29:50 Modern Astronomy
Fall 1999
Lecture 39 ...December 3, 1999
Mars (Concluded)
Reminder about exams
Mars Polar Lander enters atmosphere of Mars at 1:20 today, touches down
at 2:14PM.
See notes from Lecture 38 for material and Web links.
Last time I described evidence that liquid water existed in the past on the surface of Mars. This is seen from the numerous dry water channels (dead rivers) that are seen on the surface. The term used for these is outflow channels. From examining the relationship of these to craters, we conclude that these water flows (rivers or flash floods) occurred from the time of the formation of Mars (4.5 billion years ago) to perhaps as recently as 2 billion years ago, or even more recently. There was an extended period in which liquid water was present on the surface of Mars.
This naturally raises the question as to whether life arose during these early periods. It should be emphasized that Viking Lander data also showed that the atmosphere of Mars in these early periods had a much higher pressure and was warmer than presently is the case.
The Viking spacecraft carried three instruments for detecting life.
See notes for Lecture 38
Ancient Oceans on Mars
There has recently been scientific discussion that not only was there flowing water on Mars in the past, but there may also have been true oceans. This is described in a nice article in the November issue of Sky and Telescope.
The evidence comes from an instrument on the Mars Global Surveyor called MOLA for
Mars Orbiting Laser Altimeter. From orbit, it precisely measures the height of the
terrain it passes over. This permits us to make a 3D representation of Mars.
Picture of Mars from URL in lecture 38.
These data show what sure looks like an ancient ocean floor occupying much of the northern hemisphere. What is more intriguing is measurements showing evidence for an ancient shoreline. The places where the water channels flow into the northern plane are all at the same elevation, precisely as one would expect for an ocean. This interpretation is not without scientific controversy, and we will not know until we land a spacecraft there. However, the evidence seems very strong to me.
Sky and Telescope article with artists conception of ancient oceans on Mars.