Earth days have mysteriously increased in length – scientists don’t know why

Careful astronomical observations, combined with atomic clocks, revealed that the length of the day is suddenly increasing. Scientists do not know why.

This has crucial implications not only for our timekeeping, but also for things like GPS and other precise technologies that govern our modern lives.

The rotation of the Earth on its axis has accelerated over the past few decades. Since this determines the length of the day, this trend is making our days shorter. In fact, in June 2022 We set a record! For the shortest day in half a century or so.

However, despite this record, since 2020, this strangely constant acceleration has turned into a slowdown. Now, the days are getting longer again, and the reason so far remains a mystery.

While the clocks in our phones indicate that there are exactly 24 hours in a day, the actual time it takes the Earth to complete one cycle can vary slightly. Sometimes these changes occur over periods of millions of years, and other times almost instantly. For example, even earthquakes and storm events can play a role.

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

The ever-changing planet

The Earth’s rotation has slowed over millions of years due to the effects of friction associated with the moon’s tides. This process adds about 2.3 milliseconds to the length of each day every 100 years. A few billion years ago, Earth Day was approaching 19 hours.

Over the past twenty thousand 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 lowered surface pressure, and the Earth’s mantle began to move steadily toward the poles.

Just as ballerinas spin faster when they point their arms toward their body—the axis they rotate around—the rate of rotation of our planet increases as this mantle mass moves closer to the Earth’s axis. This process was shortened every day by about 0.6 milliseconds per century.

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

Aside from these large-scale changes, over shorter periods, weather and climate also have important effects on the Earth’s rotation, causing differences in both directions.

Bimonthly and monthly tidal cycles move mass around the planet, causing variations in the length of a day of up to milliseconds in either direction. We can see the tidal variations Records the length of the day over periods of up to 18.6 years. The movement of our atmosphere has a particularly strong effect, and ocean currents also play a role. Seasonal snow cover, rain or groundwater extraction changes things even more.

Why is the earth suddenly slowing down?

Since the 1960s, when operators of radio telescopes around the planet began to invent technologies Detecting cosmic objects such as quasars at the same timewe have very accurate estimates of the rate of Earth’s rotation.

The use of radio telescopes to measure the Earth’s rotation includes observations of radio sources such as quasars. attributed to him:[{” 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.