The bits inbetween..

I thought this morning about covering Comet Swan in today's post then figured I'd talk about meteorites instead... and then thought why not cover the 'minor bodies' (asteroids/meteorites and comets) in general?

Comet Swan should be at about its brightest (magnitude ~6) this week and is already good enough for binoculars. Having never spotted one before (somehow I missed both Halleys' and Hale-Bopp), it may be one I look out for - since due to its orbit, it's destined never to return. With the aid of these diagrams you should be able to find it with a little luck.

There's a fanastically gorgeous picture on the APOD website of Comet Swan.

Moving on (slightly), I'd dearly love to be able to carry out my dream PhD project on the effects of 'space debris' (for want of a better term) on Earth's climate and its multitudes of species'. It's such a rich field to be able to research in. Comets, asteroids and interstellar dust all have their part to play in the evolution of the Solar System and our 'pale blue dot'.

The fact that our local space isn't empty - despite looking like it is - can be seen easily enough when we witness zodiacal light (the reflection of sunlight at dusk upon interstellar dust) or when we look at diagrams of asteroid locations. Populations of asteroids crop up all over the place other than the asteroid belt. We also have the Centaurs, the Plutons (which are in 3:2 resonance with Neptune (as is Pluto)) and a number of other populations including scattered disk objects. We know that asteroids, meteorites and comets have a tendency to hit planets, moons and each other from looking at any body with a surface (and even sometimes without, thinking of Comet Shoemaker-Levy 9). These impacts are evidenced by the craters they leave behind especially on worlds believed geologically 'dead' like our Moon but they also have their part to play in our being here. Without these impacts, we'd likely have no Moon; and no Earth either...

Crater formation via comets & asteroids has three main stages - compression, excavation & modification. In short, the whole crater-forming process can last from a few seconds to a few minutes (even the Chixculub crater was believed formed in around 3-4 minutes). That's an extremely short timescale when we consider the geological age of the Solar System being at around 4.6 billion years.

The important issue here is the large number of "Potentially Hazardous Asteroids" (PHAs) that are orbiting near to Earth. These are known to cross Earth's orbit at various times and so far there are believed to be about 400 of these...

While the Chixculub asteroid (approximately 10km diameter) and the mass extinction of many species (including the dinosaurs) may be under some debate about exactly what happened 65 million years ago, there can be no doubt that if we were struck by a large asteroid it'd do considerable damage to the planet.

Some of the effects:
1) Vaporisation of any species/animals in the reasonably immediate vicinity (perhaps up to 100km away for a 10km land-based asteroid) and extinctions & death much further out that this.
2) A large enough meteorite would bore a hole in the atmosphere and large amounts of matter from the impact process would be sucked back up into the temporary vacuum and high into the Earth's atmosphere eventually leading to the possibility of a 'nuclear winter'.
3) Some of the ejecta thrown up by the impact may reach escape velocities and 'rain down' on other areas of the planet. These 'spherules' would be extremely hot and may cause forest fires and the burning of other organic matter. Larger pieces of ejecta & rock fragments would be melted into aerodynamic, 'glassy' shapes called tektites - the passage of these through the atmosphere would likely heat it up also.
4) If the impact was into a large body of water, such as an ocean, we'd be likely looking at a devastating tsunami.

All of these things are clearly troublesome... and worth investigating further. A few years down the line this is what I hope I'll be writing about as part of a larger project.