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List of Earth-crossing asteroids

From Wikipedia, the free encyclopedia

Diagram showing different asteroid paths. The yellow band marks the Earth's orbit; the red line marks the asteroid's path.
Outer-grazer(†): middle, bottom
Crosser: right, bottom
Close approach trajectory of 2004 FH in the Earth–Moon system
Flyby of the near-Earth asteroid 2004 FH in March 2004. The other object that flashes by is an artificial satellite. Images were by Stefano Sposetti and composite by Raoul Behrend of Geneva Observatory

An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earth's orbit.[1] The known numbered Earth-crossers are listed here. Those Earth-crossers whose semi-major axes are smaller than Earth's are Aten asteroids; the remaining ones are Apollo asteroids. (See also the Amor asteroids.)

An asteroid with an Earth-crossing orbit is not necessarily in danger of colliding with Earth. The orbit of an Earth-crossing asteroid may not even intersect with that of Earth. This apparent contradiction arises because many asteroids have highly inclined orbits, so although they may have a perihelion less than that of Earth, their paths can never cross. An asteroid for which there is some possibility of a collision with Earth at a future date and which is above a certain size is classified as a potentially hazardous asteroid (PHA). Specifically, an asteroid is a PHA if its Earth minimum orbital intersection distance (MOID) is <0.05 AU and its absolute magnitude is 22 or brighter.[2] The concept of PHA is intended to replace the now abandoned strict definition of ECA (Earth-crossing asteroid) which existed for a few years. Determining if an asteroid was an ECA required calculation of its orbits millennia into the future, including planetary gravitational perturbations, to assess whether a collision with Earth was possible and this has proved to be impractical.[3]

Having a small MOID is not a guarantee of a collision. On the other hand, small gravitational perturbations of the asteroid around its orbit from planets that it passes can significantly alter its path. For instance, 99942 Apophis will approach Earth so closely in 2029 that it will get under the orbit of the Earth's geostationary satellites.[4]

Of the Earth-crossing asteroids, 3753 Cruithne is notable for having an orbit that has the same period as Earth's.

List

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Notes: † outer-grazer

See also

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References

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  1. ^ Report of the Task Force on potentially hazardous Near Earth Objects, p49, Department of Trade and Industry (UK), September 2000, Pub 4990/5k/9/00/NP.URN00/1041, retrieved online Archived 7 March 2009 at the Wayback Machine, 16 May 2009.
  2. ^ "Near Earth Object Program", National Aeronautics and Space Administration, retrieved online 3 May 2009.
  3. ^ Brian G. Marsden, "Press Information Sheet:Potentially Hazardous Asteroids", Harvard-Smithsonian Center for Astrophysics, retrieved online Archived 23 April 2012 at the Wayback Machine 3 May 2009.
  4. ^ Dr. Tony Phillips, "Friday the 13th, 2029", Science@NASA, retrieved online Archived 24 March 2010 at the Wayback Machine May 3, 2009.
  5. ^ MPEC 2020-Q51 : 2020 QG Archived 24 August 2020 at the Wayback Machine, Minor Planet Center, https://www.minorplanetcenter.net/mpec/K20/K20Q51.html Archived 24 August 2020 at the Wayback Machine, 17 August 2020, accessed 17 August 2020.
  6. ^ Newly-discovered asteroid ZTF0DxQ passed less than 1/4 Earth diameter yesterday, making it the closest-known flyby that didn't hit our planet. Archived 9 January 2021 at the Wayback Machine, Tony Dunn, 17 August 2020.
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