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Influential U.S. astronomy wish list calls for giant space telescope to spot an Earth analog


Why change a winning formula? After nearly 3 years of deliberation, a panel of U.S. astronomers says the country’s biggest priority for the field should be an $11 billion, 6-meter space telescope—roughly the same cost and size of the James Webb Space Telescope, set to launch next month—but centered on the optical part of the spectrum rather than the infrared. The panel’s report, known as the U.S. astronomy decadal survey, says such a telescope, which wouldn’t launch until the 2040s, would “have the potential to profoundly change the way that human beings view our place in the universe,” through its ability to illuminate the evolution of stars, galaxies, and the universe, as well as probe planets around other stars, including ones that are direct analogs of Earth.

Astronomers have been waiting expectantly for months on the decadal report, and its ranking of proposals is sure to disappoint many. But this one’s mix has won early endorsement. “A general purpose optical observatory is the right choice,” to answer the scientific questions set out in the report, says Garth Illingworth, an astronomer at the University of California, Santa Cruz, who was one of the early architects of the Hubble Space Telescope.

The report, overseen by the National Academies of Sciences, Medicine, and Engineering, is the seventh in a series of regular agenda-setting exercises for U.S. astronomers that began in the 1960s. They distill the field’s priorities, both in space and on the ground, in the hopes that Congress and government agencies will fund them—a model that has been copied by other fields and by astronomers elsewhere in the world.

Although the optical telescope was top priority in space, the report says it should be just the first in a “great observatories” program like the one in the 1990s and 2000s that produced the Hubble, Spitzer, Chandra, and Compton space telescopes working across different wavelengths. “To propose a new great observatories program for NASA astrophysics was both bold and visionary,” says Matt Mountain, director of the Association of Universities for Research in Astronomy, which operates observatories for the National Science Foundation (NSF) and NASA. The report also calls for a new mission line within NASA’s astrophysics division—a series of once-per-decade, $1.5 billion medium-size observatories similar to mid-size planetary missions like NASA’s Juno mission to Jupiter.  

For the top priority on the ground, the report favors NSF paying $1.7 billion to buy into two enormous optical telescopes that are already in development—the Giant Magellan Telescope (GMT) and the Thirty Meter Telescope (TMT). Runners-up include the development of a new array of radio telescopes spanning North America, as well as a set of microwave telescopes in Chile and Antarctica that would study the afterglow of the big bang.

The report isn’t only about infrastructure. It also calls for boosting NSF’s grant program to individual astronomers and teams and providing better support for early career scientists. To make better use of existing facilities, the report calls for a bigger budget to operate them and improve data archiving. And it chides universities and funding agencies over their records on diversity and openness to underrepresented groups, as well as their dealings with Indigenous people on whose land many facilities are built. It calls for increased funding to recruit and retain a diverse workforce, making harassment and discrimination a form of scientific misconduct, and making diversity of project teams a criterion for funding. “There’s a lot of talent that is untapped and people who don’t feel they have a place in astronomy,” says John O’Meara, chief scientist of the W. M. Keck Observatory in Hawaii. “The committee has charged us with change.”

To produce the report, chairs Fiona Harrison of the California Institute of Technology and Robert Kennicutt of the University of Arizona led a 20-person steering committee that weighed recommendations from 140 other astronomers spread among 13 subpanels. Other input came from hundreds of submitted white papers and numerous town hall meetings. The strictures of the COVID-19 pandemic meant almost all deliberations were done virtually, which added 1 year to the process.

In preparation for the decadal survey, NASA commissioned four studies of potential large cornerstone missions, so the committee could get a better sense of their capabilities and costs. The committee’s recommendation for a 6-meter optical telescope falls squarely between two of the mission studies: HabEx and LUVOIR. HabEx, with a 4-meter single mirror, would use a distant, separately orbiting starshade to block a star’s light so its planets can be seen. The LUVOIR team developed two major concepts: foldable 8-meter and 15-meter segmented mirrors that would rely on internal masks to block starlight and see exoplanets.

Illingworth was surprised by the survey’s relative modesty in its call for an $11 billion cost envelope and a 6-meter mirror, because some astronomers consider 8 meters the minimum to see enough nearby Earth-like planets to have a good chance of discovering life. But in the report, the steering panel said it did not want to pick a particular size or architecture and prejudice NASA between HabEx and LUVOIR. And after past decadal surveys offered up unrealistic slates of missions whose budgets soon ballooned, the current panel may have wanted to leave NASA more financial leeway. It even hired independent consultants to double check the study team cost estimates for HabEx and LUVOIR. O’Meara suspects the aim is to get the ball rolling on the telescope, and then for NASA to do its “homework and nail down the architecture and the cost box.”

The other two mission studies that were in contention, an x-ray observatory (Lynx) and a far-infrared telescope (Origins), can take some solace in the call for a new series of NASA great observatories, which would likely require an influx of federal money to NASA. “It will enable a fleet, not just a flagship,” O’Meara says. The report suggests that after 5 years developing the optical telescope, NASA should begin parallel technology development for an x-ray and far-infrared observatory. 

The decision to support the ground-based giants, the GMT and the TMT, came after the two privately funded projects failed to raise enough money to continue to completion. In 2018, the longtime rivals buried the hatchet and made a joint pitch to the decadal review for help. The report says NSF should assess the viability of the two projects until 2023 before deciding whether to contribute $1.7 billion to their $5.1 billion combined budgets, buying U.S. astronomers nationally at least 25% of observing time on the two scopes. During the 2-year assessment period the TMT must confirm its site, the report says,

Some in the field think NSF support could help resolve a stalemate over the TMT’s first choice for a site, Mauna Kea in Hawaii, which has been blocked for years by Native Hawaiians who consider the mountain sacred. “NSF’s involvement could be hugely positive,” says Mauna Kea astronomer Thayne Currie. Federal support would require an independent assessment of environmental, historical, and cultural impacts of building on Mauna Kea. “NSF has resources that are simply beyond the capabilities of the state of Hawaii,” Currie says. Should one of the two telescopes fail to make the grade, the report favors supporting a single scope and gaining up to 50% of observing time.

In radio astronomy, the report says NSF should replace the aging Karl G. Jansky Very Large Array in New Mexico and Very Long Baseline Array with a next generation VLA (ngVLA), made up of 244 dishes stretching across North America. Although U.S. astronomers declined to join the international Square Kilometre Array project, recently greenlighted for construction in Australia and South Africa, the ngVLA complements it by focusing on shorter wavelengths, and the two teams have discussed collaborating. The panel suggests several more years of development and prototyping of ngVLA antennas before approving construction to start in 2027. Equal prominence was given to an effort to map the cosmic microwave background (CMB), an echo of the big bang, in exquisite detail via a 7-year survey using multiple new telescopes in Chile and Antarctica. That effort, known as CMB Stage 4, is led by the Department of Energy, but the report says NSF should take a $273 million—40%—share.

In space, although the large cornerstone missions typically get the headlines, the report supported NASA plans to maintain diversity in its astrophysics fleet with a regular series of midsize “probe” missions with $1.5 billion budgets. The panel suggested NASA’s first two probe launches should be x-ray and far-infrared telescopes, which would have the added benefit of feeding technology into the proposed great observatories at those wavelengths. “It’s smart,” O’Meara says.   

The majority of the 614-page report is spent asking for new things and more money. But in an unusual call out, the report says that one existing NASA mission—an infrared telescope that rides in the bay of a jumbo jet—should end by 2023, consistent with agency plans that have been repeatedly thwarted by Congress. The Stratospheric Observatory for Infrared Astronomy (SOFIA) costs $85 million per year to operate, nearly as much as Hubble. But the survey noted its “modest scientific productivity.” “I’m delighted to see an ending of support for SOFIA,” Illingworth says. Continuing to fund it, “doesn’t send a good message.”

Related story

Report suggests ways to reverse ‘abysmal’ diversity in astronomy

By Jeffrey Mervis

The 2020 decadal study for U.S. astronomy has, for the first time, made the status of underrepresented groups one of its priorities. However, its assessment of the problem—laid out in a 51-page appendix to the main study—comes to a disturbingly similar conclusion as previous reports that barely mentioned the topic.

“Racial/ethnic diversity among astronomy faculty remains, in a word, abysmal,” it declares, using the same word as the 2010 report did. “African Americans comprise a mere 1% of the faculty [and] Hispanics 3%. This collective representation is roughly an order of magnitude below their joint representation in the U.S. population.” In terms of diversity, astronomy and physics fall near the bottom compared with other disciplines, according to other reports looking across the scientific landscape.

That stasis is the reason the leaders of the new decadal study created a 15-member Panel on State of the Profession and Societal Impacts, says its co-chair, Enrico Ramirez-Ruiz, an astrophysicist at the University of California, Santa Cruz. And it breaks from past analyses in telling universities, contractors, and funding agencies exactly what needs to happen to improve that situation. (The 1980 decadal study, for example, simply observed that “past progress in this area has been inadequate” but offered no path forward.)

Topping the list are a slew of new—or revived—diversity programs at the National Science Foundation (NSF), NASA, and the Department of Energy, the three federal agencies that fund astronomical research and training. The panel also describes how academic astronomy and physics departments need to change how they teach introductory courses, recognize the different backgrounds of students who are taking those courses, and teach faculty to be better mentors in helping them pursue careers in the field. “We need to remove the barriers standing in the way of making use of all our human capital,” Ramirez-Ruiz says.

The report recommends each of the three agencies spend an additional $40 million a year to advance diversity, equity, and inclusion (DEI) in astronomy. The novel programs include providing additional administrative support for current faculty who have shown an ability to promote equity, and money to hire those with strong track records of fostering diversity. The goal is to give those academics a bigger role in shaping institutional DEI policies. “The profession’s power structure indirectly but systematically discriminates and perpetuates the underrepresentation of leaders … from historically marginalized groups,” the report notes.

The negative impact of that power structure can be seen even at the undergraduate level. The report notes that minority students interested in majoring in astronomy or physics are three times less likely to earn a degree than their white counterparts, the result of a hostile culture that leaves minority students feeling they don’t belong. Closing that gap would have the greatest impact on diversity in the long run, notes panel member Keivan Stassun, an astrophysicist at Vanderbilt University. “But they won’t be joining the professorial ranks for another decade or more,” he says. “So in the meantime, we also need to do everything we can” for the people already in the career pipeline.

In addition to offering those carrots, the report says, federal funding agencies need to demand results from grantees. “Funding drives culture change, so agencies wield enormous power,” Ramirez-Ruiz says. Although he says the panel deliberately chose not to be too prescriptive, the report gives examples of how agencies could tweak their grantmaking process to foster greater diversity. “NASA might give extra weight in its selection process to missions with diverse leadership and participation,” it suggests—which could lead to a noticeable impact because of the large numbers of astronomers involved in such missions.

NSF already incorporates the “broader impacts” of a proposal in choosing which proposals to fund, Ramirez-Ruiz says, but it’s not always clear what that phrase entails and how it will be measured. “There’s no clear message of how to define and report it,” he says. In any case, he adds, “it is evident that the current ‘broader impacts’ criterion is not creating the change we need.”



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