Skip to main content
You have permission to edit this article.
Life outside our atmosphere should be evident, but it’s not

Life outside our atmosphere should be evident, but it’s not

  • Updated

Mars waxes large in our current imagination. Matt Damon provides a compelling performance as an astronaut botanist stranded on the Red Planet, in a Ridley Scott film lauded for its scientific accuracy. The future in space shines bright, it seems. But is this really so?

Shortly after the Second World War, my father assembled arguably the cheapest technological innovation leading to a multibillion dollar scientific endeavor, Gamma Ray Astronomy, locally represented on Mt. Hopkins. It involved a garbage can, a war surplus mirror, and a photomultiplier, which he used to detect the light produced by the interaction of “cosmic rays” with the earth’s atmosphere.

Cosmic rays are a puzzle. They are the remnants of atoms hurtling through the galaxy at inconceivable energies. Inconceivable is not used lightly here: The most energetic cosmic rays have energies roughly 40 million times greater than the particles we can produce in the Large Hadron Collider in Geneva. We do not know how they can be formed. And yet they exist, and they permeate the universe, continuously bathing the earth.

A major part of the magic of life on earth is associated with the atmosphere. Not only do we breathe it, but it also acts as a vital shield against cosmic rays since, when they hit the atoms in the atmosphere, their energies are converted into the harmless light that my father detected.

Why do we need protection? The most energetic cosmic rays pack a punch of a 56 mph baseball. Just as a body can be damaged by a baseball, so a cell can be damaged by a cosmic ray. How much damage can it do? Scientists have recently tested this question, exposing mice to amounts of radiation that would be experienced by astronauts during a trip to Mars which has very little atmosphere and minimal protection from cosmic rays. Extensive destruction of the brains of these mice was seen, with drastic deterioration in cognitive tests.

Our astronauts have already described interactions with cosmic rays during brief trips to the moon, reporting random flashes of light, a consequence of the explosive interaction of a cosmic ray with the cells in the retina. During the much longer trip to Mars, and the establishment of a permanent colony there, the brains of the astronauts would experience lethal levels of cosmic radiation.

Enrico Fermi, Nobel Laureate and the first to harness nuclear fission for energy generation, famously posited his paradox, asking “Where are they all?” His point is that the sun is just one of many billions of similar stars in the Milky Way galaxy, and that many of these stars are older. These stars should have many earth-like planets, and many of these planets should have developed civilizations more advanced than ours. They should already have populated the galaxy through space travel, and the evidence for aliens should be out there. But it is not.

Many reasons are suggested to explain this paradox, including that we are unique, that intelligent life always destroys itself, or is destroyed by natural cataclysms, that the parameters of distance and time are incompatible with communication across the universe, that we live in a simulation or an otherwise incomprehensible reality.

An alternative, and very simple explanation of Fermi’s paradox, is that the universe is a sterilizing system: cosmic rays prevent access of living organisms, alien or human, to our immediate space neighborhood and beyond. Accepting and coming to terms with this disturbing concept will have far-reaching consequences, both practical, political, philosophical, and, perhaps, theological. The only things that remain shining, as we keep looking up, are the inaccessible stars, and my father’s ironic gift, the faint Cerenkov radiation in the night sky formed by cosmic rays.

David Galbraith is professor of plant sciences and in the BIO5 Institute at the University of Arizona. He was educated at Cambridge University and was a NATO postdoctoral research associate at Stanford University. He is a fellow of the American Association for Advancement of Science, and is internationally recognized for his contributions in biological instrumentation. Email:

Subscribe to stay connected to Tucson. A subscription helps you access more of the local stories that keep you connected to the community.

Catch the latest in Opinion

* I understand and agree that registration on or use of this site constitutes agreement to its user agreement and privacy policy.

Related to this story

Get up-to-the-minute news sent straight to your device.


News Alerts

Breaking News