Life beyond Earth: A universe of possibilities
Life beyond Earth: A universe of possibilities
Is there life beyond Earth? Whether elsewhere in our own solar system, or farther out among the exoplanets, that question is still unanswered. But the answers might be getting closer. And many recent discoveries seem to bolster the possibility of extraterrestrial life. September 2022 has been a great illustration, with the announcements of several new tantalizing findings. These include the ocean of Saturn’s moon Enceladus being even more habitable than previously thought, super-Earth exoplanets that might be more habitable than Earth, new evidence for a wet and warm early Mars, including many more lakes than first thought, and an ancient ocean.
New optimism for life in Enceladus’ ocean
First, Enceladus. Like Jupiter’s moon Europa, this small moon of Saturn is thought to have a subsurface ocean of liquid water. In 2018, a new analysis of data from NASA’s Cassini spacecraft – obtained when the spacecraft flew through water vapor plumes, erupting into space from this subsurface ocean – found some tantalizing ingredients suggesting Enceladus’ ocean as a potential habitat for life. The 2018 analysis revealed water vapor, ice particles, salts, methane and organic compounds in Enceladus’ plumes. But one key ingredient – phosphorus – was missing. Now a new study from researchers at the Southwest Research Institute (SwRI) suggests the phosphorus is there. Geochemist Christopher Glein said on September 19, 2022:
In the years since NASA’s Cassini spacecraft visited the Saturn system, we have been repeatedly blown away by the discoveries made possible by the collected data. What we have learned is that [Enceladus’ plumes] contain almost all the basic requirements of life as we know it.
The SwRI team didn’t find the phosphorus directly. But they did uncover evidence for its availability in the ocean beneath the moon’s icy crust. They performed thermodynamic and kinetic modeling that simulates the geochemistry of phosphorus, based on insights from Cassini about the ocean-seafloor system on Enceladus. Their model predicted that phosphate minerals would be unusually soluble in the ocean. Glein added:
The underlying geochemistry has an elegant simplicity that makes the presence of dissolved phosphorus inevitable, reaching levels close to or even higher than those in modern Earth seawater. What this means for astrobiology is that we can be more confident than before that the ocean of Enceladus is habitable.
Super-Earths more habitable than Earth?
Astronomer Chris Impey posted another intriguing article in The Conversation on September 23, 2022. In it, he makes the case that super-Earths – exoplanets larger and more massive than Earth but smaller and less massive than Neptune – might not just be habitable. They might be even more habitable than our own Earth.
They are also common, estimated now to comprise about one-third of known exoplanets. As Impey wrote:
Based on current projections, about a third of all exoplanets are super-Earths, making them the most common type of exoplanet in the Milky Way. The nearest is only six light-years away from Earth.
You might even say that our solar system is unusual since it does not have a planet with a mass between that of Earth and Neptune.
And, super-Earths – at least some of them – may be more habitable than Earth. Impey wrote:
Researchers have come up with a list of the attributes that make a planet very conducive to life. Larger planets are more likely to be geologically active, a feature that scientists think would promote biological evolution. So, the most habitable planet would have roughly twice the mass of the Earth and be between 20 percent and 30 percent larger by volume. It would also have oceans that are shallow enough for light to stimulate life all the way to the seafloor and an average temperature of 77 degrees Fahrenheit (25 degrees Celsius).
It would have an atmosphere thicker than the Earth’s that would act as an insulating blanket. Finally, such a planet would orbit a star older than the sun to give life longer to develop, and it would have a strong magnetic field that protects against cosmic radiation. Scientists think that these attributes combined will make a planet super habitable.
By definition, super-Earths have many of the attributes of a super habitable planet. To date, astronomers have discovered two dozen super-Earth exoplanets that are, if not the best of all possible worlds, theoretically more habitable than Earth.
The Webb telescope will be able to take a closer look at some of these exotic worlds and analyze their atmospheres for possible chemical signs of life known as biosignatures.
A warmer, wetter early Mars?
For decades, scientists have debated whether Mars was warmer and wetter a few billion years ago. Or was it cold and wet? Or cold and mostly dry? A new press release from the SETI Institute outlines new evidence that Mars was born wet, with a dense atmosphere. That could have allowed warm oceans to exist for millions of years.
The researchers developed the first-ever model of the evolution of the Martian atmosphere that links the high temperatures from Mars’ formation in a molten state through to the formation of the first oceans and atmosphere. The results implied that, just like on Earth, water vapor was concentrated in the lower atmosphere and condensed as clouds. SETI Institute research scientist Kaveh Pahlevan said:
We believe we have modeled an overlooked chapter in Mars’s earliest history in the time immediately after the planet formed. To explain the data, the primordial Martian atmosphere must have been very dense (more than ~1000x as dense as the modern atmosphere) and composed primarily of molecular hydrogen (H2). This finding is significant because H2 is known to be a strong greenhouse gas in dense environments. This dense atmosphere would have produced a strong greenhouse effect, allowing very early warm-to-hot water oceans to be stable on the Martian surface for millions of years until the H2 was gradually lost to space. For this reason, we infer that – at a time before the Earth itself had formed – Mars was born wet.
Mars: Land of lakes?
Another study, from researchers in Hong Kong, also supports a previously wetter Mars. The study suggests that scientists have underestimated the number of lakes that once existed on Mars. According to Joseph Michalski, a geologist at the University of Hong Kong:
We know of approximately 500 ancient lakes deposited on Mars, but nearly all the lakes we know about are larger than 100 square kilometers. But on Earth, 70 percent of the lakes are smaller than this size, occurring in cold environments where glaciers have retreated. These small-sized lakes are difficult to identify on Mars by satellite remote sensing, but many small lakes probably did exist. It is likely that at least 70 percent of Martian lakes have yet to be discovered.
According to the new paper, most of the already known Martian lakes date back to about 3.5 to 4 billion years ago. They also may have lasted only 10,000 to 100,000 years. Some of them may have been quite muddy and murky, due to the lower gravity and fine-grained soil. That might have been a challenge for any supposed photosynthetic organisms (using photosynthesis) in those lakes. But, as Michalski also noted, other lakes could have been deeper and longer-lived, with hydrothermal systems capable of supporting life.
Further exploration is needed to find the evidence for these other smaller lakes. However, if they existed, then that supports the possibility of life having existed, even if only microbial, on ancient Mars.
More evidence for ancient ocean on Mars
Finally, Space.com reported that China’s Zhurong rover has found new evidence for an ancient ocean on Mars. Zhurong is exploring the ancient plains of Utopia Planitia. If, as some scientists contend, Mars did once have an ocean, then Utopia Planitia, a huge basin, was likely part of it. According to the China National Space Administration (CNSA), the rover has sent back 1,480 gigabytes of raw data so far. Some of that data supports the ocean hypothesis.
The scientists report the detection of hydrated minerals in the duricrust. Duricrust is a hard mineral layer on top of soil that typically forms due to the evaporation of groundwater. As Space.com reported, the researchers said that this is evidence for “substantial liquid water activity” in the region sometime during the last billion years.
In addition, Zhurong has found evidence for “high bearing strength and low friction parameters” in the soil. That could be due to erosion from wind or water, or both.
A previous PNAS study from last January also supports the existence of an ancient circumpolar ocean in the northern hemisphere.
Life beyond Earth: Where will we find it first?
While none of these new findings prove there is extraterrestrial life, they do show that the possibilities are increasing. While we still only know about life on Earth, there may be multiple scenarios – both in our solar system and far beyond – in which living organisms could originate and evolve. Where will we find the first definitive evidence? In ancient Martian rocks? In the waters of an ocean moon in the outer solar system? On a distant exoplanet? The possibilities may be endless!
Bottom line: Several new reports and discoveries, including five new papers, support the possibility of life beyond Earth. Are we getting closer to finding alien life?