Alien life could be found on a rocky planet 11 light years away, a new study which analysed the chemical composition of its host star for the first time suggests.
An exoplanet called Ross 128 b, which could be the closest ever located to Earth that can host life, hit the headlines after it was discovered last November.
Understanding which elements are present in a star and in what quantities can help researchers work out the makeup of the exoplanets that orbit them.
This can help them predict how similar the planets are to the Earth and, therefore, how likely they are to have liquid water and other precursor chemicals to life.
Experts measured light coming from the star, Ross 128, and how it interacted with the planet to make their determination.
Researchers from Brazil’s National Observatory used the Sloan Digital Sky Survey’s Apogee spectroscopic instrument at Apache Point Observatory in New Mexico to make the finding.
The team measured the star’s near-infrared light to work out how abundant carbon, oxygen, magnesium, aluminium, potassium, calcium, titanium, and iron are in the star system.
When stars are young, they are surrounded by a disk of rotating gas and dust from which rocky planets can form.
The star’s chemistry can influence the contents of the disk, as well as the resulting planet’s mineral content and interior structure.
For example, the amount of magnesium, iron, and silicon in a planet will control the mass ratio of its internal core and mantle layers.
The team determined that Ross 128 has iron levels similar to our sun.
Although they were not able to measure its abundance of silicon, the ratio of iron to magnesium in the star suggests that the core of its planet, Ross 128 b, should be larger than Earth’s.
‘Until recently, it was difficult to obtain detailed chemical abundances for this kind of star,’ said lead author Diogo Souto.
‘It’s exciting what we can learn about another planet by determining what the light from its host star tells us about the system’s chemistry
‘Although Ross 128 b is not Earth’s twin, and there is still much we don’t know about its potential geologic activity, we were able to strengthen the argument that it’s a temperate planet that could potentially have liquid water on its surface.’
Because they knew Ross 128 b’s minimum mass, and the chemicals it absorbed from its star, the team was also able to estimate a range for the planet’s radius.
This is not possible to measure directly due to the way the planet’s orbit is oriented around the star.
Knowing a planet’s mass and radius is important to understanding what it’s made of, because these two measurements can be used to calculate its bulk density.
What’s more, when quantifying planets in this way, astronomers have realised that planets with a radius greater than about 1.7 times Earth’s are likely surrounded by a gassy envelope, like Neptune,
Those with a smaller radius are likely to be more-rocky, as is our own home planet. The estimated radius of Ross 128 b indicates that it should be rocky.
Lastly, by measuring the temperature of Ross 128 and estimating the radius of the planet the team was able to determine how much of the host star’s light should be reflecting off the surface of Ross 128 b.
This revealed that our second-closest rocky neighbour likely has a temperate climate.
The newly discovered world, named Ross 128b, was found orbiting a red dwarf star 11 light-years away from Earth last November.
With current technology, it would take us around 141,000 years to reach the planet.
Although it is currently 11 light-years from Earth, the planet is moving towards us, and is expected to become our nearest stellar neighbour in ‘just’ 79,000 years – a blink of the eye in cosmic terms.
Astronomers working with the European Southern Observatory’s High Accuracy Radial velocity Planet Searcher (HARPS) at the La Silla Observatory in Chile found that the red dwarf star Ross 128 is orbited by a low-mass ‘exoplanet’ every 9.9 days.
The star was named after the Californian astronomer Frank Elmore Ross who discovered it.
The Earth-sized world is expected to be temperate, with a surface temperature that may also be close to that of the Earth.
Ross 128 is the ‘quietest’ nearby star to host such a temperate exoplanet.
Study co-author Dr Nicola Astudillo-Defru, of the University of Geneva in Switzerland, said at the time: ‘This discovery is based on more than a decade of HARPS intensive monitoring together with state-of-the-art data reduction and analysis techniques.
‘Only HARPS has demonstrated such a precision and it remains the best planet hunter of its kind, 15 years after it began operations.’
Red dwarfs are some of the coolest, faintest – and most common – stars in the universe.
These qualities make them very good targets in the search for exoplanets and so they are increasingly being studied.
Many red dwarf stars, including Proxima Centauri, are subject to flares that occasionally bathe their orbiting planets in deadly ultraviolet and X-ray radiation.
Ross 128 is a much quieter star, and so its planets may be the ‘closest known comfortable abode for possible life’, researchers said at the time.
Although it is currently 11 light-years from Earth, Ross 128 is moving towards us and is expected to become our nearest stellar neighbour in ‘just’ 79,000 years – a blink of the eye in cosmic terms.
Ross 128b will by then take the crown from Proxima b and become the closest exoplanet to Earth.
With the data from HARPS, the team found that Ross 128b orbits 20 times closer than the Earth orbits the sun.
This places it in what astronomers call the ‘Goldilock’s zone’ – getting enough sunshine to be ‘not too hot’ and ‘not too cold’, which would help it support life.
But, despite the proximity, Ross 128b receives only 1.38 times more irradiation than the Earth.
As a result, Ross 128 b’s equilibrium temperature is estimated to lie between -60 and 20°C (-76° to 68°F), thanks to the cool and faint nature of its small red dwarf host star, which has just over half the surface temperature of the sun.
The whole planet is also though to be bathed in an eerie red light, experts said, as it is orbiting a red dwarf star.
While the scientists involved in the discovery consider Ross 128b to be a temperate planet, uncertainty remains as to whether the planet lies inside, outside, or on the cusp of the habitable zone, where liquid water may exist on a planet’s surface.
Astronomers are now detecting more temperate exoplanets, and the next stage will be to study their atmospheres, composition and chemistry in more detail.
Vitally, the detection of biomarkers such as oxygen in the very closest exoplanet atmospheres will be a huge next step, which ESO’s Extremely Large Telescope (ELT) is in prime position to take.