Week In Images

Giving up forests

Marking the International Day of Forests, this Copernicus Sentinel-2 image shows an area of Bolivia that was once covered by trees but has now been cleared for resettlement schemes and agriculture.

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Bolivia’s city of Santa Cruz can be seen at the mid-left. One of the fastest growing cities in the world, this important commercial centre lies on the Pirai River in the tropical lowlands of eastern Bolivia. To the east of the city, and particularly east of the Guapay River, or the Río Grande, a huge patchwork of agricultural fields can be seen. Back in the 1960s this was an area of largely inaccessible thick Amazon forest. However, as an area of relatively flat lowland with abundant rainfall, it is suited to farming.

As part of a drive to develop and improve the economy, there has been rapid deforestation since the 1980s to accommodate programmes to resettle people from the Andean high plains and develop the area for agriculture, particularly for soybean production. This has resulted in the region being transformed from dense forest into a large mosaic of fields. As well as countless rectangular fields, radial features can be seen where individual farmers have worked outwards from a central hub of communal land.

This image was captured by the Copernicus Sentinel-2A satellite on 30 September 2017, and processed in false colour.

An all-inclusive astronomical atlas

All-sky view of the content of ESASky, ESA’s interactive portal to access astronomical data from space science missions.

By zooming out to see half of the sky and displaying the footprints from all the missions (visualised as squared in different colours), the users get a coverage map of all observations ever done from the X-ray to the far-infrared in one single map.

ESASky is a discovery portal that provides full access to the entire sky. The open-science application contains a universe of data - over half a million images, 300 000 spectra and more than one billion catalogue sources.

Netherlands ice

The Dutch are now starting to see their famous spring flowers poke through the winter soil, but a few weeks ago it was a different story as a cold snap took grip.

This Copernicus Sentinel-2 image from 2 March 2018 shows Amsterdam and the IJmeer and Markemeer freshwater lakes covered by a thin layer of ice. As famous as the Netherlands is for flowers, it’s arguably equally renowned for ice skating. While the cold snap caused havoc throughout much of Europe, the Dutch were busy dusting off their skates and eager to hit the ice. The ice on these big lakes was much too thin to skate on, but some canals in Amsterdam were closed to boats to give the ice a chance to thicken and skaters took what is now a relatively rare opportunity to enjoy a national pastime.

A possible consequence of climate change, the Netherlands doesn’t see the ice that it used to. The Royal Netherlands Meteorological Institute rates winters using an index: those scoring above 100 are considered cold. Between 1901 and 1980, there were seven winters above 200 - very cold. The last time the index exceeded the magical 100 mark was in 1997. In fact, this was also the last time the weather was cold enough for an ’Elfstedentocht’: a 200 km skating race between 11 towns in the north of the country. In 2014, for the first time since measurements began, the index fell to zero.

While people enjoyed the ice below, this Sentinel-2 image, which is also featured on the Earth from Space video programme , allows us to view the beauty of this short-lived layer of ice from above.

A red, metal-rich relic

This idyllic scene, packed with glowing galaxies, has something truly remarkable at its core: an untouched relic of the ancient Universe. This relic can be seen in the large galaxy at the centre of the frame, a lenticular galaxynamed NGC 1277. This galaxy is a member of the famous Perseus Cluster - one of the most massive objects in the known Universe, located some 220 million light-years from Earth.

NGC 1277 has been dubbed a "relic of the early Universe" because all of its stars appear to have formed about 12 billion years ago. To put this in perspective, the Big Bang is thought to have happened 13.8 billion years ago. Teeming with billions of old, metal-rich stars, this galaxy is also home to many ancient globular clusters: spherical bundles of stars that orbit a galaxy like satellites. Uniquely, the globuar clusters of NGC 1277 are mostly red and metal-rich - very different to the blue, metal-poor clusters usually seen around similarly-sized galaxies. In astronomy, a metal is any element heavier than hydrogen and helium; these heavier elements are fused together in the hot cores of massive stars and scattered throughout the Universe when these stars explode as they die. In this way, a star’s metal content is related to its age: stars that form later contain greater amounts of metal-rich material, since previous generations of stars have enriched the cosmos from which they are born.

Massive galaxies - and their globular clusters - are thought to form in two phases: first comes an early collapse accompanied by a giant burst of star formation, which forms red, metal-rich clusters, followed by a later accumulation of material, which brings in bluer, metal-poor material. The discovery of NGC 1277’s red clusters confirms that the galaxy is a genuine antique that bypassed this second phase, raising important questions for scientists on how galaxies form and evolve: a hotly debated topic in modern astronomy.

Examples of layers used for mapping

Details of the geological mapping layers for the Western Sahara demonstration area. From top to bottom: Sentinel-2 natural colour composite, Sentinel-2 principal components analysis, Shuttle Radar Topography Mission-based elevation and the resulting geological map at 1:50000 scale.

Read full story: Sentinels helping to map for minerals

Crab Nebula in ultraviolet

The Crab Nebula is a supernova remnant some 6500 light-years from Earth in the constellation of Taurus. At the centre of the nebula is a pulsar - the remnant of a star that exploded to form the nebula. The pulsar rotates around 30 times a second, sweeping a beam of radio waves across the Galaxy. Some of the material surrounding the pulsar was ejected before the star exploded, and the rest was expelled during the supernova. The wind from the pulsar escapes at high speed, creating a dynamic structure by interacting with the ejected material.

The nebula is currently expanding at around 1500 km/s, as revealed by images taken a few years apart. By tracing this backwards it is possible to pinpoint the year in which the star exploded, and this coincides with observations by Chinese astronomers in 1054 of a star bright enough to be seen during daylight.

The image shown here is in ultraviolet light taken by ESA’s XMM-Newton telescope, which has been surveying the sky since 2000. While this is primarily a telescope for observing X-rays, the Optical Monitor enables optical and ultraviolet observations to be made simultaneously with X-ray observations. The image is a composite of 75 individual images taken between 2001 and 2015. Very few ultraviolet images of the Crab Nebula were available before this one.

The ultraviolet emission is thought to come from ’synchrotron radiation’, created when atomic particles spiral around magnetic field lines. The XMM-Newton image reveals ’bays’ indenting the east and west sides of the nebula. It is thought that a magnetised torus of material surrounded the star before it exploded, which then blocked the high-speed particles and thus the synchrotron radiation. The bays are also evident in radio images , although the eastern bay is better defined owing to intricate features around the borders of the radio image.

This image was taken as part of detailed multi-wavelength study of the Crab Nebula, with images also taken in X-rays, radio waves, infrared and optical wavelengths.

A new composite of the Crab Nebula comprising NASA Chandra and Spitzer data and NASA/ESA Hubble data was also released last week.

Grasping Gerst

What does an astronaut in the few months before flying to the International Space Station? Answer: baseline data collection.

Don’t let the wording fool you. This is an essential step before flight, when researchers collect information they will compare with data taken during and after flight.

Here, ESA astronaut Alexander Gerst is providing data for the Grasp experiment using a virtual reality headset.

The focus of this experiment is on how a brain combines the perception of its body with visual information to coordinate hand movement. Researchers suspect that, on Earth, the brain uses gravity as a reference. When reaching for an object, the brain will calculate how far your hand is by using visual clues as well as how shoulder muscles counteract the downward force of gravity to keep your arm straight.

To understand how an astronaut’s brain copes with weightlessness, Alexander is reaching for virtual objects so researchers can determine how important gravity is compared to the other factors.

The sensation of floating for months on end is something our brains never had to deal with until last century and seeing how they adapt offers interesting clues to their workings.

Virtual reality headsets offer a way to present specific situations and understand how an astronaut brain adapts to its new environment - so France’s CNES space agency had one sent to the International Space Station.

The research will help us to identify the workings of the vestibular system that keeps our balance, and how it connects to the other sensory organs. In other words, Grasp is researching the physiology behind eye-hand coordination as well as shedding light on how to treat patients showing a loss of vestibular function on Earth.

For astronauts, the research will be useful during spacewalks, where coordination in weightlessness with few visual clues is of utmost importance.

Sentinel-3B satellite container

The Copernicus Sentinel-3B satellite container arriving at the launch facilities in Plesetsk, Russia. Here, it will be unpacked and prepared for launch on 25 April 2018.

Satellite panel following reentry testing

Ideally, no parts of a reentering satellite would survive their fiery return through the atmosphere, so testing is being used to understand how satellites break apart as they fall.

ESA subjected samples of typical satellite structures - such as the one shown, with a structural joint between two aluminium sandwich panels - to conditions equivalent to atmospheric reentry.

The testing made use of the Plasma Wind Tunnel of the DLR German Aerospace Center in Cologne and the Reentry Chamber of Austria’s AAC company in Wiener Neustadt to produce the hypersonic winds and high heat flux required.

"The objective was to understand the failure modes of the current structural joining technologies used on satellites," comments ESA materials researcher Benoit Bonvoisin.

In future, the aim is to design satellites to disintegrate during reentry, known as ’design for demise’ or D4D.

Engineer Tiago Soares is working on D4D as part of ESA’s Clean Space initiative, reducing the environmental impacts of the space sector on both Earth and in orbit: "The next step is to develop and test promising new technologies to ensure better fragmentation during reentry."