Claire Bretherton answers your questions about shooting stars, planetary rings and stardust
Claire Bretherton answers another selection of your questions. Listen in to find out more about shooting stars, why some planets have rings around them, and if it’s true we’re all made from stardust.
Hello, I’m Dr Claire Bretherton from the Royal Observatory, Greenwich, and welcome to the latest episode of our Big questions answered podcast. We’ve had some fantastic questions this month, and we’ve chosen three of our favourites to tackle. So, let’s start with the first one from Ryan.
Hi Claire, this is Ryan. I’ve always wondered why you get shooting stars and wondered if you could tell me why they happened and whether you can predict them. Thank you! Bye.
Thank you Ryan. Well, first of all shooting stars aren’t actually stars at all. They’re meteors – tiny bits of dust that come into the atmosphere around our planet. When they do, they get very hot and they burn up and we see this bright streak of light across the sky.
Now you can see meteors any night of the year, but there are certain times when you’re more likely to spot them, during the meteor showers. There are several dozen of these throughout the year, and they’re fairly easy to predict, but there are some that are more famous than others.
One of the best known is the Perseids in mid-August, usually peaking around August 12th. Perseids is when the Earth passes through the path taken by the comet Swift-Tuttle and all the bits of dust left over, the debris of that comet, hit our atmosphere. If you go somewhere reasonably dark during the Perseids, you may see more than one meteor every minute.
Another famous shower is the Leonids, and this is around the middle of November each year. And every 33 years or so we have a meteor storm, and the number of meteors drastically increases. You may see many thousands each hour. Again, this is caused by the debris of a comet, this time the comet Temple-Tuttle.
There’s actually a meteor shower coming up in the next few days: the Geminids. We see it between the 7th and the 17th of December, but usually peaking around the 14th. This has been getting stronger and stronger each year, so if you go somewhere dark, once again you may see as many as two each minute.
OK. On to our second question which is from Jose.
Hi Claire, this is Jose. I was just wondering why some planets have rings and others don’t. Thanks for looking into it. Cheers! Bye.
Thank you, Jose. That’s a great question. Of course, the most famous planet to have rings in our own Solar System is the wonderful Saturn. It has these big, bright, and very complex rings made of mainly ice and some dust, like dirty snowballs all going around the planet.
They’re so bright you can actually see them with a small telescope or even a good pair of binoculars. We think that an icy moon got too close to Saturn and got ripped apart into countless pieces, some as small as my little fingernail, some as large as a house, which now all go around the planet forming these fabulous rings.
But Saturn’s not the only planet to have rings. Jupiter, Uranus and Neptune have rings, too, but they’re made of much darker material. We can’t see them as clearly, but we do think that moons were important in forming these rings, either by colliding with each other and breaking up into smaller pieces or by collisions with smaller objects, causing dust to be blasted off into orbit around the planets.
Now, the only planets in our own Solar System that nowadays have rings are the larger gas giants, but Mercury, Venus, Earth, and Mars may have had rings in the past. But of course, these planets are much smaller. Their gravity is not as strong, so it’s harder for them to retain these rings.
As we’ve seen, moons are probably very important in both creating the rings and keeping them stable going around the planet, so because these planets are much smaller, they’ve not been able to build up such large moon systems, and so it’s harder for them to create the dust and the particles that form the ring around the planet.
On to our final question from David.
Hi Claire, this is David. My question for you is: is it true that we’re made out of stardust?
Thank you, David. You’re right, we are all made of stardust. When the Universe began, it was made up mainly of hydrogen, a little bit of helium, and a few tiny traces of other elements. All of the other elements that make up us, our Earth, and everything else we know, were created in the stars.
Stars are formed out of huge clouds of gas, mainly hydrogen and helium, and that gas is pulled together by gravity. As it gets pulled further and further together, it gets denser and denser and hotter and hotter until it reaches a temperature around 10 million degrees and nuclear fusion can start, turning hydrogen into helium and creating huge amounts of heat and huge amounts of light.
In larger stars, this process can continue and helium can fuse to become carbon, oxygen, silicon – heavier and heavier elements, up until iron, but to make elements heavier than iron actually takes more energy than it releases, so this can only happen when massive stars end their lives.
When a star more than eight to ten times the mass of the Sun dies, it does so in a violent explosion called a supernova, releasing huge amounts of energy. This allows iron to be fused to form heavier and heavier elements. So, absolutely everything that we know of and that we’re made of does originate in the stars.
Well thanks everybody for the fantastic questions this month. Do keep them coming in, and again we’ll pick a selection of our favourites for the next episode in the new year. Thank you very much and goodbye.