Earth, portrayed in most depictions, is a smooth sphere with a polished appearance—a blue marble, as captured by photographs taken from space. However, Earth scientists understand that this depiction is not entirely accurate. In reality, Earth is an ellipsoid, slightly flattened at the poles and bulging at the equator, not to mention adorned with mountain ranges. Then there are the geoid enthusiasts—the ones who view Earth less as an imperfect sphere and more as a lumpy potato.
C. K. Shum, a professor at Ohio State University, falls into this category. He specializes in geodesy, which involves the study of Earth’s gravity field, and he sees the planet through a unique lens. Imagine that Earth’s shape is influenced solely by its own gravity—no tides, winds, or currents—and that water is distributed accordingly across the entire planet. Protrusions correspond to denser regions of the planet, which exert stronger gravity, while indentations indicate less dense areas with weaker gravity. Scientists refer to this as the geoid. The disparities in Earth’s gravity are relatively small, so most visual representations exaggerate the bumpiness to emphasize this aspect, as explained by Shum. In this perspective, Earth appears ready to be drizzled with olive oil, sprinkled with herbs, and thrown into the oven.
Over the years, Potato Earth has sparked confusion on the internet, with some individuals mistakenly believing it to be an accurate representation of Earth without water. In reality, our planet’s surface is far from having a tuber-like appearance. However, the geoid serves as a reminder that Earth is more peculiar than we previously recognized—a delightful peculiarity. Behold our imperfect potato planet! It may be strange, but it’s our own.
The concept of the geoid is complex, particularly for those who are not well-versed in the subject. After all, it’s not a shape that can be naturally observed. “We cannot measure it,” explained E. Sinem Ince, a scientist at the GFZ German Research Center for Geosciences. “We can only collect gravitational data and roughly model it.” The idea was first conceived in the early 19th century by the German mathematician Carl Friedrich Gauss, but it wasn’t until the 20th century, with the advent of satellite technology, that geodesists could precisely outline the potato shape. One well-known visualization of the geoid, known as the Potsdam potato, was created from tens of thousands of space-based gravity measurements of Earth and originates from the institute where Ince works, in Potsdam, Germany.
Although the Potsdam potato may not perfectly resemble Earth’s true appearance, it is not entirely fictional. The geoid has practical applications in our daily lives. According to geodesy experts, using an imaginary ocean at rest as a reference point is immensely helpful in infrastructure planning. For instance, considering the geoid ensures that each floor of a newly constructed skyscraper is level, as explained by Shum. If the Tower of Pisa were to be built today, with the knowledge of the potato, it would likely stand much closer to upright.
Potato Earth is not a static model, clarified Marcelo Santos, a geodesy professor at the University of New Brunswick in Canada. This is because Earth itself is in a constant state of flux due to volcanic activity and plate tectonics, which redistribute mass. “Any mass possesses its own gravity, so if you move mass, you shift gravity,” Santos elaborated. Some changes occur over millennia; certain parts of Earth are still rebounding from the previous ice age, similar to a sagging sofa springing back after someone gets up. Other alterations take place over shorter periods, such as during floods and droughts.
Monitoring these changes holds significant scientific value. Exploring the geoid enables scientists to measure the loss of ice in polar regions caused by climate change, according to the geodesy experts, and provides deeper insights into the behavior of Earth’s interior. By studying areas with higher or lower gravity than average, researchers can investigate the processes behind mass redistribution. The most recent buzz around the 3D geoid rendering revolved around a story concerning a “gravity hole” in the Indian Ocean and the potential magma plumes responsible for it.
Irregularities are not unique to Earth; the solar system is filled with potato-like worlds in terms of gravity. Mercury, Mars, Venus, and even our own moon possess similar rugged features, as explained by Shin-Chan Han, a geodesy professor at the University of Newcastle in Australia. Compared to Earth, Mars displays even greater unevenness, thanks to its enormous volcano Olympus. Celestial potatoes likely exist throughout the universe, making them more common than gravitationally uniform spheres. Whether alien geodesists compare them to extraterrestrial root vegetables is an open question.
I asked Santos how life would be different if Earth were a homogeneous rocky sphere and the geoid a perfect sphere as a result. He assured me that no catastrophic events would occur. In fact, things might be a little simpler. Scientists would not have to constantly refine their measurements of the ever-changing geoid. “It would be boring, and I would be unemployed,” Santos joked. A more uneven world is far more intriguing. It has already altered my perception. For starters, I will never look at a potato in the same way again.
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