Impact event. Artist's impression of a major impact event. The collision between a planet and an asteroid a few kilometers in diameter may release as much energy as several million nuclear weapons detonating simultaneously. An impact event is a collision between celestial objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or meteoroids and have minimal impact. When large objects impact terrestrial planets like the Earth, there can be significant physical and biospheric consequences, though atmospheres mitigate many surface impacts through atmospheric entry. Impact structures are dominant landforms on many of the System's solid objects and present the strongest empirical evidence for their frequency and scale.
Impact events appear to have played a significant role in the evolution of the Solar System since its formation. Impacts and the Earth[edit] What would happen if a large object hit the Earth? By the end of 2003, astronomers had discovered about 400 asteroids whose orbits crossed the Earth's. These are prime candidates for eventual impacts with the Earth in the distant future. The largest of these is called 1627 Ivar and is 8 kilometers across and contains 1 trillion tons of mass. The asteroid Ida in the image below gives you some idea of what these huge rocks look like! The smaller an asteroid, the more numerous they are, is the general rule of thumb for our solar system.
According to the best estimates, objects 3 meters across impact the Earth and deliver about 2 kilotons of TNT of energy. Objects 100 meters across collide with the Earth every few hundred years and deliver about 2 Megatons of TNT equivalent. A 1 kilometer-sized object impacts the Earth every million years or so and delivers about 100,000 Megatons of TNT. The consequences of asteroidal impacts depend on the size of the asteroid. Return to Ask the Astronomer. What would be the environmental effects if the earth collided with a large comet? For instance, what would the climate be like afterward, and what forms of life would be most likely to survive?
David Morrison of the National Aeronautics and Space Administration's Ames Research Center, replies: "The effects of an impact on the earth depends critically on the size, and hence the energy, of the impact. For example, a comet less than 100 meters across will explode high in the atmosphere and probably do no harm whatsoever. If the comet is 10 kilometers across or larger (that is, if the impact carries an energy of more than about 100 million megatons), the resulting global environmental damage will be so extensive that it will lead to a mass extinction, in which most life forms die.
This is what happened 65 million years ago at the end of the Cretaceous era, when the dinosaurs went extinct. The environmental consequences of a giant impact take many forms; the worst effects come from a global firestorm ignited by backfalling impact debris, and from a global pall of darkness that lasts for many months due to dust suspended in the stratosphere. " Gerrit L. Provisional designation in astronomy. Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery.
The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calculated. In the case of minor planets, so many have been discovered that many will never be named by their discoverers. Minor planets[edit] The first element in a minor planet's provisional designation is the year of discovery, followed by two letters and, optionally, a number. The first letter indicates the half-month of the object's discovery within that year —"A" denotes discovery in the first half of January, "D" is for the second half of February, "J" is for the first half of May ("I" is not used), and so on until "Y" for the second half of December. The first half is always the 1st through to the 15th of the month, regardless of the numbers of days in the second "half".
Further examples[edit] Survey designations[edit] Comets[edit] See also[edit]