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Skywatching

Starry senior citizen

Among the stars of our galaxy, the Milky Way, there is a small, dim red star that is attracting a lot of interest. It is only about 14 per cent of the mass of the sun, barely enough to graduate as a star.

It is one of a class of stars known as red dwarf stars.

There are lots red dwarf stars, but this one is of particular interest because it is estimated to be 13.5 billion years old, almost as old as the universe.

How could we possibly know this? Unlike many issues in science, this one is reasonably simple. Let's start with the star we know most about.

The sun formed from a big cloud of gas that collapsed into a ball. In the core, nuclear fusion converts the sun's fuel — hydrogen — into other elements, and produces the energy that makes the Sun shine.

Those waste products will stay hidden in the sun's core until it dies, when most of its material will be ejected into space, to be added to the clouds that will eventually make new generations of stars.

When we analyze the visible part of the sun, that yellow ball in the sky, we are looking at the unprocessed, raw material from which the sun formed. The composition of that material tells us the star generation in the history of the universe to which the sun belongs.

This fact about stars has led to an intriguing discovery: one of the oldest stars in the universe.

When the universe began, almost 14 billion years ago, it consisted almost totally of just two elements, hydrogen and helium. The carbon, oxygen, phosphorus, iron and other elements making up our bodies and our world did not exist.

Then the first stars formed. They were blue super giant stars that shone brightly and rapidly turned hydrogen into the other elements.

They got through their fuel in millions of years or less, blew up and distributed those elements into the surrounding clouds.

Those stars are long gone, and the ones we see in the sky, including the sun, are of later generations. We know this because the sun's unused fuel, which forms its surface layers, contains elements manufactured by earlier generations of stars.

We know the elements we see there did not originate in the fusion reactions in the sun's core because all those "waste products" stay there.

This brings us back to that ancient red dwarf star. Its outer layers contain nothing much other than hydrogen and helium, which means it formed from material so old that there had been no build-up of waste materials from earlier generations of stars. We could be looking at a "first generation star.”

However, the big question is why, in an era of blue, super giant stars, there was born a red dwarf?

Our solar system provides a clue.

When it formed, only one lump of material became big enough to become a star. However, we also have some giant planets, the largest of which is Jupiter, currently visible in the eastern sky before dawn.

If the lump of material that became Jupiter had just been a few times larger, it would have become a red dwarf star. It is just possible that long, long ago, when a blue super giant star formed, one of that first burst of star formation in the young universe, some of the material from its birth cloud formed a second, much smaller star — a red dwarf.

Even though red dwarfs have low masses, they are so frugal with their energy production they can shine almost indefinitely.

They can have lives as long as the universe. It would be interesting to wonder about ancient beings on ancient planets orbiting such stars, but back then there was nothing from which to make those planets.

Having material to make planets and people had to wait a few more stellar generations.

  • Mars lies in the southwest after dark.
  • Venus lies in the southeast in the early hours
  • Jupiter and Saturn (the fainter of the two) are close together in the dawn glow.
  • The moon will be full on the 19th and will reach Last Quarter on the 26th.


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An old, far-flung rock

Our Earth, along with the other bodies in the solar system, formed some 4.5 billion years ago from the collapse of a cloud of gas and dust.

Tiny bits collided and stuck together making larger bits, and so on. Sometimes large bits collided and smashed each other back to smaller bits, and the building process had to start over.

The moon may have been formed from debris ejected when the Earth was hit by something big.

The solar system in its youth was a busy place, with growing bodies, collapsing clouds of dust and flying collision debris.

Around four billion years ago, the drama gradually slowed, and more and more of the material had become incorporated into planets. There are still major lumps of building material with collision potential around the solar system today — the asteroids with orbits crossing the Earth's path around the sun are good examples.

Debris from these high-energy impacts can be thrown off into space where, maybe after many millions of years, they fall on another planet. This is how pieces of rock from Mars have been found here on Earth.

However, we have only recently found an example of the reverse process, a piece of the Earth, ejected into space and found on the moon.

One of the primary objectives of the Apollo missions to the moon was to bring back samples of lunar material. So quite a lot of lunar dust and rock samples are now sitting in laboratories on Earth.

The sample we are discussing here was brought back by the Apollo 14 astronauts, in 1971. It was in a lump of a rock called impact breccia.

When a body such as a small asteroid hits a planet or moon, the impact releases a huge amount of energy. Some of the material making up the two bodies is vaporized, some of it is smashed into fragments, and a lot is melted.

When it cools, the melted part glues the fragments together into a rock we call an impact breccia. A huge impact that occurred about 1.9 billion years ago, near Sudbury, Ont., produced a lot of impact breccia.

The Earth and moon have both suffered many impacts. However, on Earth, the impact craters are erased by erosion and plate motions, which continually recycle the Earth's surface rocks.

The moon has no plate motions, so we see the surface covered with craters and the other results of high-energy impacts, such as impact breccias. Surprisingly, one sample of lunar breccia was found to contain a fragment of rock that did not fit.

First of all, it bore the signature of having formed on a water-rich planet. That rules out the moon.

Second the mix of minerals in it corresponded to conditions in the Earth's crust, about 20 kilometres deep.

The next step was to establish the age of the rock. One way to do this is to find some zircons — crystals of zirconium silicate. This material is present in lava, and solidifies into crystals when the lava cools. Uranium dissolves in zirconium silicate, but lead does not. So newly formed zircon crystals contain uranium, but not lead. 

However, uranium is radioactive, which means over time its atoms split, forming other elements, such as lead. So if we find lead in a zircon it came from the uranium.

Moreover, since the rate at which uranium turns into lead is known and does not change, the relative proportions of uranium and lead tell us how long ago the crystal formed. That rock fragment turned out to be 4.4 billion years old, about the same as the oldest rocks here on Earth. 

However, due to the continuous recycling of rock by plate motions, really old rocks are rare on Earth, so maybe we have just found the best place to seek the oldest Earthly rocks — the moon.

  • Mars lies in the southwest after dark.
  • In the predawn sky, Jupiter shines brightly in the southeast
  • Venus, even brighter, is to its left
  • Further left and much fainter, almost lost in the dawn glow, lies Saturn.
  • The moon will reach first quarter on the 12th and full on the 19th.


Rivers run through Titan

Titan, the largest moon of Saturn, is, like Earth, a world with an atmosphere, rivers, lakes and seas.

However, lying almost 10 times the Earth's distance from the sun, Titan gets only around one per cent of the light and heat we get, and it is very cold, around —180 degrees Celsius.

On Titan, water is a permanently frozen rock mineral; those oceans are made up of liquid hydrocarbons, mainly methane and ethane. However, with an atmosphere, rivers, lakes and oceans, could there be living creatures swimming around?

There certainly are the ingredients for life as we know it, except one: liquid water. Water is unique, and for our kinds of living things, not just any liquid will do.

Do you remember those school chemistry experiments, where you dissolved substance A in water in one test tube, and dissolved substance B in water in another test tube?

You then poured one solution into the other, and the mixture fizzed, changed colour, or formed a solid precipitate which went to the bottom, or some combination of these.

If you took substances A and B and mixed them, perfectly dry, nothing would have happened, until you added some water.

Life as we know it is based on chemical reactions, and water makes most chemical reactions easy. More things dissolve in water than in almost any other liquid.

When we dissolve substances like common salt (sodium chloride) in water, something interesting happens. Interaction with the water molecules causes the salt molecules to break into sodium and chloride ions.

When you dissolved substance A in water, it broke into bits, and so did the molecules of substance B. These bits then moved around in the water, joining briefly up to form different combinations.

If one of these combinations was a gas, it fizzed off and escaped. If one was a solid, it precipitated to the bottom, and some of these combinations might have been coloured. All this rearranging of the bits into new combinations was made possible by the unique qualities of water.

One other useful property of water is it does not dissolve fatty, greasy stuff, so we can be made of cells that can contain water, where all the interesting chemical reactions of life can take place, without dissolving us.

These useful properties are not possessed by liquid methane and ethane. If there is life on Titan, it will have to be distinctly different from us.

This is why we are most interested in searching for life on worlds where liquid water is a possibility, such as under the ice on Jupiter's moon Europa and on Saturn's moon Enceladus.

This is also why we got so excited by the possible discovery of a liquid water lake under the ice on Mars.

If we think of living creatures as things that take in energy and material from their environment, discarding waste energy and material, growing and then replicating themselves in a manner that makes it possible for them to evolve to accommodate environmental changes, the possibilities are probably endless.

We just need environments where all these processes are possible, and where conditions change slowly enough for the living things to adapt. However we might not even recognize such life forms.

Imagine creatures on a frigid object beyond Pluto, where solar energy is a mere trickle and environments change only over billions of years, with lives so long that they would never notice us or we them, or plasma creatures living in the atmosphere of a star, living very short lives.

In our search for life we are mainly looking at places with liquid water, where we have the best chance of detecting life that is enough like us for us to notice it.

  • Mars, fading as it recedes, lies in the southwest after dark.
  • In the predawn sky, Jupiter shines brightly in the southeast
  • Venus, even brighter, is to its left,
  • Saturn, further left and much fainter, is almost lost in the dawn glow.
  • The moon will reach first quarter on the 12th.


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Dancing with the bear

Ursa Major, The Great Bear, is a big constellation.

It fills a substantial chunk of the northern sky and looks like a large animal, maybe something like a bear.

Most of the stars are faint, apart from seven of them, with which we are very familiar; they make up the shape of the Big Dipper, The Plough, The Saucepan or many other names, depending on where you're from.

Starting from the end of the handle, the stars are named Alkaid, Mizar, Alioth, and going counterclockwise around the "bowl", Megrez, Phad, Merak and Dubhe.

These names are part of the enormous contribution to astronomy made by Arab scientists. Merak and Dubhe, marking the side of the bowl opposite the handle, are special.

They are known as The Pointers because they show the direction to Polaris, the North, or Pole Star, which is an important navigation reference, although maybe, in these days of GPS, less so.

Look closely at Mizar. On a dark night those of average sight will see a faint star close by. If necessary, try using averted vision. Mizar has a companion, named Alcor. If you point a telescope at Mizar, you'll see another companion star orbiting it. Alcor has a very close companion too.

This time of year the constellation of Taurus, The Bull, is prominent in the sky. Look right from Orion or left from the Pleiades. Find Aldebaran, a bright, orange-red star. It lies at the top of a "V" of stars, which represent the bull's head.

Aldebaran is his angry red eye. Look halfway down that leg of the "V" and you will see Theta Tauri (our modern star names are nothing like as romantic as the Arab, Greek or Latin names). Each of the two stars is actually a close double star.

There are many other double stars. Two of the prettiest and easiest to find are Albireo, a blue and orange pair in Cygnus, The Swan and Epsilon Lyrae, in Lyra , The Lyre.

This is a quadruple star. Both look wonderful through binoculars or a small telescope. Actually, a large fraction of stars are in fact double or multiple. Why this is takes us back to how stars form.

A cloud of gas and dust collapses into a disc. As it shrinks, it rotates faster and faster, just as a skater spins faster when she pulls in her arms. The core of the cloud collapses to form a star, but the rest of the disc is spinning too fast to fall onto the new star, so it forms a number of other lumps, all circling the star.

The planets of the solar system formed in this way. Whether a lump becomes a planet or a star depends only on the size of the lump. If the lump is large enough, the pressure and temperature in the collapsing lump may become high enough for nuclear fusion to start, in which case we have a second star, or maybe a third or fourth.

If the lump is too small, nuclear fusion does not start and we end up with a planet, asteroid or some other small rocky body. Many planetary systems have some large planets, gas giants. Jupiter, Saturn, Uranus and Neptune are examples in our solar system.

If Jupiter, for example, were a few times larger, it would have become a red dwarf star. Luckily for us it didn't.

One of the most memorable scenes in the first Star Wars move was Luke Skywalker looking wistfully at sunset on the desert planet of Tatooine, with two suns heading below the horizon.

This scene would be improbable in reality. It is likely that double-star systems have planets too. However, their orbits would be very complicated and the temperature variations on those planets as they pass closer to one star or the other would make them highly unpleasant places to live.

If we seek potentially life-bearing planets, double star systems will not be the best places to look.

  • Mars, fading as it recedes, lies in the southwest after dark.
  • Venus and Jupiter lie close together in the eastern sky before dawn. Venus is the brighter one.
  • The moon will be new on the 4th.


More Skywatching articles

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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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