But how about the much smaller members of our solar system? Asteroids, most of which orbit the sun in broad belt between Mars and Jupiter, may not attract the blaze of publicity of photogenic planets, but they are many and varied, and scientists are showing a lot of interest in them – at this very moment the Dawn spacecraft is investigating the largest one, Ceres, having already taken a good look at the next largest one, Vesta; and three of the five projects shortlisted for the NASA Discovery programme (see my last post) aim to explore asteroids.
So why the interest in a motley collection of misshapen space rocks?
From a scientific point of view, asteroids are particularly intriguing as they are thought to be remnants from the birth of the solar system. It's thought that they never managed to clump together enough to make a planet because of the disrupting influence of Jupiter's gravity. By examining what they are made of, scientists hope to learn more about the original composition of the solar system, and about the processes by which planets were formed. Their great variety makes them particularly interesting. For example, the largest one, Ceres (now officially termed a 'dwarf planet), appears to be made of a mixture of rock and ice, like some of the bodies in the outer solar system – a recent image from Dawn clearly shows a bright white patch which is thought to be ice; whereas the next largest asteroid Vesta is suspected to have a metallic core beneath a rocky mantle, like the rocky planets of the inner solar system. And the very unusal asteroid Pysche is believed to be 90% metallic.
Which brings us to another compelling reason for interest in asteroids – the possibility of using them as a resource for raw materials in the future, if space travel becomes more developed and less costly. Some asteroids contain economically valuable minerals and metals, and their reserves of water could prove vital for supplying space missions in the future. NASA is planning to launch a mission in 2016, known as OSIRIS-Rex, with the specific aim of collecting samples of asteroid rock for analysis back on earth.
Impact on Earth
Asteroids often feature in the popular press for another reason – the risk of collision with the Earth! This has certainly happened in the past – the extinction of the dinosaurs is believed to have been caused by a massive impact from a space rock. Although asteroids mostly orbit in a particular belt, their orbits can be disrupted by the gravitational pull from each other and from Jupiter, and now and again one does head our way. NASA's 'Near Earth Object scans all known asteroids and predicts potentially hazardous ones – but what could be done to protect ourself if a major hazard was identified?
At the moment – nothing unfortunately! But a consortium of space agencies is currently working on a method of deflecting an incoming asteroid by impacting it with a spacecraft – the programme is known as AIDA (Asteroid Impact and Deflection Assessment), and the plan is to test it out on an actual asteroid (Didymos) in 2022. Lets hope it proves successful!
http://www.universetoday.com/32856/asteroid-belt/ Description of asteroids and asteroid belt
http://dawn.jpl.nasa.gov/ Official page for the Dawn mission, currently at Ceres
https://www.nasa.gov/content/goddard/new-nasa-mission-to-help-us-learn-how-to-mine-asteroids
http://www.esa.int/Our_Activities/Space_Engineering_Technology/NEO/Asteroid_Impact_Deflection_Assessment_AIDA_study
1. http://spaceplace.nasa.gov/review/ice-dwarf/solar-system-lrg.png
2. NASA/JPL Image modified by Jcpag2012
3. NASA/Goddard Space Flight Center