Since this is an FBO notice, it is not a complete or verbatim summary of the newly amended APEXMO program element appendix or any, if necessary, future amendments or clarifications. NASA's Science Mission Directorate is amending APEXMO to defer to Step-2 the requirement for a data analysis plan. In addition, language is added to clarify that investigations may propose to use small amounts of radioactive materials. Please note that the Deadline for Proposal Submission is not changed from August 1, 2019.

Comments and questions may be addressed by email only to: Dr. Linda S. Sparke, Astrophysics Explorers Program Scientist, Astrophysics Division, Science Mission Directorate, NASA Headquarters, Washington, DC, E-mail: [email protected] (subject line to read "Explorer MO PEA"). The period for questions/comments will close three weeks before the proposal due date, and the period for responses will close ten days before the proposal due date.

Responses to all inquiries will be posted as Questions and Answers (QA). APEXMO QAs are linked from the 2019 APEXMO Acquisition website at: https://explorers.larc.nasa.gov/2019APSMEX/MO/index.html. Anonymity of persons/institutions who submit questions will be preserved.

In the event of Government funding lapses that impact NASA operations, proposers should visit NSPIRES, the official NASA source for the full APEXMO program element appendix.