Exoplanets: how we will look for signs of life

US, WASHINGTON (ORDO NEWS) — Is there life elsewhere in the universe – this is a question that people have been pondering over for millennia; and over the past few decades, great strides have been made in our search for signs of life beyond our solar system.

NASA missions, such as the Kepler space telescope, have helped us register thousands of exoplanets – planets that revolve around other stars. NASA’s current missions, such as the Transiting Exoplanet Survey Satellite (TESS), are expected to significantly increase the current number of known exoplanets.

Dozens of planets are expected to be rocky planets the size of the Earth, orbiting in the habitable zones of their stars, at distances where water can exist in liquid form. These are promising places to look for life.

This can be achieved with missions such as the James Webb Space Telescope, which will be launched soon. It will complement and expand the discoveries of the Hubble Space Telescope by conducting observations at infrared wavelengths. It is expected that it will be launched in 2021 and will allow scientists to determine whether there is oxygen in the atmosphere on rocky exoplanets.

Oxygen in the Earth’s atmosphere is formed as a result of photosynthesis by microbes and plants. Because exoplanets resemble Earth, oxygen in their atmosphere can also be a sign of life.

However, not all exoplanets will be similar to Earth. Some will, but others will be so different from the Earth that oxygen will not necessarily be formed by living organisms. So, having studied all current and future exoplanets, how do scientists narrow the area to those planets for which oxygen is most indicative as a sign of life?

To answer this question, an interdisciplinary research team led by Arizona State University (ASU) has provided a structure called the “detectability index” that can help prioritize exoplanets that require further study. Details of this index were recently published in the Astrophysical Journal of the American Astronomical Society.

“The goal of the index is to provide scientists with a tool to select the best targets for observation and maximize the chances of finding life,” says lead author Donald Glaser of the ASU School of Molecular Sciences.

The oxygen detection index for a planet such as Earth is high, which means that oxygen in the Earth’s atmosphere is, of course, driven by life and nothing else. To see oxygen is to see life. The team’s amazing finding is that the detectability index drops sharply for exoplanets not too different from Earth.

Although the surface of the earth is largely covered by water, the oceans of the earth make up only a small percentage (0.025%) of the total mass of the earth. In comparison, satellites in the outer solar system typically contain 50% water ice.

“It’s easy to imagine that in another solar system like ours, a planet like Earth can have 0.2% of the water’s mass of the planet,” says co-author Stephen Desh from the School of Earth and Space Research.

“And that would be enough to change the detectability index. Oxygen would not be an indicator of life for such a planet, even if we were to observe it. This is because a planet similar to Earth, in which water makes up 0.2% of the planet’s mass (eight times more than on Earth), would not have open continents or land.”

Without land, rain would not carry important nutrients such as phosphorus. Microbial life cannot produce oxygen at a rate comparable to other non-biological sources.

“The detectability index tells us that it’s not enough to observe oxygen in the exoplanet’s atmosphere. We must also watch the oceans and land, ”says Desh.

“This is changing our approach to finding life on exoplanets. This helps us interpret the observations made by us on exoplanets. This helps us choose the best targeted exoplanets to search for life. And that helps us design the next generation of space telescopes. so that we get all the information we need to identify life.”

Scientists from various fields have been brought together to create this index. The formation of the team was facilitated by NASA’s Nexus for Exoplanetary System Science (NExSS) program, which funds interdisciplinary research to develop strategies for finding life on exoplanets. Their disciplines include theoretical and observational astrophysics, geophysics, geochemistry, astrobiology, oceanography and ecology.

“This kind of research requires a team, we cannot do it as individual scientists,” said co-author Hilary Hartnett, who holds joint meetings at the ASU School of Earth and Space exploration and the School of Molecular Sciences.

This team hopes that their detectability index structure will be used in the search for life.

“Finding life on a planet outside our solar system would change our understanding of our place in the universe,” says Glaser. “NASA is investing heavily in the search for life, and we hope that this work will be used to maximize the likelihood of finding life.”

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