National Academies Press: OpenBook

Finding Hazardous Asteroids Using Infrared and Visible Wavelength Telescopes (2019)

Chapter: 7 Impact Hazards Not Explicitly Considered by the George E. Brown, Jr. Act

« Previous: 6 The Role of Archival Data
Suggested Citation:"7 Impact Hazards Not Explicitly Considered by the George E. Brown, Jr. Act." National Academies of Sciences, Engineering, and Medicine. 2019. Finding Hazardous Asteroids Using Infrared and Visible Wavelength Telescopes. Washington, DC: The National Academies Press. doi: 10.17226/25476.
×
Page 45
Suggested Citation:"7 Impact Hazards Not Explicitly Considered by the George E. Brown, Jr. Act." National Academies of Sciences, Engineering, and Medicine. 2019. Finding Hazardous Asteroids Using Infrared and Visible Wavelength Telescopes. Washington, DC: The National Academies Press. doi: 10.17226/25476.
×
Page 46

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

7 Impact Hazards Not Explicitly Considered by the George E. Brown, Jr. Act Near Earth objects (NEOs) are not the only objects in space that can potentially impact Earth. As understanding of the solar system has advanced and more telescopic observations have been made, scientists have identified other objects that could pose an impact hazard and are also of scientific interest. These are summarized in this chapter for the sake of completeness. JUPITER‐FAMILY AND LONG-PERIOD COMETS It is possible for comets from the outer solar system to cross Earth’s orbit.  Jupiter-family comets (JFCs). Referred to as short-period comets with orbital periods less than 20 years—they are a source region for bodies that evolve to become NEOs.  Long-period comets (LPCs). Take more than 200 years to orbit the Sun. They originate from the Kuiper belt. LPCs can be NEOs.  Isotropic comets, which encompass LPCs and Halley-type comets (HTCs), generally have periods greater than 20 years and have an arbitrary boundary in orbital period at 200 years. All of these comets originate in the Oort Cloud. The contribution of multiple NEO source regions is shown in Figure 7.1. Most NEOs come from the inner and central main belts; few come from the outer main belt or JFCs. For LPC and HTC populations, the goal should be to know the number-flux density of such comets (i.e., the number of comets per unit time per size bin) through near-Earth space, because the absolute number is huge and it is extremely difficult to identify them all individually, because the vast majority are too distant. FIGURE 7.1 The main near Earth asteroid source regions are two asteroid groups (Hungaria and Phocaea), four main-belt escape routes (via the ν6 secular resonance; 3:1, 5:2, and 2:1 mean-motion resonances with Jupiter), and the Jupiter-family comets (JFCs). SOURCE: G.H. Stokes et al., 2017, Report of the Near-Earth Object Science Definition Team: Update to Determine the Feasibility of Enhancing the Search and Characterization of NEOs, NASA Science Mission Directorate, https://cneos.jpl.nasa.gov/doc/2017_neo_sdt_fi nal_e-version.pdf, p. 11. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 7-1

OBJECTS WITH DIAMETERS LESS THAN 140 METERS The George E. Brown, Jr. Near Earth Object Survey Act specified 140 meters as the lower limit for the NEO survey requirements in the 2005 NASA Authorization Act. Objects smaller than 140 meters are being found and catalogued in existing visible surveys. Although the completeness level of these surveys is low, it is important to discover and catalogue these objects. The 2013 Chelyabinsk fireball and the December 2018 fireball that exploded over the western Pacific Ocean had energies of 440 and nearly 200 kilotons, respectively. The Chelyabinsky fireball resulted in major damage to buildings. Both meteoroids were estimated to be significantly smaller than 140 meters in diameter (see Figure 7.2). INTERSTELLAR OBJECTS Interstellar objects, of which only one has been discovered in the history of astronomy, can be treated as part of the LPC population and are a miniscule fraction thereof.  The probability of an impact by an LPC is only 1 percent that of a NEO impact.1  The energy of an Earth impact would be high, because velocity at Earth orbit would be high, and energy is proportional to square of velocity and is calculated at ~30 percent larger than a typical NEO impact. Definitions of these types of NEOs are included in this report for the sake of completeness and to explain why they should be considered within the context of the George E. Brown Act requirement, although they are not a driver in meeting the requirement. FIGURE 7.2 Fireballs reported by U.S. government sensors between April 15, 1988, and March 15, 2019. The 2013 Chelyabinsk fireball is visible at upper center right, and the December 2018 Bering Sea event is at upper right. These objects were all well below 140 meters in diameter. SOURCE: NASA Jet Propulsion Laboratory, Center for Near Earth Object Studies, “Fireballs Reported by U.S. Government Sensors,” https://cneos.jpl.nasa.gov/fireballs, accessed March 15, 2019; courtesy NASA/JPL-Caltech. 1 G.H. Stokes, et al., 2017, Report of the Near-Earth Object Science Definition Team: Update to Determine the Feasibility of Enhancing the Search and Characterization of NEOs, NASA Science Mission Directorate. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 7-2

Next: Appendixes »
Finding Hazardous Asteroids Using Infrared and Visible Wavelength Telescopes Get This Book
×
Buy Paperback | $45.00
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

Near Earth objects (NEOs) have the potential to cause significant damage on Earth. In December 2018, an asteroid exploded in the upper atmosphere over the Bering Sea (western Pacific Ocean) with the explosive force of nearly 10 times that of the Hiroshima bomb. While the frequency of NEO impacts rises in inverse proportion to their sizes, it is still critical to monitor NEO activity in order to prepare defenses for these rare but dangerous threats.

Currently, NASA funds a network of ground-based telescopes and a single, soon-to-expire space-based asset to detect and track large asteroids that could cause major damage if they struck Earth. This asset is crucial to NEO tracking as thermal-infrared detection and tracking of asteroids can only be accomplished on a space-based platform.

Finding Hazardous Asteroids Using Infrared and Visible Wavelength Telescopes explores the advantages and disadvantages of infrared (IR) technology and visible wavelength observations of NEOs. This report reviews the techniques that could be used to obtain NEO sizes from an infrared spectrum and delineate the associated errors in determining the size. It also evaluates the strengths and weaknesses of these techniques and recommends the most valid techniques that give reproducible results with quantifiable errors.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!