Tiangong-1: Defunct China space lab comes down over South Pacific

China’s defunct Tiangong-1 space lab mostly broke up on re-entering the Earth’s atmosphere above the South Pacific, Chinese and US reports say.

It re-entered the atmosphere around 00:15 GMT on Monday, China’s Manned Space Engineering Office said.

Tiangong-1 was launched in 2011 to carry out docking and orbit experiments.

It was part of China’s efforts to build a manned space station by 2022, but stopped working in March 2016.

What do we know about where it came down?

The rather vague “above the South Pacific” is the line from space officials.

Experts had struggled to predict exactly where the lab would make its re-entry – and China’s space agency wrongly suggested it would be off Sao Paulo, Brazil, shortly before the moment came.

The European Space Agency said in advance that Tiangong-1 would probably break up over water, which covers much of the Earth’s surface.

It stressed that the chances of anyone being hit by debris from the module were “10 million times smaller than the yearly chance of being hit by lightning”.

It’s not clear how much of the debris reached the Earth’s surface intact.

Why did the space lab fall like this?

Ideally, the 10m (32ft)-long Tiangong module would have been taken out of orbit in a planned manner.

Traditionally, thrusters are fired on large vehicles to drive them towards a remote zone over the Southern Ocean. This option appears not to have been available after the loss of command links.

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    Thirteen space agencies, under the leadership of the European Space Agency, used radar and optical observations to follow Tiangong’s path around the globe.

    Tiangong means ‘Heavenly Palace’

    • The module was launched in 2011 to practise rendezvous and docking
    • Two astronaut crews visited in Shenzhou capsules – in 2012 and 2013
    • They included China’s first female astronauts Liu Yang and Wang Yaping
    • China plans a more permanent space station in the next decade
    • It has developed a heavy-lift rocket, Long March 5, for the purpose

      Is this the biggest space hardware to fall out of the sky?

      Tiangong was certainly on the large size for uncontrolled re-entry objects, but it was far from being the biggest, historically:

      • The US space agency’s Skylab was almost 80 tonnes in mass when it came back partially uncontrolled in 1979. Parts struck Western Australia but no-one on the ground was injured
        • Nasa’s Columbia shuttle would also have to be classed as an uncontrolled re-entry. Its mass was more than 100 tonnes when it made its tragic return from orbit in 2003. Again, no-one on the ground was hit as debris scattered through the US states of Texas and Louisiana

          Astrophysicist Jonathan McDowell believes Tiangong is only the 50th most massive object to come back uncontrolled.

          Skip Twitter post 2 by @planet4589

          By my calculations, Tiangong-1 will be the 50th most massive uncontrolled reentry from Earth orbit in history.

          — Jonathan McDowell (@planet4589) March 25, 2018

          Report

          End of Twitter post 2 by @planet4589

          China has launched a second lab, Tiangong-2, which continues to be operational. It was visited by a re-fuelling freighter, Tianzhou-1, just last year.

          China’s future permanent space station is expected to comprise a large core module and two smaller ancillary modules, and will be in service early in the next decade, the Asian nation says.

          A new rocket, the Long March 5, was recently introduced to perform the heavy lifting that will be required to get the core module in orbit.

Antarctica ‘gives ground to the ocean’

Scientists now have their best view yet of where Antarctica is giving up ground to the ocean as some of its biggest glaciers are eaten away from below by warm water.

Researchers using Europe’s Cryosat radar spacecraft have traced the movement of grounding lines around the continent.

These are the places where the fronts of glaciers that flow from the land into the ocean start to lift and float.

The new study reveals an area of seafloor the size of Greater London that was previously in contact with ice is now free of it.

The report, which covers the period from 2010 to 2016, is published in the journal Nature Geoscience.

“What we’re able to do now with Cryosat is put the behaviour of retreating glaciers in a much wider context,” said Dr Hannes Konrad from the University of Leeds, UK.

“Our method for monitoring grounding lines requires a lot of data but it means you could now basically build a permanent service to monitor the state of the edges of the continent,” he told BBC News.

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    Although the end product is quite simple, the process of getting to it is quite a complex one.

    Viewed from above, the position of grounding lines is not always obvious.

    The glaciers themselves are hundreds of metres thick, and where they begin to float as they come off the continent can be hard to discern in simple satellite images.

    But there are radar techniques that can find their location by spotting the up and down tidal movement of a glacier’s floating ice. This, however, is just a snapshot in time.

    What Dr Konrad and colleagues have done is use these known positions and then combine the data with knowledge about the shape of the underlying rock bed and changes in the height of the glaciers’ surface to track the evolving status of the grounding lines through time.

    The new study triples the coverage of previous surveys.

    On the face of it, the results are pretty much as expected.

    Of the 1,463km² of grounded ice that has been given up, most of it is in well documented areas of West Antarctica where warm ocean water is known to be infiltrating the undersides of glaciers to melt them.

    Dr Konrad explained: “If you take 25m per year as a threshold, which is sort of the average since the end of the last ice age, and you say anything below this threshold is normal behaviour and anything above it is faster than normal – then in West Antarctica, almost 22% of grounding lines are retreating more rapidly than 25m/yr.

    “That’s a statement we can only make now because we have this wider context.”

    The new data-set confirms other observations that show the mighty Pine Island Glacier, one of the biggest and fast-flowing glaciers on Earth, and whose grounding line had been in major retreat since the 1940s, appears now to have stabilised somewhat.

    The line is currently going backwards by only 40m/yr compared with the roughly 1,000m/yr seen in previous studies. This could suggest that ocean melting at the PIG’s base is pausing.

    Its next-door neighbour, Thwaites Glacier, on the other hand, is seeing an acceleration in the reversal of its grounding line – from 340m/yr to 420m/yr.

    Thwaites is now the glacier of concern because of its potential large contribution to global sea-level rise. And the UK and American authorities will shortly announce a major joint campaign to go and study this ice stream in detail.

    Elsewhere on the continent, 10% of marine-terminating glaciers around the Antarctic Peninsula are above the 25m/yr threshold; whereas in East Antarctic, only 3% are.

    The significant stand-out in the East is Totten Glacier, whose grounding line is retreating at a rate of 154m/yr.

    Overall, for the entire continent, 10.7% of the grounding line retreated faster than 25m/yr, while 1.9% advanced faster than the threshold.

    One fascinating number to come out of the study is that grounding lines in general are seen to retreat 110m for every metre of thinning on the fastest flowing glaciers. This relationship will constrain computer models that try to simulate future change on the continent.

    Leeds co-author Dr Anna Hogg said: “The big improvement here is Cryosat, which gives us continuous, continent-wide coverage, which we simply didn’t have with previous radar missions.

    “Its capabilities have allowed us to build up a picture of retreat rates, especially at the steeply sloping margins of the continent, which is where these changes are taking place. We have eight years of coverage now and it’s guaranteed in the future for as long as Cryosat keeps working,” she told BBC News.

    Since conducting the study at Leeds, Dr Konrad has now moved to the Alfred Wegener Institute in Bremerhaven, Germany.

    Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

Space junk demo mission launches

A UK-led experiment to tackle space junk has been sent into orbit.

It takes the form of a small satellite that will practise techniques for tracking debris and capturing it.

The RemoveDebris system is heading to the International Space Station where astronauts are expected to set the experiment running in late May.

Space junk is an ever-growing problem with more than 7,500 tonnes of redundant hardware now thought to be circling the Earth.

Ranging from old rocket bodies and defunct spacecraft through to screws and even flecks of paint – this material poses a collision hazard to operational missions.

RemoveDebris will showcase technologies that could be used to clean up some of this techno-garbage.

The 100kg demonstrator left Earth on Monday onboard a SpaceX Falcon 9 rocket. It should arrive at the ISS on Wednesday.

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    The satellite will be stored at the station for a number of weeks, before being released by the orbiting platform’s robotic arm to begin a series of manoeuvres.

    RemoveDebris carries its own “junk” – two small cubesats that it will eject and then track.

    For one of these, the “mother” satellite will demonstrate the laser ranging (Lidar) and camera technology needed to monitor and characterise debris in orbit; for the the other cubesat, it will actually try to snare the object with a net.

    There will also be a demonstration of a small harpoon.

    The RemoveDebris satellite will extend a boom with a target on the end.

    The sharp projectile will be fired at this to learn more about how such devices move and impact a surface in micro-gravity.

    At the end of its mission, RemoveDebris will deploy a large membrane.

    This “sail” will increase the drag from air molecules high in the atmosphere and act to pull the satellite down to Earth much faster than would otherwise be the case.

    The project, which draws on expertise from across Europe, is led from the University of Surrey’s Space Centre.

    Its principal investigator is Prof Guglielmo Aglietti. He said the jury was still out on the best way to capture and remove space junk.

    “As you know, there are other people who are going with the idea of a robotic arm. All these different technologies have their advantages and disadvantages,” he told BBC News.

    “For example, the ones we are testing – the net and the harpoon – are simple and low cost, but could be considered more risky in certain circumstances than a robotic arm.

    “On the other hand, if your piece of debris is spinning very fast, it becomes very difficult to capture it with a robotic arm and an approach with a net could work better.”

    He added: “The reason we are doing this mission this way is because it is low cost. In my opinion, whether or not there are going to be real missions to remove debris will depend on cost. And I worry that if they are extremely expensive, people will think about other priorities.”

    The entire RemoveDebris project is costing €15m (£13m). Half of this is coming from the European Commission; the other half is coming from the 10 partners involved.

    These include Airbus, which supplied the harpoon technology, and Surrey Satellite Technology Limited, which assembled the spacecraft.

    The mission has been organised through NanoRacks, a Houston, US, company that specialises in deploying small satellites from the space station.

    Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

Dozen black holes found at galactic centre

A dozen black holes may lie at the centre of our galaxy, the Milky Way, researchers have said.

A new analysis provides support for a decades-old prediction that “supermassive” black holes at the centres of galaxies are surrounded by many smaller ones.

However, previous searches of the Milky Way’s centre, where the nearest supermassive black hole is located, have found little evidence for this.

Details appear in the journal Nature.

Charles Hailey from Columbia University in New York and colleagues used archival data from Nasa’s Chandra X-ray telescope to come to their conclusions.

They report the discovery of a dozen inactive and low-mass “binary systems”, in which a star orbits an unseen companion – the black hole.

The supermassive black hole at the centre of the Milky Way, known as Sagittarius A* (Sgr A*), is surrounded by a halo of gas and dust that provides the perfect breeding ground for the birth of massive stars. These stars live, die and could turn into black holes there.

In addition, black holes from outside the halo are believed to fall under the influence of Sgr A* as they lose their energy, causing them to be pulled into its vicinity, where they are held captive by its force.

Some of these bind – or “mate” – to passing stars, forming binary systems.

Previous attempts to detect this population of black holes have looked for the bright bursts of X-rays that are sometimes emitted by black hole binaries.

Faint and steady

“The galactic centre is so far away from Earth that those bursts are only strong and bright enough to see about once every 100 to 1,000 years,” said Prof Hailey.

Instead, the Columbia University astrophysicist and his colleagues decided to look for the fainter but steadier X-rays emitted when these binaries are in an inactive state.

“Isolated, unmated black holes are just black – they don’t do anything,” said Prof Hailey.

“But when black holes mate with a low mass star, the marriage emits X-ray bursts that are weaker, but consistent and detectable.”

A search for the X-ray signatures of low-mass black hole binaries in the Chandra data turned up 12 within three light-years of Sgr A*.

By extrapolating from the properties and distribution of these binaries, the team estimates that there may be 300-500 low-mass binaries and 10,000 isolated low-mass black holes surrounding Sgr A*.

Prof Hailey said the finding “confirms a major theory”, adding: “It is going to significantly advance gravitational wave research because knowing the number of black holes in the centre of a typical galaxy can help in better predicting how many gravitational wave events may be associated with them.”

Gravitational waves are ripples in the fabric of space-time. They were predicted by Albert Einstein’s general theory of relativity and detected by the Ligo experiment in 2015. One way these ripples arise is through the collision of separate black holes.

European Space Agency teams with ICEYE Finnish start-up

The European Space Agency is to work with Finnish start-up ICEYE on ways to exploit its novel radar satellites.

ICEYE-X1 was launched in January – the first of multiple spacecraft that will go up in the coming years.

About the size of a suitcase, these are the world’s smallest synthetic aperture radar satellites and cost a fraction of traditional platforms.

The Esa/ICEYE cooperation will focus on technology development and uses for the forthcoming constellation.

It will see future satellites – in particular, their radar antenna design – being tested at the agency’s technical centre (ESTEC) at Noordwijk, Netherlands.

Esa’s Earth observation headquarters (ESRIN) at Frascati, Italy, will also assist with calibration and validation of the ICEYE data.

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    The agency is keen to see how radar images from the mini-satellites can be drawn into the European Union’s Copernicus programme, the broad system of services that depend on space data.

    Areas of interest are likely to include maritime applications such as ship monitoring, and oil-spill and iceberg detection.

    “This is how we can best help so-called ‘New Space’ companies,” said Esa’s director of Earth observation, Josef Aschbacher.

    “They don’t need us to build their radar instrument or their satellites; they’re doing that themselves, and I would say faster than if we were involved. But there is a lot of engineering expertise here at Esa that is based on radar missions of more than 20 years,” he told BBC News.

    “We want to help ICEYE grow the market by testing and evaluating their value for Copernicus which is potentially a huge customer for them.”

    Esa’s own radar missions currently in service include the Sentinel 1a and 1b spacecraft.

    • In this preliminary flood analysis exercise image, ICEYE has combined and processed Esa’s Sentinel-1 satellite data with ICEYE-X1 satellite data to visualise potential change detection capabilities. The image features the River Seine as it ran past Paris-Orly airport in France at the start of the year when water levels were extremely high.

      ICEYE-X1’s bus, or chassis, which contains the radar instrument and spacecraft sub-systems, measures 80cm by 60cm by 50cm. Its radar antenna, after being unfolded in orbit, is 3.5m in length.

      These dimensions are much smaller than those of past radar missions.

      Like all New Space companies, the Helsinki-based outfit is exploiting the use of cheap electronics normally found in consumer products to reduce both the size and cost of its designs.

      The first satellite has now taken hundreds of images from an altitude of 505km.

      ICEYE is exploring how these pictures, and the analysis of them, could best benefit commercial partners.

      Radar’s great advantage is that it senses the ground in all weathers and at night.

      ICEYE wants to couple this vision with high temporal resolution, meaning a single spot on the Earth’s surface would be surveyed several times a day. Algorithms will scour the data to detect significant changes.

      High-repeat requires a network of satellites, and ICEYE envisages perhaps 30 platforms in orbit.

      Such a constellation could observe London or Paris, say, 15 times a day.

      Spatial resolution is important, too. ICEYE-X1 has been returning 10m-resolution pictures, meaning they see any features bigger than that. But iterations of the instrument and the radar antenna are expected to bring the resolution down to 3m.

      “ICEYE-X1 has far exceeded our expectations,” said Rafal Modrzewski, CEO and co-founder of ICEYE.

      “We did expect it to perform well, obviously; but for a first spacecraft from a start-up to perform so well – it’s been a great mission and a really exciting period for us,” he told BBC News.

      ICEYE-X2 is scheduled to go up in August and ICEYE-X3 is aiming for a November launch.

      ICEYE is working with a Polish company to part-manufacture ICEYE-X2.

      For ICEYE-X3, the entire bus will come from York Space Systems, a Colorado, US, concern.

      Mr Modrzewski said his company was trying to establish how much in-house building to do versus external sourcing.

      “We’re also looking into at least one more satellite because the sooner we get our constellation up and running, the sooner it will be providing our customers and partners with the capability. But we have to be careful. We don’t want to launch too fast and then fail.”

      Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

Curiosity rover: 2,000 days on Mars

Nasa’s Curiosity rover, also known as the Mars Science Laboratory (MSL), is celebrating 2,000 martian days (sols) investigating Gale Crater on the Red Planet. In that time, the robot has made some remarkable observations. Here are just a few of them, chosen by the Curiosity science team.

Looking back: In the history of the space age, some of the most dramatic planetary images ever taken have been of Earth, but photographed looking back from deep space. This image by Mastcam on the Curiosity Rover shows our planet as a faint pinpoint of light in the martian night sky. Every day scientists from across the world drive the Curiosity rover and study the Red Planet about 100 million miles from Earth.

The beginning: The first image that Curiosity took came back just 15 minutes after landing on 5 August 2012. Getting our imagery and other data relies on the timing of Mars Reconnaissance Orbiter (MRO) overpasses, a pattern which determines the structure of the martian working day, or sol. It shows a grainy Front Hazard Camera image – the team normally use these to help avoid obstacles – of our ultimate goal Mount Sharp. When this image came back we knew it was going to be a successful mission.

River pebbles: Once we had started driving (16 sols after landing), we soon came across these pebble beds. The rounded shape of the clasts shows that they formed in an ancient, shallow river, flowing from the surrounding four-billion-year-old highlands into Gale Crater. The inset Mastcam image shows one of the pebbles in close-up. Contrary to our expectations before MSL, the crust being eroded by the rivers was not all dark, primitive basalt but a more evolved composition and mineralogy. Pebbles caught up in this ancient martian river are causing us to rethink our view of how the underlying igneous crust and mantle of Mars formed.

Ancient lake: Before landing and in the early part of the mission, the team wasn’t sure what all of the terrains identified from MRO HiRISE orbital imagery were. They might have been lava flows or lake sediments, without close-up “ground truth” it was impossible to be certain. This image settled the debate and was a seminal stage in Martian exploration. Yellowknife Bay is made of layers of fine grained sand and muds, which were deposited as rivers flowed into an ancient Gale Crater lake. We made our first of 16 drill holes on sol 182 – we do this to get rock in to the spectrometers housed in the body of our rover – here at the John Klein site. The results – including identifying clays, organics and nitrogen-bearing compounds – showed us that this had been a habitable environment for microbial life. The next discovery step – Was There Life? – remains to be determined.

Deep water: The Pahrump Hills section Curiosity encountered around sol 753 was key for developing our understanding of Gale’s past environment. Here the rover observed thinly layered mudstones, which represented mud particles settling out from suspension within the deeper lake. The Gale Lake has been a long-standing, deep body of water.

An unconformity: At Mount Stimson, the rover identified from sol 980 a thick sandstone unit overlying the lake deposits, separated by a geological feature called an unconformity. This unconformity represents a time where erosive processes took over after millions of years when the lake had finally dried up – to form a new land surface. This shows evidence of events happening over “deep time”, similar to those that the pioneering geologist James Hutton described in his field work in the late 18th Century at Siccar Point on the Scottish Coast.

Desert sands: The Namib dunes encountered close up by Curiosity at sol 1192 is a small part of the great Bagnold dune field. Its the first active dunefield explored on the surface of another planet and Curiosity had to pick its way carefully along and through the field as moving sands are an obstacle for rovers. Although the Martian atmosphere is a fraction of the density of that of Earth’s, it is still capable of transporting sediment and is capable of creating such beautiful structures akin to those we see in the deserts of Earth.

Wind sculptures: The Murray Buttes, photographed by Mastcam on sol 1448, formed of the same sandstones observed at Mount Stimson and represent a lithified dune field created by dunes similar to those in the present day Bagnold dune field. These desert-formed sandstones sit above an unconformity, and this suggests that after a long period with a humid climate, the climate became drier and wind became the dominant agent shaping the environment at Gale Crater.

Dried muds: Curiosity is able to perform detailed analyses of the Gale rocks with the ChemCam laser and telescope mounted on its mast. Here on sol 1555 at Schooner Head we came across a set of ancient mudcracks and sulphate veins. On Earth, lakes typically dry up in places around their margins and here on Mars the Gale lake was no different. You can see the red crosses where we fired the laser at the rock, creating a small plasma spark, with the wavelength of light in the spark telling us the composition of the mudstone and veins.

Cloudy skies: This sequence of images was taken with Curiosity’s Navigational Cameras (NavCam) on sol 1971 as we pointed them towards the sky. Occasionally on the cloudiest of Martian days we are able to make out faint clouds in the sky. These images are processed to highlight differences, allowing us to see the clouds move across the sky. This sequence shows previously unseen cloud features with prominent zig-zag patterns visible. The three images, from start to finish, cover approximately 12 minutes on Mars.

Obligatory ‘selfie’: The Curiosity rover has gained a reputation over the years that rivals those of Instagram users for its many “selfies” taken along its traverse. These selfies are not all for show though as they help the team track the state of the rover throughout the course of the mission for changes such as wheel wear and dust accumulation. Curiosity’s self-portraits are taken using the rover’s Mars Hand Lens Imager (MAHLI) situated on its robotic arm and are generated by merging a series of high-resolution images into a mosaic. This one taken on sol 1065 at the Buckskin locality shows the main mast of Curiosity with its ChemCam telescope used to determine rock compositions, and the Mastcam cameras. In the foreground you can see that Curiosity has just been drilling, leaving a small grey pile of tailings.

Long drive: This panorama taken with the rover’s Mastcam shows Curiosity’s 18.4km drive over the last 5 years from the Bradbury landing site to its current location on the Vera Rubin Ridge (VRR). VRR was formerly known as Hematite Ridge due to the high concentrations of the iron oxide mineral hematite detected here from orbit. As hematite largely forms in the presence of water, this location was a high-priority target for the Curiosity rover science team to investigate in order to assess how the conditions in Gale Crater changed over its geological history. This key location is the perfect spot for Curiosity to spend its 2000th sol, and for all of us to look back on the many discoveries made so far in the mission.

By John Bridges, Ashwin Vasavada, Susanne Schwenzer, Sanjeev Gupta, Steve Banham, Candice Bedford, Christina Smith, Brittney Cooper & the MSL Team

Curiosity rover: 2,000 days on Mars

Nasa’s Curiosity rover, also known as the Mars Science Laboratory (MSL), is celebrating 2,000 martian days (sols) investigating Gale Crater on the Red Planet. In that time, the robot has made some remarkable observations. Here are just a few of them, chosen by the Curiosity science team.

Looking back: In the history of the space age, some of the most dramatic planetary images ever taken have been of Earth, but photographed looking back from deep space. This image by Mastcam on the Curiosity Rover shows our planet as a faint pinpoint of light in the martian night sky. Every day scientists from across the world drive the Curiosity rover and study the Red Planet about 100 million miles from Earth.

The beginning: The first image that Curiosity took came back just 15 minutes after landing on 5 August 2012. Getting our imagery and other data relies on the timing of Mars Reconnaissance Orbiter (MRO) overpasses, a pattern which determines the structure of the martian working day, or sol. It shows a grainy Front Hazard Camera image – the team normally use these to help avoid obstacles – of our ultimate goal Mount Sharp. When this image came back we knew it was going to be a successful mission.

River pebbles: Once we had started driving (16 sols after landing), we soon came across these pebble beds. The rounded shape of the clasts shows that they formed in an ancient, shallow river, flowing from the surrounding four-billion-year-old highlands into Gale Crater. The inset Mastcam image shows one of the pebbles in close-up. Contrary to our expectations before MSL, the crust being eroded by the rivers was not all dark, primitive basalt but a more evolved composition and mineralogy. Pebbles caught up in this ancient martian river are causing us to rethink our view of how the underlying igneous crust and mantle of Mars formed.

Ancient lake: Before landing and in the early part of the mission, the team wasn’t sure what all of the terrains identified from MRO HiRISE orbital imagery were. They might have been lava flows or lake sediments, without close-up “ground truth” it was impossible to be certain. This image settled the debate and was a seminal stage in Martian exploration. Yellowknife Bay is made of layers of fine grained sand and muds, which were deposited as rivers flowed into an ancient Gale Crater lake. We made our first of 16 drill holes on sol 182 – we do this to get rock in to the spectrometers housed in the body of our rover – here at the John Klein site. The results – including identifying clays, organics and nitrogen-bearing compounds – showed us that this had been a habitable environment for microbial life. The next discovery step – Was There Life? – remains to be determined.

Deep water: The Pahrump Hills section Curiosity encountered around sol 753 was key for developing our understanding of Gale’s past environment. Here the rover observed thinly layered mudstones, which represented mud particles settling out from suspension within the deeper lake. The Gale Lake has been a long-standing, deep body of water.

An unconformity: At Mount Stimson, the rover identified from sol 980 a thick sandstone unit overlying the lake deposits, separated by a geological feature called an unconformity. This unconformity represents a time where erosive processes took over after millions of years when the lake had finally dried up – to form a new land surface. This shows evidence of events happening over “deep time”, similar to those that the pioneering geologist James Hutton described in his field work in the late 18th Century at Siccar Point on the Scottish Coast.

Desert sands: The Namib dunes encountered close up by Curiosity at sol 1192 is a small part of the great Bagnold dune field. Its the first active dunefield explored on the surface of another planet and Curiosity had to pick its way carefully along and through the field as moving sands are an obstacle for rovers. Although the Martian atmosphere is a fraction of the density of that of Earth’s, it is still capable of transporting sediment and is capable of creating such beautiful structures akin to those we see in the deserts of Earth.

Wind sculptures: The Murray Buttes, photographed by Mastcam on sol 1448, formed of the same sandstones observed at Mount Stimson and represent a lithified dune field created by dunes similar to those in the present day Bagnold dune field. These desert-formed sandstones sit above an unconformity, and this suggests that after a long period with a humid climate, the climate became drier and wind became the dominant agent shaping the environment at Gale Crater.

Dried muds: Curiosity is able to perform detailed analyses of the Gale rocks with the ChemCam laser and telescope mounted on its mast. Here on sol 1555 at Schooner Head we came across a set of ancient mudcracks and sulphate veins. On Earth, lakes typically dry up in places around their margins and here on Mars the Gale lake was no different. You can see the red crosses where we fired the laser at the rock, creating a small plasma spark, with the wavelength of light in the spark telling us the composition of the mudstone and veins.

Cloudy skies: This sequence of images was taken with Curiosity’s Navigational Cameras (NavCam) on sol 1971 as we pointed them towards the sky. Occasionally on the cloudiest of Martian days we are able to make out faint clouds in the sky. These images are processed to highlight differences, allowing us to see the clouds move across the sky. This sequence shows previously unseen cloud features with prominent zig-zag patterns visible. The three images, from start to finish, cover approximately 12 minutes on Mars.

Obligatory ‘selfie’: The Curiosity rover has gained a reputation over the years that rivals those of Instagram users for its many “selfies” taken along its traverse. These selfies are not all for show though as they help the team track the state of the rover throughout the course of the mission for changes such as wheel wear and dust accumulation. Curiosity’s self-portraits are taken using the rover’s Mars Hand Lens Imager (MAHLI) situated on its robotic arm and are generated by merging a series of high-resolution images into a mosaic. This one taken on sol 1065 at the Buckskin locality shows the main mast of Curiosity with its ChemCam telescope used to determine rock compositions, and the Mastcam cameras. In the foreground you can see that Curiosity has just been drilling, leaving a small grey pile of tailings.

Long drive: This panorama taken with the rover’s Mastcam shows Curiosity’s 18.4km drive over the last 5 years from the Bradbury landing site to its current location on the Vera Rubin Ridge (VRR). VRR was formerly known as Hematite Ridge due to the high concentrations of the iron oxide mineral hematite detected here from orbit. As hematite largely forms in the presence of water, this location was a high-priority target for the Curiosity rover science team to investigate in order to assess how the conditions in Gale Crater changed over its geological history. This key location is the perfect spot for Curiosity to spend its 2000th sol, and for all of us to look back on the many discoveries made so far in the mission.

By John Bridges, Ashwin Vasavada, Susanne Schwenzer, Sanjeev Gupta, Steve Banham, Candice Bedford, Christina Smith, Brittney Cooper & the MSL Team

Curiosity rover: 2,000 days on Mars

Nasa’s Curiosity rover, also known as the Mars Science Laboratory (MSL), is celebrating 2,000 martian days (sols) investigating Gale Crater on the Red Planet. In that time, the robot has made some remarkable observations. Here are just a few of them, chosen by the Curiosity science team.

Looking back: In the history of the space age, some of the most dramatic planetary images ever taken have been of Earth, but photographed looking back from deep space. This image by Mastcam on the Curiosity Rover shows our planet as a faint pinpoint of light in the martian night sky. Every day scientists from across the world drive the Curiosity rover and study the Red Planet about 100 million miles from Earth.

The beginning: The first image that Curiosity took came back just 15 minutes after landing on 5 August 2012. Getting our imagery and other data relies on the timing of Mars Reconnaissance Orbiter (MRO) overpasses, a pattern which determines the structure of the martian working day, or sol. It shows a grainy Front Hazard Camera image – the team normally use these to help avoid obstacles – of our ultimate goal Mount Sharp. When this image came back we knew it was going to be a successful mission.

River pebbles: Once we had started driving (16 sols after landing), we soon came across these pebble beds. The rounded shape of the clasts shows that they formed in an ancient, shallow river, flowing from the surrounding four-billion-year-old highlands into Gale Crater. The inset Mastcam image shows one of the pebbles in close-up. Contrary to our expectations before MSL, the crust being eroded by the rivers was not all dark, primitive basalt but a more evolved composition and mineralogy. Pebbles caught up in this ancient martian river are causing us to rethink our view of how the underlying igneous crust and mantle of Mars formed.

Ancient lake: Before landing and in the early part of the mission, the team wasn’t sure what all of the terrains identified from MRO HiRISE orbital imagery were. They might have been lava flows or lake sediments, without close-up “ground truth” it was impossible to be certain. This image settled the debate and was a seminal stage in Martian exploration. Yellowknife Bay is made of layers of fine grained sand and muds, which were deposited as rivers flowed into an ancient Gale Crater lake. We made our first of 16 drill holes on sol 182 – we do this to get rock in to the spectrometers housed in the body of our rover – here at the John Klein site. The results – including identifying clays, organics and nitrogen-bearing compounds – showed us that this had been a habitable environment for microbial life. The next discovery step – Was There Life? – remains to be determined.

Deep water: The Pahrump Hills section Curiosity encountered around sol 753 was key for developing our understanding of Gale’s past environment. Here the rover observed thinly layered mudstones, which represented mud particles settling out from suspension within the deeper lake. The Gale Lake has been a long-standing, deep body of water.

An unconformity: At Mount Stimson, the rover identified from sol 980 a thick sandstone unit overlying the lake deposits, separated by a geological feature called an unconformity. This unconformity represents a time where erosive processes took over after millions of years when the lake had finally dried up – to form a new land surface. This shows evidence of events happening over “deep time”, similar to those that the pioneering geologist James Hutton described in his field work in the late 18th Century at Siccar Point on the Scottish Coast.

Desert sands: The Namib dunes encountered close up by Curiosity at sol 1192 is a small part of the great Bagnold dune field. Its the first active dunefield explored on the surface of another planet and Curiosity had to pick its way carefully along and through the field as moving sands are an obstacle for rovers. Although the Martian atmosphere is a fraction of the density of that of Earth’s, it is still capable of transporting sediment and is capable of creating such beautiful structures akin to those we see in the deserts of Earth.

Wind sculptures: The Murray Buttes, photographed by Mastcam on sol 1448, formed of the same sandstones observed at Mount Stimson and represent a lithified dune field created by dunes similar to those in the present day Bagnold dune field. These desert-formed sandstones sit above an unconformity, and this suggests that after a long period with a humid climate, the climate became drier and wind became the dominant agent shaping the environment at Gale Crater.

Dried muds: Curiosity is able to perform detailed analyses of the Gale rocks with the ChemCam laser and telescope mounted on its mast. Here on sol 1555 at Schooner Head we came across a set of ancient mudcracks and sulphate veins. On Earth, lakes typically dry up in places around their margins and here on Mars the Gale lake was no different. You can see the red crosses where we fired the laser at the rock, creating a small plasma spark, with the wavelength of light in the spark telling us the composition of the mudstone and veins.

Cloudy skies: This sequence of images was taken with Curiosity’s Navigational Cameras (NavCam) on sol 1971 as we pointed them towards the sky. Occasionally on the cloudiest of Martian days we are able to make out faint clouds in the sky. These images are processed to highlight differences, allowing us to see the clouds move across the sky. This sequence shows previously unseen cloud features with prominent zig-zag patterns visible. The three images, from start to finish, cover approximately 12 minutes on Mars.

Obligatory ‘selfie’: The Curiosity rover has gained a reputation over the years that rivals those of Instagram users for its many “selfies” taken along its traverse. These selfies are not all for show though as they help the team track the state of the rover throughout the course of the mission for changes such as wheel wear and dust accumulation. Curiosity’s self-portraits are taken using the rover’s Mars Hand Lens Imager (MAHLI) situated on its robotic arm and are generated by merging a series of high-resolution images into a mosaic. This one taken on sol 1065 at the Buckskin locality shows the main mast of Curiosity with its ChemCam telescope used to determine rock compositions, and the Mastcam cameras. In the foreground you can see that Curiosity has just been drilling, leaving a small grey pile of tailings.

Long drive: This panorama taken with the rover’s Mastcam shows Curiosity’s 18.4km drive over the last 5 years from the Bradbury landing site to its current location on the Vera Rubin Ridge (VRR). VRR was formerly known as Hematite Ridge due to the high concentrations of the iron oxide mineral hematite detected here from orbit. As hematite largely forms in the presence of water, this location was a high-priority target for the Curiosity rover science team to investigate in order to assess how the conditions in Gale Crater changed over its geological history. This key location is the perfect spot for Curiosity to spend its 2000th sol, and for all of us to look back on the many discoveries made so far in the mission.

By John Bridges, Ashwin Vasavada, Susanne Schwenzer, Sanjeev Gupta, Steve Banham, Candice Bedford, Christina Smith, Brittney Cooper & the MSL Team

UK will lead European exoplanet mission

A telescope to study the atmospheres of planets beyond our Solar System will be launched by the European Space Agency in the late 2020s.

The mission, to be known as Ariel, was selected by the organisation’s Science Programme Committee on Tuesday.

The venture will be led scientifically from the UK by University College London astrophysicist Giovanna Tinetti.

“In the next decade we will see many, many planets being discovered – thousands, actually,” she said.

“All this is amazing, but we want to go beyond that and start to understand the nature of those planets, how they formed, how they evolved, and ultimately to put our Solar System in the bigger picture,” the principal investigator told BBC News.

Ariel will use a metre-sized mirror and instrumentation designed to analyse, in visible and infrared light, the chemical make-up of the gases that shroud distant worlds, or exoplanets as they are known.

This information should provide insights on how certain types of planets come to form around particular stars.

Prof Tinetti explained: “We want to sample lots of planets – some that are small like the Earth or very big like Jupiter; and at different temperatures – extremely hot, warm or temperate – around very different types of stars.

“We want to sample all the extremes and the more normal cases, because what we want to try to understand is the ‘standard model’ for planets, if such a model even exists.”

Ariel (Atmospheric Remote-Sensing Infrared Exoplanet Large-survey)

Ariel is the latest selection in Esa’s Medium Class portfolio. To win the launch opportunity in 2028, the proposal had to beat competition from an X-ray telescope (Xipe) and a mission to study energetic particles around the Earth (Thor).

A detailed technical assessment will now be conducted before the Ariel project is formally “adopted” – Esa legal-speak for “final go-ahead”. This sign-off, which should happen in the next two years, paves the way for manufacture of the flight hardware.

Ariel is the third exoplanet venture chosen by Esa in recent years.

Already coming down the line is a small telescope called Cheops that should go up next year to better measure the size of these far-off worlds; and this will be followed in 2026 by Plato, a telescope that aims to find “true Earths” – planets the same size as our home world that orbit at the same distance from Sun-like stars.

And the Americans, too, have their dedicated planet-hunters, with the newest, the Transiting Exoplanet Survey Satellite (Tess), launching in the next few weeks.

But at some point, the science of exoplanets has to move beyond simply finding and counting objects; their chemical compositions and physical conditions have to be determined.

The telescope that will start to make big inroads into this problem is the James Webb observatory, the successor to Hubble.

Due in orbit next year, it will study planetary atmospheres in exquisite detail with its 6.5m-diameter mirror. But the US space agency-led mission will probably only get to look at perhaps 150-200 exoplanets in its first five years of operation because of all the other demands on its time from astronomers.

Ariel, on the other hand, will have the single quest and that should see it characterising in the region of 500-1,000 planets during its primary years in orbit.

Steady platform

And one aspect that would work in Ariel’s favour is the absence of any moving parts in its build, commented Plato team-member Dr Don Pollaco from Warwick University, UK.

“The issue with all of these planet experiments is that the signals you are looking for are so incredibly small that any systematics in the instrument itself will dominate the signal,” he explained.

“And the systematics are often associated with bits that move. So the great thing about Ariel is that it is fixed-format – nothing changes,” he told BBC News.

Ariel is likely to cost Esa about €460m (£405m) for the spacecraft chassis, the launch vehicle and operations. As is customary for science missions like this, the agency’s individual member states pick up the cost of the scientific payload.

The UK will have the technical lead on the project and the instrumentation therefore will be assembled at the Rutherford Appleton Laboratory at Harwell in Oxfordshire.

Dr Graham Turnock, the chief executive of the UK Space Agency, said: “It is thanks to the world-leading skills of our innovative space community that a UK-led consortium has been chosen to take forward the next ESA science mission. This demonstrates what a vital role we continue to play in European collaboration on research in space.

“The Ariel mission is a prime example of the scientific innovation underpinning the wider economy. It relies on the UK’s science and engineering expertise, which are at the forefront of the government’s Industrial Strategy.”

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

Big harpoon is ‘solution to space junk’

Airbus is testing a big harpoon to snare rogue or redundant satellites and pull them out of the sky.

The 1m-long projectile would be attached, through a strong tether, to a chase spacecraft.

Once the target was captured and under control, the chase vehicle would then drag its prey down into the atmosphere to burn to destruction.

Airbus has been working on the concept for a number of years now, developing ever bigger systems.

It is a response to the growing problem of orbital junk – old pieces of hardware that continue to circle the globe and which now pose a collision threat to operational satellites.

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    Something in the region of 20,000 items of 10cm or larger are currently being tracked.

    The latest Airbus harpoon is being designed with the capability to capture one of the biggest rogue items of the lot – Europe’s defunct Envisat Earth observation platform.

    This 8-tonne behemoth died suddenly in orbit in 2012. “Envisat is the outlier,” explained advanced project engineer Alastair Wayman.

    “If we can design a harpoon that can cope with Envisat, then it should be able to cope with all other types of spacecraft including the many rocket upper-stages that remain in orbit.”

    The testing at the aerospace company’s facility in Stevenage, UK, involves firing the harpoon, using compressed air, into a panel that is representative of the kinds of material used to build satellite structures.

    Typically, this takes the form of 3cm-thick, composite honeycomb panels that incorporate a lot of aluminium.

    “The harpoon goes through these panels like a hot knife through butter,” said Mr Wayman.

    “Once the tip is inside, it has a set of barbs that open up and stop the harpoon from coming back out. We’d then de-tumble the satellite with a tether on the other end.”

    This is where harpoons should come into their own, over other methods of capture such as nets and robotic arms. A harpoon is relatively simple. You line up the target and shoot.

    “Many of these targets will be tumbling and if you were to use a robotic arm, say, that involves a lot of quite complex motions to follow your target,” Mr Wayman explained.

    “Whereas, with the harpoon, all you have to do is sit a distance away, wait for the target to rotate underneath you, and at the right moment fire your harpoon. And because it’s a really quick event, it takes out a lot of the complexity.”

    You still have to bring the tumbling satellite under control using thrusters on the chase vehicle – but computer simulations show this should be possible.

    The European Space Agency, which is responsible for Envisat, is considering all options at the moment, and the demonstration missions that fly in the next few years will almost certainly go for easier, more cooperative targets first. Indeed, a miniature version of the Airbus harpoon is set to launch next month on a mission called RemoveDebris.

    This demonstrator satellite, developed at the Surrey Space Centre, will carry its own piece of junk which it will release and then attempt to retrieve. It will trial a net, but will perform a harpoon test as well to further knowledge about how such systems will behave in the weightless environment of space.

    For the big harpoon back in Stevenage, it is now ready to move to its next development stage. This will involve firing the projectile over a distance of 25m, the sort of separation over which the real flight model would have to work.

    Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos