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Stellar Data for

Type of Star:

Spectral Class:

Distance:

Luminosity:

Mass:

Surface Temperature:

Yellow Subgiant

F6IV

44 Lightyears

3,33 L

1,34 Solar Masses

6250 K

The Triple Planetary System of Upsilon Andromedae

Sun

Upsilon Andromedae

The Three Planets

Ups And b

Mass:

Orbital Radius:

Orbital Period:

Temperature:

Eccentricity:

0,71 Jupiter Masses

0,059 AU

4,6 Days

~ 2.000°C

0,03

Ups And c

Mass:

Orbital Radius:

orbital Period:

Temperature:

Eccentricity:

2,11 Jupiter Masses

0,83 AU

241,2 Days

85°C

0,18

Ups And d

Mass:

Orbital Radius:

Orbital Period:

Temperature:

Eccentricity:

4,61 Jupiter Masses

2,5 AU

3,5 Years

-40°C

0,41

Speculations About the Worlds of Upsilon Adromedae

This is the only system for which three planets are known. Upsilon Andromedae is also one of the few stars with exoplanets, which has already left the main sequence and reached the stage of subgiant. The innermost planet, Upsilon Andromedae b, is an ultra-hot, structureless giant world, with its superheated atmosphere glowing intensely on the night side.

Closer to our usual image of a planet is Upsilon Andromedae c. This world has an almost Earth-like orbit, but receives four times as much light from its evolved sun. As a gas giant of two Jupiter masses, it may have an army of moons, though. Such a world is portrayed here, heated to above 80°C and dried out long ago. Violent storms of dust are raging through its dense carbon dioxide atmosphere, and the oxidized rocks have long since eroded.

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Much farther outside, on a highly eccentric orbit, we find Upsilon Andromedae d, four times as massive as Jupiter. This distance, combined with the higher energy output of the parent star, would give to its moons a more Mars-like climate. Here we show the sunrise over such a moon of Upsilon Andromedae d - morning haze covers the dry desert valley. The planet is on the opposite side of the moon.

JIANG Y. & IP W., 2000: The Planetary System of Upsilon Andromedae. Astron. & Astrophys., preprint

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