Answer:
The Solar System is <em>natural</em> because it was created <em>without any</em> <em>intervention of human beings.</em>
Explanation:
Different definitions for word Nature:
"The material world, especially as <em>surrounding humankind</em> and existing<em> independently of human activities".</em>
(Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019)
"All the animals and plants in the world and all the features, forces, and processes that exist or happen <em>independently of people</em>, such as the weather, the sea, mountains, reproduction, and growth"
(Definition of “nature” from the Cambridge Academic Content Dictionary © Cambridge University Press).
And for System:
"An assemblage or combination of things or parts forming a complex or unitary whole".
"A number of heavenly bodies associated and acting together according to certain natural laws".
(Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019).
These definitions have something in common: all consider that something is natural, or coming from nature because "[it] exists or happens independently of people".
So, The Solar System is <em>natural</em> because it was created <em>without any</em> <em>intervention of human beings, </em>and acts as an <em>unitary whole </em>according to <em>natural </em>laws.
All systems that are not natural, are <em>artificial</em>, that is, created by human activities, like a robot, an airplane, a clock, among many others artifacts, inventions or the like.