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These electric currents should create magnetic fields, making the planets behave as if they have giant bar magnets inside them. We expect that some of the core of each of the inner planets is molten, and we expect that this liquid metallic core must generate electric currents inside the planet as the core rotates with the rest of the planet. Because the core of Mercury is probably mostly made up of iron and nickel and it fills so much of the planet's interior, Mercury is the densest inner planet. That is, it fills up most of the interior of this planet. Curiously, we find that, compared to the other planets, Mercury's core is relatively large.
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Just like the Earth, Mercury, Venus, and Mars are differentiated. First, consider the interior structure of these planets. There are several peculiarities about these planets, but we can understand the likely causes of these properties when we contrast them to the Earth. The most visited planet in our Solar System, including several recent missions, Mars Exploration Rovers Spirit and Opportunity, the Phoenix Lander, Curiosity, and MAVEN.Two small, irregularly shaped moons-Phobos and Deimos.Frozen water in a permafrost layer (recently confirmed).Polar caps of dry ice and water ice that change with the seasons.One Mars day is only slightly longer than an Earth day (24.6 hours).The surface is red because of the presence of iron oxide (rust).Has an atmosphere that is much thinner than Earth or Venus, mostly CO 2.Giant volcanoes (largest of any in the entire Solar System).Temperature always below the freezing point of water.Credit: Space Telescope Science Institute Mars