This is a purely imaginary gas giant planet (green) shown with an Earth-like moon orbiting in close attendance. It is not yet known if habitable moons such as this can actually exist, though....

In this image I imagine an Earth-like world in orbit around not a single star but a close binary. What beautiful sunsets could be witnessed from this world. In the sky I have added a giant satellite, its night side illuminated by cities, betraying in...

This is the same kind of binary star system (a cataclysmic variable) as depicted Cataclysm III and VI this time seen from a cave on a purely hypothetical, watery and rocky planet. Admittedly, though, such a situation is highly unlikely to exist in re...

This image shows a total eclipse, complete with diamond ring effect, but not necessarily an eclipse on Earth. I have made the moon larger than it would appear in Earth's sky, so this is an alien but Earth-like planet somewhere else in the galaxy – ...

This was a commission for Scientific American, in their September 2000 edition. It was to illustrate an article about finding extrasolar planets via occultation – by detecting the dip in light levels as the planets transit in front of their stars. ...

This is an alternative impression of the extrasolar planet Gliese 581c, which resembles the Earth but which is five times its mass. I show the planet as seen from one of two hypothetical satellites....

Another impression of the extrasolar planet Gliese 581c, which resembles the Earth but which is five times its mass. I show the planet with two hypothetical satellites and a system of rings....

This is Gliese 581 c, one of three planets orbiting the star Gliese 581. Gliese 581 c has garnered much attention because it is very small compared to virtually all other known exoplanets to date, at only 1.5 times the radius of the Earth and five ...

... nd bigger than the Earth, so it has the gravity to retain heavy gases, unlike Mercury and Mars. It also orbits in its star's habitable zone - theoretically, a region surrounding a star within which liquid water can exist on an the surface of orbiting ...

Artwork of a Stanford Torus. This is a design for a space station proposed by NASA in 1975 at Stanford University. It consists of a torus with a radius of 1800km and a cross-sectional radius of 130m for the habitable section. The ring is connected to...