https://phys.org/news/2018-11-lander-humans-fascination-mars.html

Scientists consider Mars a tantalizing time capsule. It is less geologically active than the twice-as-big Earth and so retains much of its early history. By studying the preserved heart of Mars, InSight can teach us how our solar system's rocky planets formed 4 1/2 billion years ago and why they turned out so different.

"Venus is hot enough to melt lead. Mercury has a sunbaked surface. Mars is pretty cold today. But Earth is a nice place to take a vacation, so we'd really like to know why one planet goes one way, another planet goes another way," said InSight's lead scientist Bruce Banerdt of NASA's Jet Propulsion Laboratory in Pasadena, California.