Who pays for the United States’ astronomy and astrophysics projects—our collective staring into the void, seeking cosmic answers? Well, we all do, via taxes, which the government decides how to divvy up via an annual appropriations budget.
But how does NASA decide to use the funds it’s given—around $23 billion in 2021? For its scientific missions in space and on the ground, the agency—and pretty much all of the space scientists in the US—take their cues from the Astrophysics and Astronomy Decadal Survey. Every decade since the 1960s, teams of hundreds of experts, led by a steering committee organized by the National Academies of Sciences, Engineering, and Medicine, have produced these massive reports aimed at recommending space exploration and research for the next ten years and beyond.
This year’s survey—officially called “Pathways to Discovery in Astronomy and Astrophysics for the 2020s”—was released today. It’s been dubbed “Astro2020” for short, despite its release in late 2021. It was due last year, but the Covid-19 pandemic caused significant delays in an already difficult process for the approximately 150 scientists who made up its 13 panels focusing on topics like cosmology, galaxies, stars, particle physics, and the state of the profession. To complete the survey, they pored over nearly 900 white papers submitted by researchers from around the globe, and completed hundreds of hours of Zoom meetings.
“It’s a very difficult process to complete over Zoom rather than face-to-face meetings,” says Rachel Osten, an astronomer at the Space Telescope Science Institute, researcher at Johns Hopkins, and member of the Astro2020 Steering Committee. “So we had to figure out how to make it work with what we had.”
Those Zoom meetings steered the future of science itself. “What they decide affects what scientists will do,” says Paul Goldsmith, a group supervisor at NASA’s Jet Propulsion Laboratory. A decadal survey typically calls for specific large and medium-sized missions at certain budgets; it also highlights important areas of scientific exploration for the next decade, asking researchers to fill gaps with their work. Projects get funded—or not—based on what’s in the survey.
Today’s 500-plus-page report prioritizes three scientific areas: Hunting for habitable exoplanets, probing the beginnings of the universe, and studying gases to understand the evolution of galaxies. Within these categories, it calls for several missions, including a creating a large infrared/optical/ultraviolet space telescope, funding far-infrared and x-ray missions, the continued growth of important ground-based astronomy assets, a steady drumbeat of smaller “probe”-class missions, and an increased investment in the equity of the field.
It also recommends revolutionizing the way major mission proposals mature into realized projects, by creating a billion-dollar-plus program that would shepherd concepts from their early stages to help make sure they are delivered on time and on budget. Suggesting an overall process change, instead of just choosing a top-line project or two, is “a game-changer in terms of how decadal surveys are usually run,” says Osten. “Usually it selects a single project that’s the winner, and everyone else can go home.”
A New Pipeline for Massive Missions
Decadal surveys from the 1960s to the ‘90s laid the groundwork for NASA’s “Great Observatories”—the Hubble Space Telescope, the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope. For decades, they have sent us images and seas of information from deep space about black holes, exoplanets, and more.
These projects, while incredibly important, are also famous for running late and over budget. (Take, for instance, the James Webb Space Telescope, which will launch this fall after being included in the decadal survey all the way back in the year 2000.) “A decade is not the appropriate timescale when thinking about grand visionary projects,” says Osten. It’s just not long enough to see a space mission through from concept to launch; as such, it’s also often nearly impossible to estimate their actual cost while they are still in early phases.
That’s why the Astro2020 report’s authors are calling for NASA to create what they’re dubbing “The Great Observatories Mission and Technology Maturation Program.” Its budget would be $1.2 billion over the next decade to support extensive cost analyses, risk studies, and mission architecture reviews for any major astronomy missions, as well as to build out supportive technologies and to target the projects’ science objectives. “We view it as a pipeline for all future large missions,” Osten says.
“Before, it was a winner-take-all approach,” she continues. “We’re saying, yes we do want to emphasize certain areas, but we recognize that these projects are very early in their development. This program is designed to put the money in upfront to develop tech, and the idea is that we will have a far better-bounded understanding of what the cost for this mission will be after this program.”
Homing in on Habitable Exoplanets
Though the Astro2020 committee didn’t select a specific mission concept for approval, they did designate the first participant for the tech maturation program: a large infrared/optical/ultraviolet (IR/O/UV) space telescope with a budget of roughly $11 billion and a main telescope mirror that’s at least 6 meters in diameter. The report calls for the launch of a telescope in the early 2040s capable of spotting planets that are 10 billion times dimmer than their host star.
One of the main tasks for this telescope would be to search the far universe for signs of exoplanets that might host life, or even offer the potential for human habitation. “Planets are common,” the report reads. “It is an exciting time in which to practice the astronomical craft, as humanity edges ever closer to being able to answer the age-old question ‘Are we alone?’”
Two current NASA mission concepts, HabEx (Habitable Exoplanet Imaging Mission) and LUVOIR (Large UV/Optical/IR Surveyor), are aimed at pulling this off. Both would use large, extremely clear mirrored optical telescopes, UV rays, and infrared to hunt for exoplanets with signs of water, oxygen, and ozone. HabEx would use a “starshade” to block out light from stars to reveal the planets surrounding them; LUVOIR would use a very large system of unfolding mirrors. (Blocking the light is important, as NASA research astrophysicist and LUVOIR study scientist Aki Roberge explains, because “stars are bright, and planets are faint.”)
Both take inspiration from the Hubble Space Telescope, which was only initially expected to be used until 2005 or so. But Hubble has continued to conduct science operations—until late October, when it unexpectedly went into “safe mode,” apparently due to a synchronization issue which is being investigated.
“LUVOIR is a super-duper-duper-Hubble,” says Roberge. The proposed craft would be a long-lasting, flexible, multipurpose space observatory, with a primary optical telescope that’s either 8 meters or 15 meters in diameter. (Hubble’s is 2.4 meters.) “It could cover all the astrophysics and solar systems science topics that Hubble could do, with much more power and sensitivity,” Roberge says. “In addition, it has capabilities that go far beyond Hubble, and any of the other currently-planned NASA large astrophysics missions. In particular, it’s got the key goal to be able to find dozens, not a handful, of potentially Earth-like exoplanets around nearby sunlight stars—the true Earth-analogs out there that might actually be like this pale blue dot.”
HabEx, too, aims to go beyond what Hubble could do. “The objective of HabEx is to replace and improve on the capability lost at the end of the Hubble Space Telescope’s lifetime,” says Bertrand Mennesson, a NASA JPL scientist and HabEx co-chair. To do this, he and his team designed a space telescope with a second object, an external starshade that would fly some 77,000 miles in front of the telescope itself. This starshade would block out the light of far-off stars—like a hand held up to the sun—revealing traces of the planets orbiting them. A starshade and space telescope flying in formation has not been used this way in astrophysics before, but, says Mennesson, “It’s a funny thing. When we talk to engineers, they are not too afraid of that formation flying.”
The proposed HabEx design offers a trade-off between science performance and budget; it has a smaller telescope array than LUVOIR, at 4 meters, and it is projected to be the less expensive of the two missions.
Both crafts would detect a planet by using their powerful mirrored optical telescopes, and then investigate it using infrared and UV light tools to reveal what the planet’s made of, and whether it has an atmosphere or holds water or oxygen. Roberge says those would be “signs of a planet that looks like this one—with a biosphere that is so abundant that it’s changing the chemistry of the whole planet’s atmosphere.”
The two concepts have enough overlap in their missions plans that Roberge refers to them as “LUVEX.” This may be convenient, since the Astro2020 survey calls for a telescope somewhere between the size of LUVOIR-B, the smaller version of the telescope’s design, at 8 meters, and HabEx, at 4 meters. “Given the budget requirements and realistically achievable yearly funding levels,” the report concludes, “an 8 [meter] aperture telescope of the scale of LUVOIR-B would be unlikely to launch before the late 2040’s or early 2050’s. On the other hand, a smaller telescope such as the HabEx 4H design may fall short of providing a robust exoplanet census.”
A blend of the two, though—now that might be just right for a mission that “combines a large, stable telescope with an advanced coronagraph intended to block the light of bright stars,” as the survey states, and is “capable of surveying a hundred or more nearby Sun-like stars to discover their planetary systems and determine their orbits and basic properties. Then for the most exciting ~25 planets, astronomers will use spectroscopy at ultraviolet, visible, and near- infrared wavelengths to identify multiple atmospheric components that could serve as biomarkers.” Howdy neighbors!
Smaller Missions for Far IR and X-Ray
Two other NASA mission concepts for telescopes—the Origins Space Telescope and the Lynx X-Ray Observatory—were not recommended for top-level funding, but they weren’t kicked out of the party, either.
Origins is a do-it-all mission—able to use mid-infrared to study exoplanets, and far infrared to study the formation of young galaxies and the first stars at the edge of the universe. An ultra-cold mirror would increase its far-IR sensitivity a thousandfold over previous missions, and could read longer wavelengths than the James Webb Space Telescope will be able to.
Lynx is a next-generation X-ray telescope. It would be 100 times more sensitive than the best current X-ray observatory, Chandra, and would be used to study the dawn of black holes, the formation of galaxies, the cosmic web, a “tenuous filamentary structure that spans the universe and connects clusters of galaxies,” says Jessica Gaskin, a Lynx study scientist who works at NASA Marshall Space Flight Center. Lynx would also help us understand the nature of stars themselves. “But the most important thing to remember about any of these flagship proposals is that they are designed to discover things we haven’t even thought about yet,” Gaskin says.
The Astro2020 steering committee’s report calls for $3 to $5 billion to be spent on maturing the missions and technologies surrounding for far-infrared missions like Origins and X-Ray missions like Lynx, which could study star and black hole formation, active galaxies, and violent supernovae. It also specifies that preliminary studies for both types of missions should begin five years after the IR/O/UV project begins to make its way through the pipeline program.
Ground-Based Astronomy Keeps Marching Ahead
Space missions get all the attention, but ground-based astronomy provides incredibly important tools that many astrophysicists need for their research. “These observatories will create enormous opportunities for scientific progress over the coming decades and well beyond, and they will address nearly every important science question across all three priority science areas” of the survey, the committee wrote.
They recommended funding for several massive ground-based astronomy tools, including the Extremely Large Telescope (ELT), currently under construction in Chile, the Giant Magellan Telescope, and the next-generation Very Large Array (ngVLA), which would comprise 244 radio antennas spread across North America listening to a wide range of wavelengths beamed from across the universe. The radio waves it picks up could “see through” the dust surrounding young stars to help us understand how they form, or detect the aftermath of gravitational waves rippling out from black holes.
Two others include the CMB-24, or the Stage 4 Cosmic Microwave Background Observatory, a proposed array of 21 telescopes in Chile and the South Pole that would give us the best look yet at inflation that occurred during and just after the Big Bang; and IceCube Gen 2, a plan by the The University of Wisconsin–Madison to build a high-energy neutrino detector that could further study the high-energy neutrino particles that occasionally whizz into Earth from … somewhere. (The current IceCube, located in Antarctica, detected the first cosmic neutrinos in 2013.)
Studying The Dynamics of Galaxies
“The time is ripe for major breakthroughs” in the study of galaxies, the report declares, while listing many of the cosmic mysteries left to solve, including how galaxies grow and what the connection might be between them and the supermassive black holes that form in their interiors. It notes that while the Webb telescope will help us understand galactic beginnings, and while the Vera C. Rubin Observatory (expected to begin operations in Chile in 2023) and the Nancy Grace Roman Space Telescope (which launches later this decade) will provide crucial information about wide swaths of millions of galaxies, their role “will be profound but will not on their own be able to address the central problem of understanding how galaxies grow.”
Instruments that collect all kinds of cosmic waves and particles—infrared, UV, radio, electromagnetic, X-ray, and neutrinos—will have a place in the astrophysics pursuits of the 2020s and 2030s. Many of the missions previously name-checked in the report, including a far-infrared mission like Origins, X-ray observatories like Lynx, ground-based radio telescopes like the ngVLA, and exoplanet hunters like HabEx and LUVOIR will help scientists study a living, breathing universe. “Arguably the single most important lesson in the last ~30 years of understanding the origin of structure in the universe,” the survey continues, “is that it is not a one-way street, dictated solely by gravity from large scales to small. The formation of some of the smallest and densest objects in the universe, stars and massive black holes, dramatically alters how most other astronomical objects form, from planets and galaxies to stars and black holes themselves.”
Equity and the State of the Field
For the first time, the survey also hosted a panel on a non-technical topic; the “Panel on the State of the Profession and Societal Impacts” addressed issues including diversity, equity, and workforce development. It pulls few punches.
“Racial/ethnic diversity among astronomy faculty remains, in a word, abysmal,” the committee’s report concludes. “African Americans and Hispanics comprise 1 and 3 percent of the faculty, respectively. Up until 2012 there was not a single astronomy department that had representation of both African American and Hispanic faculty, and roughly two-thirds of astronomy departments had representation of neither.”
The survey also discusses sexual harassment issues in the field—citing a 2018 report that physical sciences workplaces have an extremely high rate of sexual harrassment issues, second only to the military—and a lack of outreach to local and Indigenous communities, both to recruit a more diverse work community and to partner fairly in places where astronomy facilities are built.
The report criticizes the profession’s most controversial construction plan, the proposed Thirty Meter Telescope on the summit of Mauna Kea, a volcanic peak that is both desirable for astronomy and held as sacred by native Hawaiians, who are blocking construction workers from building the telescope. Although the report calls for the National Science Foundation to prioritize investment in the telescope, “Lack of an authentic partnership with Kanaka Maoli (the Indigenous people of Hawai’i) impedes the efficacy of the astronomy workforce, significantly risks facilities’ investments, negatively impacts Kanaka Maoli, and diminishes public support. It puts into question the integrity upon which scientific discovery is realized,” the report reads. “All investments to date are at risk if these issues are not resolved with a long-term plan in place. Instead, the value of these investments and the integrity of the Profession is realized should the Profession work in collaboration with Kanaka Maoli.”
The report also denounces discrimination and harrassment in the workplace, encouraging agencies to address harassment by individuals as form of scientific misconduct. And it recommends increasing funding incentives for improving diversity among the college/university astronomy and astrophysics faculty—“for example, by increasing the number of awards that invest in the development and retention of early-career faculty and other activities for members of underrepresented groups.”
“Generally, when we talk about astrophysics and this survey, we’re talking about the skyscrapers—large missions that take decades,” Osten says. “But if you’re building a skyscraper, you have to ensure the foundation is firm. And that’s the people doing the work in the next decade or two.”