I'm one of the 60 million people who've recently watched and fell in love with the new sci-fi movie Project Hail Mary. If you're also part of this club, you'll find this article especially intriguing — it delves into the science behind the material upon which the beloved alien Rocky's civilization is built: xenon. Xenon is an extraordinary element, shaping medicine and space exploration right here on Earth.

Formula: Xe
MW: 131.293 g/mol
Melting point: −111.75°C
Boiling point: −108.1°C
Physical properties: colourless, odourless

First isolated in 1898 by Scottish chemist William Ramsay and English chemist Morris Travers, it was the first noble gas to ever be discovered by humans [1].

But What Is a Noble Gas?

Noble gases are a family of elements containing a full outer shell of valence electrons. This makes them inert — chemically unreactive. The term noble is a deliberate analogy for this property: like aristocrats historically being above interactions with other social classes, noble gases remain apart from the chemical reactions around them.

Xenon gets its name from the Greek word xénos, meaning stranger or alien. Its name reflects its rarity — xenon is the rarest stable element on Earth, found in trace amounts in the air we breathe (less than 1 part per million) [2].

Xenon in Outer Space

Xenon's most exciting real-world role is in space propulsion. NASA's Dawn spacecraft used xenon as fuel for its ion propulsion system, enabling it to become the first craft ever to orbit two different bodies in our solar system [3].

How It Works

Neutral xenon atoms are bombarded with high-energy electrons, causing ionisation — an electron is knocked off the xenon atom, creating a positive ion. These ions are then accelerated through a series of electrodes and propelled outward at high velocity, producing the thrust force that allows the craft to move through space [4].

Why Xenon Over Other Fuels?

Xenon offers the best combination of [5]:

  • Thrust force per atom — thanks to the heaviness of xenon atoms
  • Low ionisation potential
  • High storage density — xenon is highly polarisable, meaning its atoms can be compressed together, taking up less storage space
  • Inertness — much safer on spacecrafts, to lower explosion risk

Xenon on Earth: Medicine

Xenon is used in medicine in several ways [1]:

  • Clinical imaging
  • Anaesthesia
  • Neuroprotection

As an anaesthetic, xenon inhibits glutamate from binding to N-methyl-D-aspartate (NMDA) receptors in the brain, preventing stimulation of the nervous system and inducing a state of unconsciousness. Xenon anaesthetics have a stronger analgesic (pain-relieving) effect than commonly-used nitrous oxide — by a factor of about 1.5 [1] — and they don't pose an addiction risk the way opioids and nitrous oxide do.

So Why Aren't Xenon-based Anaesthetics more widely used?

Cost. Xenon is rare and must be extracted from liquefied air, which is expensive. Until this process is further economised, we have to settle for the current common anaesthetics.

There's also emerging research showing xenon's potential as a treatment for neurological conditions including Alzheimer's disease, epilepsy, and OCD [1,6]. One clinical trial in the United States, set to complete in 2027, is evaluating xenon's efficacy in treating a type of grand mal seizure [7]. We're still uncovering xenon's potential.

If you're interested in exploring emerging xenon research, ClinicalTrials.gov is a great resource — you can browse ongoing clinical trials from around the world! Its run by the United States' National Library of Medicine.

Back to Project Hail Mary

In Project Hail Mary, xenon is just one element in Rocky's xenonite compound. Humans have yet to find a way to make xenon into a malleable building material — so faraway alien civilisations may still be ahead of us in this sector. If you're interested in exploring more of the science behind the film, check out NASA's in-depth article: The Science Behind Project Hail Mary →

References

  • [1] Bajaj, Cascella & Borger (2022) — Xenon, StatPearls Publishing: ncbi.nlm.nih.gov
  • [2] Joint Propulsion Conferences (2022) — Technological Requirements for Terraforming Mars: doi.org
  • [3] NASA — Ion Propulsion, Dawn Mission: science.nasa.gov
  • [4] David, Varghese & Nadarajan (2020) — NASA's Evolutionary Xenon Thruster (NEXT): doi.org
  • [5] Joint Propulsion Conferences (2022) — Technological Requirements for Terraforming Mars: doi.org
  • [6] Maze & Laitio (2019) — Neuroprotective Properties of Xenon, Molecular Neurobiology: doi.org
  • [7] ClinicalTrials.gov (2026) — Xenon Seizure Trial NCT05667142: clinicaltrials.gov
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