"Rocks From Space!!"
A talk by Dr. Jonti Horner from University of NSW at the Macarthur Astronomy Forum.
The April guest speaker was Jonti Horner and here are some of his slides:
This was a very well-structured and well-illustrated talk, which started with video of the recent large meteriorite explosion over Chelyabinsk in Russia.
Due to the excellent video captures of this event, astronomers were able to accurately calculate that the object was about 17 metres in diameter; weighed 10 kilotonnes; travelled at 30 km/sec on atmospheric entry; slowed to 15 km/sec at the time of the exposion at a height of 20 km; its origin was the asteroid belt; and the explosion was around 30 times that of the Hiroshima bomb. Amazing stuff!
We then roamed through the solar system, looking at:
- the various types of objects - from dwarf planets; Trans-Neptunian objects; asteroids; trojans; long period comets; short period comets; and small rocks - and at
- the huge reservoirs of these objects located around the Solar System - in the Asteroid belt (between Mars and Jupiter); along Jupiter's orbit; in the region beyond Neptune; in the the Oort Cloud; and in the inner Solar System where they become a threat as Near Earth Objects.
These rocks were all left over from the formation of the Solar System, 4.5 billion years ago. The smaller the object, the more likely they are to be nudged, by impact or gravitational attraction, from the outer Solar System into the inner Solar System where they can threaten our existence.
We looked at the world-wide distribution of "recent" major impacts and noted that oceanic impacts would leave no crater but that the impactor would probably distintigrate and settle on the sea floor as rubble.
As this table indicates, we believe we know about 90% of the kilometre-sized Near Earth Objects; about 50-60% of those sized 500m-1000m; and 30-60% of those sized between 300 and 500 metres in diameter. There are many, many smaller sized objects that we have yet to find.
The Chelyabinsk explosion of an object, which is in the smallest of these categories, has focussed the world on the dangers of impacts from unlisted solar system objects - it was the largest recorded event since the Tunguska event in 1908 - but whether research funding will be boosted to locate more objects is another matter!
Dr. Jonti Horner (left) with MAS President, Chris Malikoff, as the members start to roll in.
Next up at the Macarthur Astronomy Forum: An international visitor to Australia - Dr. Mark Phillips, an American astronomer working in Chile as Associate Director of the Las Campanas Observatory, Chile - will present a talk entitled: "Exploding Stars and the Fate of the Universe." Dr. Phillips is well known for his work on supernovae. |