Protecting Earth is one of the main reasons why scientists keep a close eye on asteroids, which are space rocks of all shapes and sizes that can be found scattered throughout the Solar System. It’s unclear how meteoroids, the rocks that become meteors when they crash into Earth’s atmosphere, were generated from asteroids. Still, NASA isn’t ruling a link out and is examining asteroids to learn more about how the Solar System was formed.
Since planetary scientists believe planets gradually grew from rocks crashing into each other, the asteroid belt between Mars and Jupiter could be made up of the leftovers of the early Solar System. Therefore, ferreting out the secrets of asteroids could also give scientists clues as to how the Solar System came to be. Possibly, it could even reveal how the Earth was born.
Studying asteroids is a challenge for scientists, however, because they are so small. A typical space rock is perhaps just a few metres across. However, the largest known asteroid in our Solar System, Ceres, is 950 kilometres (590 miles) in diameter and makes up a third of the mass of the known asteroid belt.
However, through a telescope sitting on Earth, an asteroid of this size looks incredibly small. This makes asteroids difficult to see and study, but scientists are pretty crafty when it comes to getting information from a distance.
Most asteroids, according to NASA, can be classified in three groups: C-type (carbonaceous), S-type (siliceous) and X-type (various compositions). Around 75 per cent are C-type asteroids that lurk in the outer asteroid belt. They are very dark and probably lack helium, hydrogen and other lighter ‘volatile’ elements. S-type asteroids, about 17 per
cent of the population, make up most of the inner belt rocks in the asteroid belt.
They’re a little more reflective and are usually made of metallic iron mixed with silicates of iron and magnesium. Squeezed in between these asteroids are X-types, which are mostly made up of metallic iron asteroids and the like. These are found in the middle of the asteroid belt.
While most asteroids sit safely between Mars and Jupiter, some approach Earth and sometimes cross its orbit. Scientists think most of these asteroids were ‘disturbed’ into different orbits due to Jupiter’s gravity or collisions with other asteroids.
There are three types of near-Earth asteroids. Amors cross the orbit of Mars, but don’t get very close to Earth. Apollos cross Earth’s orbit in a period of one year or longer, while Atens also cross the orbit but in a shorter time frame – a year or less. In the past two decades, space agencies and observatories around the world have discovered thousands of these types of asteroids.
In 1995, there were only 335 known near-Earth asteroids, however, today there are more than 9,700 catalogued, according to NASA.
Since scientists believe we have now found more than 90 per cent of threatening asteroids that are more than one kilometre (0.6 miles) in diameter. NASA is now emphasising the search for finding near-Earth objects of 140 metres (460 feet) or greater. Still, a much smaller object can cause a lot of damage.
The dinosaurs were probably wiped out by a small body just ten kilometres (6.2 miles) in diameter that hit the Mexico area about 66 million years ago. In Russia this year, more than 1,000 people were injured when a house-sized asteroid – 17 metres wide (56 feet) – detonated in the atmosphere. The event caught both the public and astronomers by surprise, demonstrating we still have a lot to learn about predicting meteor strikes on Earth.
In more recent years, several space missions have ventured out to asteroids to get more information from closeup. NASA’s Dawn mission, for example, scooted by the asteroid Vesta in 2011 and is now en route to Ceres.
Its closeup views revealed a battered world that, surprisingly, has some links to how the Moon was formed Vesta and the Moon were each peppered by a population of space rocks ejected into the inner Solar System early in the Earth’s history.
Both Jupiter and Saturn shifted their orbits in less than a million years. Their motions perturbed the asteroid belt and sent the rocks into planet-crashing orbits. This bombardment had been known about for decades. Astronauts on the Apollo missions even discovered evidence of it on the Moon. But scientists didn’t know until recently that Vesta had also experienced it.
The next step will be obtaining a sample of an asteroid and studying it here on Earth. Origins Spectral Interpretation Resource Identification Security Regolith Explorer (OSIRIS-REx) will journey into space in 2016. It will scoop up a bit of dirt from the Apollo asteroid (101955) 1999 RQ36, and return it to Earth by 2023 for further investigation.