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Headshot of Emily Lakdawalla

The solar system at 1 kilometer per pixel: Can you identify these worlds?

Posted By Emily Lakdawalla

25-09-2015 14:27 CDT

Topics: pretty pictures, scale comparisons, fun

The image below contains 18 samples of terrain on solid worlds across the solar system. Each square covers the same area: the squares are about 500 kilometers on a side, and when fully enlarged, the pixels are about 1 kilometer square. Before you even try to identify worlds, I'd like you to just step back and appreciate the diversity of terrain; even when things look superficially similar (i.e. lots of craters), there are major differences in the size distribution and shape of those craters. Remind yourself: all of these are the same scale.

The solar system at 1 kilometer per pixel
The solar system at 1 kilometer per pixel

Many of you are probably already trying to guess which square represents which world. I'm going to give you all the weekend to try to figure that out. I've included every solid-surfaced world that is (a) large enough to completely fill the square and (b) for which we have imagery at or very close to the target 1 kilometer-per-pixel resolution. (There are two worlds here for which the squares actually show about 430 kilometers on a side because images that have exactly the right compromise between resolution and areal coverage aren't available; I figured that was close enough for the purposes of this comparison.) Each world is on here only once. Almost all the images were taken in visible wavelengths, but there are two worlds for which we have appropriate imagery only in infrared or radar. Sadly, none of the Uranian satellites is present, because all our imagery has a resolution too coarse for inclusion here, except for Miranda, which is too small to be included.

How many of these worlds can you identify? Don't give it away in the comments; let other readers enjoy the mystery. And come back next week for me to reveal their identities to you. I'm not sure how I would do on this challenge -- there are many I could guess right off the bat, but several that I'd have trouble telling apart.

See other posts from September 2015


Read more blog entries about: pretty pictures, scale comparisons, fun


Jonathan Ursin: 09/26/2015 01:45 CDT

I only feel confident about one. I feel 50/50 about three others.

Mewo: 09/26/2015 08:32 CDT

I got six. Some of the more cratery ones are hard to tell apart.

Ralph Lorenz: 09/26/2015 08:45 CDT

For a related experiment (how much of a world at 1 pixel/degree do you need to see to know whether it is Earth, Mars, Titan etc.) to understand the relative incremental value of coverage, see

Ralph Lorenz: 09/26/2015 08:49 CDT

I think I get 11 for sure. The others would just be guessing - seen one airless, cratered fossil, seen 'em all..... (almost)

Bob Ware: 09/26/2015 02:22 CDT

Top row down, left to right; 8, 9, 13, 15 & 18 are the best I can do.

SbySW: 09/27/2015 12:16 CDT

Looks like a great idea for a poster :-)

rickray777: 09/27/2015 06:42 CDT

I only got about eight of them; but one thing is certain: the majority of these were just points of light, even in the largest telescopes not too long ago (i.e., up till the advent of the Space Age!).

ozprof: 09/27/2015 10:34 CDT

I think I have been following planetary exploration for too long. Most of them looked quite straightforward!

hendric: 09/28/2015 12:23 CDT

I am 100% on 8, 50% on 3, and like Ralph "airless cratered world" on the rest.

David Frankis: 09/28/2015 01:58 CDT

Looking forward to the big reveal. Ralph: 1) I'd love to see a current version of your Fig. 1 for all the bodies depicted above. 2) 11/18 reminds me of how astronomers don't know the constellations and mathematicians can't add up. If you're going to study something for real, first abandon geeky knowledge...

Bjorn Jonsson: 09/28/2015 07:38 CDT

13 bodies I'm absolutely sure about, 4 where I'm pretty sure and one (#14) where I'm uncertain but might be able to guess correctly.

Vladimír Havierník: 09/29/2015 06:48 CDT

I miss here Mimas and Enceladus. my guesses from picture are down: (first 3 saturn moons are maybe mess up) . . . . . . . . . . . . . . . . . . . . . . . . 1: Moon 2:Ceres 3:Earth 4:Iapetus 5:Ganymede 6:Rhea 7:Calisto 8:Pluto 9:Mercury 10:Titan 11:Triton 12:Dione 13:Io 14:Thetis 15:Europa 16:Charon 17:Mars 18:Venus

southerncrossi: 09/30/2015 04:02 CDT

Didn't know too many to start with, but enjoyed the 'hunt' to identify the various worlds, I think I got most of them (with lots of help from the internet), but still not sure on a couple. I hope the reveal will provide some identification of (at least some) locations as well as the names of the worlds.

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