‘We have an ambitious program tempered with realism,’ says Robert Kennicutt of the University of Arizona and Texas A&M University, committee cochair for the 2020 astronomy and astrophysics decadal survey. ‘We expect a wave of discovery that will continue unabated in the coming decades.’

The committee’s report, Pathways to Discovery in Astronomy and Astrophysics for the 2020s (Astro2020), is the culmination of the community’s seventh decadal survey and was carried out for the National Academies of Sciences, Engineering, and Medicine. The recommendations are mainly for the survey sponsors- NASA, NSF, the Department of Energy, and the US Air Force Office of Space Research. More than 3500 people tuned in for an online briefing marking the survey report’s debut on 4 November.

Like previous decadal surveys, it was a massive endeavor- The 20-member committee and 13 scientific and program panels hosted more than 25 meetings to solicit input and considered the nearly 900 white papers they received. Because of the government shutdown in the winter of 2018–19 and restrictions of the pandemic that arose a year later, the 600-plus-page report was delayed and its recommendations shifted accordingly to 2022–32.

The committee framed its recommendations around three broad scientific themes. ‘Worlds and Suns in Context’ focuses on understanding the formation and evolution of exoplanets and characterizing other solar systems. ‘New Messengers and New Physics’ deals with the use of gravitational waves, particles, and temporal monitoring of the sky across the electromagnetic spectrum to probe energetic processes and the nature of dark matter, dark energy, and cosmological inflation. And ‘Cosmic Ecosystems’ links observations and modeling of how stars and galaxies form and evolve.

The main deviations from previous decadal surveys are the recommendations to introduce a new approach to mission development and to give workforce issues—including the need to eliminate sexual harassment, collect demographic data, and involve Indigenous communities—equal priority with space missions and ground-based telescopes.

‘It’s a really exciting program overall,’ says Risa Wechsler, director of the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University and the SLAC National Accelerator Laboratory. ‘The committee did a good job of synthesizing the best ideas of the community and presenting a compelling vision.’

Mission maturity

On the space side, the top priority is for NASA to form a ‘Great Observatories Mission and Technology Maturation Program’ as a framework for mission development, science definition, and technology. The idea is to invest early in multiple large-scale projects in parallel and to build in clear guidelines and times for deciding whether and how to proceed; the decision points are an intentional approach to adapt to shifting budget landscapes and project uncertainties and risks. ‘By investing more in the maturation process, NASA could develop missions to a level where there is significantly more confidence in the costs and requisite cost profiles before seeking congressional approval,’ the report says.

If the four space missions that NASA proposed to the committee were to advance in series, says committee cochair Fiona Harrison of Caltech, ‘it would take 80 to 100 years to accomplish them. We felt a different approach was needed. That’s why we didn’t rank the mission proposals 1, 2, 3, 4.’

Instead, the committee recommended conflating two of the four space missions proposed by NASA into one UV-optical-IR craft with a roughly 6-meter aperture. This should be the first mission in the new maturation program, the report says, and development should begin immediately. If all goes well, that mission would come in at about $11 billion and be ready for launch in the first half of the 2040s. In five years, work on the far-IR and x-ray missions with costs in the $3 billion to $5 billion range should enter the maturation program, says the report.

Martin Elvis of the Center for Astrophysics|Harvard & Smithsonian, who served on one of the survey’s panels on electromagnetic observations from space, says that it normally hasn’t mattered what the second-ranked priority was because ‘it never happened. Number two was overwhelmed by the cost of the first project on the list.’ The new approach, he says, is a welcome change. But, he adds, it’s disappointing that the first launch would be two decades away. ‘That leaves a big window for other countries to scoop the best science. I hope we can persuade Congress to accelerate funding and have the US lead in this dramatic field of science.’

Astro2020 notes that a balance of missions with different sizes and time scales is important for advancing science, training, and maintaining expertise. It recommends a new line of ‘Probe’ missions with a cap of $1.5 billion and a launch rate of one per decade.

For example, prompted by the European and Japanese space agencies’ decision to drop a proposed joint IR mission, SPICA, Astro2020 jumped in to fill the gap by recommending a far-IR mission in the Probe category that can do imaging, spectroscopy, or both. ‘We believe it would advance very exciting science while a larger mission is being planned,’ says Harrison. The mission’s scientific aims could include tracing astrochemical signatures of planet formation; measuring the formation over time of galaxies, heavy elements, and interstellar dust; or probing the coevolution of galaxies and their supermassive black holes across time. In addition, smaller-scale Explorer missions should continue to be developed, the report says. The missions have a cap of $290 million.

The aim was to put forward a program that is so exciting ‘it motivates [the agencies] to get more money for the missions,’ says Harrison. The committee worked within the optimistic budget projections the sponsoring agencies gave them. The combined projected budgets from NASA and NSF total roughly $950 million in 2023 and rise to about $2.4 billion in 2032. DOE didn’t provide budget numbers.

Assuming next month’s launch of the James Webb Space Telescope is successful, the public interest it generates and science it delivers could serve as a catalyst for more money. That’s Elvis’s hope- ‘It will be a terrific telescope, and we want to do things like that on a quicker time scale.’

Large aims on the ground

As its top recommendation on the ground, Astro2020 says NSF should join at a 25% share in both US-led extremely large telescopes (ELTs). This is a turnaround from the previous decadal survey- It had urged the foundation to quickly choose between the 24-meter Giant Magellan Telescope (GMT), which would be built in Chile, and the Thirty Meter Telescope (TMT), which would be sited either on Mauna Kea, Hawaii, or on La Palma in the Canary Islands.

But NSF didn’t choose between the two ELT projects. Instead, it stayed focused on the top ground-based priority in Astro2010, the Vera C. Rubin Telescope (previously known as the Large Synoptic Survey Telescope), which is expected to see first light in late 2022.

Now, a decade-plus later, the most compelling reasons to join both ELTs are the science and the anticipated community demand. And having both telescopes would give astronomers access to the skies in both hemispheres. Moreover, Europe is already building an even larger ELT in Chile. For the US to maintain leadership, the report says, both telescopes are needed, and realizing neither ‘will gravely damage the U.S. astronomy community for decades.’

Even with NSF participation at the recommended level of $800 million each, both projects would need to raise significant additional funding—around $700 million for the TMT and $1 billion for the GMT.

On top of the financial risks in the projects, the preferred TMT site—on Mauna Kea—has for years been mired in controversy (see Physics Today, July 2016, page 31). Some members of the Native Hawaiian community see little or no room for negotiation for continued building on what for them is sacred land.

Having the US government on board through NSF would ‘give hope that the telescope could actually be built in Hawaii,’ says Doug Simons, head of the Institute for Astronomy at the University of Hawaii. The conversation with opponents may be different with the federal government involved, he explains. ‘There are more means for providing benefits to those impacted by the project.’

Astro2020 recognizes risks associated with both projects, and it shies away from specifying a telescope preference or a favored site for the TMT. In the same vein as its recommendations for space missions, the report recommends decision points for ground-based projects; it says large projects should be started only if funding has been secured for construction, operations, and maintenance. For the ELTs, the report says NSF should reach a decision in 2023 about going ahead with one or both. It also says that if NSF joins only one of them, it should do so with a higher share, up to 50%.

Astro2020 also gives an enthusiastic nod to two other major ground-based observatories. The next-generation cosmic microwave background observatory, CMB–Stage 4, would be a $660 million facility supported roughly 40-60 by NSF and DOE. The project is well along in planning and could achieve first light in five years.

A next-generation Very Large Array (ngVLA), comprising up to 244 antennas across North America, would replace two current US radio array observatories. Astro2020 recommends starting development work. After a positive review, NSF could put $2.5 billion toward the $3.2 billion array, with the rest to be raised from international partners. The ngVLA would be NSF’s largest facility investment; if funding is secured, construction could begin in 2027, and operations with a partial array could start in 2034.

Scott Ransom, a staff astronomer at the National Radio Astronomy Observatory and head of NANOGrav, the pulsar timing search for gravitational waves (see Physics Today, July 2017, page 26), notes that the high-frequency range of the ngVLA, 1.2–116 GHz, would be complementary to the lower frequencies of the Square Kilometre Array (SKA), an international project without US participation under construction in South Africa and Australia. ‘Astro-politically speaking, the ngVLA will be like ‘SKA-high,’ and if we play nicely, we can share with the rest of the world,’ Ransom says.

Astro2020 also recommends that NSF restore support for its Advanced Technologies and Instrumentation Program. Funding for the program, which supports development of small-scale instruments, has eroded over the past decade. NSF should increase funding to a target of $20 million annually in 2028, the report says. ‘The need . . . is, if anything, greater than it was a decade ago.’ Areas of urgency include advanced adaptive optics systems for optical wavelengths and new radio instrumentation.

Similarly, Astro2020 recommends that NSF increase funding for midscale programs to $50 million annually. And within that level of program, the report says, the foundation should create a new track to be ‘responsive to decadal and community strategic priorities.’ The report singles out time-domain astrophysics as the top strategic priority for midscale programs, followed by—with equal priority—radio instrumentation and highly multiplexed spectroscopy.

Getting the most out of space- and ground-based facilities requires investigators who can translate the data into discoveries. Yet over the past two decades, the success rate for NSF grant proposals for astronomy and astrophysics research has taken a dive from 45% to 25% or less because funding has not kept pace with the growing numbers of proposals. The report recommends that by 2028 NSF and NASA increase by 30% their annual funding pots for individual investigators and for theoretical work, respectively.

Harassment is misconduct

For the first time, the decadal survey included a panel devoted to evaluating the ‘state of the profession and societal impacts.’ Among other things, it considered workforce demographics and diversity, sexual harassment and discrimination, climate change, and engaging with communities where telescopes are located. Out of 24 recommendations in total, 10 address those issues.

For example, the report recommends that the funding agencies collect, evaluate, and publicly report demographic data on grant proposals. ‘It is not possible to assess whether any strategy is working without the associated data to measure what is happening,’ the report notes.

‘We would like to have a clear idea about success rates,’ says Harrison. ‘Are there inequities in gender representation? Are there other inequities?’ Since NASA switched to dual anonymous evaluation—in which both reviewers’ and proposers’ identities are suppressed—for some of its observing programs, she adds, a larger percentage of proposals by early-career researchers has been funded.

Several recommendations focus on improving inclusiveness and diversity in astronomy. They include introducing incentives for advancing diversity and supporting programs to attract and retain people from underrepresented groups at different junctures in the educational and professional path. NASA, NSF, DOE, and professional societies should, the report says, treat harassment and discrimination as forms of scientific misconduct. Well-established practices and guidelines exist for creating an inclusive professional culture, the report notes, making the persistence of harassment and discrimination a ‘disgrace,’ a ‘profound injustice to people who have been harmed’ and ‘morally wrong.’

Given ongoing conflicts with Indigenous peoples, such as the tensions on Mauna Kea, the report recommends that NSF work with experts to define a ‘model of engagement that advances scientific research while respecting, empowering and benefiting local communities.’

Other recommendations are for NSF and appropriate regulatory agencies to work to mitigate the interference of radio frequencies, satellites, and light pollution on astronomy. The report also calls for decreasing carbon emissions by increasing the use of remote observing and hybrid and remote conferences.