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Why Mars Missions Run in Packs
If you pay attention to science news you will know that not one, not two, but three spacecraft will arrive at the Red Planet this week.
The missions are Perseverance (U.S.), Tianwen-1 (China) and Hope (United Arab Emirates). The first two will be attempting to put rovers on the surface to study soil composition and look for signs of life. Perseverance also has a buddy, Ingenuity, a helicopter-style drone designed to fly in the Martian atmosphere. Hope, meanwhile, is an orbiter-only that will do experimental observation of the planet’s atmosphere and weather.
So, why do we have three Mars missions arriving at the same time.
No, it’s not a coincidence.
Orbital Mechanics
It boils down to a simple, basic fact of orbital mechanics: Earth and Mars don’t travel at the same speed.
The Earth orbits the sun at a speed of about 67,000mph. We don’t notice because everything on Earth is moving at more or less the same speed. Mars travels a bit more slowly, because it’s further out…the Red Planet is moving at about 54,000mph.
So, this means that the Earth will catch Mars, then pull ahead, then come around and catch it again. Sometimes the sun is between the two planets, which we call conjunction. The last precise Mars-sun conjunction was…