Source: BBC News | Author: Pallab Ghosh : Strongest Evidence
What’s the news?
Scientists from Cambridge University, using NASA’s James Webb Space Telescope (JWST), have found the strongest signs yet of potential life on a distant exoplanet named K2-18b, located 700 trillion miles from Earth.
Why it matters:
The planet’s atmosphere contains dimethyl sulphide (DMS) and dimethyl disulphide (DMDS)—gases that, on Earth, are only produced by living organisms like phytoplankton. This marks the second, but most promising, detection of life-associated chemicals on the same planet.
But here’s the catch:
- The signal’s certainty is currently at 3 sigma (99.7%), which is not enough to confirm a scientific discovery (5 sigma or 99.99999% is needed).
- Other experts suggest non-biological explanations are possible—like volcanic activity or the planet being a mini gas giant with no surface.
Why scientists are hopeful:
The absence of ammonia points to the possibility of a vast ocean, which would support the idea of habitability. If proven, this could imply that life is common across the galaxy.
Quote:
“This is the strongest evidence yet there is possibly life out there… we may look back and recognise it was when the living universe came within reach.”
— Prof Nikku Madhusudhan, Cambridge University
Published in: The Astrophysical Journal Letters
Here is how “sigma” is used in the context of that space discovery news:
In the news about the possible discovery of life-related molecules on the exoplanet K2-18b, “sigma” refers to a statistical confidence level—a measure of how certain scientists are that their observations are real and not just random noise or errors.
In this context:
- The researchers detected dimethyl sulphide (DMS) or dimethyl disulphide (DMDS)—molecules that, on Earth, are only produced by living organisms.
- They report a “3 sigma” confidence level for this detection.
What does that mean?
- “3 sigma” = There’s a 99.7% probability that the signal they detected is real.
- But it also means there’s a 0.3% chance the detection is due to random variation or error in the data.
Why is that not enough?
In astrophysics and particle physics, scientists typically require “5 sigma” (99.99994% certainty) to confirm a discovery. Until then, the result is considered tentative or unconfirmed.
So in short:Sigma is a statistical term representing how confident scientists are in a result. A higher sigma means greater certainty. In the K2-18b study, 3 sigma means promising signs, but more data is needed to say “yes, life might really be out there.”
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