Astronomers don't conclude that the crust on Mars is thicker than Earth's crust. In fact, the opposite is true: Mars' crust is generally thinner than Earth's crust.

Here's why:

* Mars is smaller than Earth: With a smaller overall size, Mars has less gravitational force pulling its crust inward. This means its crust can be thinner than Earth's.

* Mars has a less active core: Earth's core is much more active, with plate tectonics constantly reshaping the surface. Mars' core is thought to be less active, leading to less geological activity and less crustal thickening.

* Evidence from spacecraft: Data gathered by spacecraft like Mars Global Surveyor and Mars Odyssey has provided evidence suggesting a thinner Martian crust. For example, observations of Mars' gravitational field indicate a less dense interior than Earth's, hinting at a thinner crust.

However, Mars' crust is not uniformly thin. There are some regions where the crust is thicker, like the Tharsis bulge, a massive volcanic plateau. This is a result of volcanic activity, which can build up thick layers of lava and rock over time.

Overall, the average crustal thickness on Mars is estimated to be about 37 kilometers (23 miles), while Earth's average crustal thickness is about 40 kilometers (25 miles). This difference is mainly due to the size and geological activity of the two planets.