This Revolutionary New Observatory Will Locate Threatening Asteroids and Millions of Galaxies

The casual observer may envision the night sky as being static: When we look at Orion, for example, or the stars that make up the Big Dipper, our view is very similar to what our grandparents, or even their grandparents, would have seen—worsening light pollution aside. But this apparent lack of change is an illusion.

When astronomers look at the sky more closely, countless “transient” phenomena come to light. Stars that change in brightness, known as variable stars, get brighter and dimmer; supernovas burst into view and then gradually fade away; and thousands of objects too faint to see with the unaided eye, like asteroids, move steadily across the sky. Now a new telescope designed specifically to track these changeable objects is set to give astronomers their clearest picture ever of the dynamic processes at work in the cosmos. At the same time, the telescope is expected to yield new insights into the universe’s unseen elements, such as dark matter and dark energy.

The Vera C. Rubin Observatory, nearing completion on a mountaintop in northern Chile, features a telescope that’s enormous but also incredibly agile. The telescope, with a primary mirror 28 feet across and a 3.2-gigapixel camera, will sweep across the sky night after night, requiring a mere five seconds to reposition itself after each 15-second exposure. Thanks to its large field of view—encompassing an area equivalent to 40 full moons—and its ability to move swiftly, the telescope will scan the entire visible sky every three days. Over the course of its planned ten-year run, it will photograph everything visible from its latitude some 800 times, flagging anything that pops into view, disappears from view or changes position during that time.

“Everything about it is big,” says Robert Blum, the observatory’s director for operations. The telescope’s weight means it has a lot of inertia, he explains, which means that once it’s been moved it settles down quickly into its new position. “We routinely discuss saving fractions of a second in the overall process of moving, settling and exposing,” says Blum, who is also an astronomer at the National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory in Arizona. “Because a fraction of a second in each element of the observing program, over ten years, can actually make a big difference.”

At the heart of the telescope is the world’s largest digital camera, which is about the size of a compact car and weighs around 6,600 pounds. The camera, together with the telescope’s optics, will have enough resolving power to see an object the size of a golf ball 15 miles away—or, equivalently, an object the size of the White House on the moon. Built at the SLAC National Accelerator Laboratory in California, the camera was shipped to Chile on a Boeing 747 cargo jet this spring and arrived at the observatory on May 16. The primary mirror was built at the University of Arizona’s mirror lab in Tucson, and it was shipped to Chile and installed at the observatory in 2019. The $1.9 billion facility is due to begin operations early next year.

Recording images is just the first step. Every time a particular patch of sky is photographed, computer algorithms will automatically compare the view to what was seen when the same patch was previously imaged, flagging anything that’s changed.

“Every night we’ll see about ten million things change in brightness or position,” says Mario Jurić, an astronomer at the University of Washington in Seattle. “Out of those ten million, you want to select a handful that may be worth following up.” That process, Jurić explains, will be highly automated, given that the camera will be recording more than six million gigabytes of data per year. Researchers are still developing the algorithms that will ultimately be used to sift through the enormous volumes of data. “When it [the observatory] starts in 2025, it’ll be a gold rush to figure out what’s the best algorithm to find the most interesting objects,” says Jurić. “So that’ll be super fun.”

The Rubin Observatory is expected to discover millions of previously unknown asteroids—small rocky bodies that have been circling the sun for billions of years but have eluded detection because they reflect only a tiny amount of sunlight. Jurić says the observatory will reveal some five million of these objects, ranging from marble-sized up to a few hundred miles across.

Of particular interest would be objects like ʻOumuamua, the cigar-shaped interstellar object that zipped through our solar system in 2017. If such an object were detected, alerts would be sent out to the astronomical community within hours, so that other telescopes could zoom in on the object, says Jurić. “And since Rubin will be able to detect these objects early, we’d have months, rather than days or weeks, to study it.” With enough lead time, a space mission such as the European Space Agency’s proposed Comet Interceptor could rendezvous with the object and examine it in more detail.

Tracking asteroids is also vital to planetary defense. Today, astronomers are aware of only about 40 percent of potentially hazardous asteroids—close-flying objects that are large enough to cause continent-wide destruction if they were to impact Earth, Jurić says. With Rubin, astronomers should be able to detect up to 80 percent of such objects. “This is one discovery that all of us are hoping we won’t make,” he says. “But the idea is, if there is an object like that, we want to find it while it’s maybe 40 or 50 years out, because that gives us enough time to figure out how we’re going to deflect it.”

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Further afield, Rubin will image millions of galaxies, flagging those where exploding stars known as supernovas are spotted. Supernovas are incredibly useful to astronomers, who can use the exploding star’s physical properties to work out the distance to their host galaxies. This, in turn, allows researchers to create 3D maps of the cosmos. Studying this distribution of galaxies can provide clues about the abundance and distribution of dark matter—an unknown substance that holds galaxies and galaxy clusters together—which, along with gravity, has shaped the evolution of the universe.

Such 3D maps also allow scientists to study the effects of dark energy, a mysterious force that appears to be causing the universe not only to expand but also to accelerate. Accurately mapping the distribution of galaxies will help pin down dark energy’s characteristics, says Renée Hložek, an astronomer at the University of Toronto and a spokesperson for the Dark Energy Science Collaboration, a team that will be using data from Rubin to study the mysterious force. “Rubin will allow us to test different models for what dark energy could be,” Hložek says. “Is it changing with time? Is it changing in space? With data from Rubin, we can actually put these ideas to the test, which is really exciting.”

The observatory had originally been referred to as the Large Synoptic Survey Telescope, but it was renamed in 2019 in honor of Vera C. Rubin, an American astronomer who made pioneering measurements of galactic rotation speeds in the 1960s and ’70s, providing the strongest evidence for the existence of dark matter. The decision to name the observatory after Rubin “is a real nod to her contribution in the field, which some would say has historically been undervalued,” says Hložek.