Editing Viking lander biological experiments (section)

=== Effects of landing rockets ===
A press commentary argued that, if there was life at the Viking lander sites, it may have been killed by the exhaust from the landing rockets.<ref name="viking killers">{{cite web |title=Did probes find Martian life ... or kill it off? |url=http://www.nbcnews.com/id/16516952 |archive-url=https://web.archive.org/web/20131205002852/http://www.nbcnews.com/id/16516952/ |url-status=dead |archive-date=December 5, 2013 |last=Borenstein |first=Seth | name-list-style = vanc |publisher=Associated Press via NBC News |date=2007-01-07 |access-date=2007-05-31 }}</ref>  That is not a problem for missions which land via an [[airbag]]-protected capsule, slowed by parachutes and retrorockets, and dropped from a height that allows rocket exhaust to avoid the surface.  [[Mars Pathfinder]]'s ''Sojourner'' rover and the [[Mars Exploration Rover]]s each used this landing technique successfully.  The [[Phoenix (spacecraft)|Phoenix Scout]] lander descended to the surface with retro-rockets, however, their fuel was [[hydrazine]], and the end products of the plume (water, nitrogen, and ammonia) were not found to have affected the soils at the landing site.