Who's Who at NASA

NASA’s Planetary Defense Coordination Office (PDCO), managed at NASA Headquarters in Washington, D.C., is responsible for early detection of potentially hazardous objects, like asteroids and comets, and issuing warnings about their potential impacts. This requires teamwork from observatories around the world. NASA’s Planetary Defense Officer, Lindley Johnson leads the global effort to detect and follow near-earth objects

Tech Briefs: What is your day-to-day work as it relates to asteroids?

Lindley Johnson: NASA funds survey teams run by university and space institutes and we have a partnership with the Air Force to use the space situational awareness assets they use to track objects and debris in geosynchronous orbit. We are also using a spacecraft that was originally designed to support astrophysics work. We finished its initial mission back in 2010, and now we’re using it full time for asteroid detection and characterization.

The observations of moving objects in the sky that are determined to be asteroids are sent to the IAU Minor Planet Center (Cambridge, MA) — the internationally sanctioned data and analysis facility for small bodies in the solar system. The Center maintains data collected from observatories around the world. Our work is monitoring those efforts to detect, track, and characterize asteroids and comets.

Tech Briefs: Have you recently detected any potentially dangerous objects.

Johnson: On Wednesday, April 19, an asteroid missed Earth by 1.1 million miles – a distance closer than you might think. The asteroid, named 2014 JO25, was originally discovered by astronomers in May 2014 through NASA's Near-Earth Objects Observations (NEO) Program. The team, in collaboration with the University of Arizona, first spotted the asteroid at the Catalina Sky Survey near Tucson.

Tech Briefs: What kinds of damage could be done by an asteroid like that if it were to reach earth?

Johnson: It was an ugly shaped asteroid. It was what we call a bifurcated object. It looks like two asteroids stuck together. Sometimes we call them contact binaries, because they look like a couple of objects that probably came together at some time in their past. According to the radar measurements, it was just under 1 km in its long axis, across the two lobes of the object and about 2/3 that distance, 650 meters, in the short axis. An object of that size, if it were to impact on land, could wipe out a region of a large state and affect the climate globally for a period of several months. This is not something we want to get hit by.

Tech Briefs: How are you able to spot asteroids — especially ones that are going to potentially impact us here on Earth?

Johnson: Currently we are using ground-based telescopes to do this — telescopes that were originally built for other purposes. We have worked with universities and space institutes to modify and adapt them to the kind of wide-field survey work needed to detect dim objects, down to the 21st or 22nd visual magnitude, and cover a wide patch of sky each night. The CCD imagers we’re using will image about a 6-degree field of view at a single take. That’s about 8x the area of a full moon. Yet even these will need a month to cover the sky accessible from their location.

Tech Briefs: How much warning is there between when you detect a possibly dangerous asteroid, and the window of time to address that asteroid?

Johnson: It all depends on when we detect the object — It’s very much dependent on the orbit. Most of these objects, if we are looking wide enough and deep enough, will come within a distance that could be detected from the Earth, or from a spacecraft near the Earth. They would probably be sighted several times before being on an impact trajectory.

However, we are just in the early years of this surveying effort and there’s always a chance that one or more objects could be on their final orbit before impact. If that’s true, we may, for larger objects, have weeks to a month or two of warning. Smaller objects, those still large enough to penetrate Earth’s atmosphere and do damage at the surface, would not come within range of ground-based telescopes until a day or two before the impact.

Tech Briefs: If there is an asteroid about to enter Earth’s atmosphere, what is the best technique for taking care of it?

Johnson: The average velocity relative to the Earth is about 18 km (12 miles) per second. Once it enters Earth’s atmosphere, it’s only 10 seconds before the impact occurs.

We need to find these things while they’re still well out in space, preferably, several orbits before they would impact, so we have the time to mount a mitigation mission. We need to change the velocity of the object just slightly, only a cm per second difference in velocity. If it’s done years in advance, that is enough to make the encounter a miss instead of a hit, to slow the object down enough so that it would not reach the same point in space as the Earth at that predicted encounter.

Tech Briefs: Tell us about your encounter with JO25.

Johnson: The asteroid was discovered on its previous path by the Earth in 2014. Since it takes a little under three years to orbit the Sun, we knew it would return around this time — we were predicting this close pass for several months.

In its current orbit, we could not see it from our ground-based optical observatories because it was coming at us from the direction of the Sun. Our ground-based interplanetary radars were the first to pick it up.

Objects have to come within 5 million miles of the Earth before they can be spotted on the radars. Once the asteroid passed over the top of Earth’s orbit and into the night sky, the optical telescopes, like NASA’s IR telescope facility in Hawaii, followed by observatories around the world, started taking observations.

Tech Briefs: What are some of the difficulties in detecting asteroids?

Johnson: Relatively small ones that come into the inner solar system are very dim. It takes telescopes that have wide-field views that can cover large parts of the sky each night, but also are able to go very deep and very dim. The reflectivity of these objects is on average about the same as a lump of coal — they’re very dark, reflecting only about 10 to 15 percent of the sunlight that hits them.

Tech Briefs: How optimistic are you about being able to address this kind of threat?

Johnson: We need a space-based observatory that can operate 24/7 and not be affected by daylight. By going to space, we could operate in the infrared part of the spectrum, where the signature of these objects is brighter. Instead of looking for the reflection of sunlight from dark objects, we could detect their glare as they absorb the sunlight then re-emit it as heat. Re-emitting the sunlight as heat and seeing that against the cold background of the sky, gives them a higher signature. An infrared telescope operating in space would be a much more effective way of detecting and tracking these objects. We have the technology — we just need the funding to build it.

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