Editing Mars 5 (section)

==Mars orbit==

The probe reached Mars on 12 February 1974. At 14:44:25 the spacecraft's engines ignited to begin its orbit insertion burn, which successfully placed it into an Areocentric orbit with a [[apsis|periapsis]] of {{convert|1760|km}}, an [[apsis|apoapsis]] of {{convert|32586|km}}, and 35.3 degrees [[orbital inclination|inclination]].<ref name="NSSDC"/><ref name="DSC73"/>

The spacecraft's pressurised instrument compartment began to leak as soon as the spacecraft entered orbit around Mars, which controllers believed to be the result of a micrometeoroid impact during orbital insertion. It ceased operations on 28 February, having returned 180 photographic frames, 43 of which were of usable quality.<ref name="DSC73"/> The probe's original planned lifetime in Mars orbit had been three months.<ref name=Harvey161>{{cite book |last=Harvey |first=Brian |date=2007 |title=Russian Planetary Exploration History, Development, Legacy and Prospects  |publisher=Springer-Praxis |pages=161–165 |isbn=9780387463438}}</ref> The probe's gamma ray spectrometer measured the uranium, thorium and potassium content of the surface the probe passed over and found they were similar to [[igneous rock]]s on Earth.<ref name=Harvey161 /> The exact ratios of the elements varied with the age of the surface.<ref name=Harvey161 /> Mars 5's Infrared radiometer reported a daytime surface temperature of between {{convert|-44|and|-2|C}}.<ref name=Harvey154 /><ref name=Harvey161 />  Night time temperatures were measured at {{convert|-73|C}}.<ref name=Harvey161 /> 

The probe also made a number of observations of Mars's atmosphere.<ref name=Harvey161 /> It found an ozone layer at an altitude of {{convert|30|km}} and observed clouds.<ref name=Harvey161 />