Astronomers have seen at least 45 planets orbiting distant stars that possess Earth-like properties including a similar atmosphere and life-sustaining liquid water.
Experts from Luleå University of Technology, Sweden, have created a new way to determine the habitat of distant worlds by studying their environment.
The team found a way to use information on ‘atmospheric species’, that is, chemicals in the atmosphere, and how quickly they can escape into space to determine how close an exoplanet is in terms of temperature and composition to Earth.
They then used their new model in 55 potential residential worlds listed in the existing exoplanet catalog ̵1; dedicated to custom zone and star host.
Only 17 of the 55 planets in the catalog met the standard defined by Swedish researchers for being ‘Earth-like’ but the team found another 28 planets in the wider exoplanet list that also met standard – brings the whole world like Earth to 45.
The TRAPPIST-1 system contains one planet in the new list of 45 worldly potential worlds – in this system it is known as TRAPPIST-1 d – the fourth star
This graphic shows the list of all potential Earth-like worlds identified by the Swedish team. The planets with blue are already on the Exoplanet Catalog list of habitable worlds
Advanced ground and space based missions including the current CHEOPS and future James Webb telescopes can now use this research to focus their searches.
Discovering living exoplanets is a difficult challenge because we cannot ‘send an investigation’ the vast distances between the stars, the team explained.
The nearest exoplanet with a potentially accessible environment is Proxima b around the star Proxima Centauri 4.22 light-year – or 25 trillion miles away.
NASA’s Juno investigation reached a speed of 165,000 miles per hour as it approached Jupiter – at those speeds it would take 17,157 years to reach Proxima b.
This is an impression of the Kepler-1649 c artists revolving around this host star. It is a planet on the list of potential worlds like Earth that are not yet on the habitat list that can be used by the exoplanet catalog
Currently, determining the ability of an exoplanet to host life depends on the restricted low-resolution spatial and spectral information of their atmospheres.
To create a ‘short list’ of aging worlds, the team used the ‘theological theory of gases’ – how gases move about the atmosphere – and a list of possible chemicals preserved in current atmospheres well-known exoplanets.
“We have concluded that, based on our current knowledge of detected exoplanets, 45 of these are good candidates for residential studies,” the authors write.
‘These exoplanets can have Earth-like atmospheres and must maintain solid liquid water.’
As part of the study the team used the planetary environment in our own solar system – where we know true makeup – as a reference base.
They then listed exoplanets with hydrogen, oxygen, dinitrogen and carbon dioxide atmospheres in their list of candidates like Earth.
We also propose a conservative list of 45 exoplanets with favorable conditions such as temperature and the ability to retain vital life-related gases in their atmospheres for further habitual studies, ‘wrote the group.
The team also recommends that the current definition of a habitable area around a star be revisited when considering whether a planet can host life.
Ross 128 b is a terrestrial Earth-mass planet 11 light-years away. Swedish researchers say it does not exist in the exoplanet catalog availability but is likely to have a secular environment
They said the planet’s ability to host an Earth-like environment to support liquid water stability should be added to the necessary conditions for habitat.
‘The discrimination of gas-based exoplanets [chemicals] that they can keep in their atmosphere will help to determine the most possible candidates for potential accommodation, ‘the team explained.
These future missions may look ‘for further studies in atmospheric composition and for photochemical models.’
One of the major developments made by the Swedish team was the reduction in the amount of information needed to assess the habitat of a distant world.
‘We present an aerial model capable of estimating the corresponding composition of atmospheric exoplanets using easily available or estimated parameters and with minimal assumptions,’ they wrote.
Star of Teegarden b and c. Two planets orbiting an ultracool red dwarf 13 light-years away. The planet is on the same list of exoplanet-like Earth
‘Our model is designed for low-mass, low-irradiated exoplanets. These exoplanets have an evolutionary atmosphere driven by classical thermal escape, ‘the team added.
The researchers said that data from future observations, including actual temperature profiles, albedo and elemental abundance could help them further refine their own model and become better at painting picture of their true environment.
The team plans to continue updating their list of potential world-class worlds by studying new exoplanets as they discover.
The study was published in the journal Proiding of the Royal Society A.
Scientists study the environment of distant exoplanets using massive satellite spaces such as Hubble
Distant stars and their rotating plans often have conditions unlike anything we see around us.
To understand new worlds, and what they are made of, scientists need to see what their atmospheres are made of.
They usually do this by using a telescope similar to Nasa’s Hubble Telescope.
These massive satellites scan the sky and are locked into exoplanets that Nasa thinks might be of interest.
Here, on-board sensors perform various forms of analysis.
One of the most important and useful is called absorption spectroscopy.
This form of analysis measures the light that emits into the atmosphere of a planet.
Each gas absorbs a slightly different wavelength of light, and when this happens a black line appears in a complete spectrum.
These lines correspond to a very specific molecule, indicating its existence on the planet.
They are often called the Fraunhofer lines after the German astronomers and physicists who first discovered them in 1814.
By combining all the different wavelengths of light, scientists can identify all the chemicals that make up the atmosphere of a planet.
The key is what is missing, giving clues to find out what is there.
It is very important that telescopes do this in space, because it will interfere with the Earth’s atmosphere.
Absorption from chemicals in our environment can change the sample, so it is important to study the light before there is a chance to reach Earth.
It is often used to find helium, sodium and even oxygen in alien atmospheres.
This diagram shows how light passing through a star and in the atmosphere of an exoplanet produces Fraunhofer lines indicating the presence of key compounds such as sodium or helium