Aquatic planets are common in our Milky Way galaxy, study suggests | Astronomy, planetary science

In a study published in the journal Scientific advances, a team of European astronomers shows that water can be supplied to a terrestrial planet in the form of “pebble snow” in the early stages of the planet’s growth.

“All of our data suggests that water was part of the building blocks of the Earth from the start,” said Professor Anders Johansen, researcher at the Center for Star and Planet Formation at the University of Copenhagen and the Observatory of Lund.

“And because the water molecule is common, 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 between the planet and its star.”

Using a computer model, Professor Johansen and his colleagues calculated how quickly planets form and from which building blocks.

Their results indicate that 4.5 billion years ago, millimeter-sized ice and carbon dust particles increased in the formation of what would become Earth.

“At the point where the Earth was 1% of its current mass, our planet grew by capturing masses of pebbles filled with ice and carbon,” said Professor Johansen.

“The Earth then grew faster and faster until, after five million years, it became as large as we know it today.”

“Along the way, the surface temperature has risen sharply, causing ice to evaporate in the pebbles as it descends towards the surface, so that today only 0.1% of the planet is made up of water, even though 70% of the Earth’s surface is covered with water. “

The team’s pebble accretion theory is that planets are formed by pebbles that clump together, and the planets then get bigger and bigger.

“The water molecule is found everywhere in our galaxy, so the theory opens up the possibility that other planets formed in the same way as Earth, Mars and Venus,” said Professor Johansen.

“All of the planets in the Milky Way can be formed by the same building blocks, which means that planets with the same amount of water and carbon as Earth – and therefore potential places where life can be present – are frequently occur around other stars in our galaxy, provided the temperature is right. “

If the planets in our galaxy had the same building blocks and temperature conditions as Earth, there is also a good chance that they have roughly the same amount of water and continents as our planet.

“With our model, all planets receive the same amount of water, which suggests that other planets may not only have the same amount of water and oceans, but also the same amount of continents as here on Earth. It offers good opportunities for the emergence of life, ”said Professor Martin Bizzarro, researcher at the Center for Star and Planet Formation at the University of Copenhagen.

“If, on the other hand, the amount of water present on the planets was random, the planets could be very different. Some planets would be too dry to develop life, while others would be completely covered with water.

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Anders Johansen et al. 2021. A pebble accretion model for the formation of terrestrial planets in the solar system. Scientific advances 7 (8): eabc0444; doi: 10.1126 / sciadv.abc0444