EVERYTHING TEXTILES: The ancient fabric that no one knows how to make

The ancient fabric that no one knows how to make

(Image credit: Drik/ Bengal Muslin)

A model wearing a muslin stole from the 19th century (Credit: Drik/ Bengal Muslin)

By Zaria Gorvett16th March 2021

Nearly 200 years ago, Dhaka muslin was the most valuable fabric on the planet. Then it was lost altogether. How did this happen? And can we bring it back?

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In late 18th-Century Europe, a new fashion led to an international scandal. In fact, an entire social class was accused of appearing in public naked.

The culprit was Dhaka muslin, a precious fabric imported from the city of the same name in what is now Bangladesh, then in Bengal. It was not like the muslin of today. Made via an elaborate, 16-step process with a rare cotton that only grew along the banks of the holy Meghna river, the cloth was considered one of the great treasures of the age. It had a truly global patronage, stretching back thousands of years – deemed worthy of clothing statues of goddesses in ancient Greece, countless emperors from distant lands, and generations of local Mughal royalty.

There were many different types, but the finest were honoured with evocative names conjured up by imperial poets, such as "baft-hawa", literally "woven air". These high-end muslins were said to be as light and soft as the wind. According to one traveller, they were so fluid you could pull a bolt – a length of 300ft, or 91m – through the centre of a ring. Another wrote that you could fit a piece of 60ft, or 18m, into a pocket snuff box.

Dhaka muslin was also more than a little transparent.

While traditionally, these premium fabrics were used to make saris and jamas – tunic-like garments worn by men – in the UK they transformed the style of the aristocracy, extinguishing the highly structured dresses of the Georgian era. Five-foot horizontal waistlines that could barely fit through doorways were out, and delicate, straight-up-and-down "chemise gowns" were in. Not only were these endowed with a racy gauzy quality, they were in the style of what was previously considered underwear.

In one popular satirical print by Isaac Cruikshank, a clique of women appear together in long, brightly coloured muslin dresses, though which you can clearly see their bottoms, nipples and pubic hair. Underneath reads the description, "Parisian Ladies in their Winter Dress for 1800".

Meanwhile in an equally misogynistic comedic excerpt from an English women's monthly magazine, a tailor helps a female client to achieve the latest fashion. "Madame, ’tis done in a moment," he assures her, then instructs her to remove her petticoat, then her pockets, then her corset and finally her sleeves… "‘Tis an easy matter, you see," he explains. "To be dressed in the fashion, you have only to undress."

Still, Dhaka muslin was a hit – with those who could afford it. It was the most expensive fabric of the era, with a retinue of dedicated fans that included the French queen Marie Antoinette, the French empress Joséphine Bonaparte and Jane Austen. But as quickly as this wonder-cloth struck Enlightenment Europe, it vanished.

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19th century satirical printmakers enjoyed highlighting the perils of muslin dresses, such as the risk of appearing nude in strong sunlight, wind or rain (Credit: Alamy)

By the early 20th Century, Dhaka muslin had disappeared from every corner of the globe, with the only surviving examples stashed safely in valuable private collections and museums. The convoluted technique for making it was forgotten, and the only type of cotton that could be used, Gossypium arboreum var. neglecta – locally known as Phuti karpas – abruptly went extinct. How did this happen? And could it be reversed?

A fickle fibre

Dhaka muslin began with plants grown along the banks of the Meghna river, one of three which form the immense Ganges Delta – the largest in the world. Every spring, their maple-like leaves pushed up through the grey, silty soil, and made their journey towards straggly adulthood. Once fully grown, they produced a single daffodil-yellow flower twice a year, which gave way to a snowy floret of cotton fibres.

These were no ordinary fibres. Unlike the long, slender strands produced by its Central American cousin Gossypium hirsutum, which makes up 90% of the world’s cotton today, Phuti karpas produced threads that are stumpy and easily frayed. This might sound like a flaw, but it depends what you’re planning to do with them.

Indeed, the short fibres of the vanished shrub were useless for making cheap cotton cloth using industrial machinery. They were fickle to work with, and they’d snap easily if you tried to twist them into yarn this way. Instead, the local people tamed the rogue threads with a series of ingenious techniques developed over millennia.

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The full process involved 16 steps, each of which was so specialist, it was carried out by a different village around Dhaka, which was then part of Bengal – some in what is now Bangladesh, some in what is now the Indian state of West Bengal. It was a true community effort, involving the young and old, men and women.

First, the balls of cotton were cleaned with the tiny, spine-like teeth on the jawbone of the boal catfish, a cannibalistic native of lakes and rivers in the region. Next came the spinning. The short cotton fibres required high levels of humidity to stretch them, so this stage was performed on boats, by skilled groups of young women in the early morning and late afternoon – the most humid times of day. Older people generally couldn’t spin the yarn, because they simply couldn’t see the threads.

Dhaka muslin was a favourite of Joséphine Bonaparte, the first wife of Napoleon, who owned several dresses inspired by the classical era (Credit: Alamy)

"You'd get tiny, tiny little joins between the cotton fibres, where they were linked together," says Sonia Ashmore, a design historian who authored a book about muslin in 2012. "It lent the surface a kind of roughness, which gives a very nice feel."

Finally, there was the weaving. This part could take months to complete, as classic jamdani designs – mostly geometric shapes depicting flowers – were integrated directly into the cloth, using the same technique that was used to create the famous royal tapestries from medieval Europe. The result was a minutely detailed artwork rendered in thousands of silvery, silky strands.

An Asian wonder

The region’s Western customers found it hard to believe that Dhaka muslin could possibly have been made by human hands – there were rumours that it was woven by mermaids, fairies and even ghosts. Some said that it was done underwater. "The lightness of it, the softness of it – it was like nothing we have today," says Ruby Ghaznavi, vice president of the Bangladesh National Craft Council.

The same weaving process continues in the region to this day, using lower-quality muslin from ordinary cotton threads instead of Phuti karpas. In 2013, the traditional art of jamdani weaving was protected by Unesco as a form of intangible cultural heritage.

But the real feat was the thread counts that could be achieved.

It was all going so well – then the British turned up

Higher thread counts are seen as desirable because they make materials softer, and tend to wear better over time – the more strands there are to begin with, the more there will remain to hold the fabric together when some begin to fray.

Saiful Islam, who runs a photo agency and leads a project to resurrect the fabric, says most versions made today have thread counts between 40 and 80 – meaning they contain roughly that number of criss-crossing horizontal and vertical threads per square inch of fabric. Dhaka muslin, on the other hand, had thread counts in the range of 800-1200 – an order of magnitude above any other cotton fabric that exists today.

Though Dhaka muslin vanished more than a century ago, there are still intact saris, tunics, scarves and dresses in museums today. Occasionally one will resurface at a high-end auction house such as Christie’s and Bonhams, and sell for thousands of pounds.

A colonial shambles

"The trade was built up and destroyed by the British East India Company," says Ashmore.

Long before Dhaka muslin was draped over aristocratic women in Europe, it was sold across the globe. It was popular with the Ancient Greeks and Romans, and muslin from "India" is mentioned in the book The Periplus of the Erythraean Sea, authored by an anonymous Egyptian merchant around 2,000 years ago.

Dhaka muslin came in thread counts up to 1,200, but the highest achieved in recent years is 300 (Credit: Drik/ Bengal Muslin)

The Roman author Petronius may have been the first person on record to raise an eyebrow over its transparency, writing: "Thy bride might as well clothe herself with a garment of the wind as stand forth publicly naked under her clouds of muslin." Over the coming centuries, the fabric is praised in the works of the renowned 14th-Century Berber-Moroccan explorer Ibn Battuta and the prolific 15th-Century Chinese voyager Ma Huan, as well as many others.

But the Mughal era was arguably the fabric’s heyday. The South Asian empire was founded in 1526 by a warrior chieftain from what is now Uzbekistan, and by the 18th Century it ruled across the entire Indian subcontinent. During this period, muslin was traded extensively with merchants from Persia (modern-day Iran), Iraq, Turkey and the Middle East.

The cloth was thoroughly endorsed by Mughal emperors and their wives, who were rarely painted wearing anything else. They went so far as to bring the best weavers under their patronage, employing them directly and banning them from selling the very finest cloth to others. According to popular legend, its transparency led to yet more trouble when the emperor Aurangzeb scolded his daughter for appearing in public naked, when she was, in fact, ensconced in seven layers of it.

It was all going so well – then the British turned up. By 1793, the British East India Company had conquered the Mughal empire, and less than a century later the region was under the control of the British Raj.

Dhaka muslin was first showcased in the UK at The Great Exhibition of the Works of Industry of All Nations in 1851. This spectacular event was the brainchild of Queen Victoria’s husband Prince Albert, intended to showcase the wonders of the British Empire to their subjects. Some 100,000 objects from the farthest corners of the globe were gathered together in a glittering glass hall, Crystal Palace, which was 1,851ft (564m) long and 128ft (39m) high.

At the time, a yard of Dhaka muslin fetched prices ranging from £50-400, according to Islam – equivalent to roughly £7,000-56,000 today. Even the best silk was up to 26 times less expensive.

Spinning phuti karpas cotton is notoriously tricky – if you get it wrong, the thread will snap (Credit: Drik/ Bengal Muslin)

But while Victorian Londoners were fawning over the fabric, those who produced it were being pushed into debt and financial ruin. As the book Goods from the East, 1600–1800 explains, the East India Company first started meddling with the delicate process of manufacturing Dhaka muslin in the late 18th Century.

First the company replaced the region’s usual customers with those from the British Empire. "They really put a stranglehold on its production and came to control the whole trade," says Ashmore. Then they came down hard on the industry, pressurising the weavers to produce higher volumes of the fabric at lower prices.

"You needed such a special skill to convert it [Phuti karpas] into cloth," says Islam. "It's a very arduous, expensive process – and at the end of the day, after all that you'd only get about eight grammes of fine muslin for one kilogramme of cotton."

As weavers struggled to keep up with these demands, they fell into debt, explains Ashmore. They were paid upfront for the cloth, which could take up to a year to make. But if the fabric was not considered to be up to the required standard, they would have to pay it all back. "They could never really keep up with these debt repayments," she says.

The final blow came from competition. Colonial enterprises such as the East India Company had been engaged in documenting the industries they relied on for years, and muslin was no exception. Every step of the process of making the fabric was recorded in meticulous detail.

As the European thirst for luxury fabrics increased, there was an incentive to make cheaper versions closer to home. In the county of Lancashire in northwest England, the textile baron Samuel Oldknow combined the British Empire’s insider knowledge with state-of-the-art technology, the spinning wheel, to supply Londoners with vast quantities. By 1784, he had 1,000 weavers working for him.

The team at Bengal Muslin enlisted the help of local villagers during the search for the lost plant (Credit: Drik/ Bengal Muslin)

Though the British-made muslin didn’t come close to Dhaka’s original – it was made with ordinary cotton, and woven at significantly lower thread counts – the combination of decades of mistreatment and a sudden decline in the need for imported textiles killed it off for good.

As war, poverty, and earthquakes struck the region, some weavers switched to making lower-quality fabrics, while others became full-time farmers instead. In the end, the whole enterprise collapsed.

"I think it’s important to remember that it was really a family occupation – we often talk about the weavers and how fantastic they were, but behind their work was the women, doing the spinning," says Hameeda Hossain, a human rights activist who has written a book about the muslin industry in Bengal. "So the industry involved a lot of people."

As the generations passed, the knowledge of how to make Dhaka muslin was forgotten. And with no one to spin its silky threads, the phuti karpas plant, which had always been hard to tame – no one had been able to grow it away from the Meghna river – retreated back into wild obscurity. The legend of the loom was no more.

A second chance

Islam was born in Bangladesh and moved to London about 20 years ago. He first became aware of Dhaka muslin in 2013, when the company he works for – Drik – was approached about adapting a British exhibition on the material for a Bangladeshi audience. They felt that it was lacking in detail, so they conducted their own research.

Over the next year, Islam and colleagues met people from the local craft industry, explored the region where it had been produced, and looked for tangible examples of Dhaka muslin at museums in Europe. "The V&A has a superb collection with hundreds of pieces of it," he says. "And if you go to the English Heritage Trust they've got 2,000 pieces. And yet Bangladesh didn't have any."

The team eventually curated several exhibitions on the subject, commissioned a film and published a book, authored by Islam. At some point, they started to think that maybe, just maybe, it might be possible to bring the legendary fabric back. Together they founded Bengal Muslin, a collaborative enterprise aimed at doing just that.

Resurrected phuti karpas cotton plants look identical to the kind used to grow Dhaka muslin hundreds of years ago (Credit: Drik/ Bengal Muslin)

The first task was to find a suitable plant. Though there are no phuti karpas seeds in any collection today, they found a neat booklet of its dried, preserved leaves at the Royal Botanic Gardens, Kew, from the 19th Century. From this, it was possible to sequence its DNA.

Armed with their target’s genetic secrets, the team went back to Bangladesh. They looked at historical maps of the Meghna river and compared them to modern satellite images to see how its course had changed over the last 200 years, and find the best spots for potential candidates. Then they hired a boat and scoured its immense breadth – it’s 12km (7 miles) wide in places – for wild plants that resembled old drawings.

Any promising options were sequenced and compared to the original. Eventually they found a 70% match – a dishevelled shrub which may have had phuti karpas ancestors.

To grow it, they initially settled on a plot of land on a small island in the middle of the Meghna, in Kapasia, 30 km (19 miles) north of Dhaka. "It was a very ideal spot. The land is fertile because it was formed through the accumulation of river sediment," says Islam. It was there that in 2015, they planted some test seeds. Soon there were orderly rows of pluti karpas among the dry earth – the first to be cultivated for more than a century.

The team harvested their first batch of cotton the same year. Though they didn’t yet have enough of the resurrected plants to make 100% authentic Dhaka muslin, they collaborated with Indian spinners to combine ordinary and phuti karpas cotton into a hybrid thread. Next it was time for the weaving – and this proved to be trickier than expected.

Because there are still weavers in Bangladesh making jamdani muslin, albeit coarser versions at lower thread counts, initially Islam hoped to simply upgrade their skills and teach them how to produce a higher-quality product that’s closer to the old fabric.

Many of the skills needed to make Dhaka muslin have been lost which makes matching the quality of the fabric a challenge (Credit: Drik/ Bengal Muslin)

"But none of them wanted to work on this, as a matter of fact," says Islam. When he told them he wanted to make 300-thread count saris, "they all said that this is crazy".

"They said: 'Thank you very much for telling us that story and heritage, but no thanks’," he says. Out of the 25 people he approached, one eventually agreed.

Most weavers in the region are poor, and work in simple huts. So Al Amin, now their master weaver, agreed to have temperature controls and humidifiers added to his workshop, to create the specific conditions needed for making this tricky fabric. Meanwhile some of the 50 or so tools required were no longer available, so the team made their own. One example is the shana, a piece of bamboo cut to have thousands of artificial teeth that can keep the thread in place while it’s worked.

Six gruelling months, many more improvisations and plenty of snapped threads later, Amin had made a 300 thread count sari – nowhere near the original Dhaka muslin standard, but significantly higher than any weaver had achieved for generations. "He had the dogged patience that was needed to work with us," says Islam. "We contributed 40% of the effort, but the rest came from him."

Fast-forward to 2021 and the team have made several saris from their hybrid muslin, which have already been exhibited all over the world. Some have been sold for thousands of pounds – and Islam feels the reception they received proves the fabric has a future. "In this day and age of mass production, it's always interesting to have something special. And the brand is still powerful," he says.

Today the team have plants growing continuously, though they were forced to abandon the old farm plot due to flooding issues. Now they’re growing the resurrected phuti karpas on a nearby riverbank, which has the added benefit of being accessible without a boat. Islam hopes that one day they’ll be able to make a pure Dhaka muslin sari at an even higher thread count.

As it happens, so does the Bangladeshi government, who have given the project their backing. "It’s a matter of national prestige," says Islam, who is also keen to upgrade the country’s image. "It’s important that our identity is not poor, with a lot of garment industries, but also the source of the finest textile that ever existed," he says.

Who knows, perhaps soon a new generation will be wearing this ancient fabric – and grappling with its somewhat risqué transparency.

* Zaria Gorvett is a senior journalist for BBC Future and tweets @ZariaGorvett

This article was updated on 17 March 2021. The original version stated that the rediscovered phuti karpas were grown on an island in the middle of the Ganges, in northerm India. In fact the land was on the Meghna river, in Bangladesh.

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THE LOST INDEX | PHYSICS

If Planet Nine exists, why has no one seen it?

(Image credit: ESA/Hubble, M. Kornmesser)

An artist’s depiction of Planet Nine (Credit: ESA/Hubble, M. Kornmesser)

By Zaria Gorvett16th February 2021

Strange things are happening at the outer edges of our solar system. An object up to ten times the mass of Earth is pulling others towards it. Is it a planet, or something else?

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Percival Lowell was a man of many errors.

The 19th-Century travel writer and businessman – fabulously wealthy, perennially moustachioed, and often found in crisp three-piece suits – had read a book on Mars, and on this basis, decided to become an astronomer. Over the coming decades, he made a number of wild claims.

First up, he was convinced of the existence of Martians, and thought he had found them (he hadn't). Others had documented strange lines traversing the planet, and Lowell suggested that these were canals, built as the last attempt of a dying civilisation to tap water from the polar ice caps. He used his fortune to build an entire observatory, just to get a better look. It turned out they were an optical illusion, created by the mountains and craters on Mars when viewed through low quality telescopes.

Lowell also believed that the planet Venus had spokes – seen in his notes as spidery lines emanating from its centre (it doesn't). Though his assistants tried to find them, it seemed that only he could see this unexpected detail. It's now assumed that they were shadows cast from the irises in his own eyes, as he looked through his telescope.

But most of all, Lowell was determined to find the ninth planet in our solar system – a hypothetical "planet X", which at the time was thought to be responsible for the rogue orbits of the furthest-known planets from the Sun, the cool-blue ice giants Uranus and Neptune. Though he never set eyes on this phantom behemoth, the quest consumed the last decade of his life – and after several nervous breakdowns, he died at the age of 61.

Little did he know, the search would still be going – with a few tweaks – in 2021.

A false trail

Undeterred by his own mortality, Lowell left a million dollars to the cause of finding planet X in his will. So, after a brief interlude involving a legal battle with his widow, Constance Lowell, his observatory kept looking.

Just 14 years later, on 18 February 1930, a young astronomer was looking at two photos of star-studded skies, when he noticed a speck amongst them. It was a tiny world. He had found Pluto – for a while considered the elusive planet X.

Pluto was demoted to a dwarf planet in 2006, leaving an opening for a new ninth planet (Credit: NASA/ Johns Hopkins University /Southwest Research Institute)

Alas, it was not to be. Soon scientists realised that this could not be what Lowell was looking for – it was not nearly large enough to pull Neptune and Uranus away from their rightful positions. Pluto was just an accidental interloper, which happened to be in the area.

The final blow to planet X came in 1989, when the Voyager 2 spacecraft swept by Neptune and revealed that it's fractionally lighter than anyone had originally thought. With this in mind, eventually a Nasa scientist calculated that the orbits of the outer planets had made sense all along. Lowell had instigated a search that had had never been needed.

But just as the concept of a hidden planet was killed off, the groundwork was laid for its resurrection.

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In 1992, two astronomers who had "doggedly scanned the heavens in search of dim objects beyond Neptune" for years, according to Nasa, discovered the Kuiper Belt. This cosmic donut of frozen objects, extending just beyond the orbit of Neptune, is one of the largest features in the solar system. It's so vast, it's thought to contain hundreds of thousands of objects larger than 100km (62 miles) across, as well as up to a trillion comets.

Soon scientists realised that Pluto was unlikely to be the only large object in the outer reaches of the solar system – and began to question whether it was actually a planet at all. Then they found "Sedna" (around 40% of the size of Pluto), "Quaoar" (around half the size of Pluto), and "Eris" (almost the same size as Pluto). It became clear that astronomers needed a new definition.

We thought 'this is quite interesting – how can this be?' – Konstantin Batygin

In 2006, the International Astronomical Union voted to demote Pluto's status to a "dwarf planet", along with the newcomers. Mike Brown, a professor of planetary astronomy at the California Institute of Technology – Caltech – who led the team that identified Eris, is self-styled as the "man who killed Pluto" to this day. The ninth planet was no more.

A ghostly signature

At the same time, the discovery of these objects uncovered a major new lead in the search for a hidden planet.

It turns out that Sedna is not moving in the way everyone expected – tracing elliptical rings around the Sun, from within the Kuiper Belt. Instead, this dwarf planet takes a bizarre and unexpected path, swinging from just 76 Earth-Sun distances (roughly 11 billion k/7 billion miles) from the centre of our solar system to more than 900 (roughly 135 billion km/84 billion miles). Its orbit is so meandering, it takes 11,000 years to complete – the last time Sedna was at its current position, humans had only just invented farming.

Percival Lowell established his observatory in Flagstaff, Arizona to look for intelligent life on Mars. Eventually it was used to find Pluto (Credit: Alamy)

It's as though something is tugging at Sedna and dragging it away.

Enter a hypothetical new addition to our solar system – but not as it was thought of before. In 2016, the same Mike Brown who had slain Pluto, together with his colleague Konstantin Batygin – also a professor of planetary science at Caltech – co-authored a paper proposing a massive planet, between five and 10 times the size of Earth.

Their idea came from the observation that Sedna was not the only object out of place. It was joined by six others, and all of them are being pulled in the same direction. There are also other clues, such as the fact that each is tilted on its axis in exactly the same direction. The pair calculated that the probability of all six objects being pulled in the exact same direction, with the same tilt by chance was just 0.007%.

"We thought 'this is quite interesting – how can this be?'" says Batygin. "It was quite remarkable because such a clustering, if left alone for a sufficiently long period of time, would disperse, just due to interaction with the gravity of the planets."

Instead, they proposed that Planet Nine had left its ghostly imprint in the outer reaches of our solar system, distorting the orbits of the objects around it with its gravitational pull. Several years on, and the number of objects that fit the eccentric orbital pattern and tilt has continued to increase, "We now have around 19 overall," says Batygin.

Though no one has yet seen the hypothetical planet, it's possible to infer a surprising amount about it. As with the other objects beyond the Kuiper Belt, the orbit of the new Planet Nine would be so distorted that its farthest reach is expected to be twice as far away as its nearest – around 600 times the distance from the Sun to Earth (90 billion km/56 billion miles), vs 300 (45 billion km/28 billion miles). Scientists have also hazarded a guess at its aesthetic – icy, with a solid core, like Uranus or Neptune.

Then there's the slippery question of where Planet Nine might have come from in the first place. So far, there are three main ideas. One is that it formed where it currently hides, which Batygin dismisses as relatively unlikely because this would require the early solar system to have stretched out as far as its distant refuge.

There's also the intriguing suggestion that the ninth planet is actually an alien imposter, an object that was stolen from another star long ago when the Sun was still in the stellar cluster in which it was born. "The problem with such a story is that you're just as likely to then lose the planet upon the next encounter," says Batygin. "So, statistically, that model runs into trouble."

Neptune is currently the most distant known planet in our solar system, but there might be another lurking beyond the Kuiper Belt (Credit: Nasa/JPL)

Then there's Batygin's personal favourite, which he admits is also "not a complete slam dunk". In this scenario, the planet formed much closer to the Sun, at a time when the solar system was in its early stages and the planets were just beginning to coalesce out of the surrounding gas and dust. "It kind of hung around the giant planet formation region, before being scattered out by Jupiter or Saturn, and subsequently had its orbit modified by passing stars," he says.

An obscure hiding place

Of course, all this begs an obvious question – if Planet Nine is really there, why has no one seen it?

"I didn't have a particularly strong appreciation for just how difficult would be to find Planet Nine until I started looking together with Mike using telescopes," says Batygin. "The reason it's such a tough search is because most astronomical surveys are not looking for a single thing."

For example, astronomers would normally be looking for a class of objects, such as a particular kind of planet. Even if they're rare, if you survey a wide enough expanse of space, you're likely to find something. But hunting down a specific object such as Planet Nine is a whole different exercise. "There's only one tiny portion of the sky that has it," says Batygin, who explains that another factor is the slightly more prosaic challenge of booking time slots to use the right kind of telescope.

"Really, at the moment the only game in town for finding Planet Nine is the Subaru Telescope," says Batygin. This 8.2m behemoth – located at the summit of a dormant volcano, Maunakea, in Hawaii – is capable of capturing even the weak light of distant celestial objects. This is ideal, because the shadowy planet would be so far away, it's unlikely to be reflecting much light from the Sun.

"We have only one machine that we can use, and we get maybe three nights on it a year," says Batygin, who was fresh from a three-night run on the telescope the previous week. "The good news is that the Vera Rubin telescope is coming online within the next couple of years, and they are going to probably find it." This next-generation telescope, currently under construction in Chile, will be scanning the sky systematically – photographing the entire available view – every few nights, to survey its contents.

An intriguing alternative

However, there is one almost outrageously peculiar scenario in which the planet will never be found this way – it might not be a planet after all, but a black hole.

The Subaru telescope in Hawaii has already spotted the most distant known object in our solar system, nicknamed "Farfarout", during a search for Planet Nine (Credit: Alamy)

"All of the evidence for there being an object is gravitational," says James Unwin, professor of physics at the University of Illinois, Chicago, who first suggested the idea, along with Jakub Scholtz, a postdoctoral researcher from the University of Turin. While we're most familiar with the idea that planets exert a powerful gravitational pull, "there are other things that can generate it, which are more exotic", says Unwin.

Some plausible replacements for planet nine include a small ball of ultra-concentrated dark matter, or a primordial black hole. As black holes are among the most dense objects in the Universe, Unwin explains that it's entirely possible the latter could be warping the orbits of distant objects in the outer solar system.

The black holes we’re most familiar with tend to include “stellar” black holes, which have a mass that’s at least three times that of our own Sun, and “supermassive” black holes, which are millions or billions of times our Sun’s mass, While the former are born out of dying stars collapsing in on themselves, the latter are more mysterious – possibly beginning as colossal stars which implode, then gradually accumulate more and more mass by devouring everything in their surroundings, including other black holes.

Primordial black holes are different. They have never been observed, but are thought to originate in the hot energy-and-matter haze that formed in the first second of the Big Bang. In this uneven environment, some parts of the Universe may have become so dense, they were compressed into tiny pockets with the mass of planets.

Unwin points out that there is zero probability of the black hole being formed from a star, since they keep their potent gravitational pull – it’s just concentrated. Even the smallest stellar blackholes have masses three times that of our Sun, so it would be like having at least three extra Suns pulling at the planets in our solar system. In short, we would definitely have noticed.

However, Unwin and Scholtz say it could be a primordial black hole, since these are thought to be substantially smaller. "Because these things are born during the early stages of the Universe, the dense regions they formed from could have been particularly small," says Scholtz. "As a result, the mass contained in this black hole that eventually is formed out of it can be much, much less than a star – they even can be just a couple of pounds, like a chunk of rock." This is more in line with the predicted mass of Planet Nine, which is thought to be equivalent to up to ten Earths.

The dwarf planet Sedna has an unconventional orbit which might be explained by the gravitational pull of a massive undiscovered planet (Credit: Nasa/ JPL-Caltech)

What would it look like? Should we be worried? And could this be even more exciting than discovering a planet?

First, even primordial black holes are dense enough that no light can escape. They are the truest form of black. This means that this one would not show up on any kind of telescope that currently exists. If you were to look straight at it, the only clue to its presence would be a blank void – a tiny gap in the blanket of stars in the night sky.

Which brings us to the real snag. While the mass of this black hole would be the same as that of the proposed Planet Nine – up to 10 times Earth's – it would be condensed into a volume roughly the size of an orange. To find it would require some ingenuity.

So far, suggestions include looking for the gamma rays that are emitted by objects as they fall into black holes, or releasing a constellation of hundreds of tiny spacecraft, which might – if we're lucky – pass close enough so that they'd be pulled towards it ever-so-fractionally, and accelerate by a detectable amount.

Since the mysterious gravitational pull is emanating from the farthest reaches of our solar system, the probes would have to be sent via an Earthbound laser array, which could propel them to 20% of the speed of light. If they travelled any slower, they might take hundreds of years to arrive – an experiment that would, naturally, stretch well beyond a human lifetime.

As it happens, these futuristic spacecraft are already being developed for another ambitious mission, the Breakthrough Starshot project, which aims to send them to the Alpha Centauri star system, 4.37 light-years away.

If we were to discover a lurking black hole, rather than a frigid planet, Unwin says there would be no need to panic. "There's a supermassive black hole in the centre of our galaxy," he says. "But we don't worry about our solar system falling into it, because we're in a stable orbit around it." So, while a primitive black hole will suck up anything within its path, this would not include the Earth, which – like the other inner planets – doesn't ever come close.

"It's not like a vacuum cleaner," says Unwin. He explains that from the perspective of anyone on Earth, having an undiscovered black hole in the solar system is not that different to having a concealed planet there.

But while stellar and primordial black holes are essentially the same, the latter have never been found or studied – and difference in scale is expected to lead to some bizarre phenomena. “I would say that the things that happen with small black holes are more interesting than what happens with large black holes," says Scholtz.

In 2019, the Event Horizon Telescope (EHT) captured an image of the shadow of a supermassive black hole in the centre of the galaxy Messier 87 (Credit: Alamy)

One example is the aptly-named process of “spaghettification”, which is often illustrated by the fable of an astronaut who ventured too near a black hole’s event horizon – the point beyond which no light can escape – and fell in headfirst. Though her head and feet were just metres from each other, the difference in the gravitational forces acting on them would be so great, she would be stretched like spaghetti.

Intriguingly, the effect should be even more dramatic, the smaller the black hole is. Sholtz explains that it’s all about relative distances – if you’re two metres tall, and you’re falling through an event horizon that’s one metre from a primordial black hole’s centre, the discrepancy between the location of your head and feet is larger, compared to the size of the black hole. This means you’ll be stretched far more than if you fell into a stellar one that’s a million miles across.

"And so, peculiarly enough, they're more interesting," says Scholtz. Spaghettification has already been seen via a telescope, when a star got too close to a stellar black hole 215 million light years from Earth, and was ripped apart (no astronauts were harmed). But if there is a primordial black hole in our own solar system, it would provide astrophysicists with the opportunity to study this behaviour – and many others – up close.

So what does Batygin make of the possibility that the long-sought ninth planet could actually be a black hole instead? "It's a creative idea, and we cannot constrain what its composition is even in the least bit," he says. "I think maybe it's just my own bias, being a planetary science professor, but planets are a little bit more common…"

While Unwin and Scholtz are rooting for a primeval black hole to experiment with, Batygin is just as keen for a giant planet – citing the fact that the most common type throughout the galaxy are those which have around the same mass as Planet Nine.

"Meanwhile most exoplanets that orbit Sun-like stars, are in this weird range of being bigger than the Earth and considerably smaller than Neptune and Uranus," he says. If scientists do find the missing planet, it will be the closest they can get to a window into those elsewhere in the galaxy.

Only time will tell if the latest quest will be more successful than Lowell's. But Batygin is confident that their missions are totally different. "All of the proposals are quite distinct in both the data they seem they seek to explain, as well as the mechanisms they use to explain it," he says.

Either way, the search for the legendary ninth planet has already helped to transform our understanding of the solar system. Who knows what else we'll find before the hunt comes to an end.

Zaria Gorvett is a senior journalist for BBC Future and tweets @ZariaGorvett

This story was updated on 22/2/2021. An earlier version incorrectly stated that the Voyager 2 mission led to the discovery of the Kuiper Belt.

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THE LOST INDEX | GEOLOGY

The missing continent it took 375 years to find

(Image credit: Getty Images)

A view of New Zealand from the sea (Credit: Getty Images)

By Zaria Gorvett7th February 2021

It took scientists 375 years to discover the eighth continent of the world, which has been hiding in plain sight all along. But mysteries still remain.

Article continues below

It was 1642 and Abel Tasman was on a mission. The experienced Dutch sailor, who sported a flamboyant moustache, bushy goatee and penchant for rough justice – he later tried to hang some of his crew on a drunken whim – was confident of the existence of a vast continent in the southern hemisphere, and determined to find it.

At the time, this portion of the globe was still largely mysterious to Europeans, but they had an unshakeable belief that there must be a large land mass there – pre-emptively named Terra Australis – to balance out their own continent in the North. The fixation dated back to Ancient Roman times, but only now was it going to be tested.

And so, on 14 August, Tasman set sail from his company's base in Jakarta, Indonesia, with two small ships and headed west, then south, then east, eventually ending up at the South Island of New Zealand. His first encounter with the local Māori people did not go well: on day two, several paddled out on a canoe, and rammed a small boat that was passing messages between the Dutch ships. Four Europeans died. Later, the Europeans fired a cannon at 11 more canoes – it’s not known what happened to their targets.

And that was the end of his mission – Tasman named the fateful location Moordenaers (Murderers) Bay, with little sense of irony, and sailed home several weeks later without even having set foot on this new land. While he believed that he had indeed discovered the great southern continent, evidently, it was hardly the commercial utopia he had envisaged. He did not return.

(By this time, Australia was already known about, but the Europeans thought it was not the legendary continent they were looking for. Later, it was named after Terra Australis when they changed their minds).

Little did Tasman know, he was right all along. There was a missing continent.

Abel Tasman arguably did find the great southern continent, though he didn’t realise 94% of it is underwater (Credit: Alamy)

In 2017, a group of geologists hit the headlines when they announced their discovery of Zealandia –Te Riu-a-Māui in the Māori language. A vast continent of 1.89 million sq miles (4.9 million sq km) it is around six times the size of Madagascar.

Though the world's encyclopaedias, maps and search engines had been adamant that there are just seven continents for some time, the team confidently informed the world that this was wrong. There are eight after all – and the latest addition breaks all the records, as the smallest, thinnest, and youngest in the world. The catch is that 94% of it is underwater, with just a handful of islands, such as New Zealand, thrusting out from its oceanic depths. It had been hiding in plain sight all along.

"This is an example of how something very obvious can take a while to uncover," says Andy Tulloch, a geologist at the New Zealand Crown Research Institute GNS Science, who was part of the team that discovered Zealandia.

But this is just the beginning. Four years on and the continent is as enigmatic as ever, its secrets jealously guarded beneath 6,560 ft (2km) of water. How was it formed? What used to live there? And how long has it been underwater?

A laborious discovery

In fact, Zealandia has always been difficult to study.

More than a century after Tasman discovered New Zealand in 1642, the British map-maker James Cook was sent on a scientific voyage to the southern hemisphere. His official instructions were to observe the passing of Venus between the Earth and the Sun, in order to calculate how far away the Sun is.

Possibly due to a quirk of geology, the enigmatic kiwi bird’s closest relative hails from Madagascar (Credit: Alamy)

But he also carried with him a sealed envelope, which he was instructed to open when he had completed the first task. This contained a top-secret mission to discover the southern continent – which he arguably sailed straight over, before reaching New Zealand.

The first real clues of Zealandia's existence were gathered by the Scottish naturalist Sir James Hector, who attended a voyage to survey a series of islands off the southern coast of New Zealand in 1895. After studying their geology, he concluded that New Zealand is "the remnant of a mountain-chain that formed the crest of a great continental area that stretched far to the south and east, and which is now submerged…".

Despite this early breakthrough, the knowledge of a possible Zealandia remained obscure, and very little happened until the 1960s. "Things happen pretty slowly in this field," says Nick Mortimer, a geologist at GNS Science who led the 2017 study.

Then in the 1960s, geologists finally agreed on a definition of what a continent is – broadly, a geological area with a high elevation, wide variety of rocks, and a thick crust. It also has to be big. "You just can't be a tiny piece," says Mortimer. This gave geologists something to work with – if they could collect the evidence, they could prove that the eighth continent was real.

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Still, the mission stalled – discovering a continent is tricky and expensive, and Mortimer points out that there was no urgency. Then in 1995, the American geophysicist Bruce Luyendyk again described the region as a continent and suggested calling it Zealandia. From there, Tulloch describes its discovery as an exponential curve.

Tasman’s ships left New Zealand after a bloody encounter with the Māori people – but he believed that he had found the legendary southern continent (Credit: Alamy)

Around the same time, the "United Nations Convention on the Law of the Sea" came into force, and finally provided some serious motivation. It states that countries can extend their legal territories beyond their Exclusive Economic Zone, which reaches 200 nautical miles (370km) out from their coastlines, to claim their "extended continental shelf" – with all the mineral riches and oil this encompasses.

If New Zealand could prove that it was part of a larger continent, it could increase its territory by six times. Suddenly there was an abundance of funding for trips to survey the area, and the evidence gradually built up. With every rock sample that was collected, the case for Zealandia improved.

The final flourish came from satellite data, which can be used to track tiny variations in the Earth's gravity across different parts of the crust to map the seafloor. With this technology, Zealandia is clearly visible as a misshapen mass almost as large as Australia.

Satellite data can be used to visualise the continent of Zealandia, which appears as a pale blue upside-down triangle to the east of Australia (Credit: GNS Science)

When the continent was finally unveiled to the world, it unlocked one of the most sizeable maritime territories in the world. "It is kind of cool," says Mortimer, "If you think about it, every continent on the planet has different countries on it, [but] there are only three territories on Zealandia."

In addition to New Zealand, the continent encompasses the island of New Caledonia – a French colony famous for its dazzling lagoons – and the tiny Australian territories of Lord Howe Island and Ball's Pyramid. The latter was described by one 18th-Century explorer as appearing "not to be larger than a boat."

A mysterious stretching

Zealandia was originally part of the ancient supercontinent of Gondwana, which was formed about 550 million years ago and essentially lumped together all the land in the southern hemisphere. It occupied a corner on the eastern side, where it bordered several others, including half of West Antarctica and all of eastern Australia.

Then around 105 million years ago, "due to a process which we don't completely understand yet, Zealandia started to be pulled away", says Tulloch.

Continental crust is usually around 40km deep – significantly thicker than oceanic crust, which tends to be around 10km. As it was strained, Zealandia ended up being stretched so much that its crust now only extends 20km (12.4 miles) down. Eventually, the wafter-thin continent sank – though not quite to the level of normal oceanic crust – and disappeared under the sea.

Despite being thin and submerged, geologists know that Zealandia is a continent because of the kinds of rocks found there. Continental crust tends to be made up of igneous, metamorphic and sedimentary rocks – like granite, schist and limestone, while the ocean floor is usually just made of igneous ones such as basalt.

When the supercontinent of Gondwana broke up, fragments drifted all across the globe. Many of its ancient plants still live in the Australian Dorrigo forest (Credit: Getty Images)

But there are still many unknowns. The unusual origins of the eighth continent make it particularly intriguing to geologists, and more than a little baffling. For example, it's still not clear how Zealandia managed to stay together when it's so thin and not disintegrate into tiny micro-continents.

Another mystery is exactly when Zealandia ended up underwater – and whether it has ever, in fact, consisted of dry land. The parts that are currently above sea level are ridges that formed as the Pacific and Australian tectonic plates crumpled together. Tulloch says opinion is split as to whether it was always submerged apart from a few small islands, or once entirely dry land.

This also raises the question of what lived there.

With its mild climate and 39 million-sq-mile (101 million-sq-km) range, Gondwana itself was home to a vast array of flora and fauna, including the first four-limbed land animals and later, an abundance of the largest to ever live – the titanosaurs. So, could the rocks of Zealandia be studded with their preserved remains?

A debate about dinosaurs

Fossilised land animals are rare in the southern hemisphere, but the remains of several were found in New Zealand in the 1990s, including the rib bone of a giant, long-tailed, long-necked dinosaur (a sauropod), a beaky herbivorous dinosaur (a hypsilophodont) and an armoured dinosaur (an ankylosaur). Then in 2006, the foot bone of a large carnivore, possibly a kind of allosaur, was discovered in the Chatham Islands, about 500 miles (800km) east of the South Island. Crucially, the fossils all date to after the continent of Zealandia split from Gondwana.

The elephant bird stood 3 m (9.8 ft) tall and fragments of its eggshells still litter beaches to this day (Credit: Alamy)

However, this doesn't necessarily mean there were dinosaurs roaming over the majority of Zealandia – these islands may have been sanctuaries while the rest was drowned, as it is now. "There's a long debate about this, about whether it's possible to have land animals without continuous land – and whether without it, they would have been snuffed out," says Sutherland.

The plot thickens with one of New Zealand's weirdest and most beloved inhabitants, the kiwi – a dumpy, flightless bird with whiskers and hair-like feathers. Oddly, its closest relative is not thought to be the Moa, which is part of the same group – the ratites – and lived on the same island until its extinction 500 years ago, but the even-more giant elephant bird, which stalked the forests of Madagascar until as recently as 800 years ago.

The finding has led scientists to believe that both birds evolved from a common ancestor that lived on Gondwana. It took 130 million years to fully break up, but when it did, it left behind fragments which have since been scattered all across the globe, forming South America, Africa, Madagascar, Antarctica, Australia, the Arabian Peninsula, the Indian Subcontinent, and Zealandia.

This, in turn, suggests that at least part of now-submerged Zealandia has remained above sea level the whole time. Except around 25 million years ago the entire continent – even possibly the entirety of New Zealand – is thought to have been plunged underwater. "It was thought that all the plants and animals must have colonised afterwards," says Sutherland. So what happened?

New Zealand is one of the highest points of Zealandia, after being pushed up by the movement of tectonic plates (Credit: Alamy)

Though it's not possible to collect fossils from the seafloor of Zealandia directly, scientists have been plumbing its depths by drilling. "Actually the most helpful and distinctive fossils are the ones which form in the very shallow seas," says Sutherland. "Because they leave a record – there are zillions and zillions of tiny, tiny little fossils that are very distinctive."

In 2017, a team undertook the most extensive surveys of the region so far, and drilled more than 4,101ft (1,250m) into the seabed at six different sites. The cores that they collected contained pollen from land plants, as well as spores and the shells of organisms that lived in warm, shallow seas.

"If you have water, which is only you know, 10m (33ft) deep or something like this, then there's a good chance that there was land around as well," says Sutherland, who explains that the pollen and spores also hint at the possibility that Zealandia was not quite as submerged as was thought.

A (literal) twist

Another lingering mystery can be found in Zealandia's shape.

"If you look at a geological map of New Zealand, there are two things that really stand out," says Sutherland. One of these is Alpine Fault, a plate boundary that runs along the South Island and is so significant, it can be seen from space.

The red band of rock – the Median Batholith – should travel all the way down Zealandia in a diagonal line, but instead it has been twisted out of shape (Credit: GNS Science)

The second is that the geology of New Zealand – as well as that of the wider continent – is oddly bent. Both are split in two by a horizontal line, which is where the Pacific and Australian tectonic plates meet. At this exact point, it looks like someone has taken the lower half and twisted it away, so that not only do the previously-continuous ribbons of rock no longer line up, but they are almost at right angles.

An easy explanation for this is that the tectonic plates moved, and somehow deformed them out of shape. But exactly how or when this happened is still totally unresolved.

"There are various interpretations, but this is quite a large unknown thing," says Tulloch.

Sutherland explains that the continent is unlikely to give up all its secrets anytime soon. "It's quite hard to make discoveries, when everything is 2km (1.2 miles) underwater, and the layers that you need to sample are 500m (1,640ft) beneath the seabed as well," he says. "It's really challenging to go out and explore a continent like that. So, it just takes a lot of time, money and effort to go out and ships and survey regions."

If nothing else, the world's eighth continent surely shows that – nearly 400 years after Tasman's quest – there is still plenty to be discovered.

Zaria Gorvett is a senior journalist for BBC Future. Twitter: @ZariaGorvett

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