"The contrast between the vicious coldness of space and the warm nurturing of Earth below filled me with overwhelming sadness.
"Every day, we are confronted with the knowledge of further destruction of Earth at our hands: the extinction of animal species, of flora and fauna … things that took five billion years to evolve, and suddenly we will never see them again because of the interference of mankind. It filled me with dread."
The Boston Legal star went on to compare the feeling of being in space to being "at a funeral" and explained that he was experiencing a common feeling known as the Overview Effect.
Writing in his new autobiography Boldly Go: Reflections on a Life of Awe and Wonder, he added: "My trip to space was supposed to be a celebration; instead, it felt like a funeral. It is called the Overview Effect and is not uncommon among astronauts, including Yuri Gagarin, Michael Collins, Sally Ride, and many others. Essentially, when someone travels to space and views Earth from orbit, a sense of the planet's fragility takes hold in an ineffable, instinctive manner.
"Author Frank White first coined the term in 1987: 'There are no borders or boundaries on our planet except those that we create in our minds or through human behaviours. All the ideas and concepts that divide us when we are on the surface begin to fade from orbit and the moon. The result is a shift in worldview, and in identity'."