Encyclopedia of Astrobiology

Living Edition
| Editors: Muriel Gargaud, William M. Irvine, Ricardo Amils, Henderson James Cleaves, Daniele Pinti, José Cernicharo Quintanilla, Michel Viso


  • Robert Hazen
Living reference work entry
DOI: https://doi.org/10.1007/978-3-642-27833-4_18-2



The term “achiral” is applied to any object – in astrobiology most commonly a molecule, a two-dimensional crystal surface, or a three-dimensional crystal structure – that is invariant (i.e., superimposable) with its mirror image. Achiral objects possess a plane of symmetry, either a mirror or a glide plane symmetry operator. Common achiral objects include a soccer ball, a pencil, and the letter “X,” in contrast with chiral objects such as a snail shell, your left hand, and the letter “R.” Common achiral molecules are H2O, CH4, and NH3 in contrast with such chiral biomolecular species as alanine and ribose. In chemistry, achiral should not be confused with racemic, although in neither case is the optical rotation of polarized light affected.

See Also


Mirror Image Crystal Structure Bioorganic Chemistry Crystal Surface Plane Symmetry 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Geophysical LaboratoryCarnegie Institution of WashingtonWashingtonUSA