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Skywatching

Avoiding the fate of the dinosaurs

Nudging asteroids in space

Around 65 million years ago, an asteroid 10 kilometres to 15 kilometres in diameter hit the Earth close to what is now the Yucatan Peninsula.

Already stressed ecosystems were devastated, leading to the extinction of 75% of the species living at the time, including the dinosaurs, ammonites, belemnites and others.

We now live in a world filled with people, in highly stressed ecosystems. We would be very unlikely to survive a similar impact were it to happen now. Therefore, we are working hard to avoid it. There are telescopes dedicated to detecting potential Earth-threatening asteroids, and programs to estimate whether they are an immediate or long-term threat and the probability of an impact.

Of course, detection is only part of the solution. If we find a potentially threatening asteroid, what can we do to remove that threat? Proposed solutions include sending a missile to the object and blowing it up or finding a way to nudge it onto a different and safer path.

A lot depends upon what asteroids are like. Are they rigid lumps of rock or are they rubble piles held together by their weak gravity. That has led to space missions to asteroids to see what they are like and, recently, an experiment to see if we could change its orbit enough to avert a hit.

A few close encounters with asteroids by spacecraft suggest most of them are basically loosely consolidated rubble piles. Whether one of these could be diverted into a new orbit using available space technology led to a NASA mission to Dimorphos, an asteroid with a diameter of about 180 metres (small, but large enough to do a lot of damage). This asteroid happened to be orbiting a somewhat larger asteroid, Didymos, with a diameter of around 780 metres.

The spacecraft, named DART, was intended to smash into Dimorphos and see whether its orbital path was changed by a useful amount. A double asteroid was chosen because the change in their orbits around one another would be far easier to detect, over less time.

The spacecraft was launched in November 2021 and hit it head-on in September 2022. The mission was a success in that the orbit was changed by more than expected.

However, something else happened. The shape of the asteroid was changed. Dimorphos was a rubble pile and it is likely that, if it were hit harder, it would have come apart. If it was an Earth-threatening asteroid, that could be a disaster.

Being shot with a rifle is bad. Being shot by a shotgun is far worse. If a larger rubble pile were heading in our direction, how hard could we hit it in order to change its path without smashing it? Another important consideration is the spacecraft took close to a year to get to the asteroid. We have to know at least a year in advance in order to act usefully.

The need to apply a push that changes the path enough without smashing the asteroid, together with having enough time to reach it, means we need to identify the threatening asteroids well in advance. That way we can apply a gentler push, or over a longer time.

We certainly know how to determine orbits with precision. However, predicting where an asteroid will be in a few years' time is made harder by the constantly changing gravitational influences of the other planets, especially Jupiter, the largest planet in the Solar System. Small perturbations build up rapidly over time, changing asteroid orbits significantly.

On the other hand, we are getting better at it, and spacecraft can be made that make small navigational changes en route. It is a challenge spotting small, dark objects against a black sky early enough to identify threats and act on them. However the incentive is certainly there.

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• Venus and Mars are getting lost in the dawn glow.

• Jupiter shines high in the southwest after sunset.

• The Moon will be new on March 10.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



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Fast radio bursts raise questions about highly magnetized star

Magnetism in space

Fast radio bursts (FRBs) are intense bursts of radio emissions, just milliseconds duration. They were discovered by accident.

A large radio telescope, which could "see" a patch of sky far smaller than the full Moon, just happened to be pointing in the right direction at the right time. Now we have radio telescopes like CHIME, a Canadian instrument located at our observatory, which have a field of view large enough to capture a good fraction of the sky and thousands of these FRBs have been captured, turning up all over the sky.

Most of them come from galaxies millions, or billions, of light years away, showing how much energy must go into producing each of them—more energy than the Sun produces in a year. A few months ago, one of them was detected from an object in our own galaxy. It was a highly-magnetized neutron star, or “magnetar,” named, poetically, SGR 1935+2154.

Since then, astronomers watched, and waited for it to do it again, which it did in October 2022. And CHIME spotted it.

NASA was monitoring the object with two advanced X-ray satellites—NICER (Neutron Star Interior Composition Explorer) is on the International Space Station, and NuSTAR (Nuclear Spectroscopic Telescope Array) is in low-Earth orbit. They observed over several hours, bracketing the fast radio burst so it was possible to put together a picture of what happened.

First some background. Giant stars can end their lives as neutron stars, where the explosion in the outer part of the star compresses the atoms in the core to the point where they collapse completely. Atoms are mostly empty space, so collapsing them completely can take an object around 1.5 million kilometres in diameter down to around 15 km.

The electrons and protons in the atoms have been squeezed together, becoming neutrons. The gravitational attraction on the surface of a neutron star is tens of billions of times the attraction at the surface of the Earth. The magnetic field is around 1e12 (1 followed by 12 zeroes) times stronger than the magnetic field at the surface of the Earth. The highest mountains on a neutron star would be just a few centimetres high.

However, there's one factor that makes the geology of a neutron star very different from the geology of the Earth or other rocky planets. Rock is really good for handling compression, which is why we make buildings out of it. However, it is much worse at handling shear or stretching. On a neutron star the magnetic field makes things different. The surface is pervaded by the intense magnetic fields, which link the neutron star to material orbiting around it. The result is the stresses stored in the stressed surface material before a “starquake” can be enormously stronger. The neutron star discussed here has particularly intense magnetic fields, and is thus is known as a magnetar".

The NASA telescopes detected a "glitch", a small increase in the rotation rate of the object. That happens when a starquake occurs and where material cracks and falls inward, like a skater spinning faster when she pulls in her arms. Large earthquakes here on Earth cause the same thing. There was a glitch - a starquake, and soon after the fast radio burst was detected. About four hours later the rotation rate had fallen to what it was before the glitch, then there was another. The magnetic fields could easily have stored enough energy to drive the fast radio burst.

One suggestion as to why the rotation rate slowed again is that the first starquake caused the surface layers to rotate a bit faster than the deeper layers. Over the next few hours, the surface layers were dragged back into step with the rest of the star.

There is still a lot of vigorous discussion going on here, but on the other hand, it is stunning how much we have learned so far. There is more to do.

•••

• Venus and Mars lie close together low in the dawn glow.

• Jupiter shines high in the south after sunset.

• The Moon will reach it last quarter on the March 3.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



The impact of stellar flares

Space weather

These days most of us are familiar with the term “space weather.”

But “solar weather" is a more accurate term because what we mean by space weather is what the Sun is sending in our direction and what its effects are on our space neighbourhood, the Earth, and our activities. The main things we have to consider are the solar wind, solar flares, and coronal mass ejections.

The solar wind is a continuous and highly variable blast of particles and magnetic fields moving outward from the Sun at speeds up to hundreds to thousands of kilometres per second. Most of this is held away from the Earth by our planet's magnetic field.

If left alone, that field should be shaped like a doughnut. The solar wind blowing over and around it has shaped it into a long teardrop. How important our magnetic field is to us is shown by what we see on Mars. That planet's magnetic field decayed long ago, and since then the solar wind has scoured away most of the planet's atmosphere.

The Sun is a nuclear fusion-powered ball of hot plasma threaded by magnetic fields. These fields emerge through the surface and form huge loops, filled with trapped, million-degree Celsius plasma.

This "magnetoplasma" is rather like a mass of elastic. It can be stretched, twisted or compressed. The constant motion of the solar surface leads to these loops getting tremendously stressed, and a colossal amount of energy stored in them. In most cases there are processes that can relax the stresses and release the energy slowly.

However, on occasion instabilities develop which release that energy catastrophically, resulting in a huge explosion, known as a solar flare. Huge bursts of high-energy radiation, such as X-rays are produced, electrons are accelerated to almost the speed of light and shot off into space, along with beams of other high-energy particles.

Here on the Earth's surface, protected by our magnetic field and atmosphere, those hazards pose little threat. However, for those in space, or flying over the poles at high altitudes, the radiation and high-energy particles from the Sun can pose problems.

Coronal mass ejections, or "solar storms" are loops that have snapped off at the roots and catapulted out into space at thousands of kilometres per second. They are mostly stopped by the Earth's magnetic field, but they can cause intense magnetic storms, which in turn cause power outages and other issues.

For us on Earth, over history solar activity has, as far as we know, posed little threat to living things. The main thing was the occasional spectacular and beautiful displays of aurora. However, over the last few decades, things have started to change. Our increasing dependence on high-tech infrastructure has made us more and more vulnerable to disruptions of our hi-tech lives.

A big question here is how big solar flares can get. Is it possible they could threaten our lives as opposed to our technical infrastructure? Astronomers recently detected a flare on another star that released millions of times the energy of the biggest solar flare observed so far.

This star, designated as HD 283572, lies some 400 light years away. It is young star, only around three million years old, and is about 40% more massive than the Sun. If the Sun produced such an event, it is not clear that our atmosphere and magnetic field could protect us from the environmental damage it could produce. Such flares could have devastating effects on life starting up on young planets.

It looks as though when we are looking for life on planets orbiting other stars, we will need to consider the behaviour of those stars. Only one of those megaflares has been detected so far, so we have no idea how rare they are.

•••

• Venus and Mars lie close together low in the dawn glow.

• Jupiter shines high in the south after sunset.

• The Moon will be full on Feb. 24.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



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A look at Titan, Saturn's largest moon

Saturn's largest moon

Italian astronomer Giovanni Cassini and Dutch astronomer Christiaan Huygens both made detailed observations of Saturn and its moons.

Huygens discovered Titan, Saturn's largest moon. Actually, calling these men astronomers is selling them short. They were scientists in a more general sense, making contributions in many different fields. Back in the 17th century, when they lived, doing cutting edge science did not involve the degree of specialization that is required today.

When a space mission was planned to make closer observations of Saturn and its moons, it was logical to name the mission after these men. The mission involved two spacecraft. One, named Cassini, would orbit around the Saturn system making detailed observations of the planet, its rings and its moons. The other, named Huygens, would make a soft landing on Titan. The pair were launched on Oc. 15, 1997 and entered orbit around Saturn on July 1, 2004.

The trip took that long because the launcher was not powerful enough to give the spacecraft a direct trip to Saturn, it had to do flybys of Venus, Earth and Jupiter to gain the speed needed to reach Saturn.

On reaching the Saturn system, the Huygens spacecraft separated and headed for Titan. After surviving the heat of atmospheric entry, where it used the drag of the atmosphere to slow from many kilometres a second down to a few hundred kilometres an hour, it deployed a parachute, and descended slowly to manage a gentle landing on Titan's surface. There is a fascinating NASA video of the view from Cassini as it descended. https://science.nasa.gov/resource/a-view-from-huygens/

More information about the Huygens mission and more images are available here. https://science.nasa.gov/mission/cassini-huygens/

There are reasons for our particular interest in Titan, compared with the other moons in the Solar System. As soon as telescopes improved enough, astronomers noticed that whereas the other moons in the Solar System are largely colourless or very subtly coloured, like our moon, Titan is orange-brown. Whereas the other moons have either no atmosphere, or maybe a very thin one, Titan has a very thick atmosphere, thicker than the Earth's.

Around 9.6 times further from the Sun than the Earth, Titan receives only about 1% of the solar heat and light. This makes Titan a really cold place, with a surface temperature of about -180 C. At that temperature water would be a permanently frozen rock mineral. However, under Titanian conditions, methane can be present as a gas or a liquid, playing the same role as water on Earth, forming lakes and rivers. Huygens landed on a dry streambed.

The brown atmosphere is due to hydrocarbons and other organic (carbon-based) molecules. A witches brew of chemicals have been detected so far, probably formed in the upper atmosphere, in chemical reactions driven by sunlight.

Here on Earth, the foundation of life was organic molecules dissolved and interacting in seawater. Could organic molecules dissolved in liquid methane provided a foundation for life on Titan?

There is little or no oxygen in Titan's atmosphere, but when life first started on Earth there was no oxygen here either. One important difference is water is a solvent in which chemicals can easily break up and then combine to make new ones. Liquid methane is less effective for this. However, that does not rule out the possibility of life. If it exists it will be very different from life here. We need to have a closer look at that world.

•••

• Venus lies low in the dawn glow.

• Jupiter shines high in the south after sunset.

• The Moon will reach first quarter Feb. 16.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



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The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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