Mars has two small satellites, PHOBOS and DEIMOs, . They are irregularly shaped, very dark objects liberally covered with craters . This gives them the appearance of modestly-sized asteriods but their almost circular orbits make it unlikely that they are simply captured asteroids. Several astronomers have suggested that they are the shattered remains of an […]
Compared TO the Earth. Mars has a thin atmosphere and Venus & thick one whereas Mercury and the Moon do not have one at all. Table 10.3 lists some of the gases which we might expect to find in planetary atmospheres because they are volatile compounds of the cosmically common elements. If a planet ever […]
From measurements of radioactive decay products, it is possible to measure the age pattern of the Earth’s continents. They are found to have an ancient nucleus, at least 2.5 billion years old, onto which successively younger extensions have been welded, a process still continuing today. The growth has not been regular and in particular there […]
Owing to the thick clouds we know little of the surface of Venus. Reference has already been made to the craters observed by radar. There is a scarcity of small craters; this is to be expected because the dense atmosphere would burn up the smaller meteoroids which would otherwise produce these craters. Venus is a […]
Because Mercury is so much nearer to the Sun, it receives ten times as much solar energy per unit surface area when it is at perihelion than does the Moon. Because of the coupling between Mercury’s orbital motion and rotation the meridians at 0° and 180° longitude receive two and a half times more radiation […]
Perhaps the most remarkable aspect of the Martian surface is the distribution of craters larger than 10km in diameter, which are much commoner in the southern hemisphere than hi the northern. Much of the northern hemisphere has been flooded with lava and this has evidently obliterated the craters that must have existed at one time. […]
The surface of the Moon can, roughly speaking, be divided into two contrasting types – dark, comparatively smooth areas called MARIA (singular: mare) and brighter, more rugged regions called TERRAE. The maria cover about one-third of the Moon’s near side but are almost completely absent from the far side. Maria is the Latin word for […]
The most obvious features on the surface of the Moon are the circular walled areas called craters. These have been known since telescopic observations began. The Earth has very few easily recognizable craters of any great size, although in recent years careful observations have revealed many more which are somewhat obscured by water, vegetation, erosion […]
A glance at any atlas shows that the Atlantic coastlines of Africa and (South America have very similar shapes. The coastline does not truly represent the shape of a continent, as it depends on the level of the oceans. A much more significant feature is the edge of the continental shelf where the sea bottom […]
In 1889. G.V.Schiaparelli announced that his extensive observations of Mercury had shown that the planet rotated on its axis in the same time. 88 days, that it took to revolve around the Sun and that as a result it always kept the same face turned towards the Sun. This result was confirmed by several other […]