The most promising places to look for life in the Solar System are in the ocean moons Europa and Enceladus. But all that warm, salty, potentially life-supporting water is under thick sheets of ice: up to 30 km thick on Europa and up to 40 km thick for Enceladus.
The main obstacles to exploring all that water are the thick ice barriers. Assuming a spacecraft can be designed and built to melt its way through all that ice, what then?
Submarines can do the actual exploring, and they needn’t be large.
Recently I wrote about the discovery of a hycean world. A potentially habitable exoplanet with a deep warm ocean and thick, hydrogen-rich atmosphere. Such planets are thought to be somewhat common orbiting red dwarf stars, and they are an excellent candidate for life. While it’s an exciting discovery, buried in the research article was something even more exciting. Tentative evidence of a biosignature, hinting at the presence of life. You can guess which discovery started making headlines. But have astronomers really found life on another planet?
Along with still operational missions, these observatories will gather massive volumes of high-resolution spectroscopic data. Sorting through this data will require cutting-edge machine-learning techniques to look for indications of life and biological processes (aka. biosignatures). In a recent paper, a team of scientists from the Institute for Fundamental Theory at the University of Florida (UF-IFL) recommended that future surveys use machine learning to look for anomalies in the spectra, which could reveal unusual chemical signatures and unknown biosignatures.
The surface of Venus is like a scene from Dante’s Inferno – “Abandon all hope, ye who enter here!” and so forth. The temperature is hot enough to melt lead, the air pressure is almost one hundred times that of Earth’s at sea level, and there are clouds of sulfuric acid rain to boot! But roughly 48 to 60 km (30 to 37.3 mi) above the surface, the temperatures are much cooler, and the air pressure is roughly equal to Earth’s at sea level. As such, scientists have speculated that life could exist above the cloud deck (possibly in the form of microbes) as it does on Earth.
Unfortunately, these clouds are not composed of water but of concentrated sulfuric acid, making the likelihood that life could survive among them doubtful. However, a new study led by scientists from the Massachusetts Institute of Technology (MIT) reveals that the basic building blocks of life (nucleic acid bases) are stable in concentrated sulfuric acid. These findings indicate that Venus’ atmosphere could support the complex chemistry needed for life to survive, which could have profound implications in the search for habitable planets and extraterrestrial life.
There are plenty of places for life to hide. Even on our blue planet, where we know there is abundant life, it is sometimes difficult to predict all the different environments it might crop up in. Exploring worlds other than our own for life would make it exponentially more difficult to detect it because, realistically, we don’t really know what we’re looking for. But life will probably present itself with some sort of pattern. And there is one new technology that is exceptional at detecting patterns: machine learning. Researchers at the SETI Institute have started working on a machine-learning-based AI system that will do just that.
To date, 5,250 extrasolar planets have been confirmed in 3,921 systems, with another 9,208 candidates awaiting confirmation. Of these, 195 planets have been identified as “terrestrial” (or “Earth-like“), meaning that they are similar in size, mass, and composition to Earth. Interestingly, many of these planets have been found orbiting within the circumsolar habitable zones (aka. “Goldilocks zone”) of M-type red dwarf stars. Examples include the closest exoplanet to the Solar System (Proxima b) and the seven-planet system of TRAPPIST-1.
These discoveries have further fueled the debate of whether or not these planets could be “potentially-habitable,” with arguments emphasizing everything from tidal locking, flare activity, the presence of water, too much water (i.e., “water worlds“), and more. In a new study from the University of Padua, a team of astrobiologists simulated how photosynthetic organisms (cyanobacteria) would fare on a planet orbiting a red dwarf. Their results experimentally demonstrated that oxygen photosynthesis could occur under red suns, which is good news for those looking for life beyond Earth!
While the Earth absorbs a lot of energy from the Sun, a lot of it is reflected back into space. The sunlight reflected from Earth is called Earthshine. We can see it on the dark portion of the Moon during a crescent Moon. The Farmer’s Almanac said it used to be called “the new Moon in the old Moon’s arms.”
Earthshine is one instance of planetshine, and when we look at the light from distant exoplanets, we’re looking directly at their planetshine without it bouncing off another object.
If distant astronomers were looking at Earthshine the way we look at exoplanet shine, would the light tell them our planet is rippling with life?
For astrobiologists, the scientists dedicated to the search for life beyond Earth, the moons of Saturn are a virtual treasure trove of possibilities. Enceladus is especially compelling because of the active plumes of water emanating from its southern polar region. Not only are these vents thought to be connected directly to an ocean beneath the moon’s icy surface, but the Cassini mission detected traces of organic molecules and other chemicals associated with biological processes. Like Europa, Ganymede, and other “Ocean Worlds,” astrobiologists think this could indicate hydrothermal activity at the core-mantle boundary.
Both NASA and the ESA are hoping to send missions to Enceladus that could study its plumes in more detail. These include the Enceladus Orbitlander recommended in the Planetary Science and Astrobiology Decadal Survey 2023-2032 and the ESA’s Enceladus Moonraker, which could depart Earth in the next decade, taking advantage of a favorable alignment between the planets. In anticipation of what these missions could find, an international team of researchers used data from the Cassini mission to establish how samples of plume material could constrain how much biomass Enceladus has within it.
Less than a year after it went to space, the James Webb Space Telescope (JWST) has already demonstrated its worth many times over. The images it has acquired of distant galaxies, nebulae, exoplanet atmospheres, and deep fields are the most detailed and sensitive ever taken. And yet, one of the most exciting aspects of its mission is just getting started: the search for evidence of life beyond Earth. This will consist of Webb using its powerful infrared instruments to look for chemical signatures associated with life and biological processes (aka. biosignatures).
The chemical signatures vary, each representing a different pathway toward the potential discovery of life. According to The Conversation’s Joanna Barstow, a planetary scientist and an Ernest Rutherford Fellow at The Open University specializing in the study of exoplanet atmospheres, there are four ways that Webb could do this. These include looking for chemicals that lifeforms depend on, chemical byproducts produced by living organisms, chemicals essential to maintaining a stable climate, and chemicals that shouldn’t coexist.
In a recent study accepted to the Monthly Notices of the Royal Astronomical Society, an international team of researchers led by Texas A&M University investigate how the James Webb Space Telescope (JWST) can detect a variety of exoplanets orbiting the nearest 15 white dwarfs to Earth using its Mid-Infrared Instrument (MIRI) Medium Resolution Spectrograph (MRS). This study holds the potential to expand our knowledge of exoplanets, their planetary compositions, and if they can support life.