Enceladus plumes
One recommended mission in the planetary science decadal survey would send a mission to Enceladus, an icy, potentially habitable moon of Saturn with a subsurface ocean and plumes. Credit: NASA/JPL-Caltech

WASHINGTON — A study outlining priorities in planetary science for the next decade backs continued efforts to return samples from Mars while recommending NASA pursue missions to the planet Uranus and an icy moon of Saturn.

The final report of the planetary science decadal survey, developed by a committee of the National Academies and released April 19, also recommended work on a space telescope to track near Earth objects, a Mars lander to look for evidence of life and a lunar rover to collect samples that would be returned by astronauts.

“This report sets out an ambitious but practicable vision for advancing the frontiers of planetary science, astrobiology and planetary defense in the next decade,” Robin Canup, co-chair of the steering committee for the decadal survey and assistant vice president of the Planetary Sciences Directorate at the Southwest Research Institute, said in a statement about the decadal.

The previous planetary science decadal in 2011 recommended as its highest priority large, or flagship, mission, a Mars rover to collect samples to return to Earth. NASA implemented that recommendation as the Mars 2020 mission, whose Perseverance rover is now on Mars collecting samples.

The decadal recommends NASA continue with the later phases of Mars Sample Return (MSR), which involve missions being jointly developed with the European Space Agency to take those samples, launch them into orbit around Mars and return them to Earth in the early 2030s.

“The highest scientific priority of NASA’s robotic exploration efforts this decade should be completion of Mars Sample Return as soon as is practicably possible with no increase or decrease in its current scope,” the report states.

It warned, though, about potential cost growth, citing a current estimate of $5.3 billion for the overall Mars Sample Return effort, a figure NASA had not previously publicized. The cost of MSR “should not be allowed to undermine the long-term programmatic balance of the planetary portfolio,” the report stated, recommending NASA seek a “budget augmentation” from Congress if its costs grow by 20% or more above that estimate.

The decadal treated Mars separately from other proposed flagship missions. The report recommended as the top-ranking flagship mission concept the Uranus Orbiter and Probe, which would go into orbit to study the planet, its rings and moons, as well as deploy a probe into the planet’s atmosphere. Uranus has been visited only once by a spacecraft, the Voyager 2 flyby in 1986.

The mission “will transform our knowledge of ice giants in general and the Uranian system in particular,” the report stated, calling Uranus “one of the most intriguing bodies in the solar system.” The mission, with an estimated cost of $4.2 billion, could launch as soon as 2031 on a Falcon Heavy or similar heavy-lift vehicle, arriving at Uranus 13 years later using a Jupiter gravity assist.

The second-ranked flagship mission the decadal recommended was Enceladus Orbilander, which would fly a spacecraft to Saturn’s moon Enceladus, an icy world with a subsurface ocean and plumes bursting through its crust into space. “Conditions at Enceladus thus allow for direct investigation of the habitability of an ocean world and assessment of whether or not it is inhabited,” the report stated.

Enceladus Orbilander would spend a year and a half orbiting Enceladus and sampling those plumes before landing for a two-year mission to study materials for evidence of life. The mission, with an estimated cost of $4.9 billion, could launch in the late 2030s on an SLS or Falcon Heavy with a landing in the early 2050s.

The report considered four other flagship mission concepts: a Europa lander, Mercury lander, Neptune orbiter and probe, and a Venus mission that included orbiters, a lander, and a “aerobot” that would operate in the planet’s atmosphere. The decadal survey declined to endorse them because of issues such as cost and technology readiness.

New Frontiers, Mars and the moon

The decadal survey selected potential destinations for future missions in NASA’s New Frontiers line of competed medium-sized planetary science missions. For the New Frontiers 6 mission late this decade, it proposed concepts that include a mission to a Centaur, a family of icy bodies orbiting between Jupiter and Neptune; a sample return mission from Ceres, the largest body in the main asteroid belt; a comet sample return mission; a spacecraft to perform multiple flybys of Enceladus; a network of lunar landers to collect geophysical data; a Saturn probe; a Titan orbiter; and a mission to perform in situ studies of the atmosphere of Venus.

The following New Frontiers competition, likely to take place in the early to mid 2030s, would include those same mission themes with the exception of the one selected for New Frontiers 6, and add a mission to Neptune’s largest moon, Triton. The report also recommended the cost cap for New Frontiers missions be raised to $1.65 billion (in fiscal year 2025 dollars) to reflect experience such as the Dragonfly mission to Titan under development.

For Mars, the decadal survey recommended that, once MSR passed the peak of its spending profile in the late 2020s, NASA start work on a lander mission called Mars Life Explorer that would look for evidence of current life on Mars by drilling into ice deposits to search for biosignatures. The lander, described as a “notional mission concept” in the report, would cost $2.1 billion and launch in the mid-2030s.

Studies of the moon, the decadal stated, would involve an interplay with human exploration with the Artemis series of crewed landings scheduled to begin as soon as 2025. “The successful integration of science into programs of human exploration has historically been a challenge and remains so for Artemis,” the report stated. “Currently, science requirements do not drive the Artemis capabilities. However, in the committee’s view it is imperative that Artemis support breakthrough, decadal-level science.” [Emphasis in original.]

One way of doing so involves combining robotic and human exploration capabilities. The report endorsed a mission concept called Endurance-A that would send a robotic rover to the moon’s South Pole Aiken Basin on a commercial lander. The rover would travel 2,000 kilometers across the basin and collect 100 kilograms of samples. Those samples would be returned to Earth on a crewed Artemis mission. The $1.9 billion mission would cost a billion dollars less than an alternative that involved both a robotic rover and sample return spacecraft that would have returned only about two kilograms of material.

Planetary defense and budgets

The planetary science decadal included a review of planetary defense programs at NASA. It supported continued work to achieve a goal set by Congress in 2005 of discovering 90% of near Earth objects (NEOs) at least 140 meters across. It added, though, that NASA should also work to discover as many smaller objects as possible.

The decadal backed continued work on the NEO Surveyor mission, calling for a “timely launch” of the space telescope designed to more effectively search for NEOs. That recommendation comes weeks after the agency’s fiscal year 2023 budget proposal cut the budget for the mission, pushing back its planned 2026 launch by at least two years.

After NEO Surveyor, the decadal recommended NASA pursue a “rapid-response” mission to fly by a near Earth object between 50 and 100 meters across. “Such a mission should assess the capabilities and limitations of flyby characterization methods to better prepare for a short-warning-time NEO threat,” it stated.

To accommodate all its recommendations, the decadal survey offered two budget profiles. A “level program” assumes 2% annual growth in NASA’s planetary sciences budget from 2023 through 2032, while the “recommended program” would increase overall spending in the decade by 17.5%. That latter profile “captures the highest priorities of the community as outlined in this report and is both aspirational and inspirational,” the report stated.

Both profiles would fully fund Mars Sample Return and the other ongoing flagship-class mission, Europa Clipper, as well as planetary defense, lunar exploration programs and the Discovery line of relatively low-cost planetary missions. The recommended program provides additional funding for research and the New Frontiers line of missions. The recommended program would fully fund the Uranus flagship mission for launch in the early 2030s and start work on the Enceladus Orbilander, while the level program would push back the Uranus mission to the late 2030s and not provide any funding for the Enceladus mission.

“In summary, the reductions associated with the Level Program would result in a less balanced portfolio with a significantly lower science return compared to the Recommended Program,” the report stated.

Like the astrophysics decadal survey released last November, the planetary science decadal survey included a “state of the profession” assessment. The report recommended steps to gather more demographic information about the planetary science community, broaden opportunities and address bias, such as having NASA implement codes of conduct for its missions and for conferences it participates in.

“While scientific understanding is the primary motivation for what our community does, we must also work to boldly address issues concerning our community’s most important resource, the people who propel its planetary science and exploration missions,” said Philip Christensen, an Arizona State University planetary science professor and other co-chair of the decadal survey steering committee. “Ensuring broad access and participation in the field is essential to maximizing scientific excellence and safeguarding the nation’s continued leadership in space exploration.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...