On Tuesday, InSight, NASA's Martian exploration device, successfully landed on its destination site. Guokr.com comments:

Unlike its predecessors that stressed exploring the surface of Mars or analyzing its atmosphere, InSight focuses on in-depth underground exploration of the red planet. For that purpose, it carries devices that can collect earthquake (or, more exactly, Marsquake) shock wave data and do thermal imaging of its inner structure.

Some might ask why the inner structure of Mars is so important to us. The answer is simple: Because the geological structure of Mars contains the records of the planet's evolution over billions of years, which in turn reflect its long history and might provide an answer to the origin of life on Earth.

As rocky planets, the Earth and the Mars are close neighbors and they formed from the same materials. Yet their destinies vary: Life began on the Earth about 3.5 billion years ago and prospered across the planet, while Mars has always remained cold and lonely, without any sign of life.

Some argue the chief reason for the fundamental difference lies in distance from the sun, namely the Earth is in the so-called habitable zone, which makes it possible for water to stably exist as liquid. However, that's not the whole story. The moon as the natural satellite of the Earth is also in the habitable zone but it is without any life, either.

A quite reliable guess is about size. The Earth has a good size that helps it to keep enough heat inside its core and air and water at its surface. These conditions in turn propel geological movements that can update the surface of the Earth, maintain the atmospheric layer that produces diverse climate, and produce a magnetic field that protects the planet's surface from fierce solar winds.

But it is difficult to find evidence to support this guess because the Earth had experienced so many geological movements in the past billions of years. Mars is different because its core has been cold for about 3 billion years. It has no sign of life, but its conditions might offer insights.

That's the mission of InSight. By studying in-depth underground of Mars, it will hopefully provide an answer to these questions.