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Mars will get a close-encounter with a comet this weekend

Posted 5 years ago
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This Sunday, October 19th, Comet C/2013 A1 (Siding Spring) will make a very close flyby of Mars. Many of the orbiters and rovers on Mars will hopefully be making some amazing photos of the comet as it passes by. When originally discovered last year, it looked like the comet might impact Mars, but as the orbit was refined, it was found that it would pass within a couple hundred thousand miles of Mars. Close enough that some of the orbiters around Mars are being repositioned to avoid possible impacts from cometary debris during closest approach.

You can query Wolfram|Alpha to see an orbit diagram. Another alternative is to use the Wolfram Language to construct your own 3D graphic.

Graphics3D[{ColorData[1][1], PlanetData[PlanetData[], "OrbitPath"], 
  Orange, CometData["CometC2013A1SidingSpring", "OrbitPath"], Red, 
  PointSize[.02], 
  Point[QuantityMagnitude[
    EntityValue["Planet", 
     EntityProperty["Planet", 
      "HelioCoordinates", {"Date" -> DateObject[{2014, 10, 19}]}]], 
    "AstronomicalUnit"]], 
  Point[QuantityMagnitude[
    CometData["CometC2013A1SidingSpring", 
     EntityProperty["Comet", 
      "HelioCoordinates", {"Date" -> DateObject[{2014, 10, 19}]}]], 
    "AstronomicalUnit"]]}, PlotRange -> 2, Axes -> True]

enter image description here

The orbits of the inner planets are shown in blue and the comet's orbit is shown in orange. Its hard to tell visually because they are so close, but the comet and Mars are nearly on top of each other and look like one point here.

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When I execute this I get this error message:

Coordinate QuantityMagnitude[Missing["UnknownQualifierSyntax"], "AstronomicalUnit"] should be a triple of numbers, or a Scaled form.

and a pink box'd result without the planets in the graphic:

enter image description here

The problematic portion of the code is

QuantityMagnitude[
 EntityValue["Planet", 
  EntityProperty["Planet", "HelioCoordinates", 
   "Date" -> DateObject[{2014, 10, 19}]]], "AstronomicalUnit"]

which, for me, returns

{QuantityMagnitude[Missing["UnknownQualifierSyntax"], 
  "AstronomicalUnit"], 
 QuantityMagnitude[Missing["UnknownQualifierSyntax"], 
  "AstronomicalUnit"], 
 QuantityMagnitude[Missing["UnknownQualifierSyntax"], 
  "AstronomicalUnit"], 
 QuantityMagnitude[Missing["UnknownQualifierSyntax"], 
  "AstronomicalUnit"], 
 QuantityMagnitude[Missing["UnknownQualifierSyntax"], 
  "AstronomicalUnit"], 
 QuantityMagnitude[Missing["UnknownQualifierSyntax"], 
  "AstronomicalUnit"], 
 QuantityMagnitude[Missing["UnknownQualifierSyntax"], 
  "AstronomicalUnit"], 
 QuantityMagnitude[Missing["UnknownQualifierSyntax"], 
  "AstronomicalUnit"]}

I get the same error. OS X, Mathematica 10.0.1.0

Looks like I had a missing set of curly brackets around the Qualifier specification in the first EntityValue call. The released versions don't like that. I have edited the code in the original post above. Hopefully this should now work.

Works fine now... I guessed you were using a pre-release version....

I have a lot of trial and error to discover how to get an EntityValue and use it. A lot of the documentation gets the entities from Wolfram|Alpha (or the equivalent key combination), and there seems to be some art to using the resulting structures. Any chance of a tutorial sometime?

The code works now, of course, and I will be reading the entrails.

I completely agree George. I started to write out a tutorial for myself but got side-tracked. I think that the content of what's available in the Entity-verse is a moving target: all being added to as the curated data content on the cloud expands. So, the discovery of things (from what I can tell) often depends on using the Option-= key combination for Entity discovery.

And a key thing that separates these Entity-related items from "core Mathematica" for me is the speed issue. Accessing that data is vastly slower than any local computation, so that limits a number of things that one might want to do. An example is the graphic above if one tries to make it interactive using a Manipulate to move the date. So there's a conceptual difference between how one envisions code written that makes use of these curated data on the cloud a code that does not...

I've been working w/the solar system data plots. Here is my version of the Siding Spring comet orbital path metadata - except with the planets given some scale and surface imagery.

It is created using an interactive CDF viewer available at http://theoryofeverything.org/MyToE/?page_id=755 (Selecting the interaction pane for Universal NBody gravitational simulator and selecting the current "Solar System" Epoch. Siding Spring

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