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Now, folks, you can just enjoy this as a pretty picture, in glorious stereo and in motion too. But if you’re interested, below is an account for what this actually is, and how I made it, with a little help from my friends !
For ages I’ve been scanning the photographic output of NASA and ESA missions to explore comets – with the expert help of my Astro-collaborator Claudia Manzoni – looking for the opportunity of making a proper stereo of a jet eruption from a comet’s nucleus. We got close, but never as close as this. My friend Joel Parker has worked on NASA and ESA missions, and in particular for the New Horizons team (he looked after me when I visited) which just pulled off that incredible fly-by of Pluto, and the Rosetta mission which stunned the world by not only putting a probe in close proximity to a comet, and stalking it all the way to Perihelion (its closest approach to the Sun) but landing a tiny mobile laboratory called Philae on the comet’s surface. It’s Rosetta, and in particular its OSIRIS camera, that has given this opportunity.
Comet 67P is properly known by the names of its discoverers … Churyumov and Gerasimenko. Stroke 67P ! It’s only about 3 km across, so it has very little gravity. So the Rosetta probe is not so much ‘in orbit’ around the comet, as floating around it, always under the direct control of the team back on Earth, flying it a bit like a remote controlled plane. So the Rosetta folks tell it to emit little puffs of ‘smoke’ to change its course every now and then, setting it each time on a new path. Each new path is a fly-by of the comet at quite close range, so Rosetta can send back amazing close-up pictures as it almost grazes the surface of the comet. Joel sent me a sequence of three of these pictures, in which a huge jet of gas and dust spurted from the surface, and then was gone. This was the opportunity we needed.
In the time the Rosetta craft took these fabulous photographs, it moved a few km, giving a perfect baseline for a stereo view of the comet’s surface. It needed a lot of patience to align, because of course the probe’s distance from the comet was changing too, along with its orientation. This can be sorted out, but the bigger problem with making stereos for this comet is the fact that it’s rotating too, and pretty fast (its day is about 12 hours). In fact 67P’s rotation is the dominant factor in a sequence of pics of this kind. Why is that a problem ? It means the shadow detail changes between shots, so the stereo effect is messed up. So there was a lot of shadow correction to be done here.
OK. Now the terrain is nicely captured in stereo. But what of the jet ? Well, to make it part of the action I mixed this part of the centre image on to the last one, adding in the jet in the exact place it needed to be. What I didn’t realise initially was that, when the pictures were enhanced, the ‘sky’ above the comet was seen to be absolutely filled with lesser jets – so the mixing of the ‘skies’ had to be very carefully done, in order not to lose anything. We then needed a stereo with no jet, to make the animation. This meant doing the same process the opposite way round, adding in the part of the sky with no jet to the centre image. In stereo. Tricky little job, but rewarding, because there was a lot of real 3-D information in that ‘sky’.
So … the result ? I now had two stereo pairs – one with the big Jet and one without. My friend and colleague 3-D Denis Pellerin combined the two pairs into a GIF. And Hey Presto ! There it is ! Maybe the first flashing Comet jet ever to be pictured in 3-D !
My grateful thanks to Matt Taylor, metal hero and Project Leader of Rosetta – who’s been so encouraging to me in this … and we have another 3-D goody for you shortly.
Cheers all Bri
CREDITS : Images courtesy of ESA/ROSETTA/OSIRIS, Matt Taylor, Joel Parker
- Title Outburst in action
- Released 11/08/2015 10:00 am
- Copyright ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
A short-lived outburst from Comet 67P/Churyumov–Gerasimenko was captured by Rosetta’s OSIRIS narrow-angle camera on 29 July 2015. The image at left was taken at 13:06 GMT and does not show any visible signs of the jet. It is very strong in the middle image captured at 13:24 GMT. Residual traces of activity are only very faintly visible in the final image taken at 13:42 GMT.
The images were taken from a distance of 186 km from the centre of the comet. The jet is estimated to have a minimum speed of 10 m/s and originates from a location on the comet’s neck, in the rugged Anuket region.
Full story: Comet’s firework display ahead of perihelion
Stereo images by Brian May. Gif by Denis Pellerin. Thanks to Claudia Manzoni.
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