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As far as I can tell, we do not yet have the precision to even put reasonable bounds on an exoplanets obliquity, but wikipedia seems to indicate that this may be possible in the "near future." It seems like this would have to be accomplished by direct imaging, either by directly observing rotational flattening of an exoplanets, or by looking for moons and assuming that the planet is tidally locked to the same plane as its satellite.

How close would you estimate we are to this kind of precision? Are there other approaches to measuring planetary obliquity?

Obviously, I'm not expecting a definite answer. Just wondering if anyone knows of any research in this area or has any thoughts about it.

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  • $\begingroup$ It may, in the "near" future, be possible to detect color changes in reflected light off of a planet's surface. If cyclical, this could indicate seasonal vegetation changes which could help us determine obliquity. Of course, we may be a little more excited about the vegetation!! $\endgroup$
    – Jack R. Woods
    Sep 14 '15 at 18:30
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    $\begingroup$ Do you mean the obliquity of their orbits? If so, this has nothing to do with planetary vegetation (and assuming that vegetation exists elsewhere is a huge assumption to make in the first place). $\endgroup$
    – probably_someone
    Dec 30 '16 at 5:09
  • $\begingroup$ Are you talking about obliquity, or oblateness? $\endgroup$
    – HDE 226868 ♦
    Jan 8 '17 at 16:35
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Carter & Winn (2010) suggest that the most promising means of detecting exoplanet obliquity would be through miniscule signatures imprinted on the transit light signal at ingress and egress (~ 200 parts per million for a planet as oblate as Saturn). Zhu et al. (2014) use this technique to make the first tentative detection of exoplanet obliquity from a Kepler object, the 18 Jupiter mass brown dwarf Kepler 39b (KOI-423.01). They measure an oblateness of 0.22±0.11. They also place some upper constraints on the oblateness of other planets in the Kepler catalogue.

Transit signal for KOI-423.01 over 12 orbits. The residuals of two models, one with oblateness and one without, are plotted at bottom. The Oblateness model is a better fit to the data. Transit signal for KOI-423.01 over 12 orbits. The residuals of two models, one with oblateness and one without, are plotted at bottom. The Oblateness model is a better fit to the data.

Oblateness variations are thought to be conducive to exoplanet habitability by regulating temperature modulations, so I expect that measurements of this property over time will be a priority in future exoplanet observations for astrobiology and SETI studies.

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