The Most Powerful Camera Ever Will Capture the Entire Southern Sky

The Large Synoptic Sky Survey will find countless objects and phenomena, near and far, never seen before.


The world's most powerful camera will spend a decade staring at the southern sky. Its survey will find near-Earth asteroids, faraway exoplanets, brightly exploding stars, and distant galaxies. Taking nightly pictures, the Large Synoptic Survey Telescope (LSST) and its 3.2-gigapixel camera will produce a volume of data that's hard to comprehend.

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The project just got its official approval from the Department of Energy, meaning this ambitious mission is a step closer to getting under way. With the approval of the DOE, the LSST can start fabricating parts and begin construction of the camera in the Andes Mountains of Chile. The construction is managed by SLAC National Accelerator Laboratory and sponsored by private donations, the National Science Foundation, and the Department of Energy, the LSST needed the final go ahead from the Department of Energy before full construction of the camera could begin.

Thousands of pictures of the entire sky

When it goes online in 2019, the telescope will use an 8.4-meter mirror to gather light from the sky. From there, roughly every 30 seconds it will take a picture of about 10 square degrees of the sky before moving along to the next ten square degrees. (Ten degrees is about the size of a balled fist held at arm's length, or the apparent distance between the top two stars in the "cup" of the Big Dipper.) Altogether it will take on the order of 100 pictures per hour, and 800 pictures per night covering a little over 8,000 square degrees. Every third night, it will return roughly to the same spot and take another picture. 

"What's really new and unique about LSST is resolution is not taking finer pictures," Steve Kahn, director of the LSST project, said in a phone interview. "What's really new and unique is covering the entire sky."

That all translates to 20 terabytes of data per night, and hundreds of petabytes of data by the end of the decade-long survey, creating a massive trove stored across a network of computers that astronomers will be able to query. As the information comes in, computers will sort through it, looking for interesting events and creating alerts that can then be sent to researchers working in particular fields within astronomy.  

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The goal is to find not just new objects, but evidence of movement and change. A picture of one part of the sky on one night will be compared to the same area of sky on another night. Objects that move will be cataloged against existing knowledge of solar system objects to determine asteroids, comets, or dwarf planets, including near-Earth asteroids that could pose a danger. This will  help to create a catalog of near-Earth objects—from 70 to 90 percent of all asteroids and other large orbital debris. By tracking them over time, LSST will establish their orbits and figure out if an asteroid is a danger to the planet.

"LSST will make a major dent in finding near-earth asteroids, objects that could potentially impact the earth," Kahn says.

Stars that change in brightness can be studied more in depth. Changes in brightness could indicate a transiting companion (planetary or otherwise), variable-brightness stars, gamma ray bursts, or even the beginning of a supernova. "We'll find whole new classes of variable phenomena in the universe," Kahn says. 

Finding a primordial mystery

In addition to tracking stars, planets, and asteroids, the telescope will be able to hunt for ancient galaxies. While it won't have the resolution of the Hubble Space Telescope (because it has to look through the Earth's atmosphere), LSST will have an advantage over Hubble: covering the entire sky rather than simply a portion, a drawback of many of NASA's space telescope projects. That's another way LSST may find transiting planets that the Kepler Space Telescope couldn't, since it looked at only one small area of the sky. 

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LSST can even hunt for dark matter and dark energy, the mysterious force in the universe that contributes to its expansion while hiding from direct detection. By analyzing galaxies over time and taking small and subtle but detectable measurements, the telescope could indicate more of the behavior of dark energy and give a clue to its origins. 

"One of the mysteries of modern physics is to understand why the universe is expanding, and one way to understand that is a survey of all of the galaxies in the universe," Kahn says.

Minor limitations

There are some things LSST won't be able to find. Mike Brown, the Caltech astronomer who discovered a large volume of dwarf planets and other Kuiper Belt Objects, believes there are no bright objects left to find in the "third zone" of the solar system—the region out beyond Neptune where Pluto and other Kuiper Belt objects live. 

This means LSST is unlikely to discover any new dwarf planet candidates,and any large planets hiding in or beyond the Oort Cloud are unlikely, as the survey won't be scanning in infrared. (The spectrum runs ultra-ultraviolet to near-infrared, with different color filters on the camera.) It also won't be able to find long-period exoplanets (those that have orbits more in line with our solar system, where orbits are months long instead of days or weeks), or exoplanets much smaller than gas giants. 

While the survey won't take the highest-resolution images of the cosmos, but it will take one of the most comprehensive pictures of half of the visible universe. The data taken by LSST will be used by astronomers around the world for follow-up observation. So for example, should LSST discover a new exoplanet, a future telescope like James Webb, TESS, or the 30 Meter Telescope could make follow-up observations of the solar system to find others. Should it detect a distant galaxy from the early universe, the European Extremely Large Telescope can try to get a close-up and hunt for its origins. 

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In other words, the LSST will be a pathfinder for our knowledge of the cosmos in the coming decades. 

"LSST will detect everything that moves in the sky and everything that changes brightness in the sky," Kahn says. "So we'll see lots of interesting events."

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