sentences:  In addition to its orbit, a planetary mass object must have the potential for sufficient atmospheric pressure to support liquid water and a sufficient supply of hydrogen and oxygen at or near its surface.The Gliese 581 planetary system contains multiple planets that may be candidates for surface water, including Gliese 581c, Gliese 581d, might be warm enough for oceans if a greenhouse effect was operating, and Gliese 581e.Gliese 667 C has three of them are in the habitable zone including Gliese 667 Cc is estimated to have surface temperatures similar to Earth and a strong chance of liquid water.