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  1. Before and after: fragment impact in space
    31 August 2016

    ESA engineers have discovered that a solar panel on the Copernicus Sentinel-1A satellite was hit by a millimetre-size particle in orbit on 23 August. Thanks to onboard cameras, ground controllers were able to identify the affected area. So far, there has been no effect on the satellite’s routine operations.

    A sudden small power reduction was observed in a solar array of Sentinel-1A, orbiting at 700 km altitude, at 17:07 GMT on 23 August. Slight changes in the orientation and the orbit of the satellite were also measured at the same time.

    Following a preliminary investigation, the operations team at ESA’s control centre in Darmstadt, Germany suspected a possible impact by space debris or micrometeoroid on the solar wing.  

    Detailed analyses of the satellite’s status were performed to understand the cause of this power loss. In addition, the engineers decided to activate the board cameras to acquire pictures of the array. These cameras were originally carried to monitor the deployment of the solar wings, which occurred just a few hours after launch in April 2014, and were not intended to be used afterwards.

    Following their switch-on, one camera provided a picture that clearly shows the strike on the solar panel.

    The power reduction is relatively small compared to the overall power generated by the solar wing, which remains much higher than what the satellite requires for routine operations.

    Sentinel-1

    “Such hits, caused by particles of millimetre size, are not unexpected,” notes Holger Krag, Head of the Space Debris Office at ESA’s establishment in Darmstadt, Germany.

    “These very small objects are not trackable from the ground, because only objects greater than about 5 cm can usually be tracked and, thus, avoided by manoeuvring the satellites.

    “In this case, assuming the change in attitude and the orbit of the satellite at impact, the typical speed of such a fragment, plus additional parameters, our first estimates indicate that the size of the particle was of a few millimetres.

    “Analysis continues to obtain indications on whether the origin of the object was natural or man-made. The pictures of the affected area show a diameter of roughly 40 cm created on the solar array structure, confirming an impact from the back side, as suggested by the satellite’s attitude rate readings.”

    This event has no effect on the satellite’s routine operations, which continue normally.

    The Sentinel-1 satellites, part of the European Union’s Copernicus Programme, are operated by ESA on behalf of the European Commission.

  2. Colles Nili
    13 October 2016

    This jumble of eroded blocks lies along the distinctive boundary between the Red Planet’s southern highlands and the northern lowlands, with remnants of ancient glaciers flowing around them.

    Colles Nili in context

    This boundary is one of the oldest and most prominent features on Mars, marking a height difference of several kilometres.

    The scene presented here, captured by the high-resolution camera on ESA’s Mars Express on 29 May, is just one example of the terrain found along this ancient boundary, and focuses on part of the Colles Nili region.

    ‘Colles’ comes from the Latin word for ‘hill’, and indeed this region hosts a swath of such features. They are likely erosional remnants of a former plateau, as suggested with their similarity in height seen in the topography map.

    Zooming in to the main colour image and perspective views shows that some of the mounds are surrounded by smooth, layered deposits gently sloping away from the sides of the hills.

    Topography of Colles Nili

    An even closer look reveals other finer features on the channel floors around the mounds and inside some of the impact craters: series of ridges and troughs.

    Both the layered deposits and the ridges and troughs are thought to be associated with buried ice that has since been covered over by wind-blown dust and local debris from the eroding plateau, perhaps as an underlying ice sheet retreated.

    Perspective view in Colles Nili

    Similar features are found all along the planet-wide boundary and are thought to represent multiple episodes of glaciation within the past several hundred million years.

    Later, volcanic dust has blown in from elsewhere to create the striking streaks of dark material seen in various spots, but particularly dominant in the right-hand side of the main colour image.

    Looking inside the large impact crater seen in the top right of the main image, and also in the top left of the perspective view, shows this dark material has been piled up into dunes inside the crater, presumably by prevailing winds.

    3D view of Colles Nili

    Mars Express has been orbiting the Red Planet since 2003. Next week it will play an important role in listening for signals from Schiaparelli, the ExoMars entry, descent and landing demonstrator, as the lander makes its six-minute descent through the atmosphere to the surface.

    Mars Express, Schiaparelli mothership Trace Gas Orbiter and NASA’s Mars Reconnaissance Orbiter will record signals from Schiaparelli to confirm its safe arrival, and they will subsequently act as data relays from the surface.

    For more about ExoMars see esa.int/exomars.

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