For as long as we have been looking up to the skies for answers, we have been looking for proof other life. In the modern era, Astronomers have been looking for signs of water on distant exoplanets but have they got it all wrong?
Researchers from the Universtiy of Boston think they have a better way of finding life. Instead of looking for signs of water via the light spectrum they think that examining a planet’s thin upper atmosphere (the Ionosphere) will yield the best results.
Earth’s ionosphere is packed with single oxygen ions and if you can find a similar one on an exoplanet then you have a strong case for life. The first exoplanets confirmed outside of our solar system were Poltergeist and Draugr in 1992 but since then we have discovered over 3728 exoplanets in 2794 systems.
“Throughout the history of human civilization, we have never gotten to the point—until basically the last 15 years—where we could see planets around other stars. And now we’re at the point where we’re coming up with ideas to discover life outside Earth,” says John Clarke, professor of astronomy at Boston University, and director of the Center for Space Physics. “This is a great intellectual adventure that we’re on.”
Their work on ionosphere began many years ago when they were tasked with comparing all of them from our own solar system. Every planet except Mercury has one but they are all very complicated, except Earth’s. Where other planets in our solar system have carbon dioxide or hydrogen, Earth’s ionosphere is mostly single atom oxygen with a positive charge. “I started thinking, how come our ionosphere is different than the other six?” recalls Mendillo.
The team racked their brains for answers to this difference but finally found that the concentration of O+ was from plants and algae. “It’s because we have this atomic oxygen that traces its origin back to photosynthesis,” says Mendillo. “We have atomic oxygen ions, O+, in the ionosphere as a direct consequence of having life on the planet. So why don’t we see if we can come up with a criterion where the ionosphere could be a biomarker, not just of possible life but of actual life.”
Most of the planets in our solar system have oxygen but Earth has about 21% more than most. The plants and organisms on earth have been pumping out oxygen for almost 3.8 Billion years. “Destroy all the plants on Earth and our atmosphere’s oxygen will vanish away in mere thousands of years,” says Withers, “To most people, O2, the oxygen we breathe, is not a very exciting molecule. To chemists, however, O2 is a wild, exhilarating, and perilous beast. It just will not sit still; it chemically reacts with almost any other molecule it can find and it does so very quickly.”
O2 molecules that are not used up will generally float upward until around 150km up, ultraviolet light splits it in two. These lighter single oxygen atoms float all the way to our ionosphere where more ultraviolet light and x-rays from the sun rip electrons from their outer shells, leaving charged oxygen.
The bulk of Astronomers on the search for extraterrestrial life focus on M-class stars. These stars are super common and normal have planets orbiting them in the ‘Goldilocks zone’. This zone is where water can exist in a liquid state, in other words, not too hot and not too cold.
“If we only had the Mediterranean, would that have been enough? Do we need the Pacific, but not the Atlantic?” asks Mendillo. “If you look at the ionosphere, you don’t need to know the number. You just need to know that if the maximum electron density is associated with oxygen ions, then you’ve nailed it—you’ve got a planet where photosynthesis is happening and life.”
This is course is assuming that life requires water and oxygen and would also probably rely on factors like temperature ranges, magnetic fields and more. There is also one other factor that is slowing down this research; we don’t yet have the technology to detect ionospheres on exoplanets. “If you look at the space telescopes that might come next, a lot is going to be possible, I think in ten years we will have the technology to do this experiment.”
“Just the idea of using the ionosphere as a signature is a captivating idea,” he says. “We don’t have the observational capability yet, but I’m optimistic. We offer this up as a challenge.”
Source: Boston University