The vision seems to show a large ball burning with green-blue light in the night sky.<\/p>\n
Different colours are released when different elements burn. Yellows and reds are released when space-junk passes through the atmosphere. Greens and blues are telltale signs of iron and nickel, says Tucker.<\/p>\n
Most space rocks are the left-overs of ancient failed protoplanets.<\/a><\/p>\n Stony chondrites,<\/a> the more common type of meteor, come from the surface, while rarer metallic chunks come from the protoplanet\u2019s core.<\/p>\n Loading<\/p>\n And it was going fast. Space junk \u2013 such as old satellites and bits of rocket \u2013 typically orbits the Earth about 30,000 km\/h. Meteors are a lot quicker, travelling at up to 100,000 km\/h.<\/p>\n That accounts for the large explosion, despite the rock being relatively small.<\/p>\n \u201cIt is not as big as people might imagine \u2013 we\u2019re not talking a car coming in,\u201d says Brown. \u201cBut because it\u2019s coming in at 30 kilometres a second, there\u2019s a lot of energy being released as that thing slows down in the atmosphere.\u201d<\/p>\n The bang was likely a sonic boom, the same as the loud crack heard from an accelerating jet fighter (or, on a smaller scale, a bullet being fired).<\/p>\n When an object travels quickly through the air, it pushes pressure waves in front of it \u2013 similar to a boat creating a bow wave. These waves move at the speed of sound. But if the asteroid is travelling faster than the speed of sound, it compresses these waves together, merging them together into a single powerful shockwave.<\/p>\n \u201cThat\u2019s really important. That\u2019s a sign it slowed down and probably broke apart \u2013 you only get that reverb and rattling from a fragmentation of a meteor,\u201d says Tucker. Small meteors typically don\u2019t produce sonic booms. \u201cIn this case, there is a good chance there could be meteors on the ground from this one.\u201d<\/p>\n Was there any danger to human life? Will we be able to find bits today?<\/p>\n The meteor was so small the risk it posed to human life was tiny, the astronomers said. By the time it had reached cloud-level, most of the rock\u2019s energy would have been expended. It would take an extremely unlucky direct hit to cause harm.<\/p>\n \u201cThere\u2019s not going to be huge craters. These things lose most of their energy when they break up. They are pretty much falling at free-fall speed, and they are relatively small,\u201d says Tucker.<\/p>\n There may be debris and pieces of meteorite, although at this stage it is not clear exactly where they may have landed.<\/p>\n Preliminary estimates from the Desert Fireball Network,<\/a> which has several cameras trying to track meteorites above Victoria, suggest it may have landed somewhere west of Castlemaine and Bendigo.<\/p>\n \u201cIt\u2019s a big meteor. We think there\u2019s probably [a] very high chances there\u2019s meteor on the ground,\u201d says Professor Andy Tomkins, who runs the network in Victoria. His team plans to send scientists searching for fragments on Monday afternoon.<\/p>\n Loading<\/p>\n If you want to go searching, look for small rocks that appear different to others in the area.<\/p>\n The outside will be covered in \u201cfusion crust\u201d<\/a>: a smooth, black surface left over after the meteorite\u2019s surface melted in the atmosphere. There will also be characteristic dimples, like those on a golf-ball, caused by the molten crust being reshaped by the air as the meteor fell. It is likely magnetic, and will feel deceptively heavy in the hand.<\/p>\n