Question: Which planets have aurooras been observed on?
About the article "Aurora", section "On other planets".

Candidate passages:
Kepler-70c (formerly called KOI-55.02; sometimes listed as KOI-55 c) is a planet discovered orbiting the sdB star Kepler-70.
It orbits its host along with another planet, Kepler-70b, both of which orbit very close to their host star.
Kepler-70c completes one orbit around its star in just 8.232 hours.
It is also the one of the hottest exoplanet as of mid-2013.
It has a high density, suggesting that it is largely composed of metals.
Kepler-70b passes 240,000 km away from Kepler-70c during their closest approach.
This is currently the closest recorded approach between planets.
Such orbital configuration is relatively stable due to orbital resonance between planets and small hill spheres of planets due to proximity of the star.
According to the main author of the paper in "Nature" which announced the discovery of the two planets, Stephane Charpinet, the two planets "probably plunged deep into the star’s envelope during the red giant phase, but survived.” However, this is not the first sighting of planets orbiting a post-red giant star - numerous pulsar planets have been observed, but no planet has been found with such a short period around any star, whether or not on the main sequence. 
Although each planet has unique physical characteristics, a number of broad commonalities do exist among them.
Some of these characteristics, such as rings or natural satellites, have only as yet been observed in planets in the Solar System, whilst others are also commonly observed in extrasolar planets. 
The official definition of "planet" used by the International Astronomical Union (IAU) only covers the Solar System and thus does not apply to exoplanets.
As of April 2011, the only definitional statement issued by the IAU that pertains to exoplanets is a working definition issued in 2001 and modified in 2003.
That definition contains the following criteria:However, the IAU's working definition is not universally accepted.
One alternate suggestion is that planets should be distinguished from brown dwarfs on the basis of formation.
It is widely believed that giant planets form through core accretion, and that process may sometimes produce planets with masses above the deuterium fusion threshold; massive planets of that sort may have already been observed.
This viewpoint also admits the possibility of sub-brown dwarfs, which have planetary masses but form like stars from the direct collapse of clouds of gas.
Also, the 13 Jupiter-mass cutoff does not have precise physical significance.
Deuterium fusion can occur in some objects with mass below that cutoff.
The amount of deuterium fused depends to some extent on the composition of the object.
The Extrasolar Planets Encyclopaedia includes objects up to 25 Jupiter masses, saying, "The fact that there is no special feature around 13 MJup in the observed mass spectrum reinforces the choice to forget this mass limit,".
The Exoplanet Data Explorer includes objects up to 24 Jupiter masses with the advisory: "The 13 Jupiter-mass distinction by the IAU Working Group is physically unmotivated for planets with rocky cores, and observationally problematic due to the sin i ambiguity.
"The NASA Exoplanet Archive includes objects with a mass (or minimum mass) equal to or less than 30 Jupiter masses.
Another criterion for separating planets and brown dwarfs, rather than deuterium burning, formation process or location, is whether the core pressure is dominated by coulomb pressure or electron degeneracy pressure. 
On November 13, 2008, Christian Marois of the National Research Council of Canada's Herzberg Institute of Astrophysics and his team announced they had directly observed three planets orbiting the star with the Keck and Gemini telescopes in Hawaii, in both cases employing adaptive optics to make observations in the infrared.
A precovery observation of the outer 3 planets was later found in infrared images obtained in 1998 by the Hubble Space Telescope's NICMOS instrument, after a newly developed image-processing technique was applied.
Further observations in 2009–2010 revealed the fourth giant planet orbiting inside the first three planets at a projected separation just less than 15 AU which has now also been confirmed in multiple studies.
The outer planet orbits inside a dusty disk like the Solar Kuiper belt.
It is one of the most massive disks known around any star within 300 light years of Earth, and there is room in the inner system for terrestrial planets.
There is an additional debris disk just inside the orbit of the innermost planet.
The orbital radii of planets e, d, c and b are 2 to 3 times those of Jupiter, Saturn, Uranus, and Neptune, respectively.
Because of the inverse square law relating radiation intensity to distance from the source, comparable radiation intensities are present at distances formula_1 = 2.2 times farther from HR 8799 than from the Sun, meaning that corresponding planets in the solar and HR 8799 systems receive similar amounts of stellar radiation.
These objects are near the upper mass limit for classification as planets; if they exceeded 13 Jupiter masses, they would be capable of deuterium fusion in their interiors and thus qualify as brown dwarfs under the definition of these terms used by the IAU's Working Group on Extrasolar Planets.
If the mass estimates are correct, the HR 8799 system is the first multiple-planet extrasolar system to be directly imaged.
The orbital motion of the planets is in an anticlockwise direction and was confirmed via multiple observations dating back to 1998.
The system is more likely to be stable if the planets "e", "d" and "c" are in a 4:2:1 resonance, which would imply that the orbit the planet "d" has an eccentricity exceeding 0.04 in order to match the observational constraints.
Planetary systems with the best-fit masses from evolutionary models would be stable if the outer three planets are in a 1:2:4 orbital resonance (similar to the Laplace resonance between Jupiter's inner three Galilean satellites: Io, Europa and Ganymede as well as three of the planets in the Gliese 876 system).
However, it is now believed that planet b is not in resonance with the other 3 planets.
If confirmed, the HR 8799 planetary system would be the second extrasolar system to be observed with multiple resonances.
The 4 planets are still glowing red hot due to their young age and are larger than Jupiter and over time they will cool and shrink to the size of 0.8 to 1.0 Jupiter radii.
The broadband photometry of planets b, c and d has shown that there may be significant clouds in their atmospheres, while the infrared spectroscopy of planets b and c pointed to non-equilibrium CO/CH4 chemistry.
Near-infrared observations with the Project 1640 integral field spectrograph on the Palomar Observatory have shown that compositions between the four planets vary significantly.
This is a surprise since the planets presumably formed in the same way from the same disk and have similar luminosities. 
Kepler-70b (formerly called KOI-55.01; sometimes listed as KOI-55 b) is a planet discovered orbiting the subdwarf B star (sdB) Kepler-70.
It orbits its host along with another planet, Kepler-70c, both of which orbit very close to their host star.
Kepler-70b completes one orbit around its star in just 5.76 hours, one of the shortest orbital periods of any exoplanetary system yet discovered, only second to PSR 1719-14 b with a period of 2.2 hours.
It is also the hottest exoplanet as of mid-2013, with a surface temperature of 7178 K. Its density is 5500 kg/m3 which is not much different from Earth.
Kepler-70c passes 240,000 km away from Kepler-70b during their closest approach.
This is currently the closest recorded approach between planets.
According to the main author of the paper in "Nature" which announced the discovery of the two planets, Stephane Charpinet, the two planets "probably plunged deep into the star’s envelope during the red giant phase, but survived.” However, this is not the first sighting of planets orbiting a post-red giant star - numerous pulsar planets have been observed, but no planet has been found with such a short period around any star, whether or not on the main sequence.