'Earth clone' likely to be covered in oceans

Rocky planet Proxima b in the habitable zone of its closest star to the Sun likely harbors an ocean of liquid water similar to Earth's.

Graphic simulation of planet Proxima b. Photo: ESA.

Astrophysicists at the French National Institute for Scientific Research (CNRS) calculated the size and surface features of planet Proxima b and concluded that an Earth-like ocean could cover the planet, Phys.org reported yesterday.

The European Space Agency (ESA) announced the discovery of Proxima b last month and said it is the first exoplanet that humans can send a robot to in the future. The planet orbits the parent star Proxima Centauri, 4 light years away from the Solar System, in the habitable zone. Proxima b has an estimated mass 1.3 times that of Earth and is 7.5 million km from its parent star.

"Contrary to expectations, the close distance does not necessarily mean that Proxima b's surface is too hot to allow water to exist in liquid form," the CNRS team commented.

The star Proxima Centauri is 1,000 times smaller and dimmer than the Sun, suggesting that Proxima b is at the right distance to concentrate the right conditions for life. According to the CNRS team, the planet is likely to have liquid water on its surface, along with some form of life.

The size of an exoplanet is calculated by measuring the amount of light that is blocked by the planet when it passes in front of its parent star. However, because the transit of Proxima b has not yet been observed, the team has had to rely on simulations to estimate the planet's composition and radius.

They calculated the radius of Proxima b to be about 6,371 km, 0.94 - 1.4 times that of Earth. Assuming a minimum radius of 5,990 km, the planet is very dense, with a metallic core accounting for two-thirds of its mass, surrounded by a rocky crust. If liquid water exists on the surface, the total amount of water would contribute more than 0.05% of the planet's mass, similar to Earth's rate of about 0.02%.

In the larger radius case of 8,920 km, Proxima b's mass would be divided equally between the rocky core at the center and the surrounding water. "In this case, Proxima b would be covered by a liquid ocean 200 km deep. In both cases, a thin atmosphere would exist around the planet, similar to Earth, making Proxima b a suitable place for life to develop," the CNRS team concluded.

According to VNE