Answer to Question 1
Terrestrial planets are small, dense, rocky worlds with little or no atmosphere. The Terrestrial planets have densities like that of rock or metal. According to the solar nebula theory, in the inner regions of the solar system, close to the Sun, the only materials that could form grains were compounds with high melting points, such as metal oxides and pure metals, which are very dense. Mercury, Venus, Earth, and Mars are evidently composed of a mixture of metals, metal oxides, and silicates, with proportionately more metals close to the Sun and more silicates farther from the Sun.
Answer to Question 2
As the planet circles the star, the star wobbles slightly, and that very small motion of the star is detectable by Doppler shifts in the star's spectrum. The Doppler shifts are more easily detected with larger-mass planets.
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