A recent study published in the Proceedings of the National Academy of Sciences reveals a significant impact of melting polar ice caps on Earth's rotation. According to the study, the influx of water from Greenland and Antarctica is redistributing mass around the planet's equator, causing Earth to spin more slowly. This phenomenon is unprecedented and is resulting in an increase in the length of days.
Co-author Surendra Adhikari from NASA's Jet Propulsion Laboratory compared this effect to a figure skater extending her arms during a pirouette, which slows down the rotation due to increased inertia away from the axis.
Earth, typically seen as spherical, is more accurately described as an "oblate spheroid," slightly bulging around the equator like a satsuma. Its shape is not static; it changes over time due to various factors such as daily tidal impacts, movements of tectonic plates, and sudden shifts caused by earthquakes and volcanoes.
The study utilised advanced observational techniques like Very Long Baseline Interferometry and the Global Positioning System to measure Earth's orientation and length of day variations with high precision. It also examined historical eclipse records spanning millennia.
The implications of a slower Earth rotation are significant for space travel and navigation. Even a slight increase in the length of day, currently around 86,400 seconds, can impact space missions. The study highlights that while lunar gravitational pull has historically been the main cause of rotational slowdown, ongoing climate change may surpass this effect by the end of this century.
Since 1900, climate change has already lengthened days by approximately 0.8 milliseconds. Under high greenhouse gas emission scenarios, this could extend to 2.2 milliseconds by 2100. While imperceptible to humans, such changes are critical for precise space navigation, where even minor deviations in Earth's orientation can lead to significant discrepancies over long distances.
Co-author Adhikari emphasised the importance of understanding Earth's exact orientation for space missions, citing the Voyager probes as examples where accurate positioning is crucial for communication beyond our solar system.
The study underscores the complex interplay between Earth's environmental changes and its impact on fundamental astronomical measurements and space exploration.
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