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The Gravity Assist Podcast is hosted by NASA Chief Scientist Jim Green, who talks with some of the world's leading planetary scientists, taking a guided tour of the solar system and beyond. This week he is joined by Lindley Johnson, NASA's Global Defense Officer, charged with keeping the Earth safe from countless small bodies that cross the orbit of our planet. As we say in this case, it is not a question of if, it is only a matter of time.
You can listen to the full podcast here, or read the shortened transcript below.
Jim Green: Lindley, you are NASA's first planetary defense officer. What is the first step to protect the Earth from asteroid or comet attacks? [Potentially Dangerous Asteroids (Images)]
Lindley Johnson: Well, you have to find them first. You have to search for them, find out what's going on or what can get closer to the Earth's orbit, and you have to find them well before any approach or impact on the Earth, because it will take time … years , in fact – to be able to go out and do something about them before they impact the Earth.
Jim Green: Is it because they are so small? I mean, they are so much smaller than planets and moons.
Lindley Johnson: Well, it's certainly harder to find them, but it's just the time it takes to build a spaceship. to the object and interact with it in a certain way to change its speed. This is the main principle behind attenuating an impact – simply by simply changing the speed of the object so that the object appears late to the point of expected impact [and therefore misses us].
Now, if the object is small enough, just hitting it with a spaceship – what we call a kinetic impactor – would be enough to change its speed enough to slow it down. In fact, we are working on demonstrating this capability now. This is what is known as double asteroid redirection test (DART) and it is about to enter its large-scale development phase.
Jim Green: Let's talk about DART. This will be our first attempt to intentionally change the orbit of an asteroid.
Lindley Johnson: That's right. We chose the target asteroid, Didymos, because Didymos is a binary asteroid. The main object is about half a mile in diameter (780 meters) and is orbited by a moon about 170 meters (500 feet) in diameter. Thus, the DART spacecraft will affect the moon and change its speed and orbit around the primary. We can observe this change from the ground, both optically and radar. Of course, the radar will give us more accurate measurements and provide us with the data that more accurately shows the strength we have been able to transmit to this moon. And since we do not change the orbit of this whole system around the Sun, we will not increase the danger to Earth of this asteroid.
Radar observations of the asteroid Didymos and his little moon, which will be the target of the next NASA DART mission
Credit: Arecibo Observatory
Jim Green: How are we able to see these relatively small objects? Are not they very black and black?
Lindley Johnson: Yes. There is certainly a population of these objects that are as dark as coal, which makes them very difficult to see in the visible part of the spectrum, where we are now mainly looking for ground telescopes. This is one of the reasons we would like to be able to look for them in the infrared part of the spectrum, because these objects absorb heat from the Sun and then re-emit that heat as radiation that can then be detected in the infrared light. The problem is that you need a sensor spaced to look for them because the atmosphere of the Earth blocks the infrared.
Jim Green: We currently have a telescope in the space that looks into the infrared.
Lindley Johnson: Yes, that's right. We have the Wide Field Infrared Survey Explorer (WISE), launched by the Astrophysics Division of NASA, to build an infrared sky map. He constantly imagined the sky to build this map and we quickly realized that with all the images he took, we could search for an asteroid that was moving across the sky in these images. After the astrophysicists had finished, NASA's planetary defense program resumed the operations of the spacecraft [it became the NEOWISE mission] and we made it not only a full-time asteroid hunter, but it also characterizes them, in calculating their size. .
Jim Green: How many asteroids close to the Earth are there?
Lindley Johnson: Up to now, we have found more than 18,000 asteroids of all sizes approaching Earth's orbit. But we think that's a very small part of the overall population. At present, our task is to find asteroids more than 140 meters (460 feet) in diameter near the Earth's orbit. We have several ground projects to do it. Our prediction is that there are 25,000 objects of more than 140 meters in size and so far we have found only 8,000 in the 20 years that we have been looking for here.
Jim Green: How Many Are Really Threats to the Earth?
Lindley Johnson: We must take several observations over a period of time to be able to determine their orbit and whether they will come close enough to Earth to be a danger of impact. At the present time, with known objects, there is none that has a significant possibility of impacting the Earth. There are several who are very close and if their orbits were to deviate from our current predictions, they could become dangerous. So this subclass of near-Earth objects, which we call potentially dangerous asteroids, needs to be monitored more closely. We now have about 1900 of these objects that we are watching closely.
Jim Green: Well, let's talk about the one who flew over the Earth quite recently. This is what is called Asteroid 2010 WC9. Tell me a little about it
Lindley Johnson: From his designation, we know that this object was found in 2010. The WC9 tells us what month he found it. It starts with a W, so we know it was the last part of November 2010, and then 9 is a sequential number [the ninth object discovered during that part of November 2010]. It's a complicated designation system, but it works for astronomers.
It was observed for the first time by the Catalina Sky Survey in Arizona and only a few observations were made during this period. So we did not have a very good orbit for that at that time; we could not project the orbit more than a year with a certain degree of certainty.
[But] we knew that there would be another approach closer to the Earth in May 2018, but we did not know how far away. In fact, the uncertainty as to when the closing approach would occur was 18 days. Moving at the speed it does, it covers a lot of distance in 18 days. The Catalina Sky Survey, however, retrieved this object again on May 8 and began taking observations. The Minor Planet Center, where all the observations from all over the world go, was able to quickly correlate these observations with the orbital data that they had on that object. So, now we have significantly expanded the scope of observation on its purpose and can predict its orbit more accurately.
A diagram of how NASA's DART mission will work, shooting a kinetic impactor into Didymos' moon, dubbed "Didymoon".
Source: NASA
Jim Green: One of the most interesting things about this WC9 from o2010 is that it went under the Earth and the Moon. I thought that all these objects had about Earth-like orbits near the plane of the solar system?
Lindley Johnson: The vast majority of them do it. They are close to what we call the ecliptic, which is the orbital plane of the Earth in the solar system, but there are many that are more orbital orbits. Their orbital plane intersects the orbital plane of the Earth at an angle we call the tilt. For this asteroid, its orbital inclination is 18 degrees, which is quite high. In fact, it gets closer to the orbit of Venus in the Sun and then returns to the asteroid belt beyond Mars. It probably appeared at a given moment following a gravitational encounter with Mars or Jupiter who placed it in this more steeply inclined orbit.
Jim Green: Another way to characterize not only near-Earth asteroids, but to get better orbital data, is through the radar. How does it work?
Lindley Johnson: We must first find them optically. We do not have enough radar capable of scanning the sky and finding these objects. We need to know the orbit enough so that we know when to expect the radar echo when it bounces off the object because we have to get it out of the noise. If we did not know where to look, we would not see it at all. So, that 's the first thing, and with enough energy bouncing off the object, we can do what they call radar imagery. It's a little different from optical imaging, but it's sort of the same principle, and we can get a good indication of the size of the asteroid, much more precisely than we can optically, and we can also measure the speed of rotation. The other thing that the radar does for us is that it determines whether these objects are binaries. We now know several binary asteroids – asteroids with a small moons encircling them – and all this was done by radar.
Jim Green: If they get close enough to the Earth and the radar hits them, you can see features on their surfaces
Lindley Johnson: C & # 39 is true, you can see craters or big rocks on their surface. It's really very interesting to see these radar images come back
Jim Green: What kind of damage would we expect if one of these larger objects was to cross the atmosphere and hit the Earth?
Lindley Johnson: It depends on the size of the object. This object, WC9 2010, is estimated between 50 and 120 meters. This could be a very damaging impact. For example, the object believed to have created Meteor Crater in Arizona is estimated to be only 50 meters away. So, it's at the lower limit of our estimate of the size of this object. NASA's WISE spacecraft has found most near-Earth asteroids larger than one kilometer, but many smaller and potentially dangerous objects remain undiscovered. “/>
NASA's WISE spacecraft found most near-Earth asteroids larger than one kilometer, but many smaller and potentially dangerous objects remain undiscovered.
Source: NASA / JPL-Caltech
Green Jim: What about objects of half this size, maybe 20 meters? Do they go to the surface?
Lindley Johnson: Pieces of them will certainly do it. It depends on how they are composed. If they are middle rock asteroids, they will disintegrate in the Earth's atmosphere. This is what happened recently in February 2013 over Chelyabinsk, Russia, when an object of about 20 meters entered the Earth's atmosphere around 9 o'clock. morning hours and exploded about 23 kilometers above the surface. The release of energy was equivalent to about half a megatonne of energy
Jim Green: The sooner we will have a warning about the impact, the better. Are there other approaches that we model or think about?
Lindley Johnson: There are at least some other techniques that we think are effective against an asteroid. A technique we used for modeling and development called a gravity tractor. If you have enough time and the asteroid is not too big, all you have to do is snuggle up with a spaceship and get away, and the mutual attraction between the spacecraft and the object, by gravity, slowly asteroid out of its natural orbit into a new orbit. We would simply use nature's tug rope, gravity, to pull the asteroid into a more benign orbit. It would take several months to several years to do it. But, the other good thing about this is that we can put it in the exact orbit we want. We could pull it a little bit and take action to see if we have changed the orbit enough, and if we have to do more, we will do it longer.
Jim Green: What do you think is the most common misconception in the media or in the press when they talk about these asteroids?
Lindley Johnson: I think it's something that There have been films about the impacts of asteroids, then all the asteroids that we announce are going to have a near approach, which triggers a worry: "Oh, will this asteroid touch us?" I do not think that they understand that once we have observations on the object and we can establish its orbit, it will stay in that orbit. He is not going to walk randomly in the solar system. All this is controlled by the laws of nature, the laws of orbital mechanics, and once you have established a stable orbit, you can predict where this object is going to be many years in advance. With our current modeling capabilities, and if we have enough observations, we can confidently predict the orbit of an asteroid 100 years later.
Lindley Johnson, NASA's first global defense officer, makes a presentation to representatives of NASA and FEMA – the Federal Emergency Management Agency – on the dangers of environmental impacts. asteroids.
Source: The Aerospace Corporation
Jim Green: One of the things I ask each of my guests in this program is to know how serious they were. In other words, what activity or event in their past has propelled them forward and allowed them to become the scientist and engineer that they are today. Lindley, how serious were you?
Lindley Johnson: I have had so many of them in my career. I think the Apollo program, when I was young, interested me in space and being part of the space program. In my turn, it has interested me to be part of the Air Force and to be part of the Air Force space program, where the opportunities that have been offered to me and the confidence that I have been witnessed have really helped me develop my program management skills. look forward to the future with these kinds of things. Then, I arrived at NASA 15 years ago and I am responsible for this Earth-based program and I work with the solar system exploration missions, which allowed me to become NASA's first global defense officer. 19659007] This story was provided by Astrobiology Magazine, an online publication sponsored by the astrobiology program of NASA. This version of the story published on Space.com. Follow us on @Spacedotcom Facebook or Google +
