Physics in perspective lecture 2012

The second lecture was Dust from Outer Space and given by Dr Matt Genge. He is a senior lecturer in Earth and planetary science at Imperial College.

Despite the fact that Dr Genge is a geologist he started his talk by saying something very important. Physics underlines everything.

10000 tonnes of extraterrestrial dust lands on Earth per year. 1011 dust particles about 200 microns in size. 10 particles per m2 fall per year. Only a small amount of the dust actually reaches the Earth’s surface. The atmosphere can actually stop very large objects. They explode and cause the sort of damage seen at Tungaska.

The history of collecting cosmic dust   

John Murray Challenger expedition of 1872 found Ni- bearing sphericules from meteorites.

Nodenskjold found cosmic dust in Iceland in 1888.

Nininger in the 1920s tried collecting it in buckets of water on the roof of the University of Arizona. However most actually came from diesel motors and other terrestrial sources.

In the 1960’s Don Browlee showed that cosmic dust particles were dust particles in space not from meteorites. Deep sea sediments accumulated 3mm2 of cosmic dust over ten years.

In the 1970s NASA collected dust at 20-40km in the stratosphere and found <30 microns of interplanetary dust.

In the 1980s Maurette collected dust from Greenland cryoconite lakes.

In the 1990s 100000 cosmic dust particles were collected by melting Antarctic blue ice giving >25 microns. The dust had been there 2 million years.

The variation of the particles is due to temperature as the particles pass through the atmosphere.

Magma cooled very quickly has no crystals. Carbon strips oxygen away from the cosmic sphericule. Droplet metal occurs. Astronomers have seen the meteorite splitting and the metal bits falling off.

Where did cosmic dust come from? 

Zodiacal lights is light scattered from dust particles in our solar system. Infra red radiation is perfect to see dust.

Dust is concentrated on the plane as it and the planets orbit the Sun. Dust travels 35kms-1 away from the Sun and 70kms-1 towards the Sun. There are two main sources of dust on Earth from the solar system: Comets – dust trails behind them. There are two distinct tails. A blue gas tail and a whiter dust tail.                                                                                                                                                                             Asteroids are debris from the formation of the solar system. Jupiter prevented them forming a planet. Collectively they have 1/5th of the mass of the Moon. There are relatively few asteroids considering the area.

Dust works its way to the Earth because it is affected by sunlight. PR light drag – light slows down the orbiting dust particles. Spiralling in 10000 years to reach the Earth. Asteroids and meteorites are important as they tell us about the past.

Shockwaves involve gas drag heating by collisions of high velocity gas molecules. Interplanetary dust particles are 50% asteroid/meteorite.

NASA stardust probe collected comet dust particles but unfortunately the particles did not survive capture.

A cosmic “football” particle passes through the Earth’s atmosphere four times.

Interstellar rock is shiny, black, has a layer of magma, round outside (fusion crust) and dimples.

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