Do 3D films make you dizzy – or is it just your imagination?

3D films had a strange effect on Jason. Shutterstock

The realism of today’s 3D blockbusters can blow audiences away. By using 3D glasses to present different images to the two eyes, stereoscopic 3D technology fools the brain into believing it is viewing a real scene rather than a flat image on a screen. Now 3D televisions enable viewers to experience the effect at home as well.

Yet 3D has not become as popular as some might have hoped. Many people say watching 3D gives them unpleasant side-effects such as headache or nausea. Scientists don’t fully understand why this is. It’s true that badly made 3D effects can cause discomfort. However, makers of 3D content are well aware of the possible issues and work hard to avoid them.

A more fundamental problem may be conflict between different senses. When we watch a film such as Avatar, our visual system may tell us that we are wheeling high in the skies of a distant moon, but other senses tell us that we are sitting motionless in a chair. Of course, 2D films present this kind of conflict as well, but our brains may simply be more used to accepting that 2D content is not “real”.

Some people have suggested that 3D content may cause more serious side effects. For example, Samsung’s safety leaflet links its 3D TV set to a vast range of possible symptoms – not only headache, fatigue, motion sickness and eye strain, but also decreased postural stability, altered vision, dizziness, cramps, convulsions and even loss of awareness. Clearly if 3D TV has such effects, there are important safety implications. But to date, very little work has been done to assess this.

We recently invited 433 volunteers, aged from 4 to 82 years, into my lab to watch the film Toy Story on either a 2D or 3D TV. We used two common types of 3D TV, known as “active” and “passive”. Participants carried out a battery of tests designed to assess their balance and coordination, both before and after viewing. They wore two triaxial accelerometers – small devices to record their body movements – as they walked around a simple obstacle course. To assess eye-hand coordination, participants played a “buzz the wire” game, guiding a hoop along a convoluted wire track without allowing the two to come into contact.

We argued that, if viewing 3D made participants dizzy, they would take longer to complete the obstacle course, and/or the accelerometers would show that their body movements were less stable. If it affected their vision, they would take longer to complete the “buzz the wire” game, and/or make more mistakes.

Some people have suggested that adverse effects with 3D reflect underlying visual problems. So we also had our volunteers’ vision thoroughly assessed by eye care professionals before they visited the lab.

Of course, Holly’s nausea had nothing to do with the 1kg of popcorn she’d just eaten. Shutterstock

On our objective tests of balance and coordination, we couldn’t detect any effects of 3D at all. Not surprisingly, people tended to perform a little better the second time round. But it didn’t seem to matter whether they had watched the film in 2D or 3D, or whether the 3D was active or passive. We also couldn’t find any links between age or eyesight and whether people were affected by 3D.

We did find that people who had viewed the 3D movie reported that the depth was more realistic. They also reported more adverse effects, mainly headache and eye strain, but also including dizziness or nausea. However, it’s not clear that the dizziness was really due to 3D.

Craftily, we gave some of our volunteers 3D glasses, making them think they were viewing in 3D, but showed them the film in 2D. These people reported dizziness at about the same rate (3%) as those viewing real 3D. In contrast, people viewing real 3D were much more likely to report headache or eyestrain (around 10%) than people who just thought they were viewing 3D. This suggests that while 3D gives some people a headache, it doesn’t really make people dizzy – people just expect it to.

Of course, it’s possible that 3D caused an impairment that was so subtle or transient that our tests failed to detect it. On the other hand, that also implies less cause for concern in everyday life. We also tested only one 3D film, choosing Toy Story as something fun and engaging for all age-groups. Even if computer-generated 3D from the experts at Pixar doesn’t cause dizziness, it remains possible that less carefully-controlled 3D content -– say, live-action football –- could do so.

Nevertheless, given the lack of previous work in this area, our study provides welcome reassurance. Can 3D effects give you a headache? Yes, for some people. Can they make you dizzy? Probably not. Do they make Toy Story more exciting? That depends who’s watching.

When the phones went dead: 7/7 showed how disasters call for tomorrow's tech

The greater capacity of 4G phone networks means emergency services can use more than just voice. Rui Vieira/PA

One aspect of the London bombings of 7/7 that many who were there remember is that their phones went dead. Mobile phone coverage in parts of central London was almost unavailable. This was not due to damage; the emergency services had shut down public access to the networks.

At times of crisis communications are essential. The emergency services need to coordinate their response while the general public want to contact loved ones and find out what’s happening. The problem is that there simply isn’t enough capacity for everyone to use the networks simultaneously, particularly in densely populated areas like central London.

Networks of all types are designed to cope with typical traffic demands, and so in exceptional circumstances they become massively overloaded. Operators need to prioritise access. At such times, the emergency services invoke the government’s Mobile Telecommunication Privileged Access Scheme (MTPAS) procedure. This is where the police “Gold” commander – the senior officer managing a disaster or emergency event – can notify mobile network operators that they should start prioritising calls and messaging from the emergency services over others. This can be set to operate within defined geographic areas.

SIM, the key to the network

All mobile phones contain a Subscriber Identity Module, universally known as a SIM card, which stores network-specific information that authenticates and identifies subscribers on their network. Each SIM is also assigned to a privilege access class, which is a code number between 0-14. For general users this will be in the range 0-9, while emergency services responders are assigned classes 12-14.

When connected to a mobile network via a nearby base station, the details in the SIM card are transmitted over the network. During an emergency when MTPAS has been invoked, the privilege access class is checked and the network will drop attempts to connect from non-emergency class SIMs.

So while the network is certainly still up and running, it will seem unobtainable until the phone moves further from the MTPAS-controlled area where a connection can be re-established. Emergency 999 calls are unaffected. This way the mobile network cells in the area are free for use by the emergency services.

Packing TETRA

On July 7 2005, police requested O2 to invoke MTPAS (or rather its predecessor, Access Overload Control or ACCOLC) within one square kilometre of the Aldgate Tube Station for a period of four hours. Unfortunately this was only partially successful because not all emergency service personnel at the time had MTPAS-equipped mobiles, which meant their calls were blocked too. Following an inquiry after the event, that problem has been addressed.

In addition to using a mobile network, since 2005 the emergency services have had their own dedicated digital communications network called TETRA (TErrestrial Trunked RAdio). But TETRA has not been without its problems – and now the government is planning to replace it on the grounds of cost and its limited capability for transmitting data.

Today’s emergency services want to make better use of video and exploit the potential of real-time mapping applications – both of which demand a network with a greater data-handling capacity.

The future is 4G (until 5G comes along)

The natural place to find this capacity is the 4G mobile network that is now being rolled out around the world. But this will require new services to be designed and built for emergency services use. For example, the walkie-talkie style push-to-talk feature offered by TETRA for police officers, firefighters or paramedics who don’t want to be scrolling through menus and contact lists – they need to be able to quickly just push and talk to colleagues.

The demand for this sort of feature has been sufficient that the next release of the international 4G network standards now incorporate this feature as part of an effort to support mission-critical and public safety use.

Of course, moving all emergency services’ communications to the mobile network won’t mean they start monopolising the network over the general user. Emergency service use will need to be partitioned and managed separately from that of the general public – and for those emergency situations, MTPAS will still be available to fall back on.

Tempting as it may seem, there's no evidence to suggest life on Comet 67P

No green little men as far as the eye can see. ESA/Rosetta/NavCam , CC BY-NC-SA

As far as underwhelming headlines go: “No Alien Life Found on Comet” must rank very close to the top. An article with this title appeared in the Guardian on July 6 in response to a story claiming that there could be life on comet 67P/Churyumov-Gerasimenko.

But there simply isn’t enough evidence behind this theory. The chance that life could flourish on a freezing body with no sunlight or oxygen is in fact vanishingly small.

The claims were made at the National Astronomy Meeting in Llandudno, Wales, as well as in a press release ahead of the conference. I was asked to comment on the press release, and remarked that I found the claim ‘highly unlikely’ Nevertheless, the story got picked up by the media and naturally created a storm on social media.

Of course, there has been enormous interest in reports about the comet, which is the target of the European Space Agencey’s Rosetta mission, before. Other discoveries about the comet have been published in peer-reviewed journals and many amazing images of the comet’s surface have been reproduced on websites and in newspapers across the globe.

But in all this coverage, there has until now not been one sniff of a hint of a rumour that the comet, currently speeding towards the Sun (and coming closer to Earth), might be bearing alien life.

Shaky ground

So what is the story behind the headline? It comes from interpretation of images of features on 67P’s surface in terms of production by microbial organisms. In fact, the press release was entitled: “Do micro-organisms explain features on comets”, a question which, in my opinion, leads to the succinct answer “No”.

The authors, astrobiologists Max Wallis from the University of Cardiff and Chandra Wickramasinghe from the University of Buckingham, propose that the environment of the comet might be suitable for microbes to survive.

Alien life in the eye of the beholder? ESA/Rosetta/NAVCAM, CC BY-SA

They argue that some micro-organisms on Earth can survive temperatures as low as -40°C (although most studies suggest that -20°C is the limit). And the comet’s temperature should have heated up to around that now that it is closer to the Sun, meaning micro-organisms could be active. In particular, they argue that the presence of water ice and organic compounds on the surface of the comet – along with cracks and fissures which bacteria could colonise – are all signs that life could be present.

Indeed, it is not completely impossible. The lack of light and no atmosphere does not necessarily mean that living organisms can’t exist on a comet. Abundant fauna thrive in the dark of Earth’s deep ocean floor. Similarly, bacteria and other micro-organisms can survive at low temperatures – and have been preserved and found to be viable following freezing.

But one of my greatest problems with this argument is that there are many non-biological mechanisms which can produce organic compounds: organic molecules, which are precursors for life, are not necessarily biotic (created by living organisms). Also, photosynthesis is out, as there is no light. What chemical reactions are taking place that might drive an ecosystem? I am not certain that there is one.

Leaving all that aside and accepting that microbes might survive on the comet in some form of hibernation, one very significant question remains. Where have they come from? That is one of the main issues I have with the authors' version of Panspermia, which states that life came to Earth via bodies from outer space.

The origin of life on Earth is not fully understood, but we are making great strides towards recognising the mechanisms that make up each stage. Placing those mechanisms in an unknown environment and suggesting that life on Earth was seeded by microbes on comets solves nothing. It merely moves the problem further away, making it even harder to study.

Is it a slow summer? Are we already fatigued by the heatwave which lasted a couple of days? I suppose if there is nothing else to worry about, then we can ponder the chances of finding alien life beyond the Earth. Now, what’s that Curiosity Rover up to on Mars?

Disclosure

Monica Grady receives funding from the STFC and is a Trustee of Lunar Mission One.

Whisper it – jet engines are getting quieter

Run silent, run high. Engine by Christian Lagerek/shutterstock.com

With no sign of our appetite for air travel diminishing, we need to create quieter aircraft that are easier to live with. In fact, while those living near airports may beg to differ, data included in the Airports Commission report into a new runway for London shows a very significant reduction in aircraft noise over several decades.

The noisiness of an individual aircraft at departure and approach is described by its Effective Perceived Noise Level (EPNL). This is measured when the aircraft enters service, and is used to track noise improvements between successive generations of aircraft.

Noise levels have, despite what some may feel, been falling. Airports Commission/Crown Copyright

As this Airports Commission report chart shows, EPNL has fallen since modern turbojet and turbofan engines were first introduced – roughly a halving of radiated acoustic energy per decade. This is a remarkable technical achievement – a 95% reduction in the sound power generated by aircraft jet engines since their introduction.

However, over the same period there has been an explosion in air travel and the number of flights and passengers has risen exponentially. The issue then is not whether aircraft are getting quieter, but whether they are doing so sufficiently quickly to compensate for the fact that there’s so many more of them.

The answer also depends upon how quickly older, noisier aircraft are retired from service. In the UK, the net effect has been positive – aircraft are becoming quieter at a rate that outweighs the increase in traffic and the Airports Commission expects this trend to continue.

When air is too loud

Aircraft noise is generated by turbulent flows of air over and around surfaces. This includes air going into and out of the engine, and air flowing around the airframe – fuselage, wings and other aerodynamic surfaces such as flaps, slats and landing gear.

What has brought about the continuing reductions in aircraft noise since the 1970s? The largest factor driving down aircraft noise has been a move towards higher and higher “bypass ratios” – originally sought after for greater engine efficiency, but which fortunately generate lower noise too.

Lockheed Tristar, a classic airliner of the 1970s. Jon Proctor

The bypass ratio is the proportion of the air which enters the engine inlet but bypasses the turbojet and exits at low speed, in comparison to the hot, high-speed jet coming from the engine core.

This ratio has risen – all the air entering turbojet engines of the earliest airliners passed through the engine. In the turbofan designs of the 1960s and early 1970s this fell to around a third, while the engines powering large modern aircraft today such as the Airbus A380, Boeing 787 and Airbus A350 draw only a tenth of the air into the engine core. These engines have larger, more slowly-rotating fans with fewer blades – all features that reduce the aircraft’s noise profile.

Quieter engines

This process still has some way to run. Turbofan engines in smaller aircraft have lower bypass ratios than those in larger, wide-bodied aircraft, but development of new engines is underway for the venerable Airbus A320 and Boeing 737 families, and newer jets such as the Bombardier CSeries and the Mitsubishi MRJ. Such narrow-bodied jets constitute 70% of the commercial fleet, so this will have a profound impact on noise levels as they replace older jets.

Better engines for larger aircraft are coming too, based on the same turbofan technology. Using a gearbox to uncouple the fan and the low pressure turbine will improve performance and reduce noise. A market leader here is the Pratt and Whitney PW1000G geared turbofan developed over the last decade and due to enter service, is anticipated to lead to larger, quieter and more fuel-efficient engines with bypass ratios approaching 15:1.

Computer simulation of acoustic energy streaming out of a turbofan intake at different fan speeds Z Rarata/University of Southampton, Author provided

Other techniques to quieten engines include acoustic liners on the inner walls of the intake and bypass ducts which absorb acoustic energy, and improved aerodynamic fan design and outlet vanes. Both of these have been made possible by the power of modern computers to accurately simulate airflow dynamics – there is scope for further advances in this area.

Quieter airframes

Reducing airframe noise is more challenging. The use of flaps and slats and deploying of landing gear at approach are necessary to slow the aircraft while maintaining lift, but they all create additional noise. It’s hard to have one without the other. Perhaps the most effective means to ensure both will come from new, improved aerodynamic aircraft designs that can provide better low-speed performance without sacrificing fuel efficiency at cruise.

In the longer term, after 2050, completely new aircraft geometries that use blended wing designs, and even morphing geometry – aircraft that change shape – will potentially lead to major reductions in airframe noise, greater efficiency and improved environmental impact. All just as well, as by then there’ll be many more people still wishing to fly.

We all age at a different speeds – and scientists have worked out how to calculate it

Turns our we are as old as we feel - and look. wavebreakmedia /Shutterstock

A study has confirmed what many of us have been saying for years: age is nothing but a number. The researchers developed a method to determine the pace of ageing in individuals by looking at a range of biomarkers – including blood pressure and gum health. The study participants, all aged 38, varied widely in “biological age” and those ageing more quickly also looked older and reported more health problems.

The concept of biological age is often thought of as the proportion of an individual’s ultimate lifespan that has elapsed. In the context of this study, however, its measurement and meaning are slightly different. Examining 954 men and women in the Dunedin Birth Study Cohort, the researchers determined the biological ages of the participants to years above or below 38, which gave a range from 28 years to 61 years.

The only definition of ageing that really works is based on populations rather than individuals. Ageing is an increase in the likelihood of dying with increasing chronological age, as shown in this table. That is one reason why this work is significant; because it gives an idea of ageing in an individual.

According to population measures, in the absence of any other information, two people aged 65 have an equal risk of dying in the coming year. If one is destined to die from an undiagnosed cancer within two years and the other lives to 95, which individual is older? This is one reason the search for biomarkers of ageing is important, but the authors of this study give yet another reason.

Studying age-related diseases vs studying ageing

Age is the major risk factor for more than 75% of the mortality suffered by those aged over 64 (based on UK ONS 2013 mortality data), including cancers, circulatory and respiratory illness and neurodegeneration. The traditional view is that each of these many conditions have their own particular causes. This view has driven much research – and funding.

However, the view of biogerontologists, who study the biology of ageing, is that there are a few causes of ageing which substantially contribute to all of these age-related conditions. According to this view, if just a fraction of the billions spent on researching individual conditions were spent on finding and treating the basic causes of ageing, the payoffs could be huge, not least in terms of extended productive (tax-paying) lifespan and reduced healthcare costs.

This sort of basic research has been poorly funded in the past, but the logic of, and evidence for the biogerontologists’ view is beginning to be understood. Treatments to delay the onset of ageing and hence extend healthy lifespan in a majority of the population are likely to be found in the next 20 years.

Ageing alogorithm

They may already be being tested in animal models in a lab somewhere. But because humans are so long-lived, we can’t wait 40 or 50 years to see if it works. To test it in humans we need measures of biological age. To generate their estimates of biological age, the researchers used a previously described algorithm based on seven fairly common biomedical parameters.

They then produced a “pace of ageing” measure based on 18 parameters covering a range of organs and systems and known to change with age. Measures were taken at ages 26, 32 and 38. These included waist-hip ratio, lung and kidney function, blood pressure, cholesterol, even gum health. Study members with higher biological ages also showed a more rapid pace of ageing over the previous 12 years.

Study members with older biological ages and a faster pace of ageing looked older than others and reported more health problems. They also had poorer cognitive function, vascular health, grip strength, balance and motor ability.

Can the wrinkles on your face actually reveal your pace of ageing? Goodluz/Shutterstock

Pace of ageing was scaled so that the mean was one year of physiological change per chronological year, with a range of 0-3 years of change per chronological year. It is frightening to think that the study member with a biological age of 61 may physiologically age 18 years within the next six chronological years, taking him (most likely a man, as men typically die earlier than women) to near his mean population life expectancy (around 80-years-old). According to the model this 38-year-old person may die within six or seven years.

Advances in anti-ageing therapies and in estimating biological age raise big questions for society, both at an individual level and in the public and private sectors. We should not be frightened of them, but we should start talking about these changes now, before they arrive.

The science of strawberries: why do they taste so good?

Mmm you can really taste that spicy methyl cinnamate. Philip Toscano PA

Each year, spectators at the Wimbledon tennis tournament get through a whopping 30 tons of strawberries in the course of a summer fortnight. It is no wonder that the association between Wimbledon and strawberries is such a marketing triumph. But why do we fall for it?

Scientists have actually worked out what it is we love so much about strawberries by pinning down the molecular basis of the its aroma. This can also explain why wild strawberries often taste better than shop-bought ones. The good news is that the work is helping them uncover how to make them even more delicious.

Serendipitous strawberries

Strawberries have a long and proud history – even the ancient Romans ate them. We know this from the works of poets Virgil and Ovid, which referred to them as fraga. The medieval artist Hieronymus Bosch had several strawberries in his triptych the “Garden of Earthly Delights”, painted around 1500.

Some 500 years ago, the wood strawberry, Fragaria vesca, was around in Europe and the musk strawberry, Fragaria moschata, was starting to be cultivated. These were what we would recognise today as wild strawberries, characterised by small, misshapen fruit.

The Garden of Earthly Delights central panel Hieronymus Bosch/wikimedia

The most common type of strawberries we eat today came to us by coincidence via the transatlantic explorations of Christopher Columbus and his successors. First the very hardy Virginia strawberry (Fragaria Virginiana), a native of North America, reached Europe in the 17th century. Then early in the 18th century, the large Chilean strawberry (Fragaria Chiloensis) came to France.

As a result of an initial fortuitous pollination, these two species were crossed, giving rise to the cultivated strawberry we eat today, Fragaria ananassa, sometimes known as the “garden strawberry”. This combined in one fruit two particular traits inherited from its forerunners: hardiness and large fruit.

The chemistry of taste and smell

When I was young – in the 1950s – you only saw strawberries in the shops for a couple of weeks of the summer, roughly coinciding with Wimbledon. Now we have them all the year round.

This is because strawberry breeders have been aiming for fruit with particular (and marketable) properties such as uniform appearance, large fruit, freedom from disease and long shelf-life. But by concentrating on genetic factors that favour these qualities, other genes have been lost, such as some of the genes responsible for flavour.

The balance of sweetness and acidity is very important to the taste of a strawberry. As strawberries ripen, their sugar content rises from about 5% in unripe green fruit to 6–9% on ripening. At the same time, the acidity decreases, meaning ripe strawberries taste much sweeter.

The ripening process is controlled by a hormone called auxin. When its activity reaches its peak, it causes the cell wall to degrade and so a ripe strawberry becomes juicy as well as sweet. At the same time, gaseous molecules from the strawberries make their way up the back of the throat to our nose when we chew on them, where they plug into “smell receptors".

But how do scientists know which molecules are responsible for taste and smell? More than 350 molecules have been identified in the vapour from strawberries – and around 20 to 30 of those are important to their flavour.

Unlike raspberries, there is no single molecule with a “strawberry smell”. So what we smell is a blend – these molecules together give the smell sensation we know as “strawberry”. Chemists made up a model strawberry juice containing what they thought were the most important odorants, at the same concentration found in the original juice extract. Sensory testers agreed that this model closely matched the real extract.

They then made up a series of new mixtures, each containing 11 of the 12 main odorants, with a different molecule missing from each. The testers could therefore find out if omitting that molecule made any difference to the odour. For example, leaving out 2,5-dimethyl-4-hydroxy-3(2H)-furanone or (Z)-3-hexenal was noticed by virtually all the testers – and omitting compounds known as esters – chemical compounds – such as methyl butanoate, ethyl butanoate or ethyl 2-methylbutanoate were also spotted by most.

This analysis led to the characterisation of basic sensory impressions of strawberries. One of these was a sweet caramel-like scent, which is due to two molecules with a structure containing five-membered rings of carbon atoms called furaneol and mesifuran.

Common or garden strawberry. David Monniaux/wikimedia, CC BY-SA

Another impression was a fruity scent, due to the esters, which are responsible for the aroma of many other fruit, including banana and pineapple. They can make up 90% of the aroma molecules from a strawberry. It’s important that the contribution of the esters are balanced – too much gamma-decalactone for example, and the strawberries will start to taste like peaches. The analysis also pinpointed a green note due to (Z)-3-hexenal responsible for the smell of “cut grass”.

Fragaria futura?

Some modern varieties of strawberry are lacking in the quantity and range of molecules. Scientists have analysed wild varieties of strawberries, like the musk strawberry and wood strawberry to find out why.

It turns out that while this fruit may not look so good, it produces a greater quantity of flavour molecules, as well as molecules that are not found in many of the strawberries we buy in the shop. Methyl anthranilate is one of these, it is also found in grapes and contributes a strong and sweetish edge to the aroma. Another is methyl cinnamate with a spicy note.

In their quest for better tasting fruit, scientists are starting to investigate the genes responsible for making particular flavour molecules.

Some 20 years ago, experiments on the effect of adding cream to the flavour of fresh raspberries were carried out. These found that heating enhanced raspberry aroma, but adding cream decreased it.

While this exact experiment does not seem to have been carried out in strawberries, scientists working with the food chain Morrisons recently reported that the perfect strawberry-to-cream weight ratio is 70:30. What’s more, you should eat it within two minutes and 50 seconds of serving, before the strawberries start to get soggy and shrink. Perhaps you should carry out this experiment yourself this summer? Enjoy your strawberries.

NASA mission brings Pluto into sharp focus – but it's still not a planet

Artist's impression of New Horizons approaching Pluto and its moons. NASA

The new pictures that NASA’s New Horizons probe has begun to beam back have revealed Pluto and its largest moon, Charon, in ever greater detail from what is the first ever spacecraft fly-by.

Pluto has an atmosphere and five known moons which have been glimpsed by New Horizons as it closes in, and while we can’t predict what we will find, whatever is revealed is sure to lead to renewed cries that Pluto be re-classified as a planet – a status it lost in 2006.

Two sides of Pluto (larger and browner) and Charon (smaller and greyer) seen as New Horizons approaches. NASA/John Hopkins University APL/SWRI

Pluto was embraced as the solar system’s ninth planet upon discovery by Clyde Tombaugh in 1930. He’d been looking for a planet where faulty data suggested a planet-sized body was perturbing the orbit of Neptune. This, he felt, was it – and the world agreed. Pluto’s mass was at first thought to be roughly the same as the Earth’s, but by 1948 estimates had shrunk it to the size of Mars.

When Pluto’s largest moon Charon was discovered in 1978, Charon’s orbit showed that Pluto’s mass is actually about only 0.2% of the Earth’s (one-sixth that of the Moon), and we now know that its diameter is about 2368km, or two-thirds that of the Moon.

Being so insubstantial, then, should Pluto be classed as a planet? There may seem no obvious reason why not. After all, the Earth is only 0.3% the mass of Jupiter. Planets clearly span a wide range of masses. But the main reasons why delegates to the International Astronomical Union (IAU) voted to demote Pluto from planet status are not based primarily on mass or size.

Pluto is one of many

Since the 1990s, many other roughly Pluto-sized bodies have been discovered beyond Neptune, such as Eris, Huamea and Makemake. There are more than a thousand objects now documented in what is called the Kuiper belt, a region beyond Neptune where it seems no large objects were able to form.

If Pluto had been discovered along with the others rather than 60 years earlier, there can be little doubt that no one would have called it a planet in the first place. There is nothing special about Pluto, other than the accident of having been the first to be discovered.

Eight of the so-called trans-Neptunian objects, including Pluto, and their moons. Lexicon

The crucial part of the definition of planet adopted by the IAU in 2006 is that a planet should have “cleared the neighbourhood of its own orbit”. Neptune, 8,600 times more massive than Pluto, has achieved this because neither Pluto nor anything else that crosses Neptune’s orbit comes close to rivalling Neptune’s mass. On the other hand Pluto clearly does not comply to this definition – it has rivals of comparable mass in addition to being overshadowed by the vastly more massive Neptune.

While it may be that this definition is hard to apply in other solar systems, it works for ours and is a far neater approach than including every Kuiper belt object as a planet – thousands of them, which would be ridiculous. The alternative of defining a size or mass minimum at which an object ceases to be a planet would suffer from our variable and imperfect ability to measure their size or mass remotely.

The Kuiper belt is a busy place. NASA/Johns Hopkins University APL/SRI/Alex Parker

A linguistic fudge

Nevertheless, the IAU shied away from completely stripping the Pluto of its appellation of planet by inventing a new term, dwarf planet. This denotes an object orbiting the sun that has not cleared its orbit, but which has sufficient mass for its own gravity to have pulled it into a near-spherical shape (described as hydrostatic equilibrium). This applies to Pluto, Eris and a few other Kuiper belt objects, and also to the largest asteroid, Ceres.

‘Pluto a planet, Jim? You’ve got to be kidding me.’ NBC Television

I think that was an unnecessary concession to the Pluto-is-a-planet lobby, though it proves that the IAU is not controlled by “a clique of Pluto-haters” as one astronomer has claimed. In fact it’s messy for two reasons. First, shapes cannot be precisely determined for objects that have not been visited by a spacecraft; they have to be assumed on the basis of mechanical models that could easily be wrong. Second, whereas the giant planets (Jupiter, Saturn, Uranus and Neptune) are planets, by the IAU’s own definition the dwarf planets are not planets. As Mr Spock might have said, “That’s illogical, Captain.”

Planetary scientists have a duty to describe the nature of the solar system as clearly as possible, and to lead the public to a clearer understanding of nature – irrespective of how its elements are classified. Appealing to sentiment, seeking celebrity endorsement and posting photos of presidential candidates with “Pluto is a planet” T-shirts is not a good way to advance anyone’s understanding. It’s time to let go of the past, and embrace Pluto a fascinating world and the most interesting member of the Kuiper belt.