Life on Earth is quite unlikely

Scientists have concluded that life is unlikely to form on planets around stars like our Sun because these stars emit high levels of x-rays and ultraviolet light early in their existence – both deadly to life as we know it.

“The Sun does not seem like the perfect star for a system where life might arise.” said Professor Edward Guinen from Villanova University in the USA, who carried out the work alongside other researchers from the USA and from the Netherlands. Guinen and colleagues suggest that smaller, cooler stars called orange dwarfs are the best places to look for life. Orange dwarfs live much longer than yellow stars like our Sun, and their “goldilocks zone” – the area of space surrounding the star in which planets are most likely to harbour life – will also last much longer, giving life a better chance of getting started.

And it doesn’t stop there. According to Guinen, “we have also found indications that planets like Earth are also not necessarily the best suited for life to thrive”. Instead, larger planets may be better suited to harbouring life because they can hold on to their atmospheres for longer due to their stronger gravity. They also have much larger iron cores, which support a more powerful magnetic field for longer, protecting the atmosphere and any developing life from harmful cosmic rays.

The researchers made their surprising discovery by looking at other stars very similar to our Sun, but which are much younger. The Sun, at 4.5 billion years old, is in a relatively calm phase of its lifecycle. In its early days, when it was less than half a billion years old, the Sun went through a wild phase, throwing out massive amounts of destructive radiation and making it very hard for life to survive.

Obviously life on Earth has survived despite the odds, but the work could alter where we look in our ongoing hunt for extraterrestrial life. There are many more orange dwarfs than there are Sun-like stars in the galaxy, so maybe it will be easier than we thought to find life out there.

Stars - they grow up so fast... Image: IAU

A 200,000 year gestation

Compared to a nine-month pregnancy, 200,000 years may seem an unbelievably long time to wait for a birth. Yet a team of Spanish and German astronomers think it will take this long for a new star to be born from the collision of two dark molecular clouds which sit 410 light years from Earth.

The happy parents – one called Barnard 68 and the other a smaller, un-named, companion – are coming together at a speed of 370 metres per second. The collision is disturbing the dust and gas of both clouds, and this will cause them to collapse to form a new solar-type star in a process expected to last 200,000 years!

The discovery will help astronomers learn more about where stars come from (and no, it doesn’t involve some sort of intergalactic stork!). Our best theories of star formation suggest that when the density of gas in a nebula reaches a critical point it collapses under its own gravity. As the temperature and pressure of the collapsing cloud rise, nuclear fusion is initiated and a new star begins to shine. The question for astronomers is what triggers this collapse?

Several possibilities have been put forward, including shockwaves from nearby supernovae, or the massive tidal forces as entire galaxies collide. The latest work suggests the impact of a second nebula is also sufficient to trigger the birth of new stars.

Hypothesis Now wishes the new parents well. It’s just a shame we won’t be around to witness what will certainly be a spectacular birth!

Barnard 68: dark nebula and expectant parent. Image credit: European Southern Observatory (ESO)