The Solar System : Paige's guest post

 

On a clear night, you might look up towards the moon and see a bright spot is peeking out nearby. Your night sky app tells you it’s Venus. You take a good long look, maybe even pulling out your small telescope, because it won’t be there very long to ogle at - just a few days and it’s moving on. Sometimes this bright, un-twinkling dot is Jupiter, Mercury, or Saturn. We call these stray moving lights the planets, which comes from the Greek word planetes, or “wanderer”.

If you grew up before the '90s, then you were taught that Pluto is a planet. Despite our personal investment in Pluto’s stature, planetary science has come a long way since the discoveries of exoplanets in other solar systems and finding other bodies even bigger than Pluto orbiting our Sun that were the ultimate deciding factor for changing Pluto’s identity to a dwarf planet. Pluto fans have no fear, Pluto remains close to our hearts on Becky’s Solar System necklace.

Even though our understanding, sample size, and albeit definition of a planet has changed in the last decade, we are still just as freshly exploring our own neighborhood planets as we were before we kicked out Pluto. Many missions like Cassini and New Horizons are so fresh in our minds that we can’t help but wonder how we have gone this long without knowing the beauty in the wanderers.

 An image of Saturn and its rings taken by Cassini in 2006. Credit:  NASA

An image of Saturn and its rings taken by Cassini in 2006. Credit: NASA

Can I take a day trip to Mars?

That happens to be an easy one to answer, though, because these “neighbors” are really super far away. With current technology, it takes nearly 9 months to get to Mars. But asking how far away each planet is from Earth is kind of arbitrary, because all of the planets are constantly moving in their orbits around the Sun, and so are we, so that distance changes dramatically, and it changes all the time.

Instead, the distance to each planet is calculated as its average distance from the Sun. This kind of goes along with the whole “heliocentric” not “geocentric” way of living we are adjusted to in this modern world.

So this distance is measured in what’s called an Astronomical Unit. One Astronomical Unit, or AU for short, is 93 million miles. That is the distance from the Sun to the Earth (I didn’t say we were completely heliocentric). 

For our terrestrial friends, Mercury and Venus are closer to the Sun at 0.4 and 0.7 AU, respectively and Mars is 1.5 AU from the Sun. 

The gas giants Jupiter and Saturn are 5 and 9.5 AU away,

And the ice giants Uranus and Neptune are 19 and 30 AU away.

Our little Pluto is a whopping 39.5 AU from the Sun.

 Fab graphic from the folks at https://upcosmos.com/au/, demonstrating the distance of each planet from the Sun.

Fab graphic from the folks at https://upcosmos.com/au/, demonstrating the distance of each planet from the Sun.

So that might not mean much in an elevator conversation because it’s not a measurement we are familiar with on a daily basis, but if it helps, Earth orbits the Sun every 365 days (not a coincidence). It takes Pluto 248 Earth years to orbit the Sun. That would make for a REALLY long winter.

Can I walk on Jupiter?

You might also have noticed that the type of planet changes based on how far away it is. This isn't a coincidence, as this happened when the solar system formed and some planets are too hot and some are too cold and some are just right. 

The closest planets to the Sun- Mercury, Venus, Earth, and Mars- are the terrestrials, the ones we can walk on (if you ignore 800 degree Fahrenheit temperatures on Mercury, sulfuric acid rain on Venus, and an atmosphere 0.6% the pressure of Earth’s on Mars, but who’s keeping score?)

Next in line are gas giant planets- Jupiter and Saturn. These are the hottest topic of study in planetary science right now because they are the farthest we can easily send probes on a normal career-long timescale. Beyond Saturn are Uranus and Neptune, the ice giants, which makes sense because it’s pretty dang cold out there at over 1.7 billion miles from the Sun.

 Five bright planets all visible in the night sky. Image credit: Museum Victoria/Stellarium

Five bright planets all visible in the night sky. Image credit: Museum Victoria/Stellarium

If you want to take your planetary knowledge outdoors, next time you are looking at the night sky, try to pick out the bright white dot that isn’t twinkling. A star doesn’t technical twinkle, but all of the interstellar gas and dust makes a tricky path for the light to get to us. The planets, however, are so much closer that they don’t experience such a struggle, and shine steady and bright for us to look at.

Unfortunately, due to the huge distance between Earth and the outermost planets, we’ll never see them all with the naked eye, and we’ll probably never set foot on them all either. But you can accessorize with the planets, and really, that’s the next best thing.


 
 
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About the author

 Hi fellow earthlings, my name is Paige and I am an academic astronomer turned space-enthusiast. I dabble in writing, public outreach, and wearing all the space attire I can find. Working in New York City, I noticed that we humans spend so much time watching where we’re going, that we forget to look up. Just be careful you don’t trip.

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