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Asteroid orbital properties

Last year, after asking Twitter for people's favourite astro plots, Emily Lakdawalla wrote:

I have a particular fondness for graphs where a mass of points, each point representing one entity (one sample, one asteroid, one event), displays structure that emerges from the patterns of points' presence and absence on the plane.

She showed (and annotated) some graphs from the Minor Planet Center, plotting either eccentricity or inclination against the semi-major axis for a large set of asteroids. They're wonderful plots! Stable orbital resonances with Jupiter show up as clusters of points at or near some semi-major axis value (the trojans and the Hilda family); more fascinating to me are the little gaps at the unstable resonances. There are other clusters of points, some representing an older body that got broken up, or unusual orbital dynamics. An example of the latter is the Hungaria family, which have semi-major axes just less than 2 AU and quite high inclinations; Wikipedia tells us that any asteroids orbiting at that distance at lower inclinations would be too strongly perturbed by Mars's gravity to stay there.

The Sloan Digital Sky Survey's Moving Object Catalog also contains some colour data, and I've made some effort at following the suggestions here to convert them to an interesting colour scheme for points, with somewhat less success than either that blog post or the paper by Parker et al. which it's based on. But you can still some colour features below! The trojans are quite distinct, there's more blue at the outer edge of the main belt and green further in, and there are other little distinct clusters.

The axes are the semi-major axis a (in AU), the eccentricity e, and the inclination i (in degrees). I've used plotted the first 50,000 entries in the MOC which have linked ASTORB values, and have non-null values of A_MAG, I_MAG, and Z_MAG. (This selection appears to exclude many of the near-earth asteroids seen in the Minor Planet Center's plots.)

Mouse controls: Left-click and drag to rotate; alt (Mac)- or ctrl (Windows)-click-drag or middle-click-drag to pan; scroll or shift-click-drag to zoom. Touch screen controls: one finger to rotate; two-finger scroll to pan; pinch to zoom. Click/tap on the cube icons to snap to a side-on view.

You can see how the plot is constructed in the HTML source (although perhaps you don't want to see what I cobbled together for the colours).

The main data file for the Moving Object Catalog is sdssmocadr4.tab; it's in fixed-width format, and the R script I used to turn the relevant fields into JavaScript (after deleting the non-data rows) is here, which sources my main JS-writing function write_three_d.R.

Posted 2016-10-02.


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