LSST to the rescue

We hope the Large Synoptic Survey Telescope (LSST), under construction in Chile on a timeline that would have it begin science work in 2022, works. There are a bunch of astronomers banking on it to make their lives a lot easier. A group of them—the LSST Solar System Science Collaboration—met earlier this month in Seattle, and four of them gave talks at a special edition of Astronomy on Tap Seattle at Peddler Brewing Company in Ballard.

David Trilling of Northern Arizona University noted that the LSST will have an 8.4-meter mirror and a camera the size of a small car.

“In terms of telescopes, this is a really, really, really big machine,” he understated. That car-sized camera will boast 3.2 billion pixels.

“You’d need 1,500 HDTV screens to look at a single LSST image,” Trilling said. LSST will scan the entire night sky every three to four nights for ten years.

“That’s about ten terabytes of data every night, which is a huge computational challenge,” he noted.

It’s an asteroid. It’s a comet. It’s complicated…

Michael Mommert of Lowell Observatory studies asteroids and comets. He said that sometimes it’s difficult to tell one from another. An asteroid can look like a comet if the asteroid is “active.” This could be because it collided with something else, or it is spinning rapidly, or it was warmed by its proximity to the Sun.

“If we can understand those active asteroids we can better understand the average asteroid,” Mommert said. “We can learn a lot about the mechanisms that are going on in asteroids from those active asteroids.”

Similarly comets can go dormant, with no tail, and look more like asteroids. As they often share similar properties, Mommert said comets and asteroids are on something of a continuum rather than being two distinct types of objects.

In his research Mommert is tracking about 20 active asteroids and 50 dormant comets. He figures he spends 30 nights per year using a telescope. He’ll be able to cut down that time tremendously with LSST; he’ll be able to find his targets and pull data collected by the telescope.

“LSST will improve our understanding of small body populations,” Mommert said. “Asteroids, comets, active asteroids, everything that is out there.”

Tales from the Outer Solar System

Kat Volk of the University of Arizona focuses her research on objects in the outer solar system. Pluto, Eris, and other far-out objects have been discovered by comparing photos of an area of sky and looking for something that moved. In fact, Pluto was the first object discovered in this way.
There are about 2,000 known objects in the Kuiper Belt. That’s about how many asteroids we knew of a century ago.

“Kuiper Belt science is a hundred years behind Asteroid Belt science because these things are just so much more difficult to find,” Volk said, because they’re far away, faint, and move slowly. “We had to wait until we had digital cameras and computers to process those images.”

Volk said we probably have discovered all of the 10-kilometer asteroids and most of the 1-kilometer ones. They’re easier to spot because they’re brighter, and there’s money for the hunt because of the potential threat asteroids pose to Earth.

“For comparison, the smallest ever observed Kuiper Belt object is 30 kilometers across, very roughly,” Volk said, adding that we only found that one because the Hubble Space Telescope was used to look for another target for the New Horizons mission after it passed Pluto.

“We’re pretty incomplete in terms of our object inventory in the outer solar system,” Volk said. She said LSST will change that.

“They expect 40,000 new Kuiper Belt ojects,” Volk said. “It’s going to be an entirely new era for the Kuiper Belt with a huge playground of new objects to look at.”

“I am realy excited to see what we’re going to find with LSST, and it’s going to completely revamp our idea of the outer solar system.”

A Crash Course in Asteroid Defense

Andy Rivkin of the Johns Hopkins University Applied Physics Laboratory said that even a 20-meter asteroid packs a wallop when it smashes into Earth. That was roughly the size of the Chelyabinsk meteor in 2013.

Doing the math tells us that there should be about 10 million objects of that size zipping around the solar system, but so far we’ve found only around 10 thousand of them. Back in 2005 Congress told NASA to find 90 percent of objects 140 meters or larger.

“LSST is going to be a critical piece in reaching this goal,” Rivkin said, “and we expect that by 2034 about 86 percent of hazardous asteroids will be found.”

So, what do we do when we spot one headed our way? Rivkin said that for really small ones, like Chelyabinsk, and really large ones, the best idea might be duck and cover. There’s not much to be done about something very large, and small ones don’t pose much of a threat. For those in between, a few options are viable. For one, we could try to deflect the asteroid with a nuclear bomb.

“A lot of people are uncomfortable with nuclear explosions in space, for good reason, and so there’s been a lot of interest in having something else that could work,” Rivkin said.

That something else is a kinetic impactor, which is a fancy way of saying we’ll just smash something into the asteroid to change its speed, and therefore its orbit. It’s a fine idea in theory, but we have no idea if it would actually work. Rivkin is involved in a project that will give it a try.

It’s called DART, which is for Double Asteroid Redirection Test. DART is on schedule to launch for the asteroid Didymos in June of 2021, and then crash into its satellite, nicknamed “Didymoon,” in October 2022. Astronomers will watch through ground-based telescopes and see what happens. Rivkin called it a dress rehearsal for the day we might have to do something about an incoming asteroid.

“A dress rehearsal for, needless to say, a performance we hope never to actually stage,” he said, “demonstrating that we could do this, allowing us to pin these computer simulations to something real, allowing us to better understand asteroidal properties, and giving us a lot of science as an ancillary benefit.”



Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington.