Chapter 4 of 5

A winter postcard

Photographing frost and comparing seasons

Told in Viking 2’s imagined voice · the events are real · source

First Color Image of the Viking Lander 2 Site
Viking 2My rocky neighborhood did not always keep the same colors.
NASA/JPL
01At northern Utopia Planitia, my cameras could follow seasonal changes. Looking repeatedly mattered: a pale coating on the rocks could be compared with the same landscape at other times, rather than treated as a whole new kind of terrain.
In May 1979, I photographed a thin coating of frost.
02NASA’s caption describes water ice on the rocks and soil in the May 18 image. Viking Orbiter 1 relayed it to Earth on June 7. The picture’s exposure date and the date it reached Earth are different parts of the same journey.
Viking Lander 2 First Picture On The Surface Of Mars http://photojournal.jpl.nasa.gov/catalog/PIA00396
Viking 2The scientists proposed a way for dust, water and carbon dioxide to work together.
NASA/JPL
03Their explanation involved water ice on dust grains, carbon dioxide ice helping the particles settle, and warming that returned carbon dioxide to the air. The residue included water and dust. The caption presents this as an interpretation, not a measured guarantee of pure ice or a universal temperature switch.
A returning frost pattern made a single photograph much more useful.
04The caption compared the frost with its appearance a Martian year earlier, when it persisted for about a hundred days. Repetition helped investigate a seasonal cycle. A thin surface coating still did not prove a particular buried ice deposit directly beneath my feet.

The big idea

Compare the same place over time, and distinguish the visible observation from a proposed explanation. Surface frost and subsurface ice are different kinds of evidence.

Think about it

What extra question could an earlier photograph help answer about this frost?

Fact file

Frost photograph
PIA00571 / 18 May 1979
Relayed by Viking Orbiter 1 on June 7. NASA instrument metadata lists Camera 1.
Source ↗
Earlier frost persistence
About 100 days
The caption compares the prior Martian year. Not a guarantee for every winter.
Source ↗

In this chapter: Cameras, meteorology instruments and the orbiter relay

Sources: Main record · Viking 2 · NASA Science · Viking Lander 2 (Gerald Soffen Memorial Station) · HiRISE

Machine illustration: AI-made. Photos: NASA Image and Video Library, credited on each picture.

Chapter 4 of 5

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