Comet Swift-Tuttle

False colour image of Comet Swift-Tuttle taken with the Spacewatch Telescope. Credit: Jim Scotti, University of Arizona

As you may know, we are right in the heart of the Perseid meteor shower. You can all thank Comet Swift-Tuttle for this beautiful annual spectacle! This comet, that is 26 km in diameter, has been observed for many thousands of years by ancient as well as modern astronomers, and has a fairly stable and well understood orbit. It was rediscovered in 1992, when it last made its closest approach to the Sun, at which point many thought it might be an impact risk to the Earth during its next approach on August 14th 2126. Its orbit has since been recalculated, and chances of an impact occurring are thought to be extremely low.

However, it is the largest Solar System object that makes repeated close passes of Earth. With its size and velocity, a collision with Swift-Tuttle would have approximately 27 times the energy of the K-T event impactor, most commonly known as the cause of the extinction of the dinosaurs. It is for this reason that many astronomers consider Comet Swift-Tuttle to be the single most dangerous object known to humanity. Marvel at the awesome power of the Universe! For more factoids on Swift-Tuttle and the Perseids, visit Space Magazine.

Ask Nathalie

An artist's depiction of the two Voyager spacecraft as they approach interstellar space. Image credit: NASA/JPL.

Hi Nathalie,

I do have a question about space-time. How is it that all the different stars can be connected to us…? They seem a lifetime away. Is there any relation between the history of space, and a spiderweb — like if you touch a spiderweb with a finger, it moves and affects the whole web…

From,
Whoa, It’s Like… Duuuuude 

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Dear Dude,

Okaaaay, err… Let me try and break this question into manageable parts I can actually answer. Alright, stars being connected to us. So I could argue that all these stars have a gravitational effect on us, since they are so massive, but gravity is a force that falls with radius squared. That means that, while we are basically controlled by the Sun’s gravitational field, the next closest star (Proxima Centauri) which is 4.24 lightyears away doesn’t have a whole lot of effect on us. Furthermore, lines of a gravitational field cannot “move” faster than the speed of light. That means that if Proxima Centauri were to suddenly vanish without a trace, whatever tiny amount of gravitational effect it has on Earth would not disappear until 4.24 years after the star’s disappearance. On a shorter distance scale, that means that we would not notice the Sun’s sudden disappearance until 8 minutes after the fact, since the Sun is about 8 lightminutes away from Earth.

The Universe is heavily interconnected. The Sun moves around the Milky Way based on the gravitational field created by the sum of all the other stars in the Galaxy. Our Milky Way moves around the Universe based on the gravitational field created by the sum of all the other galaxies in our Local Group of galaxies. Our Local Group as a whole is moving away from other clusters of galaxies based on the expansion of the Universe. These phenomena require the compounded effects of millions and billions of objects, though. Unless they’re very close to each other (like within a stellar system), single objects don’t really affect other objects.

As an example, the Voyager I probe which was launched in 1977 is on the cusp of exiting the Sun’s sphere of influence and entering interstellar space. Once it does, the magnetic and gravitational fields of the Sun will have a much weaker effect on the probe. It has travelled nearly 0.002 lightyears to get to this stage. Compare this distance to the diameter of our Galaxy, 120 000 lightyears, and we realize the Sun’s influence is short ranging. Add the Sun to all its stellar neighbours, though, and you create massive fields!

I feel there might be a really cute moral to this story along the lines of “If you work together, you can fling neutron stars out of the galaxy!”.

Enjoy!
Nathalie 

Ask Nathalie

This is not how I remember Contact....... Image credit: N. Ouellette.

Hi everyone! Welcome to the first (and maybe, but I hope not, last; please send me questions) edition of “Ask Nathalie” where you get to ask me random questions about astronomy, and I probably answer them! Nathalie is the person in the picture who hopes she doesn’t get sued by Jodie Foster, Carl Sagan’s living relative and whoever made the movie “Contact”. Also, I kind of hate the name “Ask Nathalie”, so please suggest other names. Alright, we have a triple header from a single reader, so here we go.

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Hi Nathalie!

1) Why does the Sun get hotter as you move outwards?

2) Which moon has a methane cycle? 

3) If all the material in the asteroid belt were to combine, how big would this object be?

Cheers, 
Knows Which Moon Has A Methane Cycle

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Dear Methane Cycle,

Yeah, that’s right. I’m also doing that thing where I’m giving the people who are writing in weird descriptive names. And yes, Methane Cycle, I really do believe you do actually know which moon has a methane cycle, because that sounds like an extremely pointed question for someone not in the know!!! Nevertheless, I will humour you and answer all your queries:

1) This isn’t quiiiiite true. On average, the hottest part of the sun is its core (about 15,000,000°C). As you move outwards from the core, the temperature drops until it reaches about 5,700°C at the surface, or photosphere. Temperature continues to drop once you enter the atmosphere, until you reach 500 km above the photosphere and hit the minimum temperature. Here, it’s a chilly 3,800°C. But then!… Now the weird stuff starts happening. A little higher up, you have the chromosphere that reaches 20,000°C. Further still is the corona where it’s 1,000,000°C to 2,000,000°C on average. Some hot spots can temporarily heat up to as high as 20,000,000°C, though! Toasty. Now why… Well, sadly we’re not sure (this column sucks!). In the Sun’s atmosphere, where it’s still very hot but the gravitational force is weaker, much of the gas is turned into plasma. And plasma is craaaaazy. By that I mean, of course, that it is heavily influenced by the Sun’s magnetic field. It may be that energy is transported from the cooler surface to the hotter corona (breaking the laws of thermodynamics, cringe) using a magnetic mechanism we don’t quite understand yet. So my advice to you is to become a physicist, figure this out and report back to me ASAP.

2) I think you already know this, but Saturn’s moon Titan has a methane cycle. By this, we simply mean it has a cycle very much like Earth’s water cycle (precipitation, evaporation, condensation, repeat), except with methane instead. The average temperature on Titan is about -180°C. Methane’s melting point is -182°C, and its boiling point is around -162°C. Oooh, look at that! That means Titan is covered in GIANT LAKES FILLED WITH COMBUSTIBLE FUEL. It’s thought that life may be harboured within these crazy fuel lakes, but if you’re interested in that topic, you should’ve asked that question specifically (aka send in this question).

3) It would be so easy for my to just answer “As big as your mama” here and call it a day, but I’m absolutely not that kind of a person. Instead, I will be extremely lazy and copy-paste the following from Wikipedia: “The total mass of the asteroid belt is estimated to be 2.8×10^21 to 3.2×10^21 kilograms, which is just 4% of the mass of the Moon”. I love you, Wikipedia.

SEND ME YOUR QUESTIONS!!!

Love,

Nathalie

P.S: OR ELSE.

Lifetime of our Sun

An artist's depiction of the life stages of our Sun, from birth to death as a white dwarf within a planetary nebula. Image credit: ESO/S. Steinhöfel.

It all started with a giant cloud of gas, some 4.57 billion years ago. This cloud of helium and hydrogen collapsed under its own gravity and formed a protostar. After 100,00 years, it became a fully formed star and began its hydrogen burning phase, otherwise known as its main sequence — its adulthood of sorts. This lasts a total of 10 billion years. Currently, our Sun is halfway through its main sequence stage. Even now, however, the Sun is going through changes, but they are indiscernible over a human lifetime. Every billion years, our star gets 10% brighter, as it marches towards the end of its life. Because of this, the Earth’s surface will be too hot to sustain liquid water, and, in all likelihood life, in one billion years. To make matters worse, the Sun is expected to swell up to a few hundred times its current size in 5 billion years, when it becomes a red giant. At this point, it will have swallowed up Mercury, Venus, and possibly even Earth!

In one final gigantic tremor, our red giant Sun will expel its gaseous outer layers, forming an expanding planetary nebula, and leaving only a faint white dwarf at its centre. The layers of the planetary nebula will sweep through our Solar System and reach the interstellar medium, where they might one day join a gas cloud and lead to the formation of another star. As with the living creatures on Earth, we observe a beautifully cyclic nature in the lifespan of stars.

Meteor Showers!

The 2012 Geminids over South Dakota. Image credit: David Kingham.

Meteor showers are some of the most beautiful sights one can see with their naked eye, and they have the marked advantage of appearing at almost the same time every year! Very young, we’ve learned to call these luminous streaks across our sky shooting stars, but they are not stars at all, but rather flaming space debrsi! Every year, around 15,000 tonnes of these debris, from sand grain sized to boulder sized, enter the Earth’s atmosphere. As they burn up, they leave behind brightly visible paths. While few meteors survive their journey and fall to the ground as meteorites, most are completely destroyed before impact. 

A few times a year, these shooting stars happen in swarms, sometimes inundating our skies at a rate of up to thousands of meteors per hour! In such impressive cases, they are called meteor storms rather than simple showers. But why do we witness sudden surges of shooting stars at the same time every single year? The answer is comets! We all know about comets: icy bodies orbiting around our Sun, periodically appearing in our skies as bright tailed objects. The trajectory of some of these comets crosses the trajectory of Earth’s orbit. Obviously, the comets and Earth do not cross this point at the same time or that would mean bad news for us! However, comets do leave behind long-lasting trails of debris into which Earth passes once a year, like clockwork. Some of these particles crash through our atmosphere and delight us in the form of a meteor shower. The intensity of each meteor shower depends on the density of the particle cloud leftover by the comet, the position of other planets in our Solar System, the intensity of the Sun’s activity and many more complex variables. Luckily, there are over 50 meteor showers every year, many of which are visible to the naked eye so there’s always a chance to spot a shooting star. The two most prominent showers are the Perseids in mid-August and the upcoming Leonids in mid-November!