We have seen the pictures of different planets in our solar system. Have you noticed that some planets look very bright and while some dull?Why is this so? Try to get the answer by researching on the types of elements found on each planet ant the type of reflection in them.
You are aware that planets of the solar system reflect sunlight and that's how we get to see five of them without the help of optical aid - Mercury, Venus, Mars, Jupiter, and Saturn. How bright they appear in a clear night sky depends mainly on three things (a) the size (b) the ALBEDO (2) distance from the Sun.
The albedo indicates how well a surface reflects light, and varies between 0 and 1. A value of 0 means the surface is a "perfect absorber" that absorbs all incoming energy. A value of 1 means the surface is a "perfect reflector" that reflects all incoming energy.
Mercury - Albedo 0.138, diameter 4,878 km distance from Earth ~77 million kilometers when closest
Venus: Albedo 0.75, diameter 12,100 km distance from Earth ~38 million kilometers when closest
Mars: Albedo 0.16, diameter 6,780 km distance from Earth ~ 55 million kilometers when closest
Jupiter: Albedo 0.34, diameter 139,822 km distance from Earth ~588 million kilometers
Saturn: Albedo 0.34 diameter 116,464 km distance from Earth ~ 1.20 billion kilometers
National Snow and Ice Data Center
As you can see from the above, though Mercury is closest to the Sun and receives the maximum amount of sunlight, it's albedo is only 0.138. It is difficult to spot Mercury in the sky not only because of it's proximity to the bright Sun, but also because it's albedo is so low.
Venus is so bright not only because it is the closest planet to Earth, it's thick clouds reflect most of the sunlight that reaches it - about 75% - back into space, and it is almost double the size of the next nearest neighbour to Earth, Mars. Venus can often be seen within a few hours after sunset or before sunrise as the brightest object in the sky (other than the moon). It looks like a very bright star even before the sky is dark. Apparently, everything is in favour of Venus being the brightest.
Mars is almost twice as far away as Venus and only half as large; added to that, the albedo is only 0.16.
Jupiter and Saturn, though they are about ten times larger than Venus, they are 20 times and 40 times farther away respectively with albedos of 0.34 only.It may be of interest to you to know that the albedo of the Moon is only 0.123 - if it was more, we would have daylight, not moonlight! Albedo of Earth is 0.29 only - that's how the mean temperature is around 16°C.
Venus is the brightest object in the sky, after sun and the moon. This is because Venus has a dense cover of clouds above its surface. This cover reflects a large amount of sunlight which falls on it. The light we receive from Venus is actually emitted from the sun, and reflected from Venus's surface. Primarily because of the dense cloud cover above the Venusian surface, Venus appears bright.
Jupiter the fourth brightest in the solar system, after Sun, Moon and Venus. Because it has a giant surface area compared to planets like earth and venus, the quantity of sunlight emitted from its surface is also large. As a result, it looks bright. Jupiter also has emissions of its own, but they are not in the form of visible light. Some of the other emissions are radio waves and infrared light.
Another important factor in the observed brightness of a planet is its distance from earth. Jupiter, being far away, looks much less bright than how it would look if it was at the distance of Venus from earth. The farther a planet is from earth, the more of its light is lost in the space and doesn't reach us. It's exactly why sun appears such bright to us, but the star Sirius A (being nearly 25 times more luminous than the sun) appears dim.
Earth and the other three inner planets of our solar system (Mercury, Venus and Mars) are made of rock, containing common minerals like feldspars and metals like magnesium and aluminum. So is Pluto. The other planets are not solid. Jupiter, for instance, is made up mostly of trapped helium, hydrogen, and water. In our solar system, the four "gas giants" are Jupiter, Saturn, Neptune, and Uranus.