Science Goals

The goals of the SAM investigation are to investigate three questions:

What does the inventory of carbon compounds, or lack thereof, near the surface of Mars reveal about its potential habitability?

What are the chemical and isotopic states of the lighter elements in the rocks, soils, and atmosphere and what do these reveal about potential habitability?

How were past environmental conditions different from today's?

Just from reading these questions, you can get a pretty good idea of SAM's capabilities. It can detect carbon compounds in Mars rock and soil samples, if they exist, and can tell us what compounds they are. It can measure isotopic ratios of light elements. The compounds it finds can tell us about the environmental conditions that prevailed when they form.

Why are we asking these specific questions about Mars? It's more or less accepted that Mars' presently not-very-habitable environment wasn't always that way. Today it's cold, dry, and exposed to ionizing radiation. In the past, a magnetic field, thicker atmosphere, and warmer temperatures may have fostered the presence of liquid water sheltered from ionizing radiation. Even if the past climate wasn't nicer, past Mars definitely did have more liquid water, at least briefly or episodically, than Mars does now.

Life originated on Earth at or before 3.8 billion years ago. At the same time, it's possible life originated on Mars too, or maybe it originated on one world and was carried to the other. This possible Mars life is not obvious today, so if it ever existed, it either went extinct or underground. Since Mars hasn't been too geologically active since then, it's possible that evidence for this possible life that may have thrived in this possibly better ancient environment might be preserved in rocks exposed at the surface.

Interestingly, the odds of preservation of such ancient evidence for life are higher for Mars than for Earth because of Mars' substantially lower rate of geological activity. Most of Earth's most ancient rocks are destroyed or massively altered. Mars still has very, very ancient rocks exposed at the surface, very little changed from when they formed. Curiosity has been sent to a landing site exposing more ancient rocks than any lander or rover has ever studied. Unfortunately, even if any organic remains of any ancient Mars organisms were preserved in rocks, anything close enough to the surface to be accessible to Curiosity will have been attacked by radiation or oxidizing chemicals. Evidence of the original compounds will be in the form of different compounds, made from the breakup of more complex ones, that might possibly bear isotopic signatures that indicate a biogenic origin.

If you look back at the last two paragraphs, you'll see words like "possible" and "may" showing up quite a lot. The fact is, we know very little about Mars' ancient past, so it's really hard to predict what we'll find, and if it can tell us much of anything about whether or not ancient life existed. We will learn what we can, by exploring rocks ancient enough to preserve a record of what was happening way back then. Curiosity's mission goals are designed so that the mission will succeed at teaching us a great deal about Mars even if the rover finds zero evidence for ancient life.

Even if SAM does find carbon compounds, they are not likely to have been created by life. Meteorites called carbonaceous chondrites contain a lot of carbon, in chemicals like kerogens, amino acids, carboxylic acids, and nucleobases. A million kilograms of this material rains down on Mars every year. So near-surface carbon compounds are most likely from meteorites. Organics stuck inside rocks might be from ancient meteorites, or from Mars life.

The conservative assumption is that all the carbon is meteoric. No one will be able to make a claim for evidence of past Mars life without first eliminating the possibility that the carbon compounds came from meteorites. Since it's hard to prove a negative, there will not be any slam-dunk finding from SAM that says "Mars life was here."

There will have to be a story pieced together using multiple lines of evidence over a lengthy period of investigation. What the SAM inventory of organic compounds will really tell us is what raw materials would have been present when life was first getting started, either on Earth or on Mars.

Physical Description

This is SAM.