- The planet, named Proxima b, orbits our closest star, Proxima Centauri
- It is around 1.3 times the size of Earth
- New study simulated water on the planet
- Concluded it 'very well host liquid water on its surface, and therefore also some forms of life'
- Hoped we could send a robotic explorer to the planet
A team including CNRS astrophysicists have calculated the size and surface properties of the planet dubbed Proxima b, and concluded it may be an 'ocean planet' similar to Earth.
Scientists announced Proxima b's discovery in August, and said it may be the first exoplanet—planet outside our Solar System—to one day be visited by robots from Earth.
The planet orbits within a 'temperate' zone from its host star Proxima Centauri, some four light years from us.
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An artist's impression of a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. A team including CNRS astrophysicists have calculated the size and surface properties of the planet dubbed Proxima b, and concluded it may be an 'ocean planet' similar to Earth.
It is estimated to have a mass about 1.3 times that of Earth, and orbits about 7.5 million kilometres (4.6 million miles) from its star—about a tenth the distance of innermost planet Mercury from the Sun.
'Contrary to what one might expect, such proximity does not necessarily mean that Proxima b's surface is too hot' for water to exist in liquid form, said a CNRS statement.
Proxima Centauri is smaller and 1,000 times weaker than our Sun, which means Proxima b is at exactly the right distance for conditions to be potentially habitable.
Proxima Centauri is smaller and 1,000 times weaker than our Sun, which means Proxima b is at exactly the right distance for conditions to be potentially habitable.
'The planet may very well host liquid water on its surface, and therefore also some forms of life,' the statement said.
In a study to be published in The Astrophysical Journal Letters, an international team led by researchers at the Marseille Astrophysics Laboratory (CNRS / Aix-Marseille Université) has determined its dimensions.
The size of exoplanets are generally calculated by measuring how much light they block out, from Earth's perspective, when they pass in front of their host star.
But no such transit of Proxima b has yet been observed, so the team had to rely on simulations to estimate the planet's composition and radius.
What Proxima b xould look like: From left to right: Proxima b with the smallest attainable radius (65% metallic core surrounded by a rocky mantle separated into two phases), Earth (ditto with 32.5% core) and b with the Proxima maximum authorized range (50% of rocky mantle surrounded by a layer of water in solid and liquid form).
They calculated the radius was between 0.94 and 1.4 times that of Earth, which is 6,371 kilometres on average.
Assuming a minimum radius of 5,990 km, the planet would be very dense, with a metallic core making up two-thirds of the entire planet's mass, surrounded by a rocky mantle.
If there is surface water, it would not contribute more than 0.05 percent to the planet's total mass, the team said—similar to Earth, where it is about 0.02 percent.
In the larger planet scenario, with a radius of 8,920 km, Proxima b's mass would be split 50-50 between a rocky centre and surrounding water.
'In this case, Proxima b would be covered by a single, liquid ocean 200 km deep,' said the CNRS.
'In both cases, a thin, gassy atmosphere could surround the planet, like on Earth, rendering Proxima b potentially habitable,' it concluded.
Earlier this year, a group of researchers, using the European Southern Observatory (ESO) telescopes, have named the exciting world Proxima b.
Thousands of exoplanets have been discovered before, but unlike the others, this planet is within our reach.
While four light years is a long way - more than 25 trillion miles - future generations of super-fast space craft could conceivably travel to the planet within the next few decades.
If there is surface water, it would not contribute more than 0.05 percent to the planet's total mass, the team said—similar to Earth, where it is about 0.02 percent.
A comparison of several exoplanets. Curves correspond to specific compositions used in the model of internal structure. The existing area of Proxima b is drawn in gray and takes into account the uncertainty of its mass and its different possible compositions.
Much further in the future the planet may even be colonised by space travellers from Earth.
One possible obstacle to life evolving and flourishing on the planet is the way it hugs its parent star.
Proxima b is only 4.6 million miles (7.5 million km) from the star, 5 per cent of the distance between the Earth and the sun, and takes just 11.2 days to complete one orbit. It is around 1.3 times as massive as Earth.
But because Proxima Centauri is a dim red dwarf star radiating much less heat than the sun, it still occupies the 'habitable zone' where temperatures are mild enough to permit liquid surface water.
The temperature on the surface of the planet could be between -90° and 30° Celsius (-130 and 86 Fahrenheit).
On the other hand, the planet is blasted by powerful ultraviolet rays and X-rays from the star. Any life that evolved on its surface would have to be hardened against the radiation.
But the prospect of finding life on Proxima b has excited scientists.
'Many exoplanets have been found and many more will be found, but searching for the closest potential Earth-analogue and succeeding has been the experience of a lifetime for all of us,' Dr Guillem Anglada-Escudé, lead author of the paper, said.
'Many people's stories and efforts have converged on this discovery. The result is also a tribute to all of them. The search for life on Proxima b comes next.'
Two separate papers were published , describing the habitability of Proxima b and its climate.
The papers find the existence of liquid water on the planet today 'cannot be ruled out'.
This means water may be present over the surface of the planet. But it would only be in the sunniest regions, either in an area in the hemisphere of the planet facing the star.
The way Proxima b rotates, strong radiation from its star and the formation history of the planet makes its climate quite different from that of the Earth.
It is unlikely that Proxima b has seasons. But if liquid water does exist on the planet, it could mean alien life might thrive there.
If this is the case, we could discover it within decades, experts have said.
Artist's impression of an Earth-like exoplanet. The still nameless planet is believed to be Earth-like and orbits at a distance to Proxima Centauri that could allow it to have liquid water on its surface - an important requirement for the emergence of life
A team called Pale Red Dot is behind the discovery, which includes researchers from the University of Hertfordshire, Queen Mary University of London, the Instituto de Astrofísica de Andalucía in Granada, Spain and the University of Göttingen in Germany, among others.
The researchers used the High Accuracy Radial velocity Planet Searcher (HARPS), an instrument on the European Southern Observatory's 3.6-metre La Silla telescope in Chile's Atacama Desert.
The telescope measured light from Proxima, the fingerprints that reveal what the star is made of.
Small shifts in the frequency of the starlight can be used to work out tiny movements of the star in response to an orbiting planet's gravitational pull.
'The first hints of a possible planet were spotted back in 2013, but the detection was not convincing,' said Dr Anglada-Escudé.
'Since then we have worked hard to get further observations off the ground with help from ESO and others. The recent Pale Red Dot campaign has been about two years in the planning.'
The Pale Red Dot data, when combined with earlier observations made at ESO observatories and elsewhere, revealed the clear signal of an exciting result.
At times Proxima Centauri is approaching Earth at about 3 miles (5km) per hour and at times it is receding at the same speed.
This pattern of changing velocities repeats with a period of 11.2 days, meaning that is how long it takes to orbit its sun.
The orbit of the planet around Proxima Centauri (Proxima b) with the same region of the Solar System.
Careful analysis of the tiny light shifts showed the planet has a mass at least 1.3 times that of the Earth, orbiting about 4.3 million miles (7 million kilometres) from Proxima Centauri.
Some questions about whether life could exist are left unanswered, however.
'If Proxima b has an atmosphere and if there is water there, and these are big 'ifs', it is intriguing to think that the simple ingredients - water, carbon dioxide, and rock - that are needed for the formation of biochemical cycles that we call life, could all be present and interacting on the planet's surface,' said Dr Mikko Tuomi, from the Centre for Astrophysical Research at the University of Hertfordshire.
'But we do not really know. We need to study this system a lot more over the coming decades in order to be able to start answering such questions.
'However, it is a great place to start looking for life outside the solar system and it is a very exciting discovery.'
'It certainly seems possible that we could find something out of this world within our lifetime,' said Martin Archer, Space Plasma Physicist, Queen Mary University of London, writing for The Conversation.
At least some additional information about the environmental conditions on Proxima Centauri b should come sooner rather than later, the researchers say.
Now that the planet has been detected, there is an opportunity for follow-up observations.
A possible detection of life, or at least of conditions suggestive of the presence of life, is likely to be decades off
But these observations provide opportunities to learn about a planet around the most common type of star in our galaxy – with lessons that are interesting in their own right, for astronomers seeking a systematic understanding of planet formation in our home galaxy.
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