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The Planetary Society WeblogBy Emily Lakdawalla
Aug. 21, 2008 | 14:17 PDT | 21:17 UTC Tweet Tweet TweetAs Phoenix approached Mars, it suddenly acquired a voice and began broadcasting status updates to Earth via an Internet service called Twitter. For those of you not in the know (a group that, admittedly, included me, before I was forced to figure it out as a result of Phoenix' activity), Twitter is a service that allows people to write to, and read, a blog, using the sorts of devices from which you might send text messages. It is sometimes referred to as a "micro-blogging" service because each post is limited to 140 characters. (FYI, a Twitter post is called a "tweet.") For those of you who do know what Twitter is, skip the next couple of paragraphs. People not using text-messaging devices have also found Twitter handy for rapidly changing events, for which the blog format is unwieldy. For instance, it would have been really great if I had had my act together to use Twitter to blog the Phoenix landing. Such comments as "PHOENIX HAS LANDED!" (19 characters) and "Just got a press release that told me the landing time was 23:53:44, as received on Earth." (90 characters) and "PICTURES!! We got solar panels, footpad, and the postcard!!! It is super duper duper flat, just slightly tilted, as they said." (126 characters) are perfect Twitter fodder. Twitter can also be used to ask and answer questions. When you see a tweet that has an "@" sign in it, that indicates that another Twitterer is being addressed directly. So, for instance, Twitter user "bayol" asked Phoenix a question by tweeting: "@MarsPhoenix If perchlorate is found in rocket fuel, Isn't it pretty obvious that it probably came from your soft landing procedure?" And Phoenix replied: "@bayol The retro rockets for landing used hydrazine fuel, not perchlorate." The Phoenix Twitter feed is remarkably successful, with more than 32,000 signed-up followers, which undercounts the actual number of readers. By comparison, television personality Stephen Colbert, whose devotees are mostly very Internet-savvy, has (as of the time I wrote this) only 13,800 Twitter followers. Seeing the success of the Phoenix Twitter feed, a ton of other spacecraft suddenly jumped on the bandwagon and also started Twittering away. Here's a few examples of tweeting spacecraft (there are more):
Lunar Reconnaissance Orbiter and LCROSS started out a bit bumpy, with lots of tweets simply pointing to content on the mission websites. That wasn't very useful. But as the spacecraft are getting ready for launch, there have been frequent updates on each tiny step that both have to go through to get integrated, tested, and buttoned up. This is more useful, but still lacking in detail compared to MarsPhoenix. LRO tweets less-than-informative things like "I'm being tested today." and "I'm happy that my HGAS pop and catch was successfully completed." A Google search doesn't turn up what the heck the latter one is talking about. If they're going to try to communicate with the public, it would probably good to try to do it in a way that, well, communicates something! Hopefully they'll improve with time. New Horizons, too, has lately joined in, and is beginning to establish a voice for the spacecraft. But it's struggling to make good use of the medium as well. There's simply not much for New Horizons to talk about these days that would demand the use of the fast-response medium of Twitter. I think this entry sums up the problem: "Ahhhh, another day, another million miles on the road to Pluto!" I think it's a good idea for missions to use all the media out there to reach out to the public, and to evolve with the changing media environment. However, it's clear that missions need to find the right people to do the outreach, people who figure out how to use the medium to their advantage. I haven't used Twitter yet myself because I don't think I'd do any better with it than, say, LRO_NASA does. And until I'm sure I can do it well, I'm not going to do it at all. Ditto with Facebook; I've joined and have a slowly growing list of friends and well-wishers but am not real sure I can use it well to actually teach people anything, and it doesn't help that I am often too busy to visit the page for weeks at a time. (For those of you who have recently requested friendhood, I'm not snubbing you, I just haven't had time.) Maybe one of these days I'll get more comfortable with all these newfangled media! For now I'll stick with this old-fashioned blog medium, and continue to feel out streaming video. If you are really in to all this social networking stuff, you might check out all the space missions that are on Facebook. Thanks to Keri Bean, originator of the first space mission Facebook identity (Mars Rovers) for this list (sorry I didn't have time to plug them in as links): Phoenix Mars Lander, Mars Rovers, Lunar Reconaissance Orbiter, Lcross Lunar Impactor, Hubble Telescope, Webb Telescope, Glast Satellite, Snap Satellite, Swift Satellite, Xmm-Newton Satellite, Glory Mission, Kepler Mission, and Aura Spacecraft. And the International Year of Astronomy has a Facebook identity, "Iya Cosmos." I asked Keri why she thought this was valuable and she said: "I think it's a great way to reach out informally. I got tons of people asking questions after Phoenix announced the water ice, so I made a blog explaining how the scientists determined it was water ice, which got a lot of comments, including the most memorable "Now *this* is the kind of communication I like to see from NASA!" I see Facebook as a great outreach tool, especially for the younger crowd/Gen Y who would normally not keep up with NASA missions." Aug. 21, 2008 | 08:21 PDT | 15:21 UTC Watching the clouds drift byLast week in my "what's up" roundup I noted that that in the previous week's Mars weather update the MARCI camera team on Mars Reconnaissance Orbiter had reported more water-ice clouds appearing in the equatorial regions of Mars, that is, in the skies of the rovers. It seems that the rover team noticed the news too, because Opportunity looked up to watch those clouds drift overhead:
When you next go outside, look up. Are there clouds in your sky? Do they move quickly or slowly? Are they puffy, white, and full of water, or do they look like the clouds over Opportunity -- wispy and dry with ice crystals? Spend a moment looking at your clouds, and wondering what it would be like to watch them from the surface of an alien world. Aug. 20, 2008 | 16:39 PDT | 23:39 UTC Things that probably won't ever be called planets, but maybe they shouldThe longer I listened to the "great planet debate" last week, the more strongly I felt that if it were up to me, I would define "planet" to mean "everything in the universe that's smaller than a star." The fact of the matter is, every time I speak about any object visited by a spacecraft, I make frequent slips of the tongue. I call Titan a planet. I call Enceladus a planet. I've even called Tempel 1 a planet. They're all wanderers, all places to visit. Subdivide it however you like -- it makes sense to speak of giant (or Jovian) planets, ice giant planets, major planets, terrestrial planets, minor planets, dwarf planets, binary planets, whatever. But just look around at the people who call themselves "planetary scientists" and see what they study. It's all of the above. In that spirit, I went around the Internet to locate all of the really tiny Sun-orbiting worlds that have been visited by spacecraft, the ones too lumpy and common to fit into nearly anybody's definition of "planet." Yet, by virtue of having been visited by a spacecraft, they have been elevated to special status. Here's the gallery. Many thanks to Ted Stryk for rummaging through his archives and sending me his versions of many of these images. The first of these minor planets to have been visited by spacecraft was, fittingly, the first comet that was recognized to be a periodic one: Halley's comet. A flotilla of spacecraft was launched to visit Halley when it last visited the inner solar system in 1986, including ICE (USA, NASA), Vega 1 and 2 (Soviet Academy of Sciences, USSR), Sakigake and Suisei (ISAS, Japan), and Giotto (ESA). Of these, Vega 1, Vega 2, and Giotto returned photos of Halley's nucleus, finding it to be good-sized for a comet at 16 by 8 kilometers across, but incredibly dark and also extremely low-density (if you're curious, the density was 0.1 grams per cubic centimeter). Here's a photo from Vega 2:
One thing I always wonder when I look at such photos is: how big are they? In particular, how do their sizes relate to each other? Here you go, all of the minor planets pictured above at the same resolution, 200 meters per pixel. Itokawa really is there, it's just a nearly invisible 2-by-1-pixel speck.
Aug. 19, 2008 | 08:06 PDT | 15:06 UTC Beautiful mosaic from the Enceladus encounterIn an amazingly quick piece of work, the imaging team has already assembled the 8-frame mosaic captured by Cassini as it receded from its close encounter with Enceladus last week. This is a really difficult piece of work. There are 32 separate camera images in this mosaic -- 8 high-resolution images taken through a clear filter to get the detail, and 24 taken at half the resolution through ultraviolet, green, and infrared filters to get the color.
Cassini, on the other hand, was flying quickly away from Enceladus while Enceladus was moving in its own orbit around Saturn. So, to begin with, all of those multi-filter sets of images aren't correctly registered. For example, the imaging sequence started with a clear-filter photo taken when Cassini was 4,742 kilometers from Enceladus. Then it rotated the ultraviolet filter into place and snapped the next picture, but by then it was 5,800 kilometers from Enceladus. The different distance means that the ultraviolet image is about 35 kilometers across, while the clear image covers much less area, less than 29 kilometers across. To build each color frame, the component color images had to be resized and coaligned. Then that low-resolution color data had to be overlaid on each clear-filter image. When it came time to assemble the eight color images into a single mosaic, the rotation of Enceladus also had to be taken into account. To do that, it wasn't enough just to stretch the images; the geometric distortion caused by the rotation of the moon during imaging would really create a warped image. So each of the eight frames had to be tagged with geometric information about where each of its corners were, and where the spacecraft was when it captured the images. Then all the images were stretched -- the official terminology is "transformed" or "reprojected" -- to how they would appear to a viewer located a very long distance above Enceladus at 63.0 degrees south latitude, 281.3 degrees west longitude. (Technically, this is called an "orthographic projection" -- it assumes the point of view of a viewer at infinity.) Once they were transformed to a common map projection, they could finally be assembled into a finished mosaic. It's difficult work and amazing it was done so quickly! Kudos to Jason Perry. If you'd like to mess about with the images, I've completed updating my Enceladus flyby raw images page. There was an error in the original map showing the footprint locations for this eight-frame mosaic, which I've now fixed. One last comment about this mosaic: it is in enhanced color, which helps you see the true color differences from place to place, but doesn't accurately show how Enceladus would appear to the human eye. Here is one amateur's attempt to show how Enceladus would appear if you were there.
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