The 2013–22 decadal survey in solar and space physics
DOI: 10.1063/PT.5.010186
Last Wednesday the National Academy of Sciences held a press conference in Washington, DC, to introduce its newly completed report on priorities for the coming decade in solar and space physics. Daniel Baker of the University of Colorado chaired the committee that wrote the report. Thomas Zurbuchen of the University of Michigan was the vice chair. Together, they summarized the report’s highlights for the assembled reporters, scientists, and bureaucrats.
Like its counterparts in astronomy and planetary science, the latest solar and space physics decadal survey is more than just a shopping list of missions and facilities. Its authors begin by defining their field in a broad and inspiring way:
We live on a planet whose orbit traverses the tenuous outer atmosphere of a variable magnetic star, the Sun. This stellar atmosphere is a rapidly flowing plasma—the solar wind—that envelops Earth as it rushes outward, creating a cavity in the galaxy that extends to some 140 astronomical units (AU). There, the inward pressure from the interstellar medium balances the outward pressure of the solar plasma forming the heliopause, the boundary of our home in the universe. Earth and the other planets of our solar system are embedded deep in this extended stellar atmosphere or “heliosphere,” the domain of solar and space physics.
The report goes on to review past and present accomplishments in solar and space physics before defining the four overarching goals that guided the committee members as they drew up their final recommendations:
- Determine the origins of the Sun’s activity and predict the variations in the space environment.
- Determine the dynamics and coupling of Earth’s magnetosphere, ionosphere, and atmosphere and their response to solar and terrestrial inputs.
- Determine the interaction of the Sun with the solar system and the interstellar medium.
- Discover and characterize fundamental processes that occur both within the heliosphere and throughout the universe.
As I listened to Baker and Zurbuchen’s presentation, it became clear that two other overarching considerations informed the report. The first is a conceptual emphasis on viewing Earth’s aurorae, the solar wind, coronal mass ejections, and other heliospheric phenomena as part of a single system. It will be interesting to see whether this systemic view becomes manifest in journals, conferences, and courses. I, for one, have tended to think of solar physics as belonging more to astronomy than to heliospheric physics.
The second consideration is a realistic and—to use Baker’s word—responsible approach to costs. The committee retained Aerospace Corp , a nonprofit consultancy based in El Segundo, California, to carry out an independent cost appraisal and technical evaluation (CATE) of potential missions. For the most part, the total cost of the committee’s recommended suite of programs lies within the budget envelope that NASA provided the committee for the years 2013–22.
Physicists who remember chuckling when they first encountered the zeroth law of thermodynamics might be amused to learn that the committee’s first recommendation is also numbered zero—for good reason. As NASA and NSF, the other principal sponsor of heliospheric research, look to future missions and facilities, the committee recommends that they first complete their current program.
Among the lineup is Solar Probe Plus (shown here in an artist’s impression). The ambitious mission, whose price tag is $1.4 billion, aims to fly as close as possible to the Sun to determine how the solar corona is heated and how the solar wind is accelerated.
Diversify, realize, integrate, venture, educate
The committee’s second recommendation, numbered 1.0, is to implement an initiative that goes by the acronym DRIVE (for “diversify, realize, integrate, venture, educate”). As far as I can tell, DRIVE aims to reorganize and reinvigorate the way researchers and their students practice heliospheric science.
Surprisingly, given its high priority, DRIVE is not expensive. The committee projects that the initiative will cost at most about $50 million a year. To fulfill the goals embodied by its name, DRIVE seeks to make research opportunities more accessible to universities through small and mid-sized missions, including the shoebox-sized spacecraft called CubeSats .
Funding the analysis and interpretation of data adequately is a key element of DRIVE, as is fostering interdisciplinary approaches to heliospheric research. Indeed, the committee urges NASA and NSF to establish heliospheric science centers, where observers, theorists, and modelers can work together to solve the grand challenges of solar and space physics.
When Baker and Zurbuchen introduced DRIVE, it sounded somewhat woolly to me. Now, having read the DRIVE section of the report, I think it’s a bold and worthwhile model that could be profitably emulated in other fields, such as green energy or neuroscience. But to be effective, DRIVE will probably need a light administrative structure.
Accelerate and expand the Heliophysics Explorer program!
Recommendation 2.0 seeks to revitalize NASA’s Explorer program of modestly sized and priced spacecraft. Begun in 1958, the program, according to the committee, is “arguably the most storied scientific spaceflight program in NASA’s history.” Despite its success, which includes three Nobel prizes, funding for the Explorer program fell in 2004 and has languished since. To quote the report:
The medium-class (MIDEX) and small-class (SMEX) missions of the Explorer program are ideally suited to advancing heliophysics science and have a superb track record for cost-effectiveness. Since 2001, 15 heliophysics Explorer mission proposals have received the highest category of ranking in competition selection reviews, but only 5 have been selected for flight. Thus there is an extensive reservoir of excellent heliophysics science to be accomplished by Explorers.
Because MIDEX and SMEX missions are comparatively cheap, developing and launching more of them would not require a big outlay. The committee recommends that NASA augment the current Explorer program for solar and space physics by $70 million per year.
In addition to more money for the Explorer program, the committee also recommends establishing a faster, more nimble way of accommodating missions of opportunity—that is, missions that are conceived in response to new technologies, new scientific knowledge, or new partnership opportunities with other space agencies.
NASA: Let academia lead space science
Perhaps by coincidence, a commentary by Baker appeared in Nature two weeks before his committee released its report. Entitled “NASA: Let academia lead space science,” the commentary urged the space agency to fund more missions that are small enough in scope that university-based principal investigators (PIs) can develop and lead them.
Whether Baker’s fellow committee members endorsed his commentary is not clear. They do, however, evidently share his belief in the merits of PI-led missions. Recommendation 3.0 calls for NASA to transform its Solar Terrestrial Probes program from a large, centrally directed program to “a moderate-sized, competed, PI-led mission line that is cost-capped at approximately $520-million per mission.”
The STP program aims to elucidate the physics of the Sun’s influence on Earth, on the other bodies in the solar system, and on the interstellar medium. To avoid the risk that a competitive free-for-all would omit important aspects of STP science, the committee outlined three kinds of missions that it would like to see fly:
- IMAP (Interstellar Mapping and Acceleration Probe) to characterize the zone where the Sun’s magnetohydrodynamic influence ceases to prevail in the solar neighborhood.
- DYNAMIC (Dynamical Neutral Atmosphere) to study how Earth’s ionosphere and thermosphere influence, and are influenced by, processes that occur at lower and higher altitudes.
- MEDICI (Magnetosphere Energetics, Dynamics, and Ionospheric Coupling) to determine how the magnetosphere-ionosphere-thermosphere system responds to solar and magnetospheric forcing.
The committee’s enthusiasm for modest missions is not unbridled, however. In the committee’s view, tackling the problem of how and why the Sun varies is a job for large, integrated missions. NASA’s Living with a Star program already includes the Solar Probe Plus and the Radiation Belt Storm Probes missions. Recommendation 4.0 is for Geospace Dynamics Constellation, a set of six formation-flying spacecraft that will characterize how the energy of geomagnetic storms is deposited and transformed in Earth’s atmosphere.
Recharter the National Space Weather Program
In March 1989 a geomagnetic storm caused the collapse of Hydro-Québec’s electricity grid. Five months later another geomagnetic storm shut down electronic trading on Toronto’s stock exchange.
Anticipating such storms—or space weather—and predicting their effects is more important, now that the world’s electrical infrastructure has expanded, the number of Earth-orbiting satellites has increased, and telecommunications have become economically and socially more important.
The current solar cycle, the 24th since records began in 1755, is set to peak next year. To monitor the cycle’s activity, the US relies on a set of spacecraft, such as the Solar and Heliospheric Observatory, whose principal purpose is basic research and whose engineering lifetimes are coming to an end.
To avoid gaps in coverage, the committee recommends that NASA, the National Oceanic and Atmospheric Administration, and the Department of Defense should plan ahead and plan together. Of particular importance, the committee says, is maintaining a permanent monitoring capability at L1, the first Lagrange point of the Sun–Earth system. Lying between the two bodies 1.5 million km from Earth, L1 is an ideal vantage for tracking solar activity.
The US has a comprehensive plan, the National Space Weather Program , for dealing with space weather. The trouble is, as the committee puts it, “implementation of such a program would require funding well above what the survey committee assumes to be currently available.” Accordingly, the committee recommends that the NSWP
should be rechartered under the auspices of the National Science and Technology Council and should include the active participation of the Office of Science and Technology Policy and the Office of Management and Budget. The plan should build on current agency efforts, leverage the new capabilities and knowledge that will arise from implementation of the programs recommended in this report, and develop additional capabilities, on the ground and in space, that are specifically tailored to space weather monitoring and prediction.
I haven’t read all 455 pages of the committee’s report. In venturing to summarize it, I have no doubt missed some important points and emphases. But what I have read has impressed me. Here is a plan to study the heliosphere as a system in a comprehensive, multidisciplinary, and cost-effective way. I hope its recommendations are heeded.