Now how

How does kryptonite serve as Superman’s one weakness?


As everyone who is even remotely familiar with the DC comic universe knows, kryptonite is the one weakness of the otherwise indestructible Superman. Kryptonite is described as radioactive remains of Superman’s home planet of Krypton and has not only detrimental effects on Superman but on other Kryptonians as well.

As the Superman mythos developed, kryptonite was discovered to come in many different forms, each having their own unique effect on Superman. One form removes his powers and makes him human, another makes him utterly reckless, yet another gives him animalistic superpowers. It’s actually quite, um, impressive shall we say how many different forms of kryptonite exist – there’s even “periwinkle kryptonite” that makes Superman into a suave, dancing Prince Charming. The term kryptonite, though, most commonly refers to green kryptonite, the form which induces Superman’s weakness.


Kryptonite was introduced in the first volume of Superman in issue #61 back in 1949 as a way of humanizing the Man of Steel and is probably the most famous example of an Achilles’ heel since the story of Achilles himself. Nowadays, the word “kryptonite” has permeated our language so much that, similar to “Achilles’ heel,” kryptonite is universally understood as a term describing a person’s fundamental weakness.

Kryptonite’s effect on Superman varies between adaptations of the story, with some depicting Superman as merely weakened with his powers blocked and others showing him collapsing and completely unable to move. Either way, though, kryptonite gives the villain an easy advantage over Superman and if a villain understands how it works, he could strategically use its effects to defeat the man of steel.


Superman’s home planet of Krypton orbits a large red sun called Rao and is located about 50 light-years from Earth. A light-year, as defined by the International Astronomical Union is the distance that light travels in a vacuum in one year, approximately 10 trillion km or 6 trillion miles (“What is a”). In short, Krypton very very very far away from Earth.

Krypton is much larger than Earth, and so it has a much greater gravitational pull. According to the current Superman story, Kryptonians are not naturally super; they are only super on Earth due to its relatively weaker gravitational pull, ,allowing them to perform their gravity-defying feats.

At the beginning of every Superman origin story, it’s shown that baby Kal-El was sent from Krypton to Earth to escape the planet’s destruction. The reason why the planet was destroyed differs, with some saying it was the result of a war and others saying that Rao’s immense gravitational force pulled the planet apart. All scenarios, though, result in Kal-El traveling through space toward Earth while pulling fragments of Krypton, made radioactive in the explosion, along with him. This radioactive debris became what we now know as kryptonite.kryptonite-krypton

Radioactivity in general can be dangerous to all living beings, Kryptonians or otherwise. On Earth, many substances emit radiation by undergoing one of several processes. Alpha decay occurs when the nucleus of a decaying atom emits alpha particles (alpha particles are also called helium atoms, which are made of two protons and two neutrons).kryptonite-alpha

Beta decay occurs when a neutron in a decaying atom’s nucleus spontaneously becomes a proton, an electron, and an antineutrino because the neutron to proton ratio is too great for atomic stability. The atom then ejects the electron and the antineutrino, keeping the proton. The ejected electron becomes a beta particle.kryptonite-beta

Spontaneous fission occurs when an atom spontaneously splits into two atoms of two different elements, potentially ejecting neutrinos during this process.

Atoms undergoing any of these processes have extra energy that must be released. They emit this energy in gamma rays, which are essentially electromagnetic pulses. In radioactive materials, alpha and beta particles that are released cannot penetrate far into matter. Emissions of pure energy, such as gamma rays, though, can penetrate matter and can displace electrons from atoms, causing cells to mutate.

It’s never made clear how exactly kryptonite decays, but its radiation seems to behave like gamma radiation since it can penetrate objects and affect living bodies. Kryptonite’s debilitating effect on Superman is the result of its interactions with Superman’s cells.

Since Superman’s power comes from the Earth’s yellow sun, we can envision him as either a particularly handsome and muscular plant (if that’s not too weird of a mental image) or a living solar panel. Plants use the sun’s energy to turn water and carbon dioxide into oxygen and sugar, the way that Superman can use the sun’s energy to turn ordinary movements into superpowered movements.

If he functions more like a solar panel, we can think of him as being composed of solar cells (also known as photovoltaic cells) that can store energy from the sunlight and convert these storages into his superpowers. Photovoltaic cells contain semiconductors such as silicon. When light comes into contact with these semiconductors, electrons are released and an electric field forces them to flow in a particular direction, producing an electric current.kryptonite-sun

In either case, it’s understood that Superman utilizes energy from the sun at the cellular level. Kryptonite interferes with this process, but the method by which this happens is left ambiguous. The radiation from green kryptonite might interfere with and overpower the solar radiation providing Superman with his powers. Kryptonite could simply interrupt some organic process within his body the way that a plant’s photosynthetic process could be blocked. Or, if Superman functions like a solar panel, then the radiation from kryptonite displaces electrons in Superman’s cells, preventing the movement of the electrons to create energy flow (Wilson).

In each of these scenarios, Superman can no longer access the powers gained from Earth’s yellow sun, making him vulnerable and leading to his death if the kryptonite exposure is sufficient.


Although kryptonite essentially renders Superman useless, it’s a driving reason behind why Superman is such a fantastic superhero and why his character is so successful. If Superman was invincible all the time, no villain would ever stand a chance again him, and he would simply be a boring stock character that never faces any real conflicts. With kryptonite, villains are able to gain the upper hand and make the drama of Superman’s universe a worthwhile adventure.

 Written by Constance Kaita

Works Referenced 

Superman images courtesy of,, and

Images of atomic processes courtesy of Jefferson lab,

Wilson, Tracy V. “How Kryptonite Works.” 19 June 2006. Web. 02 July 2013.

“What is a light year?” 01 April 2000. Web. 02 July 2013.

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