America is building two gigantic telescopes, but only has the money to finish one

The world is building three gigantic optical telescopes whose size will dwarf anything we have today. It is hoped that together these three will answer some of the big questions of the universe that have proven themselves beyond existing instruments. However, a proposed budget cap from the National Science Foundation (NSF) puts one leg of the stool at risk.

Despite the continued wonders revealed by the JWST, the future of astronomy does not lie solely in space. We can build much larger telescopes on the ground than we can currently do in space, and it is also much easier to repair, maintain and upgrade them here. Plans for a telescope on the moon and associated base are far in the future.

The projects on which astronomers are pinning their medium-term hopes are the Giant Magellan Telescope (GMT), the Thirty Meter Telescope (TMT), and the Extremely Large Telescope (ELT), along with telescopes such as the Square Kilometer Array that operate at wavelengths well beyond the human eye (confusingly, all three are sometimes called Extremely Large Telescopes, not just the ELT) . Even if the atmosphere was in the way, they would all provide much sharper resolution than the JWST.

A comparison of existing and proposed telescopes shows how much larger the big three will be than anything currently in use.

A comparison of existing and proposed telescopes shows how much larger the big three will be than anything currently in use.

However, a new proposal would eliminate one of the first two.

Astronomy is so collaborative that many may not care who will build and own it, but the TMT and GMT will be American-led, while the third will be a collaboration of European and South American countries. This gives the ELT a certain degree of protection against cuts. None of the consortium partners wants to look bad to the others by going back on their obligations. Work on the ELT began in 2017. It takes a long time to build something so massive and yet so precise, so first light isn’t expected to take place until 2028. Even if there are delays, there are few doubts that this will happen eventually.

However, the TMT and GMT are both American projects, even though the latter will be based in Chile. Funding for the GMT comes primarily from the US NSF through a range of universities and scientific institutions, although six other countries contribute. The TMT is an even more American project, despite Indian, Japanese and Canadian involvement; it was initiated by two California universities and would be based in Hawaii.

However, the National Science Board, which advises the NSF, has proposed a $1.6 billion cap on NSF funding for giant telescopes. That’s less than either of the two is expected to cost on their own, although taking the other contributors into account, it should be about enough for one of them.

An artist's rendering of what the Grand Magellan Telescope might look like once it's built, if it's built.

An artist’s rendering of what the Grand Magellan Telescope could look like if it were ever built.

Image credit: GMTP Corporation

The Board of Directors’ statement makes it clear that they are not just trying to delay costs, but are moving slowly until more funding comes through. Instead, it includes the recommendation: “NSF will discuss with the Board of Directors at its May 2024 meeting its plan to select which of the two candidate telescopes the Agency plans to continue supporting, including estimated costs and a timeline for the project.”

It’s possible that the NSF could reject the recommendation, or even that Congress could decide to pour an additional billion and a half into astronomy because they think it’s so important. So far, that’s what each team’s representatives are counting on, at least publicly, rather than bickering over who should get priority. However, you wouldn’t want to bet on new money coming in even if we weren’t in an era when government is paralyzed by partisan fighting that makes any budget allocation difficult.

Theoretically, other contributors could increase their share, but John O’Meara, chief scientist at Keck Observatory, told, “To my knowledge, neither telescope today has a path forward without the investment by NSF.”

Astronomers have voiced their concerns and emphasized why both are needed.

Those associated with other areas of science may have little sympathy; perhaps quietly mocking those who thought they were getting two shiny new toys and had to settle for one. However, the two tools are specifically designed to work together. No location on Earth can see the entire sky; only one instrument in the Northern Hemisphere and one in the Southern Hemisphere provides complete coverage. Each of them is designed to maximize certain capabilities, with the assumption that the other will pick up the slack in other areas.

Areas of the sky that can be seen by the proposed Giant Magellan Telescope and Thirty Meter Telescope.  Without any of them, much of the sky will be exposed.

Areas of the sky that can be seen by the proposed Giant Magellan Telescope and Thirty Meter Telescope. Without any of them, much of heaven will be laid bare.

Image credit: US-ELTP (TIO/NOIRLAb/GMTO)

At first glance, the TMT seems like the logical survivor. Being in the Northern Hemisphere allows it to work with the ELT, and a proposed location in the US could provide a constituency to lobby for it.

However, the TMT is so strongly opposed to the native Hawaiians that consideration has been given to moving them to the Canary Islands – still in the north, but part of Spain. Moreover, dumping both would mean losing almost all the money spent so far, much more for the GMT, which is much more advanced, than for the TMT.

Most people can think of plenty of other valuable uses for $1.5 billion, whether it’s medical research to cure diseases, other forms of science that address global crises, or outside of science entirely. On the other hand, basic research has a long history of paying for itself in ways that were quite unexpected at the time. Building both telescopes would mean an additional $5 in taxes per American, not annually, but one-time. Their combined cost will be much less than the JWST, and each will last much longer.

Allocating budgets is always difficult, and becomes even more difficult when you compare the benefits that are likely to be so different – ​​in this case knowledge for knowledge’s sake versus options with clear practical, if uncertain, outcomes. In comparison, the NSF may conclude that the choice between two instruments with different but overlapping capabilities is relatively simple.

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