1. We have some pieces of rock that we believe came from Mars (including the famous one that may or may not have bacterial spore fossils). They are much less than 4.6 billion years old. We also have measured the age of meteorites, and only a few of them have grains that are older than 4.6 billion years.
Originally Posted by dirty_g
2. We know the mass of the Sun because of knowing the gravitational constant, the sizes of the planetary orbits around it, and the duration of the planetary orbits. This is something we know to a high degree of precision.
Forming opinions as we speak