According to an ecology professor of mine, the question isnt really "Is there alien life in space". Its "Is the alien life using DNA as a method of replication".
Biologist can make the components of cells in labs. This was first done in the Miller-Urey experiment (1953):
"A warmed flask of water simulated the primeval sea. The "atmosphere" consisted of H2O, H2, CH4, and NH3. Sparks were discharged in the synthetic atmosphere to mimic lightning. A condenser cooled the atmosphere, raining water and any dissolved compounds back to the miniature sea. As material circulated through the apparatus, the solution in the flask changed clear to murky brown. After one week, Miller and Urey analyzed the contents of the solution and found a variety of organic compounds, including some of the amino acids that make up the proteins of organisms"
