Earth’s days are getting mysteriously longer, and scientists don’t know why

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

over the past few decades, EarthThe rotation around its axis – which determines how long a day is – is accelerating. This trend is making our days shorter; In fact, in June 2022 we set the record for the shortest day in the past half a century.

But despite this record, the steady pace since 2020 has gradually turned bearish – the days are getting longer again, and the reason is still a mystery.

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 sometimes varies slightly. These changes occur almost instantaneously over a period of millions of years – even earthquakes and hurricane events can play a role.

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

ever changing planet

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

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. . And this process reduces every day by about 0.6 milliseconds every 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 increased the Earth’s rotation by a relatively small 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 tides in the day-to-day record over a period of 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 techniques to simultaneously observe cosmic objects such as quasars, we had very accurate estimates of the rate of Earth’s rotation.

A comparison between these estimates and an atomic clock showed that the length of the day has been decreasing over the years.

But once we take away the fluctuations in rotation speed there is a surprising reveal that we know is caused by tidal and seasonal effects. Despite Earth reaching its shortest day on June 29, 2022, the long-period trajectory has shifted from shortening to lengthening since 2020. This change is unprecedented in the last 50 years.

The reason for this change is not clear. This may be due to changes in weather systems with back-to-back La Nia events, although these have happened before. This may be extended to the melting of the ice sheets, although they have not deviated much from their steady rate of melting in recent years. Could this be related to the huge volcanic eruption in Tonga pouring huge amounts of water into the atmosphere? Probably not, considering that happened in January 2022.

Scientists have speculated that the recent, mysterious change in the planet’s rotation speed is related to a phenomenon called the “Chandler’s wobble”—a small deviation in Earth’s rotation axis with a period of about 430 days. Observations from radio telescopes also show that wobble has decreased in recent years; Both can be combined.

A final possibility, which we consider plausible, is that nothing conspicuous has changed in or around Earth. It may be long-term tidal effects acting in parallel with other periodic processes to produce temporary changes in the Earth’s rotation rate.

Do we need ‘negative leap seconds’?

Accurately understanding the Earth’s rotation rate is important for many applications – navigation systems such as GPS would not function without it. Also, every few years the timekeepers put leap seconds into our official timescale to ensure that they are not going out of sync with our planet.

If Earth were to move in even more days, we might need to include “negative leap seconds” – that would be unprecedented, and could break the Internet.

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

This story has been published without modification in text from a wire agency feed. Only the title has been changed.

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