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Skywatching

Red Planet still alluring

The latest flotilla of spacecraft to arrive at Mars must make that world the most-visited planet in the Solar System.

There are two reasons for this group visit. The missions were timed to be when Mars was particularly close to us. A shorter trip and an easier rendezvous means a given launcher can accommodate a bigger and more capable spacecraft.

Since our current method for travelling between planets involves a big shove followed by "falling all the way there,” the laws of orbital dynamics apply, which requires the launches to fall within a restricted window of time.

It is like throwing a baseball into the air and then throwing another one so that it gently nudges it.

We want to arrive at Mars with a low enough relative velocity to require just a small rocket shove to enter orbit or to dive into the atmosphere at the right angle.

The second reason is that Mars is a candidate for being the most fascinating object in the Solar System.

Even today, as a cold desert world with a thin atmosphere, out of all the planets in the Solar System, it is the one most like ours, and one we could live on for long periods, with a lot of technical help, of course.

Then there is the discovery that Mars was once a warmer, wetter world, with a thick atmosphere. There are dry watercourses, canyons, lakes and seas over most of the surface. The dry riverbeds are floored with water-worn pebbles and little round pellets of salts precipitated as the water disappeared.

Actually, today there is a lot of water on Mars, as layers of ice below the surface. On a really warm, summer day, close to the equator, temperatures may reach 20 C.

This melts some of the underground ice, causing short-lived water flows down sandy slopes. Even on those summer days, the temperature dives to far below zero at night. This raises the next fascinating issu: billions of years ago, when Mars was warmer and wetter, was there life?

We know that life appeared on our world very early, around 3.5 billion years ago, more or less as soon as our world had cooled enough for liquid water to accumulate on its surface.

Why could it not have been the same for Mars too?

We are looking hard for traces of that ancient life, or even better, some it its hard-bitten descendants eking out a tough existence somewhere below soil level.

Thanks to our robot explorers, we are learning about Martian geology and weather, and are piecing together what happened to Mars, and just as important, why it didn't happen here.

In addition to our scientific curiosity, we have a special cultural attachment to the Red Planet.

Ever since Percival Lowell mapped the canals, which were actually a combination of wishful thinking and poor observing conditions, and launched the idea of the Martians working hard to sustain life on a dying planet, we got the idea that the Martians might just want to come here.

This launched a stream of novels, movies and radio plays. We were usually saved by sheer luck. In War of the Worlds, it was our bacteria, to which the Martians were not immune. In Mars Attacks, it was the lucky discovery that Martians could not tolerate yodelling country music.

Actually, it is unlikely that Martian life had a chance to evolve to the point of achieving interplanetary travel. Until around 500 million years ago, life here was single-celled bacteria and algae. Then things started to happen, with complex life forms appearing.

It looks as though Mars became the hostile place it is today, more than a billion years ago. Since Earth and Mars formed at the same time, it is reasonable that if life appeared on Mars, it happened at the same time as it did here, but never had time to get past the bacterial and algal stage.

We could be wrong!

These videos of Mars are well worth watching:

https://www.youtube.com/watch?v=7zpojhD4hpI

https://www.youtube.com/watch?v=0NRFk_jNhek

  • Mars is high in the southwest after dark.
  • The Moon will be Full on the 27th.




Loss of an icon

Last December, when the Arecibo radio telescope collapsed, radio astronomy lost an icon.

This instrument was regarded as a research tool for radio astronomy, but actually a nice, big dish antenna can be used for a variety of radio projects.

In short, for almost anything requiring collecting a lot of weak radio energy coming from something in the sky, such as radio astronomy, or detecting radio signals from distant spacecraft, or even extraterrestrial civilizations.

It was also used for interplanetary radar, which involves squirting an immense amount of radio energy in the direction of a distant planet or asteroid, and then detecting the incredibly weak signal echoed back.

The echoes could be used to measure the precise distance and movement of an object and even image it. Until spacecraft landed on the surface of Venus, the only way we had seen the surface of that permanently cloud-shrouded world was by radar. The antenna also had military applications.

However, for us it was a radio astronomy icon, a key instrument of its time.

Back in the 1960s when young, wanna-be radio astronomers were getting radio astronomy books from their local libraries — yes, those libraries did have books on radio astronomy — there were always pictures of two iconic radio telescopes, which were state-of-the-art at the time.

They were the 75-m diameter dish at Jodrell Bank, in the U.K., and the 305-m diameter antenna at Arecibo, Puerto Rico.

The Jodrell Bank instrument was mounted so that it could be pointed at any point in the sky, and was probably the largest radio telescope of that kind achievable at the time.

It was, and still is an engineering challenge to make a large dish that will stay precisely in shape as it moves around, and is subject to the wind and uneven temperatures across it. Something bigger would require a completely new approach.

That's when, in the early 1960s someone pointed out the potential of a large, saucer-shaped sinkhole, located near Arecibo, in Puerto Rico.

The idea was to mount a fixed dish in that depression. It could be solidly and precisely mounted because it was not intended to move. Of course, a fixed antenna like this has one huge shortcoming; it is permanently looking straight up.

However, the engineers got around this problem to some extent by making the dish with a spherical profile rather than a parabola, like almost all dish antennas, and by moving the signal collection point to different positions over the dish.

Collecting signals from a spherical antenna is not easy, because they are not fully focused, which is why everyone uses parabolic antennas.

On the other hand, the result was a dish with a diameter of 305 metres, easily the biggest in the world, capable of seeing a large patch of sky centred overhead.

There are still some radio telescopes being built that use large, fixed antennas.

The CHIME instrument at our observatory is an example, but by using modern signal processing techniques, it can see most of the sky over the observatory, without mechanically moving anything.

However, the mainstream these days is to make huge radio telescopes out of lots of small dishes. The Square Kilometre Array, now under construction in South Africa and Australia, will use thousands of them.

The big difference is that today we have the computing power needed to process all those signals. In the 1960s we did not.

Arecibo was a film star too. It was used in the movie Contact. It also played a role in the James Bond movie, Goldeneye. This unique instrument will not only be missed by scientists; it will also be missed by moviegoers.

A video of the collapse can be seen at https://www.youtube.com/watch?v=ssHkMWcGat4

  • Mars is high in the south just after dark.
  • The Moon will reach First Quarter on the 19th.


Violence in the heavens

When we look at the sky on a clear night, far from city lights, we see blackness, speckled with a few thousand stars, and the silvery smear of the Milky Way.

Its peaceful tranquillity is deceptive, because there is a lot of high-energy stuff going on. To really see it, we need to look at other wavelengths.

Light is an electromagnetic wave; so are:

  • Ultraviolet
  • Infrared
  • Radio
  • X-ray
  • Gamma ray emissions.

The only difference is their wavelength.

Radio waves are the longest: kilometres to a millimetre or so. Infrared waves have lengths ranging from a millimetre to maybe 400 nm (a "nm" is short for nanometre, which is a billionth of a metre).

The electromagnetic waves we can see, which we call "visible light" have lengths between about 800 nm (red)
to 400 nm (blue).

Then, we get to ultraviolet (400-10nm), then X-rays (10 -0.01nm).

Waves with smaller wavelengths are called gamma rays. Electromagnetic waves come in indivisible packets called quanta. The shorter the wavelength, the more energy contained in that quantum.

To produce quanta of a given wavelength means the appropriate amount of energy needs to be available. Making gamma rays requires extreme amounts of energy. Making something "gamma ray hot" requires temperatures of billions of degrees.

These may occur in exploding giant stars, but most cosmic gamma rays are not produced by heat.

An example of a source of "non-thermal" gamma rays is a lump of radioactive material, like radium. The atoms of such substances are highly unstable, and tend to disintegrate into smaller atoms, a process called nuclear fission.

This releases a lot of energy, with some of it in the form of gamma rays. Since producing gamma rays requires large amounts of energy, they provide a powerful tool for studying the high-energy universe.

Gamma rays damage cells and destroy living tissue, so it is fortunate that incoming cosmic rays are blocked by our planet's atmosphere.

This means that to observe them, we need to put our "gamma ray telescopes" in space. The latest of these, the Fermi Gamma Ray Space Telescope, launched in 2008, is the latest of a series of orbiting gamma ray observatories.

The gamma ray sky shows a bright band coinciding with the Milky Way, and a sprinkling of many star-like sources scattered over the sky.

Some shine more or less steadily; some vary in brightness over time. Others appear for a few days or so and vanish. Then, there are some that flash on for a few milliseconds to seconds, and then vanish.

The Moon glows dimly in gamma rays, due to it being bombarded with cosmic rays, high-energy particles pervading our galaxy.

We think the gamma ray glow from the Milky Way is produced by cosmic rays. When these smash into dust grains or quanta of ultraviolet radiation, they generate quanta of gamma rays. Exploding giant stars can produce gamma rays by non-thermal, nuclear processes. Occasionally, we see some in solar flares.

A particularly interesting case arises when there are two stars closely orbiting each other. One of the stars has aged to the point where it is a white dwarf.

Then, as the other star gets old, it starts to swell, entering its own pre-white-dwarf stage, which leads to its older partner pulling that material down onto its surface.

This accumulates until a critical mass has accumulated, and it all explodes as a sort of super-sized hydrogen bomb, giving off a burst of gamma rays. Most galaxies have black holes in the middle. Some have really massive black holes.

When they pull in a particularly large mouthful of material, they produce floods of gamma rays.

Gamma rays reveal a dynamic, exotic view of the universe. However, since we enjoy those dark, clear, tranquil skies, it is a good thing we can't see them.

  • Mars is high in the south just after dark.
  • The Moon will be New on the 11th.


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Satellites made of wood?

Would you make a spacecraft out of wood?

Surely we would make spacecraft out of space-age materials: exotic alloys and other things that can stand the radiation and temperature extremes of space.

However, researchers in Japan and other countries are now looking at the possibilities of using wood for the main structures of satellites.

This old-fashioned material has a lot of possibilities in space. First, it is tough and can tolerate large temperature variations. Pouring boiling water or liquid nitrogen on a piece of wood does not destroy it.

Wood is a poor conductor of heat, so it can help smooth out the effect of wild temperature variations on the equipment inside the satellite.

It is cheap and light. Some woods are extremely hard and others very flexible, with a myriad of woods lying between these extremes.

It can be glued or fastened using entire surfaces rather than localized joints using screws. There is a centuries-long experience in the development and use of adhesives for fastening pieces of wood together.

One interesting aspect of wood is that it is transparent to most radio waves. In some cases it might be possible to put antennas and their associated electronic components inside the spacecraft body.

However, one downside of wood is that it does not reflect radar signals. Unless there are large metal structures, like dish antennas attached to the spacecraft, it might be hard to see using ground-based radar.

This is important, because being able to track satellites and space junk is an important part of managing the space around the Earth and reducing the chances of losing spacecraft in collisions, or more importantly, minimizing the risk to astronauts.

Putting a metal foil cover over the spacecraft exterior would make it reflect radar signals and make it trackable, but then the antennas will have to be back on the outside.

A major driver of the consideration of wooden satellites is what happens at the end of a spacecraft's life.

For many years, we did not think much about what happens to satellites that stop working, or the booster rockets and other kit that wind up in orbit.

After all, space is big. However, now the accumulation of space junk around the Earth is an increasingly important problem. In the next few years, we are likely to see more than 50,000 satellites being launched to provide world-wide 5G Internet access.

There is the possibility of losing satellites to space junk collisions and there is also the issue of what to do with satellites that have ceased to work.

Today, spacecraft and unused boosters are removed by slowing them down a bit, so that their orbits touch the denser parts of the Earth's atmosphere.

When satellites travelling about 30,000 km/h hit the atmosphere, friction heats them to very high temperatures and the savage deceleration forces make them come apart.

The result is they usually reach the ground in the form of fine dust that nobody notices. However, as the Japanese point out, this dust contains all sorts of rare-earth metals and other things.

At the moment, this dust fall is not particularly polluting, but when the sky is a solid mass of satellites this dust fall could become more serious.

Wood does not burn in space, because there is no oxygen. However, during re-entry all that wood would burn to ash, which is non-polluting.

There is probably a bigger fall of ash in the atmosphere all the time, due to forest fires burning around the world.

Wood is easy to make. It is manufacturing itself all over the world, all the time, without our help.

It is maybe odd that nobody thought of this sooner. Maybe just as odd is that living in a country with loads of wood, and with a substantial part of our economy based on wood, why didn't we think of it?

  • Mars is high in the south after dark.
  • The Moon will reach Last Quarter 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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