Earth’s days are mysteriously increasing in length – scientists don’t know why

planet earth sunrise

Precise measurements suggest that the Earth’s rotation has been mysteriously slowing since 2020, making the day longer.

A combination of precise astronomical observations and atomic clocks has shown that the length of a day is suddenly increasing. Scientists don’t know why.

This has a significant impact not only on our timekeeping, but also on GPS and other precision technologies that govern our modern lives.

The Earth’s rotation around its axis has accelerated over the past few decades. Since it determines how long a day is, the trend is shortening our days. In fact, in June 2022 we set a record For the lowest number of days in the past half century.

However, despite this record, the steady momentum since 2020 has gradually turned bearish. Now, the days are getting longer again, and the reason for this has remained a mystery till now.

While the clocks on our phones show that there are exactly 24 hours in a day, the actual time it takes the Earth to complete one revolution can vary so little at times. These changes sometimes occur over a period of millions of years, and other times almost immediately. For example, earthquakes and hurricane events can also play a role.

It turns out that the magic number of 86,400 seconds a day is very rare.

ever changing planet

Earth’s rotation has been slowing down over millions of years due to frictional effects associated with tidal movements driven by the Moon. This process adds about 2.3 milliseconds to the length of each day every 100 years. A few billion years ago, one Earth day was only about 19 hours,

For the past 20,000 years, another process has been working in the opposite direction, accelerating the Earth’s rotation. When the last ice age ended, the melting of the polar ice sheets reduced surface pressure and the Earth’s mantle began to move rapidly toward the poles.

Just as a ballet dancer spins faster as they bring their arms toward their body—the axis around which they spin—our planet’s spin rate increases as this mass moves closer to Earth’s axis. This process is reducing each day by about 0.6 milliseconds each century.

For decades and longer, the relationship between the Earth’s interior and the surface has also been trending. Large earthquakes can change the length of the day, although usually by small amounts. For example, the 2011 Great Tohoku earthquake in Japan, with a magnitude of 8.9, is believed to have accelerated Earth’s rotation at a relatively low rate. 1.8 microseconds,

In addition to these large-scale changes, weather and climate also have a significant effect on Earth’s rotation in the short term, causing variations in both directions.

The fortnightly and monthly tidal cycles revolve extensively around the planet, causing a change in the length of the day by milliseconds in either direction. we can see tidal variations In day-to-day records for a period up to 18.6 years. The movement of our atmosphere has a particularly strong effect, and ocean currents play a role as well. Seasonal snow cover and precipitation, or groundwater extraction, turn things around further.

Why is the Earth suddenly slowing down?

from the 1960s, when operators of radio telescopes around the planet began to develop technology Simultaneously observe quasar-like cosmic objectsWe have very accurate estimates of the rate of Earth’s rotation.

Using radio telescopes to measure Earth’s rotation involves observing radio sources such as quasars. Credit:[{” attribute=””>NASA Goddard

A comparison between these measurements and an atomic clock has revealed a seemingly ever-shortening length of day over the past few years.

But there’s a surprising reveal once we take away the rotation speed fluctuations we know happen due to the tides and seasonal effects. Despite Earth reaching its shortest day on June 29, 2022, the long-term trajectory seems to have shifted from shortening to lengthening since 2020. This change is unprecedented over the past 50 years.

The reason for this change is not clear. It could be due to changes in weather systems, with back-to-back La Niña events, although these have occurred before. It could be increased melting of the ice sheets, although those have not deviated hugely from their steady rate of melt in recent years. Could it be related to the huge volcano explosion in Tonga injecting huge amounts of water into the atmosphere? Probably not, given that occurred in January 2022.

Scientists have speculated this recent, mysterious change in the planet’s rotational speed is related to a phenomenon called the “Chandler wobble” – a small deviation in Earth’s rotation axis with a period of about 430 days. Observations from radio telescopes also show that the wobble has diminished in recent years. Perhaps the two are linked.

One final possibility, which we think is plausible, is that nothing specific has changed inside or around Earth. It could just be long-term tidal effects working in parallel with other periodic processes to produce a temporary change in Earth’s rotation rate.

Do we need a ‘negative leap second’?

Precisely understanding Earth’s rotation rate is crucial for a host of applications – navigation systems such as GPS wouldn’t work without it. Also, every few years timekeepers insert leap seconds into our official timescales to make sure they don’t drift out of sync with our planet.

If Earth were to shift to even longer days, we may need to incorporate a “negative leap second” – this would be unprecedented, and may break the internet.

The need for negative leap seconds is regarded as unlikely right now. For now, we can welcome the news that – at least for a while – we all have a few extra milliseconds each day.

Written by:

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

This article was first published in The Conversation.The Conversation

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