‘Should not be alone’: Mystery as search for alien life comes up empty
Potentially habitable planets are 100 times more common than we thought. But efforts to find signs of alien life still come up short.
Potentially habitable planets are 100 times more common than we thought. But efforts to find signs of alien civilisations continue to come up disturbingly empty.
A slew of scientific studies are being published based on fresh data from new advanced space sensors, including the $15 billion James Webb Telescope.
And according to results presented at a US geochemistry conference this week, liquid water appears to be far more common on distant worlds than previously believed.
Water is a key ingredient for life as we know it. It’s a mild solvent. And this enables life-giving chemical reactions within microbial, plant and animal cells.
And while its presence in the universe has long been found to be common, it’s mostly been believed to be in the form of ice.
But the apparent prevalence of geothermal heat generated by the decay of radioactive elements and the interaction of gravity on planetary and moon cores raises hopes liquid water may be almost common.
Jupiter’s ice moon Europa and Saturn’s Enceladus have sparked excitement in recent years after water plumes were observed jetting into space. This points to sub-surface oceans deep beneath their ice crusts.
Rutgers University planetary scientist Lujendra Ojha has told the Goldschmidt Conference in France that similar geothermal heat may be common on Earth-like planets orbiting colder stars than ours.
“We found that when one considers the possibility of liquid water generated by radioactivity, it is likely that a high percentage of these exoplanets can have sufficient heat to sustain liquid water – many more than we had thought,” he said.
Red Dwarf revival
“If there’s ice, it’s more likely to have melted and created liquid water than the other way around,” Ojha said.
Previous estimates expected only one rocky planet orbiting every 100 stars would have liquid water. But in this research, that figure may be closer to one for each star.
“That represents really good odds for the origin of life elsewhere in the universe,” he said.
Small, dull red dwarf stars are the most common type of star. They’ve also proven to be the easiest to search for traces of rocky planets.
But these planets must orbit close to these stars to warm sufficiently to meet “Goldilocks Zone” standards – where temperatures are “not too hot, not too cold” to sustain surface water. That puts them well within the range of solar flares and can cause their orbits to become elliptical – meaning the star’s warming is inconsistent.
Sub-surface oceans, such as those found on Europa, may, however, “provide habitable conditions for an extended period,” his study published in the journal Nature reports.
“Most Earth-like exoplanets that we have found today orbit around M dwarfs,” Ojha explains. “Given that basal melting was something that likely happened and, depending on who you talk to, could have been one of the main ways of generating liquid water on our solar system’s planets billions of years ago, we wanted to ascertain what would be required for basal melting, and if this could happen on other planetary bodies.”
His research team created detailed computer models of planetary bodies and how geological processes contributed to their environment. The results indicate even low levels of heat generated by decaying radioactive minerals could thaw enough water to create large lakes capable of surviving billions of years.
And another study published by the Proceedings of the National Academy of Sciences says up to one-third of the Earth-like planets observed orbiting red dwarfs are in orbits stable enough for gravitational-force generated magma to sustain life.
“It’s only for these small stars that the zone of habitability is close enough for these tidal forces to be relevant,” said co-author Professor Sarah Ballard.
“These stars are excellent targets to look for small planets in an orbit where it’s conceivable that water might be liquid and therefore the planet might be habitable.”
The search for life
Thousands of worlds have been identified orbiting distant stars since their existence was first confirmed in 1992. But none discovered so far looks like our own Solar System.
Part of this is related to the difficulty in sensing the influence of small Earth-like planets on a large star’s orbit. Or detecting the shadows they cast.
That’s why most planetary systems found so far orbit small, dull red dwarf stars, and the most common planets found are large gas giants in very close orbits.
And while space observation technology cannot yet observe the full range of planetary types in a full range of orbits, the mere prevalence of these “hot Jupiters” hints that our system is the odd one out.
The gravitational influence of these gas giants over a star’s inner “Goldilocks Zone” is likely to have prevented the formation of rocky Earth-like planets. But, in our Solar System, the presence of Jupiter in an outer orbit may have instead helped shield the smaller inner planets from comet strikes.
That still has astronomers scratching their heads. Even with the constantly changing estimations of the prevalence of liquid water in the universe, the statistics suggest our civilisation should not be alone.
So why haven’t we seen evidence of one?
A recent study of the influence of black holes on star formations suggests we may be latecomers to the party of life.
“The link between black holes and star formation allows us to draw a connection between black holes and the places and times when extraterrestrial intelligences (ETIs) had a greater chance of emerging,” associate professor David Garofalo writes.
He argues that the jets of material and gravitational flows associated with black holes generate a rich environment for the formation of stars like our sun. But this activity peaked about six billion years ago.
“To the extent that we may some day speak of a peak era for the emergence of technologically advanced life in the universe, our simplified exploration of the emergence of life … indicates that such a time is in the past,” he concludes.
“We on planet Earth are, therefore, latecomers.”
Jamie Seidel is a freelance writer | @JamieSeidel
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