AstronomicalData objects are consistently in SI units:

AstronomicalData["Mars", "Radius"]
(* Quantity[3.386*10^6, "Meters"] *)

AstronomicalData["Mars", "Density"]
(* Quantity[3934.0, ("Kilograms")/("Meters")^3] *)

However, PlanetData objects are not consistent anymore (miles are not cgs!):

PlanetData["Mars", "Radius"]
(* Quantity[2104., "Miles"] *)

PlanetData["Mars", "Density"]
(* Quantity[3.9340, ("Grams")/("Centimeters")^3] *)

Is there any way to force Mathematica into using consistent units and, even better, into SI units? I do not want to use UnitConvert as this makes the code really unreadable, what I want is curated data delivered in SI units.

  • $\begingroup$ At least, PlanetData["Mars", "Radius"] will now return a result in kilometers. $\endgroup$ May 31, 2016 at 9:54

1 Answer 1


At the beginning of your notebook set the Metric system as default.

$UnitSystem = "Metric"

This works for me. If not try below suggestion Remember you are reading the data from wolfram alpha! it's a regional thing so if the upper solution didn't work, you can try something like (I don't remember exactly though)

SetOptions[WolframAlpha, PodStates -> {"Show metric"}]
  • 1
    $\begingroup$ Thank you, that at least gives answers in km instead of miles. However, the inconsistency is still there (cgs for PlanetData and SI for AstronomicalData). $\endgroup$
    – atapaka
    Sep 16, 2015 at 18:37

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