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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.
The precession cycle is 93,000 Martian years (175,000 Earth years), much longer than on Earth. Its length in tropical years can be computed by dividing the difference between the sidereal year and tropical year by the length of the tropical year.
A Martian year is equal to 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours. [2] The gravitational potential difference and thus the delta-v needed to transfer between Mars and Earth is the second lowest for Earth. [186] [187] The axial tilt of Mars is 25.19° relative to its orbital plane, which is similar to the axial tilt of Earth. [2]
The basic time periods from which the calendar is constructed are the Martian solar day (sometimes called a sol) and the Martian vernal equinox year.The sol is 39 minutes 35.244 seconds longer than the Terrestrial solar day, and the Martian vernal equinox year is 668.5907 sols in length (which corresponds to 686.9711 days on Earth).
On both Earth and Mars, these two precessions are in opposite directions, and therefore add, to make the precession cycle between the tropical and anomalistic years 21,000 years on Earth and 29,700 Martian years (55,900 Earth years) on Mars. As on Earth, the period of rotation of Mars (the length of its day) is slowing down.
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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 ...