Category: Guide to Space

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If you give most people enough time to think, they can come up with the names of all of the planets. Most will still throw in Pluto, despite its demotion. What those same people will have difficulty with is the Solar System order. It can be difficult to remember which planet is where. The current Solar System order is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

The best thing to do is come up with a handy mnemonic. The most common one taught in school used to be My Very Educated Mother Just Served Us Nine Pizzas, then Pluto lost the prestige of planetary status. Most educators have cast about for another, just as handy mnemonic device. This one should work just fine: My Very Educated Mother Just Served Us Noodles. Of course, both devices assume that everyone knows that the Sun is at the center of our Solar System.

Here are a few details about each planet that might be of interest to you.

Mercury has a tenuous atmosphere, so, despite being the planet closest to the Sun, it is unable to retain the heat it is exposed to. The temperature ranges by a few hundred degrees Celsius each Mercurian day.

Venus has a thick atmosphere and an average surface temperature of 460 degrees Celsius. If you were standing on Venus, you would choke on the high amounts of carbon dioxide as your skin dissolved in the sulfuric acid rain.

Earth needs no introduction or details.

Mars is perhaps the most studied planet besides Earth. It has a nearly nonexistent atmosphere, so it is a cold world. Temperatures are about -140 Celsius in the winter. At the height of summer you could not comfortably wear shorts.

Jupiter is 2.5 times as massive as all of the other planets in the Solar System combined. Jupiter has 63 recognized moons, but more are thought to be in orbit. That accounts for about 1/3 of the moons in our Solar System.

Saturn is a contradiction. It is the second largest planet, yet it has a very low density. It would float if you had enough water to put it in. There are 60 acknowledged moons orbiting Saturn.

Uranus is tilted like crazy. All planets are slightly tilted on their axis, but Uranus is tilting at 98 degrees.

Neptune, is last, but not least. It orbits an average of 4.5 billion km from the Sun. It was discovered in 1846, making it the most recent recognized planet to be discovered.

And there you have the Solar System order, a way to remember it, and a few interesting facts about each planet. We encourage you to explore the NASA website to get more information.

Here’s an article from Universe Today that goes into more detail for each of the planets in the Solar System.

Here’s an article from the BBC with several suggestions down in the comments. And here are some more.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

Reference:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=SolarSys

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• Solar System Simulator – It’s not really a game, but the Solar System simulator from NASA is one of the coolest online tools you’ll find. It lets you simulate the entire Solar System, so you can see what things look like from any planet, moon or spaceship. Very cool.
• Solar System Jigsaw – This interactive tool from BBC lets you build jigsaw puzzles on the Internet of the Solar System. You can make them more difficult or easy.
• Solar System Games – Windows on the Universe has a whole system of Solar System games you can try out. Some are built in Java, and others are programmed in Macromedia Flash, so you might need to install plugins to make them work.
• Science@NASA – NASA’s science website for kids has a series of games you can play online. You can explore Mars, or compare the size of planets.
• NASA Space Place – NASA has many sites for kids, and most of these have online games you can play. This Solar System game lets you see how well you know your moons and planets.
• Surfing the Solar System – This game from the Astronomical Society of the Pacific lets you go on a treasure hunt through the Solar System.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

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The Solar System holds some big records. Want to know which are the largest in the Solar System?

Largest star
Well, there’s only one star in the Solar System: the Sun, so it’s the automatic winner here. The Sun measures 1.4 million km across. That’s so big, you could put 109 Earths side by side to match the size of the Sun. Astronomers have theorized that the Sun might have a companion star on a long orbit, but if was anywhere as large or bright as the Sun, we’d definitely see it. So this is a record that won’t fall.

Largest Planet
The largest planet in the Solar System is Jupiter, which measures 143,000 km across its equator. That’s the same as 11 Earths. In fact, Jupiter is so large that it has 2.5 times the mass of all the other planets in the Solar System… combined. One interesting note is the Jupiter actually can’t get any bigger. If you added more mass to Jupiter, the increased gravity would actually pull it together harder, and it would shrink.

Largest Moon
The largest moon in the Solar System is Jupiter’s moon Ganymede, which measures 5,268 km across. It’s actually larger than Mercury, as well as Pluto and the dwarf planets. If it orbited the Sun, it might be a planet in its own right. Astronomers used to think that Saturn’s moon Titan was the largest moon, but then they realized that Titan’s thick atmosphere made it just appear larger.

Largest Mountain
The largest mountain in the Solar System is Olympus Mons on Mars. This ancient shield volcano measures 27 km tall. That makes it 3 times the elevation of Mount Everest on Earth, and 2.6 times the height of Mauna Kea from its base below the ocean. Astronomers think that Olympus Mons got so big because Mars never developed plate tectonics. A hotspot opened up to the surface of Mars, and just stayed there for billions of years, pouring out lava and building up the mountain. Olympus Mons is also the largest volcano in the Solar System.

Largest Asteroid
The largest object in the asteroid belt is Ceres, measuring 974 km across. But there’s a problem, Ceres has been upgraded to the status of a dwarf planet, like Pluto. This means that the largest actual asteroid is Vesta, also located in the asteroid belt. Vesta measures 530 km across, and contains about 9% of the mass of the asteroid belt.

Largest Crater
The largest crater in the Solar System is on the Moon. It’s called the South Pole-Aitken Basin, and measures about 2,500 km across. Astronomers on Earth didn’t realize it was a huge crater until the first spacecraft orbited the Moon. That’s because we can’t see the crater itself from our vantage point, just a huge rim of mountains. South Pole-Aitken Basin might actually be the second biggest crater in the Solar System. That’s because new research indicates that a much larger impact site might be on Mars, called the Borealis Basin – measuring 8,500 km across, but more proof needs to be gathered.

Here’s an article about the largest planet, and the largest moon in the Solar System.

Here’s an article about that recent news on Borealis Basin.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

Reference:
NASA Solar System Exploration Guide
NASA SOHO: Our Star, The Sun
NASA: Moon’s Largest Impact Basin
NASA Photo Journal: Olympus Mons

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This is a a diagram of the Solar System. It was released shortly before the International Astronomical Union made its final decision about whether Pluto should be a planet or not. In the end, they decided that Pluto is not a planet. But for a few days, it was possible that there would be 11 planets in the Solar System, including Pluto, Eris and the asteroid Ceres. This image of the Solar System shows them all with the Sun.

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This is a montage photo of the Solar System, with a picture of a Sun and all the planets, as well as all the moons in the Solar System. This lets you see just how many objects there really are in the Solar System.

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This is another montage of the planets, dwarf planets, comets and asteroids in the Solar System. It’s one of the older Solar System pictures that we’ve seen.

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Here’s a Solar System image with all the planets correctly categorized. In this, we can see a picture of Pluto, Ceres and Eris are correctly designated as dwarf planets.

Want more images of planets? Here are some pictures of Mars, pictures of Venus, pictures of Saturn, pictures of Pluto, and pictures of Jupiter. Here’s an article about a 3D Solar System.

One of the best resources for photographs of the Solar System is NASA’s Planetary Photojournal. You can also check out Hubble’s photographs of the Solar System.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

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This image contains all of the largest objects in the Solar System. You can print this diagram of the Solar System, as well as this handy list of all the planets.

The Sun – The central star in the Solar System

Mercury – The first planet in the Solar System. It’s also the smallest planet in the Solar System. Mercury takes just 88 days to complete an orbit around the Sun.

Venus – The second planet from the Sun. In many ways, Venus is a twin to our own Earth. It has nearly the same size and mass as Earth, but the thick atmosphere on Venus makes surface temperatures hot enough to melt lead. Venus is also unusual because it rotates backwards to all the other planets.

Earth – Our home planet, the third planet from the Sun. Earth is the only planet in the Solar System known to support life. This is because we are at just the right distance from the Sun so that our planet doesn’t get too hot or too cold. We also have one moon – the Moon.

Mars – Mars is the fourth planet from the Sun, and is much smaller and colder than the Earth. Temperatures on Mars can rise to 20-degrees C, but dip down to -140-degrees C in the northern winters. Mars is thought to be the best candidate for life elsewhere in the Solar System. Mars has two small, asteroid-shaped moons: Phobos and Deimos.

Ceres – Ceres is the first dwarf planet in the Solar System, and the largest member of the asteroid belt.

Jupiter – Jupiter is the 5th planet from the Sun, and the largest planet in the Solar System. Jupiter has as much mass as 2.5 times all the rest of the planets combined – almost all of this mass is hydrogen and helium; although, scientists think it has a solid core. Jupiter has at least 63 moons.

Saturn – Saturn is the 6th planet from the Sun, and is well known for its beautiful system of icy rings. Saturn is almost as large as Jupiter, but it has a fraction of Jupiter’s mass, so it has a very low density. Saturn would float if you could find a tub of water large enough. Saturn has 60 moons at last count.

Uranus – Uranus is the 7th planet from the Sun, and the first planet discovered in modern times; although, it’s just possible to see with the unaided eye. Uranus has a total of 27 named moons.

Neptune – Neptune is the 8th and final planet in the Solar System. Neptune was only discovered in 1846. It has a total of 13 known moons.

Pluto – Pluto isn’t a planet any more. Now it’s just a dwarf planet. Pluto has one large moon, called Charon, and then two smaller moons.

Eris – The next dwarf planet in the Solar System is Eris, which was only discovered back in 2003. In fact, it was because of Eris that astronomers decided to reclassify Pluto as a dwarf planet.

I hope you find this diagram of the Solar System helpful.

Reference:
NASA Solar System Exploration Guide

Everyone seemed to enjoy the answer to my daughter’s question, “what’s the biggest star?”, so I thought I’d give you another insight into space science at the Cain household. A couple of months ago, we built a scaled map of the Solar System. I thought I’d share my process and resources with you, and throw in a few cute pictures of the kids. So come on, let’s build a solar system scale model in your neighborhood. And for those who might be interested, we also put up links of amazing Solar System collectibles from Amazon.com. Your kids will surely enjoy them!

This project happened when I casually mentioned to Chloe that it might be fun to build a scale model of the solar system. You know, some day, when we had time. Chloe and Logan thought it was a great idea, and even though there was half a metre of snow on the ground, it had to happen… right now!

We decided that we wanted to put the Sun in Chloe’s room, and then put all the planets to scale, so that we could walk to Chloe’s school (about a kilometer away), and have all the planets fit nicely – we even included Pluto (which will always be a planet in our hearts).

I found a great calculator that lets you calculate various scale model versions of the Solar System. You put in the size for the Sun and then it calculates both the diameters of the scale model versions of the planets, as well as the scale distances.

We were really fortunate. A version of the Solar System scale model that fit within the distance from our house to Chloe’s school allowed for a Sun that could be cut out of a single sheet of printer paper. I used a protractor to measure out the circle for the Sun, and then cut it out. While the kids were colouring it yellow, I made tiny versions of all planets.

Here are the sizes:

Object	Size (mm)	Size(in)
Sun	200	7.8
Mercury	0.6	0.0275
Venus	1.7	0.0684
Earth	1.8	0.072
Mars	0.9	0.0382
Jupiter	20	0.7892
Saturn	16.7	0.6586
Uranus	6.7	0.2655
Neptune	6.5	0.257
Pluto	0.3	0.012

Then we put our mock planets out into their proper orbits using clear sticky tape. With the Sun just inside Chloe’s room, Mercury was at the top of the stairs. Venus was just outside our front door. Earth at the end of our sidewalk. Mars is on a parking sign across the street from our front door. Jupiter is part way down the next block, stuck to a tree. Saturn is on another tree further down that same block. Neptune is on a parking sign 2 blocks further. Uranus is on a fire hydrant. And finally, tiny Pluto was affixed to a power pole just in front of Chloe’s school.

If you want to get really clever, you can even put in tiny moons. For example, you could put in the moons of Pluto: Charon, Nix and Hydra.

Here are the kids with Mars. Look closer, it’s there.

Here are all the distances:

Object	Distance (m)	Distance (feet)
Sun	0	0
Mercury	8	27
Venus	15	51
Earth	21	71
Mars	32	107
Jupiter	111	367
Saturn	205	673
Uranus	412	1353
Neptune	647	2121
Pluto	850	2787

I was fairly careful measuring distances for the inner planets. But then I just made a rough estimate of my stride length, and used that to mark off the longer distances. Here’s a link to a stride length calculator.

It’s scary to think that a version of Alpha Centauri at this scale would still be 5804.4 km (3606.7 miles) away. That would require a road trip across Canada.

And, now, every day that I walk Chloe to school, we follow the route of our miniature Solar System, and think about just how big the place really is. Even though it’s been a few months since we made our model, most of the planets are still there (we lost Saturn a few weeks back, but we’ll replace it).

Have you built a Solar System scale model for a school project? Let me know how it went and send pictures. Maybe I’ll do a follow up with some more astronomy project ideas.

For extra credit, get your kids to model some of the recently discovered extrasolar planets. Here’s a page that lists their sizes and distances from their parent stars. With so many hot jupiters out there, you could fill a wall with scale versions.

If your kids want to learn more about the Solar System, listen to Astronomy Cast. We did a special tour through each of the planets in the Solar System. Start your tour here with Mercury, then Venus, Earth, Mars, the Asteroid Belt, Jupiter, Jupiter’s Moons, Saturn, Saturn’s Moons, Uranus, Neptune, Pluto, and then the outer reaches of the Solar System.

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The Solar System consists of the Sun, and everything bound to it by gravity. This includes the 8 planets and their moons, the asteroids, the dwarf planets, all the Kuiper belt objects, the meteoroids, comets and interplanetary dust. Since the gravitational effects of the Sun are thought to reach out almost 2 light-years away – almost half the distance to the next star – there could be any number of objects out there, as part of the Solar System.

There are separate regions in the Solar System. First, there’s the Sun, of course. Then there are the inner terrestrial planets: Mercury, Venus, Earth, and Mars. Then comes the asteroid belt; although, not all the asteroids are located in this region. The largest dwarf planet, Ceres, is located in the asteroid belt. Then come the outer gas giants: Jupiter, Saturn, Uranus, and Neptune. Then comes the Kuiper Belt, which includes 3 more dwarf planets: Pluto, Makemake, and Eris. Beyond the Kuiper Belt is thought to be the Oort Cloud, which could extend out to a distance of 100,000 astronomical units (1 AU is the distance from the Sun to the Earth).

Between the planets are smaller objects which never formed a planet or moon. This can range from microscopic dust, up to asteroids hundreds of kilometers across. Beyond the orbit of Neptune, much of this material is icy.

The solar wind emanating from the Sun blasts through the Solar System, interacting with the planets, and pushing material out into interstellar space. The region where this solar wind blows is called the heliosphere, and where it stops is called the heliopause.

The immediate neighborhood around the Solar System is known as the Local Interstellar Cloud. It has high-temperature plasma that suggests that there were nearby supernovae.

The closest star to the Solar System is the triple star system Alpha Centauri.

Are you wondering how many planets there are in the Solar System, or what is the biggest planet in the Solar System?

One of the best pages about the Solar System is the Nine Planets, and Kids Astronomy has more info for kids.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

[/caption]The largest asteroid in the Solar System is 4 Vesta. Ceres is much more massive, but has been promoted to dwarf planet status, leaving Vesta the largest asteroid. Ceres and Vesta will be orbited and studied by the Dawn spacecraft.

Vesta was first discovered on March 29, 1807 by Heinrich Wilhelm Olbers. The asteroid measures 578 km by 458 km and has a mass of 2.67 x 10²⁰ kg. It has a magnitude of +5.4 to +8.5 and can be easily observed with binoculars on a clear night. It has been seen with the unaided eye on several occasions. Vesta rotates on its axis every 5.342 hours and has an axial tilt of 29º. Temperatures on the surface range from a frigid -188ºC (85 K) to -18ºC (255 K). Hubble images have revealed ancient lava flows. This is a direct contradiction of the belief that asteroids are simple cold, dead rocks floating in space. There is a gigantic impact basin so deep that it exposes the asteroid’s mantle at the South pole. The mantle is thought to be 10 km below the asteroid’s surface.

Several NASA scientists have concluded that Vesta is the parent body of many meteorites. That means that we have parts of only five celestial bodies here on Earth: Earth(obviously), the Moon, Mars, Vesta, and the comet Wild 2. Vesta is the parent body of the eucrite meteorite group. The group formed approximately 4.56 billion years ago. Many of them metamorphosed to temperatures up to 800° C and were brecciated and heated by large impacts into the parent body surface. The less common basaltic, unbrecciated eucrites also formed near the surface, but presumably escaped later brecciation. The cumulate eucrites formed at a depth where metamorphism may have persisted for an undetermined amount of time. These meteorites may have originated from the large impact at the south pole of the asteroid.

The Dawn mission is designed to be the first spacecraft to orbit two non-Earth objects. It arrived in orbit around Vesta on July 15, 2011. It will study the largest asteroid in the Solar System for about a year before leaving orbit for Ceres in 2012. Vesta was chosen as a destination because of its unique qualities. It accounts for 9% of the mass in the main asteroid belt and it is an evolved object(has a mantle, core, and crust). NASA scientists fully expect to make several interesting discoveries from the study of Vesta. Be sure to check back later for updates.

Here’s an article about how Vesta formed fast and early in the Solar System, and some Hubble images of the asteroid.

Here’s more on Vesta from Solar Views, and some images from NASA.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

Sources:
http://research.jsc.nasa.gov/PDF/Ares-6.pdf
http://www.nasa.gov/multimedia/podcasting/jpl-cassini-20080428.html
http://www.nasa.gov/mission_pages/dawn/news/dawn20110716.html
http://www.nasa.gov/mission_pages/dawn/news/dawn20110329.html

Defining the diameter of the Solar System is a matter of perspective and characterization. You can look at the Solar System’s diameter as ending at the aphelion of the orbit of the farthest planet, the edge of the heliosphere, or ending at the farthest observable object. To cover all of the objective bases, we will look at all three.

Looking at the aphelion(according to NASA figures) of the orbit of the farthest acknowledged planet, Neptune, the Solar System would have a radius of 4.545 billion km and a 9.09 billion km diameter. This diameter could change if the dwarf planet Eris is promoted after further study.

Sedna is three times farther away from Earth than Pluto, making it the most distant observable object known in the solar system. It is 143.73 billion km from the Sun, thus giving the Solar System a diameter of 287.46 billion km. Now, that is a lot of zeros, so let’s simplify it into astronomical units. 1 AU(distance from the Earth to the Sun) equals 149,597,870.691 km. Based on that figure, Sedna is nearly 960.78 AU from the Sun and the Solar System is 1,921.56 AU in diameter.

A third way to look at the diameter of the Solar System is to assume that it ends at the edge of the heliosphere. The heliosphere is often described as a bubble where the solar wind pushes against the interstellar medium and edge of where the Sun’s gravitational forces are stronger than those of other stars. The heliopause is the term given as the edge of that influence, where the solar wind is stopped and the gravitational force of our Sun fades. That occurs at about 90 AU, giving the Solar System a diameter of 180 AU. If the Sun’s influence ends here, how could Sedna be considered part of the Solar System, you may wonder. While it is beyond the heliopause at aphelion, it falls back within it at perihelion(around 76 AU).

Those determinations of the diameter of the Solar System may seem about as clear as mud, but they give you an idea of what scientists are trying to place a definitive value on. The distances involved are mind boggling and there are too many unknowns to place a absolute figure. Perhaps, an exact number will be determinable as the Voyager probes continue their outward journey.

Here’s an article on Universe Today about the closest star to Earth, and another about how long it would take to travel to the closest star.

Here’s an article from the Physics Factbook about the diameter of the Solar System, and a cool way to visualize it using the Earth as a peppercorn.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

References:
Neptune Fact Sheet
NASA: Planet-Like Body Discovered at Fringes of Our Solar System
NASA Science: Heliophysics
Wikipedia