Decadal Survey: After Europa and Mars Sample Return — Uranus

The much-anticipated Decadal Survey for Planetary Science and Astrobiology hit the streets today. Experts spent two years deliberating over the key planetary science questions to be addressed over the next 10 years — a decade — and agreed that the top priorities are finishing two flagship programs recommended in the last Decadal Survey: Europa Clipper and Mars Sample Return. For this round, they identified Uranus as next in line, pointing out that the Ice Giant may be the most common type of planet in the universe, but one we have investigated the least.

Study co-chairs Robin Canup of the Southwest Research Institute and Phil Christensen of Arizona State University presented the study’s findings and recommendations today.

The study, Origins, Worlds, and Life, was sponsored by NASA and the National Science Foundation and performed by a committee organized by the National Academies of Sciences, Engineering, and Medicine. The Academies conduct Decadal Surveys for all five of NASA’s science disciplines — astrophysics, biological and physical sciences in space, earth science, heliophysics, and planetary science.

The committee enthusiastically embraced the ongoing Europa Clipper and Mars Sample Return missions, which were the top two flagship missions recommended by the previous planetary Decadal Survey, Vision and Voyages.

“We want to begin with a very strong endorsement of Europa Clipper,” Christensen said when starting his summary of the report’s programmatic recommendations. Scheduled for launch in 2024, he called it “a foundation for the exploration of ocean worlds” and “we clearly encourage NASA to continue to support that wonderful mission.”

As for Mars Sample Return, a campaign of four missions to Mars in partnership with the European Space Agency, he said it is of “fundamental strategic importance to NASA, to our leadership in planetary science and international cooperation.”

But they are worried about potential cost growth above their $5.3 billion estimate, which includes not just the mission itself, but building a facility to house the samples once they are back on Earth. If the cost grows more than 20 percent above that, or to more than 35 percent of the Planetary Science Division’s budget in any given year, NASA should seek a “budget augmentation” to cover the cost rather than take the money from other planetary science efforts.

The first of the four missions, Perseverance, is already on Mars collecting samples to be retrieved and returned to Earth later by NASA and ESA spacecraft. The campaign was to involve two other spacecraft, a lander/fetch rover and a spacecraft to bring the samples back to Earth, but NASA recently concluded two landers will be needed instead of one.

Looking at the budget numbers they were given, the committee concluded that funding for Europa Clipper and Mars Sample Return will be ramping down just in time to fund a mission to Uranus beginning in FY2024.

Why Uranus?  Only one spacecraft, Voyager 2, has flown past Uranus close enough to take rudimentay data and images. That was in 1986. Although the Hubble Space Telescope and telescopes on Earth can see it in more detail, NASA wants to be able to study it directly with instruments on a spacecraft rather than from 1,783,744,300 miles away.

Canup said the committee thought long and hard about whether to recommend Uranus or Neptune since both are “amazing objects.”

“Understanding the composition and the properties of either one would revolutionize our understanding of Ice Giant systems and solar system origins,” she asserted.

NASA spacecraft have discovered thousands of “exoplanets” in the universe outside our solar system and many appear to have characteristics similar to our ice giants. “This may, we think, be the most common class of planets in the universe” according to Canup.

Uranus got the nod over Neptune because the technology for that mission is more mature. “No new technologies” are required for the Uranus Orbiter and Probe mission, Canup said, and it is “technically ready to start now.” She thinks there is significant international interest, too.

The committee’s recommendation is to plan for launch in 2031-2032 when the spacecraft can get a gravity-assist from Jupiter at just the right time, but “there are also flexible opportunities every year essentially after that point” although it would take longer to get there.

The Uranus mission is just one of many recommendations in the Decadal Survey. A second priority flagship is an “Enceladus Orbilander” that would study Saturn’s moon Enceldaus both from orbit and after landing on the surface.

Like Jupiter’s moon Europa, Enceladus is thought to have a water ocean under an icy crust. Images taken by the Cassini spacecraft that spent years in the Saturnian system showed plumes erupting into space from beneath the ice.

Canup said the committee is so excited about learning more about Enceladus that it not only is a second-priority flagship mission, but is also recommended as a potential New Frontiers mission.

NASA divides its planetary missions into small (Discovery), medium (New Frontiers), and large (flagship) classes. The Discovery and New Frontiers missions are managed by scientists, Principal Investigators (PIs), who periodically compete to win approval for new missions based on scientific merit. The missions are cost-capped. The Decadal Survey endorsed all the Discovery and New Frontiers missions now underway, and recommended increasing the cost caps substantially to make them more realistic.

The programmatic recommendations are just the tip of the iceberg in the 781-page report “Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023-2032.” They don’t even appear until Chapter 22, more than 600 pages in. The early part of the report goes into detail on 12 key scientific questions identified by the committee from which the programmatic recommendations stem. The report also devotes a lot of discussion to the State of the Profession, including the need for diversity, equity, inclusion, and accessibility.

How far NASA can go to implement the programmatic recommendations is largely budget dependent. Although NASA’s FY2023 budget request for the Science Mission Directorate is the largest it has even been, it is only slightly more than FY2022 and the suite of programs and activities already underway is a heavy drain.

The committee’s aspirational plan is based on a budget that is “<20% higher over the decade,” but it also offers a “level” program that assumes an inflationary growth of 2 percent per year.

This Decadal Survey addresses planetary defense for the first time as well as scientific aspects of NASA’s Artemis lunar exploration program. It is enthusiastic about both, strongly recommending NASA proceed with the NEO Surveyor mission to search for asteroids that might threaten Earth, and the Endurance-A robotic lunar rover mission that will collect samples from various locations on the South Pole-Aitken basin on the far side of the Moon for astronauts to bring back to Earth, what the report calls an “ideal synergy between NASA’s human and scientific exploration of the Moon.”

Speaking of budget realities, however, NASA is proposing in the FY2023 budget request that NEO Surveyor be delayed and the International Mars Ice Mapper (iMIM) mission be terminated. That is despite a $3.16 billion request for planetary science, underscoring both the existing demands on the budget as well as the fact that the outyear numbers for planetary science in the FY2023 request are less than projected last year. Compared to last year’s projections, planetary science would get $36 million less in FY2023 and $81 million less in FY2024.

Decadal Survey committees are asked to offer “decision rules” on what to do if NASA does not get as much funding as anticipated. The commitee offered this prioritized list of what to cut if absolutely necessary, with reductions to Research and Analysis (R&A) as the last resort.