Asteroids, vermin of the skies?

Tuesday 3rd December, 2019

Our speaker was Mark Gibbons from Cotswold Astronomical Society who came to talk to us about "Asteroids: vermin of the skies?". Before his main talk he told about some success he had had with using a GoPro Action Camera to photograph meteors. He uses its Night Lapse Photo mode with settings of ISO 400, an exposure time of 30 seconds, and the images are stored in the jpeg format. To increase its operational time he powers it with a powerbank battery in a waterproof case. He fixes the camera on his upstairs window with a strong suction cup and then leaves it working. He said it captures about 1,300 images overnight, and, so far, over 42 nights he has captured 60 meteor trails.

Mr Gibbons then began his main talk by explaining what asteroids were and said that they are small rocky objects, much smaller than planets, which orbit the Sun in great numbers. Most of them are found in the main asteroid belt, which is a circular region between the planets Mars and Jupiter. However, this is not the only place they can be found as they can also accumulate in groups ahead of and behind the planets in their orbits as well as having various other types of orbit around the Sun.

They can be thought of as the left over debris from the formation of our Solar System, which began roughly 4.6 billion years ago. It all began when something triggered the collapse of a huge cloud of rotating gas and dust. Most of the material fell to the centre to form our Sun, and other clumps condensed to form our planets, but some of it never gained enough mass to be classed as a planet. In fact the International Astronomical Union (IAU) redefined the definition of a planet in 2006 so that it had to: be in orbit around the Sun, be approximately spherical in shape, have cleared all other large bodies from its orbit. This meant that Pluto lost its planet status and became known as a "dwarf planet".

He then explained that astronomers used to think of asteroids as "vermin of the skies" as they appear as long streaks in astronomical photographs — effectively photobombing the subject that they were trying to study. However, this has changed in recent years as scientists have started to warn governments about the threat of a large or even medium-sized asteroid colliding with Earth and threating human civilisation.

There are now various asteroid hunting programmes looking for any whose orbits suggest that they may impact our planet, and ongoing projects to think of plans to divert them from their collision course. There is even a citizen science Zooniverse project called "Hubble Asteroid Hunter" where the general public can help to classify asteroid trails in Hubble Space Telescope images, so that their future trajectories can be refined.

Other scientists are purely interested in examining the make-up of different asteroids so they can understand our Solar System and how it formed. A Japanese spacecraft, Hayabusa 2, is currently returning to Earth with a sample from the asteroid Ryugu, which it will parachute back to Earth, to land in the Australian Outback at the end of 2020.