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National Academies experts warn against rushing into two initiatives pushed by Congress.
A new report praises NASA’s recent and in-progress work in planetary science, but it also warns that some missions under consideration would privilege the search for extraterrestrial life at the expense of other science priorities.
The National Academies of Sciences, Engineering, and Medicine released its midterm reviewof the latest decadal survey for planetary science on 7 August. Issued in 2011, the decadal survey, Vision and Voyages, covers the period from 2013 to 2022. It is considered an authoritative summary of the needs and priorities of the planetary science community and is the primary planning document for NASA’s planetary science division (see Physics Today, May 2011, page 23).
The new midterm report lauds recent discoveries in planetary science, stating this decade has been one of the field’s “most important and scientifically productive periods ever.” It also praises NASA’s “impressive progress” in developing new missions, including the Mars 2020 and Europa Clipper flagships, in spite of budgetary limitations.
However, the report points out deviations from survey recommendations. In particular, it warns the survey did not recommend or vet a lander mission to Jupiter’s moon Europa that Congress has directed NASA to undertake. It also criticizes NASA’s circumvention of the decadal survey process in opening its medium-scale New Frontiers program to proposals focused on exploring extraterrestrial liquid environments for evidence of life.
Europa lander on ice?
The midterm review committee was charged with summarizing progress in planetary science since 2011 and assessing how well NASA has implemented the decadal survey’s recommendations. Its report makes numerous recommendations for how NASA can best implement the survey’s priorities going forward. The committee was not permitted to alter those priorities.
The review report points out that Vision and Voyages made its recommendations for large-scale missions to Mars and Europa contingent on NASA controlling costs to avoid crowding out other parts of the planetary science portfolio. It affirms that the descoped Mars 2020, a rover that will analyze some Martian rocks and deposit others for collection by a future mission, and Europa Clipper, which will study the icy moon during multiple flybys, conform with that recommendation.
But the review does not approve of the Europa lander that Representative John Culberson (R-TX) has been pushing in addition to the Clipper. Culberson, who chairs the House subcommittee responsible for NASA’s budget, hopes the second mission could find evidence of life in Europa’s subsurface ocean and has cited the decadal survey in justifying funding for it.
The review stresses that the survey specifically identified a lander as a possibility for the “far term.” It observes that NASA’s preliminary lander studies have not included a technical evaluation or a cost, which could be “in the multiple billions of dollars range.” Accordingly, the review recommends that NASA wait until the committee for the next decadal survey evaluates the lander studies and prioritizes such a mission.
NASA continues to study the Europa lander mission and has not formally approved it. However, current appropriations law requires the agency to target a 2024 launch date and provides funding commensurate with that goal. Were NASA to abide by the review’s recommendation, it would have to delay advanced work on the lander until 2023 at the earliest and then proceed only if the next survey recommends it.
Ocean Worlds skips the queue
Another target for criticism in the review is NASA’s new Ocean Worlds program, which focuses on extraterrestrial liquid environments as a key to understanding how life might emerge elsewhere in the universe. Again led by Culberson, Congress created the program through the fiscal year 2016 appropriations law. In late 2016, NASA included Ocean Worlds missions among those it would consider for its next New Frontiers mission. Last year, NASA selected Dragonfly, an Ocean Worlds mission that would use a rotorcraft to explore Saturn’s moon Titan, as one of two finalists for the mission. A final selection is due next year.
The review notes that the inclusion of Ocean Worlds missions took place “outside the decadal survey process.” It reports that, of the scientific groups that advise the planetary science division, only the Outer Planets Assessment Group supported the addition. Other groups representing researchers who study the Moon, Venus, Mars, and asteroids and other small bodies did not. “Such a process could undermine the scientific priorities of the decadal survey and community support for them,” the review warns.
As with the Europa lander, the review suggests an Ocean Worlds program could be implemented after consideration in the next decadal survey.
Recognizing that new discoveries and other factors can “compel NASA to reassess decadal survey priorities,” the review acknowledges the agency should be allowed to deviate from survey recommendations between surveys. It stresses, though, that any deviations should be subject to “thoughtful consideration” and be “consistent with the general philosophy and approach of the decadal survey.”
Vision and Voyages recommended an aggressive timetable for the selection and launch of missions in both the New Frontiers program and the Discovery program, which supports small-scale planetary science missions. The review notes that, owing largely to constrained budgets in the earlier part of the decadal period, NASA has fallen behind pace. Finding the funding situation has now improved, it recommends the agency catch up by selecting three Discovery missions from its next two announcements of opportunity and pushing up the next New Frontiers announcement of opportunity from 2023 to late 2021.
Following a provision in last year’s NASA Transition Authorization Act, the midterm review also devotes an entire chapter to NASA’s Mars exploration architecture. It concludes that NASA’s long-range plans for a “lean and rapid” program to return samples collected by the Mars 2020 rover should fulfill the decadal survey’s science goals. However, it also warns the telecommunications infrastructure currently in orbit around Mars is “fragile and aging” and that a failure of a single orbiter would compromise the science return from missions on the surface.
In addition to the Mars and Europa flagship missions, Vision and Voyages also recommended a flagship mission to Uranus, while noting that Neptune, the solar system’s other ice giant, is an equally attractive destination. The review expresses no dismay that NASA has yet to approve an ice giant mission. But it sharply criticizes a planning study for such a mission released last year. In particular, it rejects the study’s suggested inclusion of a bulky Doppler imager as an unjustified technical risk.
NASA is expected to issue its statement of task for the next decadal survey in late 2019, with the goal of having the National Academies deliver its final report in early 2022.
This article is adapted from a 9 August post on FYI, which reports on federal science policy with a focus on the physical sciences. Both FYI and Physics Today are published by the American Institute of Physics.