HowDoWhy

With all this talk about stars, planets and moons in previous posts, it’s about high time I mentioned a solar system. A solar system is exactly what the name implies - the system associated with a sun (star). Our own solar system contains 8 planets. We once had nine but the planet Pluto was downgraded as discussed in some previous posts - Weren’t there 9 planets? What happened to Pluto? and What is a planet? There’s actually more to a solar system than the planets, though. The greatest influence on a solar system is that from which it begets its name - the star. The star is the center around which everything else in a solar system is built. It “binds” everything together and influences everything that surrounds it.

You can imagine a solar system starting as a mass of gas and elements. Nothing is really cohesive but since every bit of matter has a tiny bit of gravity, things are gradually attracted to one another. Eventually, enough gas and matter come together to collapse into a star. The remaining matter surrounding the new star eventually does the same, coalescing into larger and larger bits until something recognizable as a rock or chunk of ice orbits chaotically around the star. Eventually, the evolution of a solar system leads to these chunks joining together to form planets.

A young solar system is a hellish place. Newly formed planets travel in a very chaotic neighborhood and are frequently bombarded by all the coalesced “stuff” still drifting around aimlessly or plummeting inward towards the star. As more objects, dust and gas are caught up in the early planet’s gravity wells, the solar system gradually quiets down until you have an established system like our own. The large mass bodies (planets) act like vacuum cleaners, sucking up all the dirt and debris in their paths. Impacts become less frequent, orbits more stable, stray objects more rare.

Though we’ve not traveled out to see other solar systems, I’d venture a guess that each one is unique in its own right. There are plenty surprises awaiting us, I’m sure. But, using our solar system as a general model, we can expect them to include the star, planets, a Kuiper belt (a belt of material on the same general orbital plane as the planets) in which primitive, loose material still orbits in the form of comets and icy bodies, and even an Oort cloud. An Oort cloud is a very loose conglomeration of leftover “stuff” that completely envelops a world. It differs from a Kuiper belt in that the belt is on an orbital plane with the rest of the relevant matter and an Oort cloud wraps around the entire star like an eggshell around a yolk. The Oort cloud marks the edge of the solar system, a point at which the star’s gravitational and dynamic (think solar winds) influence effectively ends. We can see stars shine through Oort clouds (and can see out through our own) because the material is so loose and widely spaced as to be invisible to the naked eye.

In addition to the physical, or more accurately, visible stuff, a solar system is packed full of radiation cast off by its star. Solar winds, which are actually streams of highly charged particles streaming from the star, also influence the objects around them. Evidence of this can be seen in comet tails (which always point away from the star rather than trailing behind the comet in the opposite direction of travel) and in a phenomenon known as Aurora Borealis, a dazzling show of mysterious light in the sky caused by charged particles interacting with particles in our magnetosphere.

The few indirect observations we’ve made of other solar systems imply that ours isn’t necessarily the definitive model. Some alien planets behave in ways that are counter intuitive to the lessons we’ve learned from our own neighborhood. Future generations will make shocking and exciting discoveries for centuries to come.  

Mighty Jupiter is the largest planet in our solar system with a mass 318 times that of the Earth. In fact, its mass is more than twice that of all the other planets in the solar system combined. Aside from mass, the planet also takes up a lot of space. It is 88,736 miles in diameter or more than 11.2 times the diameter of the Earth. By volume, Jupiter could hold over 1300 Earths with room to spare.

Jupiter is like a miniature solar system in its own right. In fact, one of its moons (Ganymede) is bigger than Mercury. Another, Callisto, is comparable in size and appearance to Mercury. These two moons make up two out of four of what are known as the Galilean Moons, so called because Galileo was able to observe them with his primitive telescope. You can see them too with just an average pair of binoculars on a good night.

The other two Galilean Moons are Europa and Io which are as interesting as any planet in our solar system. It is believed that Europa hosts an ocean beneath miles of ice. Evidence of life independent of light on our own planet has led to speculation that Europa may just harbor life around hydrothermal vents.

Io is famous as the most volcanically active body in our solar system. The volcanism is caused by tidal forces as Io orbits close to massive Jupiter. The stretching and pulling of Jupiter’s massive gravity and the counter pull of the other moons heats the interior of Io. To experience how bending and stretching produces heat, try bending a paper clip back and forth multiple times and then feel how the heat builds up at the point where it bends. Now imagine that on the scale of a paper clip the size of our moon!

Poor Pluto. Discovered in 1930 by Cylde W. Tombaugh, Pluto was thought to be the missing planet theorized to exist based on inaccurate calculations. It was added as our ninth planet and actually sparked quite a fan following with its popularity, even inspiring the name of a famous Disney character. For 36 years, humble little Pluto quietly orbited our Sun, oblivious to all the fuss it inspired. The enthusiasm gradually waned as more exciting (and accessible) planets grabbed the spotlight.

As discussed in my previous post - What is a planet? - a meeting of the IAU in 2006 finally settled on the definition of a planet. The unfortunate side-effect of that decision was Pluto being downgraded from planet to “Small Solar System Body” or SSSB. This decision was largely driven by the discovery of several new “planets” in a very short period of time. With improving optics and observational techniques, it became clear that it isn’t at all unreasonable to imagine we’ll find dozens of “planets” similar in size to Pluto orbiting in the Kuiper belt or the Oort Cloud beyond. With the assumption that Pluto-like bodies are a dime-a-dozen, the not-entirely-popular decision was made to downgrade Pluto and any similar objects found in the future. This decision was made despite a fairly vocal outcry that diminutive little Pluto be grandfathered in and retain its planet status. Scientists aren’t much for compromise, it seems.

Charon, formerly known as Pluto’s moon, has actually been upgraded to equal footing with the SSSB formerly known as planet. Pluto and Charon are now a binary SSSB pair rather than a Planet and a moon.

If you’re interested in learning more about Pluto, visit Nine Planets and read Dr. Alan Stern’s detailed write-up on our distant little friend who, despite all the fuss it caused, still quietly orbits our star, oblivious to the new hooplah it inspired 36 years after it was first discovered.

There’s a lot more to our solar system than the planets. I’ll cover some of the less known objects and phenomenon such as the Oort Cloud, Kuiper Belt and other strange stuff in a future post, but when people think solar system, they usually think of the planets in orbit around the Sun. Our solar system boasts 8 planets; four terrestrial and 4 gas giants. Starting closest to the Sun and working out the planets are:

• Mercury - Terrestrial. Average distance from the Sun is 36 million miles
• Venus - Terrestrial. Average distance from the Sun is 67.5 million miles
• Earth - Terrestrial. Average distance from the Sun is 92.75 million miles
• Mars - Terrestrial. Average distance from the Sun is 141.5 million miles
• Jupiter - Gas giant. Average distance from the Sun is 484 million miles
• Saturn - Gas giant. Average distance from the Sun is 889 million miles
• Uranus - Gas giant. Average distance from the Sun is 1.95 billion miles
• Neptune - Gas giant. Average distance from the Sun is 2.79 billion miles

Each of the planets above has been linked to the corresponding statistics page on Windows to the Universe, but the site offers so much more information than just that shown on the stats pages. Pay them a visit and look around! The site is available in English and Spanish.

There are several things in our solar system bigger than the Earth; the Sun and all the gas giants like Jupiter. But of the four terrestrial planets - the rocky worlds you could actually walk on if appropriately attired (Venus has a strict jacket and tie requirement) - the Earth is the largest. You have to take the Earth’s shape into consideration when measuring its diameter as the planet bulges along its equator at 24,901.5 miles circumference and is slightly shorter if you measure around its poles with a circumference of 24,859 miles. The difference is due to the planet’s rotation.

Earth’s mass comes in at about 6.0 X 10²⁴ kilograms (derived by using Newton’s Law of Gravity - F=GmM/r² ) but the measurement of mass is out of date almost as soon as its made. The Earth is constantly gaining mass from dust and material that falls into its gravity well.

To see how the Earth stacks up in size relative to the other planets in our solar system, visit Rense.com. This site has a mind boggling set of pictures that show how everything stacks up. Even better, it shows how truly tiny the Sun is relative to some other monstrous stars.

The Earth circles peacefully around the Sun at about 149 million kilometers or 92.75 million miles on average. Our orbit is slightly elliptical so our distance swings from anywhere as far as 94.5 million miles and as close as 91 million miles. There are a lot of interesting facts about the Earth I’ll save for another post but to keep the theme going, I’ll give you an idea of just how far that distance is and how it translates into concepts we’re all familiar with.

A Boeing 747 cruises at a speed of about 570 miles per hour. If you were to fly one non-stop, with an unlimited fuel supply, to the Sun from the Earth it would take 162,719 hours or 6780 days or 18 ½ years. Hope you REALLY like airline food.

To drive to the Sun at a comfortable 60 miles per hour would require a trip of 1,545,833 hours or 64409 days or about 176 years. I’d suggest getting a tune up and your tires rotated before setting out.

Want to walk? It’s too insane to contemplate but if you were so inclined you would be looking at 26,500,000 hours or about 1,104,166 days or about 3025 years to complete your trip and I bet there’d be no vacancies at the hotels when you finally got there.

The distance between the Earth and the Sun is so vast that it takes light leaving the Sun’s surface over 8 minutes to reach us!

Just a quick intermission from the space stuff - We’re living in tight times. Gas prices are rising, housing values are falling and it’s harder than ever to get a loan these days. But don’t despair; there is some good news in all of this mess. For one thing, look at a recession as a sale on stocks. You won’t find better deals or a better opportunity to accomplish the number one rule of stock purchasing - buy low, sell high.

Another positive is that this is a great time for all of us to grow up a little and take ownership for our circumstances. Review your savings, review your spending habits, write up a budget, and plan on reducing your debt. If an economic down-turn isn’t enough to force you to change your habits, the alternative is waiting until it’s too late. Consumerist.com has produced a nice, easy-to-adopt list of 10 things you can do today to make a difference in your financial life. What are you waiting for? Go visit them now!

Our solar system has an interesting and diverse cast of characters. We even have a black sheep in our solar family in the form of Pluto and at the center of all the recent controversy about its status has been one surprisingly difficult question to answer - what is a planet?

You’d think that pretty much any response that includes “big round thing orbiting the Sun” ought to hit the mark but it turns out answering the question is more complicated than that and, while the International Astronomical Union (IAU) may have finally settled on a set of definitions that has resulted in one very notable change in our solar inventory, the truth of the matter is that there are still plenty folks out there who disagree with the terms and conditions. The 2006 gathering of the IAU defined a planet as follows:

• A planet is a celestial body that has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape.
• Is in orbit around a star, and is neither a star nor a satellite of a planet.
• It has cleared the neighborhood of other objects in the path of its orbit.

This definition was adopted rather than the originally proposed draft which would have added at least three new planets to our solar system - Ceres, Sedna and Eris. All three are comparable in size to Pluto and in a similar orbit. The long debate essentially settled the question by assigning them the classification of Small Solar System Bodies (SSSB). Basically, any object (other than a moon orbiting a planet) that meets only #1 is now an SSSB. If it meets two of the definitions above, it would be considered a “dwarf planet.”

While it’s great that we’ve finally settled on the definition for a planet, there was a casualty in all of this. We lost Pluto. I’ll write more about what happened to poor Pluto in an upcoming post this week.

I considered answering this in my previous post - How big is the Sun - but found the question so well answered elsewhere that I’ll give it its own post. The short answer is - 1 million. As explained by Ask an Astrophysicist at NASA’s Goddard Space Flight Center - Imagine the Universe, it helps to imagine the Sun as a fishbowl and the Earth as a marble. The diameter of the Sun is 100 times that of the Earth so it would take 100 marbles to stretch from left to right across the inside of solar fishbowl. But you also have to consider front and back; and up and down and everywhere in between. That adds up to a lot of marbles!

Visit GSFC’s Ask an Astrophysicist to read the full answer to - how many times would the Earth fit in the Sun. I think that will wrap up coverage of our amazing little star for now. Please don’t hesitate to ask any questions if I left something out you’re curious about. Check back tomorrow as we’ll begin covering planets!

The Sun is about 1,392,000 kilometers or 875,000 miles across. If you wanted to put a belt on the sun to hold up its pants you would want to know its circumference and for that you just apply a little math. The circumference of a sphere is determined by multiplying 2 times pi (3.14) times r (the radius). If you know the diameter is 875,000 miles then you also know the radius (radius is just half the diameter). In this case, to determine the circumference of the Sun you must multiply 2 times 3.14 times 437500 which gives you a circumference of 2,747,500 miles. The Sun needs a pretty big belt to hold up its fireproof jeans!

How long would it take to drive around the Sun? At 60 miles per hour, it would take 45,791.6 hours to drive around the Sun once. That’s just shy of 1908 days or 5.22 years (not counting stops for gas at your local solar gas station)! If you were to walk around the Sun without ever stopping at a man’s average pace of 3.5 miles per hour it would take you 785,000 hours or 32,708 days or 89.6 years! If you insist on 8 hours of sleep a night, add another 29.8 years on to the trip.

But there’s more to the Sun than just how much space it occupies. Another consideration is how densely packed the material is in the Sun. Think of it this way - If there were a balloon shaped exactly like you and inflated so it was just as tall and wide as you are, would it still be as “big” as you? Technically, yes. It would occupy the same amount of space. But it wouldn’t weigh nearly as much or contain as many atoms. It wouldn’t have the same mass as you. But a block of lead carved to exactly your shape would actually have MORE mass than you do. The atoms in the lead are more densely packed than the atoms in your body.

Remember from our previous post - What is the Sun and what is it made of - that the Sun is made up of some of the lightest stuff there is - Hydrogen and Helium. Together, these two elements make up about 98% of the entire Sun and individually these elements are so light that they weigh less than air and will float if you fill up a balloon with them. But the Sun is so large, has so much Hydrogen and Helium and is so densely packed together with the stuff that its mass comprises more than 98% of all the mass in our solar system. If you took all the planets, all the moons, all the asteroids and comets and dust and gas and squeezed it all into a ball, it would equal less than 2% of all the mass in the solar system and the Sun would make up the remaining 98%!