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A NASA Mars article says:

Mars' orbit is more elliptical than Earth's, so the difference between perihelion and aphelion is greater. Over the past centuries, Mars' orbit has been getting more and more elongated, carrying the planet even nearer to the sun at perihelion and even farther away at aphelion. So future perihelic oppositions will bring Earth and Mars even closer.

Eccentricity of mars orbit currently = 0.093

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    $\begingroup$ Are you asking whether the statement that you copy-pasted from the nasa.gov article is true? $\endgroup$
    – notovny
    Jul 1 at 16:11
  • $\begingroup$ @notovny perhaps just checking to see if their understanding of it is correct? $\endgroup$
    – uhoh
    Jul 2 at 23:05
  • $\begingroup$ I can see how the orbit can be calculated based on historical records, (e.g. - as detailed by Jean Meeus: "When Was Mars Last This Close?" 2003) - but what is the basic cause of this increasing eccentricity? $\endgroup$ Jul 4 at 22:41
  • $\begingroup$ @RobClennell don't put this information in a comment where it might not be seen. You should edit your post to add this information to the body of your question. :-) $\endgroup$ Jul 8 at 12:24
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Yes, "future perihelic oppositions will bring Earth and Mars even closer."

No, in the long term (after about 25000 years), Mars's eccentricity will start to decrease, and then perihelic opposition will not be as close.

enter image description here

By frankuitaalst from the Gravity Simulator message board. - Data generated with Gravity Simulator written by Tony Dunn.Source JPG on server, GPL, https://commons.wikimedia.org/w/index.php?curid=6438409

Note the axes, the vertical axis for Mars and Mercury is 10 times greater than for Earth and Venus, so the variation in eccentricity is also much greater for Mars

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  • $\begingroup$ Thanks James K. Is there any 'simple' way to explain 'why' Earth and Mars are getting closer? - and why Mars' orbit will start to become increasingly less elliptical 25,000 years from now, if this is the case? $\endgroup$ Jul 2 at 14:58
  • $\begingroup$ Earth and Mars are not getting closer on average, but Mars's orbit is getting more elliptical, so it's closest point is getting closer to the sun and it's furthest point is getting closer from the sun. So when the Earth is close to Mars at the same time as when mars is at perihelion, this is the minimum distance between Earth and Mars, and this minimum distance is getting less. $\endgroup$
    – James K
    Jul 2 at 21:04
  • $\begingroup$ There's no easy reason as to why Mars's orbit will become less elliptical after 25000 years. It is due to perturbations by other planets. These can tend to switch (for example) elliptical orbits for inclination. These tendencies are long term, but are cyclic. First the orbit gets more eccentric, then less, then more.... $\endgroup$
    – James K
    Jul 2 at 21:09
  • $\begingroup$ Is the 'spin' of Earth and the 'spin' of Mars taken into account as a contribution to the conservation of angular momentum? (and a contribution to the increasing/decreasing eccentricity) Or - is the spin regarded as too small to be measurable? $\endgroup$ Jul 6 at 18:39

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