HD 85512 b

An extrasolar planet, HD 85512 b orbits the orange dwarf star Gliese 370. It is located some 36 light years from Earth in the Vela constellation.

Diameter: 1.05 x 1010 km
Mass: 2.15 x 1025 kg
Composition: unknown
Orbit: 54.4 Earth days around its star

HD 85512 b was discovered in 2011 by scientists from the University of Geneva using the High Accuracy Radial Velocity Planet Searcher (HARPS). This instrument operates at the European Southern Observatory in the Atacama Desert, northern Chile. The planet has a mass 3.6 times that of Earth. It orbits the edge of the habitable zone of Gliese 370 and is a strong candidate to be classified as a habitable planet.

The planet has a 54-day orbital period around its star and may be tidally locked to it. It orbits at an average distance of 0.26 astronomical units (AU), or 38.7 million kilometres, from its star and has a slightly elliptical orbit with an eccentricity of 0.11.

There is no firm information about the composition of the planet’s surface and core. Astronomers have used Doppler spectroscopy to determine its minimum mass. It has a minimum gravitational force equivalent to 1.4 times that of Earth. The surface temperature could be around 24.5C.

The first astronomical observation of Gliese 370, an orange-red dwarf star, was made in the late 19th century at the Astronomical Observatory of Cordoba in Argentina. Its luminosity is just 0.126 that of the Sun. This means that HD 85512 b receives radiation from its star that is about 1.86 times the sunlight received by Earth, but it receives slightly less sunlight than Venus, which receives 1.92 times as much radiation as Earth.

The strength of its star’s radiation has lead astronomers to speculate that, had there been oceans on the surface of the planet, they would have boiled away into the atmosphere in a reverse greenhouse effect. This is the process that is believed to account for the arid surface of Venus, yet some water vapour remains in its atmosphere.

Calculations based on the NASA Star and Exoplanet Database have indicated that the inner and outer edges of the habitable zone around Gliese 370 star could be 0.295 AU (43.9 million kilometres) to 0.591 AU (88 million kilometres). The inner edge of this zone, however, could be extended further towards the HD 85512 b orbit if the planet had sufficient cloud cover. This would also mean that the planet could have water on its surface. The planet could be habitable if it has more than 50% cloud (water vapour) coverage.

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