Is Jupiter still an anomaly?

  • I remember a few years ago hearing that Jupiter was an anomaly in the landscape of exoplanets. Back then, most Jupiter-mass planets discovered were Hot Jupiters, orbiting very close to their host star.



    In the last few years since I heard this, many new exoplanets have been discovered. Do we know now if there are many more Hot Jupiters and our own Jupiter is a rather rare occurrence, or if this was an observational bias and there are many more "Cold Jupiters"?


    Jupiter is a possible solution to the Fermi Paradox, the rare Earth hypothesis. https://en.wikipedia.org/wiki/Rare_Earth_hypothesis#The_right_arrangement_of_planets It's hypothesized that Jupiter protects Earth from comets by sweeping up stray debris with its large gravitational field. Along with a big moon and a few other attributes.

    Note that all else equal, Hot Jupiters will be much easier to find than Cold Jupiters, using the techniques we use to observe planets in other solar systems. This is a common problem in astronomy :)

  • It depends on how you define Jupiter analogues. There are several possible factors, including mass, eccentricity and orbital period cutoffs. Given there's no consistent definition, comparison of results between the various papers is difficult.



    For example, the recent paper by Wittenmyer et al. considers "cool Jupiters" to be planets with masses greater than 0.3 Jupiters with orbital periods longer than 100 days. These planets do seem to be much more common than the hot Jupiters but this category is a lot broader than just "Jupiter analogues". It includes objects like HD 208487 b, a planet which would be located between Mercury and Venus in our Solar System and has a far more eccentric orbit (e=0.3) than any of our major planets: hardly a Jupiter analogue.



    Many of the long period planets have high eccentricities. Imposing an eccentricity cutoff would tend to change things a bit. Other considerations might involve imposing upper limits on the mass, or a different lower limit. The paper notes that their conclusions about the rate of occurrence of Jupiter analogues is consistent with previous studies once the different criteria are imposed.


    I think we need to be careful how we "classify" things. If you look at the paper mentioned in this answer, it estimates that there are about 8 times as many planets with periods over 100 days as those with less. Lets make an analogy. Say we make a study of 90 people and find that 10 are less than one year old. That leaves less than one per year for every other age and this may need some explaining. In addition, I think that if you look at periods between 100 and 1000 or so days you will see a higher rate of planets per 100 day period range. The rest are relatively evenly distributed.

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Content dated before 7/24/2021 11:53 AM