page_title: Asteroid impact avoidance
section_title: Deflection efforts
hierarchical_section_title: Asteroid impact avoidance / Deflection efforts
caption_attribution_description: English: New Map Shows Frequency of Small Asteroid Impacts, Provides Clues on Larger Asteroid Population This diagram maps the data gathered from 1994-2013 on small asteroids impacting Earth's atmosphere IMAGE: This diagram maps the data gathered from 1994-2013 on small asteroids impacting Earth's atmosphere to create very bright meteors, technically called "bolides" and commonly referred to as "fireballs". Sizes of red dots (daytime impacts) and blue dots (nighttime impacts) are proportional to the optical radiated energy of impacts measured in billions of Joules (GJ) of energy, and show the location of impacts from objects about 1 meter (3 feet) to almost 20 meters (60 feet) in size. DESCRIPTION: A map released today by NASA's Near Earth Object (NEO) Program reveals that small asteroids frequently enter and disintegrate in the Earth's atmosphere with random distribution around the globe. Released to the scientific community, the map visualizes data gathered by U.S. government sensors from 1994 to 2013. The data indicate that Earth's atmosphere was impacted by small asteroids, resulting in a bolide (or fireball), on 556 separate occasions in a 20-year period. Almost all asteroids of this size disintegrate in the atmosphere and are usually harmless. The notable exception was the Chelyabinsk event which was the largest asteroid to hit Earth in this period. The new data could help scientists better refine estimates of the distribution of the sizes of NEOs including larger ones that could pose a danger to Earth. Finding and characterizing hazardous asteroids to protect our home planet is a high priority for NASA. It is one of the reasons NASA has increased by a factor of 10 investments in asteroid detection, characterization and mitigation activities over the last five years. In addition, NASA has aggressively developed strategies and plans with its partners in the U.S. and abroad to detect, track and characterize NEOs. These activities also will help identify NEOs that might pose a risk of Earth impact, and further help inform developing options for planetary defense. The public can help participate in the hunt for potentially hazardous Near Earth Objects through the Asteroid Grand Challenge, which aims to create a plan to find all asteroid threats to human populations and know what to do about them. NASA is also pursuing an Asteroid Redirect Mission (ARM) which will identify, redirect and send astronauts to explore an asteroid. Among its many exploration goals, the mission could demonstrate basic planetary defense techniques for asteroid deflection.
context_page_description: Asteroid impact avoidance comprises a number of methods by which near-Earth objects could be diverted, preventing destructive impact events. A sufficiently large impact by an asteroid or other NEOs would cause, depending on its impact location, massive tsunamis or multiple firestorms, and an impact winter caused by the sunlight-blocking effect of placing large quantities of pulverized rock dust, and other debris, into the stratosphere.
  A collision 66 million years ago between the Earth and an object approximately 10 kilometres wide is thought to have produced the Chicxulub crater and the Cretaceous–Paleogene extinction event, widely held responsible for the extinction of most dinosaurs.
  While the chances of a major collision are low in the near term, there is a certainty that one will happen eventually unless defensive measures are taken. Astronomical events—such as the Shoemaker-Levy 9 impacts on Jupiter and the 2013 Chelyabinsk meteor, along with the growing number of objects on the Sentry Risk Table—have drawn renewed attention to such threats.
  In 2016, a NASA scientist warned that the Earth is unprepared for such an event.
context_section_description: According to expert testimony in the United States Congress in 2013, NASA would require at least five years of preparation before a mission to intercept an asteroid could be launched.  In June 2018, the US National Science and Technology Council warned that America is unprepared for an asteroid impact event, and developed and released the "National Near-Earth Object Preparedness Strategy Action Plan" to better prepare.
  Most deflection efforts for a large object require from a year to decades of warning, allowing time to prepare and carry out a collision avoidance project, as no known planetary defense hardware has yet been developed. It has been estimated that a velocity change of just 3.5/t × 10⁻² m·s⁻¹ (where t is the number of years until potential impact) is needed to successfully deflect a body on a direct collision trajectory. In addition, under certain circumstances, much smaller velocity changes are needed. For example, it was estimated there was a high chance of 99942 Apophis swinging by Earth in 2029 with a 10⁻⁴ probability of passing through a 'keyhole' and returning on an impact trajectory in 2035 or 2036. It was then determined that a deflection from this potential return trajectory, several years before the swing-by, could be achieved with a velocity change on the order of 10⁻⁶ ms⁻¹.
  An impact by a 10 kilometres (6.2 mi) asteroid on the Earth has historically caused an extinction-level event due to catastrophic damage to the biosphere. There is also the threat from comets entering the inner Solar System. The impact speed of a long-period comet would likely be several times greater than that of a near-Earth asteroid, making its impact much more destructive; in addition, the warning time is unlikely to be more than a few months. Impacts from objects as small as 50 metres (160 ft) in diameter, which are far more common, are historically extremely destructive regionally (see Barringer crater).
  Finding out the material composition of the object is also helpful before deciding which strategy is appropriate. Missions like the 2005 Deep Impact probe have provided valuable information on what to expect.
  REP. STEWART: ... are we technologically capable of launching something that could intercept [an asteroid]? ... DR. A'HEARN: No. If we had spacecraft plans on the books already, that would take a year ... I mean a typical small mission ... takes four years from approval to start to launch ...
  — Rep. Chris Stewart (R, UT) and Dr. Michael F. A'Hearn, 10 April 2013, United States Congress
caption: Frequency of small asteroids roughly 1 to 20 meters in diameter impacting Earth's atmosphere.
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