A solar telescope in New Mexico is being torn down, and the reason is a pool of liquid mercury hidden inside it. The mercury was the clever trick that made the telescope work. It is now the thing that dooms it.
The telescope’s optical system weighs 250 tons, and it had to turn smoothly all day. You can’t spin something that heavy on ordinary wheels. So instead the whole thing floated on a sealed pool of liquid mercury. Mercury is dense and flows easily, so the load rode on the fluid and turned with almost no friction. That is how the 250-ton optical system of the Richard B. Dunn Solar Telescope was designed to move.
However, on January 5, crews found some of that mercury where it wasn’t supposed to be.
We are not engineers, chemists, or occupational-safety specialists, and nothing here is guidance for handling mercury or any other hazardous material. This is our reading of a public engineering story and the agency documents around it, not advice.
Why a telescope floated on liquid metal
The Dunn sits at about 9,200 feet on Sacramento Peak, inside the Lincoln National Forest. The Air Force built it, and it opened as the Vacuum Tower Telescope on October 15, 1969. From the start it was one of the best high-resolution instruments in the world for studying the Sun.
As sunlight comes through the telescope, the Sun’s image slowly rotates over the course of a day. To keep that image lined up with the instruments studying it, you have to turn the whole optical assembly to match. Not just the tube, but the observing room, the lab, and the floor people stand on. That is where the 250 tons comes from. The mercury float let crews rotate the image of the Sun by turning the entire instrument.
The amount of mercury involved surprises people. The system floated on roughly 120 gallons of the liquid metal, sealed in the bearing. Mercury is so dense that this much weighs around 18,000 pounds on its own. And the bearing carrying the full load hung, according to the observatory, on just three bolts, each three inches across.
The result was a turn so smooth it sounds made up. Dave Dooling, a science writer who served as the site’s education officer, described it this way: the bearings “make rotation so smooth that a person could stand with one foot on the main floor and one on the turntable and slowly rotate all 250 tons” of it. That captures what the mercury bought: a huge instrument you could nudge by hand.
What crews found on January 5
On January 5, 2026, two New Mexico State University staff members found liquid mercury on a platform inside the tower. The site closed, along with its visitor center.
A puddle of mercury is a serious problem because of what the metal does. It is a neurotoxin, it gives off vapor at room temperature, and once it escapes a sealed system it doesn’t stay put. The real question became whether the bearing could be trusted to hold 18,000 pounds of a poison for years to come. The National Science Foundation brought in the engineering firm Thornton Tomasetti to assess that, and the answer shaped everything that followed.
Why removing the mercury ends the telescope
The mercury isn’t a part you can swap out. It is the thing the entire optical system stands on. Take it away and the telescope can’t rotate, which means it can’t do the one job it was built for. Removing the hazard and keeping a working telescope turned out to be the same decision pointing in opposite directions.
On February 24, 2026, the NSF announced it would remove the mercury, leaving the telescope permanently unusable, then demolish it. In its own words, “After assessing the engineering challenges, anticipated repair costs and safety and environmental risks, NSF determined that removing and safely disposing of the telescope’s mercury is the most prudent course of action.” That is the agency defending its own call, and worth reading as such. Preservation advocates in New Mexico dispute that demolition was the only option, and residents and lawmakers have pushed to save the wider observatory campus.
The Dunn was already near the end of its working life. The Air Force transferred it to the NSF in 1976, and in its final years it ran only in a limited mode since 2019. Much of what it once did best has moved to the NSF’s newer, far larger Inouye Solar Telescope in Hawaii.
What comes down with it
Demolition is scheduled to begin as early as September 2026, and the NSF has said it will contribute up to $100,000 toward an exhibit about the observatory. What ends is more than a building: more than half a century of solar science from a machine that, for a long stretch, was the best in the world at what it did.
About this article
This article is for general information and reflection. It is not professional advice. For your specific situation, consult a qualified professional.
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