ALIENS could be living in one of four ‘cradles of life’ outside our solar system
thanks to Mirror
The four most likely cradles of life outside our solar system have been identified by scientists.
They contain so-called ‘K’ stars, whose planets may have just the right atmospheres to be harbouring aliens.
K stars are dimmer than our Sun, but brighter than the faintest stars, known as ‘M’ stars’ or red dwarfs.
“I like to think that K stars are in a ‘sweet spot’ between Sun-like stars and M stars,” said planetary scientist Dr. Giada Arney, of NASA’s Goddard Space Flight Centre.
This dramatically narrows down the number of worlds that maybe habitable, according to astronomers.
The search for extraterrestrials faces major challenges – one of which is there are hundreds of billions of stars in our galaxy alone. Scientists can’t investigate them all.
Dr. Arney and colleagues believe K stars are the most promising candidates to be orbited by planets that have the essential ingredients for organisms – either primitive or advanced.
Firstly, they live a very long time – 17 to 70 billion years, compared to 10 billion years for the Sun. This would enable plenty of time for life to evolve.
They also have less extreme activity in their youth than M stars – which also happen to be the most common in the universe, making up three-quarters of them.
One M star, named TRAPPIST-1, is known to host seven Earth-size rocky planets. But their turbulent development presents problems – despite shining for up to a trillion years.
Stellar flares – explosive releases of magnetic energy – are much more frequent and energetic from young M stars than young Sun-like stars.
M stars are also much brighter when they are young, for up to a billion years after they form, with energy that could boil off oceans on any planets that might someday be in the habitable zone.
The study published in Astrophysical Journal Letters said ‘biosignatures’, or signs of life, on a hypothetical planet orbiting a K star would include oxygen and methane.
The gases like to react with each other in an atmosphere implying something is producing them quickly – quite possibly life.
A computer model simulating the chemistry and temperature of a planetary atmosphere showed these are likely to be richest around a K star.
Dr. Arney said: “When you put the planet around a K star, the oxygen does not destroy the methane as rapidly, so more of it can build up in the atmosphere.
“This is because the K star’s ultraviolet light does not generate highly reactive oxygen gases that destroy methane as readily as a Sun-like star.”
This stronger signal has also been predicted for planets around M stars. But their high activity levels might make them unable to host habitable worlds.
K stars can offer the advantage of a higher probability of simultaneous oxygen-methane detection – without the disadvantages that come along with an M star host.
Additionally, exoplanets around K stars will be easier to see than those around Sun-like stars – simply because K stars are dimmer.
Explained Dr. Arney: “The Sun is 10 billion times brighter than an Earthlike planet around it.
“So that is a lot of light you have to suppress if you want to see an orbiting planet. A K star might be ‘only’ a billion times brighter than an Earth around it.”
Her research also suggests nearby K stars that may be the best targets for future observations.
We don’t have the ability to travel to planets around other stars due to their enormous distances from us.
So we are limited to analysing their light to search for a signal that life might be present.
By separating this into its component colours, or spectrum, scientists can identify the constituents of a planet’s atmosphere, since different chemicals emit distinctive ones.
Dr. Arney added: “I find that certain nearby K stars like 61 Cyg A/B, Epsilon Indi, Groombridge 1618, and HD 156026 may be particularly good targets for future biosignature searches.”