The solar system that we live in seems to be located quite far from the center of the galaxy. The arms of the Milky Way show that collisions with other galactic bodies happened several billion years ago. Galactic collisions seem to stimulate stellar growth and its likely that the interaction led to the birth of the solar system some 5 billion years ago.

First lets look at the meteor belt that sites between Mars and Jupiter. These rocks originally came from supernova long ago which spewed the heavier elements. These self same rocks allowed for stars to form with a lot less mass like the sun which can survive for 10 billion years. Some slightly smaller stars can last for 50 billion years or more.

The early solar system was entirely made of meteors which condensed into the planets we see today. The outer planets clearly acquired more gasses than the inner planets from the primordial gas clouds. Jupiter is the most massive planet but Saturn, Uranus and Neptune are also massive plants. The inner plants are warmer which would tend to cause light elements to be lost.

Today the sun is 20-30% brighter then it was when it first ignited. After some 5 billion years the sun has used about half of the original hydrogen supply. In time the sun will become even brighter. Eventually as the hydrogen is exhausted the sun will expand into a red giant obliterating the solar system. At this point the sun will be burning helium is a different mode than the earlier CNO cycle.

The inner plants of Mercury, Venus, Earth and Mars are denser than the out planets. Jupiter, Saturn, Uranus and Neptune are distant enough that the sun does not warm them significantly.


Mercury is so close to the sun that it is hot enough to melt lead. The same side always faces the sun as the planet seems to be tidally locked in a 3:2 resonance, it rotates on its axis exactly three times for every two revolutions it makes around the Sun. It takes about 88 days to orbit the sun completely, Mercury is small but very massive. Geologists estimate that Mercury’s core occupies about 55% of its volume; for Earth this proportion is 17%.


The Russian Venera 7 landed on Venus but it was knocked over on its side making the signal hard to analyze. Venus has an atmosphere of 96.5% carbon dioxide and 3% nitrogen. The air pressure is some 93 times that of the Earth. The surface temperature of Venus is close to Mercury due to an extreme runaway greenhouse effect. The surface is 475°C and any water is likely to have been broken down and lost to deep space. The orbital period is 224.7 days.


The Earth seems to have been fortunate. A large object the size of Mars seems to have crashed into the planet delivering water etc. and the ejecta condensed into the moon.


Mars is less dense than Earth, having about 15% of Earth’s volume and 11% of Earth’s mass, resulting in about 38% of Earth’s surface gravity. The moons seem to be gravitationally captured from an earlier collision. The orbital period is about 687 days. Mars is only slightly longer than an Earth day: 24 hours, 39 minutes, and 35.244 seconds. The axial tilt of Mars is 25.19° gives the planet seasons.

The atmosphere of Mars consists of about 96% carbon dioxide, 1.93% argon and 1.89% nitrogen along with traces of oxygen and water. Global dust storms are problematic for exploration missions.


The asteroid belt is a toroidal cloud of mostly metallic blocks with some more volatile ices. The asteroid belt occupies the orbit between Mars and Jupiter, between 340 and 490 million km from the Sun. 


Jupiter seems to have been accumulating hydrogen but did not have enough material to reach a criticality. The planets seem to have condensed from the primordial materials. Jupiter’s upper atmosphere is about 90% hydrogen and 10% helium by volume. The orbital period is 4,332.59 days. The mass of Jupiter is 1/1000 that of the Sun.


Saturn is unusual with its ring system and did not have enough material to reach a criticality. The rings are incredibly thin but span a great distance from the inner extent. Saturn orbits about 1.42 billion km away from the sun.


Uranus is much farther away at 2.87 billion km which makes it hard to spot even with a good telescope. It also did not have enough material to reach a criticality


Neptune is so far out at 4.50 billion km that a good telescope is needed to see it properly. It also did not have enough material to reach a criticality


The Kuiper belt is a great ring of debris similar to the asteroid belt, but consisting mainly of objects composed primarily of ice. The Kuiper belt spans 4.5 and 7.5 billion km and even a large telescope has a hard time recognizing anything. Resonant trans Neptunian Objects can be either part of the main Kuiper belt population, or the more distant scattered disc population. Mostly likely the resonance effect is what provides stability in the outer solar system.

%d bloggers like this: