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Skywatching

A world of extremes

Hal Clement, a well-known science fiction writer, had a very particular story theme.

He imagined bizarre worlds with extreme conditions, such as gravitational attractions hundreds or thousands of times stronger than ours.

Some of his worlds were very cold or very hot. The stories involved living creatures on those worlds. In 1957 he wrote the book Cycle of Fire, in which he described a world with temperature variations of hundreds of degrees. It orbited a red star, which in turn orbited a bright, blue star.

The orbit around the blue star was very eccentric, so the distance from that star varied immensely over the orbital period of 100 years or so. This drove the huge temperature variations.

The living creatures on this world handled the temperature variations by alternating generations of "hot ones" and "cold ones.

Clement put together this unlikely scenario because our understanding of how planetary systems form is that the planets end up in tidy, concentric, almost circular orbits around their star.

Our solar system is a good example. No such planets would experience the huge temperature changes needed for the story, so some other recipe was needed. At least that is what we thought until very recently.

Now, a planet custom made for Clement's story has been found. Moreover, it is orbiting just a single star. No extra star is needed.

One theory for how this planet came about is just a small variation of the standard mechanism as to how planets form.

This new and exceptional planet orbits the star HR 5183, and has been named, with typical astronomical creativity, HR 5183b. Its orbit is amazingly eccentric. If it were transplanted to our solar system, its orbit would take it from as far out as Neptune and almost as close to the sun as Mars.

We don't know yet whether this planet has an atmosphere, but if it does, over its "year" it would range from so cold some of the atmospheric gases would liquefy and water would be hard frozen, to a coolish temperate environment with liquid water lakes, rivers and oceans.

How could such a planet form?

We now know of thousands of exoplanets (planets orbiting stars other than the sun) and until this recent discovery, all have been more or less planets of the usual kind, moving around their stars in almost circular orbits.

What could have happened here?

Stars and planetary systems form from the collapse of a huge cloud of gas and dust. The dust forms a disc. The core of the disc becomes a star and the other disc material forms planets.

Dust grains collide and stick together, forming larger lumps, which stick together to make bigger ones. Usually this leads to single large lumps orbiting where the future planets will be, sweeping up the other stuff, becoming bigger and bigger.

It is unlikely but possible that instead of one big lump and a lot of small stuff we could end up with two big lumps. Sharing the same orbit will inevitably lead to a collision or a close interaction.

n that interaction one body will be accelerated and thrown outwards, while the other decelerated and thrown inwards. One would be our bizarre planet, in a very eccentric orbit, with the other body either falling into its sun or thrown right out of the system.

It is unlikely there are any "conventional" planets in that system, because something moving in and out, crossing their orbits will eventually result in a collision.

Maybe this odd orbit change happened very recently, and the collision has yet to occur.

There are objects in our solar system that have highly eccentric orbits, crossing the orbits of the planets, but these are small bodies: asteroids and comets. Hitting one of them would not change our Earth's orbit, but would still be a disaster.

  • At 02:50 EST on the 23rd, or 23:50 PST on the 22nd, the sun will cross the equator heading south, marking the fall equinox. From here we will have more hours of darkness than we have of daylight.
  • Jupiter and Saturn lie low in the southern sky after dark.
  • The moon will reach Last Quarter on the 21st.


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Heating up the Earth

If, on a clear, sunny day you hold up a one-metre-square, flat piece of black cardboard to the sun, the cardboard will rapidly become very hot.

That is because it is catching solar energy at a rate of several hundred Watts (the energy output of several 100-Watt light bulbs).

If you were to try the same experiment from orbit, above the atmosphere, you would intercept over 1,400 Watts. The side of the Earth facing the sun is receiving around 18E16 (18 followed by 16 zeroes) Watts.

Almost 40% of that gets reflected straight back out into space, leaving about 11E16 Watts to be absorbed by the Earth. This warms our planet, and as it warms it radiates energy as infrared. Eventually input and output balance and the temperature stops rising.

However, when we calculate that temperature, we end up with a world with an average temperature way below freezing. There is an additional factor at work — the greenhouse effect.

If we impede the efficiency with which our planet reradiates energy, then the equilibrium temperature will be higher. The greenhouse effect is what makes our planet inhabitable. This raises a serious issue.

Thanks to years of study and with billions of examples to look at, we now have a pretty good idea of how stars work. They produce energy through nuclear fusion in their cores. Over time the cores become loaded with the waste products of energy production, so the star develops a core of material that is producing no energy, with energy production taking place in a skin surrounding that inert core.

This causes the star to brighten slowly during its mature life, the period between its birth and the point where it starts to run out of fuel.

Our sun was born along with the Earth and other bodies in our solar system about 4.5 billion years ago, and since then it has steadily brightened by some 30%. That would suggest that until very recently, the Earth should have been frozen solid.

However, we know that it wasn't.

In the warm, shallow waters of Shark Bay, Australia, and at some other tropical locations around the world, we find strange stony, mushroom-shaped structures. These are stromatolites.

Colonies of bacteria secrete slime. This catches sand and grit, forming a layer. The bacteria work to the surface and make more slime, which catches more sand and grit. The result is a stony structure composed of onion-like layers which fossilizes well.

The fossil stromatolites look exactly like the stony stromatolite structures we find today. The oldest ones found so far are in rocks about 3.5 billion years old, which means life got going on Earth almost as soon as the Earth had cooled after forming.

Another point is that there must have been warm, liquid oceans back then despite the sun being substantially dimmer than it is today. We are confident in our conclusions about the sun, so the explanation comes from another direction.

It turns out that the atmosphere of the young Earth was substantially different from what it is today. It had no oxygen, but lots of methane and other greenhouse gases.

The much more intense greenhouse effect made our planet warm enough for liquid oceans and life - simple plants and bacteria - to get going.

Through photosynthesis they removed greenhouse gases and released oxygen, and intriguingly, they did this at the right rate to compensate for the brightening sun.

Some years ago, scientist James Lovelock proposed the Gaia Hypothesis, named after the Earth Goddess, where, through evolutionary processes, organisms do not just adapt to their environment, providing conditions change slowly enough, they can also change that environment to keep it more suitable to them.

Ironically, our species seems, at least so far, intent on making its environment as unsuitable as possible.

  • Jupiter and Saturn lie low in the southern sky after dark.
  • The moon will be full on the 13th.


Mission to Europa

When the Voyager spacecraft sent back the first close-up images of Jupiter's moon Europa, we all had a shock.

It looked nothing like what we expected. Until then we thought that the moons of other planets would be just like ours, except maybe colder and icier. It did not turn out like that. Europa was one of the biggest exceptions. Instead of an airless, cratered surface floored with ancient lava flows.

We saw a body entirely covered by a smooth layer of ice, punctuated by cracks, some ancient, some more recent. Around some of the cracks are reddish and brownish patches.

We can start to understand Europa by considering Io, the closest moon to Jupiter. Io is by far the most volcanic body in the solar system; its surface is coloured by flows of sulphur-rich lava.

There are always eruptions taking place somewhere on Io, with a lot of material being ejected into space.

On Earth, volcanism is mainly driven by plate motions and subduction. Io has nothing like that. Instead, it is being continuously stretched and kneaded by Jupiter's intense gravity. This generates a huge amount of heat inside Io, driving the volcanism.

Europa is more distant from Jupiter, so the tidal stretching or kneading is less. However, it is enough to sustain a huge ocean under the outer icy layer, where the surface temperature never exceeds -200 C.

Europa's ocean is heated from the bottom, so it is constantly circulating due to convection, preventing it from freezing. On Earth, along the mid-Atlantic ridge and at other locations, jets of hot, mineral-rich water are coming through the seabed.

These are known as hydrothermal vents. As the hot water meets the cold seawater, some of the minerals precipitate out, forming tubular towers and clouds of dark powder, hence these vents often called black smokers.

Around them live communities of crustaceans, worms and other creatures. 

These communities are unique in that their survival owes nothing to the sun. They are sustained by heat and nourishment from within the Earth. Could there be life in Europa's oceans, perhaps concentrated around hydrothermal vents?

We know that life began on Earth about 3.5 billion years ago, almost certainly in the ocean, although it is not agreed yet exactly where. Some have suggested the deep ocean, others muddy shallows and rock pools, and others propose it got going around the hydrothermal vents.

However, the living creatures we see today colonizing the vents in our oceans are relatives of creatures that are found throughout the world. What we see around the vents today are colonists, not originals.

That does not rule out rudimentary life developing at the vents, and then moving off into the oceans, with their descendants returning "home" billions of years later.

Something like this could have happened on Europa and on other moons with ice-covered oceans, such as Saturn's moon Enceladus. The coloured stains on Europa's surface indicate the presence of organic chemicals in that hidden ocean — the building blocks of life.

We need to land a spacecraft on Europa, which would lower a hot probe that will melt its way down through the ice to the underlying ocean. In one proposal the probe would release a robot submarine that could head off to explore.

However, before designing this lander we have to know what we will be faced with on Europa, in particular how thick is the ice layer? If it is a few kilometres thick, getting through it to the ocean will be a challenge. If the ice is 50 km thick or more it will be a problem of a different order.

We will need to know the answer to this and other questions before designing a lander that will have the best chance of telling us what lurks in that remote, dark ocean.

A mission to do that has been announced. Launch is planned to take place in 2023.

  • Jupiter and Saturn lie low in the southern sky after dark.
  • The moon will reach First Quarter on the 5th.




Flashes from the sky

Fast radio bursts, or FRBs, are among the most puzzling things in modern astronomy.

From some place in the sky, there is a sudden flash of radio emission, lasting a few thousands of a second, then nothing. It is like having a star appear in a sudden bright, short flash, and then vanishing again. Seeing them with conventional radio telescopes involves having the antenna pointed in the right direction, at the right time.

For large, dish type radio telescopes the odds are millions to one against having that happen. We knew nothing about the existence of FRBs until in 2001 the radio telescope in Parkes, Australia was indeed pointing in the right direction at the right time.

However, short bursts of radio emission picked up by our radio telescopes are almost always human caused. It was not until several years later that someone looking at "old data" realized this particular short pulse of radio emission bore the signatures of having come from a great, distance, far outside our galaxy.

During the following years a few more were found, but there were too few observations for anyone to deduce the cause.

The construction of the CHIME (Canadian Hydrogen Intensity Mapping Experiment) radio telescope at our observatory has changed that. The instrument was constructed for mapping structure in the young universe.

This required a radio telescope that could see as much sky as possible at once, keeping a continuous eye on almost all the sky passing over the observatory. This is also exactly what we need for looking for FRBs. As soon as the instrument went into action, it started detecting them.

For FRBs to be detectable here on Earth while coming from so far away, a huge amount of energy must be involved in producing one. One way to release a lot of energy is for the source object to annihilate itself in the process.

Alternately, maybe the object survives producing an FRB and can go on to do it multiple times. Answering this question will take us a long way toward explaining them.

Most observations were of single FRBs, but there were two reports of sources that went on to do it again. Were these different types of event? There were only two of them so it was hard to tell.

Now, the CHIME researchers report detecting another eight repeaters, bringing the total to 10.

Since the FRBs from repeater sources look very much like the single events, it is likely that most, if not all, FRBs are produced by a similar, non-catastrophic process.

However, what process?

One suggestion, maybe not a very serious one is that the FRBs are attempts by alien civilizations to communicate with us. However, transmitting from random positions in the sky at random times is not probably the best way to do this.

Moreover, considering the distance of the objects, the transmitter power would have to be enormous, enough to endanger the planet sending the signal.

The best candidate sources are probably neutron stars or black holes. Only these objects can unload such huge amounts of energy in such a short time.

For example, neutron stars rotate quickly and have strong magnetic fields connecting them to the discs of trapped material orbiting around them.

Since the discs are rotating slower than the stars, the magnetic links can get stretched until they snap, releasing the stored energy in a few thousandths of a second, and driving a pulse of radio emission.

This is only one of a number of ideas being investigated. Until recently, there were more theories being proposed to explain FRBs than there were observations.

Now, thanks to the CHIME team and other workers around the world, that statement is no longer true.

However, that is still a very long way from an explanation, but at least now we are going in the right direction.

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


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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