ESA Solar Orbiter: Sunshield Undergoes extreme Solar heat test

ESA’s Solar Orbiter mission has undergone its latest major test: its protective shield has been subjected to concentrated sunlight to prove it can cope with the fierce temperatures close in to our parent star.

A ‘structural–thermal’ version of the craft’s sunshield was recently exposed to an artificial Sun for two weeks in Europe’s largest vacuum chamber at ESA’s Technical Centre in Noordwijk, the Netherlands.

The outcome ensures it will balance solar illumination, the cold of deep space and internal heat sources to maintain the perfect operating temperature.

Solar Orbiter, due for launch in 2017, sports a portfolio of instruments for in-situ measurements and high-resolution imaging of the Sun.

ESA’s next generation Sun explorer, Solar Orbiter will be launched in 2017. 

It will investigate the connections and the coupling between the Sun and the heliosphere, a huge bubble in space created by the solar wind. 

The solar wind can cause auroras and disrupt satellite-based communication.

The craft will probe to within almost a quarter of Earth’s distance from the Sun, suffering 13 times the intensity of terrestrial sunlight and temperatures of up to 520°C.

This means Solar Orbiter has been designed around its sunshield: a 3.1 m by 2.4 m sandwich of high-temperature multilayer insulation foil with a black-treated surface.

Openings allow sensors to peep through, some behind protective glass or beryllium.

The sunshield was installed in the 15 m-high and 10 m-diameter Large Space Simulator in May for testing.

Members of ESA’s Solar Orbiter team watch expectantly as an essential part of the spacecraft is lowered into Europe’s largest vacuum chamber: the multi-layered shield that will protect their probe from the Sun’s remorseless glare.

Part was blasted by a beam of simulated sunlight produced by 19 xenon lamps, each consuming 25 kW, and directed onto the shield via a mirror array.

Meanwhile, the chamber’s black walls were chilled by –170°C liquid nitrogen running through them to simulate the cold sky surrounding the craft.

The testing confirmed the design and checked the thermal computer model will accurately predict flight temperatures.

An infrared camera system monitored and measured the temperature of the shield’s front face in real time, along with heat sensors glued to various parts of the multilayer structure.

At the same time, precision ‘photogrammetric’ cameras looked for the slightest movement in the sunshield’s front face as it heated up.

NASA SDO: Giant Solar 'Tornado' Whirl Off the Sun - Video

A NASA spacecraft has captured spectacular video of an enormous plasma "tornado" spinning off the sun.

NASA's Solar Dynamics Observatory probe (SDO), watched the dark-hued twister churn and ultimately erupt over the course of one day, from April 29 to 30.

Mission scientists used the spacecraft's imagery to create an 18-second-long video of the dramatic solar tornado.

"The suspended plasma is being pulled and stretched by competing magnetic forces until something triggers the breakaway," NASA officials wrote on SDO's Facebook page, assuming the voice of the spacecraft.

"This kind of activity is fairly common on the sun, but we have only been able to view them at this level of detail since I began operations just four years ago."

The plasma appears dark in this ultraviolet-light view because it is cooler than the material surrounding it, NASA officials added.

The $850 million Solar Dynamics Observatory launched in February 2010 on a five-year mission to study the variations in solar activity that influence life on Earth.

The probe uses three different instruments to observe the sun, gathering data that is helping scientists better understand the solar magnetic field and space weather.

Over the course of its operational life, SDO has recorded many stunning images of solar flares, coronal mass ejections and other sun phenomena.

Nasa Solar Wind Mission encounters 'SLAMS' waves

Earth is surrounded by a giant magnetic bubble called the magnetosphere. 

As it travels through space, a complex system of charged particles from the sun and magnetic structures piles up in front of it. 

Scientists wish to better understand this area in front of the bow shock, known as the foreshock, as it can help explain how energy from the rest of space makes its way past this boundary into the magnetosphere. Nasa Solar Wind Mission.

Credit: NASA/GSFC 

As Earth moves around the sun, it travels surrounded by a giant bubble created by its own magnetic fields, called the magnetosphere.

As the magnetosphere plows through space, it sets up a standing bow wave or bow shock, much like that in front of a moving ship.

Just in front of this bow wave lies a complex, turbulent system called the foreshock. Conditions in the foreshock change in response to solar particles streaming in from the sun, moving magnetic fields and a host of waves, some fast, some slow, sweeping through the region.

To tease out what happens at that boundary of the magnetosphere and to better understand how radiation and energy from the sun can cross it and move closer to Earth, NASA launches spacecraft into this region to observe the changing conditions.

From 1998 to 2002, NASA's Wind spacecraft traveled through this foreshock region in front of Earth 17 times, providing new information about the physics there.

"I stumbled on some cool squiggles in the data," says Lynn Wilson, who is deputy project scientist for Wind at NASA's Goddard Space Flight Center in Greenbelt, Md.

"They turned out to be a special kind of magnetic pulsations called short large amplitude magnetic structures, (SLAMS)."

SLAMS are waves with a single, large peak, a little like giant rogue waves that can develop in the deep ocean.

By studying the region around the SLAMS and how they propagate, the Wind data showed SLAMS may provide an improved explanation for what accelerates narrow jets of charged particles back out into space, away from Earth.

Tracking how any phenomenon catalyzes the movement of other particles is one of the crucial needs for modeling this region.

In this case, understanding just how a wave can help initiate a fast-moving beam might also help explain what causes incredibly powerful rays that travel from other solar systems across interstellar space toward Earth.

Wilson and his colleagues published a paper on these results in the Journal of Geophysical Research online on March 6, 2013.

The material pervading this area of space – indeed all outer space – is known as plasma. Plasma is much like a gas, but each particle is electrically charged so movement is governed as much by the laws of electromagnetics as it is by the fundamental laws of gravity and motion we more regularly experience on Earth.

"One of the unique things about space weather is how little things can have big effects," says David Sibeck, a space scientist at Goddard who is a co-author on the paper.

"An event might seem small and just generate local turbulence, but it can have profound effects downstream.

The front of the magnetosphere is right in the line between sun and Earth, so it's a crucial place to understand which small things can lead to big results."

Since the 1970s, researchers have known that particles seem to be reflecting off the magnetosphere, creating intense particle jets called field aligned ion beams, but it's not been clear how.

Now, the Wind data helps provide a more detailed snapshot of how they form, as it travels through a slew of SLAMS and the ion beams.

The scientists' job was to map where these events happen in space and time and to try to determine which events initiate which.

Wilson says that the solar wind constantly moves toward Earth's bow shock and then reflects off it.

"What happens to Earth's magnetic field depends on what's happening here at the front of the bow shock," says Sibeck.

"And what's happening there is dramatic. It's going to affect how much energy moves into the magnetosphere. Once inside the magnetosphere, it can create powerful solar storms and impact communications and GPS satellites that we depend on daily."

ISS Solar Reflections: The solar array attached to the Zvezda Service Module

Credit: NASA

The solar array attached to the Zvezda Service Module of the International Space Station reflects bright sunlight on April 3, 2013. 

One of the Expedition 35 crew members took the photo as part of a visual inspection, or External Survey, from International Space Station windows.

This inspection has been recently added to the crew's task list because of the risk of space debris and micro-meteorite damage.

Slow Moving Solar Coronal Mass Ejection - Video

A large but relatively slow moving coronal mass ejection (CME) that erupted from the Sun on September 27 hit Earth September 30 causing a low level radio blackout and moderate geomagnetic storms.

Although the blackout has passed, storm warnings continue through October 1.

In a couple of weeks, NOAA's GOES-15 satellite, which is the primary X-ray solar sensor used to monitor solar weather, will undergo a maintenance phase as its view of the sun is eclipsed by Earth.

During that time NOAA's GOES-14 will be brought online to provide continuous coverage of solar activity.

GOES-15 is expected to be operational again around October 30.

2012 Transit of Venus | HD Video NASA - YouTube

Although we’d all like to think technological advances will keep the old bod going strong until 2117, better not to leave such things to chance and find yourself a solar telescope by June 5th, when Venus will pass the Sun.

The best thing about this event is that you won’t have to whip over to the windy plains of Siberia or somewhere equally inconvenient to see it since it should be visible on all seven continents for seven hours.

As with any solar event, it’s a definite no-no to stare at our star without the proper protection, so NASA suggests nothing short of a #14 welder’s glass or if there’s a local astronomy club in the area, see if they have a solar telescope available for the big day.

Boeing begins NASA solar electric propulsion study

Boeing has begun work on a four-month NASA contract to develop a mission concept study for solar electric propulsion technologies.

Under the $600,000 firm, fixed-price contract, Boeing will evaluate concepts that combine high-power solar arrays with advanced electric thrusters to power spacecraft and payloads to high Earth orbit and deep space destinations.

"Boeing pioneered the use of electric propulsion, and has developed an approach to integrate compact, lightweight, and highly efficient solar arrays with next-generation electric thrusters in future spacecraft," said Steve Johnston, director of Boeing Phantom Works' Advanced Space Exploration division.

"This technology offers weight and cost advantages while enabling increased on-orbit maneuverability for satellites in Earth orbit, and efficient deep space transportation for human exploration and robotic science missions."

Boeing is one of five contractors selected to develop a mission concept to demonstrate solar electric propulsion technologies, capabilities and the infrastructure required to affordably sustain a human presence in space.

Phantom Works will conduct the study in Huntington Beach with support from Boeing Space and Intelligence Systems electric power and propulsion experts in El Segundo, Calif.

Solar Orbiter EUCLID: Space mission scientists share their cosmic vision

Imperial scientists are planning to take physics to new limits with two missions given the rubber stamp by the European Space Agency (ESA) this month, known as Solar Orbiter and Euclid.

The Solar Orbiter mission will travel closer to the Sun than any other, measuring our star's magnetic field and improving our understanding of how solar activity and the harsh solar wind affect the Earth.

Professor Tim Horbury from Imperial's Space and Atmospheric Physics Group, who leads Solar Orbiter's magnetometer team, said: "Solar Orbiter will give us our first good view of the Sun's polar regions and a unique close-up view of the Sun's atmosphere and how it blows past the Earth and out to the far solar system."

In the interview below, Professor Horbury and lead engineer Helen O'Brien from the Solar Orbiter mission show off the prototype kit in their mission lab and explain why it won't be possible to send a manned mission to the sun just yet.

Watch a video of the planned Solar Orbiter mission at the ESA website.


The Euclid mission will address key questions of dark energy and dark matter, which are fundamental to physics and cosmology, and search for clues to the early expansion of the universe.

Through a massive 'near-infrared digital camera', Euclid will survey far distant parts of space using faint light that started its journey shortly after the event of the Big Bang.

Professor Steve Warren from Imperial's Astrophysics Group, who coordinates the Legacy Science teams of Euclid, said: "Euclid's highly detailed deep space maps will contain images of more than a billion galaxies and a treasure trove of rare and fascinating objects like brown dwarfs, faint halo stars, luminous giant galaxies and quasars."

In the interview below, Professor Warren discusses what we can learn about the early universe from the deep near-infrared survey of the sky to be undertaken by Euclid.

ESA announced funding for the Solar Orbiter and Euclid projects on 5 October. They will be designed, tested and built across the continent, and launched between 2017 and 2019.

Scientists and engineers from Imperial's Department of Physics have been closely involved in the development of both projects, which draw on academic expertise and collaborations with high-tech industries.

The Solar Orbiter and Euclid missions won financial backing after being selected from over 50 other proposals in ESA's Cosmic Vision strategy. Both are also supported by the UK Space Agency.

Further Information sources:

• Solar Orbiter
• Euclid
• European Space Agency (ESA)
• UK Space Agency

Imperial College London states categorically that it is not responsible for the content of the external internet sites below:

• Space and Atmospheric Physics
• Astrophysics
• Faculty of Natural Sciences

Paper Thin Solar Cells - Folding a solar cell into an airplane

MIT's been making steady progress on creating solar cell-coated paper since 2010, and are excited to report the current findings of the project.

What looks and feels like an ordinary sheet of paper with a fine layer of coloured rectangles, is no ordinary piece of paper. Once connected to a couple of wires, it instantly generates electricity from solar power.

Additionally, the technology is almost as cheap and easy as printing a family snapshot from an inkjet printer. You can even fold it, slip it in your pocket, then unfold it again for later use.



The printing process uses vapours at relatively low temperatures (less than 120C/ 248F), to transfer five fine layers of photovoltaic cells onto a piece of untreated paper, plastic or even fabric.

The process takes place in a vacuum chamber where the layers are sprayed onto the same sheet of paper in successive passes, "creating a vapor-deposition process that can be carried out inexpensively on a vast commercial scale," according to MIT.

During an experiment to test the durability of the solar cells, a team of MIT students printed the cells onto a sheet of PET plastic (a thinner version than what is commonly used for soda bottles) and folded and unfolded it 1,000 times.

Remarkably, there was no impact of each fold on the performance of the solar cells. In contrast, a commercially produced solar cell on the same PET plastic failed after the first fold.

"We have demonstrated quite thoroughly the robustness of this technology," says MIT Professor of Electrical Engineering Vladimir Bulović.

Due to the low weight of the paper or plastic, "we think we can fabricate scalable solar cells that can reach record-high watts-per-kilogram performance," he added. "For solar cells with such properties, a number of technological applications open up."

Furthermore, by laminating the solar paper, the researchers were able to demonstrate that the system can be protected from rain and wind, and thus easily used outdoors.

This achievement in itself could offer an economical solution to current solar energy systems that use glass or other expensive materials as a base.

Solar Powered aircraft Solar Impulse at Paris Air show

French Ecology Minister Nathalie Kosciusko-Morizet examines the solar-powered aircraft Solar Impulse.

Read more about this amazing aircraft here at the Solar Impulse blog.

Voyager Crosses Point Of Solar Stillness

The 33-year odyssey of NASA's Voyager 1 spacecraft has reached a distant point at the edge of our solar system where there is no outward motion of solar wind.

Now hurtling toward interstellar space some 17.4 billion kilometers (10.8 billion miles) from the Sun, Voyager 1 has crossed into an area where the velocity of the hot ionized gas, or plasma, emanating directly outward from the Sun has slowed to zero. 

Scientists suspect the solar wind has been turned sideways by the pressure from the interstellar wind in the region between stars.

The event is a major milestone in Voyager 1's passage through the heliosheath, the turbulent outer shell of the Sun's sphere of influence, and the spacecraft's upcoming departure from our solar system.

"The solar wind has turned the corner," said Ed Stone, Voyager project scientist based at the California Institute of Technology in Pasadena, Calif. "Voyager 1 is getting close to interstellar space."

Our sun gives off a stream of charged particles that form a bubble known as the heliosphere around our solar system. The solar wind travels at supersonic speed until it crosses a shockwave called the termination shock.

At this point, the solar wind dramatically slows down and heats up in the heliosheath.

Launched on Sept. 5, 1977, Voyager 1 crossed the termination shock in December 2004 into the heliosheath. Scientists have used data from Voyager 1's Low-Energy Charged Particle Instrument to deduce the solar wind's velocity.

When the speed of the charged particles hitting the outward face of Voyager 1 matched the spacecraft's speed, researchers knew that the net outward speed of the solar wind was zero.

This occurred in June, when Voyager 1 was about 17 billion kilometers (10.6 billion miles) from the Sun.
Because the velocities can fluctuate, scientists watched four more monthly readings before they were convinced the solar wind's outward speed actually had slowed to zero.

Analysis of the data shows the velocity of the solar wind has steadily slowed at a rate of about 20 kilometers per second each year (45,000 mph each year) since August 2007, when the solar wind was speeding outward at about 60 kilometers per second (130,000 mph). The outward speed has remained at zero since June.

The results were presented at the American Geophysical Union meeting in San Francisco.

Voyager Crosses Point Of Solar Stillness

2010 Eclipse, Composite Image

2010 Eclipse, Composite Image

A solar eclipse photo (gray and white) from the Williams College Expedition to Easter Island in the South Pacific (July 11, 2010) was embedded with an image of the Sun’s outer corona taken by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft and shown in red false color.

LASCO uses a disk to blot out the bright sun and the inner corona so that the faint outer corona can be monitored and studied.

Further, the dark silhouette of the moon was covered with an image of the Sun taken in extreme ultraviolet light at about the same time by the Atmospheric Imaging Assembly on Solar Dynamics Observatory (SDO). The composite brings out the correlation of structures in the inner and outer corona.

Credits: Williams College Eclipse Expedition -- Jay M. Pasachoff, Muzhou Lu, and Craig Malamut; SOHO’s LASCO image courtesy of NASA/ESA; solar disk image from NASA’s SDO; compositing by Steele Hill, NASA's Goddard Space Flight Center

Sun's Strange Behaviour Baffles Astronomers

Sun's Strange Behavior Baffles Astronomers


A solar eruption. Credit: NASA

The sun's temper ebbs and flows on what scientists had thought was a pretty predictable cycle, but lately our closest star has been acting up.

Typically, a few stormy years would knock out a satellite or two and maybe trip a power grid on Earth. Then a few years of quiet, and then back to the bad behavior. But an extremely long stretch of low activity in recent years has scientists baffled and scrambling for better forecasting models.

An expected minimum of solar activity, between 2008 and 2009, was unusually deep. And while the sun would normally ramp up activity by now, heading into its next cycle, the sun may be on the verge of a weak solar cycle instead, astronomers said at the 216th meeting of the American Astronomical Society in Miami last month.

"We're witnessing something unlike anything we've seen in 100 years," said David Hathaway of NASA's Marshall Space Flight Center in Huntsville, Ala.

The sun's constant interaction with Earth makes it important for solar physicists to keep track of solar activity. Stormy periods can force special safety precautions by satellite operators and power grid managers, and astronauts can be put at risk from bursts of radiation spat out by solar storm. Scientists need to more reliably predict what's in store.

At the conference, four solar physicists presented four very different methods of measuring and tracking solar cycles.

GOES-15 Solar X-Ray Imager Makes a Miraculous First Light

GOES-15 Solar X-Ray Imager Makes a Miraculous First Light

The Solar X-Ray Imager instrument aboard the GOES-15 satellite has just provided its first light image of the sun, but it required a lot of experts to make it happen.

Scientists and engineers from NASA and the National Oceanic and Atmospheric Administration (NOAA) have been working to bring the Solar X-Ray Imager (SXI) instrument to full functionality since the Geostationary Operational Environmental Satellite (GOES)-15, formerly known as the GOES-P satellite achieved orbit.

GOES-15 launched on March 4, 2010 from Cape Canaveral, Fla. On April 6, 2010, GOES-15 captured its first visible image of Earth and on April 26, GOES-15 took its first full-disk infrared image.

"Since the early checkout of GOES 15 (P) and the anomalous turn on of the Solar X-Ray Imager, the team has been aggressively pursuing all avenues to recover the instrument," said Andre' Dress, GOES N-P Deputy Project Manager at NASA's Goddard Space Flight Center in Greenbelt, Md." Frankly, we were down to our last straw when all the teams' hard work and efforts finally paid off.

We now believe we have a full recovery of the instrument's functionality! It's an incredible story and a true testament of our NASA/contractor teams expertise, hard work and determination."

On June 3, the GOES 15 Solar X-Ray Imager finally came on-line. Scientists and engineers had subjected SXI to a series of long duration turn on tests in the hopes of clearing the short. About 16 hours into the testing, the instrument voltages returned to normal values and SXI now appears to be functioning properly.

"We were facing a tough problem when we first attempted to bring SXI on line," said George Koerner, SXI program manager at the Lockheed Martin Space Systems Company (LMSSC) Advanced Technology Center (ATC) in Palo Alto, Calif. where the Solar X-ray Imager was designed and built.

"But because of our ability to bring together subject matter experts from both government and industry, to move forward step by step, and to work as a team patiently and persistently, together we achieved mission success. This is an enormously satisfying outcome."

Since its recovery, several test solar images have also been subsequently taken successfully. The GOES team continue to assess the health of the instrument. This new round of testing will assess SXI's total functionality. That functionality means the team will capture images of the sun with the camera to assess whether the camera is properly processing image data

NASA's New Eye On Sun Delivers Stunning First Images

NASA's New Eye On Sun Delivers Stunning First Images

NASA's recently launched Solar Dynamics Observatory, or SDO, is returning early images that confirm an unprecedented new capability for scientists to better understand our sun's dynamic processes.

These solar activities affect everything on Earth. Some of the images from the spacecraft show never-before-seen detail of material streaming outward and away from sunspots.

Others show extreme close-ups of activity on the sun's surface. The spacecraft also has made the first high-resolution measurements of solar flares in a broad range of extreme ultraviolet wavelengths.

"These initial images show a dynamic sun that I had never seen in more than 40 years of solar research," said Richard Fisher, director of the Heliophysics Division at NASA Headquarters in Washington. "SDO will change our understanding of the sun and its processes, which affect our lives and society. This mission will have a huge impact on science, similar to the impact of the Hubble Space Telescope on modern astrophysics."

NASA Solar Dynamics Observatory Launched

Solar Dynamics Observatory Launched

The Solar Dynamics Observatory and its Atlas V rocket rolled out to the launch pad at Launch Complex 41 at Cape Canaveral Air Force Station in Florida.

Weather for launch day stands at 40 percent "go" at liftoff time due to wind, cloud thickness and a slight chance of showers. The temperature at launch time is expected to be a chilly 51 degrees.

Live coverage of the launch will begin at 7:15 a.m. Wednesday on NASA TV and NASA's Launch Blog.

SDO's unprecedented mission will study the sun and its dynamic behavior. Onboard telescopes will scrutinize sunspots and solar flares using more pixels and colors than any other observatory in the history of solar physics. And SDO will reveal the sun's hidden secrets in a prodigious rush of pictures.

Sun Spot activity renewed

Two sunspots are visible on our star’s face for the first time in more than a year, possibly ending an unexpected lull in solar activity.

Solar flares rise and fall on an 11-year cycle, so scientists thought sunspot activity would pick up some time in 2008. It didn’t. And this year has been quiet, too. No sunspots have been visible on the sun for 80 percent of the days this year.

Sunspot activity is correlated with the total amount of energy we receive from the sun. If the sun’s activity were to change remarkably, it would have an influence on global climate. So, in the context of climate change, the fact that the current solar minimum has been the longest and deepest in more than a century has been of special interest.

In May, a big sunspot seemed to augur a return to normal, but it faded away and sunspotless days returned. The latest activity might not mark the end of the solar minimum, however. People have been counting sunspots since Galileo first observed one in the early 17th century. Through the 28 documented cycles, stretching from 1745 to today, some variation in cycle length has been observed.

That’s why NASA’s former chief sunspot watcher, Michael Kaiser, told us earlier this year that the minimum was “not out of the extreme ordinary.”

Goodbye Ulysses, enjoy infinity.

NASA and ESA are set to end the mission of the solar spacecraft Ulysses, which has been operating for more than 18 years (Illustration: NASA)

Ground controllers will pull the plug on the solar probe Ulysses on Tuesday, ending an epic mission that has lasted more than 18 years.

Ulysses launched in October 1990 and swung past Jupiter in 1992, putting it into an orbit that crosses the sun's poles – the first and only spacecraft ever to do so.

Over its lifetime, the probe has flown through three comet tails, studied the magnetic fields around the sun and Jupiter, and found interstellar dust blowing through the solar system.

NASA and the European Space Agency, which jointly operate the mission, had earlier predicted that Ulysses would die in 2008, when low power threatened to freeze the probe's remaining fuel. But the spacecraft team managed to prevent that from happening by firing its hydrazine-powered thrusters every two hours.

Now the probe's fuel is running low, and the space agencies have decided to turn off its transmitter, which allows it to receive its life-sustaining commands, on Tuesday. "We'd already gone a year more than we thought we could, so we thought it would be a good time to get out," says Ed Massey of NASA's Jet Propulsion Laboratory in Pasadena, California and NASA project manager for Ulysses.

Sigmoids - not so Freudian

This dramatic "sigmoid", an "S"-shaped bundle of plasma, appeared on the surface of the sun in 2007 and later erupted. Now a new model has reproduced the event (Image: NASA/STFC/ISAS/JAXA)

The formation and eruption of large "S"-shaped structures on the surface of the sun have been modelled in the best detail yet. Further refinements of the model might help sun-watchers predict severe space storms days in advance.

'Sigmoids' are S-shaped structures that appear intermittently on the sun's surface. Many produce eruptions of hot ionised gas, or plasma, such as coronal mass ejections and flares. If the eruptions are powerful enough, they can zap satellites, endanger astronauts, and knock out power grids (see Space storm alert: 90 seconds from catastrophe).

Until now, models of the structures have not been able to reproduce the full lifetime of a sigmoid from its beginnings within the sun to its eventual eruption sometimes days later. But now researchers say they have come up with a simple model that could do just that.

"For the first time, we have built a three-dimensional model that shows in a very nice and self-consistent way the evolution and final eruption of a sigmoid," says Vasilis Archontis of St Andrews University in Scotland.