Last month I wrote about the search for life elsewhere in the universe, but if we’re lucky enough to find life somewhere out there, will we recognize it as such? Here on Earth we think we know life when we see it, but what exactly is it? Living organisms are usually defined as having the capacity to grow, reproduce, respond to stimuli, and adapt to their environment over successive generations. Even here on Earth life takes many strange forms and thrives in environments once thought inhospitable, so in worlds beyond our own, might there be untold ways of creating life as we’ve never known it?
While carbon, oxygen, nitrogen, hydrogen, sulfur and phosphorus are thought to be essential for forming the kind of life we have here on Earth, alien life might be made from different combinations of molecules. For instance, it has been suggested that alien life could be silicon-based because silicon is an abundant element that, like carbon, supports bonding with up to three other atoms, which is important for making complex molecules like those required for life.
DNA, the blueprint of life, is made up of four chemical components called nucleotide bases, known as A, C, G and T, the combination of which determines the kind of life produced. Recently, however, researchers have created a new type of DNA with eight nucleotide bases, four natural and four artificial. The four new bases that don’t exist in nature fit neatly into DNA’s double helix, so enzymes can read them as easily as natural bases in order to make molecules. The fact that we’ve been able to create this new kind of DNA suggests that four based DNA may not be the only kind of DNA able to support life. The chemistry of life might well be profoundly different elsewhere in the universe.
One factor to consider in the search for life is that it takes a very long time for life forms to develop. Cosmologist George Gamow once said: “It took less than an hour to make the atoms, a few hundred million years to make the stars and planets, but five billion years to make man!” In fact, it is thought that it took about a billion years after Earth’s formation for the first microscopic life forms to appear, and another three billion for large, multicellular creatures to develop. So, in our search for life, we should forget about hot blue giant stars that would burn out way too fast, and rather focus on planets orbiting red dwarfs or main sequence stars like our Sun that are around for long enough to allow life to develop.
Astronomers employ both ground-based and space telescopes to detect radio, infrared and optical light emissions from exoplanets that could be indicators of life, known as biosignatures. Light in certain wavelengths indicates the presence of specific gases that could be such biosignatures. For instance, here on Earth plants produce oxygen as a byproduct of photosynthesis, and animals and plants give off methane gas. When both these gases are present in a planet’s atmosphere they destroy each other, so detecting signatures of both on a particular planet would mean there must be a source of replenishment, possibly some form of life.
Primitive life forms would probably be harder to detect than more advanced civilizations that, in addition to biosignatures, emit “technosignatures,” such as repetitive radio signals or polluting gases. And of course, life elsewhere might take different forms from those here on Earth and produce very different signatures.
The universe is unimaginably vast, with so many stars whose planets could potentially harbor life. However, with so many places to look, and the long time it takes for light and radio signals to reach us even from nearby stars, the task is daunting. Unless we get extraordinarily lucky, detecting signs of alien life will not be easy.
Looking within our own solar system might prove more promising in the short term. Saturn’s moon Titan has a water ocean, a nitrogen atmosphere and methane rivers and lakes, all possible ingredients for life. Jupiter’s moon, Europa, and Saturn’s moon, Enceladus, both have water oceans under ice. Mars has methane emissions, and recently, a liquid water lake was discovered under its southern ice cap, making it a prime candidate right on our celestial doorstep. With several current missions to Mars and more in the works, the red planet seems the most promising target in the search for life. Finding even the tiniest, most primitive alien life form would be both thrilling and life-changing. I would so like to be around when it happens.
Join the Springfield Stars Club on Tuesday, April 23rd at 7:00pm at the Springfield Science Museum for a talk by Dr. David Wexler on “A Taste of Space Physics,” an introduction to how we study space within the solar system by direct and remote sensing. The talk will also address how data from spacecraft helps build the general principles applied to deep-space astronomy. A graduate of Stanford University Medical School, Dr. Wexler is an ear, nose and throat specialist at Baystate Wing Hospital in Palmer. He has a Master’s degree in astronomy, is currently a PhD candidate, and participates in solar research at MIT’s Haystack Observatory. Refreshments will be served, and the public is welcome. The meeting is free of charge for members, with a suggested donation of $2 per non-member.
Also, on Friday, May 3rd at 7:30pm, the Stars Club and the Springfield Science Museum will host “Stars over Springfield,” an astronomy adventure for the whole family. To celebrate the upcoming 50th anniversary of Neil Armstrong’s first step on the moon Richard Sanderson and Ed Faits will give a talk on “Apollo 11: A look back at humanity’s greatest achievement.” A fee of $3 for adults and $2 for children under 18 will be charged.
Copyright © Amanda Jermyn