Mars Passby

Subject: MTO Questions and Answers
Date: Wed, 8 Apr 1998 00:07:01 -0700 (PDT)
From: listmgr@quest.arc.nasa.gov
To: answers-mars@quest.arc.nasa.gov

QUESTION: When the orbits of Mars and the Earth bring them in close proximity of each other, what effect can this have in regards to the asteroid belt between our planets, and the effects of the gravitational pulls on our Earth's geological aspects such as it's platelets, causing earthquakes, tidal waves and possible increased volcanic activity? I once heard a person who had aquaintances in scientific fields that speculated (perhaps there is actual research that has been done that you know of, I'm hoping) that such near Mars "passbys" have caused such aforementioned activity on our planet, causing Atlantis to disappear into the ocean, and Pompey to be destroyed by it's sudden volcanic erruption, and have moved the ancients to give Mars the title "The War Planet", because of it's concurring violent effects on our planet when in close proximity. I have learned that the next Mars "passby" is due August 28, in the year 2003, and it's distance from the Earth at that point is calculated to be .373 AU. Could you present that to me in the measurement of miles, and what effects, if any, you would anticipate from this occurrence.

ANSWER from Bruce Jakosky on March 24, 1998: The orbits of Earth and Mars (and all the rest of the planets) are well separated from each other. If two planets came close together, they would be able to perturb the orbit of the other or possibly even collide. This happened during the early history of the solar system, when there were many more planet-like objects. Now, however, after around 4.5 billion years of orbiting the Sun, the only remaining objects are spaced pretty far apart. Thus, Earth and Mars never approach each other at a close enough distance for one to have any significant effect on the other. You are right in that Earth and Mars will get as close as about 0.4 astronomical units from each other, but this is still pretty far apart. The Earth is about 93,000,000 miles from the Sun, and this is 1.0 astronomical unit. Thus, Mars can get as close as about 35,000,000 miles to the Earth; this is not close enough to have any effect.

However, the planets can affect each other a little bit, despite the large distances. Gravitational tugs from Jupiter and the other planets can cause the polar axis of the Earth or Mars to shift a little bit. The shift is very small on the Earth, no more than about 1.5 degrees, but this is still large enough to trigger the ice ages. The shifts are well understood, however, and there is no reason to think that any changes in the Earth's polar tilt or in the climate will happen suddenly or any time soon.