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The Dune Encyclopedia
This article or section refers to elements that appear exclusively in The Dune Encyclopedia.

Extaris is the fourth planet of the Canopus system/DE.

Extaris, is the smallest of the outer planetary bodies. Because of similarities of size and orbit, Menaris and Extaris are informally referred to as "the Twins." Their combination is responsible for the highly eccentric orbit of the third planet, Arrakis.


  • Equatorial radius: 8,112 km.
  • mean density: 1.31 g/cm3
  • Atmospheric pressures: >250 standard atmospheres
  • eccentricity: 0.015
  • day: 42 hours
  • moons: 5


The primary constituents of Extaris's atmosphere are:

  • atomic helium 0.83,
  • Zeon 0.15,
  • carbon monoxide 0.01,
  • trace amounts of Zenon, Krypton, and cyanogen.

Weather is essentially benign due to three factors

  1. the orbit is nearly circular
  2. the axial rotation is slow
  3. the upper atmospheric layer of Zeon ice reflects 97% of the incident radiation from Canopus back into space.

These minimize the transfer of thermal energy to the lower atmosphere. The resulting lack of thermal gradients prevent the formation of significant cyclonic or anticyclonic circulation.


Extaris has five satellites that orbit the primary at distances from 117,000 km to 399,000 km. The external satellite Aja, which perhaps was gravitationally captured eons ago.

The 4 icy satellites arc in circular orbits and were probably formed from the same molecular accretion as Extaris; they are composed of a thick ice mantel surrounding an outer core of silicate material.

At the center of the outer core is a very small, dense, inner core of nickel-iron with no fluidity and accounts for the lack of measurable magnetic fields generated by internal dynamo activity.


  • ARRAKIS, Astronomical aspects of

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