© Michael Deforge
Lindley Johnson spent 23 years in the U.S. Air Force keeping his eyes above the skies. He helped identify and tackle a growing risk to human space activity—the sheer volume of stuff orbiting the planet—in addition to helping manage and monitor military assets in orbit. In 1982, the Air Force set up a space command to coordinate its activities, not the least of which was making sure the then-new Space Shuttle fleet wouldn't have a tragic encounter with spacefaring material.

In the early 1990s, Johnson's focus turned to natural threats to the planet from near-Earth asteroids, now a large and growing class of rocks that scientists track both for their potential impact risk and to study the solar system. About 1,500 new objects are discovered every year. Since retiring as a lieutenant colonel several years ago, he's become the founding head of NASA's Planetary Defense Coordination Office, overseeing a network of ground-based telescope surveys for new asteroids and working with other agencies to prepare for the unlikely event of a direct hit. His job title—no pressure—is Planetary Defense Officer.

A sign on the credenza in his office reads, "Every Day is Asteroid Day," he said.

Q: So we can just take out asteroids with nukes, right?

A: That's Hollywood fantasy. First of all, it would be too late just to send an ICBM with a nuclear warhead on it. These things are moving at speeds like the equivalent of about 12 miles a second. They would be difficult to intercept on an impact trajectory in the last few moments. Second, you're not going to stop anything at that point. All that mass is still going to come down on us and if anything spread it over a wider area. So that's not really a viable option.

What we need to do is find them well in advance, several years in advance, so we can send a spacecraft out into interplanetary space. If you are able to catch them many years in advance, you prevent them from being an impactor by changing their velocity by just a little bit.

Q: Was there an initial event that hooked you? Somebody spring into your office and say, "Hey, any asteroids coming at us?"

A: The hazard has always been there. It's just that we began to realize it and understand it more as we were finding asteroids in orbit that came close to Earth orbit. They are very rare, but they can still happen. That realization came around in the late '80s early '90s, in parallel with the Alvarez paper on the demise of the dinosaurs probably being caused by impact from a large asteroid.

I was at the Air Command and Staff College and participated in an Air Force-led study called SpaceCast 2020. We were studying the capabilities the Air Force might need in the year 2020. I chose the topic of protecting the Earth from asteroids, after a University of Arizona professor had gotten me kind of interested in the problem.

Q: Seems like a no-brainer.

A: I was kind of considered an outlier for that study. That wasn't something they really thought was of interest to the Air Force. But it was also right at that same time that the comet Shoemaker-Levy 9 was discovered and would impact Jupiter the following year. That caught a lot of attention, and suddenly: "Well, maybe this is something we really ought to be concerned with." So my thesis for that study was the title, "Preparing for Planetary Defense."

Q: So you coined the term that 20 years later would turn out to be the title of your office.

A: The term had not existed before that paper. I did coin the term. I've been working with the community every since then.

Q: That was the early '90s. Why did it take so long to set up the actual NASA office this year?

A: There was interest in the '90s from Congress. The NASA program for detecting and tracking near-Earth asteroids actually started in '98, after studies had examined, really, what is the threat and should we be worried about it. So the language in the '98 Authorization Act for NASA set up a program. It was further reinforced in the 2005 Authorization Act for NASA for detecting and tracking any objects more than 140 meters in size.

Q: I wouldn't want an object half that size hitting me in the head.

A: Our original objective was to find everything 1 kilometer and larger. That's what started in '98, and with further study we determined it really ought to be smaller than that. The 2005 Authorization Act for NASA included detecting and tracking any objects larger than 140 meters in size. After 2013, people were worried about objects as small as 20-30 meters in size.

Q: That's when a surprise meteor hit Chelyabinsk, Russia, the same day as a different asteroid was predicted to fly by?

A: The international network of astronomers who do this had discovered an object in February 2012 that would pass closely by the Earth in February of 2013. They predicted the orbit for it and found that although it was going to come very close—within the distance of a satellite orbit—it would be a miss.

That event also coincided with the annual meeting of the United Nations Committee on the Peaceful Uses of Outer Space. The Near-Earth Object working group had been developing a recommendation to the UN about what the space-capable nations of the world ought to be doing in response to a possible impact threat. I was actually in Vienna that day getting ready to brief the committee when the Chelyabinsk incident happened.

Mother nature sort of put an exclamation point on our recommendations.

Q: You recently conducted a third wargame-like exercise with other agencies about an incoming asteroid.

A: In this scenario was we found this asteroid that had the potential to impact the Earth in four years. It takes some time to observe the asteroid and reduce the uncertainties in its orbit, so we really understand where it's going to be relative to the Earth four years later.

At a point in the exercise we determine the probability is 100 percent that we're going to have an impact. It's only in the last several days or weeks prior to impact that we can really narrow it down to a 10-kilometer area.

Q: What do we do if you really find one?

A: We're working on a couple of different projects to test and demonstrate what we think are viable capabilities to do that. The first we talk about is part of our asteroid redirect mission. A second project we have going is in collaboration with the European Space Agency, and that's a project called the Asteroid Impact Deflection Assessment.

Q: How did the official NASA office get started?

A: What was a part-time job for me prior to 2010 slowly evolved into a full-time job as it is now. Partly because of funding increases that have occurred since 2010. Prior to 2010, the program was only $4 million to $5 million a year. With the 2012 budget, it was increased to $20 million a year. Then in 2014 it was increased to $40 million a year. Management and oversight of the increased number of projects we could do, given that funding, necessitated it being more than a part-time job for one person.

Q: Do asteroids ever get mentioned in the Presidential Daily Briefing?

A: I don't know that for a fact. In 2008 we discovered a very small object a few meters in size that was going to impact us the next day. It was discovered and predicted to impact in the Sudan desert. And so we here at NASA generated a notification of that, which was sent up to the White House. We know that it was brought to their attention because George W. Bush's press secretary, in the log of her White House years, talks about it as being one of the strangest days she had at the White House.

Q: Does the U.S. do a lot of work for the world on this?

A: What we do here in the U.S. by far leads the world in the capability and surveys. Our projects are finding some 95 percent of the objects that are found every year. We're not 100 percent—there are efforts elsewhere that are doing what they can. The U.S. has the most focused and well-funded effort.

Q: Do you have a least favorite asteroid movie?

A: My least favorite is probably Armageddon, because it's total fantasy. My favorite is a movie called Meteor that was out in the late '70s. Most people don't remember it. It actually did a fairly decent job with this scenario. The reason it's my favorite is because Sean Connery plays me.