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‘Where everybody knows everybody else’: life as an instrument scientist

The intimate atmosphere of the university campus at Bath University in the UK where I studied physics reminded me of Libreville, the small town I had left behind in Gabon. After completing a year-long placement at the Institut Laue-Langevin (ILL) in Grenoble, France, in 2004, which contributed to my master’s degree in physics, I felt that same atmosphere where everybody knows everybody else.

I enjoyed the experience of my placement so much that I came back to the ILL in 2005 to do a PhD, which involved studying self-assembling filament-like systems for biomedical applications. After a postdoc developing neutron and X-ray techniques to study biological systems, in 2014 I became a staff scientist at the ILL, running the lab’s D19 neutron diffractometer. Part of my responsibility is to help researchers from all over the world make the most of this facility, applying my expertise on their behalf to carry out world-class science.

The ILL, which is located at the foot of the French Alps, is an international research centre with close to 500 people from 40 different countries. The facility has around 40 different instruments including diffractometers and spectrometers. The D19 instrument is a world-leading monochromatic thermal diffractometer that is used for detailed molecular studies in chemistry, biology and polymer science. Examples of research performed on D19 includes looking at proton hopping in molecular solids, studying enzymatic pathways connecting glucose to fructose, carrying out structural studies of DNA and analysing of the high-performance polymer Kevlar. The choice of which wavelengths to use for a particular experiment depends on the sample size and crystallographic unit cell, with D19 utilizing neutrons with a wavelength from 0.95 to 2.42 Å.

The choice of instrument and technique very much depends on the problem at hand – academic or industrial. As an instrument scientist, my tasks are diverse and variable. The primary one is to provide support to users for a variety of scientific experiments. Here my job is to assist the experimental team to obtain the best possible results from samples the preparation of which has often taken many months of work. The planning of the experiment will strongly depend on the specific nature of the sample, the length of beam time allocated to that particular experiment and obviously what the users need and expect.

The instrument-scientist role also implies a strong involvement in the development and upgrade of the instrument – something that is carried out very much in consultation with the external user community. Indeed, D19 was recently rebuilt and upgraded thanks to a grant from the UK’s Engineering and Physical Sciences Research Council.

Broadening horizons

Working at a facility like the ILL is not without its challenges. Experiments can be tough and tiring, and instrument scientists have the added worry of being responsible for users’ samples given that the result of their experiments are often crucial to their research. Sample preparation is often very demanding for users as their samples are often fragile, unstable or rare. This puts some added pressure and you have got to be as committed as if it were your own sample. Rigorousness, the ability to multitask, some creativity, patience and perseverance are great assets that you learn to develop, but it is a constant learning curve.

In addition to helping users, I am also developing my own in-house research work directly derived from both my PhD and postdoctoral work that focuses on protein folding and how this can cause neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease. But one of the advantages of working as an instrument scientist is the opportunity to collaborate on a wide variety of research projects well beyond that to which a typical researcher is exposed. Interacting with research teams from around the world opens up your mind to a variety of different ideas in dynamic and challenging fields, and can lead to interesting partnerships and open up new perspectives. Recently, I had the opportunity to be involved in studying how cellulose fibres behave when they are stretched to breaking point. These results will be useful in the manufacture of textiles and have an impact on other industrial applications.

Science facility with mountains

On a daily basis this type of role benefits greatly from the interdisciplinary nature, the scientific background, and the multiculturalism of the ILL’s working environment. For me, the single biggest aspect that distinguishes a research centre like the ILL and anywhere else is precisely this sense of variety and diversity. The Grenoble campus is unique in that we have other world-class research facilities next door, such as the European Synchrotron Radiation Facility (ESRF), the European Molecular Biology Laboratory and the Institut de Biologie Structurale.

In all areas it is very clear that there is strong emphasis on interdisciplinary science, and neutrons occupy a central role alongside other major techniques including X-rays, electron microscopy and nuclear magnetic resonance. The European Photon and Neutron campus site – combining ILL, ESRF and the EMBL – naturally fosters a sense of community spirit among its users and staff.

User demands

The work rhythm of an instrument scientist varies and is very much correlated to the reactor cycles, which typically last 50 days. During this time, one of my colleagues or myself will be responsible for running the experiments. The instrument and user experiments are always the priority, so you have to make sure that however you organize your working day, you are – or can be – made fully available to the users whenever needed. Users apply for beam time through a competitive proposal system that is very carefully peer reviewed by a scientific panel of world experts – only the best experiments that are judged feasible on the instrument are selected and a fixed number of days will be allocated to the experiment. Experiments are mostly scheduled back to back so it is very important to maximize the time allocated to each experiment. It is therefore vital to work as efficiently as possible to allow the users to collect the data they need in the time given.

The structure of the working day very much depends on the type of experiment – some are more challenging than others in that they may be less standard in terms of set-up and sample environment, or simply because the sample is not behaving as planned. There are many parameters to take into account and, of course, not everything goes according to plan. As the intervening shutdowns last anywhere from two weeks up to three months during the winter period, that time can be spent catching up with data processing for the users, spending time on your own research, and writing the papers we were too busy to draft while the reactor was on. There is really no such thing as a typical day and that contributes to the attractiveness of the job.

Targeting industry at the UK’s neutron source

“We build new instruments when we come up with new areas of science that we can explore with neutrons,” explains Chris Frost as he shows Physics World around the ISIS Neutron and Muon Source in Oxfordshire, UK. With new instruments being built and others being upgraded to meet the growing demands of industry and academia, it is apparent that there are lots of new ideas around. Indeed, some parts of the ISIS complex still look like a building site. “It’s a good thing,” adds Frost, who is industry liaison manager and instrument scientist at ISIS. “It means that someone is investing in building something here. We are regularly building new instruments or modifying the ones we already have.”

Having produced its first neutrons in 1984, ISIS is still Europe’s only pulsed source of neutrons. Today, it employs around 360 staff and is visited by more than 3000 users from over 30 different countries each year. The facility’s first target station – with 20 instruments – has been remarkably successful, with more than 10,000 research papers having been written off the back of work carried out there. In 2003 the facility won support for a £145m ($224m) second target station that began producing its first neutrons in 2008. Initially containing seven instruments – including three reflectometers, one spectrometer and three diffractometers – the facility has just completed a £30m upgrade that will see the addition of four instruments, just six short of full capacity.

We started anticipating the needs of the users over the next 10–20 years, so now there are many areas of science into which neutrons are providing key insights

ISIS is the only neutron source in the world running two target stations and the second station marks a shift in focus for ISIS from traditional areas such as magnetism and superconductivity to soft condensed matter, which includes the study of polymers and biological materials. While the first target station provided higher-energy, shorter-wavelength neutrons with a pulse rate of 50 Hz, the second target station will provide lower-energy, longer-wavelength neutrons with a pulse rate of 10 Hz – perfect for studying biological samples. “When we started at ISIS, many people were using neutrons to study magnetic systems,” says Frost. “We then started anticipating the needs of the users over the next 10–20 years, so now there are many areas of science into which neutrons are providing key insights.”

Industrial use

Neutrons are powerful probes that can provide detailed information on the structure of a range of materials from low-temperature superconductors to thin films of biological samples. Unlike X-rays, neutrons penetrate deep into a sample, revealing its bulk properties rather than just the material’s surface characteristics. As well as being electrically neutral, neutrons also have a magnetic moment, which means that they interact with magnetic materials to reveal details about their magnetic structure and spin dynamics.

Frost’s responsibility is as ISIS instrument scientist for ChipIR, which is one of the four new instruments on the second target station. Its role is to examine the damage that can be done to materials by high-energy neutrons and other particles created when cosmic rays interact with the Earth’s atmosphere. These particles can, in particular, affect chips and other electronic systems in aircraft and cars – not only by damaging the electronics, but also by wiping a device’s memory. ChipIR will be able to test components with a measuring time of just one hour – equivalent to exposing microchips to high-energy neutrons over hundreds of years of flying time in an aircraft. “ChipIR will help industry understand where the vulnerabilities are to help mitigate those problems in ways that are as cost-effective as possible,” says Frost. 

Next to ChipIR is the IMAT neutron imaging and diffraction instrument. IMAT will be used in a broad range of areas such as aerospace, civil engineering, earth sciences and cultural heritage – for example, by measuring the strain in engineering components or the mechanics of cracks in steel. As for the two other new instruments – LARMOR and ZOOM – they are both small-angle neutron-scattering (SANS) instruments that can be used to study magnetism as well as polymers and biological samples. Rob Dalgliesh, an instrument scientist, says that LARMOR “has the potential to be one of the best instruments of its type in the world”. He adds that the instrument will be able to study many samples in 10–15 minutes or less using SANS and will provide a platform for new and exciting types of measurement using multiple techniques.

An industry angle to ISIS is not, however, new. It was back in the mid-1990s, at the first target station, that ISIS built the first purpose-built instrument for industry. ENGIN, which was upgraded to ENGIN-X in 2003, measures strain within a crystalline material assessing the internal structure of an aeroplane wing, for example. With instruments such as ChipIR and IMAT, ISIS is now keen to to build on this collaboration with industry. “Neutrons can solve near-market problems, be it stress in train wheels and bolts that are used in aircraft or providing better understanding of strain in underwater pipes,” says Frost. “Neutrons are a very effective tool for the non-destructive analysis of industrial materials.” 

Users from industry, however, will have to pay for their beamtime if they want to keep the results to themselves rather than publish them in a journal. According to ISIS director Robert McGreevy, industrial participation will be an additional revenue stream for the lab with around 90% of the time on ChipIR being used by industry. Indeed, McGreevy adds that the next instrument to be built at the second target station will likely be another engineering instrument. “Neutron scattering can only be done at big facilities, so industrial engagement is increasing,” he says. “Industry use ISIS to improve their products and processes, and this benefits both the companies and the UK economy.”

Back to the future

While the second target station has taken all the focus in recent years, now some of that is changing back towards the first target station. There are plans to upgrade its target and moderator assembly – the design of which is around 25 years old – based on what has been learned during the construction of the second target station. According to McGreevy, that should result in a three- or four-fold improvement in terms of the neutron flux being delivered to each instrument. “Some instruments might see gains of more than this given the reduction in the background,” says McGreevy. “It would be for a relatively modest cost of around £15m – about the price of two instruments – so it would be a good investment.”

Further ahead, McGreevy adds that there could even be scope for a third target station. “Look at the economics and it is clear,” says McGreevy. “The accelerator is expensive, so the more science you can do with it, the more value for money you get.” Indeed, that optimism for expanding ISIS is not threatened by the upcoming European Spallation Source (ESS), which is being built in Lund, Sweden and will generate its first neutrons in 2019. The UK is a 10% partner in the project where it is building two beamlines. “Our futures are inextricably interwoven – ISIS will not become an obsolete facility,” says McGreevy. “If ISIS was not here, the ESS would not be useful for the UK because you would have no users to use it.”

As we near the end of our tour around both target stations at ISIS, Frost talks about what he sees as the strength of the facility and why it has been not only been successful for the UK, but a pioneering source worldwide. “Instruments scientists here do not just serve the academic community, they are actively part of that academic community,” he says. “We never stop thinking about what you can do next. We have been here for 30 years and we expect to be here for another 30 years.”

How neutrons are made at ISIS

A linear accelerator at ISIS

ISIS produces neutrons by firing high-energy beams of protons at a tungsten target. First, negative hydrogen ions are produced in an ion source and accelerated to 665 keV before being accelerated in the linear accelerator to 70 MeV. They are then stripped of their electrons by a 0.3 µm-thick aluminium-oxide foil to leave a beam of protons that are then accelerated to 800 MeV via a 163 m-circumference synchrotron. Four out of five of the proton pulses kicked out of the synchrotron are sent to the first target station while the fifth pulse is sent to the second target station.

The protons from each beam then hit a tantalum-clad tungsten target where each proton produces 15–20 neutrons with around 2 × 1016 neutrons being produced each second. The proton beam energy deposited in the target on the first target station is 160 kW, and on the second target station is 40 kW. The neutrons are finally slowed down to useable energies by moderators such as water (316 K), methane (100 K) and liquid hydrogen (20 K). Neutrons are then channelled along beamlines to neutron instruments surrounding the targets.

China joins the spallation club

Amid the endless green lychee orchards near China’s southern coastline lies what will be a new science hub for the country’s researchers. Set to be complete in 2018, the China Spallation Neutron Source (CSNS), located some 30 km southeast of Dongguan, will be the nation’s first “super neutron microscope” to peer into the structure and dynamics of a wide range of materials from high-temperature superconductors and polymers to metals and biological samples.

Compared with other microscopic probes, neutrons have unique advantages by having no electric charge, being able to easily penetrate materials and being sensitive to light atoms such as hydrogen. Yet because of the technical complexity and high cost of building spallation sources, only three are in operation today: the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory in the US, the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex in Tokai, Japan, and the ISIS Neutron and Muon Source in Oxfordshire, UK. The European Spallation Source in Lund, Sweden, meanwhile, is currently under construction with first neutrons due in 2019.

Joining the prestigious club will be the CSNS, which was first proposed in the early 2000s. Five years later, the CSNS was top of a list of nine big-science facilities to be built in China. While most existing large science facilities are located around Beijing and Shanghai, the CSNS will be the first to be hosted in south China, with the aim to boost science in the region, which includes Hong Kong and Macau. Construction for the 2.2 billion RMB ($350m) CSNS began in 2012 and all civil-engineering work is set to be finished by the end of this year. Delivery of the first neutron beams is expected to start in September 2017.

While China currently has two research nuclear reactors that are used for neutron scattering – one in Beijing and one in Sichuan – it is spallation that will push the country to the forefront of neutron science. “If [China] is to have access to the highest performance neutron scattering in the future, which it presumably will do as a leading research nation, then spallation is the most sensible option,” says ISIS director Robert McGreevy.

A typical spallation neutron source consists of three parts: an accelerator, target and a suite of instruments. The CSNS will feature a 200 m-long linear accelerator that will accelerate negatively charged hydrogen ions to 80 MeV. The particles, stripped of their electrons and converted into protons, will then be injected into a 75 m-diameter circular accelerator – dubbed the rapid cycling proton ring – to be further accelerated to 1.6 GeV. Upon entering the target station, the high-energy proton beams will strike a set of 15 tungsten plates – each 25 × 10 cm in size – with every proton releasing some 20 to 30 neutrons.

Yuanbo Chen, head of the Dongguan Campus of the CAS Institute of High Energy Physics, and former deputy manager for the CSNS, says the proton target was a key aspect of the project and the team initially looked into having a liquid-mercury target that is currently employed on the SNS and the MLF. “We decided to adopt the tungsten target similar to ISIS,” adds Chen.

These fast neutrons will then be slowed by a liquid-hydrogen moderator before they can be guided to different instruments for experiments. The CSNS aims to produce neutron pulses with a beam power of 100 kW, with bunches of protons being released at a rate of 25 times per second – or 25 Hz. Initially, there will be only three general-purpose instruments – a multi-purpose reflectometer, a small-angle diffractometer and a high-intensity diffractometer. “We hope that more will keep coming in within the next few years,” says Chen.

Daoxin Yao, a condensed-matter physicist at Sun Yat-Sen University in Guangzhou, who is a prospective user of the CSNS, says it is unfortunate that more instruments will not be available from day one. In particular, he points out the lack of spectrometers, which can each cost around 10 million RMB. However, Hesheng Chen, CSNS project manager, says they have put in a proposal to the Chinese government to fund delivery of 12 to 13 spectrometers.

Industrial use

As well as being a boon for academia, the CSNS will also benefit industrial users. “As China is increasingly interested in driving innovation and moving beyond manufacturing technologies developed in other countries, having strong domestic R&D facilities oriented to the studies of materials will be an important national asset,” says SNS director Thom Mason.

Indeed, the money for some of the planned spectrometers, Yao suggests, should not just come from the government but from industry. He points to manufacturing and pharmaceutical companies, including industrial giants PetroChina, Sinopec and China Guangdong Nuclear Power Group, as companies that could have a good use for neutrons.

Although the facility will not be complete for another couple of years, researchers in China are already planning to upgrade the facility to generate a 500 kW beam power, which will be met by increasing the energy of the linear accelerator to about 250 MeV. This will be done using superconducting technology that is being developed by the Institute of High Energy Physics and other partner institutions.

Land has also been reserved for a second target station, which will produce neutron beams at a different frequency. This would be more suitable for experiments in the life sciences. “With more research emphasis on areas like biophysics, it would be good for the CSNS to have a low-frequency target station, which might be 5 or 10 Hz,” adds McGreevy.

European superscope reveals its three ‘first-light’ instruments

The design of the three “first light” instruments for the European Extremely Large Telescope (E-ELT) – the biggest ever optical/near-infrared telescope to be built – has been agreed upon by the European Southern Observatory (ESO), which recently signed agreements for their construction. For the E-ELT first phase – which will begin in 2024 – the superscope will be equipped with the Mid-infrared E-ELT Imager and Spectrograph (METIS); the Multi-Adaptive Optics Imaging Camera for Deep Observations (MICADO); and the High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph (HARMONI).

Located on the summit of Cerro Armazones in the Atacama Desert, in northern Chile, the 39 m main mirror of the E-ELT will gather 13 times more light than the largest optical telescopes operating today. Indeed, the collaboration says that the telescope’s advanced adaptive optics – which adjust the telescope’s deformable mirrors in real time to correct for distortions caused by Earth’s atmosphere – will allow it to take images that are 16 times sharper than those from the Hubble Space Telescope. The colossal telescope will enable astronomers to address fundamental cosmology questions by measuring the properties of stars and galaxies, probing the nature of dark matter, and studying Earth-like exoplanets and young galaxies in great detail.

Eye on the deep sky

MICADO, the E-ELT’s first camera, is being developed by a group of European institutes, led by the Max Planck Institute for Extraterrestrial Physics. The sensitivity of the near-infrared camera will be comparable to the James Webb Space Telescope, but with six times the resolution. It will be able to detect incredibly faint astronomical objects, and reveal the structure of galaxies and nebulae in unprecedented detail. MICADO’s astronomic precision should allow scientists to track the movement of objects that currently appear static, such as star clusters and even individual stars within clusters.

“If we look at two stars on the detector, we will be able to measure their position so precisely and so repeatedly, that if we make the same measurement a year later, we can see whether they have moved apart or closer together by about 1/5 of a micron,” explains Richard Davies, from the Max Planck Institute.

Spectral point-and-shoot

HARMONI – a spectrograph that will split visible and near-infrared light into its component wavelengths – will be built by a European consortium, led by the University of Oxford. Instead of taking spectral data from a single narrow split, like most spectrographs, HARMONI will use a technique known as “integral field spectroscopy” to obtain spatially resolved spectra from across the sky. Light will be split across 152 “slitlets”, each of which will analyse its spectrum at 214 points. This means that more than 30,000 spectra will be obtained at the same time, making HARMONI much faster and more efficient than conventional instruments.

“HARMONI has been designed to be a workhorse instrument,” says Niranjan Thatte from Oxford. “We have designed it to be easy to calibrate and operate, providing the E-ELT with a ‘point-and-shoot’ spectroscopic capability.”

Complementary views

METIS will complement HARMONI and MICADO by providing imaging and medium-resolution spectroscopy across the longer wavelengths of the mid-infrared spectrum – from 3–19 μm – and high-resolution integral field spectroscopy at wavelengths of 3–5.3 μm. It will make full use of the E-ELT’s main mirror to focus on five goals: the physical and chemical properties of exoplanets, proto-planetary discs and planet formation, the history of the solar system, the growth of supermassive black holes, and high-redshift galaxies.

A group of European institutes, led by Leiden University, will develop the METIS instrument. Bernhard Brandl from Leiden told physicsworld.com that the project “is obviously a big challenge, but everyone is excited to be working on the project and we have received a lot of support from the university and the astronomical community in the Netherlands”.

Quantum cats, physicists and stamp collecting, extraterrestrial building work

By Hamish Johnston

The Internet loves cats and our readers love quantum mechanics so a new mobile app called Quantum Cats just has to be the lead item in this week’s Red Folder. Created by physicists at the Institute for Quantum Computing and researchers at the University of Waterloo Games Institute, the app immerses the user in the adventures of four cats: Classy, who obeys classical physics; Digger, who is a master of quantum tunnelling; Schrö, (above) who is a superposition of quantum states; and Fuzzy, who embodies the uncertainty principle. It’s available on Google Play and the App Store, so have a go and tell us what you think.

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Going underground to discuss alien life

By James Dacey

“Genuinely, it could be our generation that first finds life on another planet,” declared astrobiologist Lewis Dartnell last Thursday during a public talk in London. Dartnell was speaking about the possibility of life beyond Earth and what those organisms might be, based on our understanding of life here on Earth. The choice of venue ­– a pedestrian tunnel near King’s Cross Station bathed in neon lights – brought an appropriate alien vibe to the evening. Part of the reason for choosing the site is because if humans were to one day colonize Mars we would need to spend the first few years living underground to avoid the lethal radiation.

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NASA finds Pluto steeped in flowing glaciers and kilometre-high mountains

Pluto is a chilly world where glaciers of frozen nitrogen, methane and carbon dioxide flow around sturdy hills made of water ice. That’s the picture painted by scientists working on NASA’s New Horizons mission to the dwarf planet, who have revealed that it also has mountains several kilometres high, escarpments that run for 600 km and a “bedrock” made of frozen water.

Discovered in 1930, Pluto was viewed for the next six decades as a planet that did not fit in with the rest of the solar system. While the Earth and the other planets occupy near-circular orbits close to the same plane (the ecliptic), Pluto’s orbit is about 17° away from the ecliptic and much more elliptical in shape.

Pluto’s status as a planet began to wane in 1992 when astronomers discovered the Kuiper belt – a region stretching from Neptune’s orbit out to about 55 astronomical units (AU) that contains lots of protoplanetary objects. In 2006 the International Astronomical Union decided that Pluto and other small planets in the Kuiper Belt do not fulfil all the criteria to be planets, reclassifying Pluto as a dwarf planet, to the chagrin of some astronomers.

“I was astonished to see such spectacular surface colour and geological diversity” Silvia Protopapa, University of Maryland

Pluto was back in the news earlier this year when NASA’s New Horizons craft flew to within 12,500 km of the dwarf planet, sending back spectacular images. Now, scientists working on the mission have analysed those images. Publishing their initial results in the journal Science, they say that Pluto’s surface has “a wide variety of landforms and terrain ages, as well as substantial albedo, colour and compositional variation”. The researchers have also found evidence that Pluto has a crust rich in frozen water. “I was astonished to see such spectacular surface colour and geological diversity,” says Silvia Protopapa of the University of Maryland, who is part of a team studying the composition of Pluto’s surface.

Colourful vista

The Multispectral Visible Imaging Camera (MVIC) on board New Horizons paints a colourful picture of Pluto’s surface, with dark, red regions at the equator and much brighter and bluer regions at higher latitudes. This general pattern is interrupted by a huge heart-shaped region called Tombaugh Regio that varies in colour from east to west.

The western portion of this region is a plain dubbed Sputnik Planum, which is free from craters. Other parts of Pluto are pockmarked with craters so Sputnik Planum’s smooth surface suggests that it was created relatively recently by ongoing geological activity, according to the team.

Glacial flow

The surface of Sputnik Planum comprises polygonal and oval-shaped cells that are tens of kilometres across and separated by shallow troughs 2–3 km wide. The team believes that the plain comprises frozen nitrogen, methane and carbon dioxide. Patterns in this ice suggests that it flows around water-ice hills at the edge of the plain in much the same way as glaciers on Earth flow around obstacles such as hills. Other surface features spotted by the mission that could be associated with recent geological activity include escarpments and troughs up to 600 km long.

Shadow-length measurements made by New Horizons show that Pluto is home to mountains that rise 2–3 km above the surrounding terrain. According to the mission team, the mountains suggest the presence of a strong, solid “bedrock” that is made mostly of frozen water. Furthermore, the team believes that the frozen nitrogen, methane and carbon dioxide spotted by New Horizons must only form a relatively thin veneer on top of this bedrock.

Organic compounds

Meanwhile, data from the Linear Etalon Imaging Spectral Array (LEISA) instrument suggest that the reddish hues signal the presence of organic compounds called tholins. These are formed when ultraviolet light or charged particles irradiate mixtures of methane, nitrogen and carbon monoxide.

One unexpected discovery by New Horizons is that Pluto has an atmosphere that extends further than expected – to about 300 km above its surface. The atmosphere comprises nitrogen, methane and other hydrocarbons as well as a haze of dust particles.

The paper also looks at Pluto’s largest moon Charon, which is 606 km in radius compared to Pluto’s 1187 km. Like Pluto, the surface of Charon is rich in structures such as mountains, smooth and cratered plains, escarpments and other features associated with geological activity. Two of Pluto’s other four moons, Nix and Hydra, have similar surface compositions with Hydra having several crater-like features, and Nix having large crater that is a different colour than the rest of the moon.

International Year of Light 2015: our top 10 articles on light now with added videos

Celebrating IYL 2015 with a special free-to-read digital edition of Physics World – now updated to include light-themed films and a look ahead to the legacy the year will leave.

By Matin Durrani

We’re now in the final quarter of the International Year of Light (IYL 2015), which officially launched in January at the headquarters of the UN Educational, Scientific and Cultural Organization (UNESCO) in Paris. You may remember that on the very same day Physics World unveiled its own contribution to the IYL in the form of a free-to-read digital edition containing 10 of our very best feature articles on the science and applications of light.

Today we’re pleased to publish a new version of that digital edition, which contains the same 10 top articles but now includes a series of great videos and a podcast on the theme of light that we’ve been busy creating over the last few months. The refreshed digital edition also has interviews with some of the people involved in the IYL, in which they highlight some of the successes of the year so far and examine the legacy the IYL will leave behind. Click here to find out more.

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Homebrew physics

By Michael Banks

An astrophysicist from the University of Cambridge has bagged this year’s Great British Homebrew Challenge award for the quality of his beer.

Seeing off some 200 rival entries, the tipple was created by postdoc Will Alston using rhubarbs from his allotment to provide an extra twist.

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Berkeley astronomers question future of Geoffrey Marcy after harassment charge

Update 15 October: It has been reported that Geoffrey Marcy has now resigned from the University of California, Berkeley.

A group of 19 senior astronomy faculty at the University of California, Berkeley, including the department’s interim chair, Gibor Basri, have called on the university to “re-evaluate its response” to astronomer Geoffrey Marcy, who was found to have violated Berkeley’s sexual-harassment policy. The astronomers believe that Marcy, who pioneered the search for extrasolar planets, “cannot perform the function of a faculty member” despite apologizing for carrying out what he himself calls “unwelcomed” behaviour with some of his female graduate and undergraduate students between 2001 and 2010.

In June, following a six-month investigation, Berkeley concluded that Marcy had allegedly indulged in inappropriate behaviour and put him on probation, warning him to cease such actions. Any further episodes of harassment, Marcy was told at the time, would lead to his immediate suspension or dismissal. The results of Berkeley’s investigation – motivated by complaints from four women – became public only last week when Buzzfeed News broke the story. According to Buzzfeed, the women said Marcy had “repeatedly engaged in inappropriate physical behaviour with students, including unwanted massages, kisses and groping”.

Open letter

In an open letter to the astronomical community last week, Marcy wrote: “While I do not agree with each complaint that was made, it is clear that my behaviour was unwelcomed by some women. I take full responsibility and hold myself completely accountable for my actions and the impact they had. For that, and to the women affected, I sincerely apologise.” He then added: “Through deep and lengthy consultations, I have reflected carefully on my actions as well as issues of gender inequality, power and privilege in our society. I was unaware of how these factors created unforeseen contexts and how my actions and position have affected others in ways that were far from what I intended. Through hard work, I have changed in major ways for the better.”

The news of the investigation has also reverberated around the wider US astronomical community. Graduate students in Berkeley’s astronomy department have spoken out, declaring “The university’s failure to impose meaningful consequences on Geoff Marcy – offering instead vague threats of future sanctions should the behaviour continue – suggests that Berkeley’s administration values prestige and grant money over the wellbeing of the young scientists it is charged with training.” Meanwhile, another statement that has been signed by 32 Berkeley postdocs calls on the university and its astronomy department to “transform their policies and practices toward sexual harassment”.

‘Real consequences’

Berkeley’s administrators responded that it has sanctioned Marcy severely. “The university has imposed real consequences on Geoff Marcy by establishing a zero-tolerance policy regarding future behaviour and by stripping him of the procedural protections that all other faculty members enjoy before he can be subject to discipline up to and including termination,” they said in an official statement. To sack him, the statement added, the university would have had to undertake a long process of hearings, with an uncertain outcome.

Harvard University astronomer David Charbonneau has already suggested that Marcy should avoid the Extreme Solar Systems III conference next month in Hawaii – a suggestion Marcy accepted.

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