Here's what the Mars 2020 rover would do:

Objective A: Habitability
Objective B: Biosignatures
Objective C: Sample Caching
Objective D: Prepare for Humans

Mars 2020 Science Objective A:

Characterize the processes that formed and modified the geologic record within a field exploration area on Mars selected for evidence of an astrobiologically-relevant ancient environment and geologic diversity.

Mars 2020 Science Objective B:

Perform the following astrobiologically relevant investigations on the geologic materials at the landing site:

  1. Determine the habitability of an ancient environment.
  2. For ancient environments interpreted to have been habitable, search for materials with high biosignature preservation potential.
  3. Search for potential evidence of past life using the observations regarding habitability and preservation as a guide.

Mars 2020 Science Objective C:

Assemble rigorously documented and returnable cached samples for possible future return to Earth.

  1. Obtain samples that are scientifically selected, for which the field context is documented, that contain the most promising samples identified in Objective B and that represent the geologic diversity of the field site.
  2. Ensure compliance with future needs in the areas of planetary protection and engineering so that the cached samples could be returned in the future if NASA chooses to do so.
Read about Depot Caching >>

Mars 2020 Science Objective D:

Contribute to the preparation for human exploration of Mars by making significant progress towards filling at least one major Strategic Knowledge Gap (SKG). The highest priority SKG measurements that are synergistic with Mars 2020 science objectives and compatible with the mission concept are:

  1. Demonstration of In-Situ Resource Utilization (ISRU) technologies to enable propellant and consumable oxygen production from the Martian atmosphere for future exploration missions.
  2. Characterization of atmospheric dust size and morphology to understands its effects on the operation of surface systems and human health.
  3. Surface weather measurements to validate global atmospheric models.
  4. A set of engineering sensors embedded in the Mars 2020 heat shield and backshell to gather data on the aerothermal conditions, thermal protection system, and aerodynamic performance characteristics of the Mars 2020 entry vehicle during its entry and descent to the Mars surface.