JPL: Earth Not Growing or Shrinking

While Earth’s inhabitants struggle with fluctuating pants sizes, the planet, according to the findings of a JPL-led research team, doesn’t grow or shrink, as had been speculated by scientists since Charles Darwin’s time.

Why does Earth’s waistline matter?

Earth’s shape is constantly altered through volcanic activity, earthquakes, erosion, and even massive climate events such as El Niño.

But in order to put the movements and changes of Earth’s crust into the proper context, scientists must have an accurate reference against which to evaluate them, according to information released from . Any significant change in the planet’s radius would alter scientist’s understanding of how to measure Earth’s shape and gravity field and their changes over time.

So in addition to accuracy, it's all about the International Terrestrial Reference Frame: a guide used by scientists to calculate data regarding Earth’s measurements. The frame is used in ground navigation, tracking spacecraft in Earth’s orbit, and monitoring aspects of climate change including sea level fluctuations and imbalances in ice layers at Earth’s poles.

New Techniques

To calculate the Frame, scientists use a number of techniques, including satellite laser ranging, radio astronomy and GPS. But with these methods, accuracy is considered a problem due to the limitations of geographic sites and the effects of Earth’s processes.

JPL and international scientists evaluated the Frame’s accuracy by applying a new data calculation technique focused on estimating the rate of change in the solid Earth’s radius, not including the atmosphere. The Frame’s data was combined with gravity measurements provided by NASA’s Gravity Recovery and Climate Experiment (GRACE) spacecraft and ocean bottom pressure models.

The Result

The team found the average estimated change in Earth’s radius to be 0.004 inches per year – about as thick as a human hair and, therefore, not considered statistically significant. 

“Our study provides an independent confirmation that the solid Earth is not getting larger at present,'' JPL's Xiaoping Wu said in a prepared statement.

Wu led the international group of scientists whose research confirmed that yes, it is a small world after all.