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59

Yes, that's correct; it's also true for the Earth's crust. The reason is that "rocks" are typically made up of components containing combinations of silicon or one or more metals (e.g., magnesium, aluminum, iron) and oxygen, such as silica ($\mathrm{SiO}_{2}$); alumina ($\mathrm{Al}_{2}\mathrm{O}_{3}$); lime ($\mathrm{CaO}$); iron oxide ($\mathrm{...


23

Note this fact is unsurprising. Oxygen is the third most abundant element in the solar system (by mass and by number) after hydrogen and helium. Planets/moons with the size and escape velocities of the Earth and the Moon are unable to hang onto much in the way of helium- or hydrogen-rich compounds at the equilibrium temperatures at 1 au from the Sun (in fact ...


5

What are the dark spots in the “face of Mars” picture? They are called "bit errors" in the NASA JPL image catalog for PIA01141. The explanation seems a bit handy-wavy to me; so I think we'll need to dig deeper to see if they are received noise on Earth or some electrical or imaging problem on the spacecraft. Read more about the Voyagers' cameras ...


2

I have the impression these were first observed in images taken by the Mars Orbiter Camera (MOC) of the Mars Global Surveyor, probably sometime between 1997 (arrival at Mars) and 1999 (when the main mapping program began) -- or possibly as late as 2000 (when they are first mentioned). In Piqueux et al. (2003), a paper specifically focused on the spiders, ...


2

What about the possibility that Venus (and its former moon) went through a much more rapid evolution then occurs normally? Typically a planet-moon system will undergo the following sequence of events: A large object hits the planet and a moon is formed. The planet rapidly tidally locks its moon The moon gradually slows down the rotation of the planet until ...


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