145237
Skywatching

Search for aliens

On page 190 of the Observer's Book of Astronomy, published in 1962, author Patrick Moore wrote about Mars:

  • "The planet cannot be regarded as overwhelmingly hostile, and the existence of vegetation can hardly be denied, although as yet there is no positive proof.”

This statement, by a leading figure in astronomical writings, reflects accurately the thinking of the time.

Knowing what we know today about Mars, we wonder what this conclusion was based on. It also shows how much our ideas have changed regarding places to look for extraterrestrial life.

In 1877, astronomer Giovani Schiaparelli observed linear features on Mars that he described as "canali,” the Italian word for "channels.”This word can describe naturally occurring features.

However, somewhere this word was mistranslated into English as canals, which are different things entirely.

Thus was born the idea of the Martians fighting the drying up of their world by setting up a global water management system based on a complex network of canals.

In 1894, Percival Lowell built an observatory near Flagstaff, Ariz., just to map the canals and study Mars.

This created a widespread belief that the Red Planet had living things on it, and in a plethora of science fiction stories, some of those living things compared our warm, wet world with their cold, dry world and decided a move was in order.

Lowell and many others since saw that in the Martian spring, a wave of darkening moved equatorward from the polar caps. This was explained as vegetation greening up as meltwater was released by the warming poles.

This opinion was supported by our eyes making grey look green when seen against a red background.

Our delusions were shattered when spacecraft sent us back closeup pictures of Mars, firstly from nearby space and then from the planet's surface.

Mars was indeed wet and warm once, and there could have been life, but today as yet we have found no sign of it other than the odd trace of methane that is sometimes detected.

The story is a good illustration of how our search for extraterrestrial life has evolved. We used to think that we were most likely to find life in the solar system on the planet most like ours.

Today, many scientists think the most likely locations are Europa, a moon of Jupiter, and Enceladus, one of Saturn's moons.

Both are so far from the sun they should be frozen solid. However, they are getting a lot of heating from the continuous gravitational kneading due to the tidal forces generated as they orbit their giant, host planets.

Our interest in these objects has been triggered by what we have seen in our own oceans.

Around the Mid-Atlantic Ridge and assorted other places on the bottom of our deep oceans, outflows of hot, mineral-rich waters are supporting communities of bizarre creatures who owe nothing to the sun's light or heat.

The heat released by tidal forces inside Europa and Enceladus must be doing the same thing.

Fly-bys by our space probes suggest that under the icy envelopes of these bodies there are deep, dark oceans.

Moreover, there is no reason to suppose that those outflows of hot, mineral-rich water are not happening on Europa and Enceladus.

Therefore, could there also be communities of bizarre creatures living around them?

Enceladus gives us another line of evidence. The tidal heating is enough to drive eruptions of water through the icy surface and into space.

Spacecraft have analyzed this water and found it to contain the organic, chemical building blocks of life, just as we would find in the water of our own oceans.

Although our search for Martian life goes on, we now realise that when we do find life elsewhere in the solar system, there is a good chance it won't be on Mars.

Maybe the Martians will be us.

  • Jupiter and Saturn lie low in the southern sky after dark.
  • The moon will be New on the 30th.


142788


Star light, stars very bright

During clear evenings at this time of year, almost overhead you'll see the bright, bluish star Vega.

Now, scan westward to find the bright, orange star Arcturus. About halfway between the two stars, there is a circlet or tiara of fainter stars making up the constellation of Corona Borealis, The Northern Crown.

About halfway between this constellation and Vega, you'll find a tombstone or keystone shaped group of four stars. These mark the body of Hercules, the mythic hero.

Assume he is facing us, and Vega is near his right shoulder. Now, grab a pair of binoculars and scan slowly down his right side. Maybe a third of the way down you will see a fuzzy blob, appearing very different from the nearby stars.

This object is Messier 13, a globular cluster of stars, a spherical collection with more than 300,000 members. M13 lies about 22,200 light years away, which means its light takes roughly 22,200 years to get here.

A light year is just under 10 million million (10 trillion) kilometres, so that is a very great distance. It has a diameter of some 145 light years, which means on average the stars lie a mere two light years apart. However, the centre of the cluster is so crowded, our telescopes just show a bright glow.

As we look outward from the centre, the stars get far enough apart for us to see them as individuals. The stars near the centre have to be much closer than two light years. Compare this with our situation here on Earth, where the nearest star to us after the sun is 4.3 light years away, and the next closest significantly further.

What would it be like to be an inhabitant of a planet orbiting a star that is a member of a globular cluster? After sunset the sky would be filled with really bright, nearby stars. It would probably be brighter than full moonlight on Earth, and you would not need streetlights.

Life would be hard for any astronomers on the planet. The glare from those numerous bright, nearby stars would make it difficult to observe what lies beyond the cluster.

Most galaxies have globular clusters orbiting around them, although we have no idea why. So far, astronomers have found around 150 orbiting our galaxy, although there could be a few we have not yet found.

The Andromeda galaxy, which is rather larger than the Milky Way, has maybe 500, and giant galaxies, such as Messier 87 in the constellation of Virgo, may have 10,000 or more.

When we look closely at the stars in globular clusters, we see they have two things in common. They are old, and there is little gas or dust from which new cluster members can form.

Stars generate energy by converting hydrogen into other elements, such as silicon, oxygen, carbon and sulphur. When they die, they eject all these waste products out into space, where they mix with the dust and gas clouds from which new stars form.

So following generations contain traces of material from stars that went before. All the gas and dust in globular clusters has been used up in making stars, so there is nothing to make more. In addition, the cluster members contain little or no traces of material from earlier generations.

This suggests they are among the oldest and earliest generations of stars, dating back to the youth of the Milky Way or even of the universe itself. This makes globular clusters really interesting to astronomers.

Although we have found many globular clusters, as yet we have no good ideas as to how or why they form. Since most galaxies have them, the processes involved in creating these fascinating objects can't be that unusual.

Although you can see Messier 13 and some other globular clusters with a pair of binoculars, to really enjoy them you need a telescope.

Any moderate sized backyard telescope will capture a good number. Globular clusters are among the most popular targets for amateur observers.

  • Brilliant Jupiter lies in the southwest after dark
  • Saturn is low in the south.
  • The moon will be full on the 15th


Earth having meteor shower

We are about to pass through a stream of meteoric material once again.

Most of it is made up of dust and sand grain sized particles of rock or ice, but there are some larger lumps in the stream. The particles are all moving in the same direction and at the same speed, around 60 kilometres a second.

That is about 216,000 km/h.

When they hit our atmosphere, friction against the air heats and then vaporizes them. The atoms making up the air have no time to move out of the way, so they pile up in front of each particle, heating up to about 50,000 degrees.

What we see in the sky is a glowing streak or trail made up of hot, ionized air and evaporated particle.

The bigger lumps can produce more dramatic displays. As they move through the atmosphere at high speed, they tend to erode and melt into an aerodynamically stable shape, like a sphere or pancake, which gradually vaporizes away.

However, if the stresses cause part of the body to break off, it goes into a violent hypersonic tumble that causes it to disintegrate. We see the streak across the sky terminate in an explosion.

We often hear that the time to see the Perseids is the night of Aug. 12. This is partly true; that is the night the Earth passes through the core of the stream.

The stream is actually quite broad, so we can start looking for Perseids any time after mid-July through to the end of August. However, the best time is roughly Aug. 9-14.

In theory, the best time is between midnight and dawn, because that is the time our part of the Earth is facing in the direction we are orbiting the sun, "looking through the windshield."

In the evening, we are looking behind us, "through the rear window" and we always collect many more bugs on the windshield than we do on the rear window. We will still see some meteors though, because they are moving fast enough to overtake us.

Since all the meteoric objects are moving in parallel paths, they appear to us as though they are all radiating from one point in the sky, which happens to lie in the same direction as the constellation of Perseus, hence the name.

On evenings this time of year, Perseus lies fairly low in the northeastern sky, so a view in that direction will show most meteors, but in general, the more sky you can see, and the darker it is, the more meteors you will catch.

This means getting away as far as practical from our street and house lights.

Lights have two bad effects. First, if they are shining in your eyes, apart from being annoying, they stop your eyes achieving the sensitivity needed to enjoy the sky. Second there is usually some haze in the air.

This gets illuminated by all those lights, whether you can see them or not, making the sky brighter and harder to see faint objects. Get away from town if you can.

Unless you are lucky to be looking in the right direction at the right time, binoculars or telescopes are close to useless for looking for meteors. They see such a tiny patch of sky the chances of one passing through that patch while you're looking at it is minimal.

Your unaided eyes are the best tools, so the big issue is being comfortable and warm so you can just relax and take in the sky.

A chaise longue or deckchair will be ideal. Otherwise, use a blanket on the ground. It gets cold if you are sitting still for long periods, even on summer nights.

Make sure you have a blanket to lie under. Plan on spending at least an hour.

Hot chocolate helps.

It won't be boring. As your eyes get dark-adapted and your brain gets tuned in, you will see more and more stars, some wisps of cosmic gas and dust, satellites wending their way across the sky, and of course, some Perseids.

  • Brilliant Jupiter lies in the south after dark
  • Saturn is low in the southeast.
  • The moon will reach first quarter on the 7th.


145746


Dark matter is everywhere

An unfortunate thing about science is that important discoveries take a long time to hatch.

They can be utterly ignored for decades, until a new discovery makes the earlier work impossible to ignore. Even scientists get selective blindness and deafness regarding work that contradicts their favourite theories.

The research done by Fritz Zwicky in 1933 and Vera Rubin in the 1960s are really good examples of this. They were ignored for years but eventually became fundamental to our understanding of the universe.

On any summer or autumn night, we can look at the Milky Way and see dark rifts in it. These are not rifts, they are great clouds of gas and dust, the raw materials for making new stars and planets.

However, in a galaxy, how much of this invisible stuff is there? How can we find out?

In 1933, Zwicky had an idea. He looked at a cluster of galaxies and by measuring the amount of starlight, estimated the number of stars and thence the amount of material in each galaxy.

He then observed the orbital velocities of the cluster members as they were gravitationally tugged by all the others.

Since gravity is produced by mass, this would give him the mass of the whole cluster. By subtracting the total mass tied up in stars in all the cluster members from the total mass of the cluster, he could estimate the amount of gas and dust.

However, the answer did not make sense. It suggested there was far too much material to account for by the gas and dust. The research community did not believe this result, and the issue was dropped for more than 30 years.

In the 1960s, Rubin chose a nice non-controversial project to work on. She measured the motions of stars in our galaxy, the Milky Way, as they moved in their orbits, in order to determine the gravitational force acting on them and from that estimate the mass of our galaxy.

She then totalled up the mass of matter in stars and as Zwicky had found, got an answer that did not make sense. The mass was so high that what was visible accounted for only 5% of it.

As in the case of Zwicky's discovery, the research community ignored her work. So she decided to take her research further. She looked at another galaxy, the Andromeda Galaxy, which closely resembles our galaxy and close enough to study in detail.

She measured the brightness of the starlight at different distances from the core, which gave her an estimate of numbers of stars and how much material they contain.

She then used these mass estimates to calculate how fast the material should be orbiting the core of the galaxy and compared it with the observations. They did not agree; the material was orbiting far faster than it should.

This meant the gravitational attraction was stronger than it should be, and since gravity is a force due to mass, there was much more material in our galaxy than expected.

The discrepancy was huge, suggesting an amount of additional mass impossible to account for in terms of gas and dust clouds, or black holes. Once again, nobody took much notice of these important results.

The situation was changed completely by researchers working in a different area, the origin of structure in the universe.

They found that to account for the structures we see in the early universe, and the large-scale distribution of galaxy clusters today, the matter we can see can only be about 5% of what is really there. This invisible material has become known as dark matter.

This completely vindicated the work of Zwicky and Rubin, and underlines the value of looking deeply at the scientific questions nobody else is looking at, even if they are currently uncontroversial. So far, we have no idea what dark matter is.

  • Brilliant Jupiter lies in the south after dark
  • Saturn is low in the southeast.
  • The moon will be new on the 31st.


More Skywatching articles

145587
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]



140802
The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

Previous Stories



145547


146090