<\/p>\n Where is Philae?<\/strong><\/p>\n Ever since Philae touched down on Comet 67P\/Churyumov-Gerasimenko for the final time on 12 November \u2013 it is thought to have come into contact with the comet\u2019s surface a total of four times including the final landing <\/a>\u2013 the search has been on to identify it in images. While the CONSERT instrument has helped to narrow down a 350 x 30 m \u2018landing strip<\/a>\u2019 on Comet 67P\/C-G\u2019s smaller lobe, a dedicated search in OSIRIS images has so far not been able to confirm the little lander\u2019s final location.<\/p>\n Philae\u2019s descent to the surface, the initial touchdown at Agilkia at 15:34 UT (onboard spacecraft time) and first rebound were well-documented<\/a> with the OSIRIS narrow-angle camera. The team also identified what they believe to be the lander in a wide-angle shot taken at 17:18 UT above the rim of the large depression \u2013 named Hatmehit \u2013 on the comet\u2019s small lobe. The image has been used to guide subsequent lander search efforts, and provides the basis for trajectory reconstructions. According to data recorded by Philae\u2019s ROMAP<\/a> instrument, the lander may have grazed the surface at 16:20 UT \u2013 so this image may have captured the result of that encounter.<\/p>\n Philae\u2019s onboard data subsequently recorded the next touchdown at 17:25 UT and its final touchdown at 17:32 UT, at a site that has now been named \u201cAbydos\u201d (the first touchdown site remains as Agilkia). Images sent back by the CIVA imager<\/a> onboard the lander\u00a0and subsequent reconstructions <\/a>are providing clues as to the nature of the landing site, but a visual confirmation is still required to confirm its location.<\/p>\n Follow-up dedicated OSIRIS imaging campaigns that took place in late November and December from distances of 30 and 20 km from the centre of the comet (about 28 and 18 km from the surface, respectively) have not been successful in locating the lander. The campaigns specifically targeted the times that the lander would be illuminated \u2013 it is illuminated approximately 1.3 hours per comet revolution \u2013 and that Rosetta had the correct orbital position to be able to image it. However, the cameras were looking into long cast shadows from Rosetta\u2019s terminator orbit, perpendicular to the Sun direction, which does not provide the optimum conditions for detecting the lander.<\/p>\n It is also important to note that Rosetta\u2019s trajectory immediately following Philae\u2019s touchdown allowed for good viewing conditions at the original landing site. Now that Rosetta has moved to a different orbit, and is further away from the comet, the chances of observing the lander are less (watch this video<\/a> for a recap of the different trajectories following the landing).<\/p>\n The image below\u00a0is an example of the images being used to search for the lander; it is a slightly cropped 2 x 2 mosaic taken by the OSIRIS narrow-angle camera on 13 December 2014 from a distance of about 20 km to the centre of the comet. For the 20 km imaging run 18 sets of two images were taken \u2013 one each with orange and blue filters to take advantage of the reflection of the lander solar panels, which differ compared to the cometary environment. The images were taken in the 2 x 2 rasters to ensure good surface coverage. The lander, about 1 metre across \u2013 the size of a household washing machine \u2013 would measure only about three pixels across in these images.<\/p>\n \u201cWe\u2019re looking \u2013 by eye \u2013 for a set of three spots that correspond to the lander,\u201d says OSIRIS principal investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. \u201cThe problem is that sets of three spots are very common all over the comet nucleus; Hatmehit and the area around its rim where we\u2019re looking is full of boulders and we have identified several sets of three spots.\u201d<\/p>\n Although Rosetta is flying to within 6 km of the comet\u2019s surface on 14 February, the planned trajectory foresees the closest approach on the lower part of the larger comet lobe (although the trajectory also takes Rosetta over the first touchdown point). This trajectory is planned such that the Sun will be directly behind the spacecraft, allowing the acquisition of shadow-free images. The close flyby will also allow the suite of science instruments on the orbiter to take spectra of the surface with unprecedented resolution and to directly sample the very innermost regions of the cometary coma in order to learn more about how the comet\u2019s characteristic coma and tail develop.<\/p>\n \u201cRosetta\u2019s busy science schedule is planned several months in advance, so a dedicated Philae search campaign was not built into the plan for the close flyby,\u201d says ESA\u2019s Rosetta project scientist Matt Taylor. \u201cWe\u2019ll be focusing on \u201cco-riding\u201d observations from now on, that is, we won\u2019t be changing the trajectory of Rosetta to specifically fly over the predicted landing zone in a dedicated search, but we can modify the spacecraft pointing and\/or command images to be taken of the region if we\u2019re flying close to the region and the science operations timeline allows.\u201d<\/p>\n \u201cAfter the flyby we\u2019ll be much further away from the comet again, so are unlikely to have the opportunity for another dedicated lander search until later in the mission, maybe even next year,\u201d adds ESA\u2019s Rosetta mission manager Fred Jansen. \u201cBut the location of Philae is not required to be able to operate it, and neither does it need to be awake for us to find it.\u201d<\/p>\n When will Philae wake up?<\/strong><\/p>\n For those of you who followed the wake-up of Rosetta, you will know that it is not simply a case of switch on and get back to the science right away. The same goes for Philae.<\/p>\n At the original landing site, Philae was expected to receive around 6.5 hours of illumination per 12.4 hour comet day, with temperatures becoming too high by March 2015 to enable continued operations. Now, at its new location, the illumination is just 1.3 hours.<\/p>\n \u201cNow we need the extra solar illumination provided by the comet\u2019s closer proximity to the Sun by that time in order to bring the lander back to life,\u201d says DLR\u2019s Lander Project Manager Stephan Ulamec.<\/p>\n In fact, even by May, the Sun inclination will be such that it will be directly overhead of the predicted landing zone, although the lander\u2019s orientation is such that it won\u2019t be able to make full use of the maximum illumination on offer.<\/p>\n As for the process of wake up, and assuming Philae survived the low temperatures in its new residence, the earliest that the lander team expect it to be warm enough to boot up is in late March. But it will likely be May or June before there is enough solar illumination to use its transmitter, and to re-establish a communications link with Rosetta \u2013 the lander needs about 17 Watts to wake up and say \u201chello\u201d.<\/p>\n Furthermore, the orbiter also has to be commanded to listen for Philae\u2019s \u201cI\u2019m awake\u201d signal, and be in a good position relative to the landing site to pick up the signal \u2013 although it can be up to 200 km away from the comet. It will be longer still before the battery is fully charged and Philae is ready to do science again, but that means there is a chance it will have a ringside seat for perihelion.<\/p>\n \u201cWe are already discussing and preparing which instruments should be operated for how long,\u201d adds Stephan.<\/p>\n But even if Philae doesn\u2019t wake up, it\u2019s important to remember that it already completed its first science sequence on the comet, unexpectedly providing information from multiple locations on 67P\/C-G.<\/p>\n Meanwhile Rosetta will continue to follow the comet on its orbit around the Sun and as it heads back towards the outer Solar System.<\/p>\n","protected":false},"excerpt":{"rendered":" Here is a reprint of an article from the Rosetta mission team on where the lander might be: Where is Philae? When will it wake up? Where is Philae? Ever since Philae touched down on Comet 67P\/Churyumov-Gerasimenko for the final time on 12 November \u2013 it is thought to have come into contact with … Continue reading The search for the Philae lander on Comet 67P\/C-G<\/span> ![\"ESA_Rosetta_OSIRIS_20141112_LanderDescent-1024x677[1]\"](\"http:\/\/hobbyspace.com\/Blog\/wp-content\/uploads\/2015\/01\/ESA_Rosetta_OSIRIS_20141112_LanderDescent-1024x6771-1024x677.gif\")
<\/a><\/p>\n![\"Philae_above_the_comet_node_full_image_2[1]\"](\"http:\/\/hobbyspace.com\/Blog\/wp-content\/uploads\/2015\/01\/Philae_above_the_comet_node_full_image_21.jpg\")
Philae above the comet?<\/a>
\nRosetta\u2019s OSIRIS wide-angle camera captured this view of
\nComet 67P\/Churyumov\u2013Gerasimenko on 12 November 2014
\nat 17:18 GMT (onboard spacecraft time). Marked is what the OSIRIS
\nteam believe to be the Philae lander above the rim of the large
\ndepression \u2013 named Hatmehit \u2013 on the comet\u2019s small lobe. The
\nimage has been used to guide subsequent lander search efforts,
\nand provides the basis for trajectory reconstructions.
\nCredits: ESA\/Rosetta\/MPS for OSIRIS Team<\/em><\/p>\n![\"Lander_search_area_node_full_image_2[1]\"](\"http:\/\/hobbyspace.com\/Blog\/wp-content\/uploads\/2015\/01\/Lander_search_area_node_full_image_21.jpg\")
Lander search area<\/em><\/a>
\nAn example of the OSIRIS narrow-angle camera mosaics being used to search<\/em>
\n for Rosetta\u2019s lander, Philae. The image is a slightly cropped 2 x 2 mosaic <\/em>
\ncomprising images taken on 13 December 2014 from a distance of about <\/em>
\n20 km to the centre of the comet. The lander, about 1 m across \u2013 <\/em>
\nthe size of a household washing machine \u2013 would measure only about<\/em>
\n three pixels across in these images. The team are searching \u2013 by eye \u2013 for a <\/em>
\nset of three spots that correspond to the lander shape, but with the region <\/em>
\nstrewn with boulders it is soon easy to identify multiple sets of three spots.<\/em>
\nCredits: ESA\/Rosetta\/MPS for OSIRIS Team<\/em><\/p>\n![\"Philae_orientation_visualisation_node_full_image_2[1]\"](\"http:\/\/hobbyspace.com\/Blog\/wp-content\/uploads\/2015\/01\/Philae_orientation_visualisation_node_full_image_21.jpg\")
Philae orientation visualisation<\/em><\/a>
\nThe likely orientation of Rosetta\u2019s lander, Philae, in a visualisation <\/em>
\nof a\u00a0topographic model of the comet’s surface.<\/em><\/p>\n