The 7 ways we might first find life beyond Earth

Since humans first gazed upwards, we’ve wondered whether extraterrestrial life exists.

Although science has revealed much about our Universe, life beyond Earth remains elusive.

Deep under the sea, around hydrothermal vents, where no sunlight reaches, life still thrives on Earth. How to create life from non-life is one of the great open questions in science today, but if life can exist down here, perhaps undersea on Europa or Enceladus, there’s life, too. (Credit: NOAA Office of Ocean Exploration and Research)

These seven methods may first reveal extraterrestrial life’s existence.

One of the most intriguing, and least resource-intensive, ideas for searching for life in Enceladus’ ocean is to fly a probe through the geyser-like eruption, collecting samples and analyzing them for organics. (Credit: NASA/JPL-Caltech/Space Science Institute)

1.) Direct discovery within our Solar System. Many worlds could possess simple, extant life.

Scientists are all but certain that Europa has an ocean underneath its icy surface, but they do not know how thick this ice might be. This artist concept illustrates two possible cut-away views through Europa’s ice shell. In both, heat escapes, possibly volcanically, from Europa’s rocky mantle and is carried upward by buoyant oceanic currents, but the details will be different and will lead to different observable signatures for the instruments aboard NASA’s Clipper. Life, perhaps of Europan origin, may be down there as well. (Credit: NASA/JPL/Michael Carroll)

Atmospheric, exospheric, surface, and subsurface examination could reveal extraterrestrial life forms.

The proposed High Altitude Venus Operational Concept (HAVOC) mission could potentially find either past or present life in the upper atmosphere of Venus, where conditions are suprisingly similar to those found in the environment right at Earth’s surface. (Credit: NASA Langley)

2.) Fossilized, extinct, past life. Some worlds were more habitable long ago than today.

The “Martian blueberries” shown here are undoubtedly evidence of past water on Mars, as hematite spheres are only produced in aqueous environments. They may also be signposts of locations of past life on Mars, although the evidence for that has not yet been robustly established. (Credit: Mars Exploration Rover Mission, JPL, NASA)

Ancient remnants of previous creatures could be unearthed via direct sampling.

When an exoplanet passes in front of its parent star, a portion of that starlight will filter through the exoplanet’s atmosphere, allowing us to break up that light into its constituent wavelengths and to characterize the atomic and molecular composition of the atmospehre. If the planet is inhabited, we may reveal unique biosignatures. (Credit: NASA Ames/JPL-Caltech)

3.) Biosignatures from transit spectroscopy. Living exoplanets should contain atmospheric bio-hints.

When starlight passes through a transiting exoplanet’s atmosphere, signatures are imprinted. Depending on the wavelength and intensity of both emission and absorption features, the presence or absence of various atomic and molecular species within an exoplanet’s atmosphere can be revealed through the technique of transit spectroscopy. (Credit: ESA/David Sing/PLAnetary Transits and Oscillations of stars (PLATO) mission)

Filtered starlight could reveal those distinctive molecular signatures and abundances.

Left, an image of Earth from the DSCOVR-EPIC camera. Right, the same image degraded to a resolution of 3 x 3 pixels, similar to what researchers will see in future exoplanet observations. If we were to build a telescope capable of obtaining ~60-70 micro-arc-second resolution, we’d be able to image an Earth-like planet at this level at the distance of Alpha Centauri. (Credit: NOAA/NASA/Stephen Kane)

4.) Direct imaging reveals inhabited exoplanets. We’ll soon be capable of directly imaging terrestrial exoplanets.

If the light from a parent star can be obscured, such as with a coronagraph or a starshade, the terrestrial planets within its habitable zone could potentially be directly imaged, allowing searches for numerous potential biosignatures. Our ability to directly image exoplanets is presently limited to giant exoplanets at great distances from bright stars. (Credit: J. Wang (UC Berkeley) & C. Marois (Herzberg Astrophysics), NExSS (NASA), Keck Obs.)

Seasonally, changes in an exoplanet’s appearance could indicate life’s presence and ubiquity.

The Earth at night emits electromagnetic signals, but it would take a telescope of incredible resolution to create an image like this from light years away. Humans have become an intelligent, technologically advanced species here on Earth, but even if this signal were smeared out, it might still be detectable by next-generation direct imaging: a signal of planet modification undertaken by intelligent inhabitants. (Credit: NASA’s Earth Observatory/NOAA/DOD)

5.) Discovering technosignatures. Intelligent life can produce unnatural, unambiguously unique signatures.

Before its collapse in 2020, the Arecibo telescope was either the 1st or 2nd most powerful single-dish radio telescope on Earth for its entire life. Although Arecibo was the first telescope to see multiple fast radio bursts from the same source, they are likely not alien signatures. However, the radio remains perhaps the most powerful tool for searching for extraterrestrial intelligence. (Credit: Danielle Futselaar)

From messages to megastructures to planetary modification, we’re actively hunting these technosignatures.

Although many have fantasized about aliens visiting human civilization here on Earth, the robust evidence that such an event has occurred is nil. Instead, natural objects, such as potentially life-containing meteorite fragments, is our best hope for an “alien arrival” here on Earth. (Credit: Andrés Nieto Porras/flickr)

6.) Alien life could come to us. While intentional visitors are unlikely, serendipitous ones are possible.

This scanning electron microscope image of a fragment of the Allen Hills 84001 meteorite contains inclusions that resemble simple life found on Earth. Although this sample is thoroughly inconclusive, bombardment of Earth by extraterrestrial objects is a certainty. If they contain dormant or fossilized life, we could discover it via this method. (Credit: NASA)

Impacts and collisions send surface material spaceborne; their arrival could bring extraterrestrial stowaways.

Then-graduate student Chao He in front of the gas chamber in the Horst planetary lab at Johns Hopkins, which recreates conditions suspected to exist in the hazes of exoplanet atmospheres. By subjecting it to conditions designed to mimic those induced by ultraviolet emissions and plasma discharges, researchers work towards the emergence of organics, and life, from non-life. (Credit: Chanapa Tantibanchachai/Johns Hopkins University)

7.) Laboratory creation of life. Synthesizing life from non-life would be revolutionary.

By heating atmospheric gases thought to mimic exoplanet atmospheres to various temperatures and subjecting them to ultraviolet and plasma-based energy injections, organic molecules and oxygen can be produced. Experiments such as this are key as we work towards understanding the emergence of life from non-life. (Credit: Chao He et al., ACS Earth and Space Chemistry, 2018)

Unlocking life’s origins could universally decode its formula for arising.

All throughout the Universe, including around other solar systems, in interstellar space, and even in other galaxies, the same atoms, molecules, and physical processes are present. If life arose from non-life naturally, we should be able to recreate that process here on Earth, and discover where in the Universe it successfully occurred. (Credit: NASA/Jenny Mottar)

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.