My ever-popular asteroids-and-comets montage, now in color, with bonus Toutatis

Posted By Emily Lakdawalla

2012/12/18 04:26 CST

Topics: best of, pretty pictures, amateur image processing, scale comparisons, asteroids, comets, asteroid 21 Lutetia, asteroid 243 Ida and Dactyl, asteroid 25143 Itokawa, asteroid 253 Mathilde, asteroid 2867 Steins, asteroid 4 Vesta, asteroid 433 Eros, asteroid 951 Gaspra, comet Borrelly, comet Halley, comet Hartley 2, comet Tempel 1, comet Wild 2, Chang'E program, Galileo, comet Halley armada, Deep Space 1, NEAR, Deep Impact, Stardust, Hayabusa (MUSES-C), Rosetta and Philae

My collage of all the asteroids and comets visited by spacecraft is probably the single most popular image I have ever posted on this blog. I've now updated it to be in color and to include Toutatis, which Chang'E 2 photographed last week. When I first started working on a color version, it didn't seem to hang together very well as a composition, because the colors were all over the map. But when I hit upon the idea of trying to represent the bodies with correct relative brightness, it seemed to come together nicely. Vesta is not included because it dwarfs the others. (I'd have to increase the height and width of the montage by factors of three.)

Montage by Emily Lakdawalla. Data from NASA / JPL / JHUAPL / UMD / JAXA / ESA / OSIRIS team / Russian Academy of Sciences / China National Space Agency. Processed by Emily Lakdawalla, Daniel Machacek, Ted Stryk, Gordan Ugarkovic.

Asteroids and comets visited by spacecraft as of December 2012, in color, excepting Vesta

A montage of 16 of the 17 asteroids and comets that have been photographed up close as of December 2012, when Chang'E 2 flew past Toutatis. This version is in color and shows the bodies at their correct relative (though not absolute) albedo or brightness. Not included is Vesta, which would cover an area about three times the width and height of this montage.

Now I have to go into my various caveats. Although the montage is in color, the colors are approximate. Color data is only available for 11 of the 16 objects shown here, and those color images were taken through spacecraft cameras equipped with different sets of filters. No attempts were made to calibrate the color of one image to another. For the five objects for which there is no color data, I just fudged a brown color that seemed consistent with others. I would welcome comment from astronomy types on the correctness of the relative redness or blueness of different bodies shown here.

I did try to be more precise with albedo. In the version above, the relative albedo is correct: the darkest thing really is the darkest thing, and so on. Albedo varies by a factor of 20 from the brightest object, Itokawa (albedo of 0.54, which puts it in the realm of Io and Ganymede), down to the darkest object, Hartley 2 (albedo of 0.028, blacker than coal). Below is an alternate version in which I've made the brightest pixels on Steins and Annefrank (albedo 0.34) to be white, and the rest linearly scaled. This pushes Itokawa beyond the realm of reality but it's only a few pixels anyway. And the comets and Mathilde are nearly invisible. Comets are dark! Even this isn't totally precise because there's phase angle differences and other confounding issues. Don't do science on this montage. It's an illustration.

All asteroids and comets visited by spacecraft as of December 2012, in color, albedo linearly scaled

As with the previous version, anyone is welcome to use this for not-for-profit purposes. In particular, I want teachers and presenters to use this in classrooms and in talks; my original purpose in putting this together was to improve bad presentations. I do love getting emails from people who use it and like it! (I also love hearing from people who see it "in the wild" in other people's presentations.)

If you wish to publish it in a book/magazine/etc., please contact me for permission. I'm also happy to produce alternate versions as needed -- without text, without comets, comets only, with Phobos and Deimos, etc. Just ask!

Want to buy one? I've made it into a poster for sale at our store.

Comments:

Guillermo Abramson: 12/18/2012 05:04 CST

Thanks, Emily. I always show this montage in my talk "En el cielo las estrellas".

kaplanfx: 12/18/2012 05:25 CST

Poor 4 Vesta, not a dwarf planet, can't make it onto a list of visited asteroids... This is a great graphic though, keep up the good work Emily.

Ethan Walker: 12/18/2012 05:42 CST

Yay! I would still love to see Vesta on this; just the edge, for a hint at relative scale. Lutetia really looks like it is a black-and-white, I had to look up that picture to convince myself that it wasn't.

Emily Lakdawalla: 12/18/2012 08:56 CST

Ethan, I've received that request a lot, and it just won't work, at least not with available data. The images of Vesta are just not of high enough resolution, especially not ones that include the limb (the edge of the disk). Eventually I will produce other montages that it will make sense to include Vesta on. Vesta and Ceres more rightfully belong in a grouping of medium-size icy worlds, ranging from Mimas to Titania (and, eventually, once New Horizons gets there, Pluto.) They're all between 400 and 2000 km across. The next group is Triton to Earth, 2700 to 13000 km across. And then the giant planets are in a class of their own.

Stephen: 12/18/2012 09:50 CST

Very nice! . BTW (and only slightly off-topic given that it visited two of the asteroids in your pics), when will the next batch of Galileo Messenger PDFs be ready for posting in the resource library? I see the next section will be the cruise to Jupiter one, so we will presumably be able to read all about Galileo's fly-bys of Gaspra and Ida (and Dactyl).

Michael McJimsey: 12/19/2012 06:26 CST

Wonderful montage! Have you thought about adding something that would give people an idea of their absolute scale? Their size in km is useful, but adding something that people would more easily relate to might be helpful. For example, an outline of the island of Manhattan (~22km x ~4km) would be in the same size category and might be easier for people to relate to.

Chris Campbell: 01/02/2013 02:26 CST

Thank you Emily. In your next iteration, could you put a small title on it? Like "All asteroids and comets visited by spacecraft as of December 2012". Lacking that, it might be misinterpreted by laymen as an actual inventory of the largest objects, rather than just the ones we've seen up close.

David Gash: 01/05/2013 11:42 CST

A great peace of work Emily, very informative

Emily Lakdawalla: 01/09/2013 02:50 CST

Those of you who are suggesting modifications are free to modify it however you want :) Stephen, it's on my to-do list, which is depressingly long.