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The Planetary Society Blog
By Emily Lakdawalla
The Hubble Scramble
Feb. 7, 2007 | 11:23 PST | 19:23 UTC
by John Spencer
Never a dull moment in this business. Last Monday my lunch at my favorite coffee shop was interrupted by a phone call from Hal Weaver, the New Horizons Project Scientist, who has a long association with the Hubble Space Telescope (HST). He carried the bad news that HST's premier camera, the Advanced Camera for Surveys (ACS), had just suffered a major failure: a probable short circuit had blown a fuse and the camera was probably dead, except for its far ultraviolet camera component, which uses different electronics. This was a major blow for Hubble -- ACS is the most-used instrument on the spacecraft, and has produced many of Hubble's most stunning images. (Here's my all-time favorite, a huge image of the Sombrero Galaxy set off against a background of a thousand other galaxies stretching behind it in time and space. Like many ACS images, this must be seen at full resolution for maximum glory.)
The failure was an immediate problem for me, too. In just four weeks we were planning to use the ACS to take pictures of Jupiter's moons in support of the New Horizons Jupiter flyby, mostly pictures of Io and its volcanic plumes. We need Hubble to get color images of Io, because New Horizons' MVIC color camera is too sensitive for use on sunlit targets as close to the sun as Jupiter -- we are resorting to imaging Io's night side in Jupiter-shine with MVIC, but that only works on the Jupiter-facing side of the moon. We also plan ultraviolet pictures of the auroral glow of the atmospheres of the moons as they pass through Jupiter's shadow. The ultraviolet images might still be OK, if ACS's ultraviolet camera can be revived in time, but our plan for the visible-wavelength images was shot.
There was hope, though. Hubble has another visible-wavelength camera, the venerable Wide Field Planetary Camera 2 (WFPC2), installed by the Shuttle astronauts way back in 1993 as one of the first instruments to repair Hubble's original blurry vision. Thirteen years later WFPC2 is still going strong, and though its resolution is not quite so fine as ACS's, its field of view is narrower, and it's not quite so sensitive or fast, for small bright targets like Jupiter's moons it can still deliver great images. In fact, we used WFPC2 several times in the 1990s to look at Io and its plumes. Here are some examples: Eruption of Ra Patera, IoFalse-color visible/ultraviolet images of Io showing the appearance and fading of a white volcanic deposit from an eruption at Ra Patera (near the center of the disk) as seen by the Hubble Space Telescope's Wide Field Planetary Camera 2 between 1994 and 1997. Credit: Space Telescope Science Institute / Lowell Observatory / John Spencer |
Pele erupts
False-color ultraviolet image of sulfur gas from Io's Pele plume, in the eight-o'clock position, blocking light from Jupiter in the background, as seen by the Hubble Space Telescope's Wide Field Planetary Camera 2 in 1996. Credit: Space Telescope Science Institute / Lowell Observatory / John Spencer |
So like many other Hubble observers, we needed to redesign our observations to use WFPC2 instead of ACS. And we needed to do it fast -- ACS failed on Monday, and the Space Telescope Science Institute (STScI) needed our WFPC2 plan by Friday in order to get it checked in time for transmission to the spacecraft to execute during the late February New Horizons flyby. I was away at JPL all week, helping with the Cassini Extended Mission tour selection, so my colleague Kandis Lea Jessup stepped in to dust off our old WFPC2 Io designs from the 1990s and plug them into our new observing plan. On Friday she uplinked the revised plan to the STScI, and we were done.
Well no, we weren't done. Back home in Boulder on Saturday morning, I was shoveling snow from our driveway for the umpteenth time this winter, when my cell phone rang again, and it was Hal once more. Apparently, the cancellation of so many observing programs following the ACS failure had opened up empty spots in the HST schedule -- STScI wanted to know if we could use another 20 or so Hubble orbits to support the New Horizons Jupiter flyby. Hubble time is precious and hard-won -- it's not every day someone offers you 20 orbits without you even having to write a proposal. You bet we could use the time! For these bonus observations we'd want to concentrate on the planet itself, using Hubble as a wide-angle color camera to provide the broader context for New Horizons' narrower visible and infrared views of the Great Red Spot and Little Red Spot (New Horizons MVIC could do the job, except that, again, it is dazzled by the too-bright sunlight a mere 5 AU from the sun).Io transits JupiterFalse-color ultraviolet image of Io transiting Jupiter, taken by the Hubble Space Telescope's Wide Field Planetary Camera 2 in 1997. Credit: Space Telescope Science Institute / Lowell Observatory / John Spencer |
So there was a flurry of e-mails over the weekend, followed by a teleconference on Monday morning, where we thrashed out a plan and ran it by the STScI folks for a feasibility check. Again, time was short -- all the details of our first observations had to be settled by the end of the day. We left that job in the capable hands of two of our Jupiter experts, Amy Simon and John Clarke, and by Tuesday morning we had a complete observation plan ready for upload to Hubble. We'll get our first Jupiter images, a complete rotation movie of the planet similar to those taken by New Horizons in January, on February 17th. These will be impressive enough, but will merely whet our appetite for what's to come. New Horizons starts to send back its close-up images from the Jupiter encounter in early March -- we can't wait!
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