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# What is the Strongest Surface Gravity for an Exoplanet So Far?

The free-fall acceleration of an object on the surface of the planet is the surface gravity. It is a measure of the object's weight as opposed to its mass. Both a mass and a radius of a planet are required to calculate the surface gravity of the planet, but not all exoplanets have both mass and radius measurements or estimates. On 5 August 2012, only about 32% of confirmed exoplanets had sufficient data for the surface gravity to be calculated.

In order to calculate the surface gravities of the exoplanets listed in the Extrasolar Planets Encylopedia catalog, you have to download the data table, filter the rows that have both mass and radius entries filled, and then calculate the surface gravities as shown in the surface gravity distribution page. You can do this by reading the data into an analysis program that you are familiar with (for example, EXCEL).

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As an example, on 5 August 2012, the exoplanet with the strongest surface gravity was Kepler-25 b. This planet has a radius of 0.23 Jupiter radii, a minimum mass estimate of about 12.7 Jupiter masses, and a calculated surface gravity of 633.7 times that of the Earth. Make no mistake: this is a colossal value. (For reference, the surface gravity of Earth is about 9.8 meters per second per second, or 32 feet per second per second). Thus, a person weighing 150 pounds on Earth would weigh $150 \times 633.7 = 95055$ pounds near the surface of Kepler-25 b. Let's put that another way: the 150-pound person would weigh over 40 tonnes near the surface of the exoplanet. For further comparison, the surface gravity of our Sun is about 28 times that of Earth.

A word of caution: you should always try to find out what measurement uncertainties are associated with any quoted number (not just for exoplanet mass and radius values, but any measurement in general). However, the measurement uncertainties on various parameters are not often given, even in the Extrasolar Planets Encyclopedia (as is the case in the example above): you have to dig a little deeper into the literature. Remember also that most exoplanet masses are minimum masses so the calculated surface gravity for an exoplanet will also be a minimum value, or lower limit.

File under: What is the greatest value of the surface density of an exoplanet obtained so far? What exoplanet has the highest surface gravity? How can I find the latest information on the exoplanet with the strongest surface gravity?