The Earth-Mars Proximity Issue
Earth and Mars Orbits
Earth’s orbit around the sun is relatively circular. Mars, on the other hand, follows a more elliptical orbit. Also, the two planets are not in sync. Sometimes they’re both on the same side of the sun, and sometimes they’re on opposite sides.
Also, Earth and Mars are not on the same plane. In other words, their paths around the sun are tilted in relation to each other.
On top of that, the gravitational pull of the other planets tends to pull Earth and Mars out a bit, depending on their proximity.
This means that predicting when Earth and Mars are closest to each other takes a bit of math and science. It’s complicated.
One excellent resource is an interactive chart of the distance between Earth and Mars as a function of time, from TheSkyLive.com. The page is embedded below. Just scroll down about halfway to see the distance chart.
Getting to Mars
NASA’s Mars 2020 mission to deliver the Perseverance rover to the surface of Mars had to take into consideration the proximity of Earth and Mars. The trip took about 7 months. Current estimates are between 7 and 9 months for the trip. So this voyage was exceptionally well planned.
Over time, the distance between Earth and Mars differs significantly. The closest they can get to each other is 33.9 million miles (54.6 million kilometers), which no one in recorded history has ever seen, although in 2003 they got within 34.8 million miles (56 million km) of each other. The farthest apart they can get is 250 million miles (401 million km).
Unfortunately, a spacecraft can’t just hop from Earth to Mars. The Mars 2020 spacecraft traveled through space at an average speed of 59,500 mph (95,800 kph). When it left Earth, it was 60 million miles (98 kilometers) from Mars. Doing a quick calculation, it should have taken less than 2 months to get there. The problem is, Mars would no longer have been at that location when the spacecraft got there.
The Mars 2020 spacecraft ended up traveling about 300 million miles (480 million kilometers) to get to Mars.
The Axiom on the Way to Mars
In Murder on the Way to Mars, set in 2077-2078, our protagonists, victims, witnesses, and suspects are all aboard a long-haul residential spacecraft called the Axiom, on its way to Mars. The journey takes 7-1/2 months, which is on the short side of current estimates. However, one would hope that we’d get faster at this in the next 50 years.
True, but there is a very good reason to relax and take your time getting to Mars, besides the free buffet. The Axiom is fitted with five rotating habitation rings, four of which are transporting immigrants to Mars. The time spent on this voyage is used not only to educate travelers about life on Mars but to acclimate them to the reduced gravity they will face on Mars.
In particular, the habitation rings start off rotating at a rate to simulate Earth’s gravity. Over time, the rotation rate is gradually decreased so that by the time they arrive on Mars, they’re living in simulated Mars gravity. For more information about how the Axiom is designed and how it functions, be sure to check out the Long-Haul Residential Spacecraft page.