Group Q The Rocky Inner Planets

what are the rocky inner planets
the four innermost planets in the Solar System (Mercury, Venus, Earth, and Mars) are sometimes called the "terrestrial" planets because of their proximity to Earth ("Terra" in Latin) and their similarity as compact solid bodies with rocky surfaces. These four planets developed from small grains of dust that collided and stuck together to form pebbles, boulders, kilometer- and mile-sized planetesimals, and larger planetary embryos and protoplanets). They formed in the inner portion of the protoplanetary disk located closer to the developing Sun during the first 100 million years of the System's birth, where it was too warm for the four developing protoplanets to agglomerate water and more volatile ices and bulk up sufficiently in gravitational might to hold onto the abundant but lightest gases of the Solar nebulae (hydrogen and helium) to become "gas giants." Although rocky (and icy protoplanets beyond the Solar System's 2-AU "ice line") formed in the Main Asteroid Belt, the early development of Jupiter prevented protoplanets like icy Ceres from agglomerating into larger planetary bodies, by sweeping many into pulverizing collisions as well as out into the Oort Cloud or beyond Sol's gravitational reach altogether.


According to astronomer Alan P. Boss (Astronomy, October 2006), many astronomers now believe that the development of planetesimals into protoplanets as large as the moon was a runaway process, where a young Solar System may have developed a swarm of hundreds of Lunar-mass protoplanets in as little as 100,000 years. In a longer, succeeding phase of growth into Mars-sized protoplanets, however, these objects interacted gravitationally over many orbits so that their initially circular orbits became increasingly elliptical and they collided and merged into larger bodies over tens of millions of years. Colliding at speeds up to 22,000 miles per hour (36,000 kilometers per hour), such a collision may have stripped most of the rocky mantle from the protoplanet that became Mercury with its iron-rich core, while a Mars-size protoplanet struck the early Earth off-center and created a spray of mostly mantle material that later accreted to form the Moon.

Mercury is the smallest terrestrial planet in the solar system, about a third of the size of Earth. It has a thin atmosphere, which causes it to swing between burning and freezing temperatures. Mercury is also a dense planet, composed mostly of iron and nickel with an iron core. Its magnetic field is only about 1 percent that of Earth’s. The surface of Mercury has many deep craters and is covered by a thin layer of tiny particle silicates. In 2012, scientists found extensive evidence of organics — the building blocks of life — as well as water ice (in craters shaded from the sun). Mercury's thin atmosphere and close proximity to the sun make it impossible to host life as we know it.

Venus, which is about the same size as Earth, has a thick, toxic carbon monoxide-dominated atmosphere that traps heat, making it the hottest planet in the solar system. Much of its surface is marked with volcanoes and deep canyons — the biggest of which is 4,000 miles long. Few spacecraft have ever penetrated Venus’s thick atmosphere and survived. And it’s not just spacecraft that have trouble getting through the atmosphere — there are fewer crater impacts on Venus than other planets, because only the largest meteors can make it . The planet is hostile to life as we know it.

Of the four terrestrial planets, Earth is the largest, and the only one that has extensive regions of liquid water. Wateris necessary for life as we know it, and life is abundant on Earth — from the deepest oceans to the highest mountains. Like the other terrestrial planets, Earth has a rocky surface with mountains and canyons, and a heavy metal core. Earth’s atmosphere contains water vapor, which helps to moderate daily temperatures. The planet has regular seasons for much of its surface; regions closer to the equator tend to stay warm, while spots closer to the poles are cooler and in the winter, icy.

Mars has the largest mountain in the solar system, rising 78,000 feet above the surface. Much of the surface is very old and filled with craters, but there are geologically newer areas of the planet as well. At the Martian poles are polar ice caps that shrink in size during the Martian spring and summer. Mars is less dense than Earth and has a smaller magnetic field, which is indicative of a solid core, rather than a liquid one. While scientists have found no evidence of life yet, Mars is known to have water ice and organics — some of the ingredients for living things. Evidence of methane (in varying amounts) has also been found in some parts of the surface.

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