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An artistic impression of the planet's surface orbiting Barnard's star. Credit: ESO – Mr Kornmesser
The potential discovery of a planet orbiting the Barnard star – the second star system closest to the sun – has been announced by researchers today in Nature.
This discovery pushes the boundaries of what we can do with our current best astronomical instrumentation, so the authors are naturally cautious when they claim a "candidate for the planet" rather than a confirmed discovery.
The new exoplanet (if it exists) is a glacial world of just over three times the mass of the Earth and has not been discovered as a result of extensive research by teams around the world.
So what does it mean, and why is it important?
Barnard's Star – An Ancient Cosmic Way
Shining 16 times too weakly to be observed with the naked eye, Barnard's star is a former red dwarf, much older than the sun. In addition to the Alpha Centauri system, it is the closest star to the solar system.
The greatest notoriety of Barnard & # 39; s Star lies in its speed to fall asleep in the night sky. She moves so fast against the stars in the background that she would cross the diameter of the full moon in a little over 100 years.
In the middle of the last century, astronomer Peter van de Kamp was convinced that Barnard's star was accompanied by two Jupiter mass planets. For several decades, starting in the late 1930s, he studied the star, taking a myriad of images and observing it moving over the background.
Instead of moving in a straight line, his observations suggest that Barnard's star wavered as he moved, swaying back and forth as though drawn by unseen companions. Her data invoked the presence of two planets shooting the star around her while she was moving in space.
Despite their best efforts, astronomers could not find any trace of Van de Kamp's world. Where his observations showed a flickering star, theirs did not show such an oscillation – just a linear movement through space.
What was happening? Van de Kamp's observations were made using a large refractive telescope, and astronomers finally realized that the main objective of the telescope had been cleaned up and modified several times during decades of his study. These changes caused a shift in the apparent position of the Barnard star relative to the more blue stars.
The Jupiter mass planets around the Barnard star were no longer.
Successive surveys have excluded ever smaller planets. Astronomers are now convinced that there is no planet in the system with more than ten Earth masses. Which brings us to our new discovery.
Impression of the artist Barnard's Star b under the orange light of his red dwarf host. Credit: IEEC / Science-Wave – Guillem Ramisa
The new discovery
The new candidate planet, Barnard's Star B, would have a mass between those of Earth and Neptune in the solar system. While no such planet exists in our backyard, the Kepler spacecraft has revealed that such planets are common in the cosmos.
Barnard's Star orbits its host 60 million kilometers away. This might suggest a hot, temperate world – but Barnard's star is a dark object, much less bright than the sun. As a result, Barnard's Starb is located beyond what is known as the ice line, so far from the star that the water would freeze harder than the rock. It means it must be an icy world.
But this icy orbit adds to our confidence that the planet could really be there. Planets are formed over millions of years in discs of matter surrounding young stars. Grains of dust (and ice) collide slowly, widening more and more worlds. Finally, the disk of gas and dust is washed away, leaving behind all the planets he has formed.
This predicts that the planets will form faster and develop faster, just beyond the ice line, where the presence of water ice will dramatically increase the amount of solid material available to the growing world.
In other words, the most massive planet in a given system should form just beyond the ice line. This is true in the solar system (Jupiter), and also seems true for Barnard's star – if the planet actually exists.
The future – a timely discovery
If Barnard's Star B exists, his discovery could not have come at a more opportune time. Orbiting one of the closest neighbors of the solar system, it is an ideal target for future observations.
The existence of the planet can be verified in several ways. In the near future, the answer could come from the GAIA spacecraft, which has spent the last few years measuring the precise positions and distances of some two billion stars in the night sky.
Whenever GAIA observes Barnard's star, he measures his location with a much higher accuracy than any previous observer could handle. If there is a planet orbiting the star, three times the mass of the Earth, the same technique employed by van de Kamp should reveal its presence.
Graphical representation of the relative distances from the stars closest to the sun. Credit: IEEC / Science-Wave – Guillem Ramisa
In the next decade, the next generation of astronomical observatories will revolutionize our ability to peer into the near space of the nearest stars, in search of the faint glow of their planets, reflecting the light of their host stars .
As the star of Barnard is so close, the separation between the planet and the star in the sky will be relatively large. If the planet is really present, we will probably have our first direct images confirming its existence in the next ten years.
Beyond that? Who knows. The time of the exoplanets has taught us that where one planet is hiding, others will surely follow. If the existence of Barnard's star b is confirmed, this may indicate that there are other smaller worlds orbiting this former star.
Explore further:
Astronomers discover the super-Earth around Barnard's star
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