1 October, 2022

The length of Earth's days has increased and scientists don't know why

In the last decades, the rotation of the earth around its axis has been accelerated, which determines the length of the day. This trend has made our days shorter. In fact, in June 2022 we set a record for the shortest day in the last half century.

Editorial Dept. Voz de la Diaspora

World – the atomic clocks, combined with precise astronomical measurements, have revealed that the length of the day is getting longer, without scientists understanding why. This has critical repercussions not only in our way of measuring time, but also in GPS and other technologies that govern our modern lives.

In the last decades, the rotation of the earth around its axis has been accelerated, which determines the length of the day. This trend has made our days shorter. In fact, in June 2022 we set a record for the shortest day in the last half century.

But despite this record, since 2020 changed the trend and it seems that the Earth's rotation has slowed down: the days are longer again, and the reason is, until now, a mystery.

Although the clocks on our phones indicate that there is exactly 24 hours in a day, a day rarely corresponds exactly to the magic number of 86,400 seconds. The actual time it takes for the Earth to complete a single rotation varies slightly. These changes occur in periods ranging from millions of years to almost instantaneously.; even earthquakes and storms can influence.

Do we need a “negative leap second”?

Precise knowledge of the Earth's rotation rate is crucial for a number of applications.: navigation systems, like GPS, they wouldn't work without it. further, every few years timekeepers introduce leap seconds into our official time scales to make sure they don't get out of sync with our planet.

Atomic Clock

If the Earth happened to have even longer days, it would be necessary to incorporate a “negative leap second”, which would be unprecedented and could break the internet.

The need for negative leap seconds is considered unlikely at this time. For the moment, we can be satisfied with the news that – at least for a while – we all have a few more milliseconds each day.

The constantly changing planet

over millions of years, Earth's rotation has been slowing due to frictional effects associated with tides driven by the Moon. This process adds a 2,3 milliseconds to the duration of each day per century. A few billion years ago, a terrestrial day lasted only about 19 hours.

During the last 20,000 years, another process has worked in the opposite direction, accelerating the earth's rotation. we mean that, when the last ice age ended, the melting of the polar ice caps reduced the pressure on the surface, and the Earth's mantle began to move steadily towards the poles.

Images courtesy NASA

Just like a ballet dancer spins faster when she brings her arms closer to her body – the axis around which she spins –, the rate of spin of our planet increases when this mass of mantle approaches the axis of the Earth. And this process shortens each day by a few 0,6 milliseconds every century.

For decades and even more, the connection between the interior and the surface of the Earth also comes into play. Big earthquakes can change the length of the day, although usually in small amounts. For example, It is believed that the Great Tohoku earthquake of 2011 in Japan, with a magnitude of 8,9, sped up the Earth's rotation by a relatively small amount: 1,8 microseconds.

Apart from these large-scale changes, in shorter periods weather and climate also have important impacts on the rotation of the Earth, causing variations in both directions.

Biweekly and monthly tidal cycles move mass around the planet, causing changes in day length of up to a millisecond in either direction. We can see the variations of the tides in the records of the length of the day for periods of up to 18,6 years.

The movement of our atmosphere has a particularly strong effect, and ocean currents also play a key role. Snow cover and seasonal precipitation or groundwater extraction mess things up even more.

Why does the Earth suddenly slow down?

Since the decade of 1960, when radio telescope operators around the planet began devising techniques to simultaneously observe cosmic objects like quasars, we have very precise estimates of the speed of rotation of the Earth.

A comparison between these estimates and an atomic clock has revealed an increasingly shorter day length in recent years..

But there is a surprising finding once we remove the fluctuations in rotational speed that we know to occur due to tidal and seasonal effects.. Even though the Earth reached its shortest day on 29 June 2022, the long-term trend appears to have gone from shortening to lengthening since 2020. This change is unprecedented in recent 50 years.

The reason is not clear. Could be due to changes in weather systems, with consecutive La Niña events, although they have happened before. It could be a further melting of the ice sheets, although these have not deviated much from their constant rate of melting in recent years. Could it be related to the huge explosion of the Tonga volcano that injected huge amounts of water into the atmosphere?? Probably not, Since it happened in January 2022.

Scientists have speculated that this mysterious recent change in the planet's rotation rate is related to a phenomenon called Chandler wobble., A small deviation in the axis of rotation of the Earth with a period of about 430 days. Observations from radio telescopes also show that the wobble has decreased in recent years.. Both could be related.

one last chance, that seems plausible to us, is that nothing specific has changed in or around the Earth. It could simply be long-term tidal effects working in parallel with other periodic processes to produce a temporary change in the Earth's rate of rotation..

Matt King, Director of the ARC Australian Centre for Excellence in Antarctic Science, University of Tasmania YChristopher Watson, Senior Lecturer, School of Geography, Planning, and Spatial Sciences, University of Tasmania

This article was originally published onThe Conversation. read theoriginal.