errans' planetary system The required heating conies in part from radioactive decay but mostly from neutrinos emitted by the host starts) Absorption of neutrinos by the planet produces the heat Since neutrinos have no mass or charge most will pass through a planet without interaction Hence, in the absence of large external gravitational torques, the severe internal heating required occurs only when the neutrino flux is very large Very few stars produce a sufficiently large flux Suffice it to saj that Canopus does not produce a large flux of neutrinos Gravitational torques are the dominant mechanism for most planets exhibiting plate tectonics behavior Requirements are (1) adja cent planet! s) with mass considerably larger than the planet in question and/or one or more moons with mass of an appreciable fraction of the host planet, and (2) orbits of the adjacent planet(Y) and/or the moon(s) which he appreciably outside the ecliptic plane of the planet, and are preferably eccentric The resulting gravitational torques generate large stresses which tn turn cause crustal movement with associated tectonic phenomena The planet is heated internally by friction, but this heating is secondary to the entire process Arralas, as noted earlier, has larger planets on each side, Menans and Ex tans, both of which Mve highly elliptical orbits with orbital planes lying well outside that of Arrakis Plate tectonics on Arrakis is thus caused by gravitational torques The unusual closeness and large size of Menans and Ettam cause ArraJos to exhibit exceptional geologic activity Quakes are common and the amount of volcanic activity is on the high side, but certain ly not extreme Portions of the crust are displaced with respect to other crustal seg ments by the astounding amount of 30 centi meters per year (planetary mean) New moun tains are formed and old ones destroyed at a geologically rapid rate Over one 2 000 year penod the Trambhsch Range rose 3 125 meters Grabens open, oscillate, and close at equally rapid rates The north south and east west trends of all mountain ranges and gra bens is a result of the particular geometry of the Menans Extans-Arrakis system and stress field orientation so produced Arrakis is a favorite planet for planetary geologists because one can literally see geo logic proteges m action with only a short time of observation Mapping however, is a problem and the planet is a civil engineer s nightmare INTERIOR The crust of Arrakis is rather thin, averaging only 10 kilometers in thickness An mcipiently molten region, the source region for volcanic activity lies immediately below The remainder of the planet is basical ly solid except for a small, fluid central core Arrakis has a relatively weak magnetic field which is produced in the core It is of interest to note that even after many thou sands of years of study the exact mechanism by which the magnetic field is produced is still not fully understood It has been known for some time that the chemical composition of a planet depends upon Us distance from the mom btar and that same planets consist primarily of silicates some primarily of hydrogen (quasi stars) some primarily of sulfides while some are mostly metallic The Neta class is defined specifically as comprising those planets with a composition of 60 10% silicates (by mass), 30 10% metals, 10 5% sulfides and less than 5% hydrogen The crust and upper layers of Arrafas are composed almost entirely of silicates the middle and lower layers are primarily silicates, but with significant amounts of metals and sulfides, while the core is primarily metallic with a small amount of sulfides I he precise chemical composition of Arrakis is 69 723% silicates 21 388% metallics 7 691% sulfides and 1 198% hy drogen and miscellaneous J R Further references ARRAKIS ATMOSPHERE OF BEFORE THE ATREIDES Th Zed Ghralic The Geology of Arrabs Present Views Geological Record 90 748 73 H K ARRAKIS, OXYGEN SAGA 37 ARRAKIS, OXYGEN SAGA Praeshan, Arrakeen Archeology (Topaz Carolus UP), ZG Kynes, 'Surface Feature Summary of Arrakis, Bulletin of Planetology NS 901 39-49, A G Xcnach, "Comparison ofRakeen Datums, 10000-15000," Geo logical Record 79 35-40, Zhuurazh Hackelrhued, "The 'Polar Slide' Phenomenon of Airakis," Geological Rec ord 85 573-95, PR Bnacewt, The Mechanisms of Plate Tectonics, Science Occasional Papers (Loomar R1T Press) ARRAKIS.