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The smallest of these, Kepler-42d, is about the size of Mars with a radius of only 0.57 times that of Earth. Not long ago, in Dec. of 2011, the Kepler team announced the discovery of Kepler-20e and Kepler-20f -- the first Earth-size planets ever found outside the solar system.
Numerous attempts [3] [4] [5] have been made over the years to determine an absolute Martian chronology (timeline) by comparing estimated impact cratering rates for Mars to those on the Moon. If the rate of impact crater formation on Mars by crater size per unit area over geologic time (the production rate or flux) is known with precision, then ...
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[31] [32] Mars has twice as much iron oxide in its outer layer as Earth does, despite their supposed similar origin. It is thought that Earth, being hotter, transported much of the iron downwards in the 1,800 kilometres (1,118 mi) deep, 3,200 °C (5,792 °F ), lava seas of the early planet, while Mars, with a lower lava temperature of 2,200 °C ...
If placed on Earth, Valles Marineris would span the width of North America. [36] In places, the canyons are up to 300 km wide and 10 km deep. Often compared to Earth's Grand Canyon, the Valles Marineris has a very different origin than its tinier, so-called counterpart on Earth. The Grand Canyon is largely a product of water erosion.
It is known that in the past, Mars has had a much more circular orbit. At one point, 1.35 million Earth years ago, Mars had an eccentricity of roughly 0.002, much less than that of Earth today. [188] Mars's cycle of eccentricity is 96,000 Earth years compared to Earth's cycle of 100,000 years. [189]
Though differing in size and temperature, terrestrial planets of the Solar System were reported to have high Earth Similarity Index values – Mercury, Venus, Earth and Mars. Sizes to scale. The Earth Similarity Index (ESI) is a proposed characterization of how similar a planetary-mass object or natural satellite is to Earth. It was designed to ...