Our Milky Way galaxy could be swarming with planets with oceans and continents, just like Earth, according to a study.
Other planets may even have the same number of continents as Earth, researchers at the University of Copenhagen said – meaning they could be good places to harbour alien life.
The scientists believe that, rather than planets gaining water when they are hit with icy comets, Earth-like planets may form from tiny icy pebbles.
It means that water is present right from the beginning, said professor Anders Johansen from the Centre for Star and Planet Formation.
The find could mean that planets with liquid water are present throughout our galaxy, the researchers said.
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The study was published in the journal Science Advances.
Professor Johansen said: "All our data suggest that water was part of Earth's building blocks, right from the beginning. And because the water molecule is frequently occurring, there is a reasonable probability that it applies to all planets in the Milky Way.
"The decisive point for whether liquid water is present is the distance of the planet from its star."
Using a computer model, Johansen and his team worked out how quickly planets are formed, and from which building blocks.
The study suggests that it was millimetre-sized dust particles of ice and carbon – which orbit around all young stars in the Milky Way – that formed Earth 4.5 billion years ago.
Johansen said: "Up to the point where Earth had grown to 1% of its current mass, our planet grew by capturing masses of pebbles filled with ice and carbon. Earth then grew faster and faster until, after five million years, it became as large as we know it today.
"Along the way, the temperature on the surface rose sharply, causing the ice in the pebbles to evaporate on the way down to the surface so that, today, only 0.1 percent of the planet is made up of water, even though 70 percent of Earth's surface is covered by water."
The findings could have profound implications for the search for life on other planets, the researchers said.
Johansen said: "All planets in the Milky Way may be formed by the same building blocks, meaning that planets with the same amount of water and carbon as Earth, and thus potential places where life may be present, occur frequently around other stars in our galaxy, provided the temperature is right."
The researchers believe that planets which formed from the same building blocks and at the same temperature as Earth could have the same amount of water, and even the same number of continents.
Professor Martin Bizzarro, co-author of the study, said: "With our model, all planets get the same amount of water, and this suggests that other planets may have not just the same amount of water and oceans, but also the same amount of continents as here on Earth. It provides good opportunities for the emergence of life."
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