The planets in our solar system have been in their current orbital positions for a significant period of time, estimated to be around 4.6 billion years. This age corresponds to the formation of the solar system itself. The planets formed from a rotating disk of gas and dust known as the solar nebula, which eventually collapsed under its own gravity to form the Sun at its center and the planets in orbit around it.
The precise time since the planets settled into their current orbits can vary depending on the specific planet. For example, it is believed that the inner planets, including Mercury, Venus, Earth, and Mars, took several tens of millions of years to form and settle into their stable orbits. On the other hand, the gas giants like Jupiter and Saturn likely took longer, possibly a few hundred million years, to fully form and establish their current positions.
Once the planets formed, gravitational interactions with other objects in the solar system, such as asteroids, comets, and even each other, have influenced their orbits to some extent. However, over billions of years, these perturbations have generally averaged out, resulting in the relatively stable orbits we observe today.
It's worth noting that while the planets have been in their current positions for a long time, they are not entirely fixed. Over very long timescales, the gravitational interactions between the planets can cause small changes in their orbits. Additionally, the Sun's gradual loss of mass over its lifespan will also have a subtle effect on the planetary orbits. However, these changes occur over timescales much longer than the current age of the solar system.