51 Pegasi

51 Pegasi b has the distinction of being the first planet to be discovered orbiting another sun-like star. The discovery sent shock waves through the astronomical community, not only for the fact that it was one of the first known exoplanets, but because of its totally unexpected nature. 51 Pegasi b is a massive Jupiter-like planet orbiting at only 0.05 Aus from its sun, far closer than Mercury. At the time, theories of planet evolution allowed giant planets to form only at distances greater than several AU, at about the distance of Jupiter from the sun. The discovery of 51 Pegasi b forced astronomers to re-examine their theories.

Location Constellation: Pegasus Right Ascension: 22 57 27.9805 Declination: 20 46 07.796 Distance from Sol: 42 Light Years Basic Data Alternate Designations: HD 217014 HD 217014 SAO 090896 Spectral Type: G2 IV Apparent Magnitude: 5.49 B-V Color: 0.67 Radius: 1.4 Solar Radii Effective Temperature: 5770 Kelvin Habitability Inner Edge of Habitability Zone: 0.69 AU Outer Edge of Habitability Zone: 2.18 AU

51 Pegasi b

51 Pegasi b Statistics

Speculations

51 Pegasi b is the archetypical Hot Jupiter. Heated both inside and out to temperatures high enough to vaporize silicates, its atmosphere would be a bottomless inferno.

Similar to HD 209458 b, 51 Pegasi b likely has an upper atmosphere of tenuous gas extending thousands of kilometers above its surface clouds. At the upper edges of this extended region, gases may be heated enough by stellar radiation to escape the planet's gravity and fall into a toroidal cloud around the star, similar to the sodium cloud around Jupiter fed by volcanic out gassing from its moon, Io. Or, these gases may form a comet like tail. Either way, the escaped material is doomed to eventually fall into the host star.

Below the tenuous extended atmosphere is the thicker main atmosphere. 51 Pegasi b is so hot that its atmosphere is puffed up, giving the planet a larger radius than Jupiter, despite its smaller mass. 51 Pegasi b's atmosphere becomes incandescent at lower levels, giving the planet a red hue. On the planet's limb, we see through the comparatively cooler gases above this incandescent layer, so the edges of the planet appear blue due to Rayleigh Scattering. It's too torrid for normal clouds to form, but the temperature is right for sparse clouds of silicates.

Calculations show that 51 Pegasi b became tidally locked soon after it came to rest in its current orbit. This means that the planet always shows the same face to its sun, just like the moon always shows the same face to the Earth. Measurements of the planet's magnetic field would confirm this. Yet, if you were in orbit of 51 Pegasi b, you would still see clouds pass across the planet's surface faster than its four day orbital period. This is due to powerful winds driven by both internal and external heat, that move across the planet faster than it rotates. A similar situation exists for Venus. Our sister planet actually rotates backwards, and very slowly. One day on Venus is 243 Earth days long. Yet, Venus' clouds circle the planet once every four days.

Recent studies indicate that stars with Hot Jupiters, like 51 Pegasi b, might emit super flares every century or so. If this is happening within the 51 Pegasi system, then any as yet undiscovered and more distant icy worlds may have been melted smooth by these titanic stellar eruptions. However, the link between Hot Jupiters and super flares is, so far, only theoretical.

Planetary Orbit Of 51 Pegasi b