Write your abstract here. Mars Time or
Earth Time ?
What day is it? Do days exist without calendars? Does time
pass when there are no human hands left to wind the clocks? - Howard Koch, Invasion from Mars, the 1938 radio play based on H. G. Wells'' The War of the Worlds It didn’t get a mention on Entertainment Tonight, but, October 29th was
a special day for the gang over at JPL as the Mars rover Opportunity
turned two. Too late now to send a card, but imagine my confusion: the
launch date was July 7th, 2003 with orbital insertion on January 25th,
2004. Ignoring the fact that planetary survey vehicles might count
birthdays more like dogs or woman over thirty, the real problems start
when keeping track of time on Mars instead of good old Terra. It turns
out, the occasion celebrated by the spry robot was the beginning of
its’ third Martian year roughly equal to 687
earth days. The first problem is what constitutes a day since one can measure
either sidereal days or solar days. On Mars they differ by a little
more than two minutes but are both just over half an hour longer than
on earth. At least the basic units on our digital watches are the
same. Scientists finally agreed to the shorthand of calling each box
in their red
planet day planner a ‘sol,’ which is certainly easier to
use in equations than 88,775.24409 seconds. The NASA Mars operations team coined the word “yestersol” to refer to
the previous sol which is a lot more fun to say than the slew of
acronyms normally tossed around by space geeks. Apparently, the press
even picked up on the new lingo, though I can’t recall ever hearing it
on the evening news. The related neologisms “tosol” (for “today”) and
“morrowsol” or “nextersol” (for “tomorrow”) never seemed to catch on,
that is until ‘nextersol’ when this post is uploaded. The number of ‘sols’ a spacecraft lander spends making tracks in the
crimson dust must next face the same issue in the 2000 vs 2001
millennium debate: do you start counting from ‘0’ or ‘1’ ? The two
Viking missions commenced from ‘Sol 0’ after touchdown, while
Pathfinder and the two MERs defined the same moment as ‘Sol 1.’ Not so
fast, friends, it now appears the Mars Phoenix project will start the
clock at ‘Sol 0’ to continue the confusion. We wouldn’t even be debating the niceties of astronomical anniversaries
‘tosol’ had the Opportunity and Spirit missions suffered the fate of
the Mars Observer, Climate Orbiter, and Polar Lander NASA debacles. JPL
lost contact with all three of those spacecrafts before a single
experiment had been run or drop of data transmitted. In the case of
the Climate Orbiter, the problem was blamed on one engineering team
using English units and another metric. Hopefully all these Mars/Earth
clockwatching differences won’t spell disaster for the next generation
of rocket scientist, though only ‘morrowsol’ will tell. Opportunity certainly deserves some celebration after two solar years,
considering its primary surface mission was planned to last a mere 90
sols. Hopefully, the robot will not suffer roving in the shadow of
its’ older sibling Spirit that had already reached Sol 22 when
Opportunity was a wee one Sol rookie rolling around the rocks. Now
that both mobile machines have passed the 1000 sol milestone (November
17, 2006) the rivalry between the vehicles has settled, but Spirit
still refused to show up for Opportunity’s party at Cape Verde in the
Victoria Crater near Duck Bay, choosing instead to wander between sites
on the other side of the planet in an area known as ‘Home Plate.’ It
is unclear if Spirit had hoped to receive transmissions of the Red Sox
in the Earth World Series. So now that we have all gotten comfortable throwing ‘sols’ around in
our space talk, we should mention some of the variations in marking
months and loggiyears on the Martian calendar. Someday the planet
will have Wi-fi and will need a system to make drop menu choices to
fill out surveys and enter porn sites. Apparently most astronomers
prefer “Julian dates” where everyone agrees on a single “epoch” and
starts counting upwards. Here on earth that number is currently
2,454,403, but who really wants to use an integer for newspapers and
especially birthdays. Naturally, the Martian solar year is going to
need some extra months to even out that 687 sol year and a county
courthouse full of juries is still out on that one. Among the many
neat name suggestions I found are “Sagan,” “Titars,” “Ascraeus,” and
“Qzeta.” The truly anal annual analyzer should also familiarize themselves with
the differences between the sidereal year, tropical year, and March
equinox year before closing the book on this subject, as I will now.
Please don’t forget the 93,000 Martian year precession cycle of the
planet’s rotational axis. The rest of us can join together in singing
“Happy Birthday” to the intrepid Opportunity as we share a marvelous
high resolution photo from his party. Galaxy News Reported October 31st, 2007.