Our solar system (C1)

your neighbourhood

What do you consider to be your neighbourhood? Does it have specific boundaries?

Do you feel like there is some kind of sense of community in your neighbourhood?

What are the things you like the most about your neighbourhood?

Is there anything you'd like to change in your neighbourhood?

Today, we're going to take a look not at our Earthly neighbourhoods, but at our shared cosmic one.

We're going to read a text called 10 amazing facts about our solar system.

What do you think will come up in the text?

10 amazing facts about our solar system

1. A day on Venus is longer than its year

Venus rotates extremely slowly. One full turn on its axis takes about 243 Earth days, while one trip around the Sun takes about 225. To make things stranger, Venus spins in the opposite direction to most planets, so if you could stand on its surface, you would see the Sun rise in the west and set in the east.

2. The sunlight on your face is older than it looks

Light from the Sun’s surface reaches Earth in about eight minutes. The energy carrying that light, however, was produced deep in the Sun’s core, and it spent a very long time bouncing around inside the Sun before it escaped. Estimates vary, but the journey from the core to the surface probably takes tens of thousands of years, possibly more than a hundred thousand.

3. Mars has a volcano the size of a country

Olympus Mons on Mars is the tallest volcano in the Solar System. It rises about 22 kilometres above the surrounding plains, roughly two and a half times the height of Mount Everest. Its base covers an area about the size of Poland. It is so wide and its slopes are so gentle that someone standing on it would not be able to see the summit.

4. One of Jupiter’s moons is bigger than a planet

Ganymede, Jupiter’s largest moon, is the biggest moon in the Solar System. It is wider than the planet Mercury, although it has less than half of Mercury’s mass. It is also the only moon known to have its own magnetic field.

5. Saturn’s rings are enormous but incredibly thin

The main rings of Saturn stretch across roughly 280,000 kilometres, about three quarters of the distance from the Earth to the Moon. Yet in many places they are only tens of metres thick. They are made mostly of chunks of water ice, ranging from tiny grains to pieces as big as a house.

6. Uranus rolls around the Sun on its side

Uranus is tilted at about 98 degrees, so it effectively orbits the Sun lying on its side. Scientists think a huge collision early in its history knocked it over. Because of this tilt, each of its poles experiences around 42 years of continuous daylight, followed by 42 years of darkness.

7. It might rain diamonds on Neptune and Uranus

Deep inside Neptune and Uranus, the pressure and temperature are extreme. Laboratory experiments suggest that under these conditions, carbon could be squeezed into diamonds, which would then slowly sink towards the planets’ cores like rain. Nobody has seen this happen, but many scientists think it is likely.

8. The astronauts’ footprints are still on the Moon

The Moon has no wind or flowing water to wear its surface away. As a result, the footprints left by the Apollo astronauts between 1969 and 1972 are almost certainly still there, and they could last for millions of years. The main thing that will eventually erase them is the slow, steady rain of tiny meteorites.

9. There may be more water on a moon of Jupiter than on Earth

Europa, another of Jupiter’s moons, is covered in a shell of ice. Beneath that ice, scientists believe there is a salty ocean that may contain more than twice as much water as all of Earth’s oceans combined. That makes Europa one of the most promising places to look for life beyond Earth.

10. A spacecraft launched in 1977 is almost a light-day away

Voyager 1, launched in 1977, is the most distant human-made object. In 2012 it became the first spacecraft to enter interstellar space, the region between the stars. It is now so far away that a radio signal from Earth takes almost a full day to reach it, and it is still sending back data.

discussion

Were any of your predictions mentioned in the article? Which fact surprised you most? Which did you already know?

Which of these places would you most like to see with your own eyes, if it were possible?

Several facts include words like probably, scientists think and suggest. Does that make you suspicious about any of the things in the text?

One fact not mentioned in the text (but one that I absolutely love) is that Mercury is the closest planet to every other planet in the solar system. Any idea how that's possible?

Sidestep

What happens in the story of Goldilocks and the Three Bears?

Based on these events, what do you think we mean when we describe something as the Goldilocks zone?

What, specifically, do astrophysicists mean when they talk about the Goldilocks zone?

Our own Solar System shows how narrow this zone can be. Venus, the planet next to us on the inside, is roughly the same size as Earth, but its thick atmosphere of carbon dioxide traps so much heat that its surface reaches about 465°C, hotter than Mercury. Mars, the planet next to us on the outside, probably had rivers and lakes billions of years ago, but it lost most of its atmosphere. Today the air on Mars is less than one per cent as dense as Earth’s, and any water on the surface would quickly freeze or evaporate. Earth sits between the two, in the part of the zone where water can stay liquid.

The position of the habitable zone depends on the star. A star that is hotter and brighter than the Sun has a zone that lies further out. A small, cool star, such as a red dwarf, has a zone much closer in. Red dwarfs are the most common type of star in our galaxy, so many potentially habitable planets probably orbit them. However, planets that close to a star may always show the same side to it, leaving one half in permanent daylight and the other in permanent night. Red dwarfs also tend to produce powerful flares that could strip away a planet’s atmosphere.

In the children’s story Goldilocks and the Three Bears, a girl tries three bowls of porridge. One is too hot, one is too cold, and one is just right. Astronomers have borrowed her name to describe something far more serious: the region around a star where conditions are just right for life as we know it.

The scientific name for this region is the habitable zone. It is the range of distances from a star at which a planet with a suitable atmosphere could have liquid water on its surface. Liquid water matters because every living thing we know of depends on it. Too close to the star, and the water boils away. Too far, and it freezes solid.

Being in the right place is not the only requirement. Many scientists believe that a planet also needs a protective atmosphere, a magnetic field to shield it from harmful particles streaming from its star, and some way of recycling chemicals between its surface and its interior. On Earth, the movement of tectonic plates does this job. Some researchers have suggested that our large Moon has helped too, by keeping Earth’s tilt stable and its climate steady over long periods, although how important this is remains a matter of debate.

Finally, the habitable zone may not be the only place where life can exist. Europa and Saturn’s moon Enceladus lie far outside the Sun’s habitable zone, but both appear to have liquid oceans under their ice, kept warm by the pull of their giant planets. If life were found in one of these hidden oceans, our idea of what makes a place “just right” would have to change.

discussion

Was your guess about the Goldilocks zone correct?

Why do you think liquid water is so important for life?

There's a lot of talk about Mars exploration. Do you think we'll see the first manned (humannned?) mission to Mars in our lifetime?

Should we only search for life in habitable zones, or should we look in places like Europa and Enceladus too?

Do you think “life as we know it” is the only kind of life possible?

Now check out some different people's reactions to this text.

daniel, USA

Honestly, the more I read about this, the stronger my faith gets. Think about it. Right distance from the Sun, the right atmosphere, a magnetic field, a moon that keeps everything steady. Change any one of those and we wouldn’t be here. People say it’s all luck, but that’s an awful lot of luck. To me, it looks like the universe was set up very carefully, by someone who knew exactly what they were doing. Science explains how it all works, and I’ve got no problem with that. But it doesn’t explain why everything lines up so perfectly. That’s where I see God.

Maria, Estonia

What gets me is how unlikely all of it is. There’s no plan behind it as far as I can tell. It’s just physics and chemistry and billions of years of chance. Out of all the planets out there, most are probably frozen rocks or boiling balls of gas. And yet here we are, on one that happened to work out. I don’t find that depressing at all. If anything, it makes me appreciate everything more: the oceans, the trees, my cat, my morning coffee. If life is this rare, we should be taking much better care of it, and of each other.

tom, united kingdom

I honestly don’t know what to think about this stuff. I’m not religious, but I’m not sure it’s all just chance either. Mostly it just freaks me out a bit. I’ll be lying in bed and start thinking about how we’re on this tiny planet, spinning through space, and if we were a little bit closer to the Sun we’d all be cooked. Then I start wondering whether there’s anyone else out there, and whether that’s better or worse. Usually I end up getting up and making a cup of tea and trying very hard to think about something else.

your reaction

Which of these three people do you agree with most? Why?

Is there anything in any of the reactions you disagree with?

Do you have anything to add that none of them mentioned?

Have you ever felt like Tom? What do you do when it happens?

Homework

Consolidate your learning further by checking out this video