each other to run up as far as the snow. The ice felt like it was burning, it was so cold, and most kids took ten twenty steps, yelled and came running down again. But I took Gerry right up to the ridge of the hill and then, ignoring Old Roger yelling at us to come back, went far enough down the other side so that the others couldn’t see us.

“We’ve made our point now, haven’t we, John?” Gerry said, shivering. We only had waistwraps on, and buckskins round our shoulders, and our feet were hurting like they’d been skinned. “Shall we go back down to rest of them now?”

My cousin Gerry was about a wombtime younger than me – his dad was giving his mum a slip, in other words, about the time that I was born – and he was devoted to me, he thought I was wonderful, he’d do just about anything I asked.

“No, wait a minute. Wait a minute. Be quiet and listen.”

“Listen to what?”

“To the silence, you idiot.”

There was no hmmmmmmmm of forest, no hmmph, hmmph, hmmph of pumping trees, no starbirds going hoom, hoom, hoom in the distance, no flutterbyes flapping and flicking, no whoosh of diving bats. There was no sound at all except a quiet little tinkle of water all around us coming out from under the snow in hundreds of little streams. And it was dark dark. No tree-light up there. The only light came from Starry Swirl.

We could barely make out each other’s faces. It made me think about that place called Earth where Tommy and Angela first came from, way back in the beginning with the Three Companions, and where one waking we would all return, if only we stayed in the right place and were good good good. There were no lanterntrees back there on Earth, no glittery flutterbyes or shiny flowers, but they had a big big light that we don’t have at all. It came from a giant star. And it was so bright that it would burn out your eyes if you stared at it.

“When people talk about Earth,” I said to Gerry, “they always talk about that huge bright star, don’t they, and all the lovely light it must have given? But Earth turned round and round, didn’t it, and half the time it wasn’t facing the star at all but was dark dark, without lanterns or anything, only the light the Earth people made for themselves.”

“What are you talking about, John?” Gerry said, with his teeth chattering. “And why can’t we go back down again if you just want to talk?”

“I was thinking about that darkness. They called it Night, didn’t they? I’m just thinking that it must have been like this. What you get up here on Snowy Dark: it’s what they would have called Night.”

© Chris Beckett

This is an extract from by Chris Beckett (Corvus), the November read for the New Scientist Book Club. Sign up for the club here, and join the discussion on Discord .

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It is the refrain of teachers everywhere preparing their students for standardised tests: “Make an educated guess.” An answer is always better than no answer, they say, and if you can apply what you know to the question to rule out some of the choices, even better. Of course, scientific research isn’t a multiple-choice exam, and its bedrock is the idea that an educated guess without solid evidence just isn’t good enough. But the concept is still a useful one, particularly when our questions outpace the technology we currently have to answer them.

The key part of the phrase “educated guess” is the first word. Put another way, a guess based on nothing may be worse than no guess at all. “But Leah,” I hear you asking, “Do you have a framework, or a favourite example, for educated guesses?” And just because you are clamouring for it, and I’m the kind of person who has favourite equations, I will tell you about it. The Drake equation, which turns 65 years old next month, is an incredibly useful tool for framing our thinking about life in the cosmos – even though, at its core, it is simply a method for making an educated guess.

Astrobiologist Frank Drake came up with his eponymous equation in 1961, before convening the first scientific conference on the search for extraterrestrial intelligence (SETI). According to written by his daughter, science journalist Nadia Drake, he sketched out the equation on a bit of a whim to get the few attendees of the meeting talking and was, even into his later life, astonished by how important it is now considered.

The equation has seven key terms, and when multiplied together, they provide an estimate of N: the number of intelligent civilisations in the Milky Way galaxy with whom we might someday be able to communicate. It looks like this:

N = R_* × f_p × n_e × f_l × f_i × f_c × L

The first few terms are relatively simple. R_* is the rate of star formation in our galaxy, which has been measured at about 1 to 3 stars per year. The fraction of those stars with planetary systems is f_p, and we now think that number is about 1 as well – most stars seem to have planets. The number of planets per star with an environment suitable for life is n_e, and that is where things start to get more complicated. “Suitable for life” is a broad idea, and one that’s difficult to define. Even the most basic requirement – that the planet be in its star’s habitable zone, where temperatures allow liquid water on the surface – is required for Earth-like life, as far as we know, but it’s certainly possible that other lifeforms have different needs. In our own solar system, there are either 2 or 3 planets in the habitable zone, depending how you slice it – but Venus and Mars don’t seem particularly suitable for life, and there are several moons in the outer solar system that may well be.

That is the first time the equation forces us to make an educated guess. The second comes hot on its heels with f_l, the fraction of the habitable planets that go on to develop life. On this, we have an even smaller sample size. We haven’t found life anywhere but Earth, so this number could be very small, or it could be 1 – remember, this includes life that arises at any point in the history of the cosmos. But until we do find life elsewhere, it will be more of a philosophical argument than anything else. The same is true of the next two terms of the Drake equation: f_i, which denotes the fraction of life that is intelligent – the definition of which is also wily – and f_c, the fraction of intelligent lifeforms that eventually broadcast their existence into space and are thus capable of communicating with us. The final term is L, the length of time in which a civilisation of intelligent lifeforms sends detectable signals out into space. As the astronomer Carl Sagan pointed out, this depends heavily on whether such civilisations can avoid self-destruction, which isn’t something we can know for sure – but we make our best guess based on the only evidence we have: human history.

If you combine all the lowest estimates, N could be one-trillionth or even lower, implying that we are totally alone in our galaxy. If you combine the highest estimates, there could be tens of millions of civilisations in the Milky Way that we could communicate with, which to me would say it’s only a matter of time before we find them. At Drake’s original SETI meeting, the researchers set N between 1000 and 100,000,000, and the lower end of that sounds about right to me – an estimate that, like those at the meeting, is based largely on my not-particularly-scientific opinions about how long our civilisation might last.

But when it comes down to it, the number itself isn’t the important part of the equation; the important part is the process of estimating each of its terms. In doing so, we force ourselves to consider some of the biggest questions in science: How similar are other places in the universe to our own cosmic neighbourhood? How likely are those most-similar places to develop life? What is life, anyway? What does life truly need? What is intelligence? How can we search for it? And how long will we be capable of searching for it? None of those questions are answered definitively, but pondering them can help us direct our scientific research – and more than that, it gives us an idea of our place in the grand scheme of the universe. That’s why teachers tell their students to make an educated guess, and it’s why the Drake equation is still considered so important. The value in an educated guess is in taking account of what you know and what is still out there, waiting to be known.

We may be on the verge of solving the mystery of the Martian moons. On 20 October, the Martian Moons eXploration (MMX) spacecraft launches towards the larger of the two moons, Phobos, with the goal of bringing back a sample that may finally explain how Phobos and its sibling, Deimos, formed.

MMX will launch from Tanegashima Space Center in Japan. If all goes to plan, it should arrive at Mars in August 2027, entering an orbit that keeps it alongside Phobos so it can build a detailed map of the surface. Along the way, it will also observe the surface of Deimos.

Once the map is complete enough, the spacecraft’s operators at the Japan Aerospace Exploration Agency (JAXA) will use it to pick out a spot on Phobos for MMX to land. During one or two brief landings, it will take on two tasks: to drop off a small rover called IDEFIX and to pick up samples. The rover is the first anyone has ever placed on such a small cosmic body, so part of its purpose aside from scientific observations is to confirm that a wheeled rover even works on an object with such low gravity.

The samples, though, are the most important part of the mission. MMX has two different sampling devices: one that shoots a puff of gas onto the surface, blowing dust and pebbles back up into a sampling container, and another that blasts a hollow cylinder into the ground to take a sample a several centimetres deep. After the samples are taken, they will be stowed away inside the spacecraft, which will then head back towards Earth. It is expected to arrive home in 2031.

Once these samples get back to Earth and are analysed by scientists on the ground, they should finally solve the mystery of how Phobos and Deimos formed. For more than a century, researchers have debated whether the two are captured asteroids or formed from an impact on Mars, similar to how Earth’s moon formed. On first look, their shapes and surfaces resemble asteroids, but their circular orbits around Mars’s equator are more consistent with the impact hypothesis. Figuring out what they are made of should settle it once and for all.

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This will also help illuminate what the solar system was like billions of years ago when these strange moons formed. “Having the answer will help illuminate that early era when Earth and the other inner planets may have been acquiring much of their water and organic compounds,” said , part of the NASA team that is collaborating on the MMX mission, in a .

If we are very lucky, the samples from Phobos may even contain bonus bits of dust and debris from Mars itself. Impacts on the planet could have launched material into space, which would have collected on the moon’s surface and been preserved there for billions of years. That means that these samples could illuminate not just the history of Phobos and Deimos, but also of Mars.

Gatekeeping is a dirty word. For decades, the internet has steadily eroded the power of gatekeepers and democratised access to information. Attempts to resist that are seen as censorship or elitism, neither of which anyone wants to be accused of.

But our new AI era may flip the script. Social media gives anyone a voice, breaking the old model of one-to-many broadcasting from institutions, but no one is forced to listen to this cacophony. Large language models that extrude text at speed are now changing this, with institutions under a many-to-one assault by information they must attend to.

This shows up in many forms – indeed, including in literal forms, as people use AI in their bureaucratic interactions with . These systems can’t deal with the volume of information and are clogging up. The implicit gatekeepers that kept such submissions under control – time, ability, access – have fallen to AI.

The same thing is happening in science. Mathematicians are calling for more mathematicians in the face of an AI onslaught. Meanwhile, the preprint server arXiv has seen submissions double in the past two years. Although preprints aren’t formally peer-reviewed, arXiv’s small team ensures minimum standards, and it is overwhelmed. In response, it recently announced it would limit submissions to two per month – still remarkably high, with few scientists producing 24 papers a year of any quality.

A kind of gatekeeping is the only way institutions can survive the AI era

This kind of gatekeeping is the only way institutions can survive the AI era, unless we want to fully hand over the reins to AI and let it handle inputs as well as outputs. But there are good reasons not to. As we report, tools for verifying mathematical conclusions are at risk from attack by AI, so keeping a human in the loop remains the only way for us to have a handle on the truth. That goes even more so for areas that are harder to verify than mathematics, which is essentially everything. So let’s cheer on the gatekeepers – they are going to have a lot of work to do.