Signs of Life on Europa

On September 21, 2023, the journal Science published new findings from the James Webb Space Telescope, revealing significant amounts of carbon dioxide on the surface of Jupiter's moon Europa, often referred to as "Europa." This evidence enhances the possibility of life on Europa.

Let's delve into this discovery.

The discovery was made independently by two teams, one from Cornell University and the other from NASA, utilizing data from the Webb Telescope's infrared camera. When multiple independent research teams observe the same unknown entity and arrive at highly similar results, those results become more convincing.

In essence, both teams detected large quantities of carbon dioxide in a region on Europa named "Tara Regio."

What does this imply? The presence of carbon dioxide in the solar system isn't unusual. For example, Venus has an atmosphere more than 100 times denser than Earth's, with over 96% of it being carbon dioxide, yet Venus harbors no life. Mars has an atmosphere less than 1% as dense as Earth's, composed of over 95% carbon dioxide, and Mars also lacks life. So, why does the presence of carbon dioxide on Europa suggest potential life?

The hypothesis of life on Europa has been longstanding, and the recent discovery of carbon dioxide makes the signs of life more evident.

"Tara Regio," mentioned earlier, is geologically young. Scientists believe it could be a large fissure on Europa, with its terrain undergoing significant changes. Since the launch of the Galileo spacecraft in 1995, this area has been a focal point for astronomers. Over the last decade, astronomers have largely confirmed Europa's geological state:

Its surface is covered by a thick ice shell, about 20-30 kilometers thick; beneath the ice lies a salty liquid water ocean, around 100 kilometers deep; and below that is the rocky ocean floor, heated by undersea volcanoes.

The ice shell isn't completely impenetrable; "Tara Regio" is an example of a breach. This area is filled with serrated ridges, where there's substantial exchange between materials from the ice shell and the underground ocean.

In 2019, astronomers used the Hubble Telescope to detect sodium chloride and magnesium sulfate in Europa's ocean, specifically in this region. Without such fissures, observing materials beneath the tens of kilometers of ice would be impossible, even on Earth, let alone from hundreds of millions of kilometers away.

The carbon dioxide detected is highly associated with signs of life because it's dynamic, meaning it's newly generated. How recent? Possibly within 2-3 minutes.

For instance, images taken by the Webb Telescope within minutes show the distribution of carbon dioxide in this region changing visibly.

Given Europa's surface temperature can drop to -170 degrees Celsius, any emitted carbon dioxide gas would instantly freeze into dry ice. Significant changes within minutes suggest the carbon dioxide was just ejected with underground seawater.

Of course, this evidence doesn't definitively prove the existence of life on Europa. It could be the result of carbonate reactions with acid or carbon dioxide previously dissolved in water escaping due to drastic changes in temperature and pressure, unrelated to life. However, if there were life in the underground ocean, its respiration process would produce carbon dioxide, which could also emerge. Hence, the possibility of life exists.

Should such life exist, Europa's under-ice ocean world might resemble Earth's deep-sea hydrothermal vents: life thrives without sunlight, with chemosynthetic bacteria replacing green plants, deriving energy from dissolved minerals for sustenance.

Regarding how thick the ice is and whether life exists beneath, several plans are underway to determine more:

First is the "JUICE" (Jupiter Icy Moons Explorer) mission, which left Earth for Jupiter in April 2023. However, Jupiter is far, and JUICE will need to use Earth and Venus's gravity for four "gravity assist" maneuvers, arriving by July 2031. Hopefully, Science Reference will still accompany us to witness potential life in the solar system by then.

Upon reaching Jupiter, JUICE will orbit for three years, closely passing Europa twice, Ganymede 12 times, and Callisto 21 times, eventually attempting to orbit Ganymede to observe it closely at 500 kilometers altitude. When flying by these moons, the resolution could reach an astonishing 2.4 meters per pixel, compared to the 200 kilometers per pixel resolution when observing Europa with the Webb Telescope.

Although the JUICE mission primarily targets Ganymede and Callisto, with Europa being a secondary objective, there's also a specific observation plan for Europa, the "Europa Clipper," launching in October 2024. Though it departs later than JUICE, it will reach Jupiter's orbit by April 2030, focusing on Europa's ice shell, ocean, geology, and habitability for at least eight years, scouting potential landing sites for future missions.

Two parts of the Europa Clipper mission are yet to be finalized:

The first is considering making it a mother-daughter mission—where the main spacecraft orbits Jupiter, and a smaller, 250-kilogram satellite enters Europa's orbit with observation equipment and fuel, focusing specifically on "Tara Regio."

The article published in Science magazine reveals that the NASA team aims to observe "plumes" in this area. Plumes are another prediction about Europa's geological condition. This observation could settle academic disputes about Europa's geological state.

While we introduced the "Tara Regio" area as having fissures, there's academic opposition to this claim. They argue that with surface temperatures ranging from -163 to -223 degrees Celsius and an ice thickness of 10-30 kilometers, fissures are improbable. What's perceived as fissures might just be illusions from blurry images taken billions of kilometers away, with Europa's surface more likely being a tightly sealed ice shell.

Who's correct? Plumes, or streams of vapor emanating from fissures, would confirm their existence.

However, Webb Telescope's observations didn't detect plumes. Their absence doesn't negate their existence; it could mean no ejections occurred during the observation period.

Confirming their presence requires longer, closer monitoring. But Webb Telescope's observation time is scarce, requiring submission and selection of plans months in advance. The next opportunity for astronomers to focus on "Tara Regio" is uncertain.

A daughter spacecraft orbiting Europa for years could provide detailed observations, resolving debates about Europa's geological structure.

The second undecided component is a lander for surface exploration. Initially part of the plan, scientists deemed the success rate for landing on an unknown celestial body too low in 2017, deciding to separate the lander mission to allow the main mission to conduct detailed surface surveys first. A separate lander launch is planned for 2025 after finding a suitable landing site.

These ongoing missions are expected to provide key information about Jupiter's moons before 2033. More ambitious plans are in the conceptual stage, stirring the imagination further.

One such plan involves a high-impact collision, where a several-hundred-kilogram projectile crashes into Europa, with another spacecraft collecting the resulting debris and vapors. This might sound like science fiction, but humanity has undertaken similar missions, like NASA's 2005 Deep Impact mission to study the comet Tempel1's interior by crashing a copper mass into it.

The DART mission is a preventative measure against asteroid collisions with Earth, where a metal projectile would be launched to nudge the asteroid's orbit away from Earth. In September 2022, a 600-kilogram copper projectile successfully hit an asteroid 11 million kilometers away.

Targets for these missions are much smaller than Europa's "Tara Regio," making a collision not as far-fetched as it might seem.

An upgraded "impact plan" involves a "thermal drill" powered by nuclear energy to melt through Europa's ice until reaching the underground ocean. Upon contact, a submersible device would collect materials and send information back to Earth.

With telescopes like Kepler identifying over 5,000 exoplanets, even the best candidates are tens of light-years away—distances humanity cannot bridge. Discovering a habitable zone within our solar system, reachable within years, could shift our focus from Mars.

That's all for today. See you tomorrow.