Perched atop the Cerro Pachón mountain in Chile, 8,684 feet high in the Atacama Desert, where the dry air creates some of the best conditions in the world to view the night sky, a new telescope unlike anything built before has begun its survey of the cosmos. The Vera C. Rubin Observatory, named for the astronomer who discovered evidence of dark matter in 1978, is expected to reveal some 20 billion galaxies, 17 billion stars in the Milky Way, 10 million supernovas, and millions of smaller objects within the solar system.
“We’re absolutely guaranteed to find something that blows people’s minds,” says Anthony Tyson, chief scientist of the Rubin Observatory. “Something that we cannot tell you, because we don’t know it. Something unusual.”
This tremendous astronomical haul will come from the observatory’s 10-year Legacy Survey of Space and Time, which is slated to begin later this year. The first science images from the telescope were released to the public today.
Rubin’s unprecedented survey of the night sky promises to transform our understanding of the cosmos. What happened during the early stages of planet formation in the solar system? What types of exotic, high-energy explosions occur in the universe? And how does the esoteric force that scientists call dark energy actually work?
“Usually you would design a telescope or a project to go and answer one of these questions,” says Mario Juric, the data management project scientist for Rubin. “What makes Rubin so powerful is that we can build one machine that supplies data to the entire community to solve all of these questions at once.”
The telescope will create a decade-long, high-resolution movie of the universe. It will generate about 20 terabytes of data per day, the equivalent of three years streaming Netflix, piling up some 60,000 terabytes by the end of its survey. In its first year alone, Rubin will compile more data than all previous optical observatories combined.
“You have to have an almost fully automated software suite behind it, because no human can process or even look at these images,” Juric says. “The vast majority of pixels that Rubin is going to collect from the sky will never ever be seen by human eyes, so we have to build software eyes to go through all these images and identify … the most unusual objects.”
Those unusual objects—asteroids from other solar systems, supermassive black holes devouring stars, high-energy blasts with no known source—contain secrets about the workings of the cosmos.
“You build a telescope like this, and it’s the equivalent of building four or five telescopes for specific areas,” Juric says. “But you can do it all at once.”
The observatory on the summit of Cerro Pachón in Chile.NSF-DOE Vera C. Rubin Observatory/A. Pizarro D.
A Telescope Like No Other
Housed in a 10-story building, the Rubin Observatory is equipped with an 8.4-meter primary mirror and a 3,200-megapixel digital camera, the largest ever built. The telescope rotates on a specialized mount, taking 30-second exposures of the sky before quickly pivoting to a new position. Rubin will take about 1,000 images every night, photographing the entire Southern Hemisphere sky in extraordinary detail every three to four days.
“It’s an amazing piece of engineering,” says Sandrine Thomas, a project scientist who works on the optical instruments of the Rubin Observatory.
Such rapid movement requires a special, compact design. Rather than having three separate mirrors to achieve a wide field of view, as used on other telescopes, Rubin’s tertiary mirror is integrated into the center of its primary mirror. Both were made from a single piece of glass, with different curvatures for the inner and outer parts of the mirror—a unique challenge that took seven years to fabricate.
A video showing the arrangement of Rubin’s mirrors, including its combined primary and tertiary mirror.
Even with this compact design, the 350-metric-ton telescope flexes under its own weight as it rotates.
“You’ll start to have the actual mirror collapsing a little bit on itself, and we have the top of the telescope … start to sag,” Thomas says. “It is small, but it is enough that you would see it in your image if you don’t correct it.”
These corrections are done using an active optics system that includes actuators on the back of the mirrors to adjust their shapes, as well as electromechanical devices the team calls “hexapods” to adjust the positions of the secondary mirror and the camera. The active optics system corrects for not only the gravitational changes as the telescope moves, but also temperature fluctuations and other perturbations.
“That requires that mechanically everything was put in place to millimeter accuracy,” Thomas says.
Planetary History, Killer Asteroids, and a Giant in the Shadows
Within the first three years of operation, the Rubin Observatory is expected to discover between 10 and 100 times as many solar system objects as currently known.
“The amount of information we’re going to get about the solar system is going to be huge,” Juric says. “It took us 225 years to discover the first 1.4 million asteroids in the solar system. With Rubin, we’re going to find the next 1.4 million in less than a year.”
Most of those asteroids are ancient fragments, bits of rock and metal that fractured from larger bodies during the violent process of planetary formation.
In the past couple decades, astronomers have come to realize that our solar system is something of an oddball. Many other systems have large gas planets orbiting close to their stars with the smaller rocky planets farther out, the opposite of what we see around the sun.
“We know that planets in the solar system did not start out at their current positions,” Juric says. Neptune used to be twice as close to the sun, and the other gas giants began their lives closer in as well. Jupiter may have even tossed another gas giant out of the solar system entirely.
“All of this happened early in the solar system, and we’d like to know how and when,” Juric says. Using information contained in the solar system’s ancient fragments—the positions, trajectories, shapes, and sizes of millions of asteroids, comets, and other small bodies—astronomers can write a new history of our planetary system. “We tend not to be interested in any particular one, but when you find 5 million, they tell you a lot about what happened.”
Some asteroids among the millions, however, are bound to capture particular interest. A handful won’t be part of the solar system’s history at all, but rather visitors from other planetary systems, ejected from their home stars to fly, by chance, through our cosmic neighborhood. Only two such objects have been discovered so far, and one, called ‘Oumuamua, looks nothing like anything seen before.
“This is as close as it gets to actually visiting another stellar system and looking at the planets and at the components that went into the planets,” Juric says. Rubin is expected to find anywhere between 10 and 120 of these exotic interlopers. “If there’s an interstellar object passing by, and it just happens to be in the right trajectory, you can launch [a spacecraft] to intercept it. Now that would be amazing.”
A small section of the observatory’s total view of the Virgo cluster. Bright stars in the Milky Way galaxy shine in the foreground and many distant galaxies are in the background.NSF-DOE Vera C. Rubin Observatory
Rubin will also double the number of known potentially hazardous asteroids larger than 140 meters across—big enough to cause regional devastation or disastrous tsunamis if one hit Earth—from about 40 percent to 80 percent.
Perhaps the most exciting discovery Rubin could make in the solar system is confirming or ruling out the existence of Planet Nine. This hypothesized planet, between five and 10 times the mass of Earth, may be lurking in the outer reaches beyond Neptune, its presence betrayed by an unusual clustering of small objects out there, known as trans-Neptunian objects, which appear to have been nudged into place by an unseen world.
If Planet Nine exists, the Rubin science team believes there is a 70 to 80 percent chance that it will be in a position where the telescope can detect it directly. If it is somewhere harder to see, such as in the foreground of the Milky Way’s bright galactic plane, the team is still confident that they could detect the planet’s presence indirectly.
“We will find so many trans-Neptunian objects, through which Planet Nine has been inferred to exist, that we would almost certainly answer the question of whether that signal folks are seeing right now is real,” Juric says. “We either find it directly or we find extremely strong circumstantial evidence that it’s there or not there.”
Planet Nine would be the first discovery of a major planet in the solar system since Neptune was spotted in 1849.
“If we find Planet Nine,” Juric says, “then we really need to update our entire understanding of how the solar system has evolved and what happened at the beginning.”
Galactic Filaments and the “Time Domain”
In addition to millions of asteroids, the Rubin Observatory will spot billions of new stars scattered across the Milky Way. By charting these stars, scientists can conduct what they call “galactic archaeology.”
The Milky Way began its life as a much smaller galaxy before merging with or devouring its neighbors, a process that continues today as dwarf galaxies are subsumed.
“It doesn’t just eat a galaxy and then it’s gone, but it first shreds it into these long stellar streams,” Juric says. “We can see these stellar streams, and based on where they are, what their shape is, and how all these galaxies are moving, we can reconstruct how the Milky Way has been growing through time.”
What separates Rubin from other telescopes is its ability to study what astronomers call the “time domain,” or how things change over time. Historically astronomers have focused on achieving deeper and deeper images to figure out what kind of objects exist in the universe. Rubin represents a shift in focus from the deepest images possible to a rapid sequence of millions of images that capture short-term changes across the night sky.
“I think that what we discover in the time domain is guaranteed to be revolutionary,” Tyson says. “Mainly what it will find in terms of new kinds of objects that explode or move in the sky.”
Stars that suddenly pulse or erupt can help astronomers learn about highly energetic stellar behaviors that influence the evolution of entire galaxies, from brightly pulsating RR Lyrae stars in the central galactic bulge to pairs of extremely dense neutron stars spiraling toward a collision.
“The idea is we find something that’s interesting, and then we tell our friends on large telescopes with spectrographs, something like the Webb,” Juric says, referring to the James Webb Space Telescope. “And then the community uses those instruments to go and follow it up.”
Exploding Stars, Extreme Physics, and Cosmic Energy
With tens of thousands of images taken every month, Rubin will give astronomers the best chance they’ve ever had to capture rare, awesome phenomena. Giant stars pulverized by supermassive black holes, massive collisions that release gravitational waves, and bizarre scenarios that astrophysics haven’t even considered will show up in unprecedented numbers.
“We’ll provide this huge sample of very interesting things where we can test and push the boundaries of physics as we know it,” Juric says. “You test physics not in our everyday environment but in the most extreme conditions you can think of. Things like, what happens when a star comes too close to a black hole and that black hole shreds it apart and starts eating it up?”
Rubin’s images will be so comprehensive that astrophysicists believe they could even help untangle the mystery of dark energy, the force of unknown origin that drives the accelerating expansion of the universe. This acceleration began roughly 5 billion years ago, suggesting something may have changed to trigger it.
“What is the physics of dark energy? That’s the question we’re after.” Tyson says. “We know already that it’s beyond the known physics.”
To try to learn how dark energy is generated, scientists will chart the distribution of its invisible companion, dark matter. This unseen matter does not interact with light, but it can be detected through gravitational lensing, a phenomenon that occurs when light is warped by the gravity of high-mass areas, such as around galaxy clusters.
“The Rubin Observatory will do this in a magnificent way,” Tyson says. It will “look at the sort of filamentary structure of dark matter in the universe over a very wide range of scales.” With a sense of how dark matter is distributed across the cosmos, researchers “can tease out the dark matter behavior as a function of time,” leading to details that will constrain models of what may be driving dark energy.
“There’s new physics right around the corner,” Tyson says.
Like the expanding universe itself, humanity’s comprehension of the cosmos is about to accelerate.
“There’ll be a stream of discoveries,” Juric says. “Essentially every week there’ll be something new and interesting for the next couple of years.”
Staff at the observatory prepare to install the Legacy Survey of Space and Time Camera in the telescope.NSF-DOE Vera C. Rubin Observatory/H. Stockebrand
