Ask the researcher: About every 76 years, Halley’s famous comet lights up the sky. With it, we found out how comets move and what they consist of.
Currently, you can select Comet C/2022 E3 ZTF.
Another and more famous comet is Halley’s comet. Some of us may see it twice in our lives.
But what do we really know about the iconic comet? How far is it? how old? That’s what John, a reader of videnskab.dk, asked. He is a prison teacher and his students have many questions about comets.
We asked astrophysicist Michael Linden-Vørnle of DTU Space.
Detection of a frozen comet nucleus
The last time Halley’s Comet flew between the Sun and the Earth and could be seen in the sky was in 1986. Michael Linden-Fornley then captured the scene.
– When Halley’s comet approached in 1986, several space probes were sent towards it. They were supposed to show us for the first time what a comet’s nucleus looks like, Linden Fornley says.
– It pioneered and confirmed the idea that you had about comets. He explains that it consists of ice, rock and dust, with streams of gas and dust from the core.
Halley’s Comet will reach its furthest point this year
Comets are said to be deep frozen remnants from when the solar system was formed, about 4.6 billion years ago. This makes Halley’s Comet obsolete.
It takes about 76 years to travel around the sun and is likely to reach its farthest point from the sun by the end of this year. It is a distance of about 5.3 billion kilometers.
Comets are energetic bodies and their orbits are very unstable. The astrophysicist says this also applies to Halley’s Comet.
– When comets approach the sun, their temperature rises and gas and dust escape from them. Since it flows like jets, it can act as an engine that can influence the comet’s orbit. But we know when we’ll see Halley’s comet in the sky again, he points out.
It appears in prehistoric times
Halley’s comet was the first periodic comet to be discovered. It was discovered by the English astronomer Edmund Halley in 1705, when he calculated with the help of Newton’s laws that a comet would appear every 76 years.
If we look further back in history, Halley’s comet appears many times.
According to historical records from China, Halley’s comet was observed around 240 BC. And again in 1066.
– You can see Halley’s Comet woven into the famous Bayeux Tapestry from William the Conqueror. He wanted to conquer England, and when Halley’s comet appeared in the sky, he saw it as a sign of the success of the invasion. Linden-Vørnle says comets are usually interpreted as something ominous.
the countdown
It will be a long time until we see Haley’s return. This will not happen for another 38 years. In 2061 it will pass between the Sun and the Earth.
Meanwhile, other comets will fly across the sky. Both remind us of Halley’s comet and others that have not appeared in human history before.
– If you use binoculars, you can see comets regularly here from the northern hemisphere. But ten years can pass between the arrival of large, visible comets that we can see with the naked eye, Linden Fornley explains.
What we see clearly are usually comets that come every few thousand years. They are the so-called long-period comets, like the famous Hale-Bopp from 1997 and the C/2022 E3 ZTF, which appeared in early January/February of this year. C/2022 E3 ZTF has not been visited since the presence of Neanderthals about 50,000 years ago.
Long-period comets come directly from the Oort Cloud, repositories of ice and rock lurking around the solar system. When comets come from there, they contain so much ice that they can evaporate and create a cloud around the comet’s nucleus itself, the astrophysicist says.
The sun is eating Halley’s comet
In fact, comets are black in color and only appear as bright objects when they come close to the Sun and get heated up.
– The influence of the sun pushes away the gas and dust that escapes from the comet, and this is what we see in the tail of the comet. Linden Fornley explains that every time a comet passes through the sun in the inner solar system, it loses some of its mass.
– Halley’s comet is losing a few meters at a time. But he says it will likely take a long time before it either ends up as a dead comet or disintegrates.
Comets can kill us
When comets die, either by being melted by the sun or floating away with no more material to leave the nucleus, it has no consequences for us on Earth or the rest of the solar system, Linden-Fornley says.
But the living can, at worst, become the collapse of humanity.
– We are a little concerned about comets because there is a possibility that they will hit Earth, just like asteroids. But comets come without warning and can be hard to spot because they are so black. Therefore, we have to deal with them, concludes Linden Furnley.
© Videnskab.dk. Translated by Lars Nygaard for forskning.no. Read the original story on videnskab.dk here.
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