Here's why:

* Distance from the Sun: Mars is further away from the Sun than Earth, meaning the Sun's radiation is spread out over a larger area by the time it reaches Mars. This inherently results in less intense radiation.

* Thin Atmosphere: While Earth's atmosphere filters out a significant portion of harmful UV radiation, Mars has a very thin atmosphere. This means that less UV radiation is blocked, but that's not the same as receiving *more*.

However, there's a catch:

* Lack of Ozone Layer: Earth's ozone layer plays a critical role in absorbing most of the Sun's harmful UV radiation. Mars lacks a significant ozone layer, meaning the UV radiation that does reach the surface is less filtered than on Earth.

Therefore, while the total amount of UV radiation reaching Mars is less than Earth, the amount that reaches the Martian surface is more harmful due to the lack of an ozone layer. This means that Mars's surface experiences higher levels of harmful UV radiation than Earth's surface.

Important Note: It's crucial to understand that the *intensity* of UV radiation on Mars is still lower than on Earth due to the greater distance from the Sun.