In the search for alien life, it’s not enough just to ask the right questions, it’s all about finding the right answer.
That’s according to Carolyn Porco, a planetary scientist at the California Institute of Technology. She was speaking on Tuesday at a meeting of the American Geophysical Union in San Francisco, where she argued that researchers should focus less on detecting life and more on building a better toolbox to find the basic things it takes to make for a life-bearing planet.
Carolyn Porco. Photograph: AFP/Getty Images
Making “robust detection of life” is, Porco said, simply “not the same as making robust detection of the ‘intelligent life’ that we all want to believe exists”.
Porco pointed to the Kepler space telescope, which successfully spotted 3,600 planets, even though it was designed to find just 200. She cited the difficulties the European Space Agency’s Copernicus Orbiter had in finding water on the surface of an exoplanet, where it would be “impossible” to walk.
In the coming years, scientists will increasingly need to look beyond the solar system to see how habitable the planets that orbit the Sun are. Earth and Mars both had dry periods at the end of their time in the Sun’s habitable zone. Finding out whether those planets are inhabitable could point to whether or not life is possible elsewhere in the solar system.
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There’s a lot of science that needs to be done if we want to discover life, said Jerome Orosz, an astronomer at Penn State University. “You really do need the problem-solving tools to identify a new gas giant; it’s pretty easy to tell this is water,” he said. “But then you are dealing with a deep-seated question about how the atmosphere works and what the life model should be. It’s a difficult problem,” he said.
There are also problems with using exoplanets as petri dishes to see if we’re alone in the universe. Exoplanets have orbital periods that vary wildly, so they can take hundreds of years to pass in a single star’s light, giving scientists “no track record of what’s happening” in a system, said Orosz.
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A better toolbox could include looking at only smaller space rocks, said Orosz. The density of a surface planet would be one-20,000th of Earth’s, so it could take several days or weeks for any gases to even reach a surface. But if the rock were bigger, its surface would be only 100 times as thick as Earth’s – it would have to be compressed by gravity for its surface to exist in something like water. “If you only have something on Mars that takes a while to get to the surface, the only thing you can find are pure oxygen and carbon dioxide. It’s a much easier problem to solve,” he said.
The complexity of looking for alien life is also to be expected for scientific discoveries in general, said Orosz. Now that we can detect stable conditions like ocean that are still stable and untouched by fire, we need to find out if environments like that can exist around Earth-like rocky planets.
However, he said that we should still be trying to deduce how well life has evolved in other solar systems. “Everything you do is trying to help in your search for the truth. Science is the endeavour to find and explain reality. It’s a question of what we know and don’t know,” he said.