The Mars Polar Lander Spider Encounter
Today we have a post by Dr. Candice (Candy) Hansen, principal investigator (PI) of Planet Four and Planet Four: Terrains. Dr. Hansen also serves as the Deputy Principal Investigator for HiRISE (the camera providing the images of spiders, fans, and blotches seen on the site). She is also a Co-Investigator on the Ultraviolet Imaging Spectrograph on the Cassini spacecraft in orbit around Saturn. Additionally she is a member of the science team for the Juno mission to Jupiter. Dr. Hansen is responsible for the development and operation of JunoCam, an outreach camera that will involve the public in planning images of Jupiter.
My first glimpse of a “spider” on Mars was in 1998. The Mars Global Surveyor (MGS) had gone into orbit around Mars, and winter was turning to spring in the southern hemisphere. The Mars Polar Lander was en route to Mars, and we were anxiously waiting for polar night to lift so that we could see our landing site.
The Mars Observer Camera (MOC) onboard MGS started returning images just a few weeks before Mars Polar Lander (MPL) was due to arrive. We would scrutinize long rolls of film, and that was when we realized that the terrain was not exactly what we expected. Dark spidery forms and cracks that resembled caterpillars fascinated us. I was hooked on trying to understand these exotic features.
We now know that if the MPL made it safely as far as the surface it landed in very inhospitable terrain. We use the colloquial term “spiders” to describe an array of interconnected channels on the surface. The branching channels, now formally referred to as “araneiform” terrain, cover the surface where MPL was predicted to land. They occur in a wide variety of morphologies, from isolated to connected to starburst to lace, with channels that are typically 0.5 – 2 m deep, and ~5m wide.
We never heard from MPL after it entered Mars’ atmosphere. Any number of things could have gone wrong. Or everything might have gone perfectly and it landed with one leg in a channel and simply tipped over.
Help identify spiders and other araneiform terrain with Planet Four: Terrains at http://terrains.planetfour.org