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Skywatching

Dust in the Martian wind

One of the most fascinating videos sent back by the Curiosity rover, currently exploring the surface of Mars, shows a number of dust storms marching across the desert, against a backdrop of distant, low hills.

Dust storms are common on Earth, but it is exciting to see them on another world, with weather, geography and geology -— just like ours.
 
Mars' resemblance to our world was realized centuries ago. Until recently, we thought it had plant life, and fantasized about its inhabitants.

The other thing that fascinated us was that the planet has what we would call weather.

Although Mars is smaller than Earth and further from the sun, like Earth it has polar caps, seasons and clouds in its atmosphere.

Occasionally, sandstorms cover most of the planet. Landers on the surface show a desert with frost forming on the rocks during the night and evaporating in the morning sun.

There are two other differences between Earth and Mars. Earth has a thick, humid atmosphere and Mars has a thin, dry one. Earth's thick, damp atmosphere traps heat and smoothes out daily and seasonal temperature variations.

Mars' atmospheric pressure at the surface level is about half a percentage point that of the Earth's, and the Martian atmosphere is much drier. It has very little capacity to trap heat.

When the sun rises, the dry, Martian deserts warm rapidly, heating the atmosphere in contact with it, setting up vigorous convection. Cold "air" over high ground flows downhill as strong winds.  

As the air descends, it gets compressed and warms, like Chinooks. It rises and makes room for more cold air to flow down.

The result is wind systems that can be small or huge. Winds in the thin Martian atmosphere are not able to blow heavy objects round, as hurricanes and tornadoes do on our world. However, they are very good at picking up the find sand and dust that covers most of the Martian surface.

The result is dust and sandstorms that might be small and local, or big enough to cover most of the planet. They can be thick enough to completely hide the sun from anyone on the surface for days, weeks or months. This presents us with a major problem.

Although Curiosity, our main robot Mars explorer, is nuclear powered, others, like Spirit and Opportunity, are powered by solar energy. These two landed on Mars in 2004. Spirit has ceased to function, but Opportunity is still exploring, after 14 years, far longer than planned.

Opportunity survived a severe dust storm in 2007, which forced it to go into hibernation until the returning sun got its electrical supply started again. However, there is now a dust storm on Mars that is far larger than the 2007 event, which got started right over the rover, so Opportunity is likely to be in the dark for far longer.

It can go into deep hibernation, but there is a limit as to how cold its electronics can be allowed to get, and for how long.
  
Another problem with the dust is that it is fine and very dry. As it blows around, it gets electrically charged and clings to everything. It can cover solar cells and get into mechanical and electrical places where it's not wanted.

With luck, some dust-free wind following the dust storm will blow the stuff off again, as it did in 2007.

Large Martian dust storms are visible, often with quite small telescopes, from Earth. Moreover, now is a good time to get out the telescope.

We have just overtaken Mars in its orbit and we are still close to the planet.

Look for a bright, reddish-orange object in the Southeast around midnight, shining like a lamp.

Mars never appears really large in small telescopes. However, be patient, and there will be moments the air stills, the shimmering vanishes and the details suddenly leap out.

While you have the telescope out, there are some other planets to see.

  • Venus lies low in the west after sunset
  • Jupiter in the Southwest and Saturn in the Southeast after dark.
  • The Moon will reach First Quarter on the 19th.


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Lights in the sky

One night, some years ago I had a phone call from a rather worried-sounding man.

He lived a few kilometres to the north of where I live. He said that his children had come into the house excitedly reporting that there were three disc-shaped objects circling over Giant's Head, an extinct volcano to the south of his home.

He was understandably skeptical, but went out to see, and said there were three discs up there, doing exactly what his children said. Giant's Head lies to my north, so I said I would go outside to look for myself, from the other side of the mountain.

There were the three discs, circling in the sky. However, from my side of the mountain I could see what he and his children could not.

A local car dealership had three search lights pointing into the northern sky, and waving them around, and there was a very thin layer of high, icy cloud, an ideal movie screen. 

Every year, we get reports of "lights in the sky." People see something unusual in the sky and report it, and then we try to work out what it might have been. Sometimes we succeed, and often we don't.

Although alien spacecraft cannot be totally ruled out, the main cause of the unresolved reports is not enough information, with the added issue of weeks or months being allowed to pass before making that report. Here are some suggestions.

What does it look like: size, brightness and colour? Note that a bright, starlike object, such as a bright planet like Venus, Jupiter or occasionally Mars, can look bigger in the sky than it really is.

Where is it in the sky?

If you know your constellations, sketch its position with respect to at least three identified bright stars. Otherwise give the position as a compass bearing and elevation (angle above the horizon); for example, Southwest, 30 degrees elevation.

To estimate angles, use your hand at arm's length. Hold your thumb and little finger as far apart as you can get them.

  • From thumbtip to fingertip spans about 25 degrees.
  • The tip of your index finger to the tip of your little finger is around 15 degrees.
  • The width of a clenched fist is about 10 degrees.
  • Three middle fingers together span around five degrees
  • The width of your little finger is roughly one degree.

"Guesstimates" made by eye are usually useless.

Note the time and date.

Is it moving? In what direction? How fast? Use the hand angle technique and a watch.

Is it moving on a fixed course? Manmade satellites cross the sky at about the same speed, or slower than high-altitude airliners.

Unless it has to be otherwise, satellites are generally launched eastward to pick up a free 1,000 km/h from the Earth's rotation, so we see them crossing the sky in a very roughly west-east direction.

Some satellites are launched into polar or near-polar orbits, crossing the sky in a roughly north-south direction.

If it seems not to be moving, note where it is with respect to a flagpole, chimney, tree or some other reference feature and check again an hour later, from the same location. If it has moved a bit to the west it is probably a celestial object, like a star or planet.
 
The Earth is orbited by a large number of satellites with highly reflective antennas. These can catch the sunlight and reflect it in your direction.

You will see something slowly moving across the sky, brightening until it is unbelievably bright, and then fading away to invisibility after a few seconds.
 
If you see something odd in the sky, check all the things listed here, plus anything else you notice, and write it down as soon as possible. Record the accurate time and date.

Without this, nothing much can be done with your observation.

Finally, report it promptly. Then, your information can be combined with any other reports, with a higher chance we will be able to find out what you saw.

  • After dark, Venus lies low in the west, Jupiter in the Southwest and Saturn in the Southeast.
  • Mars, bright and red, rises about 11 p.m.
  • The moon will be new on the 12th.


Signs of life

In the shallow waters of Shark Bay, Australia are strange, mushroom-shaped rocks, called stromatolites. These are produced by living creatures.

Millions of bacteria form slimy mats which trap sand and mud particles. The bacteria then grow up through it to form a new layer, and the rocky structure grows larger and larger.

A cross-section of one of the "mushrooms" shows the layers like tree rings. These structures are really robust and over time become incorporated into rocks as fossils.

Their tree-ring like structures are found in rocks up to 3.7 billion years old, showing that liquid oceans existed back then, when the sun was about 30 per cent fainter and our planet should have been frozen solid.

Conversely, if things were not frozen solid then, our brighter sun means we should be frying now. That this is not the case indicates how living things change their environment to suit themselves, up to a point.
 
This idea was first put forward by James Lovelock, who suggested that evolution in living creatures is not just a process of adapting themselves to their environments, but also one of changing their environments to suit themselves.

In the case of the Earth, living creatures changed the atmosphere. When life first appeared, the atmosphere was rich in methane and carbon dioxide, both greenhouse gases. These made our planet warm when the sun was fainter.

Plants take in carbon dioxide, and use sunlight to convert it and water into carbohydrates, releasing oxygen, which is not a greenhouse gas, as a waste product. Over time the sun brightened, and plants removed more and more carbon dioxide, replacing it with oxygen, and incidentally stabilizing the Earth's temperature.

The idea that living creatures may involve themselves in a little "terraforming" influences how we may search for life on other planets.
 
On Earth, to a large extent the proliferation of plant life is dependent on the carbon dioxide supply. Animals, like us, depend on oxygen to live, breathing out carbon dioxide. The more plants there are, the more oxygen there is, allowing more animals to live, producing more carbon dioxide.

Oxygen is highly reactive, which is why it is so useful to our life processes. It also means it would rapidly disappear from our atmosphere by combining with iron and other elements, unless continuously topped up.

On Mars, the atmosphere is very thin, but what there is of it is 95 per cent carbon dioxide, with about 0.1 per cent oxygen and occasional intriguing traces of methane. There is no real evidence of a  biosphere.

Did Mars have a biosphere in the distant past? There is evidence that there was once liquid water on its surface, forming rivers and lakes, which in turn requires a thicker atmosphere than there is now. In addition, the fact that Mars is often referred to as the Red Planet is another clue.

The red comes from iron oxide, which suggests Mars originally had much more oxygen in its atmosphere. The red rocks in many parts of our world get their colour from iron oxide, formed when plants flooded the atmosphere with oxygen.

This environmental modification idea suggests that for life like ours to develop, we needed our sun to brighten as we replaced greenhouse gases with oxygen.

We often think of red dwarf stars as good places for life-bearing planets, because they are so stable. However, that would mean that life forms taking in the carbon dioxide would cool their worlds, making them less habitable.

They would never share the fecundity of our world in producing plants and animals. We should look for life like ours on planets like ours orbiting Suns like ours.

  • After sunset, Venus shines brightly in the west; Jupiter lies in the south and Saturn in the southeast.
  • Mars, bright and red, and just past its closest approach to us, rises around midnight.
  • The moon will reach last quarter on the 4th.




Little green men

In 1967, Cambridge graduate student Jocelyn Bell was investigating how the solar wind makes distant radio sources twinkle.

These observations can tell us how fast the wind is blowing, and the size and density of irregularities in it. However, the output of the custom-built radio telescope was showing something else; at one time of day, there were groups of little, regularly spaced spikes.

Southern Britain is densely populated, and with the higher population density come more cars, electric motors, power-line interference and all the other unwanted radio transmissions that people make. It is maybe not surprising that radio interference turned up.

These spikes, which Bell referred to as "scruff," turned up at the same time every day, which generated the idea that it came from a farmer's vehicle when he returned home in the evening. First, he was an unusually punctual farmer.

However, as time passed, something happened that turned that idea upside down. The scruff turned up four minutes earlier each day.

Our measurement of time is based on the apparent motions of the sun. One complete orbit around the sun is called a year, and the time interval between two consecutive noons is called a day, and is divided into 24 hours.

However, as we go around the sun, the direction in which the sun lies at noon changes by about a degree a day. So between two consecutive noons the Earth turns a little bit more than one revolution.

If you note the time a star passes due south, and when it is due south the next night, you'll see the time difference is 23 hours and 56 minutes.

This is because the stars lie so far away, they always lie in the same direction, and would appear in the south after exactly one complete revolution of the Earth, not a revolution and a bit. The scruff was originating somewhere far out in interstellar space. 

The pulses making up the scruff were exactly 1.33 seconds apart, stable, like a clock. To rule out the possibility it was some sort of technical quirk, the observation was checked using a different radio telescope.

It too picked up the object; it was real and it was cosmic. On Earth, regularly pulsed radio transmissions are generally produced by us.

This got imaginations going. Were those pulses produced by alien civilizations, maybe as  "cosmic lighthouses" for interstellar voyagers?

Somewhat humorously, the object became known as LGM-1, with LGM standing for "Little Green Men." Then, more of these mysterious pulsing radio sources were discovered. Perhaps fortunately, a non-alien theory for these objects was already available. 

In 1934, astronomers Walter Baade and Fritz Zwicky postulated that when an aging, giant star dies in a huge explosion, known as a supernova, the core region of the star can be compressed so hard that the atoms making it up completely collapse.

The electrons are forced into the nuclei of the atoms, forming neutrons. Something the size of a star would be compressed into a ball of neutrons maybe 10 kilometres in diameter. A large fraction of the star's magnetic field is also jammed into this neutron ball.

The reduction in the size of the star accelerates its rotation from once a month or so to seconds or even fractions of a second. The magnetic field and the fast rotation cause two beams of radio emission to be produced, and each time the beam sweeps across our direction, we get a pulse, just like the flash we see from a lighthouse.

The light is on all the time, but we see a flash when it points our way. Many of these objects, now known as "pulsars," have been found, some of them sitting obviously in the middle of the remains of exploded stars.

I rather liked the idea of Little Green Men and their cosmic lighthouses.

  • After sunset, Venus shines brightly in the west
  • Jupiter lies in the south and Saturn in the Southeast.
  • Mars, getting brighter every night as it gets nearer to its closest point to us on the 26th, rises around
    1 a.m. 
  • The moon will be full on the 27th.


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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