Mars Makes Closest Approach In Nearly 60,000 Years
By A.J.S. Rayl
The Planetary Society
21 August 2003
Mars is shining brightly in the night sky and moving closer to Earth with
every passing day.
Even the Big Blackout on the east coast was timed pretty well as far as
Mars watching goes. "One of the blackout benefits was that New Yorkers
were saying that they had time to look at the night sky -- and in particular
Mars," reports Lou Friedman, executive director of The Planetary Society
(TPS) who managed to get on one of the last flights out of New York last
Thursday before the east coast went dark.
In fact, next week -- on Wednesday, Aug. 27 -- Mars' orbit will bring it
into opposition, lining it up with Earth on the same side of the Sun and
moving it in closer to Earth than it has been in 59,619 years.
With media outlets around variously reporting that Mars will be closer than
it "ever has been," or "in 73,000 years," or "in nearly 60,000 years," or
"50,000 years," confusion about the matter of exactly when in the past
Mars was closer to Earth than it will be next week has had a lot of people
wondering -- just how long ago did Mars come this close, how close is
close, and what does it all mean?
TPS investigated the matter. Here's what we found:
The estimate of 56,619 years ago - put forth last year by scientist Aldo
Vitagliano of the University of Naples, Italy -- is now recognized by
leading astronomers as the most accurate date, to date, of just how long
ago Mars made its last close approach. And, for the record, that last
close approach was just a bit closer than Mars will be come next Wednesday.
"The previous, closer approach was on September 12 in astronomical year -
57,616 (57,617 BC) . . . at a distance of 55.718 million kilometers [or
34,623 million miles], versus the 55.758 Gm [or 34,648 million miles] of
the 2003 opposition, " Vitagliano confirmed for The Planetary Society via
email. To arrive at that figure, one may presume to simply add 2003 -
where we are now -- to 57,617 BC. But, Vitagliano reminds: "Historical
year zero does not exist, and [so] the time difference between 1 BC and
1 AD is one year. The correct number is 59,619."
No matter what else you've read or heard, those, it appears, are the
numbers you can take to the bank. "I trust Vitagliano's results," offers
Myles Standish, a renowned astronomer at JPL. Standish had considered
running his own set of calculations to determine Mars last closest
approach, but, after communicating with Vitagliano, changed his mind.
"Because of my confidence in him and his research, I didn't think it was
worth going after," he says.
Newtonian mechanics and customized software
Vitagliano employed Newtonian mechanics and his own customized computer
software to 'do the math.' In a nutshell, the theory behind Newtonian
mechanics allows for predicting the positions of planets and celestial
bodies by inference from their motion. In other words, if you can
determine the motions of the given objects in, say, the solar system,
you can calculate where any given planet or celestial body in that solar
system was at any point in the past or will be in the future.
Past studies have shown that the orbit of the Red Planet has been getting
slightly more eccentric, or elongated over the last 35,000 years because
of the gravitational effects of the other planets. During this time of
eccentricity, Mars' orbit has been taking it in a little closer to the
Sun at perihelion [the point at which it closest to the Sun], hence
closer to Earth's orbit, and a little farther from the Sun at aphelion
[the point at which it is furthest from the Sun].
This eccentricity has had an impact on how close Mars' orbit comes to
Earth's orbit. According to Vitagliano, the closest distance between
the Earth and Mars orbits was at a minimum 82,000 years ago. The closest
distance then increased for the next 45,000 years, but since that time
it has been decreasing and will continue to do so for another
25,000 years. As a result, there will be approaches of Mars in the
future which are even closer than the one occurring on August 27.
For Vitagliano, the task at hand however was to figure out when, exactly,
in the past Mars was closer to Earth than it will be at this year's
opposition. Using SOLEX, his celestial mechanics software program, on a
800 MHz computer Vitagliano spent just 2 hours and 45 minutes computing
time "With the present version of SOLEX and my 1700 MHz
notebook," he notes, "it now takes about one hour."
But Vitagliano is making it sound way too easy. When pressed, he admits
that the creation of the SOLEX software was "the result of long and
patient amatorial work, with the program constantly improving and
growing since its first version." Actually, creating the software to
determine the numerical integration of the nine planets, the Moon, and
asteroids Certes, Pallas and Vesta, took uncounted thousands of hours
spread out over more than a decade.
Vitagliano first began to "play around" with the numerical integration
of planetary orbits in 1990, starting from scratch. "Serious work began
in 1995 - all during my spare time, since professionally I am a c
hemist," he continues. That's when he focused on the systematic and
tedious work of inputting all the motion characteristics into a computer
program, relying on JPL's DE406 Planetary and Lunar Ephermides (calculated
positions of celestial bodies developed for use with spacecraft navigation)
as a baseline.
In 1996, Vitagliano developed "the first crude version" of his program,
which computes the positions of solar system bodies (planets, asteroids and
comets) by a method entirely based on the numerical integration of the
Newton equation of motion. The following year, he published his work --
"Numerical Integration for the Real Time Production of Fundamental Ephemerides
Over a Wide Time Span" -- in Celestial Mechanics and Dynamical Astronomy,
something that helped put his freeware software on the computational 'map.'
"He actually spent quite a bit of time with me over email back and forth,
from October 1997 to June 1999 comparing and checking with JPL's program and
getting his software programs working," offers Standish. "He then
corresponded with Jim Williams [JPL], our expert on the equations for the
Moon's motion. He got his program working and agreeing with our results over
the short-term and then he did a lot of experimentation to see if anything
could make a big difference in this. I was very impressed."
Since then, Vitagliano has continued to improve SOLEX -- the name of which
he derived from "SOLar system integration by a fast EXtrapolation method --
adding various accessory functions. "In 2001, I inserted the subroutines
that were crucial for the Mars' case, namely the online automatic search
for spatial or angular close approaches of celestial bodies," he points out.
In essence, Vitagliano has produced a simplified model of the solar system
that enables users to compute, planetary and lunar ephemerides quickly and
easily, closely matching the JPL DE406 ephemerides. Now, with the latest
version of the freeware, SOLEX 8.5, virtually any computer savvy person can
do "the same calculation with zero input effort - just reading the manual
and playing a little with the program," he says.
Finding Mars' Last Close Approach
The question of how long ago Mars made a similar close approach to Earth as
it will next week emerged as something of an issue in the astronomical
community last year.
Belgian astronomer Jean Meeus addressed - and seemingly resolved -- the
question in his book More Mathematical Astronomy Morsels, which was
published early in the year last year. Referencing two papers on long-term
variations in planetary orbits by the late French astronomer Pierre Bretagnon,
Meeus wrote that Mars might have come closer to Earth 73,000 years ago, an
estimate that was widely picked up and published widely by the
Soon after Meeus' book was published, however, Jeffrey Beish and James
DeYoung, of the Association of Lunar and Planetary Observers, reported
another, improved result, claiming that Mars came closer to Earth in
57,537 BC. On learning of that finding, Meeus realized his initial
calculations might be off, so he contacted Vitagliano, who had garnered
some renown in the area of computational celestial mechanics, at least as
far Mars' whereabouts back when goes.
Last spring, at Meeus' request, Vitagliano ran his program, analyzing the
motion of Mars by numerical integration. He determined that Mars made
quite a close approach in 57,538 BC, a year later than Beish and DeYoung
found - a time difference he found that stemmed from the fact that Beish
and DeYoung had gotten their result from using the Earth-Moon barycenter
(and not treating them as separate bodies). In any event, that close
approach was not quite as close as Mars will come next Wednesday.
It was then, last April, Vitagliano concluded that Mars came within
34,623 million miles [55.718 million kilometers] of Earth on
Sep, 12, 57,617 BC, which was just slightly closer than it will come
next Wednesday, when at 9:46 Universal Time [5:46 a.m. Eastern Daylight
Time; 2:46 a.m. Pacific Daylight Time], the centers of Earth and Mars
will come within 34,646 miles (55,758 million kilometers) of each other.
JPL's DE406 Planetary and Lunar Ephermides and the U.S. Naval
Observatory's Multiyear Interactive Computer Alamanac (MICA) softw
are are in synch, Standish points out, as far as this value for the
true geometric distance goes. [He also notes that the USNO's MICA, a
software system that provides high-precision astronomical data in tabular
form for a wide variety of celestial objects, uses JPL's ephemerides, as
does the organization's benchmark annual publication, The Astronomical
Deep - Astronomical -- Impact
So what does this unusual closeness mean? Tsunamis? Avalanches? Solar
flares? The War of the Worlds? Despite wide-eyed speculations and
doomsayer rantings circulating through public consciousness, the
opposition -- as grand an astronomical event as it is -- will only
impact us emotionally, aesthetically, and metaphorically. Physically,
Mars will do us no harm.
To put it in perspective, if some time traveler who witnessed Mars way
back when were to be teleported to the present next week, he/she would
notice no difference looking out at Mars. The Red Planet will still be,
in human eyeball terms, a long, long way away. Put another way -- you
won't exactly be able to discern the so-called Face on Mars, or any
specific craters per se, and you won't be able to spot Sojourner, the
robot rover who waits there in silent retirement. You will probably
be able to see, however, a good number of the markings that Giovanni
Schiaparelli mistook for canals back in the late 1800s, which set off all
kinds of attempts to contact the Martians and which inspired the
construction of the Lowell Observatory so entrepreneur
Percival Lowell could study the alien planet up close.
Mars' Close Approaches - Then and When
Although Myles Standish decided not to repeat Vitagliano's work with
regard to how long ago Mars came this close, he did do the calculations
to show when in the past century Mars made close approaches, and when
in the future Mars will again come as close or closer than it will
With his permission, we offer Standish's predictions in the tables
below. All times are ephemeris time (which is within about one minute
of Universal Time).
Mars' Closest Approaches to Earth in the 20th Century
Astronomical Units Kilometers Miles Estimated Time
0.37284580977 55,776,939.238 34,658,183.234 AUG 22, 1924 at 23:49:57
0.37569459433 56,203,111.341 34,922,994.302 AUG 12, 1971 at 02:31:31
0.37809337577 56,561,963.937 35,145,974.967 SEP 07, 1956 at 04:53:48
0.38788139261 58,026,230.414 36,055,827.974 JUL 27, 1939 at 20:51:52
Mars' Closest Approaches to Earth in the Future
Astronomical Units Kilometers Miles Estimated Time
0.37225399628 55,688,405.200 34,603,170.733 AUG 28, 2287 at 22:26:30
0.37238877859 55,708,568.347 34,615,699.532 SEP 02, 2366 at 08:06:43
0.37238223660 55,707,589.679 34,615,091.415 AUG 30, 2571 at 06:21:32
0.37200784918 55,651,582.118 34,580,289.931 SEP 03, 2650 at 18:00:36
0.37200417937 55,651,033.122 34,579,948.800 SEP 08, 2729 at 04:50:41
0.37230224110 55,695,622.522 34,607,655.369 SEP 11, 2808 at 15:38:05
And as for the closest Mars will come between now and 10,000 AD? We've got a
bit of a wait on that one. Standish reports that at 4:18 and 43 seconds
ephemeris time on Jan. 15, 9943, Mars will be just under 34 million miles
or 54 million kilometers - that's 33,922,721.570 miles to be precise and
54,593,328.422 kilometers or 0.36493386015 astronomical units -- close to
Bring home the Red
There you have it. The next best opportunity doesn't come around for
another 244 years, so your chance to see Mars as you never have -- or ever
will again -- is now. Pick a night, any night - Wednesday being primetime --
step outside, look up, and bring home the red.
Virtually everyone on the planet can see the Red Planet in the night sky. There
will be no other rusty-colored point of light out there, so it's particularly
easy to spot at night. Only Venus and the Moon may be brighter. For more
information on when and where to look in your part of the world go to: Mars Watch -
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