Mercury and Venus – A Comparison

Mercury

Size: 4879 km
Distance from Sun: 57,910,000 km
Atmospheric composition: 42 % helium, 42% sodium and 15% oxygen
Moons: none
Orbit: 88 Earth days (highly elliptical)
Rotation on axis: 58.6 Earth days
Discovery date: This planet is well known in ancient drawings, mythology and theological texts from many cultures. No specific date can be reasonably assigned as the discovery date for this planet, as it has been visible to humans for the full span of our species’s existence. Over the centuries, many scientific observations regarding the planet can be attributed to specific astronomers and other scientists, but discovery rights for this body belong to no one person or date.
Equatorial radius: 2439 km
Surface gravity: 0.38 of Earth gravity
Interesting fact: Mercury’s magnetic field is very weak (about 1% of the Earth’s field) due to its low rate of rotation (58.6 Earth days). Another likely culprit in this planet’s low magnetic field may be a more solid planetary core as compared to Earth’s which has more liquid content. Further, due to its size, Mercury’s core would have cooled earlier than the Earth’s which is still rather hot.

Venus

Size: 12,104 km
Distance from Sun: 108,200,000 km
Atmospheric composition: Layers of clouds consiting of 96% carbon dioxide and 4% nitrogen
Moons: none
Orbit: 224.70 Earth days
Rotation on axis: 243.01 Earth days (in retrograde)
Discovery date: Like Mercury, this planet is well known in ancient drawings, mythology and theological texts. Attempts to assign discovery credits to any specific person or date would be wishful thinking. Over the centuries, many scientific observations regarding the planet can be attributed to specific astronomers and other scientists, but discovery rights for this body belong to no one person or date.
Equatorial radius: 6052 km
Surface gravity: 0.90 of Earth gravity
Interesting fact: Often considered to be Earth’s “sister,” this planet has little in common with our home world other than its size. Venus has a hostile environment (from a human perspective) due to its high temperature and toxic atmosphere. While Venus is farther from Sol than Mercury, its surface is far hotter due to atmospheric conditions which trap the solar heat. Mercury, while closer to Sol than Venus, is able to ‘vent’ its solar heat, resulting in a lower surface temperature than that of Venus. Further, the atmosphere of Venus contains high amounts of carbon dioxide and sulfuric acid. Finally, the air pressure on Venus is approximately 100 times that of Earth’s. This high pressure crushed (within two hours at most) several Soviet probes that landed on the planet’s surface in the 1970s and early 1980s.

For more information:

• Dr. Siobahn M. Morgan – Mercury and Venus
• Sagan Planet Walk – Venus
• Sagan Planet Walk – Mercury
• Science-Park.info – Venus
• Science-Park.info – Mercury

This entry also posted in the American Military University Introduction to Astronomy newsgroup.