Important Exoplanet Discoveries so Far

What are the most important exoplanet discoveries so far? Here are just some of them.

There are types of planets that have no counterpart in our solar system. For example, there are no hot jupiters in our solar system. In our solar system the closest planet (Mercury) is no closer than about 0.3 times the Earth-sun distance but in alien solar systems planets are found closer to their host star than even a couple of percent of the Earth-sun distance. This was totally unexpected and the presence of giant planets this close to the host star is even more surprising. A convincing satisfactory explanation is yet to be found.

There appears to be a “bunching-up” (or pile-up) of hot jupiters at distances of a few percent of the Earth-sun distance. These very close-in distances lead to very short orbital periods, of the order of days. These short periods were, and still are, surpising. There are no such short-period planets in our solar system. There is no satisfactory explanation of the hot jupiter pileup.

There is a bimodal distribution in orbital periods, meaning that there are two favored (broad) peaks in the orbital period distribtion of exoplanets. One peak is at about 4 (Earth) days, and the other is in the region of about 300 to 2000 (Earth) days. Again, there is no satisfactory explanation of this effect. Take a look at this diagram of the exoplanets period distribution.

There is much larger range in mass, taking the discovered exoplanets as a whole, compared the range of masses found in our solar system. Take a look at this histogram of the exoplanet mass distribution.
It appears that there is a tentative correlation between the likelihood of a star hosting exoplanets and the star's chemical composition (in the sense that a higher abundance of elements heavier/more complex than hydrogen and helium favors planet-hosting).
Several observational results conflict with the prevailing theory of planet formation (the so-called core-accretion theory; for details, read the linked article and the two articles linked to that one; see also this article at exoplanetsdigest.com).

Learn more about exoplanets with Exoplanets and Alien Solar Systems, which goes into more depth and breadth about the astonishing new discoveries about exoplanets, and has comprehensive citations to the original literature.

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File under: Exoplanet discoveries so far; Key findings from exoplanet research.