…Planets near their suns reap the benefits of light and heat, while those farther away must endure colder temperatures. But the new research indicates that planets with hydrogen-rich atmospheres could contain liquid at their surface even out to fifteen times the distance between the Earth and the Sun.
With a hydrogen atmosphere, the greenhouse effect these planets could experience would be sufficient to allow for liquid water on their surfaces, despite their distant orbits.
The area around a star in which water can be liquid rather than ice is known as the habitable zone. Sometimes called the “Goldilocks zone,” it’s just right – not too hot (so the water doesn’t evaporate) and not too cold (so it won't freeze).
Typically, the distance calculated takes into account a rocky body having an atmosphere made up of water and carbon dioxide, the same greenhouse gases found on Earth.
… The size of a solar system's habitable zone varies, however, depending on the properties of the star. For hotter, brighter stars, the region stretches farther out into space, while its inner edge cannot be too close to the star.
The habitable zone for a G-type star such as the Sun, for instance, lies between 0.95 and 1.4 AUs (one AU, or astronomical unit, is the distance from the Earth to the Sun). The Earth, quite obviously, falls within that region. For a smaller, dimmer M-type star, the habitable zone is closer, between 0.08 and 0.12 AUs.
But according to Pierrehumbert’s research, , a rocky planet with a hydrogen atmosphere could have a habitable zone extending as far as 1.5 AUs for M-stars and 15 AUs for G-stars.
This means that for stars similar to the Sun, rocky planets beyond the reach of Saturn could contain oceans of water.
Travis Barman of Lowell Observatory notes that there might be many similar scenarios of planets that don’t mimic Earth but are still habitable. …