Asteroid 2009 DD45: A Reminder of Planetary Vulnerability to Asteroids

Planetary vulnerability to asteroid 2009 DD45

The small asteroid 2009 DD45, discovered in February 2009, belongs to the Apollo family. Its diameter is estimated between 30 and 40 meters and its mass could reach 1 × 10⁸ kg. This type of celestial body is classified as a near-Earth object because it crosses Earth's orbit. On March 2, 2009, it passed only 63,500 km from Earth, or one-fifth the distance between Earth and the Moon. The probability that an asteroid of this size will strike Earth in a given year is estimated at about 1 in 1,000 to 1 in 5,000, which remains low but not negligible over long timescales.

N.B.: The Apollos are a family of near-Earth asteroids characterized by a semi-major axis greater than 1 AU and a perihelion less than 1.017 AU (Earth's distance from the Sun varies between 0.983 AU and 1.017 AU). This means their orbit crosses that of Earth, making them potentially dangerous in case of spatial-temporal coincidence. The Apollos include several notable objects such as (1862) Apollo, which gave its name to the group, (4179) Toutatis, (6489) Golevka, and (99942) Apophis, whose close approach in 2029 is particularly studied.

Types of near-Earth objects

NEAs (Near-Earth Asteroids) are classified into four main families according to their orbits:

• Apollos: semi-major axis a > 1 AU and perihelion q < 1.017 AU. Their orbit crosses that of Earth.
• Atens: semi-major axis a < 1 AU and aphelion Q > 0.983 AU. Their orbit is mainly inside Earth's but crosses it.
• Amors: semi-major axis a > 1 AU and perihelion 1.017 < q < 1.3 AU. They approach Earth without crossing its orbit.
• Atiras (or Apoheles): orbit entirely inside Earth's (Q < 0.983 AU).

This classification helps assess their potential danger to our planet and prioritize astronomical monitoring.

Table of some notable near-Earth asteroids

Asteroid 2009 DD45: Kinetic Energy and Impact Scenario

The kinetic energy of a small object ~35 m in diameter is given by the formula E = ½ m v². Assuming an average density of 3000 kg/m³ and an approach speed of 20 km/s, the asteroid's mass is about 6.7 × 10⁷ kg. The energy released in case of impact would reach about 3.2 megatons of TNT, or about 70 times the energy of the Hiroshima bomb.

N.B.: Scientists, engineers, and media use this unit (megatons of TNT) to report the potential danger of an impact to decision-makers or the general public. This allows comparison of natural impact vs human energy (weapons, industrial explosions).

Atmospheric and Geophysical Consequences

An atmospheric impact could cause an airburst, dispersing the energy as a destructive shockwave over several hundred kilometers. If the impact occurred at sea, a regional tsunami would be likely. On land, the shockwave and fireball would have effects comparable to a strategic nuclear weapon.

Comparative table of impact scenarios

Source: NASA CNEOS – Center for Near Earth Object Studies, ESA NEO Coordination Centre.