How to search for life as we don’t know it


During my freshman seminar at Harvard last semester, I mentioned that the star closest to the sun, Proxima Centauri, mainly emits infrared radiation and has a planet, Proxima b, in the habitable zone that it surrounded. To challenge the students, I asked, “Suppose there are creatures crawling on the surface of Proxima b?” What would their infrared sensitive eyes look like? The brightest student in the class responded within seconds with a picture of the mantis shrimp, which has infrared vision. The shrimp’s eyes look like two ping-pong balls connected by ropes to its head. “Looks like an alien,” she whispered.

When we try to imagine something that we have never seen, we often default to something that we have seen. For this reason, in our search for extraterrestrial life, we generally search for life as we know it. But is there a way to expand our imaginations to include life as we don’t know it?

In physics, a similar path had already been mapped out a century ago and has proved successful in many contexts. It is about carrying out laboratory experiments that reveal the underlying laws of physics, which in turn apply to the entire universe. For example, around the same time the neutron was discovered in James Chadwick’s lab in 1932, Lev Landau suggested that there might be stars made of neutrons. Astronomers later realized that there are in fact some 100 million neutron stars in our Milky Way galaxy alone and a billion times more in the observable universe. Recently, the LIGO experiment detected gravitational wave signals from collisions between neutron stars at cosmological distances. It is now believed that such collisions produce precious gold which is forged into alliances. The moral of this story is that physicists were able to imagine something new in the universe at large and search for it in the skies by following the knowledge gained from laboratory experiments on Earth.

The search for extraterrestrial life can follow a similar approach. By creating synthetic life in various ways from a soup of chemicals in the laboratory, we could perhaps imagine new environments where life could occur differently than on Earth. The situation is similar to writing a cookbook with prescriptions for baking different types of cakes. In order to write a rich cookbook, we have to experiment with many types of chemicals. And also, as I noted in an article with Manasvi Lingam, this experimentation can use fluids other than water, which is considered essential for life as we know it.

A Harvard colleague of mine, Nobel Laureate Jack Szostak, is about to create synthetic life in his lab. Any success with just one recipe may suggest variations that would produce a variety of results, to assemble into our Synthetic Life Cookbook. By identifying the appropriate environmental conditions from our laboratory experiments, we can then search for real systems where they are realized in the sky, just as in the case of neutron stars.

In following this approach, we must be as careful as we are in the exploitation of nuclear energy. Creating artificial variants of life in our laboratories carries the risk of causing an environmental catastrophe, as Frankenstein’s story imagines. Such experimentation must be carried out in isolated environments so that the misadventures of life as we do not know it do not endanger the life we ​​know.

While the surfaces of planets and asteroids can be explored from a distance for biological signatures, alien life may be most abundant below the surface. Habitable conditions could exist in oceans that lie beneath thick icy surfaces, not only inside moons like Saturn’s Enceladus or Jupiter’s Europa, but also inside objects floating freely in space. interstellar. In other research with the Lingam, we have shown that the number of life-carrying objects can exceed the number of rocky planets in the habitable zone around the stars by several orders of magnitude.

Adapting life to extreme environments could take exotic forms, as evidenced by extremophiles on Earth. For example, frozen microscopic animals have recently been found to survive 24,000 years in Siberian permafrost, and microbial life has been shown to persist for 100 million years under the seabed. These microbes were born during the hot period of the Cretaceous Period, when dinosaurs ruled the Earth.

In the solar system, conditions closest to Earth were achieved on its closest neighbors, Venus and Mars. NASA recently selected two new missions to study Venus, and its Perseverance rover is looking for traces of life on Mars. If alien life is discovered, the key follow-up question is whether it is “life as we know it”. Otherwise, we will realize that there are multiple chemical pathways leading to natural life. But if we find evidence of a Martian or Venusian life that resembles terrestrial life, it might indicate a particular preference for “life as we know it”. Alternatively, life could have been carried by rocks that traveled between planets in a process called panspermia. My student Amir Siraj and I wrote an article showing that the transfer of life could have been mediated by asteroids grazing the planet. It is also necessary to keep in mind the very remote possibility that life was sown in the internal solar system by an “extrasolar gardener”, in particular by “directed panspermia”.

My vivid childhood memory is of dinner conversations in which the adults in the room pretended to know a lot more than they actually knew. It was definitely a form of “intellectual makeup” that they wore to enhance their appearance. And if I asked a question that these suitors didn’t have a ready-made answer to, they would dismiss it as irrelevant. My experience as a senior scientist is no different, especially when I ask the question, “Are we the smartest child in the cosmic block?”

Science offers the privilege of nurturing our childhood curiosity. The advancement of scientific knowledge through experimentation cannot be stopped. Hoping that we will find a recipe for artificial life that will allow us to imagine something much smarter than the natural life we ​​have encountered so far. It will be an experience of humility. But while we won’t discover this supreme intelligence in our labs, its byproducts could simply appear in our skies as mail posted from distant quarters of the Milky Way. And we’ll be looking for that through the telescopes of the recently announced Galileo project.

This is an opinion and analysis article; the opinions expressed by the author or authors are not necessarily those of American scientist.


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