Shaping the Future — Planetary Decadals Driving Scientific Discovery
Success in the astronomical sciences requires forethought and action from policy leaders today. The astronomical decadal surveys are widely recognized by policy makers as the pinnacle of scientific forethinking. They set ambitious and inspirational national priorities that require federal support to maintain US leadership.
Our community must continue to advocate for and steward the priorities of the decadal surveys, especially through tumultuous and uncertain federal budgets. Let’s make sure to remember and celebrate our community’s scientific successes and honor the brilliant minds who have overcome scientific, technical, and personal challenges in the pursuit of science and scientific excellence.
The AAS Policy Blog will have a series of posts written by guest authors who will assess our progress on the decadal priorities and identify new opportunities and challenges for the coming decade. Here Bethany Ehlmann and Brett Denevi walk us through the Planetary Science Decadal Survey.
Shaping the Future — Planetary Decadals Driving Scientific Discovery
By Bethany Ehlmann, a professor of planetary science at Caltech, and Brett Denevi, a principal staff scientist at Johns Hopkins APL. Both represented the planetary science community as members of the Origins, Worlds, and Life Decadal Survey Steering Committee.
It’s an exciting time to be a planetary scientist. With robotic spacecraft across the solar system (and the Voyagers beyond), new exoplanet discoveries, and plans for humans back on planetary surfaces at the Moon and next on Mars, the pace of discovery is growing.
The vibrancy is largely driven by the planetary science community speaking with a unified voice, the last 20 years championing the most important science priorities through the Decadal Survey process. Every 10 years, NASA and NSF ask the National Academies to serve in their role to advise the nation and "to develop a comprehensive science and mission strategy for planetary science.” The scope includes prioritizing space missions but also the infrastructure to enable planetary science: ground-based observatories and facilities, technology development, and research funding. The first Planetary Science Decadal Survey was in 2002, New Frontiers in the Solar System (2003-2012), followed by Visions and Voyages (V&V; 2013-2022), and most recently Origins, Worlds, and Life (OWL; 2023-2032).
We both believe that the Decadal process itself is inherently good for science: bringing people together from diverse disciplines to think about what’s been accomplished in the past 10 years, what is important, and where we should go next. Because it can take generations to answer a science question, with individual scientists working often on smaller parts of the whole, pausing to look around and assess the big picture is critical. This is especially so in planetary science where the investments in time, energy, and funding for activities in space are stupendous. The Decadal directly tells funders the top priorities, allowing for steady purpose, driven by enduring science, rather than being buffeted by the annual budget process and self-interests of individuals and institutions.
Our early careers benefited from the legacy of Decadals conducted before. One of us scientifically grew up in the Mars Exploration Program. Three Decadals in a row prioritize executing Mars exploration as a program — a concerted plan of linked missions of different sizes with each building on the other to understand the evolution of this once Earth-like world, search for life, and lay the groundwork for human exploration. Key discoveries include evidence for surface and near-surface water ice and a rock record of past lakes and long-lasting groundwater aquifers of varying chemistries in space and time. And one of us scientifically grew up with MESSENGER, the seventh Discovery-class mission and the first spacecraft to orbit Mercury. Key discoveries include an unusual crust, unlike any other solar system planet that is Fe-poor with graphite and a surprising abundance of volatiles despite being so close to the sun, including ice at the poles. Discovery and larger New Frontiers missions are the PI-led, competed missions, prioritized in every Decadal Survey. The programs are crafted to take advantage of the community's creativity and expand the leadership of science beyond NASA centers and into universities and industries around the country, driving efficient, innovative use of technology to achieve discoveries within cost constraints.
Retrospectively, the successes of V&V and the decade ending in 2022 are many. Not one but two large missions were implemented — more than was obviously possible, given the budget outlook at the start of that decade. The Mars Sample Return (MSR) campaign is underway, and samples are being cached now with Mars-2020 Perseverance, which has been sampling Martian lake sediments and water-altered lavas, with strata recording the first 500 Myr of solar system history ahead. Europa Clipper launches this year to characterize the ocean and ices of Europa. The third-ranked V&V large mission, a Uranus Orbiter, didn’t begin but the community has reaffirmed it and MSR as OWL’s top priorities for large strategic missions.
The results were mixed but largely positive on V&V recommendations for small and medium missions. Two New Frontiers, five Discovery missions, and an ESA-NASA Trace Gas Orbiter to Mars with PI-led instruments were recommended. One New Frontiers mission was selected — Dragonfly (added post-Decadal to the New Frontiers list after consultation with the Academies committee, based on the discoveries of organic lakes on Titan and ocean waters effusing from Enceladus). NASA pulled out of the Mars Trace Gas Orbiter (though ESA carried it forward alone). Four Discovery missions were selected. Lucy launched in 2021 to fly by the Jupiter Trojan asteroids and is expected to meet many of the goals of the Trojan tour recommended for New Frontiers in V&V. Psyche launched in 2023 to study a metal asteroid. VERITAS and DaVinci were selected in 2021 as an orbiter and atmospheric probe to Venus, respectively. V&V pushed for more monitoring from ground- and space-based telescopes of the outer solar system, and that was a success: we now have 10 years of Hubble monitoring for all four outer planets, which have given us new results not only on Neptune storms but also Saturn rings, Jupiter’s Great Red Spot, and more. JWST was especially interesting for Uranus (that ring structure) and Neptune (clouds).
The success of V&V is also evident in the numbers: the planetary science budget grew from $1.5 billion in 2012 to $3.1 billion in 2022 ($2.2 billion vs $3.3 billion, inflation-adjusted to today) to accomplish this rich decade of science. Scientists spoke with one voice and provided an inspirational and aspirational plan for consideration by NASA leadership — with help from Congress, particularly on Europa Clipper and the creation of a commercial lunar program.
The current OWL decadal has just begun (2023), so progress now relies on NASA and our community’s efforts to create the future, grounded in the Decadal priorities. We were inspired that even amid a global pandemic, over 1,000 members of the planetary exploration community crafted input to the Decadal in the form of white papers or presentations and ~100 volunteered on committees for over a year to craft the plan. OWL follows the inspirational and aspirational approach of V&V. New for this Decade was the organization by science questions and a broadening of scope to include recommendations for astrobiology, planetary defense, the workforce, and human exploration. The Survey’s top large-mission recommendations are the completion of the next elements of Mars Sample Return, the development of the Uranus Orbiter Flagship, and an Enceladus Orbiter/Lander. A cadence of two New Frontiers, five Discovery, and small satellites are recommended for completed missions.
We both are particularly excited by OWL’s position on what human exploration can bring for science. In a pivot, whereas V&V mostly adhered to a philosophy of separate lanes, OWL embraces collaboration between what are traditionally two funding lines (human and robotic). Astronauts on the Moon will conduct geologic field investigations, deploy instruments, and return samples. The Endurance-A rover was recommended to cache samples from across the Moon’s largest impact basin in a >1,000-km traverse to deliver them to the astronauts, providing insight into the early bombardment and dynamics of the solar system and the evolution of rocky worlds. Continued robotic landed missions in the Mars exploration program provide for science discovery — e.g., for Mars Sample Return searching for fossil life, determining what gases in the Mars atmosphere enabled surface water, and pinning solar system chronologies via age-dating — and also data on resources or technology risk-reduction, valuable for human Mars missions. OWL highlights the importance of baking in science from the beginning so that scientists and engineers together craft the human missions to enable it.
But after an excellent first year, the OWL decade is off to a rocky start with budget constraints imposed unexpectedly in the first third of fiscal year 2024 (FY24). FY24 funding was expected to look much like FY23 in the Decadal profile and the President’s budget. Instead, there will be a reduction in NASA’s Planetary Science budget in FY24. Increases in costs on missions stemming from the last Decadal, consuming $100s million in funding, contribute to a double squeeze for FY24. This has jeopardized the MSR replan process, slowed the start of a Uranus orbiter, further delayed Dragonfly, stalled both competed PI-led Discovery missions to Venus (Veritas and DaVinci), and postponed indefinitely the calls for the next New Frontiers, Discovery, and small satellite missions. It also led to layoffs at JPL and for NASA contractors across the nation, which are not simple to turn back.
There is a path forward. The Decadal Survey includes contingency plans and outlines the priorities for the field, if times get tough. You can read the details (Programmatic Chapter 22, ‘Representative Flight Programs’). But in brief: keep R&A strong for the good of the whole planetary science research community. Launch Clipper to Europa and continue all the missions in development or selected in the last decade (e.g., PI-led missions to Titan and Venus). Continue the Mars sample return campaign, whose top-priority science was reaffirmed through the Decadal process. But fix it: make a better plan, adhering to the Decadal guidance on maintaining scientific scope but never exceeding 35% of the Planetary Science budget any given year. Keep the Mars and lunar programs as robust programs, coupling to human exploration where appropriate, and start the Endurance-A mission. Be sure to invest in the community's creativity: keep the cadence of small competed missions to anywhere in the solar system at least three missions per decade (preferably five), compete and select the next New Frontiers. Get the Uranus mission going.
The bottom line is that the US needs a healthy science budget and year-to-year stability to bring the future of OWL and Decadal Surveys more generally to fruition. It is particularly important for continued US leadership in planetary science in an increasingly global landscape. Our community devoted much to crafting the Decadal Survey vision: let’s speak with one voice to Congress and NASA to make it happen.