• What is the nature of organic material in our solar system, and how has this matter evolved?

  • What global mechanisms affect the evolution of volatiles on planetary bodies?

  • What planetary processes are responsible for generating and sustaining habitable worlds, and where are the habitable zones in the solar system?

  • Does (or did) life exist in the solar system, beyond Earth?

  • Why have the terrestrial planets differed so dramatically in their evolutions?

  • What hazards do solar system objects present to Earth’s biosphere?

  • How do the processes that shape the contemporary character of planetary bodies operate and interact?

  • What does our solar system tell us about the development and evolution of extrasolar planetary systems, and vice versa?

High-Priority Missions in the SSE Decadal Survey

Addressing these key questions will, as discussed in the SSE decadal survey, require a combination of large, medium, and small space- and ground-based projects backed up by theoretical and laboratory studies, and related research and data-analysis programs.

In response to ground rules set by NASA,a the SSE decadal survey prioritized spacecraft missions in large (>$650 million), medium (between $325 million and $650 million), and small (<$325 million) cost categoriesb and ranked non-Mars and Mars missions separately. Thus, the highest-priority large, non-Mars and Mars missions were, respectively:

  • Europa Geophysical Explorer. An orbiter of Jupiter’s ice-encrusted satellite to assess the nature and depth of its putative ocean; and

  • Mars Sample Return. A program to return several samples of the Red Planet to Earth for studies to search for life, develop chronology, and define ground truth.

Priorities in the SSE decadal survey for medium-cost missions to destinations other than Mars were, in priority order, as follows:

  1. Kuiper Belt-Pluto Explorer. A flyby mission of several Kuiper Belt objects, including Pluto/Charon, to discover their physical nature and understand their endowment of volatiles;c

  2. South Pole-Aitken Basin Sample Return. A mission to collect and return to Earth samples from the solar system’s largest and deepest impact basin, which pierces the Moon’s crust and may expose the lunar mantle;d

  3. Jupiter Polar Orbiter with Probes. A mission consisting of a close-orbiting polar spacecraft equipped with various instruments that also acts as a relay for three probes to make in situ measurements of the jovian atmosphere below the 100+ bar level;e

  4. Venus In Situ Explorer. A mission to acquire and lift a core sample of Venus into the atmosphere for compositional analysis and to make simultaneous atmospheric measurements; and

  5. Comet Surface Sample Return. A mission to return several pieces of a comet’s surface to Earth for organic analysis.


These included the following: The Mars program was to be considered independently from the rest of the solar system; there would be no more than one large- and two medium-class missions per decade; only available technology could be considered; and the availability of new radioisotope power systems could not be assured within the decade 2003–2013.


Missions were assigned to the various cost categories according to the best estimates available at the time the SSE decadal survey was drafted. Note that the cost categories used in the SSE decadal survey are not the same as those used in the solar and space physics decadal survey.


Currently being implemented as New Horizons, the first mission in NASA’s New Frontiers program.


A version of this mission known as Moonrise was the runner-up in the competition NASA organized for the second New Frontiers launch opportunity.


A version of this mission known as Juno was the winner of the competition NASA organized for the second New Frontiers launch opportunity.

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