How did life arrive on Earth? Nasa scientists are hoping they will soon be able to answer this question after their first successful space collision took place on July 5
Scientists were earlier this month holding their breath as a Nasa space probe headed for a comet 134 million km from Earth. They cheered as they watched the probe slam into the side of the comet.
The mission was more successful than they dared dream. And the results, they hope, could unlock the secret of how life arrived on Earth.
So, what is a comet? They are large icy chunks of water, gas, dust and organic material that originate in the outer reaches of the solar system.
They revolve around the sun in long orbits. When they approach the sun, they heat up, leaving a trail of gas behind them which looks like a fiery tail. Two of the most recent and well-publicised comets to fly past the sun were Halley and Hale-Bopp.
Because comets weren't heated by the sun during the formation of the solar system, they have a very primordial chemical mixture.
Some scientists believe a comet might be responsible for life on Earth. They think that about 3.9 billion years ago - about the time of the first signs of life on Earth - there was a period of heavy comet activity. One of these comets might have crashed into Earth, bringing with it organic material and water.
Comets have been found to contain amino acids, the building blocks of life, further supporting the claim that that they might have brought life to Earth.
You can see comets with the naked eye about every six years, but they are only just visible. More spectacular displays occur every 10 years. Whenever the Earth passes through the tail of a comet, shooting stars dart across the sky. These are known as meteor showers.
Meanwhile, the Nasa scientists are waiting to retrieve the data from their successful collision between the Deep Impact space probe and the Temple 1 comet on July 5. It was the first time a spacecraft has come into contact with a comet. The impact would have caused a huge crater on the surface of the comet, but they haven't yet been able to determine the size of the hole because of the plumes of ice, dust and gases streaming out.
Once the gases have cleared, scientists will be able to determine how deep the probe plunged into the comet. And perhaps then they will be able to uncover the secret to life on Earth. We live in exciting times!