New Delhi, Sept. 26: A decades-old idea that rocks from interstellar space may have deposited the seeds of life on Earth has gained fresh scientific plausibility through new research by an Indian-origin astronomer and her colleagues.
Planetary scientist Renu Malhotra at the University of Arizona, Tucson, and her colleagues in the US and Europe have shown that the probability that rocks are exchanged between planetary systems is much higher than previously estimated.
Their research adds scientific credence to the hypothesis of lithopanspermia, which proposes that rocks may have served as natural vehicles ferrying molecules of life or whole microbes from one planetary system to another.
“Life could have been seeded on Earth from another planetary system and vice versa — life from Earth could have been transported to other planets beyond our solar system. Our study opens (up) both possibilities,” said Amaya Moro-Martin, an astronomer at the Centre for Astrobiology in Madrid, Spain. She is the principal author of the study, just published in the scientific journal Astrobiology.
Astronomers have for decades been weighing arguments for and against the idea of lithopanspermia, advocated by the late British astronomer Fred Hoyle and others, including Sri Lankan-origin astrobiologist Chandra Wickramasinghe at Cardiff University in the UK.
Three years ago, an international team of scientists showed through a sophisticated set of calculations that rocks more than one metre long could provide safe zones for microbes to survive tens of millions of years through interstellar space.
“Micro-organisms can be sheltered from the hazards of outer space if hidden beneath the surface of rocks. The bigger the size of the rock, the longer it can hide,” Moro-Martin told The Telegraph.
But previous calculations had suggested that the probability of the solar system gravitationally capturing such rocks from interstellar space was “negligibly small”, said Malhotra, who had studied physics at the Indian Institute of Technology, Delhi, before moving to the US for a PhD.
The earlier work had assumed that the rocks, or meteorites, would be moving at high speeds, typically about 5km per second.
In their new study, Moro-Martin, Malhotra and two other collaborators have found that slower rocks — moving at about 100 metres per second — can indeed be captured and, eventually, fall onto planets.
“There’s been an assumption that life has to start from scratch in each planetary system. This study allows the possibility that life may emerge at one place and move from one planetary system to another if they’re close enough,” Malhotra told this newspaper.
The scientists say the timing of a possible exchange of such microbe-bearing rocks in the infancy of the solar system appears to be consistent with the emergence of life on Earth.
The earliest geological evidence for life on Earth is dated to about 3.8 billion years ago. This was a period when Earth was being bombarded by meteorites, the solar system itself was ejecting meteorites, and the Sun was part a cluster of stars — a stellar birth cluster — ready to disperse.
“The conditions were just right then for rocks to be exchanged between neighbouring stellar systems,” Malhotra said.
Moro-Martin said there was independent geological evidence suggesting biological activity on Earth when the solar system was about 718 million years old (about 3.8 billion years ago).
“If this estimate is correct, it could mean life was present (on Earth) very shortly after the heavy bombardment, estimated to have ended when the solar system was 700 million years old,” she said.
The time scales are consistent, Moro-Martin said. The probability of a planetary system capturing the slow-moving rocks, she said, is a billion times higher than the probability of capturing high-speed rocks.
The proportion of slow-moving interstellar rocks is much smaller than that of the fast-moving rocks but the former are captured by planetary systems far more efficiently, the researchers said.
Mathematician Edward Belbruno at Princeton University and Dmitry Savranksy at Lawrence Livemore National Laboratory in the US collaborated in the study.
In 2009, Finnish astronomer Mauri Valtonen and his colleagues had suggested in The Astrophysical Journal that members of the Sun’s stellar birth cluster should be identified and scrutinised for evidence of planets and life on those planets.