So you want to find alien life? NASA can help.
The space agency is out with some new tips for going about your search the right way and avoiding the trap of false positives. Researchers at NASA's Astrobiology Institute’s Virtual Planetary Laboratory conducted thousands of simulations of various atmospheres and star types over the course of four years and came up with a few new recommendations.
The findings were published in the Astrophysical Journal this week.
Does the presence of oxygen mean that there was or had at one time been life on a planet? What about the presence of ozone? NASA has answers to these and some of your other burning questions.
Here are a few things you need to know:
Avoid "lone wolves"
The good news is that, despite trying very hard to come up with false positives, researchers only found a few to look out for: oxygen, ozone and methane.
As lone wolves, these molecules were thought to be signs of life all by themselves, but it turns out they can be produced inorganically -- that is, in the absence of anything living as we know it.
Your best bet is to look for them together.
"Our research strengthens the argument that methane and oxygen together, or methane and ozone together, are still strong signatures of life," said Shawn Domagal-Goldman of NASA's Goddard Space Flight Center in Greenbelt, Maryland and the study's lead author. "We tried really, really hard to make false-positive signals for life, and we did find some, but only for oxygen, ozone, or methane by themselves."
Use the dorm-room pizza test
Think of the relationship between methane and oxygen as you would the relationship between pizza and college kids. Methane won't last long in a room full of oxygen just like you wouldn't expect pizza to last long in a room full of cheap, hungry students.
Oxygen consumes methane in certain reactions -- so if they are both present, it is probably because some form of life keeps putting more methane there, Domagal-Goldman said.
"If you see pizza in a room, and there are also college students in that room, chances are the pizza was freshly delivered, because the students will quickly eat the pizza," he said. "The same goes for methane and oxygen. If both are seen together in an atmosphere, the methane was freshly delivered because the oxygen will be part of a network of reactions that will consume the methane.
He continued: "You know the methane is being replenished. The best way to replenish methane in the presence of oxygen is with life. The opposite is true, as well. In order to keep the oxygen around in an atmosphere that has a lot of methane, you have to replenish the oxygen, and the best way to do that is with life."
Consider your star
Stars are probably a bit underrated. And based on NASA's newest findings, it's even more critical to take them seriously.
The chemical reactions that might produce or destroy oxygen, ozone and methane without the presence of life are driven by the light coming from stars:
For example, massive, hot stars or stars with frequent explosive activity produce more ultraviolet light. "If there is more ultraviolet light hitting the atmosphere, it will drive these photochemical reactions more efficiently," said Domagal-Goldman. "More specifically, different colors (or wavelengths) of ultraviolet light can affect oxygen and ozone production and destruction in different ways."
We might need better tools
All of this is good and well, but some of it might require more accurate tools than we are currently being used, according to Domagal-Goldman.
"To confirm life is making oxygen or ozone, you need to expand your wavelength range to include methane absorption features. Ideally, you’d also measure other gases like carbon dioxide and carbon monoxide [a molecule with one carbon atom and one oxygen atom].
"So we're thinking very carefully about the issues that could trip us up and give a false-positive signal, and the good news is by identifying them, we can create a good path to avoid the issues false positives could cause. We now know which measurements we need to make. The next step is figuring out what we need to build and how to build it."