The Role of the Galileo Spacecraft in the Search for Life on Earth

Saturday - October 28 2023, 20:23 UTC - 1 year ago

30 years ago, the Galileo spacecraft flew past Earth and collected data that suggested, but did not prove, that life may exist on Earth. Scientists later examined samples from the Atacama desert and used similar experiments as those used on the NASA Viking spacecraft to see if life could be found in Atacama. They failed to detect signs of life, suggesting that the Viking spacecraft may have missed signs of life on Earth. Galileo's instruments detected Gaseous water, ice, liquid water of oceanic dimensions, high concentrations of Oxygen and Methane, and temperatures ranging from -30°C to +18°C, all of which helped fuel the potential existence of life on Earth.

It’s been 30 years since a group of scientists led by Carl Sagan found evidence for life on Earth using data from instruments on board NASA’s Galileo robotic spacecraft. Yes, you read that correctly. Among his many pearls of wisdom, Sagan was famous for saying that science is more than a body of knowledge—it is a way of thinking.

In other words, how humans go about the business of discovering new knowledge is at least as important as the knowledge itself. In this vein, the study was an example of a "control experiment"—a critical part of the scientific method. This can involve asking whether a given study or method of analysis is capable of finding evidence for something we already know.

Suppose one were to fly past Earth in an alien spacecraft with the same instruments on board as Galileo had. If we knew nothing else about Earth, would we be able to unambiguously detect life here, using nothing but these instruments (which wouldn’t be optimized to find it)? If not, what would that say about our ability to detect life anywhere else? .

Galileo launched in October 1989 on a six-year flight to Jupiter. However, Galileo had to first make several orbits of the inner solar system, making close flybys of Earth and Venus, in order to pick up enough speed to reach Jupiter.

In the mid-2000s, scientists took samples of dirt from the Mars-like environment of Chile’s Atacama desert on Earth, which is known to contain microbial life. They then used similar experiments as those used on the NASA Viking spacecraft (which aimed to detect life on Mars when they landed there in the 1970s) to see if life could be found in Atacama.

They failed—the implication being that had the Viking spacecraft landed on Earth in the Atacama Desert and performed the same experiments as they did on Mars, they might well have missed signatures for life, even though it is known to be present.

Galileo Results .

Galileo was kitted out with a variety of instruments designed to study the atmosphere and space environment of Jupiter and its moons. These included imaging cameras, spectrometers (which break down light by wavelength), and a radio experiment.

Importantly, the authors of the study did not presume any characteristics of life on Earth ab initio (from the beginning), but attempted to derive their conclusions just from the data. The near infrared mapping spectrometer (NIMS) instrument detected gaseous water distributed throughout the terrestrial atmosphere, ice at the poles, and large expanses of liquid water "of oceanic dimensions." It also recorded temperatures ranging from -30°C to +18°C.

Evidence for life? Not yet. The study concluded that the detection of liquid water and a water weather system was a necessary, but not sufficient argument.

NIMS also detected high concentrations of oxygen and methane in the Earth’s atmosphere, as compared to other known planets. Both of these are highly reactive gases that would rapidly react with other chemicals and dissipate in a short period of time. The only way for such concentrations of these species to be upheld were if they were continuously replenished by some means—again suggesting, but no proving, that there might be life on Earth.