Compact planetary system Kepler-11


This system*, discovered in 2010 and published in Nature in 2011, contains six planets orbiting with periods between 10 and 118 days. The planets are super-Earths, with masses of 4.3, 13.5, 6.1, 8.4 and 2.3 Earth masses (the mass of the outermost planet is not well constrained) and radii between 2 and 4.5 Earth radii. The star is very Sun-like, spectral type G6V. Compared to the Solar system, the orbits would all be contained within the orbit of Venus. Lead author Jack J. Lissauer states:

By measuring the sizes and masses of the five inner planets, we have determined they are among the smallest confirmed exoplanets, or planets beyond our solar system. These planets are mixtures of rock and gases, possibly including water. The rocky material accounts for most of the planets’ mass, while the gas takes up most of their volume.


More discoveries of this nature may soon be made from the ground at Paranal with the Next Generation Transit Survey (NGTS), which is a cost-effective venture using off-the-shelf telescopes, publicized today and led by Don Pollacco at the University of Warwick. The wide-field NGTS will survey nearby stars brighter than thirteenth magnitude, concentrating on spectral types between early M and late F. This covers the types of star thought most likely to harbour habitable planets, and will naturally feed instruments like HARPS for ground-based radial velocity follow-up observations. The figure (left) shows the detection space:

Parameter space for transit detection with the yellow area indicating the prime science parameter space search of NGTS. Transit depth is indicated as a function of planet and star radius. Approximate spectral types of stars are also indicated, as well as the radii of representative Solar system planets. Known transiting systems are marked in green where they were discovered in ground-based transit surveys, blue if they were originally identified in radial velocity surveys, and red if they were discovered from space.

The special geometry of transit observations allows masses and radii of planets to be accurately constrained, which is sought after to allow statistical comparison of bulk planetary composition with theoretical models. Moreover, the transit geometry also allows to probe the atmosphere during secondary eclipse. NGTS will make available targets for high precision transmission spectroscopy of starlight passing through the planetary atmosphere, which is only possible using large telescopes, or from space.

*Note: planet masses and radii in this link are in units of Jupiter masses and radii.


2 Responses to “Compact planetary system Kepler-11”

  1. […] which is perhaps itself similar to alpha Centauri Bb. Tiny transiting systems around M dwarfs and solar-type stars have been found by Kepler, while these new results show that truly huge planetary systems are […]

  2. Its like you read my mind! You seem to know a lot about this, like you wrote the book in it or something. I think that you can do with a few pics to drive the message home a little bit, but instead of that, this is wonderful blog. A fantastic read. I’ll definitely be back.|

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