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The Asteroid and Comet Impact Hazard

Panorama of the Barringer Crater (Meteor Crater) near Winslow, Arizona. The crater, which has a diameter of 1.2 km and a depth of 180 m, was formed by the impact of a metallic asteroid with a diameter of about 50 m some 50,000 years ago. © Alan Harris, DLR, June 2009.

The largest reservoir of asteroids is the main asteroid belt between the orbits of Mars and Jupiter. As a result of subtle thermal effects and the very strong gravitational field of Jupiter, small main-belt asteroids can drift into the inner Solar System. As a result, there exists a population of “near-Earth asteroids” (NEAs) which poses a small but real hazard to our civilization.

Artist’s impression of an asteroid impacting the Earth at night. Credit: David Hardy.

NEAs have orbits that can cross the orbit of the Earth. Collisions of asteroids with the Earth have taken place frequently over geological history. Comets can also collide with the Earth but the risk of a comet impact is thought to be much lower than that of an NEA impact, although given the potentially high relative velocities the effects in the case of a comet impact could be much more devastating.

The phenomenon of collisions in the history of our Solar System is a very fundamental process, having played the major role in forming the planets we observe today. There is no doubt that major collisions of asteroids and comets with the Earth will continue to occur in the future.

Density of oceanic water, 20 seconds after impact of a 1 km diameter asteroid into 5.5 km deep ocean. The model results give an impression of the extent of the transient water cavity and the mushroom-like chaotic structure inside containing the debris of the asteroid. Units on the axes are km. Credit: D. de Niem, DLR.

Can we protect our civilization from the next major impact? Various initiatives are being taken by space agencies, including ESA and NASA, and research groups around the world to identify potential future impactors, investigate their physical characteristics, and develop strategies to mitigate the risk. The DLR Department of Asteroids and Comets contributes to this effort with a number of programs:

• Contributions to the design, development and execution of relevant space missions, such as Rosetta, Dawn, MarcoPolo und AIDA.
• Observations of near-Earth asteroids with space-based and ground-based telescopes to characterize their physical properties.
• The maintenance of a database (EARN) of near-Earth asteroids’ physical properties, such as size, shape, rotation state, taxonomic class, etc.
• The development of models, e.g. thermal models, of asteroids and comets to facilitate the interpretation of observational data.
• Modelling the effects of impacts on the Earth.
  

The orbiting spacecraft, Sancho, of the proposed Don Quijote mission observes the effects of the impact of the second spacecraft, Hidalgo, on a small NEA. Don Quijote has been chosen by the ESA Near-Earth Object Mission Advisory Panel as a feasible and promising mission concept to test the viability of the kinetic impactor approach to NEA deflection. Credit: ESA.