(2019 Archived) ARGUMENT VII: The Journey to Mars vs. the Journey to Venus
Having written this in 2019, and originally published in 2021.. when I was 15 and 17, there would be inaccuracies that I would correct here. Having removed it, I'm publishing again, for sake of completion so that the efforts wouldn't have gone to vain: Most of this still stands true
The celestial bodies of our solar system orbit the sun in different orbits with different distances between them, eccentricities, angular placements and orbital velocities. Thus, interplanetary distances constantly change from time to time. Therefore, there comes a time where any two planets of a solar system are closer to each other. We call such planets to be in ‘opposition’. An opposition mostly occurs when the middle-planet is directly between its star and the other planet. For example, in a scenario where the Earth is directly in-between the Sun and Mars: Mars is said to be in ‘opposition with the Earth’. When Mars in opposition with the Earth; the Sun and Mars must appear at opposite sides of our sky.
But, for two planets to be closest possible to each other, they must be in ‘perihelic opposition’. That is; the middle-planet must be at its furthest point from the sun (aphelion) with the other planet being at its closest to the sun (perihelion), while the entire system is in opposition. For example, when Venus is at her aphelion with the Earth being at her perihelion, during an opposition: Venus is said to be in ‘perihelic opposition with the Earth’. In this scenario; the Earth and Venus would be at their closest possible distance, with the Sun and the Earth seen at opposite sides of the Venusian sky. For our reference: Mars is approximately 54,600,000km away from us, when in a perihelic opposition[26]. Venus, on the other hand, is approximately 38,000,000km from the Earth during a similar scenario[27]. This would makeVenus about 16,600,000km closer to the Earth than Mars in during an average opposition. This is quite a good estimate for Venus being closer than Mars: but, for a more accurate picture, we’d have to use a realm of orbital mechanics known as Hohmann transfer.
Hohmann transfer is typically an orbital mechanism used to transfer between orbits of different radii on the same plane. It accounts for the eccentricities and angular placements of the planetary orbits, when applied to the solar system. Hohmann transfer includes an elliptical orbit that is known as the ‘Hohmann transfer orbit’, which is used for transfer from one orbit to the other. But, what’s so great in using Hohmann transfer? The reason we use Hohmann transfer is because, the Hohmann transfer orbit between celestial objects (planets) “uses the lowest possible amount of energy in travelling between the two objects” [28].
More succinctly; the Hohmann transfer orbit is the most economic, effective and efficient path to a planet [28, 29]: The Hohmann transfer orbit to Mars is the most economically-sound trajectory to Mars, while the Hohmann transfer to Venus is the most efficient trip to Venus. Hohmann transfer comes with this quantity named ‘∆v’ (delta-v), which is needed to change the trajectory of the spacecraft from the orbit of the first planet, to the Hohmann transfer orbit. ∆v is basically the change of velocity of the space-craft[28, 29]. Hence, the lower the magnitude of ∆v, the more economically-sound and efficient the trip is. The below table depicts the magnitude of ∆v for Hohmann transfer to Venus as 2.5 kmh-1, and the lowest in magnitude [28]. The difference between the ∆v for Venus and that of Mars to be a meagre 0.4kmh-1; But, that slight difference is a monumental amount of money.
It should also be noted that Mars still being somewhere amounting to 16,600,000km more far-away than Venus, even with Hohmann transfer and additional distance translates to additional fuel and expense. That is, the Hohmann transfer orbit to Venus is longer than the Hohmann transfer orbit to Mars [29];
Body | Distance from sun (AU*) | ∆v needed for Hohmann transfer |
Sun | 0 | 29.8 kmh-1 |
Mercury | 0.39 | 7.5 kmh-1 |
Venus | 0.79 | 2.5 kmh-1 |
Mars | 1.52 | 2.9 kmh-1 |
Jupiter | 5.2 | 8.8 kmh-1 |
Saturn | 9.4 | 10.3 kmh-1 |
Uranus | 19.19 | 11.3 kmh-1 |
Neptune | 30.07 | 11.7 kmh-1 |
Pluto | 39.48 | 11.8 kmh-1 |
∞ (Infinity) | ∞ | 12.3 kmh-1 |
The most economically-sound path to Mars is less economically sound than the most economically sound path to Venus. Simply, Venus is the most efficient and cost-effective planet to travel to. But, we can’t simply Hohmann transfer anytime we want, in order for it to be the most economically-sound trip possible. The interplanetary distances are constantly changing, and only at the right time and right circumstances, will the Hohmann transfer orbit be the most ‘economically-sound and effective’. Perihelic oppositions might be the most ideal circumstance for effective space-travel between the planets of our solar system. But, their occurrences are quite rare. Hence, Outward bound and Inward bound missions to the various planets of the solar system are meticulously planned around time-slits known as ‘launch windows’. The below diagrams depict the Hohmann transfer orbits to Venus and Mars, when the launch windows are open [29]:
· Retrieved from (https://solarsystem.nasa.gov/basics/chapter4-1/).
The launch windows open at regular intervals for a pair of planets, and open to the shortest possible Hohmann transfer orbit between those two planets. And, since the planets are constantly moving at different velocities on different orbits, with different eccentricities and angular placements; The launch windows of different pairs of planets open at different frequencies. The same is true for Venus and Mars, with the Earth: The Martian launch window opens every 779.94 days – which is almost once every 2.2 years [30]. On the other hand; Venus opens her launch windows more often, being 584 days or 1.6 years [27].
We can conclude from these values; that Venus opens her launch window 25% more frequently than Mars does. Hence, we can undergo more Venusian missions in unit time than Mars – again, that’s efficiency! That is, more missions (with regard to Venusian colonization) can be done because the launch windows open to them more frequently; We can visit Venus more often and readily than Mars. Another advantage is that if there were to be a problem with a Venusian manned mission, the mission could abort back to the Earth more readily than a Martian mission, as it is a shorter wait for the launch window to re-open. Again, even during the opening of a launch window; the Hohmann transfer orbit to Mars is still much longer than that for Venus. It would not only mean more fuel and expenditure but also more travel time:
Lander | Time taken (days) |
Viking 1 | 335 |
Viking 2 | 360 |
Phoenix Lander | 295 |
Curiosity Lander | 253 |
The above table depicts the amount of time taken for four Martian missions to reach Mars [31], during launch window and using the shortest possible Hohmann transfer orbits. We can deduce from that table that it takes an average of 7 months to reach Mars, even with the most ideal circumstances, with present means of propulsion.As for Venus: NASA’s Mariner 2, which flew-by Venus on 14th December 1962, took 4 months to do so [27]. Thereby, the trip to Venus is ~3 months less than that of Venus. But, why is a shorter trip so significant? It is because a shorter trip means (again, coupled with the frequent launch window openings) that more Venusian missions could be done in unit time, and also the ability to minimize the risks of interplanetary travel.
Interplanetary travel is risky business with a repertoire of potential risk for the crew – the devastating effects of a zero-gravity environment on the crew’s physiology, coupled with constant 360◦ bombardment by cosmic radiation, along with the dangers of collision with alien bodies like hurdling space rocks. Loss of muscle tone is one of the most terrible physiological effects of zero-gravity along with bone demineralization: In zero-gravity, the mineral density of a space-voyager’s bones decreases by 1% on a monthly basis [12]. Old people, on the other hand, would experience this at a mere rate of 1-1.5% annually[12]! Logically speaking; space voyagers would thereby undergo mineral-loss 1200% more harshly than old people! Creepy!
The 3-extra months in space during a trip to Mars would mean that, the Martians would have lost 75% more bone mineral than a Venusian of similar calibre. Also, the Earth-like gravity of Venus would help the Venusians to recover lost minerals upon the stay. Meanwhile, the Martians would have to live-on with the loss of mineral density, which the Martian gravity cannot compensate for. Below are some of the similar effects of space travel, of which some you might recognise as those seen on how the low Martian gravity affects a Martian’s physiology [12]:
· Increased risk of osteoporosis, which might lead to related fractures in life.
· Loss of muscle tone, strength and endurance, due to lack of exercise.
· Pressure build-up in eye due to fluids shifting up to head.
· Vision problems due to pressure build-up in eye.
· Formation of kidney stones due to dehydration.
· Bone decalcification: Increased excretion of calcium from bones.
· Dizziness and reduced blood flow due to blood pooling in head and chest.
Exposure to cosmic radiation is another grave threat in interplanetary voyages with effects ranging from Radiation sickness and Tissue degeneration, to increased risk of cancer and damage to central nervous system are some of the undesirable effects of exposure [12].
Again, the Venusian gravity can compensate for most of the effects, while the Martian gravity might not be able to.
Now that we’ve seen how the journeys to Venus and Mars compare, let’s analyze as to why Venus is a better planet to travel to: (1) The Hohmann transfer orbit to Mars is longer than that to Venus. (2) The Hohmann transfer orbit to Venus is more economically-sound and efficient, than the most efficient and economically-sound path to Mars. (3) The launch windows of Venus open more frequently, meaning more missions could be done in unit time. (4) The Martian launch windows open less frequently, meaning that fewer missions could be done in unit time. (5) Less travel-time needed for Venus. (6) More travel-time needed for Mars. (7) Martian travellers are more prone to the risks of interplanetary travel. (8) Venusian travellers are less prone to the risks of interplanetary travel. (9) Everything we’ve seen so far told us that Venus is a better destination to start a colony. From the aforementioned points, we can conclude that the trip to Venus is more economically-sound, effective, efficient, quicker, and safer than the trip to Mars.
[12] Dunbar, B. (2018, June 11). The Human body in space. Retrieved from (https://www.nasa.gov/nrp/body_in_space).
[26] Sharp, T. (2017, December 14). How far away is Mars?Retrieved from (https://www.space.com/16875-how-far-away-is-mars.html).
[27] Redd, N.T. (2012, November 16). How far away is Venus? Retrieved from (https://www.space.com.cdn.ampproject.org).
[28] Wikipedia. (2019, February). Retrieved from ( https://en.wikipedia.org/wiki/hohmann_transfer_orbit)
[29] NASA Science Mission Directorate. (). Basics of Spaceflight: Trajectories. [Retrieved from https://solarsystem.nasa.gov/basics/chapter4-1/].
[30] Williams, M. (2017, April 7). When will Mars be close to Earth? Retrievedfrom (https:// www.universetoday.com/1480/when-will-mars-be-close-to-earth-1).
[31] Cain, F. (2017, March 16). How long does it take to get to Mars? Retrieved from (https://www.universetoday.com/1481/how-long-does-it-take-to-get-to-mars/).
Achinthya Nanayakkara (30.03.2025)
Originally published - 2021 (now removed)
Originally written - 2019
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