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Archive for the 'Mathematical & Physical Sciences' Category

Vintage space: Venus in 1991

By Oli Usher, on 28 July 2015

On 5 May 1989, the Space Shuttle Atlantis released the Magellan probe into low Earth orbit.

A short while later, Magellan’s rockets fired, sending it towards the sun.

Magellan being deployed from the Space Shuttle Atlantis on 5 May 1990. Photo: NASA (public domain)

Magellan being deployed from the Space Shuttle Atlantis on 5 May 1989. Credit: NASA

Swinging around our star, it arrived at its destination 15 months later: the planet Venus.

Venus is in some respects the most Earth-like planet in the Solar System. It is a similar size to our planet, has a rocky surface and a thick cloudy atmosphere. However, it is much closer to the sun, and thanks to its atmosphere, experiences a powerful greenhouse effect.

The planet Venus, seen by Mariner 10. Credit: NASA (processing by Ricardo Nunes)

The planet Venus, seen by Mariner 10. Credit: NASA (processing by Ricardo Nunes)

Surface temperatures there are well over 400 degrees Celsius, atmospheric pressure is similar to what submersibles experience a kilometre down into Earth’s oceans, and the ‘air’ of Venus’ atmosphere is full of sulphuric acid.

Exploration of Venus’ surface has been in the form of brief snapshots, taken in the few tens of minutes that landers survive the harsh conditions there. All the landers so far have been Soviet; UCL has a number of their photos in its Centre for Planetary Sciences’ image archive (with a selection available online in high resolution).

The surface of Venus seen by the Venera 13 probe. Credit: UCL RPIF

The surface of Venus seen by the Venera 13 probe. Credit: UCL RPIF

Observing Venus from space is less challenging – and less rushed.

Between 1990 and 1994, Magellan was able to study the planet’s surface at leisure from its position high above the atmosphere. Because of the thick clouds, its images had to be produced by radar rather than optical photography, so they are not in colour. But they are extremely sharp.

Here is one of these images, held in UCL’s archives:

magellan-synthetic-aperture-radar

One of Magellan’s radar images of Venus’ surface. (The image is squint in the original!). Credit: UCL RPIF

Most of the highly processed images from Magellan are produced by multiple passes of the spacecraft over the planet’s surface, building up a complete image of the surface. This particular picture, however, is incomplete, revealing how Magellan’s images are put together. The black stripes show the gaps between the strips observed during different orbits of the planet.

Also in UCL’s archives are some of the planning documents NASA produced as part of the mission, including this full map of the planet’s surface:

magellan-planning-chart-cc

Planning chart for the Magellan mission. Click here for labelled image showing the location of the above radar map. Credit: UCL RPIF

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Five years of Arctic ice

By Oli Usher, on 21 July 2015

Five_years_ice-thickness_change

Five years of sea ice changes in the Arctic. (Click picture to start animation)

New research from scientists at UCL and the University of Leeds shows an unusually cool summer in the Arctic in 2013 led to a boost in sea ice. The research, carried out with the European Space Agency’s CryoSat-2, gives researchers of the fluctuations in ice between years, and suggests that pack ice in the northern hemisphere is more sensitive to changes in summer melting than it is to winter cooling.

The image above (click to animate it) shows the variation recorded by CryoSat-2 from 2010 to 2014.

Photo credit: ESA/CPOM (free for most uses – see conditions)

Pluto and Charon: A planetary waltz

By Minna O Nygren, on 14 July 2015

NASA’s New Horizons probe is flying past Pluto today, after years of travel. It is the first ever probe to visit the Pluto system. Here, Minna Orvokki Nygren (UCL Science & Technology Studies) describes a unique art-science collaboration commissioned by UCL & Birkbeck’s Centre for Planetary Sciences to celebrate the event.

Pluto and its moon Charon, seen by New Horizons last week. Photo: NASA

Pluto and its moon Charon, seen by New Horizons last week. Photo: NASA

Pluto and Charon – A Planetary Waltz was composed in collaboration between composers Catherine Kontz and Minna Orvokki Nygren. The work was commissioned by the Centre for Planetary Sciences UCL/Birkbeck (CPS) and it received its premiere on the 24th of June 2015 at An Evening with the Planets event at the UCL by pianists Valentina Pravodelov and Kerry Yong.

The main organiser of the event, Professor Steve Miller’s support and enthusiasm towards the project were crucial in realising this new work.

The piece was inspired by two photographic plates that led to the discovery of Pluto in 1930 by amateur astronomer Clyde W. Tombaugh.

The discovery images of Pluto

The discovery images of Pluto

These plates were used to devise the overall form for the musical work. The distance the bodies travelled across the sky and their relation to other bodies was reflected in the music. When seemingly further away from other celestial bodies, the warped “waltz” of Pluto and Charon, written in 5/4 time, takes over with its prominent bass line and thick chords.

A key aspect of the composition is its gestural dimension which the pianists take on during performance, such as switching seats with each other as in an “orbital ballet,” or the use of custom planetary mallets applied to the piano interior marking off specific movements in the piece.

Other features, such as the size, temperature, consistency and albedo of the bodies were also part of the compositional process. The dwarf planet Pluto being approximately twice the size of Charon is given a more powerful and majestic voice in the work, while its counterpart Charon’s music is lighter, slower and mysterious. The Kuiper belt’s chilly conditions are reflected in the piece by combining extremely high and low pitches of the piano, and giving them an ethereal resonance through the use of distinct pedalling.

An illustrated score of Pluto and Charon was created to give the audience an opportunity to follow the movement of the bodies and the musical piece.

Illustrations from the score (© Minna Nygren, all rights reserved)

Illustrations from the score (© Minna Nygren, all rights reserved)

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Hitting rewind on cosmic history

By Oli Usher, on 9 July 2015

The universe is not smooth. Stars are clumped into galaxies. Galaxies are bound in clusters. And the clusters follow a vast universe-wide web of dark matter filaments, with huge voids between them.

Seeing how this web has changed over galactic history is one of the holy grails of astronomy.

A computer model of the filamentary structure of the universe at the age of about 2 billion years. Credit: ESO (CC-BY)

A computer model of the filamentary structure of the universe at the age of about 2 billion years. Credit: ESO (CC-BY)

Astronomers now know that the universe is not only expanding, but is doing so at an ever increasing rate. The driver for this expansion, dubbed ‘dark energy’, however, is still a mystery. Even its most basic properties, such as how it has affected the structure of the universe over time, are the subject of continued scientific debate.

If we could turn back the clock, and see snapshots of the how the universe looked at stages throughout its history, we would take a huge step closer to understanding dark energy.

Fortunately, two major projects currently under way are doing this: the Dark Energy Survey (DES) and the Kilo Degree Survey (KiDS). UCL scientists are closely involved with both, and the KiDS project has this week released its first data.

Over the next few years, KiDS will use the ESO VLT Survey Telescope in Chile to produce a detailed colour image of 1500 square degrees of sky (equivalent to a square 80 times the height and width of the full Moon). A parallel project will map the same area in five wavelengths of infrared light.

The ESO VLT Survey Telescope at Paranal Observatory in Chile. Credit: ESO (CC-BY)

The ESO VLT Survey Telescope at Paranal Observatory in Chile. Credit: ESO (CC-BY)

As light from distant galaxies and quasars passes through the cosmos, its path is slightly bent by the gravity of objects in the foreground, an effect known as gravitational lensing. Scientists can use these subtle distortions to map where the mass is located in an image – revealing the location not only of the mass of the visible galaxies, but of the dark matter. Dark matter, as its name suggests, neither emits nor reflects light, so its presence can only be inferred from this type of painstaking detective work.

This week’s first data release from KiDS only covers about a tenth of the total area of sky that will be studied in the project, but it has already produced its first useful maps of the location of dark matter.

The first dark matter map from the KiDS survey, showing the inferred location of the dark matter in pink. Credit: ESO (CC-BY)

The first dark matter map from the KiDS survey, showing the inferred location of the dark matter in pink. Credit: Kilo-Degree Survey Collaboration/A. Tudorica & C. Heymans/ESO (CC-BY)

The next step is to move back through time. This is difficult but not impossible. As the universe expands, it stretches the waves of light that pass through it. The further away you look, and the further back in time you see, the redder this makes the objects appear.

KiDS, along with its infrared counterpart, will record the colour of each object through nine different coloured filters – giving enough information on the colour profile to estimate the distance of each galaxy. Through this, it will be possible to dial back time, observing the distribution of mass at various points going back through time, charting how the size and structure of the dark matter filaments has changed throughout cosmic history.

Current theories about dark energy suggest that we should see structures rapidly growing in the early universe, with this gradually slowing down over time – and KiDS will help test whether this is indeed the case.

UCL is involved in KiDS through Benjamin Joachimi, Edo van Uitert (both UCL Physics & Astronomy) and Tom Kitching (UCL Mullard Space Science Laboratory). They work mainly on analysing the gravitational lensing effects detected in the survey.

These lensing effects can be quite dramatic – high resolution images of large galaxy clusters taken with the Hubble Space Telescope show dramatic distortions in the shapes of background galaxies.

Gravitational lensing can dramatically distort the shapes of background galaxies, as can be seen in this Hubble image which shows galaxies distended into arcs around the cluster's centre of gravity. Credit: NASA/ESA (CC-BY)

Gravitational lensing can dramatically distort the shapes of background galaxies, as can be seen in this Hubble image which shows galaxies distended into arcs around the cluster’s centre of gravity. Credit: NASA/ESA (CC-BY)

But in most cases the effect is actually very subtle – a tiny modification of the shapes of thousands of galaxies, which appear as barely more than dots in the background.

For each one of these dots, it’s impossible to say whether the shape it appears to us is down to it genuinely being slightly flattened – or whether this is a result of the light from the galaxy being distorted by gravitational lensing.

But if you look at thousands of galaxies, you can tease out the statistical likelihood – for instance, if thousands of galaxies all appear flattened in the same direction, it’s likely to be because an unseen mass of dark matter is distorting them all in the same way.

These measurements rely on extremely accurate modelling of how the telescopes work and of precisely how lensing effects occur – to the extent of even producing dummy data to test their assumptions and calibrate the observations.

A simulated image of lensed galaxies, developed by scientists to calibrate their analysis of real telescope data

A simulated image of lensed galaxies, developed by scientists to calibrate their analysis of real telescope data. Credit: R. Herbonnet/E. van Uitert

The primary goal of the KiDS project is to find out more about the evolution of the cosmos and to test the laws of gravity and general relativity.

KiDS is in friendly competition with the Dark Energy Survey to do this. To an outsider this might look like a waste of resources – but this is the cutting edge of cosmology and in truth nobody really knows what we will find. If both KiDS and DES come up with the same result, despite their different telescopes, detectors and methods, then we can have some confidence that the conclusions are accurate.

Of course if they don’t, then we’re back to square one. But at least we’ll know that we don’t know.

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Positronium beam

By Oli Usher, on 7 July 2015

UCL's Positronium Beam

UCL’s Positronium Beam

Positronium is an exotic atom made up of an electron and a positron in orbit around each other. Positrons are the antimatter equivalent of electrons, so these particles are highly unstable composite particles made up of both matter and antimatter.

Because of this, positronium atoms only last a few nanoseconds before the matter and antimatter annihilate each other.

Despite their short lives, these peculiar particles have interesting features – including being able to form compounds despite not actually being an element.

UCL is home to the only positronium beam in the world. In this device, positrons created by a radioactive source pass through a chamber of hydrogen gas, where they pick up electrons, before being guided towards a target.

Standing by the Positronium Beam in this photo are UCL PhD students Andrea Loretti (left) and Sam Fayer (right), both from the Department of Physics & Astronomy.

High resolution images

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Venus and Jupiter

By Oli Usher, on 30 June 2015

If you get a chance tonight (or in the next few nights), take a look at the Western horizon just before or after sunset. Two bright ‘stars’ will be following the Sun down. These are Jupiter and Saturn, and they are unusually close together just now from our perspective. (In reality, Venus is close to us, between Earth and the Sun, while Jupiter is in the outer Solar System far beyond).

Jupiter and Venus as they look to the naked eye. Photo: Francisco Diego (UCL Physics & Astronomy)

(Click to enlarge picture)
Jupiter and Venus as they look to the naked eye. Photo by Francisco Diego (UCL Physics & Astronomy), taken from Ruskin Park, London, last night.

The picture above (click to enlarge), taken by UCL’s Francisco Diego, shows roughly what the view looks like to the naked eye.

Francisco is a star of astronomy outreach at UCL – as well as teaching our students, he works closely with schools and runs the annual Your Universe festival.

Through a pair of binoculars or a low-powered telescope it’s even more impressive: you should be able to see Venus as a crescent (like a miniature moon), and you may see a few faint dots either side of Jupiter: the gas giant’s four largest moons, Io, Europa, Ganymede and Callisto.

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Jupiter and Venus as seen during daylight at 7pm by Francisco Diego (UCL Physics & Astronomy) with magnification similar to an ordinary pair of binoculars – they should be even clearer once the Sun has set.

Added 1 July:

There was a bit of cloud last night, but the planets were visible for a time. Here’s an amazing shot captured by Francisco on the night of 30 June (click the photo to enlarge):

Venus and Jupiter by Big Ben on 30 June. Photo credit: Francisco Diego (All rights reserved, not to be reproduced without permission)

Venus and Jupiter by Big Ben on 30 June. Photo credit: Francisco Diego (All rights reserved, not to be reproduced without permission)

Tonight, they will still be visible but a touch further apart, and crescent Venus and the disk of Jupiter will have swapped positions as they continue their journey through the Solar System.

Bringing experts together to better understand hazards and disasters

By Oli Usher, on 23 June 2015

How can we best deal with hazards and disasters?

Earthquakes aren’t just about geological processes. Hurricanes aren’t just about wind. Terrorist attacks aren’t just about gunmen and roadside bombs.

Earthquake damage after the 2009 L'Aquila earthquake in Italy: the risks posed by earthquakes are as much to do with human factors such as architecture, engineering and society, as they are to do with the geology of a region. Photo: Joanna Faure Walker (IRDR)

Earthquake damage after the 2009 L’Aquila earthquake in Italy: the risks posed by earthquakes are as much to do with human factors such as architecture, engineering and society, as they are to do with the geology of a region. Photo: Joanna Faure Walker (IRDR)

In all of these cases, complex underlying causes come together with society, culture and human behaviour. Studying risks and disasters requires interdisciplinary work. At UCL, the Institute for Risk & Disaster Reduction (IRDR) coordinates research and teaching in this area, bringing together experts from across the university, as well as building links with government, NGOs and business.

This week is the highlight of IRDR’s academic calendar, with the IRDR Academic Summit on Wednesday, and its Annual Conference on Thursday.

2014's IRDR Annual Conference in pictures

2014’s IRDR Annual Conference in pictures. Photo: IRDR

The conference will cover the following topics:

  • Future Arctic risks: As sea ice recedes thanks to climate change, we can expect substantial changes – for indigenous peoples, the environment, commercial activities and geopolitical relations. But how and when will these develop? And how can our current knowledge and understanding of the Arctic guide us?
  • Visualisation of hazards and risks: Risks can be distilled down to numbers and statistics. But how can these best be presented to non-experts? Visualisations and maps of risks and hazards are a key tool for explaining complex information to the public and policymakers.
  • Ebola: The West African Ebola epidemic is finally petering out, but it was an alarming reminder of how diseases can spread. The conference will explore how Save the Children set up and operated a treatment centre in Sierra Leone during the crisis.

There will also be a keynote speech from Sir Mark Walport, the UK Government Chief Scientific Adviser, on how to communicate risk and hazard to policymakers – a summary of which will be published on the UCL Events Blog next week.

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All set for Saturn

By Oli Usher, on 19 June 2015

Cassini shortly before launch. Photo credit: NASA

Cassini shortly before launch. Photo credit: NASA

The Cassini probe launched in October 1997 and arrived in the Saturn system in July 2004. Its Huygens lander touched down on Titan, Saturn’s largest moon, in December 2004. The photo above shows the spacecraft shortly before launch.

CAPS instrument

More than a decade on, the probe is still sending back data, teaching us about Saturn and its moons.

One of the instruments on board, the Cassini Plasma Spectrometer (CAPS) was designed in part by Prof Andrew Coates at UCL’s Mullard Space Science Laboratory. This week, he has published new research based on data from his instrument.

He has found that the interaction between the Sun, magnetic field lines and the atmosphere of Titan – Saturn’s oddly Earth-like moon – behaves similarly to what we observe here on Earth.

Ferrocene crystals

By Oli Usher, on 10 June 2015

Ferrocene

Ferrocene. Credit: Prof Andrea Sella

These two images show crystals grown by 2nd year undergraduates in UCL’s chemistry department, as part of their practical classes this week.

The orange grains in the image above are crystals of ferrocene; the darker granules below are made up of the related substance ferrocenium hexafluorophosphate (also known as ferrocenium FP6)

Ferrocenium PF6

Ferrocenium PF6. Credit: Prof Andrea Sella

High resolution images

The LHC is back in operation at record energy

By Oli Usher, on 3 June 2015

After two years of repairs and upgrades, the Large Hadron Collider (LHC) is back in operation – and UCL scientists are at the heart of the action. Engineers at CERN confirmed today that the beams of protons that circle in the 27km tunnel near Geneva are stable, and scientific data is once again being collected.

The ATLAS experiment is made of concentric rings of detectors (the particle beam passes through the centre), as seen here during shutdown in 2008. Credit: CERN (CERN licence)

The ATLAS experiment is made of concentric rings of detectors (the particle beam passes through the centre), as seen here during shutdown in 2008. Credit: CERN/Claudia Marcelloni De Oliveria (CERN licence)

UCL scientists have been closely involved in the design, construction and operation of ATLAS, one of the giant detectors that track the high-energy particle collisions in the LHC, so this is an important milestone for the university’s High Energy Physics group.

Until now, the LHC has not been operating at full power. The faults that led to its shutdown shortly after it was inaugurated in 2008 meant that it could only be used to accelerate particles to around half the energy it was designed for.

* * *

Einstein’s equation E=mc2 states that energy and matter are interchangeable.

Atom bombs, famously, create vast amounts of energy by destroying small amounts of matter.

Particle accelerators like the LHC do the opposite, pumping vast amounts of energy into tiny particles, making them move at close to the speed of light. When they collide together, some of that energy is converted into extra matter, in the form of new particles flung out from the site of the collision. The greater that energy, the heavier the particles that can be generated.

Physicists describe the world around us using the ‘standard model’ of particle physics, a set of a handful of particles which can explain the properties and makeup of all the matter and energy we see around us.

The last of those particles to be detected in the lab was the Higgs boson, discovered at CERN in 2012 shortly before the upgrade began.

This doesn’t mean there is nothing left to discover, though. Scientists, including CERN’s director, have begun speaking of a tantalising ‘new physics’ – whole new uncharted areas of science that are currently totally unknown, but which might be explored with higher-energy collisions and heavier particles generated.

One of these areas could be a solution to the riddle of dark matter.

Dark matter can be detected by astronomers (as seen in this Hubble image of a galaxy cluster), but it has not been spotted on Earth, and is known to not be made out of any of the particles in the standard model. Credit: NASA/ESA (CC-BY)

Dark matter can be detected by astronomers (as seen in this Hubble image of a galaxy cluster), but it has not been spotted on Earth, and is known to not be made out of any of the particles in the standard model. Credit: NASA/ESA (CC-BY)

Dark matter has been detected in distant galaxies, thanks to its gravitational effects, but astronomers have determined that it cannot be made of any of the particles described in the standard model.

ATLAS, the building-sized instrument that UCL participates in, played a key role in the Higgs boson discovery, and will play a starring role in the future work of the LHC, and could help explain how dark matter relates to the standard model of particle physics.

* * *

The LHC consists of two 27km-long pipes that use powerful magnets to accelerate beams of protons in opposite directions.

Inside ATLAS, the two beams are brought together on a collision course. The beams are not continuous: the protons come in pulses (“bunches”) about 10cm long and the width of a human hair, each containing around a hundred billion particles. When these bunches cross each other, protons collide and new particles cascade out through the concentric rings of detectors that make up the ATLAS experiment.

One of the detections made by ATLAS today. This picture is a cross-section of the instrument, with each concentric ring detecting particles' location or energy, and the particles' tracks (shown as multi-coloured curved lines) inferred from this data. Credit: CERN

One of the detections made by ATLAS today. This picture is a cross-section of the instrument, with each concentric ring detecting particles’ location or energy, and the particles’ tracks (shown as multi-coloured curved lines) inferred from this data. Credit: CERN (CC BY SA)

Scientists can then trace the path that the particles took – and determine their energy, mass and electrical charges. And from those, they can infer the process that take places in each proton-proton collision.

During the two-year LHC shutdown, the ATLAS scientists also made several improvements to their detector, most notably with the installation of an extra ring of detectors close to the beam pipe, making it more precise than ever before, and part of the team’s work now that the LHC is running again is to ensure that this is all properly calibrated and working as expected.

When it runs at full capacity, ATLAS detects 40 million particle collisions every second, far more than could ever be studied.

Part of the challenge is to discard the unimportant data so that scientists can focus on what’s important. One of the major contributions UCL scientists have made to ATLAS is to the design and operation of the hardware and software algorithms used to discard trivial events in real time and select only the interesting ones – reducing 40 million collisions per second down to a far more manageable 1,000 that are recorded offline.

Another challenge is the simple matter of timing and synchronisation.

With millions of events per second, and everything moving at close to the speed of light, untangling the data from different collisions is challenging. ATLAS is still detecting particles ejected by one collision while another is already taking place.

Particles from multiple events cascade through the detectors at one time, and synchronising them is not straightforward. Credit: CERN (CC-BY-SA)

Particles from multiple events cascade through the detectors at one time, and synchronising them is not straightforward. Credit: CERN (CC-BY-SA)

UCL scientists played key roles in developing the electronics that ensure that the data is accurately recorded and readouts from the different components of ATLAS are all kept properly synchronised.

* * *

So what’s next for the LHC?

It’s very hard to say – and that’s what is so exciting about particle physics today.

The standard model is complete. There could be a radical departure, revealing areas of physics never explained before.

Equally, there might just be further confirmation of the dramatic discoveries of the past few decades, giving more precision and certainty to the standard model.

In either case, there is now a chance to explore physics without the constraint of theoretical preconceptions – an unusual and liberating place for a physicist to be.

With thanks to Prof Nikos Konstantinidis for help with this article