however kepler discovered tycho had posited intersecting martian and solar orbits because he had mistakenly concluded from his data that at opposition mars was closer to the earth than the sun was. the source of the error was a research assistants' mistaken calculation of mars's daily parallax from observations during its 1582-3 opposition as greater than that of the sun's presumed 3' parallax. kepler discovered tycho’s observations revealed little or no martian parallax, implying it was further than the sun at opposition. this would have refuted tycho's system in favour of ursus's and roslin's. it seems it has yet to be determined whether the dominant astronomical system of the 17th century was the geoheliocentric system of tycho or that of ursus and roslin at least in respect of non-intersecting solar and martian orbits, and also in that of the earth's rotation or not.