Earth is one special planet.
It has liquid water, plate tectonics and an atmosphere that shelters it from the worst of the sun's rays. But many scientists agree our planet's most special feature might just be us.
"It's the only planet we know of that has life," said Alan Boss, a planet formation theorist at the Carnegie Institution of Washington in Washington, D.C.
Though other bodies in our solar system, such as Saturn's moon Titan, seem like they could have once been hospitable to some form of life, and scientists still have hope of eventually digging up microbes beneath the surface of Mars, Earth is still the only world known to support life. ...