231058
Skywatching

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.





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.



Exploring Venus, the volcano planet

Volcanic eruptions on Venus

Venus has often been referred to as the Earth's twin.

It is the second planet out from the Sun. We live on the third. It is around the same size as Earth, with a diameter of 12,104 kilometres, compared to our world's 12,756 kilometres.

Our world is hot inside, due to residual heat from its formation some 4.5 billion years ago, and from the decay of radioactive elements. Venus was formed at the same time, and made of more-or-less the same stuff, so we would expect it too to be hot and at least partially molten inside.

The resemblance ends there. Venus has a corrosive atmosphere, is permanently enveloped in a thick layer of cloud, and has a surface temperature hot enough to melt lead and tin.

The first real look at the surface of Venus was provided by the Magellan spacecraft, which used radar to map the planet's surface. Radio waves are unaffected by the clouds.

The world Magellan revealed was a surface with hundreds of volcanoes, some much larger than any on Earth. As one might expect, there were no signs of oceans or living things.

What was odd was that none of those volcanoes were seen to be erupting. We would expect the interior of Venus to be more or less as hot as the inside of our world. The Venusian volcanoes are large, dome-shaped structures—like the volcanoes forming the islands of Hawaii—not the steep, cone-shaped volcanoes like Vesuvius or Mount Saint Helens.

On Earth, we have two main classes of volcanoes—those associated with subduction zones and those lying over hot spots in the Earth's mantle. There is a subduction zone just off the West Coast of British Columbia, where the seabed of the Pacific Ocean is being pushed down and under the continent.

This mixture of rock, sediment and seawater melts and bubbles up forming volcanoes, like Mount St Helens. The upwelling magma forms a sticky lava that tends to plug up the volcano's plumbing. Pressurized with superheated steam, the volcanoes erupt explosively. These volcanoes form the familiar sharp cones, which periodically blow themselves up and reform.

The Hawaiian Islands are formed from the other type of volcano. A hot spot in the mantle produces upwelling magma that breaks through to the surface. The lava is mostly melted basaltic rock, which runs freely. These volcanoes rarely explode, and since the lava flows so easily, it forms flat dome-shaped volcanoes, like thick pancakes. The lava can flow many kilometres, covering huge areas.

Although the Magellan space mission is long over, scientists continue to analyze the data. Recently, evidence was found of a volcanic eruption. The volcano Maat Mons had a side vent that recently filled with lava, which overflowed down the side of the volcano onto the surrounding land. The surprising thing is only this one example has been found so far, although the surface of Venus is the result of continuing volcanic activity.

The Moon is covered with impact craters. That is because it has been geologically dead for billions of years, and its surface has been unchanged for a long time, apart from the accumulated effect of countless meteoric impacts.

Telescopes or binoculars will reveal countless craters. On the other hand, the Earth, which is at least as old, shows less than 200 impact craters. That is because the surface of our world is being continuously recycled by erosion and plate tectonics.

Venus has few craters, so its surface is geologically young. There are no signs of plate tectonics, but frequent outflowings of lava from the numerous volcanoes would bury the craters, renewing the surface.

It is likely our not seeing this volcanic activity is mainly due to the difficulty we have in observing our planet's twin.

•••

• Venus lies low in the dawn glow.

• Jupiter shines high in the south after sunset.

• Saturn is getting hard to see, as it sinks into the sunset glow.

•The Moon will be new on Feb. 9.

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





Why some stars 'wink' in the night sky

Winking stars

Imagine what it must have been like for ancient sky watchers when they saw a star slowly winking at them.

They were familiar with stars twinkling and planets shining steadily, but they found these long, slow winks rather unnerving. The star would shine steadily for 2.9 days, and then, for around 10 hours it would dim to around a third of its original brightness, and then brighten again.

Arab astronomers named it "Algol", meaning "The Demon". The earliest mention of the star was by the Egyptians, some 3,200 years ago, in a calendar of lucky and unlucky days. However, European astronomers did not notice this odd star until 1669, when it was discovered by Montanari, an Italian astronomer, and then, independently, in 1782 by Goodricke, an English astronomer.

This gap in time was probably due to two things, firstly that European astronomers did not believe stars could do that, and secondly, for most of the time Algol shines steadily as a moderately bright star.

Algol lies in the constellation of Perseus, where, for most of the time it is the second-brightest star. The constellation depicts the hero Perseus after he had slain the gorgon Medusa. She had snakes instead of hair and one good look from her would turn you to stone. In the constellation her head is hanging from one of Perseus' hands. Her head is of course marked by the star, Algol.

We now know Algol's winks are due to the star having a larger but much fainter companion star, and as they orbit closely around each other, they take turns passing in front of each other. The stars are so close together we only see them as a single dot in the sky. When both stars are visible, we see the greatest, steady brightness. One star is a lot dimmer than the other. When the dim one passes in front of the brighter one, we get a wink. We get a second wink when the brightest star passes in front of the dimmer one, but that wink is very small and only visible using instruments. It turns out that Algol is a system of three stars orbiting each other, but the third star takes no part in the blinking.

If the Algol system is so far away and its members so close together they appear to us as a single dot, how did we find out what the system is like, and what is happening? The tool that solved the mystery was the spectroscope, a tool for analyzing light. It tells us we are looking at two stars, alternately moving towards and away from us.

It is not clear as to whether there are planets in the Algol system. Planets orbiting two closely spaced stars would have highly unstable orbits. If there is a counterpart of Tattooine (a planet in the Star Wars movies) out there, the variations in temperature as the planet orbits its pair of suns would make it extremely hostile for living things.

Algol stands out because one star is passing in front of the other, and they are orbiting so close that they get round each other in less than three days. Other than that Algol is just an example of a multiple star, where two or more stars are born together and spend their lives, or most of their lives orbiting around one another.

There are multiple stars that are far enough apart for us to see them individually though a telescope, or in some cases our unaided eyes. The most easy to find example of this is the second star in from the end of the handle of the Big Dipper, the brightest part of the constellation Ursa Major, the "Great Bear".

If the night is reasonably clear and dark, you should be able to see that star, named Mizar, has a companion, Alcor. In some countries that companion star is known as "The Rider". If you have a small telescope, you will see Mizar has another companion, closer in. There are countless multiple stars worth looking at. The most beautiful is Albireo, marking the head of the Cygnus, "The Swan". One star is orange and the other blue.

•••

• Venus lies low in the dawn glow.

• Jupiter shines high in the south after sunset, and Saturn low in the southwest.

• The Moon will reach its last quarter on Feb. 2.

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



More Skywatching articles



230161
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]



229498
The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

Previous Stories



231375