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.

Image Credit - High resolution image of Spiders at Mars' south pole taken by the HiRISE camera - credit NASA/JPL/University of Arizona

High resolution image of Spiders at Mars’ south pole taken by the HiRISE camera – Image credit NASA/JPL/University of Arizona

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


3 responses to “The Mars Polar Lander Spider Encounter”

  1. Bob Ware says :

    Here is an interesting thought I have: From what I have heard the landing gear extension was hard enough to have triggered a surface contact thus engine stop as programmed. What if a geyser slammed into the spacecraft and triggered a false touchdown signal thus engine cutoff instead of what was believed to have happened? It would be nice to look over the telemetry again given what we now know about the Southern Pole environment.
    Has anyone found the Spacecraft yet?

  2. Meg says :

    I believe the information is that it pretty much burnt up before getting very far in the atmosphere since the thrusters stopped. I believe the telemetry from the data link indicates it was not close to the surface. The geysers only go up about 2 stories, so they’re not that tall. Also I think they landed during the summer so likely the area was defrosted, but not sure about that one.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: