In search of life on Earth and in our galaxy

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Everything we study about our planet, our solar system, and even exoplanets seems to come down to one big question: are we alone? It’s a huge question, really. Perseverance looking for evidence that Mars had life. The phosphine was in the news last year because it could have been a biological marker of Venus. Mower Europe is in the works, with teams meeting this week to discuss instruments and scientific goals, one of which is to search for molecular signs of life in geysers. And Kepler, wonderful Kepler, his mission was not to hunt exoplanets. No, his mission was to find Earth-like planets in the habitable zones of their stars.

Today we have found over 4000 exoplanets. However, we still haven’t found that Earth 2.0 that everyone is looking for. Of course, there are planets the size of Earth. There are planets in the living area. But the stars are too active, the planets too big, or a combination of both. Nothing seems to fit perfectly. And it could be that finding this Earth-like planet is even more difficult than we originally thought.

In a new study published in the Monthly notices from the Royal Astronomical Society, scientists looked at how much energy the planets receive from their host stars and whether there was enough energy available for biological life to be processed using oxygen-based photosynthesis. Some plants and animals here on Earth use the sun’s radiation to turn carbon dioxide and water into fuel, but to have carbon dioxide you need oxygen already in place. The results were not encouraging.

According to the press release: Planets around even cooler stars known as red dwarfs, which smolder at about a third of our Sun’s temperature, might not even be receiving enough energy to activate photosynthesis. Stars hotter than our Sun are much brighter and emit up to ten times more radiation in the range needed for efficient photosynthesis than red dwarfs, but generally do not live long enough for complex life to evolve.

Many researchers hoped that red dwarf stars, which are the most common type of star in the Milky Way, would be great places to harbor life. This new research actually narrows down the exoplanet window we should be looking at. On the one hand, it’s a smaller window. On the other hand, we can focus the search a little better than before.

IMAGE: The FlyPol instrument, which was used to measure biosignatures from the air, on board the helicopter. CREDIT: Courtesy of Lucas Patty

Of course, once you get past the “where do we look for life” part of the question, the next piece is “how do we detect this life?” “. In what I believe was groundbreaking research, a team of scientists used a helicopter flying 70 kilometers per hour at a distance of two kilometers above the ground to detect signatures of life here on Earth. And they found them. In fact, they were able to tell the difference between fields, forests and urban areas.

First author Lucas Patty explains: When light is reflected from biological matter, some of the electromagnetic waves in the light will travel clockwise or counterclockwise. This phenomenon is called circular polarization and is caused by the homochirality of biological matter. Similar spirals of light are not produced by abiotic nonliving nature.

A note on the term homochirality: chirality is the property of laterality – left-handed or right-handed. We use this term in biology, and particularly in molecular biology, to describe how molecules, like DNA, occur. Except that, unlike the hands, in molecules, the laterality is either left or right unpaired. And this laterality, or chirality, can be used as a biosignature.

And this team found this signature of a moving helicopter. Now we can use their technology to design systems that could be carried on spacecraft, and first of all, they are working to adapt it for the International space station(ISS). I am delighted to follow where this research is going.

A view of the Earth and the Sun
IMAGE: A view of the Earth and the Sun thousands of miles above our planet, with stars positioned to see the Earth in transit around the illuminated Sun and the Milky Way visible on the left. CREDIT: Open Space / American Museum of Natural History

One last story on the detection of life. In new research published in Nature, scientists released data on star systems that could detect life on Earth if they had intelligent species with the right technology. At a distance of 326 light years, there are over 2,000 star systems that have had the correct view. And over the next 5,000 years, more than 300 star systems will be added to this list as everything orbit inside the Milky Way.

The press release explains that the team “used positions and motions from the European Space Agency’s Gaia eDR3 catalog to determine which stars enter and leave the Earth’s transit zone – and for how long.“In this catalog of systems, seven are known to harbor exoplanets, and one of those that will reach this point – in about 1,600 years – is the Trappist-1 system.

The co-author of the study, Jackie Faherty, leaves us this reflection: One would imagine that the worlds beyond Earth that have already detected us are making the same plans for our planet and our solar system. This catalog is an intriguing thought experiment that one of our neighbors may be able to find us for.

Earth-like conditions rarer than previously thought

Helicopter used to detect life on Earth

  • University of Bern Press release
  • “Biosignatures of the Earth I. Airborne spectropolarimetric detection of photosynthetic life”, CHL Patty et al., To appear in Astronomy & Astrophysics (preprint at arxiv.org)

More than 2,000 nearby star systems could detect Earth

This article originally appeared on Moyen, June 29, 2021.


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