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The Question

(Submitted April 08, 1997)

What are some substances not found on earth but are found on other planets, or comets?

The Answer

There are two basic answers to your question:

If you are asking about Elements or Isotopes that are found in space, but not found naturally on Earth, there are many: In the center of stars and after supernova explosions many isotopes and elements are created. Some of these are radioactive, which means that they are unstable and will turn into other elements over time. Now, all the material that made the Earth and solar system (except hydrogen and helium) was created in stars and supernovae. However, that was a long time ago, so the radioactive elements have mostly already turned into stable elements.

When we observe supernovae, we see the signature of these elements decaying. So, we know they exist out there -- but not here.

Now, if you are asking about chemical compounds in our solar system that are found on other planets but not here, that is another question. Some substances are abundant on some planets but scarce on others. For example, water is abundant on Earth, but scarce on most other planets.

Your question, on the other hand, is about stuff that does not exist naturally here at all, but does exist naturally off of earth. To answer this, I asked a colleague here at NASA/Goddard Space Flight Center who is a chemist (Dr. Susan Hallenbeck).

She writes:

"Some gases exist in the hydrogen rich environments of the gas giants (Jupiter, Saturn, Uranus and Neptune) such as silane (SiH4), arsine (AsH3), and phosphine (PH3) which do not occur naturally on Earth but can be easily produced in the laboratory."

"Also, there are some highly oxidized compounds in the top layers of the Martian soil, which again do not occur naturally on Earth but can be easily produced in the laboratory."

Thank you for your interest.

Jonathan Keohane
-- for Imagine the Universe!

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