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What is the Shortest Orbital Period of an Exoplanet Found So Far?

If you would like to be able to find out yourself what is the shortest orbital period of an exoplanet found so far, here is how you do it. Go to the Extrasolar Planets Encylopedia catalog page and click on the column called Period. When you click on it, the data in the table should be sorted in order of numerical value in that column (i.e., the orbital period of the planets). An arrow just to the right of the word Period tells you whether the numerical order is ascending or descending (the arrow will point upwards for an ascending order). If you click the column header again, the numerical ordering will flip from ascending to descending or vice versa.

To find the exoplanet with the shortest orbital period, you want the period measurements to be ascending, with the smallest values appearing first. (Note that at the end of the sorted table the rows that appear first will have no entries in the Period column and these correspond to exoplanets for which the orbital period has not been measured.) The first non-blank entry in the sorted orbital period column corresponds to the confirmed exoplanet that has the shortest orbital period. The number in the cell in the Period column is the orbital period in units of Earth days (or 86400 seconds). From here you can convert to any other units by typing an appropriate statement in a Google search box.

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As an example, on 4 August 2012, the exoplanet with the shortest period was PSR 1719-14 b. This planet has a radius of 0.4 Jupiter radii, a minimum mass estimate of about 1 Jupiter mass, and an orbital period of about 0.0907063 days. This is an incredibly short period for something as massive as Jupiter: it's a little more than a couple of hours so the system is rather extreme. However, notice that the host star is not a regular star, but a pulsar (hence the “PSR” in the name). A pulsar is a star in which nuclear fusion has ceased and the object has collapsed under its own gravity to become a highly compressed mass of neutrons. A pulsar is a spinning neutron star.

If we want to find the shortest orbital period for an exoplanet that is orbiting a more “regular” star, we look at the next object on the list. On 4 August 2012, it was KOI-55 b. This object is listed as having a minimum mass of about 4.4 times that of Earth, and a radius of about 0.75 times that of Earth, orbiting a star that has mass of about half that of our Sun. The orbital period is listed as 0.24 days, or just under 6 hours. This is still remarkably short and there is no counterpart to such such short-period exoplanets in our own solar system.

A word of caution: you should always try to find out what measurement uncertainties are associated with any quoted number (not just for exoplanet orbital periods, but any measurement in general). However, the measurement uncertainties on various parameters are not often given, even in the Extrasolar Planets Encyclopedia: you have to dig a little deeper into the literature.

See also the exoplanets period distribution.

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