Rochelimit's Symbology of Astronomy: Gliese 581 System

phot-15a-09-fullres Planet E of the Gliese 581 system (foreground), the smallest planet to be discovered. The blue planet is the giant gas planet Planet D, probably have ocean in it. Small dot in the center is Planet C. White dot close to the star is Planet B (http://www.eso.org)

Today April 21, 2009, astronomers announce the discovery of Gliese 581 e, the smallest exoplanet ever found. I will use this occasion to find out more about the system.

The sun of the system is of course the star Gliese 581. The star is a red dwarf star located 20.3 light years away from Earth (a relatively close distance). It is pretty much the sun after the red giant phase, a dying and shrinking star. This sun is dim and small, only 0.013 times the brightness of our sun, and only 0.29 times the radius of our sun. This kind of star probably produces little stellar wind that planets can orbit closer and has satellites around it without being disturbed by the stellar wind.

The orbits of planets of the Gliese 581 system. All the orbits depicted here is closer than Mercury’s distance to the sun (http://www.eso.org)

Compared to our solar system, the planets of the Gliese 581 System orbit far closer to the star than that of our own system. All of the planets in this system orbits closer to its sun than Mercury’s distance to the sun. Since the star Gliese 581 is small, planets are logically orbits closer than the planets in our solar system.

Comparison between the habitable zone of our Solar System and the Gliese 581 System (Based on a diagram by Franck Selsis, Univ. of Bordeaux.)

The planets of the Gliese 581 system is relatively bulky and large compared to the planets of our solar system. They also strangely orbits closer to one another. I have the feeling that this may have been due to uncertainties and I think that it is possible for the planet to be actually 50% smaller than its initial assumption. These planet may be tidally locked the star, and is supposed to be perturbing each other, although it seems that this is not the case.

So here are the current members of Gliese 581:

Gliese 581	Third the size of our sun, and 50 times colder. This sun radiates primarily near infrared, so everything around would appears uncomfortably red.
“Planet E”	Distance 0.03AU, complete its orbit after 3 days, 1.9 earth-masses. The innermost planet of the system, and also the smallest exoplanet to be found. It is has a similar distance with the distance of Io to Jupiter. This planet is probably lack of atmosphere due to its high temperature, small size, and strong radiation from the star.
”Planet B”	Distance 0.041AU, complete its orbit after 5.3 days, 16 times earth-masses. Neptune sized planet. Largest planet in the system, probably a hot gas giant. It has a similar distance with the distance of Europa to Jupiter (imagine Jupiter 2 times as big orbited by the planet Neptune). This planet is big enough to cause the star Gliese 5811 to wobble.
“Planet C”	Distance 0.073AU, complete its orbit after 13 days, 5 times earth-masses. First low mass exoplanet found to be near its star’ habitable zone. Since the region of Planet C’s orbit is comparable to the area where Venus orbits our sun, it is now thought that this planet may experience a runaway greenhouse effect like Venus does, and so is probably not habitable.
“Planet D”	Distance 0.22 AU, complete its orbit after 67 days, 7 times earth-masses. The planet furthest out in the Gliese 581 system so far. It is probably too massive to be made only of rocky material, but astronomers speculate that it is an icy planet that has migrated closer to the star. Planet D was previously thought to be too cold for life to exist, but further studies released in April 2009 confirmed that this planet lies within the habitable zone and large deep ocean may exist.