Stellar Data for

Type of Star:

Spectral Class:




Surface Temperature:

Yellow Dwarf


42 Lightyears

1,32 L

1,05 Solar Masses

5750 K

The Planet of 51 Pegasi

First Exoplanet Around a Sunlike Star


Orbital Radius:

Orbital Period:



0,6 Jupiter Masses

0,05 AU

4,2 Days



Comparison to Solar System


51 Pegasi

Speculations about 51 Pegasi b


This was the first definite planet dicovered around a normal, main sequence star, and it was a world that should not be there, according to traditional theories. As close as 0,05 AU to its parent star, 51 Pegasi b has an average temperature of 1.300°C, sufficiently high to melt aluminium. But more surprising to the scientific world, 51 Pegasi b is almost as massive as Jupiter. As a gas giant, this planet could not have formed so close to the star. Most likely it formed in the outer ranges of the system and than migrated to its current position, possibly by interaction with a second giant planet, which was then thrown out of the system during this process. Or it may indeed have formed at its current position, but then 51 Pegasi b would be a supermassive terrestrial world. Inofficially, this planet has been named Vulkan, and it is really a place like Hell.

There was much debate about 51 Pegasi b, especially since the star shows some fluctuations with a very similar periodicity than the presumed planet. But now all remaining doubts are removed, and 51 Pegasi b is a confirmed planet, very important for all subsequent discoveries of extrasolar worlds.

The surface of 51 Pegasi b

Here we assume that 51 Pegasi b is indeed a supermassive terrestrial planet. So close to its star, it would be tormented by immense tidal forces, making 51 Pegasi b a volcanically hyperactive world. Titanic eruptions unimaginable for humans would flood the adjacent areas with lava, continuously reshaping the surface of the planet. Most of the primordial hydrogen would have been lost into space, so its dense atmosphere would contain carbon dioxide and a diversity of sulphur compounds. At 1.300°C, the atmosphere would even contain vaporized rock, enriched with iron and nickel. 51 Pegasi b is even more hostile than Venus could ever be.

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