Study estimates number of Earth-like planets in the galaxy

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A New research suggests that 18% of solar-type (G-type) stars may have an Earth-like planet orbiting their habitable zone.

Before estimating the probability that life could appear and develop elsewhere in the Universe, it is first necessary to begin by assessing the number of exoplanets capable of containing it. It is an essential first step. To our knowledge, only the Earth is known to harbor life. Starting from this principle, it therefore seems natural to look at worlds having substantially the same characteristics.

Basically, an Earth-like planet is a rocky world, roughly of equivalent mass, orbiting the habitable zone of a G-type star, like the Sun.

However, it should be noted that these worlds, smaller than the average, are more likely to be missed by our instruments. This is no doubt the reason why, of the more than 4,000 exoplanets discovered to date in the Milky Way, the vast majority are gas giants.

This therefore implies that the number of known Earth-like planets is not representative of the actual number of these worlds evolving in the galaxy.

Michelle Kunimoto of the University of British Columbia (Canada) has tried to estimate this real number. As a reminder, it was this young astronomer who, a few months ago, had discovered no less than 17 new exoplanets while reviewing the data from the Kepler telescope, now retired.

About 6 billion Earth-like planets

As part of this work, published in The Astronomical Journal, the astronomer used a technique known as “advanced modeling” which aimed to estimate the number of Earth-like planets that the Kepler telescope could have to lack.

To be considered, these worlds had to have a mass between 0.75 and 1.5 times the Earth’s mass and be in orbit around a G-type star at a distance between 0.99 and 1.7 astronomical units. Let us recall in passing that one AU is equivalent to the Earth-Sun distance, which is approximately 150 million km.

Using this approach, Kunimoto and his colleague, astronomer Jaymie Matthews, were able to estimate that 18% of solar-type (G-type) stars could have an Earth-like planet orbiting their habitable zone.

“Assuming that our galaxy has up to 400 billion stars, 7% of which are type G, this means that just under six billion stars can have Earth-like planets in the Milky Way Says Jaymie Matthews.

This is of course only an estimate. In addition, there is no guarantee that these planets can harbor life, or even be habitable. After all, the planet Mars, which is positioned about 1.5 astronomical units from the Sun, is today only a cold and dry world, a priori sterile