For decades astronomers have typically searched for extraterrestrial life by looking for biosignatures — compounds that suggest the presence of life — in other solar systems. The logic behind looking for biosignatures is that life on Earth has existed for approximately 3.7 billion years, and has been reliant on the presence of the same ingredients since its inception: carbon, water, and carbon dioxide, to name a few.
The findings hint at how life forms in the universe, and may provide scientists with the types of clues that will help them find alien life one day.
But just as astronomers are intrigued by the search for life elsewhere in the universe, they are also working on understanding the origins of Earth's necessities for life — especially water, which is a vital component of all living organisms on our planet. Now, according to a new study published in Nature, new observations by astronomers that suggest water in our Solar System formed billions of years before the sun. The findings hint at how life forms in the universe, and may provide scientists with the types of clues that will help them find alien life one day.
"We can now link to water that we find in comets in our own solar system, with water that is found toward even younger protostars and the interstellar medium," John Tobin, an astronomer at the National Science Foundation's National Radio Astronomy Observatory (NRAO) and the lead author on the new paper, told Salon in an interview. Protostars are very young stars that are still growing in mass via its parent molecular cloud; such objects may have yet to absorb or expel the remaining gas and dust in their planetary nebulae.
Tobin said that astronomers are essentially creating a map of "water's evolutionary history." Comets, which are icy, "may have provided water on Earth," Tobin said, though we also see water extending back to "protostars and the interstellar medium."
Prior to this study, as Tobin said, astronomers could connect Earth's water to comets, but they couldn't connect protostars to comets. The new observations were made with the Atacama Large Millimeter/submillimeter Array (ALMA) by looking at the protostar V883 Orionis, which is located roughly 1,305 light-years from Earth in the constellation Orion.
Protostars are often surrounded by circumstellar disks, vast ring-shaped accumulations of gas and dust that will eventually coalesce into planets and moons when the solar system reaches a later stage of evolution. Typically, observing the circumstellar disks around protostars is a challenge for telescopes, because of the interfering presence of water in the form of ice.
For this reason, astronomers usually looking for the "ice line," which is point where the water transitions from ice to gas. Since V883 Orionis' circumstellar disk is hot enough that the water in it has turned into gas, astronomers saw an opportunity to study it to help understand the evolution of water in solar systems. Astronomers measured its composition and found that it was relatively unchanged between each stage of solar system formation, which suggested that the water in Ori's protoplanetary disk went through the same process as the water in our Solar System.
"What we didn't know was whether the water that was formed in interstellar clouds is actually passed relatively unchanged, through the phases of star formation and to proto-planetary disks, comets, and planets," Tobin said. "And so we've now established the path of water to get to planets, and comets, from the interstellar medium."
"We've now established that path of water to get to planets, and comets, from the interstellar medium."
Tobin added that at least a portion of the water on Earth comes from interstellar space, "which was then incorporated into comets as our solar system was forming — and some of that made it to Earth."
Harvard astronomer Avi Loeb, who was not affiliated with the study, told Salon our own solar system is considered to be a "late bloomer" since it formed 4.6 billion years ago.
"Most stars formed billions of years earlier and produced oxygen that combined with primordial hydrogen to make water," Loeb said. "When did water start to form? In a paper I wrote in 2015 we found that water could have formed as early as hundreds of millions of years after the Big Bang, about 9 billion years before the sun."
Loeb emphasized: "The chemistry of life-as-we-know-it could have started then on planets around stars that formed long before the sun."
What does this all mean for the search for life aside from what we know exists on planet Earth?
"The way water gets to planets is still not fully understood, but it obviously does happen because we see that we see tons of water on Earth, we see water in other places in our solar systems," Tobin said. "So I think what we see is that the water is going to be available and so it's probably going to be able to end up on some planetary bodies in the other forming solar systems. I think assuming that all life needs water, I think there's going to be a lot of it out there for for the planets to have."
From a philosophical perspective, Tobin said his study gives us a greater understanding of where human life originated from in the universe.
"Carl Sagan said that 'we are star stuff' because all of the heavier atoms in our body had to be formed in stars," Tobin explained. He said that this means that much of the water in our bodies originated in "an interstellar gas cloud."
