NASA's MAVEN spacecraft has beamed back a selfie to mark its four years orbiting Mars and studying the upper atmosphere of the red planet. The image was obtained with the Imaging Ultraviolet Spectrograph (IUVS) instrument that normally looks at ultraviolet emissions from the Martian upper atmosphere. The instrument is mounted on a platform at the end of a 1.2-metre boom - its own 'selfie stick' - and by rotating around the boom can look back at the spacecraft. The selfie was made from 21 different images, obtained with the IUVS in different orientations, that have been stitched together, NASA said in a statement. "The spacecraft and instruments continue to operate as planned, and we're looking forward to further exploration of the Martian upper atmosphere and its influence on climate," said Bruce Jakosky, MAVEN principal investigator from the University of Colorado, Boulder in the US. The MAVEN mission was launched on November 18, 2013, and went into orbit around Mars on September 21, 2014. During its time at Mars, the spacecraft has acquired compelling evidence that the loss of atmosphere to space has been a major driver of climate change on Mars. It also discovered two new types of Martian auroras - diffuse aurora and proton aurora. Neither type has a direct connection to the local or global magnetic field or to magnetic cusps, as auroras do on Earth. MAVEN has demonstrated that the majority of the carbon dioxide (CO2) on the planet has been lost to space and that there is not enough left to terraform the planet by warming it, even if the CO2 could be released and put back into the atmosphere. Next year, researchers will initiate an aerobraking manoeuvre by skimming the spacecraft through Mars' upper atmosphere to slow it. This will reduce the highest altitude in MAVEN's orbit to enhance its ability to serve as a communications relay for data from rovers on the surface. Currently, MAVEN carries out about one relay pass per week with one of the rovers. This number will increase after NASA's InSight mission lands on Mars in November. MAVEN completed its primary mission in November 2015 and has been operating in an extended mission since that time, continuing its investigation of Mars' upper atmosphere and exploring additional opportunities for science that the new relay orbit will bring.