Asteroids are rocky fragments left over from the formation of the solar system about 4.6 billion years ago. Most asteroids orbit the sun in a belt between Mars and Jupiter. Scientists think there are probably millions of asteroids, ranging widely in size from hundreds of kilometres across to less than one kilometre wide.
Comets are relatively small, fragile, irregularly shaped bodies and, like asteroids, they are left over from the solar system formation process. Comets, however, are icy balls that form in the outer solar system. The icy surface is embedded with dust, grit and particles from space.
Meteors and Meteorites
While traveling through space, asteroids sometimes collide with each other and break up into smaller fragments. Comets shed dust as they roam the solar system. These ‘break ups’ result in numerous small particles and fragments, called meteoroids, which orbit the sun.
Most meteoroids are small and rocky. When one approaches Earth, it burns up as it goes through Earth’s atmosphere. Thus a meteor, or shooting star, is formed.
Some meteoroids survive passage through Earth’s atmosphere and hit the ground. These are called meteorites.
Near Earth Objects
Some asteroids and comets follow orbital paths that take them much closer to the sun — and therefore Earth — than usual.
If a comet or asteroid’s approach brings it to within 1.3 astronomical units of the sun, it is defined as a Near-Earth Object.
Small-sized (tens/hundreds of metres in diameter) NEOs deserve special attention, as they have the highest statistical likelihood of actually impacting the Earth.
Potentially Hazardous Objects
Some Near Earth Objects pass close enough to Earth and are large enough in size to warrant close observation. That’s because the gravitational tug of the planets could, over time, cause an object’s orbital path to evolve into an Earth-crossing orbit. This allows for the possibility of a future collision.
A Potentially Hazardous Object is an object larger than 140m and with an orbital intersection distance less than 7.5 million km.
Knowing the size, shape, mass, composition and structure of these objects helps determine the best way to divert one, should it have an Earth-threatening path.
Space Situational Awareness
Space Situational Awareness (SSA) refers to keeping track of objects in orbit and predicting where they will be at any given time. SSA allows monitoring of objects and natural phenomena that could harm satellites in orbit or infrastructure on the ground. This includes the monitoring of NEO that could potentially impact Earth and cause damage.
Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe. It is the practice and study of observing celestial objects with the use of telescopes and other astronomical instruments.
This marks a difference with theoretical astronomy, which calculates the measurable implications of physical models.
Responsible Research and Innovation
Responsible Research and Innovation is an attempt to systematise and promote the inclusion of social, environmental and ethical issues and procedures into the whole research and innovation chain. The aim is to minimise the potential risk that emerges from R&I, anticipate the consequences of R&I and to boost potentially positive impacts.