Solar System in fiction close to the Sun and its surface was exposed to extremes of temperature. The asteroids were too tiny and airless. By the early 20th century, prospects for life in the Solar System focused on Venus, the larger moons of Jupiter and Saturn, and especially Mars. With the onset of the Space Age, planetary probes cast increasing doubt on the likelihood of extraterrestrial life in the Solar System, at least life of any magnitude greater than organisms such as bacteria. By the mid-1960s, it was firmly established that life could have no foothold on the hostile surfaces of Mercury or Venus,
Stability of the Solar System is unlikely any of the planets will collide with each other or be ejected from the system in the next few billion years, and the Earth's orbit will be relatively stable. Since Newton's law of gravitation (1687), mathematicians and astronomers (such as Laplace, Lagrange, Gauss, Poincaré, Kolmogorov, Vladimir Arnold and Jürgen Moser) have searched for evidence for the stability of the planetary motions, and this quest led to many mathematical developments, and several successive 'proofs' of stability of the Solar System. The orbits of the planets are open to long-term variations. Modeling the Solar System is a case of the