May 28, 2020

Near Earth Objects: Mitigating the Threat.

(Editor’s Note: What follows is a scenario/article along with an original lesson plan re-written for a blog format).

Eventually, it had to happen. With scant warning, the announcement is made that a large space rock is inbound to strike Earth and is only weeks away. The news largely takes the public by surprise; this is the big one, an extinction class event. People are exasperated to learn that little can be done to deflect the large impactor; all that remains is for scientists to predict the precise impact location and for world organizations to attempt evacuations so that some of humanity might survive…

The above scenario might be terrifying, but could also happen tomorrow. The plot of many a bad made-for-the SyFy channel movie, most are surprised to learn that we don’t already have Bruce Willis waiting on the launch pad to go after that killer asteroid with our name on it. The complexity of deflecting a Near Earth Object (NEO) is tougher than one might think; simply “blowing it to smithereens” might incur problems of its own.

To be sure, the inner solar system is a dangerous place. One only has to look at the surface of our battered Moon to see a testament to the ancient volley that has taken place. Impacts such as the Shoemaker-Levy 9 fragments hitting Jupiter and meteor crater in Arizona also serve as reminders that we are not immune.

We believe a proactive defense of the Earth would be two fold; one of detection and elimination. Detection we can and are already doing to some extent tonight and every night. Already, systems such as LINEAR and PanSTARRS patiently survey the night sky, looking for new objects. Soon, even larger systems such as the Large Synoptic Survey Telescope will be in service, photographing the sky down to faint magnitudes and generating terabytes of data nightly. Dedicated amateurs are also in the fray, calling to the fore backyard instruments that would make a moderate-sized university blush. And desktop observers will have access to these mountains of data, enabling them to comb through these images before bedtime. Still, the programs dedicated to searching for NEO’s and potential threats are shoestring, and currently employ less staff than the cast of a given seasons of Big Brother

But like any threat, early detection will be the key to effective mitigation. If we know about an incoming rock years ahead of time, we just might be able to do something about it. Worst case would be an impact with no warning, although this is becoming less likely. Already, there have been some signs that detection techniques are becoming more effective. For example, in late 2008, astronomers attached to the Catalina Sky Survey detected the 3-meter asteroid 2008 TC3 before it struck the next morning in the Nubian Desert. A 24 hour margin may not seem like much, but it was a first. We need a truly comprehensive survey of everything that’s out there to make mitigation effective.

So, what about proactive defense? Ironically, “nuking” an asteroid might be the worst thing we can do. At best, it would have little effect, as the amount of imparted kinetic energy evolved would be minuscule compared to that of a large inbound rock; at worst, we could be facing a “buckshot” of incoming material instead of one large impactor.

Some innovative ideas to move a would-be hazard would be to land several automated mass drivers on the asteroid to begin a gentle push against the body. Another would be to coat the asteroid with a reflective material and allow the Yarkovsky Effect to utilize solar photon pressure to alter the orbit of the asteroid. Probably the most effective would be to park a large mass next to the asteroid and allow it to ‘tractor’ it via gravity into a new orbit.

Of course, all of these efforts would require large lead time (that’s where early detection comes into play) and technologies that we don’t yet have in place. It’s rather embarrassing to realize that we haven’t had a capability to lift large payloads beyond low Earth orbit for several decades, and such ability may be a ways off. All of the above ideas involve the development of such skills as rendezvous and landing (or do you say ‘docking’?) with an asteroid and studying just what these bodies are like and what they’re composed of. Unmanned missions such as EPOXI and the Hayabusa sample return mission are steps in the right direction. Later this year, NASA’s DAWN mission will begin reconnaissance of Vesta and then move on the Ceres.

Of course, a manned mission to a Near Earth Asteroid would be immensely beneficial, as well as raise public consciousness (and hopefully, funding). We could land, practice deflection skills, and study these curious beasts. An asteroid mission would also be a good stepping stone in getting us into manned interplanetary travel. The Obama administration has taken some steps in this direction in the past year; it remains to be seen if we have the resolve to commit to such a goal over the long term.

One such tantalizing target could be the asteroid 99942 Apophis. Discovered in 2004, this asteroid caused a brief stir when it was discovered to have a close pass on April (Friday!) the 13th, 2029 and again in 2036. Later observations lowered its rating on the Torino scale to mostly harmless, but a mission in 2029 could be feasible if the technology is in place. Such a mission could plant a transmitter on the surface for more accurate future tracking of Apophis.

One such organization that is taking a grass-roots approach to NEO hazard mitigation is the B612 Foundation. Their stated goal is to “significantly alter the orbit of an asteroid in a controlled manner by 2015.” Co-founded by astronaut Rusty Schweickart, this endeavor definitely has the ear of Congress.

A word of warning about these technologies may be in order. The ability to deflect an incoming asteroid also means that a state or organization will also have the ability to move a large rock into harm’s way. A remote threat, to be sure, but if history tells us anything, any technology that is possible will eventually be utilized, however grand or terrible. What’s needed is a truly species-wide effort to put such a technology in place, something we’ve yet to really do. Such an effort would allow for the free exchange of information and effective safeguards, and Bruce and his bad dialogue can just stay home to boot… a re-write to the tale with a happier ending could be…

The doomsday asteroid was detected years ahead of time by a network of large orbiting and lunar farside-based observatories. Soon, several automated gravity tractors loitering past the orbit of Saturn began their month’s long trek, matching orbits with the potential impactor and slowly using their mass to drag the rock into a new orbit. The citizens of the Earth are simply treated to a good show, as a naked eye asteroid drifts silently through the night sky…

Plan Title- Hazards Posed By Near Earth Objects & Orbital Debris: the Lesson Plan.

Define Learners- This unit will be designed for 9th-12th grade High School students as part of an overall Astronomy or Earth Science course. Our hypothetical school is Fort Mapleton, a northern Maine school in a primarily agricultural rural community.  The course will be a mix of individual and group activity. The night time observation activities could be adapted for an urban or suburban setting, although less meteors and satellites are likely to be seen due to light pollution.


A. Unifying Themes; Students apply the principles of systems, models, constancy and change, and scale in science and technology.

9-Diploma: Students apply an understanding of systems to explain and analyze man-made and natural phenomena.

Chapter 132

9-Diploma: Students explain the physical changing nature of our solar system and how it developed.

Topic- The main topic of this lesson plan is to demonstrate the threat posed by Earth-crossing asteroids, comets, and manmade space debris in an engaging way and show how our place the cosmos is connected to our survival as a species. By analyzing our space environment and discussing possible methods of tracking and elimination, students will come to understand how our knowledge has evolved and continues to grow. The objective will also demonstrate hands on observation skills for how amateurs and professionals contribute to our body of knowledge and lessons learned.

Curriculum Links- In a prior unit, students studied the impact and formation of the solar system, as well as a brief history of astronomy and how our knowledge evolved as to our place in the cosmos. This unit will further show how our knowledge continues to evolve via a very timely topic of direct influence.


A. Students will be able to indentify current threats and potential hazards to the earth posed by NEOs.

B. Students will understand the links between planetesimals and the early formation of the Solar System.

C. Students will problem solve the dilemma of mitigating the threat posed by NEOs.

D. Students will analyze methods past, present and future for tracking NEOs.


-Meteoracle software: used for real time tracking of meteor showers. Available at:

- Orbitron: An excellent real-time satellite tracking program. Available at:

- Rulers, Protractors, Compasses

- Pencil and Notepad

- Calculator

- Shoe Box (for constructing a “Cardboard blink comparator”)

- 5mw green laser pointer (to demonstrate occultations…for use by the instructor, only!)

Time- Time anticipated for unit block; 5 days, 60 minutes per day.

Scope and Sequence-

Day One: Concept: Introduction to topic: Purpose.

I. Why do we study Near Earth Objects? Read “What if…” from Dr Phil Plait’s: Death from the Skies!

Chapter I.

II. What are the hazards posed?

III. Student groups discuss the dangers posed and the cultural perceptions.

IV. Graph illustration depicting the typical path of an Earth crossing asteroid or comet.

V. Video clips demonstrating the common misconceptions of NEO’s from Hollywood (Armageddon, Deep Impact, When Worlds Collide, Meteor, etc) what did they get wrong and why? What did Hollywood get right?

Homework: Students write one brief essay of how they think an NEO threat may unfold.

Day Two: Concept: Historical background; How do we know what we know?

I. Read and discuss early ideas of comets and asteroids.

II. How did events in history show that meteors had a demonstrable impact on the history of Earth?

References discussed;

Baum, R. & Sheehan, W. (1997). In search of planet Vulcan. Cambridge, MA: Basic Books.

-       A look at how astronomers discovered the outer planets and asteroids such as Ceres.

Chaikin, Andrew. (January, 1984). Target: Tunguska. Sky & Telescope Magazine. January, 1984. Volume 67, Number 8. Sky Publishing Corp. Cambridge, MA.

-       An Analysis of the Tunguska Event.

Brunton, Dan. (February 2006). Frequently Asked Questions about the Collision of Comet Shoemaker- Levy 9 with Jupiter. Texas A&M University. Retrieved March 1st, 2009 from the World Wide Web: (If URL does not work, follow Link)

-       A look at the massive energy released by the shoe-maker Levy 9 impact on Jupiter.

Sanderson, Richard (November, 1998). The night of raining fire. Sky & Telescope Magazine. November, 1998. Volume 96, Number 5. Pg 30 Sky Publishing corp. Cambridge, MA.

-       A look at the Leonid meteor shower of 1833.

III. How is a comet or asteroid discovery reported? If possible, have an amateur actively involved in comet hunting talk.

IV. Have students construct a “card-board blink comparator” to demonstrate how Clyde Tombaugh discovered Pluto.

V. With a laser pointer and a darkened room, illustrate how astronomers can judge an asteroids profile as it occults a star.

Homework: weather willing, observe the night sky for meteors. Use Meteoracle to aid your search. Question…why do you see more meteors in the morning hours than the evening?

Day Three: Concept: The threat posed by NEO’s and plans to mitigate them.

I. Illustrate the previous days’ question by showing the earth in motion around the Sun and intersecting a meteor stream.

II. The two pronged approach; how do we detect asteroids and comets?

III. Discuss; what if anything can be done to protect the Earth?

References used:

Rayl, A.J.S. (November, 2005). Hayabusa: Got Sample? Yes! Planetary News: Asteroids and Comets. The Planetary Society Online. Retrieved March 2nd, 2009 from the World Wide Web:

-       Illustrates our abilities to rendezvous with an asteroid.

-       No Author, (January, 2006). The Grasslands Observatory. Retrieved February 28, 2009 form the World Wide Web:

-       Shows an example of an amateur astronomer who actively tracks and discovers asteroids.

Homework: Can you think of an appropriate method for classifying hazards?

Day Four: Concept: Analysis of an NEO.

I. Apophis: a case study.

II. Students are introduced to and discuss the merits/limitations of the Torino Scale.  Where would events such as Tunguska or Shoe-maker Levy (were it to impact Earth) fall on the scale?

III. Discuss the discovery and approach of Apophis in 2029. What could be learned from a mission to this NEO?

References Used:

Bowell, Ted & Koehn (July 2004). About LONEOS. The Lowell Observatory Home page. Retrieved March 2nd, 2009 form the World Wide Web:

-       Discusses a current NEO search program.

Schweickart, Russell. (October, 2007). Testimony before House Committee on Science and Technology. B612 Foundation.

-       A proposal by the B612 foundation to move a threatening NEO.

Don Yeomans, Steve Chesley, and Paul Chodas. (December, 2004). Near-Earth Asteroid 2004 MN4 reaches highest score to date on hazard scale. NASA Near Earth Object Program Office. Retrieved March 4th 2009 from the World Wide Web:

-       A report on the approach of Apophis.

IV. How are will filing up low Earth Orbit with debris?

Homework: Use Orbitron to track an earth orbit satellite… (Again, weather willing… if its cloudy, tracking will be done virtually) How do satellites’ orbits evolve over time? Why?  Why are satellites visible at dawn and dusk?

Day Five: Concept: How does studying NEOs relate to the formation of the early solar system?

I. Students divide into teams to propose methods of asteroid deflection and mitigation.

II. Illustrate how the accumulation of planetesimals led to the formation of planets and that NEO’s are left over from this early formation.

III. Emphasize the evolving methods (automated searches, satellites, probes such as Deep Impact, etc.) on our understanding of how to deal with these threats.

IV. Review: Students will discuss how our understanding of the NEO threat has evolved, and what steps are being taken to mitigate the danger.

V. Summative Assessment: Students will construct a model or PowerPoint demonstrating the hazards of NEO’s and the evolution of our knowledge as well as innovative techniques in dealing with them. Models should demonstrate knowledge of the concepts as well as vocabulary (asteroid, Kuiper belt, Oort cloud, etc.) discussed in the module.

Supplementary Materials-

Day One: Edited video clips of Hollywood asteroid/comet disaster movies, along with orbital outlines of known NEO’s and short period comets.

Day Two: Illustrations of telescopes and techniques used to discover Comets and asteroids throughout history.

Day Three: Depictions of proposed methods of asteroid deflection.

Day Four: Chart of the Torino Scale, along with a graphic depicting the relative amount of space junk in orbit over time.

Day Five: Teacher version of PowerPoint illustrating the planetesimal hypothesis.

Assessment of Students- Daily formative assessments will occur via classroom participation as well as completion of nightly assignments. Students who struggle with concepts will identify them via hands on observation (such as meteor showers or satellite tracking). A final summative evaluation will enforce lessons learned.

Evaluation of Lesson- The key concept for students to take away from this module is how our Solar System continues to interact with us and how it has shaped our place in it. The completion of a model or PowerPoint will reveal knowledge of skills we use to track and identify NEO’s, and a final evaluation will judge knowledge gained on the evolving threat of NEO’s, manmade space debris, and its contribution to the origin of the Solar System.

Thanks, and let us know of tales of any uses of this lesson plan in the field!


  1. [...] course, it’s always handy to know just how well these things are put together, should we need to deflect one. Their formation and composition may also provide clues to the formation of the primordial [...]

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