Planetary scientists have come together to prioritize the most compelling, cutting-edge questions across our entire field. Some of these questions are best addressed by ambitious, sophisticated, large-scale missions. Others are best addressed by smaller, more focused missions. Some require continued operations of existing plantary orbiters or rovers. All require a commitment to maintaining the existing planetary science community. While the future of large-scale missions has been receiving the most headlines, the other priorities have uncertain, worrying futures, and American planetary exploration may suffer greatly as a result.

The relationship between planetary science and NASA is deeply intertwined and fraught with complications. Almost every US planetary scientist depends on the space agency in some way: either directly as civil servants employed by NASA, recipients of peer-reviewed science grants funded by NASA, participants in the operations or science planning of ongoing or anticipated planetary missions, or simply as users of the vast quantity of data returned by those missions since the first one 50 years ago.

Every ten years a "Decadal Survey" (DS) is conducted across planetary science to identify the highest-priority science questions and chart a course for answering those questions. The DS is conducted by the National Research Council, sponsored and initiated by NASA and the NSF. While it does not carry the force of law, the recommendations of the DS are seen by Congress, the public, and planetary scientists themselves as representing the consensus of the planetary science community. Usually, NASA then uses these recommendations to ensure that it plans and implements the most scientifically productive suite of projects possible. The most recent DS was completed in 2011.

The highest profile DS recommendations relate to spacecraft missions. Three cost classes exist for NASA planetary science missions, the first two of which are the direct result of past DS recommendations: Discovery (roughly $500 million), New Frontiers (a bit less than $1 billion), and Flagship (everything more than $1 billion). The selection process differs from class to class: Discovery and New Frontiers missions are chosen after a two-step competitive proposal process that first winnows the dozens of submitted proposals down to a handful, then picks a final winner from the remaining few. The destinations and goals of Flagship missions are set by NASA, and scientists then compete to provide and work with individual instruments, while the mission as a whole is run from a specific NASA Center. Discovery missions can be targeted anywhere in the solar system that compelling science can be addressed within the allotted budget. A set of acceptable New Frontiers destinations are generated through the DS process, along with the desired science to be done at each destination.

The top priority Flagship mission, according to the DS, is Mars Sample Return, sort of. A mission to collect and return a sample of the martian surface to Earth is a project that will cost at least $7-8 billion, an eye-opening cost even in the best of budgetary times, which this is not. So the sample return mission was divided into three easier-to-swallow pieces, the first of which is this decade’s priority Flagship and simply identifies and collects the desired samples and caches them for later retrieval. The unspoken assumption is that this retrieval and subsequent return to Earth will occur in the following decade, possibly as the next two highest-priority Flagships in the queue. The Office of Management and Budget (OMB) is rumored to be wary of committing the government to such a large outlay and biasing future decadal surveys toward completing the sample return, especially since the caching mission has uncertain immediate science value on its own.

In all, the priorities in the Decadal Survey are pretty clear. If Mars Sample Return cannot be achieved within budget constraints, a Europa mission that fits should be attempted. In either case, as resources become scarcer, the largest projects (i.e. Flagships) should be descoped or postponed to protect the smaller mission projects, with continued operations of existing missions and funding of research and analysis grants (R&A) the highest priority for continued funding, even when budgetary conditions are bad. This, to me, is most obviously interpreted as putting highest priority on these grants and continued operations, the PI-led Discovery and New Frontiers programs second, and the largest-scale Flagship missions last.

However, for reasons that are obscure to me but which some of my colleagues find compelling, an alternative set of priorities has been asserted focusing on the "balanced program" preference in the Decadal Survey. In this view, some progress should always be occurring on missions at all scales, though this balance is only applicable to mission classes and potentially targets: R&A, technology development, and ongoing missions are clearly intended to be exempt from this “balance”, with a separate protected status. There has been considerable effort placed on studying and restudying large missions to find some way to fit them into the available budgets. This has led, in some way, to the announcement that the Curiosity rover currently on Mars will be rebuilt for a 2020 launch as the next Flagship-class mission. It is thought that the 2020 rebuild, if a close copy to the original, can be done more cheaply than Curiosity’s final cost, perhaps for $1.5 billion. However, such a rebuild is not obviously motivated by science reasons. While connections to the DS and Mars Sample Return can be imagined for this new rover, none have been explicitly made.

It has been argued in some circles that the 2020 rover represents a good-faith effort to fly the highest priority mission in the DS. It is definitely the case that Mars Sample Return is the consensus choice for the next large mission. However, it is neither the case that the community thinks Mars Sample Return is the top priority for planetary science, nor that Mars is the highest priority mission target.

It may be the case that a copy of Curiosity could be built for $1.5 billion. However, it is not the case that such a copy is responsive to the recommendations of the planetary science community. It may be the case that a Curiosity copy could be made responsive to those recommendations, but the necessary alterations would make it less likely it can be built for $1.5 billion. While the startup funds for a 2020 rover may be present in the current Mars Program budget, any overruns or unforeseen additions will have consequences for other projects, as we have unfortunately seen in the past in similar situations.

Furthermore, even if everything runs smoothly, the majority of funding will be required several years from now, beyond the time for which budgets are currently planned. The temptation to put off the Discovery and New Frontiers program for yet another year (or two or three) will be present, especially if doing so supports a more capable Mars rover.

Beyond all of this, lost in the maneuvering and rescoping and ruckus with respect to the Flagships are the other priorities in the DS. In my opinion there is simply no honest, rational reading by which the Flagship missions are higher priorities than Discovery or New Frontiers, as outlined above. Yet, there has been too little attention paid to the constantly slipping timelines and lengthening years between opportunities for these programs.

As originally conceived and still recommended in the DS, Discovery opportunities would be available every 24-36 months, if not more often, with multiple selections per competition. Yet only one selection was made in the entire 2002-2011 decade, and while InSight (a Mars mission) was selected in 2012, the next Discovery opportunity is not scheduled before 2015. This is an astonishing slowdown compared to the 1992-2001 period when 10 missions were selected. While NASA leadership has focused on large missions in general and Mars specifically, there has been no obvious effort to maintain the desired pace of smaller missions, which have provided amazing and varied science results and trained tomorrow’s leading planetary scientists.

Furthermore, there have been threats to the operation of ongoing missions. The MESSENGER spacecraft orbiting Mercury has enough fuel to remain in orbit for two more years, and plans to fill those years with follow-up science investigations that have been in place. However, scientists close to the mission report that it is unclear whether sufficient funds will be available to continue its operation beyond 2013, and supporters are now fighting for its life. The Cassini spacecraft orbiting Saturn has also been the subject of shutdown rumors. Again, this is despite the exceedingly high priority placed on continuing these missions by the planetary science community.

Finally, the highest priority to the science community, the maintenance and expansion of R&A, has also been largely neglected. A recent analysis by Mark Sykes of the Planetary Science Institute shows that recent increases in R&A funding have been concentrated in near-Earth object studies (good for my personal interests, not great for colleagues who study Venus or the rings of Saturn), and that proposal success rates have been dropping precipitously over the past decade from upward of 40% to a current rate of 25% or lower. Astonishingly, even this 25% success rate may be cut further, with recent evidence that rates as low as 10% are planned for coming years. This will cripple the scientific community that NASA relies on to make its exploration missions successful and generate the ideas and research that leads to future missions.

The bottom line for many concerned planetary scientists is this: we have been asked by NASA to rally behind the DS since its publication, but we are watching NASA by and large abandon the recommendations of the DS. The people working at the agency are in a difficult situation and are working hard for planetary science, but a lack of transparency and a steady stream of surprises makes too many scientists feel more like pawns than partners. The technical workers and engineers who enabled amazing Mars landings are being rightfully acknowledged and their skills protected, but it appears that the rest of the planetary science community is not considered important enough by NASA to maintain.

It would be naive to assume that the goals and agendas of NASA as an agency are always aligned with the best interests of the field of planetary sciences (or earth sciences, or astrophysics, and so on). It would be folly to demand that science always take precedence over political or financial constraints. What I think we can ask for, as scientists and as citizens, is that decisions made due to non-science considerations are honestly presented as such. If we are to get coal in our stockings, don't tell us it's because that's what we put on our wish list to Santa.

One solution to these problems is for NASA to follow the Decadal Survey’s recommendations (and Congressional instructions: see the House report language for Planetary science) to protect and expand R&A, maintain a steady rate of cost-effective Discovery and New Frontiers missions, and delay major investments in Flagship missions until funds are available. A better solution is not necessarily a politically popular one: increasing NASA's budget for planetary science so that all these goals can be achieved.

NASA is such a high-profile agency that the public thinks it spends much more money than it actually does. If every American old enough to vote decided to give up one cup of coffee or a six-pack of soda and could donate that money to support planetary science, we would have been able to start work on all three recent finalist mission candidates for the Discovery program – not only the Mars seismic station that was selected, but also a boat to sail the seas of Titan and a spacecraft to explore the surface of a comet.

In these difficult economic times, however, scientists know we must share sacrifice with our fellow citizens, and we are doing so and have been doing so. Eventually, however, we all hope and expect easier times to return to our country. As long as humans have sent machines to explore the solar system, Americans have played a leading role, and our achievements along with those of other spacefaring nations have thrilled the world. With the long lead times necessary to plan planetary missions, it is not too soon to start thinking about missions that may not launch for a decade, as evidenced by the beginning of work on the 2020 Mars rover. Yet NASA’s apparent disregard for the clear recommendations of the Decadal Survey concerning the relative priorities of Flagship vs. Discovery missions causes much concern.

Given the complicated relationship mentioned earlier, many of us are uncomfortable appearing to criticize NASA or wondering if we are breaking a law against lobbying by doing so. However, professional societies and citizen supporters are starting to be more active in promoting the benefits of planetary science, and all of the high-priority items in the DS, to our government and fellow Americans. The Division for Planetary Sciences and American Geophysical Union, major professional societies, have made several statements related to the NASA budget, as have groups of science enthusiasts like the Planetary Society. We hope to increase our engagement and improve the prospects of achieving the highest-priority goals in planetary science, including sustaining the health of the scientific community. With continued support from NASA and the American people, we will continue to learn more about all objects in the solar system from the sun-baked plains of Mercury to the expanses where the Voyager spacecraft still gather data, and beyond. Yes, including Mars.

Images: Comet Hartley 2 (Credit: NASA/JPL-Caltech/UMD); Europa (Credit: NASA/JPL/USGS); Saturn and Titan (Credit NASA/JPL-Caltech/SSI); Opportunity looking back at its tracks on Mars (credit: NASA/JPL-Caltech).