Kepler's laws of planetary motion law" is what became the Second Law in the set of three; but Kepler did himself not privilege it in that way. Johannes Kepler published his first two laws about planetary motion in 1609, having found them by analyzing the astronomical observations of Tycho Brahe. Kepler's third law was published in 1619. Kepler had believed in the Copernican model of the solar system, which called for circular orbits, but he could not reconcile Brahe's highly precise observations with a circular fit to Mars' orbit—Mars coincidentally having the highest eccentricity of all planets except Mercury. His first law reflected this discovery.
Planetary Science Archive Planetary Science Archive The Planetary Science Archive is the central repository for all scientific and engineering data returned by the European Space Agency's Solar system missions: currently Giotto, Huygens, Mars Express, Rosetta, SMART-1, and Venus Express, as well as several ground-based cometary observations. It uses NASA's Planetary Data System standards as a baseline for the formatting and structure of all data contained within the archive. All of the data sets are peer reviewed and undergo an additional internal validation procedure. All data on the PSA are free to download and use.The Principal Investigator(s) as well as the ESA Planetary Science