Glossary

Astronauts:

People who train for space travel.

Carbohydrate:

A type of chemical composed of carbon, hydrogen, and oxygen atoms joined in a 1:2:1 ratio. Sugars, starches, and cellulose are common carbohydrates found in living organisms. The presence of carbohydrates is a sign of life. In this guide, students test for life with a carbohydrate test using iodine. A positive (+) result on the iodine test indicates that there is (or was) life present.

Control:

In a well designed experiment, an experimental group is compared to a control group. The experimental group will have one variable factor, while the control group is identical in all other respects, except for this variable. In this guide, the experimental Petri dish is exposed to the air, while the control dish is not; all other factors (medium, temperature, etc.) are the same for both dishes. By comparing the experimental dish with the control, you can determine the effect of the variable.

Dormant:

An organism that is alive, but not currently active (not obviously active and moving; there will be some metabolism). Seeds, spores, fertilized eggs, and hibernating animals may be called dormant.

Dry ice:

Frozen carbon dioxide, CO2 (one carbon atom bound to two oxygen atoms). This solid looks like water ice, but it sublimates instead of melting (it goes directly from a solid to a gas without becoming a liquid). On Mars, water ice would behave like dry ice on Earth. On Mars, the ice caps include both water and dry ice.

Earth:

In our solar system, the third planet from the sun. Our home world!

Earth

Gravity (Earth = 1):
Mean Distance from the Sun (millions of km): 149.6
Mean Distance from the Sun (AU): 1
Period of Revolution: 365.26 days
Period of Rotation: 23 hr., 56 min., 4 sec.
Axial Tilt: 23 degrees 27'
Equatorial Diameter (km): 12,756
Volume (Earth = 1): 1
Main Component(s) of Atmosphere: Nitrogen, Oxygen
Atmospheric Pressure (Earth = 1): 1
Known Natural Satellites: 1

Experimental:

In a well designed experiment, an experimental group is compared to a control group. The experimental group will have one variable factor, while the control group is identical in all other respects, except for this variable. In this guide, the experimental Petri dish is exposed to the air, while the control dish is not; all other factors (medium, temperature, etc.) are the same for both dishes. By comparing the experimental dish with the control, you can determine the effect of the variable.

Exobiologist:

A scientist who studies life outside or beyond the Earth or the possibility of life outside or beyond the Earth. The prefix "exo" comes from Greek meaning outside of, external, or beyond; that "bio" comes from the Greek word "bios" and means life; and "-ology" means the study of.

Extraterrestrial ("ET"):

Any living organism found outside of the Earth, as on Mars or Venus. Often, this term assumes intelligence. Currently, we know of NO extraterrestrials, intelligent or otherwise. In this guide, students imagine being the extraterrestrials looking at our solar system, including Earth; this should shift their viewpoint.

Gas Exchange Experiment:

One of the three life detection tests done by the Viking Mission, this test measured changes in gas composition above a Martian soil sample after addition of a warm, liquid nutrient.

Hypothesis:

A tentative explanation of an observation. An educated guess. A hypothesis must be testable. After enough experimental results confirm a hypothesis so that the scientific community is in general agreement on its validity, it becomes a theory. A theory is considered to be true and factual; the best available scientific explanation.

Inorganic:

Chemicals that do not contain the element carbon are called "inorganic".

Labeled Release Experiment:

One of the three life detection tests done by the Viking Mission, this test tried to detect the release of tagged carbon compounds into the gas above a Martian soil sample after the addition of a warm, liquid nutrient which contained tagged carbon atoms.

Lander:

The portion of a spacecraft that is designed to land on a planet's surface. This can sometimes be the entire spacecraft.

Life:

There is no simple definition for life. Living things have specific structures, metabolism, respond to stimuli, and reproduce themselves. On Earth, all life is cellular and has DNA and/or RNA (except Viruses, which are not considered to be alive).

Magellan Mission:

A NASA Mission which sent a spacecraft to orbit Venus to use radar to penetrate the cloud cover and send back images of the nearly the entire surface of Venus. There were no special life detection tests involved with the Magellan Mission, but it has sent back most of the data used to create our present understanding of Venus. It was launched in 1989, and it arrived in orbit around Venus in August, 1990. Its radar can resolve images 120 m across, showing detail ten times finer than any previous images.

Mars:

In our solar system, the fourth planet from the sun.

Mars

Gravity (Earth = 1): 0.38
Mean Distance from the Sun (millions of km): 227.9
Mean Distance from the Sun (AU): 1.524
Period of Revolution: 687 days
Period of Rotation: 24 hr., 37 min., 23 sec.
Axial Tilt: 23 degrees 59'
Equatorial Diameter (km): 6,787
Volume (Earth = 1): 0.15
Main Component(s) of Atmosphere: Carbon dioxide
Atmospheric Pressure (Earth = 1): 0.006
Known Natural Satellites: 2

Microbe or microorganism:

In this guide, "microbes" include bacteria (Kingdom Monera) , fungi (Kingdom Fungi), and even certain small algae (Kingdom Plantae); any microscopic, single-celled (or colonial in a few cases) organism.

Orbit:

The path an object follows around another object, such as a planet follows around its Sun, a moon follows about its planet, or a satellite or spacecraft around a moon, planet, or Sun.

Orbiter:

The portion of a spacecraft that is designed to orbit a planet.

Organic:

Any complex chemical which contains carbon is said to be organic. Organic chemistry includes biochemistry, the study of the metabolic reactions of living organisms. At one time, it was believed that organic chemicals were only produced by living things, but it is now realized that they may be synthesized from inorganic chemicals in a laboratory.

Penicillium notatum:

One species of microorganism. This is the fungus that is the source of penicillin. In this guide, it is used as the microbe in the "Mars jars" and "Venus plates". Urge caution when working with the Penicillium. Some students may have an allergic reaction to this organism.

"Plate out":

A term used in microbiology to describe putting a microbe in a Petri dish.

Planet:

A substantially large body which is held in orbit around a star, such as the Earth, Mars, or Venus which orbit around the sun. Planets do not generate their own light, but only reflect the light of a nearby star. In this guide, our search for life is a search for life on planets, either in their soil or atmosphere.

Planetology:

The study of planets. Comparative Planetologists explore and compare the planets to learn of their composition, formation, and the dynamics responsible for their major features. These questions are important to our understanding of life in our solar system.

"Powers of 10":

Exponential scales. In this guide, "ZOOM! Cards" are used; each card is either ten times larger or ten times smaller than the last card in the series. For instance, if one card shows the view at 10-4 meters, then the next card will show the same site at 10-3 meters or at 10-5 meters.

Protein:

A complex type of chemical or macromolecule, composed of a chain of amino acids. Our bodies are largely made of proteins, and run by special proteins called enzymes. Proteins are complex organic molecules. While amino acids, the building blocks of proteins, can form from non-living reactions, proteins are too complex to form and persist in most natural situations. The presence of proteins is also good evidence that life is, or was, present, since they must have been produced by a living organism. In this guide, students test for life with a protein test using Ninhydrin. A positive (+) result on the Ninhydrin test indicates that there is (or was) life present.

Pyrolitic Release Experiment:

One of the three life detection tests done by the Viking Mission, this test tried to detect the release of tagged carbon compounds in a roasted Martian soil sample after it was exposed to tagged compounds in the air above the soil.

Satellite:

An object in orbit around another object. Satellites can be natural, as Earth's moon is, or artificial, as telecommunications satellites are.

SETI:

The Search for ExtraTerrestrial Intelligence. This search is being conducted by the SETI Institute of Mountain View, CA, and by other organizations and researchers around the world. They are using radio telescopes to search for radio signals coming from planetary systems around likely stars in a "targeted search".

Spacecraft:

A vehicle designed for Earth orbital or interplanetary travel. In this guide, the term is used to describe the portion of the vehicle that travels through space, as opposed to the "lander" which is sent down to a planet's surface. Sometimes one vehicle can take on both roles.

Star:

A hot, glowing mass, a sphere of gas that emits energy (light and heat) from nuclear fusion reactions in its core. Stars have gravity, which holds planets in orbit around them. Stars could not support life as we know it.

Starch:

Starch is a complex carbohydrate. While simple carbohydrates, such as simple sugars like glucose, can form from non-living reactions, starch is too complex to form and persist in most natural situations. The presence of starch is good evidence that life is, or was, present, since it must have been produced by a living organism. A positive (+) result on the iodine test indicates that there is (or was) life present.

Sun:

The star that the Earth orbits around. Our star is named Sol. It is a very typical star, which only appears so unique because we are so close to it, while all of the other stars are far away.

Venus:

In our solar system, the second planet from the sun. Venus Gravity (Earth = 1): 0.91
Mean Distance from the Sun (millions of km): 108.2
Mean Distance from the Sun (AU): 0.723
Period of Revolution: 224.7 days
Period of Rotation: -243 days (Retrograde)
Axial Tilt: 3 degrees
Equatorial Diameter (km): 12,104
Volume (Earth = 1): .88
Main Component(s) of Atmosphere: Carbon dioxide
Atmospheric Pressure (Earth = 1): 90
Known Natural Satellites: 0

Viking Missions:

In 1976, NASA landed two spacecraft on Mars. These were called the Viking I and Viking II. Each consisted of an orbiter and a lander. Three life detection tests were performed on random soil samples taken at two different sites by landers. The experiments were the Gas Exchange Experiment, the Pyrolitic Release Experiment, and the Labeled Release Experiment.