[i] “… a heavy gravity, nitrogen/oxygen atmosphere planet…”
“The Earth’s atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth’s gravity. It contains roughly (by molar content/volume) 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, trace amounts of other gases, and a variable amount (average around 1%) of water vapor. This mixture of gases is commonly known as air. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.
There is no definite boundary between the atmosphere and outer space. It slowly becomes thinner and fades into space. Three quarters of the atmosphere’s mass is within 11 km of the planetary surface. In the United States, people who travel above an altitude of 80.5 km (50 statute miles) are designated astronauts. An altitude of 120 km (~75 miles or 400,000 ft) marks the boundary where atmospheric effects become noticeable during re-entry. The Kármán line, at 100 km (62 miles or 328,000 ft), is also frequently regarded as the boundary between atmosphere and outer space.
The atmosphere of Mars is relatively thin, and the atmospheric pressure on the surface varies from around 30 Pa (0.03 kPa) on Olympus Mons’s peak to over 1155 Pa (1.155 kPa) in the depths of Hellas Planitia, with a mean surface level pressure of 600 Pa (0.6 kPa), compared to Earth’s 101.3 kPa. However, the scale height of the atmosphere is about 11 km, somewhat higher than Earth’s 6 km. The atmosphere on Mars consists of 95% carbon dioxide, 3% nitrogen, 1.6% argon, and contains traces of oxygen, water, and methane. The atmosphere is quite dusty, giving the Martian sky a tawny color when seen from the surface; data from the Mars Exploration Rovers indicates the suspended dust particles are roughly 1.5 micrometres across.
The atmosphere of Venus, the second planet from the Sun, is much denser and hotter than that of Earth. The surface temperature and pressure on Venus are 740 K (467°C) and 93 bar, respectively. The Venusian atmosphere supports thick persistent clouds made of sulfuric acid, which make optical observations of the surface impossible. The information about surface features on Venus has been obtained exclusively by radar imaging conducted from the ground and Venera 15-16 and by Magellan space probes. The main atmosphereric gases on Venus are carbon dioxide and nitrogen, which make up 96.5% and 3.5% of all molecules. Other chemical compounds are present only in trace amounts.
The atmosphere of Venus is in state of a vigorous circulation and super-rotation. The whole atmosphere circles the planet in just four days (super-rotation), which is a short time compared with the sideral rotational period of 243 days. The winds supporting super-rotation blow as fast as 100 m/s. Near the poles of Venus anticyclonic structures called polar vortexes are located. In them the air moves downward. Each vortex is double eyed and shows a characteristic S-shaped pattern of clouds.
Only the ionosphere and thin induced magnetosphere separate venusian atmosphere from the space. They shield the atmosphere from the solar wind, which usually does not penetrate deep into it. However they are incapable of preventing the loss of water, which is continuously blown away by the solar wind through the induced magnetotail.
Despite the harsh conditions on the surface, at about a 50 km to 65 km level above the surface of the planet the atmospheric pressure and temperature is nearly the same as that of the Earth, making its upper atmosphere the most Earth-like area in the Solar System, even more so than the surface of Mars. Due to the similarity in pressure, temperature and the fact that breathable air (21% oxygen, 78% nitrogen) is a lifting gas on Venus in the same way that helium is a lifting gas on Earth.”
– Reference: Wikipedia.org