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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 certain orbital zones from which they may be ejected under the influence of Jupiter 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 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 very fundamental, having played the major role in forming the planets we observe today. It is an irrefutable scientific fact that major collisions of asteroids and comets with the Earth will continue to occur at irregular, unpredictable intervals 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 against impacts. 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, AsteroidFinder, Don Quijote, ASTEX.
• Observations of near-Earth asteroids with space-based and ground-based telescopes, such as the Spitzer Space Telescope, NASA Infrared Telescope Facility, with the goal of characterizing their physical properties.
• The maintenance of a database of near-Earth asteroid physical properties, such as size, shape, rotation state, taxonomic class, etc. (EARN). 
• The development of models, e.g. thermal models, of asteroids and comets to facilitate the interpretation of observational data.
• Studies and modeling of 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.

• Participation of Department staff in high-level committees and working groups of space agencies and other organizations, e.g. ESA Near-Earth Object Mission Advisory Panel, United Nations Committee on the Peaceful Uses of Outer Space Action Team on Near-Earth Objects, the International Astronautical Federation Technical Committee on Near-Earth Objects.
• The supervision of doctoral students working in relevant research fields.
• Public outreach: contributions to responsible TV, radio, and press coverage of developments in the field; lectures and talks at universities and public events, and talks to school and other interested groups.