; and (2) to understand global change. (b) Earth science missions and programs With respect to the missions and programs of the Earth Science Division, the Administrator shall, to the maximum extent practicable, follow the recommendations and guidance provided by the scientific community through the decadal survey for Earth science and applications from space of the National Academies of Sciences, Engineering, and Medicine, including— (1) the science priorities described in such survey; (2) the execution of the series of existing or previously planned observations (commonly known as the program of record ); and (3) the development of a range of missions of all classes, including opportunities for principal investigator-led, competitively selected missions. 308. Science missions to Mars (a) In general The Administrator shall conduct 1 or more science missions to Mars to enable the selection of 1 or more sites for human landing. (b) Sample program The Administrator may carry out a program— (1) to collect samples from the surface of Mars; and (2) to return such samples to Earth for scientific analysis. (c) Use of existing capabilities and assets In carrying out this section, the Administrator shall, to the maximum extent practicable, use existing capabilities and assets of NASA centers. 309. Planetary Defense Coordination Office (a) Findings Congress makes the following findings: (1) Near-Earth objects remain a threat to the United States. (2) Section 321(d)(1) of the National Aeronautics and Space Administration Authorization Act of 2005 ( Public Law 109–155 ; 119 Stat. 2922