Lasers for propelling miniature spacecrafts

C Sivaram, May 17, 2016

A  recent report of a proposal supported by Mark Zuckerberg, Yuri Milner and Stephen Hawking among others, envisages the launch of several miniature spaceships pushed by the light pressure exerted by powerful laser beams, which would accelerate them to a fifth of the speed of light. 

This would enable these spacecrafts to reach the Alpha Centauri star system (nearest to the Solar System), 40 trillion km away, in about 20 years. It is believed that an earthlike planet could be orbiting one of the stars in the system.

Stephen supports this by saying that if we are to survive as a species, we must ultimately spread out to the stars. Conventional spacecraft (including the ones to the Moon or Mars) have to carry considerable amount of fuel. As an example, the Apollo spacecraft which put men on the moon, weighed 3,000 tonnes at start, while the final payload which came back to Earth was barely 6 tonnes! More than 90% was fuel. The idea of using solar sails for propulsion has been around for quite some time. Sunlight also exerts pressure; the thrust is about 10 Newton per kilometre square area of sail. The sail is made of lightweight Teflon, coated with a highly reflective material like aluminium or gold foil. Its material must be no denser than 1 g/m². 

Better alternatives

Carbon fibres, graphene and related materials are better than this limit. A sail 5 km² can deliver 30 tonnes from Earth to Mars within a year. The fuel is just sunlight which exerts pressure on sail. Already, many sails have been launched, like the Russian Znamya (300 m²) and the planetary Society’s 600 m² sail. Spacecraft to Pluto by such sails are planned. 

Lasers operating from the ground can push up interstellar spacecraft with highly directional powerful beams. As sunlight is perennial, a solar sail would be continuously accelerated and can cross the solar system in months. A previous plan had a 3 TW (trillion watts) laser continuously operating which would get a 500 tonne payload to Barnard’s Star (next nearest star) in 50 years. Again recently, there was a proposal to have a laser-powered spacecraft to reach Mars in a few days. It can be calculated that a 50 GW (billion watts) laser (quite common now) illuminating a 50 m diameter gold plated sail (gold is very malleable) can send 40 kg to Mars in a week!

As far as Alpha Centauri is concerned, the current plan is to launch several spacecrafts, each weighing a few gram only, containing a camera, communication devices, navigation equipment (all miniaturised). They would be attached to light spacecrafts of few hundred atoms thick. These chip-sized crafts could be accelerated by directed gigawatt beams to several thousand times Earth’s gravity (g) and reach 1/5 light velocity in about 10 minutes. This push would enable them to reach the nearest star in 20 years. They need not carry any fuel. Laser beams would be ubiquitously used in future rocket propulsion enabling us to reach the stars within a human life time.

Our conventional spacecraft like Voyager or even the new Horizons spacecraft to Pluto would take 1,00,000 years or more to reach the nearest stars.

To keep obesity at bay, exercise may trump diet

Gretchen Reynolds, May 24, 2016, The New York Times

Young rats prone to obesity are much less likely to fulfill that unhappy destiny if they run during adolescence than if they do not, according to a new animal study of exercise and weight. They also were metabolically healthier, and had different gut microbes, than rats that keep the weight off by cutting back on food, the study found. The experiment was done in rodents, not people, but it does raise interesting questions about just what role exercise may play in keeping obesity at bay.

For some time, many scientists and dieting gurus have been pointing out that exercise by itself tends to be ineffective for weight loss. Study after study has found that if overweight people start working out but do not also reduce their caloric intake, they shed little and may actually gain weight. The problem, most scientists agree, is that exercise increases appetite, especially in people who are overweight, and also can cause compensatory inactivity, meaning that people move less overall on days when they exercise. Consequently, they wind up burning fewer daily calories, while also eating more. 

There has been much less examination of whether exercise might help to prevent weight gain in the first place and, if it does, how it compares to calorie restriction for that purpose. So for the new study, which was published in Medicine & Science in Sports & Exercise, researchers at the University of Missouri in Columbia and other schools first gathered young rats from a strain that has an inborn tendency to become obese, starting in adolescence. 

After weighing them, the researchers divided the animals into 3 groups. One group was allowed to eat as much kibble as they wished and to remain sedentary in their cages. These were the controls. Another group, the exercise group, also was able to eat at will, but these animals were provided with running wheels in their cages. The final group, the dieting group, was put on a calorie-restricted meal plan. Their daily kibble helpings were about 20% smaller than the amount that the runners ate, a portion size designed to keep them at about the same weight as the runners, so that extreme differences in body size would not affect the final results.

After 11 weeks, all of the animals were moved to specialised cages that could measure their metabolisms and how much they moved around. They then returned to their assigned cages for several more weeks, by which time they were effectively middle-aged. At that point, the control animals were obese, their physiques larded with fat. The runners and the lower-calorie groups, however, although they also had gained ounces, had put on far less weight than the controls. None were obese.

Both exercise and portion control, in other words, had effectively protected the animals against their fated fatness. But beneath the skin, the runners and the dieters looked very unalike. By almost all measures, the runners were metabolically healthier, with better insulin sensitivity and lower levels of bad cholesterol than the dieters. They also burned more fat each day for fuel, according to their metabolic readings, and had more cellular markers related to metabolic activity within their brown fat than the dieting group. Brown fat, unlike the white variety, can be quite metabolically active, helping the body to burn additional calories.

Interestingly, the runners also had developed different gut microbes than the dieters, even though they ate the same food. Perhaps most striking, “the runners showed no signs of compensatory eating or compensatory inactivity,” said Victoria Vieira-Potter, who oversaw the study. They didn’t scarf down more food than the control group, despite running several miles every day and, according to the specialised cages, actually moved around more when not exercising than either of the other groups of rats.

This study involved young, normal-weight rodents and cannot tell us whether exercise or dieting alone or in combination would aid or hinder weight loss in people (or animals) who already are overweight, Victoria said. Metabolisms change once a body contains large amounts of fat, and it becomes increasingly difficult to permanently drop those extra pounds.So, better to avoid weight gain in the first place, if possible. And in that context, she said, “restricting calories can be effective,” but exercise is likely to be more potent in the long term and, of course, as common sense would tell us, doing both — watching what you eat and exercising — is best of all.

A carnival of the mind

George Johnson, May 24, 2016, The New York Times

At the Science of Consciousness conference recently in Tucson, Arizona, USA I was faced with a quandary: Which of the 8 simultaneous sessions should I attend? In one room, scientists and philosophers were discussing the physiology of brain cells and how they might generate the thinking mind. In another, the subject was free will — real or an illusion? Next door was a session on panpsychism, the controversial (to say the least) idea that everything — animal, vegetable and mineral — is imbued at its subatomic roots with mind-like qualities. 

For much of the 20th century, the science of consciousness was widely dismissed as an impenetrable mystery, a morass of a problem that could be safely pursued only by older professors as they thought deep thoughts in their endowed chairs. Beginning in the 1990s, the field slowly became more respectable. There is, after all, a gaping hole in science. The human mind has plumbed the universe, concluding that it is precisely 13.8 billion years old. With particle accelerators like the Large Hadron Collider at the European Organisation for Nuclear Research (CERN), scientists have discovered the vanishingly tiny particles, like the Higgs boson, that underpin reality.

But there is no scientific explanation for consciousness — without which none of these discoveries could have been made. Faced with this vacuum, hundreds of people gathered in Tucson where wild speculations and carnivalesque pseudoscience were juxtaposed with sober sessions and data-filled talks about probing conscious brain states with PET scans and EEGs.

Neural sparks 
Because I couldn’t clone my brain, I found myself sitting, late one afternoon, in Vibrations, Scale, and Topology, where a musician from Tulsa, Oklahoma, who called himself Timbre Wolf, was strumming a guitar and singing the ‘Bing’ song. ‘Bing’ is a word that Stuart Hameroff, the University of Arizona professor who organises these mindfests, uses to describe the moment when the spark of consciousness lights up the brain. Imagine a mad scientist hooking together neurons one by one until suddenly they reach a threshold of complexity and — bing — consciousness emerges. We all know the feeling, one that science has been powerless to explain. 

Before launching into the tune, Timbre Wolf played a recording of an eerie composition called Brain Dance, derived from vibrations generated by tiny molecular structures called microtubules, which are part of the scaffolding of brain cells. The music, to his ear, was reminiscent of Philip Glass, Steve Reich, Cuban rumba, Gustav Holt’s The Planets, and the visual rhythms of strange mathematical objects called Penrose tiles. All of this, he suspected, had something to do with quantum mechanics and consciousness, an idea that Stuart has long been pursuing. That all made for good metaphysical fun. More disconcerting was the starring role given to the new age entrepreneur Deepak Chopra. 

Deepak believes that human consciousness directs the unfolding of human evolution. There were talks on psychic phenomena and retrocausality, the hypothesis that the future can affect the past through quantum emanations. Presentations that didn’t make it into prime time were laid out in colourful posters attached to rows of bulletin boards: What Might Cause a Star’s Consciousness? The X-Structure: The Basic Nature of Life and Existence. 

Beyond all of that, there was still plenty of serious theorising. For a rapid-fire summary, you can hear Baba Brinkman, a rap artist who provided a daily report on the meeting, which he called “half science lab and half Burning Man.” Late one night at an event called Club Consciousness, Baba joined Dorian Electra and the Electrodes as the band regaled the crowd with songs like “Mind-Body Problem” and “Brain in a Vat”.

“Chinese Room” was about a thought experiment that the philosopher John Searle claims to be a refutation of the possibility of artificial intelligence. But the big hit of the night, “Sensual,” which has been made into a rock video, was about a famous intellectual conflict that has raged since the 17th century when John Locke went to the mat with René Descartes over the source and nature of human knowledge.

For John and the empiricists, the mind begins as a blank slate (a tabula rasa) and truth comes to us through our senses. But Descartes and the rationalists insisted that some knowledge was innate, prefigured into the mind of every newborn. Electra opened the debate. “There ain’t nothin in the mind which ain’t been in the sensations. Let me take you on a sensation vacation. Through sense experience, the mind is created. As well as rules to process raw sense data.”

Ultimately they concluded, as many philosophers have, that the truth lies somewhere in between. In the past, these conferences were called Toward a Science of Consciousness. Recently, the organisers dropped the first 2 words of the title, as if the fog was finally lifting. But as I left the auditorium, I wondered if their confidence was premature.

In even the wildest presentations, one could sense a longing for an answer to the question of consciousness, a fuller accounting of what we are and how we fit into the cosmic machinery. For all of the effort, the goal of providing a compelling explanation — one so clear it would make your head go bing — seemed as remote as ever.

Decoding the past

Palahalli Vishwanath, May 24, 2016,

The gap between the orbits of Mars and Jupiter in the Copernican model of the solar system was large enough to get the attention of many great people like Johannes Kepler, Isaac Newton and Immanuel Kant. The Italian astronomer, Giuseppe Piazzi working in Palermo, Sicily discovered a small planet in that gap in 1801. This coincidentally was in the exact position predicted by astronomers Johann Daniel Titius and Johann Elert Bode. Giuseppe named the object ‘Ceres’ after the patron goddess of Sicily. 

Later, many objects were discovered moving in that orbit, the most important of them being Vesta (smaller than Ceres). It turns out that a planet, which existed in the beginning of the solar system, broke up completely due to the gravitational tug from the nearby giant planet of Jupiter and the broken objects were called asteroids. Basically, asteroids are the leftovers of the solar system formation. There are roughly 1.5 million of these objects with diameter larger than 1 km and only 5% of them have names. 

Flying through space
Since asteroids fly through space uninhibited, they sometimes crash into surrounding planets. Their high-velocity impact creates craters in the planets. Many meteors from Vesta have been found on Earth, which is supposed to be due to the  huge impacts on Vesta itself. Ceres and Vesta have surface areas sightly less than that of India and Pakistan, respectively. Ceres has about 7% of the mass of Pluto and Vesta’s mass is about one-third of Ceres. While Ceres cannot be seen through naked eyes, the very reflective surface of Vesta makes it visible without a telescope. 

Ceres and Vesta are at twice and thrice the distance of Mars from Earth respectively. Ceres is the only asteroid that has a shape rounded by the force of its own gravity. Therefore, Ceres was also included as dwarf planet along with Pluto and Eris in 2006.

A study of these asteroids will tell us how our Earth was in the dawn of the solar system. The planets of the solar system took long time to get to their present shape. For instance, the planets Earth and Mars went on accruing mass for 50 and 30 million years respectively. 

However, asteroids acquired their present shape quite soon: Ceres and Vesta in 10 and 7 million years respectively. They could not acquire more mass because of the overwhelming presence of Jupiter. With this aim, there have been many specific observations of asteroids in the last few decades. As for Ceres, there were observations by the Hubble telescope in 2004 and by the Herschel IR telescope in 2014. 

An aptly-termed space vehicle called Dawn departed Earth in 2007 for the exploration of Ceres and Vesta. This was the first ever vehicle to orbit 2 celestial bodies beyond Earth. It was also the first to orbit an object in the main asteroid belt of the solar system. With a speed of 40,000 km per hour, it passed Mars in 2009 and reached Vesta in July 2011. It surveyed the asteroid from about 200 km from the surface for several months. It left Vesta in September 2012 and took about 3 years to reach Ceres. 

After travelling nearly 5 billion km, it started orbiting Ceres from March 2015. In December 2015, it started surveying the planet from a height of 385 km and has provided magnificent views of the celestial body. While the mission could end in 2016, Dawn will remain in orbit forever around Ceres though it won’t be sending any signals. In its lowest-altitude mapping orbit, at a distance of 385 km from Ceres, Dawn is nearer to the planet surface than International Space Station is to Earth! 

Sighting water
An important feature of Ceres from the earlier days has been the presence of large bright spots suggesting watery ice on the surface. Dawn has been able to take a very close look at these bright spots from a close distance. The two big ones are the  the Occator and the Haulani craters with breadths of 100 km and 34 km. One has a  dome-like structure in the pit and the other has a central ridge. The intricate geometry of the craters and the colour of the ejected material suggest geological activities and impacts in the recent past. 

The spots could be due to briny water erupting from the interior and later sublimating, leaving behind the salt deposits. There is also the possibility that the interiors of the asteroid is supplying fresh salts (containing Magnesium, Ammonia etc) to the region. Even the polygonal shape of the craters can shed light on many things as most of the craters elsewhere are circular in nature.   

There are also further evidences to believe that Ceres has large amount of ice and may even have subsurface liquid water. A few years ago, Herschel IR telescope  showed water vapour coming from 2 dark patches of ground with the estimate that the loss was about 6 kg of water per second. This proves that Ceres has a icy surface and also an atmosphere. Dawn has shown in the past few months that the 10-km-wide Oxo crater , the second-brightest feature on Ceres, harbours water either in the form of ice or hydrated minerals.

It is possible that Ceres has more water than all the fresh water on Earth. However, Ceres’s water, unlike Earth’s, would be in the form of water ice and located deep in the mantle. While the presence of water has been noted in several comets, finding  of water on Ceres shows that impact of asteroids also must have brought water to Earth. For this reason, the idea of colonising Ceres someday has some appeal, compared to distant objects like Europa and Titan.

Envying the starfish, regenerator of limbs

C Claiborne Ray, May 31, 2016,

Why can creatures like starfish and some reptiles regenerate a lost limb or tail while humans cannot? That question has been the target of considerable study, but the answers are far from clear, according to EuroStemCell, a European organisation that tracks stem cell research.

People can regenerate some tissues, notably liver and skin. Many animals can regenerate complex body parts with many kinds of tissue using a variety of mechanisms, but most of the replacement mechanisms rely on special stem cells that collect at the injury site and then multiply and differentiate into the necessary kinds of tissue.

These special stem cells come in 2 varieties: pluripotent cells, which can give rise to all tissue products, and multipotent tissue-specific cells, which can give rise only to certain kinds of tissue. In one extreme case, scientists recently discovered that a single cell could be made to create a new flatworm. 

That research was reported in the journal Science in May 2013. The scientists concluded that such stem cells, called adult pluripotent neoblasts, were not derived from the embryo but were present in adult flatworms and were behind the remarkable regenerative ability of the relatively simple animal.

In more complex animals, multipotent, tissue-specific stem cells can regenerate an entire limb in a frog or salamander, but it is not yet known why similar cells in humans cannot do so. Scientists are studying the process to determine if some kind of internal map assigning new cells to a specific place has been lost in mammals.

Another kind of regeneration relies on cells that have stopped dividing but are induced after injury to divide once more and develop into useful tissue. This process is seen in zebra fish and newborn mice, which can regenerate heart tissue. Again, scientists are studying the mechanism to find out why it does not happen in humans.
C Claiborne Ray

Cellphone screens, sharper and brighter
Tiny crystals called quantum dots could make television or cellphone screens sharper and brighter, but the manufacturing process can be toxic to the environment. 

Chemical engineers at Lehigh University, USA may have found an environmentally friendly alternative: Feed metal to a single bacterial enzyme.

The vials are filled with the results, tiny crystals that can generate electricity and coloured light. Under UV lights, they glow like plastic pegs on a Lite-Brite screen.

Bryan Berger stumbled across the enzyme while studying a superbug spreading on metal surfaces in a hospital in Pennsylvania: Stenotrophomonas maltophila. The microbe appeared to be taking in electrical charges, he found, and spitting out clusters of metallic particles — quantum dots. Understandably leery of working with an infectious superbug, he and his colleagues went on to isolate the enzyme responsible for the alchemy. “As an engineer, it’s extremely exciting,” Bryan said. “But as a medical scientist, it’s extremely scary.”
Joanna Klein

Where can a PhD take you? Back to school, usually
Doctoral students in the sciences are more like the rest of us than previously thought: They don’t know what they want to do with their lives, either. When deciding what to do with newly minted doctorates, they tend to keep marching in a straight path, pursuing postdoctoral research positions.

In a study published in Science, researchers tried to figure out why, given the relatively low odds of landing a full-time faculty position, traditionally the goal of such work.

Their results were somewhat inconclusive. But the authors did find evidence that many students pursued postdocs as a default option after graduate school, or as part of a “holding pattern” until the job they wanted was available. The authors, who did not receive postdoctoral degrees themselves, conclusively demonstrated the need for more career planning among graduate students, and that graduate students should consider their career paths before they even begin a PhD programme.

“It’s probably not a controversial conclusion,” said Henry Sauermann, an associate professor at Georgia Tech and an author of the report. “But what might be a little different here is thinking about whether the PhD is the right path in the first place.”

One lesson may be to not get a PhD until you know what you want to do with it. But this may require further study.
Tatiana Schlossberg
The New York Times

Using lactate for stroke

Nishita Bhembre, May 31, 2016,

Stroke is caused when there is a restricted flow of blood to some parts of the brain, which starves the brain cells of oxygen and glucose. This leads to damage and death of brain cells, also called neurons, which cannot be fully replaced after they are lost. The oxygen and glucose-starved cells accumulate ‘lactate’ in the spaces between neurons. 

Lactate is a metabolic substance found in human body. It is a component of lactic acid that gives a sour taste to curd. Prof Sujit K Sikdar and his group at the Molecular Biophysics Unit, Indian Institute of Science (IISc), Bengaluru are focussed on understanding various aspects of neurons and astrocytes (brain cells that support neurons) during disease states by measuring their activity using electrophysiological techniques. Recently, they have tried to answer the question whether lactate produced during stroke has a protective role in reducing death of neurons. Electrophysiological methods are used to assess the electrical properties of individual cells and biological tissues.

Neurons talk to each other via electrical signals and thus control the functions of all of our body parts. So, how does this happen? Neurons have specialised ‘gates’ called ‘channels’ on their membrane, which allow select ions to pass through i.e., to enter or leave the cell. TREK1 is one such channel, regulating the flow of potassium ions out of the neurons, to maintain their normal functional state. 

Natural solution
Lactate, accumulated during stroke is known to protect neurons, by preventing the excess release of chemicals (termed neurotransmitters) that initiate electrical signalling. 

This prevents adjacent neurons from firing unnecessarily, getting damaged and then dying as a consequence, thus reducing the neurological deficits of stroke. Few studies have even reported that lactate reduces size of infarct (a localised area of dead tissue) caused by stroke. Prof Sikdar’s students, Aditi Banerjee and Swagata Ghatak are engaged in studying the interaction of lactate with TREK1 channels in the context of stroke.

According to Aditi, both lactate and TREK1 channels have been independently proven to protect neurons during stroke by several studies. This made them wonder whether lactate and TREK1 channels possibly worked together to protect neurons. They investigated this, by recording the activity of a single TREK1 channel and measuring whole cell TREK1 current in astrocytes in the presence of lactate using patch clamp technique. This technique is used to record the current in patches of cell membrane (either attached to cell or excised).

“Astrocytes are a cleaner system than neurons, where TREK1 currents can be easily isolated and recorded. We used astrocytes as they express TREK1 channels to a much larger extent than neurons,” explains Aditi. Their results confirmed that TREK1 channel activity increased with increase in lactate concentration. Further, Swagata explored the nature of this interaction between lactate and TREK1 channel and a single amino acid (i.e., histidine at position 328 in the TREK1 protein chain was found to be the crucial site for this interaction). She discovered that without this particular amino acid at the site, the lactate — TREK1 channel interaction was lost, inhibiting the protection of neurons by means of lactate.  

Furthermore, Aditi observed that, in response to lactate, astrocytes produce more TREK1 protein and there was increased TREK1 activity as well. These results were obtained using double immunofluorescence-staining studies, western blotting and quantitative PCR techniques. Once they confirmed that lactate and TREK1 do interact, they wanted to verify whether this interaction was indeed responsible for neuroprotection in stroke. 

So next, they analysed the effect of lactate on neuronal death in the hippocampus, an area of the brain most susceptible to stroke, also involved in memory formation. It was found that lactate reduced the number of dying neurons, while failing to do so in presence of TREK1 channel blockers which inhibit channel activity. Furthermore, lactate also requires the presence of healthy astrocytes to prevent death of neurons by excessive firing.

All these findings led to one important question, “Can lactate be used for treating stroke?” The current treatment against stroke includes anticoagulant therapy, antiplatelet therapy, and thrombolytic therapy (all of which serve to prevent or remove the blood clots blocking blood supply). 

However, several studies have reported serious drawbacks in these methods. Since lactate is a physiological metabolite found in the body that has a protective effect on brain cells, it has been proposed as a novel and ideal therapeutic agent to combat stroke. 

Even so, “Clinical trials are a long way from here. It is too early to comment whether lactate administration will be more effective than the current treatment for stroke. More experimental and clinical studies need to be done, before we can safely administer lactate to a patient suffering from stroke,” states Aditi. 

(The author is with Gubbi Labs, Bengaluru)

Talc and cancer

Roni Caryn Rabin, May 31, 2016, The New York Times

Deane Berg thought she was going to die, and she wanted to know why. She was 49, way too young, she thought, to have advanced cancer in her ovaries. As she scrolled through websites that listed possible causes of ovarian cancer, one jumped out at her: talcum powder. She did not have risk factors like infertility or endometriosis, but she had dusted baby powder between her legs every day for 30 years. “I went into the bathroom, I grabbed my Johnson’s Baby Powder and threw it in the wastebasket,” recalled Deane, now 59, a physician assistant in Sioux Falls, South Dakota. “I said, ‘What else could it be?’”
Deane was the first of thousands of women with ovarian cancer to file a lawsuit against the consumer products giant Johnson & Johnson, claiming that Baby Powder caused their disease and pointing to a long trail of studies linking talc to the cancer. The research dates to 1971, when scientists in Wales discovered particles of talc embedded in ovarian and cervical tumours. Since then, numerous studies have linked genital talc use to ovarian cancer, including a report earlier this month that among African-American women, genital use of powder is linked with a 44% increased risk for invasive epithelial ovarian cancer.

Johnson & Johnson says its trademark Baby Powder is safe, and it plans to appeal 2 multimillion-dollar jury awards, including $55 million in damages awarded to a cancer survivor earlier this month and a $72 million award in February. 

The International Agency for Research on Cancer in 2006 classified talcum powder as a possible human carcinogen if used in the female genital area. But the agency, part of the World Health Organization, has also said pickled vegetables and coffee are possible carcinogens and that hot dogs cause cancer. 

Johnson & Johnson says research implicating talcum powder is flawed and points to studies that absolve talc of any cancer risk. “We have children ourselves,” said Tara Glasgow, the research and development lead for the company’s baby products franchise worldwide. “We would never sell a product we didn’t believe was safe.” 

So did the juries get it right or wrong? Is it plausible that Johnson’s Baby Powder — that clean-smelling soft stuff that’s a medicine cabinet staple, packaged in milky-white containers and supposedly mild enough for babies’ bottom — can cause cancer? It’s not an easy question to answer. 

Difficult to blame
“There is no way we’re ever going to know for certain that any exposure is necessarily causal to a disease,” said Shelley Tworoger, an associate professor of medicine and epidemiology at Brigham and Women’s Hospital at Harvard. “We might be 99% sure,” in some cases, she said, “but there’s usually no way to guarantee that what you see is actually the truth.”

Cancer is hard to study because it develops over a long period of time and is influenced by many factors, including genes, behaviours and environmental exposures. The best we can do, Shelley said, “is look at the preponderance of the evidence.” Talc is a naturally occurring clay mineral composed of magnesium and silicon. Known for its softness, it is used in cosmetic products like blush because it absorbs moisture and prevents caking. It is also an additive in tablets, chewing gum and some rice. It’s often mined in proximity to asbestos, a known carcinogen, and manufacturers have to take steps to avoid contamination.

Many women use the powder on their inner thighs to prevent chafing, while others sprinkle it on their perineum, sanitary pads or underwear to stay “fresh” and dry. A 1980s ad campaign for a once-popular powder promised with a catchy jingle that “a sprinkle a day helps keep odour away.” There has never been an experiment to see what happens when you deliberately expose women to talcum powder — for practical and ethical reasons, there never will be — so scientists must rely on observational studies that can link an exposure to a disease but cannot determine a cause-and-effect relationship.

In 1982, Daniel W Cramer, a Harvard professor, and his colleagues compared 215 women with ovarian cancer and 215 healthy women who served as a control group. Compared with non-users, women who used talcum powder were at nearly twice the risk for having ovarian cancer, and those who used it regularly on their genitals and sanitary pads were at more than 3 times the relative risk. At least 10 subsequent studies echoed the results, with varying degrees of increased risk. But a small number of studies did not find a heightened risk for talc users.

When researchers pooled the results of similar studies involving nearly 20,000 women, they found powder use was associated with a 24% increased risk for ovarian cancer, an uncommon disease but one that is often fatal. If the finding is true, it means that for every 5 or 6 talcum powder users who develop ovarian cancer, one may be a result of talcum powder use, Steven A Narod, an expert in cancer genetics from Toronto, said.

Why talc use might lead to cancer is not clear. Studies have shown that talc crystals can move up the genital-urinary tract into the peritoneal cavity, where the ovaries are. 

Indeed, a pathology report on Berg’s tumour found talc particles embedded in the tissue.There is also a plausible mechanism, Tworoger said, because talc particles can set off inflammation, and inflammation is believed to play an important role in the development of ovarian cancer.

Although Johnson & Johnson’s talc supplier added warning labels in 2006, J&J did not add similar warnings to its products, according to litigation documents. Baby powder does carry a warning to keep it out of the reach of children and many pediatricians discourage its use on babies, who can become ill or die after breathing in the particles. Inhalation studies in female rats demonstrated carcinogenicity, according to the National Toxicology Program. Condom and surgical glove makers have stopped dusting their products with talc.

“Talcum powder is an interesting case, because it’s not something that’s necessary,” said Dr Anne McTiernan, an epidemiologist with the Fred Hutchinson Cancer Research Center in Seattle. “If there’s any doubt, why should anyone use it?”As for Berg — the Sioux Falls woman with advanced ovarian cancer — she won her lawsuit against Johnson & Johnson, but the jury did not award damages. She hopes other talc lawsuits will raise awareness.“I knew nothing about this before,” she said. “I figured baby powder is for babies, it must be safe.”