5. Concluding remarks
It is generally thought that molecules vital to living systems on earth may have started from scratch. In this Letter , we have explored the possibility of formation of a DNA base, namely adenine, and a few of the simpler amino acids during a generic molecular cloud collapse and show that mass fraction of adenine is significant which might have contaminated the planetary disk even before the formation of the planets themselves. In a static evolution of a cloud of constant density and temperature, the formation of adenine is also important, and therefore our conclusion may be very generic. The rates we have chosen are reasonable, though uncertainties of an order of magnitude cannot be ruled out at this stage as more accurate estimates require one to have temperature dependent rate coefficients of both forward and reverse reactions.
Since earth is a generic planet and since it seems apparent that bio-molecules are as naturally produced as any other complex molecules, we believe that DNA bases produced in collapsing cloud could have contaminated the earth, and at the same time there should be many such planets in each galaxy where DNA based lives should flourish. It is not yet clear whether or not these molecules survived during further evolution of planetary disks leading to eventual formation of planets or actual contaminations were made much later by comets carrying away protecting these molecules. These vital issues will be addressed in due course.
© European Southern Observatory (ESO) 2000
Online publication: January 31, 2000