Daniel Sevo's Astronomy Pages

Our Solar System

| Earth & Moon | Our Solar System | Our Galaxy | The Universe | Historical Overview | Formulas | Links |

What is a solar system?

'Solar' refers to the Sun our host star. However, we use the phrase 'Solar system' for all kinds of star-systems, not just our own. Our system consists of a star (Sun) and a number of planets.


The ancient greeks had a (for it's time) decent model of our solar system although not a correct one. Ptolemaos was the philosopher who developed the famous Geocentric model with everything orbiting Earth in perfect circular orbits. (Geocentric means the Earth was thought to be the center of the Universe as opposed to the Heliocentric model where the Sun is placed at the center.) Another philosopher at the time (~260BC)presented a Heliocentric model. His name was Aristarchus and as good as his idea was, he could not find a way to prove it. Not much happened until the early 1540's when Nikolai Copernicus presented the revised Heliocentric model. He is generally recognized as the father of the Heliocentric model, although others may beg to differ.
The 1540's though wasn't a very good time for scientist to propose theories that contradicted those of the Church at the time (Geocentric view). It would take some more effort by Tycho Brahe and later Johannes Kepler to scientifically prove that the Geocentric model was inaccurate. Kepler also realized that the planetary orbits weren't perfect circles at all, but rather elliptical. The work of Galileo Galilei and perhaps most importantly, Isaac Newton finally brought an accurate model of the Solar system and with the mathematics to prove it.
         Later of course, the model was refined once more when Albert Einstein's theory of relativity was presented. But in fact, for most simpler calculations, Kepler's laws of planetary motion are still in use to this day.

Since the beginning of the last century, we have a very accurate model of our Solar system, but for a long time, we had no idea if our system is one of a kind or if there are lot's of systems like ours out there. There were those who thought that our type of system is very common and others who thought that it's not even certain other stars than our Sun have planets at all. (Stupid, yes)
For the past couple of years, our methods for observing other stars have become better and these days we can actually detect planets around other stars. As you read this, more than 100 planets have been found outside our own solar system. (Take a look here.) That may sound a lot, but we need to remember that our observational technique is in it's infancy. So far, we've only detected those that were easy to spot (the big planets). In about 10-15 years we will have new tools at our disposal and the number of detected planets will then likely grow extensively.

The members

Our solar system consists of numerous objects, no one knows exactly how many, simply because we have not yet examined the outer regions of the system and we do not have the technology to detect objects below a certain size.
What we do know, is the number of planets and large moons. Our Sun is orbited by at least 9 planets and a bunch of smaller objects (Planetoids, Asteroids, comets etc). Many of these planets have their own moons. As you know of course, the Earth has only one moon, but the much larger Jupiter has over 60 moons.
Let's take a look at the larger members in the solar system. As I mentioned on the previous page, it is impossible to show the true size and distance relationships between planets. Below is a picture showing the Sun and the planets with approximate size relations, but the relative distances are of course completely inaccurate. Sun and the planets
Here are some facts about our solar system:

If you click on any of the bodies names, it will open up a new browser window with info from nineplanets.org
Our solar system: Overview
Body Sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto
Mass (Earth=1) 333946 0.055 0.815 1 0.107 317.89 95.17 14.52 17.25 0.002
Mass (metric tonnes) 2*10e27 3.3*10e20 4.9*10e21 6*10e21 6.4*10e20 1.9*10e24 5.7*10e23 8.7*10e22 1*10e23 1.3*10e19
Diameter (km) 1392000 4878 12104 12756 6787 142800 119300 51120 49530 2270
Volume (Earth=1) 1303600 0.056 0.86 1 0.15 318.7 744 67 57 0.0055
Density (Water=1) 1.409 5.5 5.25 5.517 3.94 1.33 0.71 1.27 1.77 ~2.07
Axis Angle - 0 178 23.5 24 3.1 26.7 97.5 29.9 ~90(?)
Escape Velocity (km/s) 617.5 4.3 10.36 11.18 5.03 60.22 32.26 22.5 23.9 1.22
Surface Temp (°C) 6000 -170/+350 +480 +22 -23 -150 -180 -210 -220 -215
Albedo - 0.06 0.76 0.36 0.16 0.43 0.61 0.35 0.35 0.6
Orbital period - 87days 224days 365days 686days 11.8years 29.4years 84years 164.9years 247.8years
Rotational period ~26days 58d, 15h, 30min 243d, 3h, 50min 1d 24h, 37min 9h, 55min 10h, 39min 17h, 12min 16h, 7min 6d, 9h, 17min
Distance from Sun (AU) - 0.38 0.72 1 1.52 5.2 9.54 19.2 30.06 39.44
Distance from Sun (M km) - 58 108 150 228 778 1427 2870 4497 5900
Number of moons - 0 0 1 2 at least 60 at least 34 at least 21 at least 11 1
Click here to download a 3dsmax(v4) model of the Solar system. Scale is 1:1000000000. This is a simple model only displaying the relative size between orbits and the size of the bodies. A more advanced (+animated) model might become available in the future.

Major moons in our solar system
Body Luna (The Moon) Callisto Europa Ganymede Io Titan Triton
Orbiting: Earth Jupiter Jupiter Jupiter Jupiter Saturn Neptune
Orbit from host planet (km) 384,000 1,883,000 670,900 1,070,000 422,000 1,221,830 354,760
Orbital period 27d 7h (Siderial) 16d 17h 3d 13h 7d 4h 1d 18h 11d 20h 5d 21h
Diameter (km) 3476 4806 3138 5262 3630 5150 2700
Mass (Metric tonnes) 7.35e19 1.08e20 4.8e19 1.48e20 8.93e19 1.35e20 2.14e19

As you can see in the table above, some of the moons are actually bigger than some of the planets. Ganymede and Titan are both larger than our innermost planet, Mercury. And there are no less than 7 moons in our solar system bigger than planet Pluto. Most of the moons in our system are fairly "boring" rocky bodies, but there are a few that are very interesting indeed.
Scientists believe that Europa may have liquid water under its icy surface. This would also mean that Europa may be the best place to look for present life outside Earth. Io is also an interesting place with its active volcanoes. And then there is of course Saturn's Large moon Titan which is still being observed by the Cassini orbiter. Titan is the only moon in our solar system with a thick atmosphere.

The outer limits

In 2002, a large body was detected outside Pluto's orbit. This has been dubbed Quaoar and is roughly 1,200km in diameter. Then in 2003, another major body was discovered in far reaches of our solar system. This body has been named Sedna (although the name may be changed at a later date). It's size has not been precisely determined yet but it is thought that the upper limit is about 1770km in diameter (Pluto is 2270km and our Moon is 3476km). Sedna may be smaller than that but not larger.

Below is an image provided by NASA. It shows the orbit of Sedna relative to the rest of the solar system. Note the extremely elliptical shape of the orbit. The highly elongated orbit means that Sedna's distance from the Sun varies greatly depending on where in it's orbit it is at the time of measurement.
Outer reaches of our solar system, incl. Sedna orbit

Here is some technical data for these two so called Kuiper Belt objects:
Kuiper Belt Object: Quaoar Sedna
Av. Distance from Sun ~43AU ~509AU
Orbital period 286 years 11487 years
Diameter ~1200km Min ~1200km, Max ~1800km

Moving on...

| Our Galaxy |

You can also navigate via the menu at the top of each page.

Return home
Return Home