Frozen super-earths in the orbit of Barnard’s star: what hides our “neighbor”?

Every night, touching the stars, astronomers closer to see how populated our universe — or at least our galaxy. After a quarter-century after orbiting other stars were discovered the first exoplanets, statistical data showed that, on average, every star in the milky Way must be at least one planet side. If long enough, and staring in the neighborhood of each individual stars in our galaxy, sooner or later are almost guaranteed to find something.

But even crowded universe can be a lonely place. Our rich planets of the milky Way may be completely lifeless. Of all known worlds in the galaxy, only a handful of planets similar to Earth in size and position on the orbit — that is, are in a conditional isepisode “Goldilocks zone”. Such a peace must be not too big, not too small, not too hot and not too cold, to maintain the state of liquid water and life on its surface. Instead, most of the planets in the milky Way do not conform to any notion of viable: this is “super-earths” that are bigger than our planet, but smaller than Neptune. No supertall, which swirled around our Sun, and which could be explored directly, there is, therefore, to find out how they behave near other stars is very difficult. Anyway, to drive fitness for life in some narrow bounds, given how little we know, seems very naive.

The Goldilocks Zone

Trying to cope with these mysteries of astrobiology, scientists dream of new generations of telescopes and spacecraft to find and learn the signs of zhizneobitanija and possible life beyond our Solar system.

But the evidence refuting the lonely but crowded universe can be at arm’s length, in the language of the stars. In 2016, studies have shown that a planet the size of Earth, is very close, at a reasonable orbit near the small member of the family of the alpha Centauri system of three stars is about 4.4 light-years from our Sun. Moreover, another tiring search of the nearest neighbor to our Solar system, Barnard’s star, some six light years from us, has revealed a suitable planet and there. It’s a big, cold super-earths, called Barnard’s Star b (Barnard”s Star b).

An international team of more than 60 astronomers using observatories around the world, elaborated in detail the detection of a planet in the Nature issue of 14 November (we briefly mentioned this discovery). All this opens the door to future studies and comparisons of two such friends, and at the same time alien planets in the near Solar system.

Frozen super-earths

“If you live in a city with a million people, you do not need to meet every one of them — but you might want to meet with their immediate neighbours,” says the study’s lead author Ignasi Ribas, astronomer of the Institute of space studies of Catalonia in Spain. “That’s what we’re doing with planetary systems, the stars that surround us. Otherwise, we would not be able to answer the big questions. As our Solar system and our Earth correspond to the rest of the galaxy? Are there other inhabited or uninhabited planets? Barnard’s star b does not give us while the answers to these questions, but tells us of the story we would like to know.”

Located in the constellation Ophiuchus, Barnard’s star so faint in visible light that cannot be seen with the naked eye. However, it has been a favorite of astronomers since 1916, when measurements showed that its apparent movement across the sky was bigger than any other star relative to our Sun — this indicated that it is extremely close in space. The proximity of the star to us is only temporary — through tens of thousands of years its trajectory would lead it from the list closest to our Solar system of stars.

According to Ribas and his colleagues, the planet-candidate at least three times heavier than ours and is rotated to the 233-day orbit around its star. In our system it would be within the orbit of Venus, but Barnard’s star relative to our small and dim, red dwarf star. This means that her companion is near the “snow line” beyond which water will almost certainly be in the form of frozen ice. This area is near the stars are believed to be jam-Packed planets, but this has yet to know for sure.

Barnard’s star b needs to obtain 2% of the stellar light that the Earth receives from the Sun — it is enough that the surface temperature was -150 Celsius. Perhaps, suggests Ribas, the planet is solid and covered with a thick layer of ice, its surface resembles the surface of frozen moons of Jupiter and Saturn. The prospects of life on such a world would be very remote — unless, of course, it will not have a subsurface ocean, maintained in the liquid state the internal heat. In this case, the bowels should stay warm for a very long time — the age of the planet should be somewhere between six and eleven billion years old. For comparison, the age of the Earth is four and a half billion years.

Alternatively, the planet may be covered with a thick insulating blanket of the remaining hydrogen after the birth in a rotating disk of gas and dust around the star. Although the hydrogen into smaller and hot worlds should dissipate into space, the cold super-earths in orbits can hold it long enough for the gas launched a massive greenhouse effect, warming the planet. If this mechanism will be launched at Barnard’s Star b, or other cold supersense, “our dream that each star may have habitable planet can be,” said Sara Seager, hunter planet of the Massachusetts Institute of technology, was not involved in the study of Ribas. “Somewhere there may be a completely insane worlds.”

In the footsteps of history

Some worlds, alas, too good to be true. In 1963, Dutch astronomer Peter van de Kamp “discovered” the planet near Barnard’s Star — bound estimated shifts in the movement of stars in the plane of the sky to the gravitational influence of unseen planets. But by the 1970s, evidence of the existence of the planets van de Kamp has evaporated, they are blamed on various errors and omissions in the observations. The faith van de Kamp in their beliefs were unwavering; he continued to believe in the existence of planets throughout his life.

This cautionary tale pursues, and contemporary hunters of the planet. Despite the fact that the modern confirmation world around Barnard’s Star is much more confident than at the time, scientists do not hurry with the statements.

Some experts still are not sure about the discovery of the planet. “As the planets are everywhere, I guess, and near the Barnard’s Star they should be,” says Debra Fischer, an astronomer and well-known hunter of planets from Yale University. “Maybe even one with a few Earth masses, and rotation period of 233 days. But this analysis does not give strong enough confidence, in my opinion”.

On the contrary, Xavier Damascus, an astrophysicist at Geneva Observatory in Switzerland, was also not associated with the study of Ribas finds evidence that Barnard’s Star b quite convincing. “From the point of view of the probability of the existence of this planet, I think no doubt can not be. The signal is very clear”.

The case of Barnard’s Star b represents an incredible feat in the collection and analysis of data collected during hundreds of measurements on seven world-class instruments on large ground-based telescopes for over 20 years. Each measurement monitors the radial acceleration of Barnard’s Star is its motion toward the Earth or away from it, which may vary if the star is the gravitational influence of planets nearby. The signal attributed to the Barnard’s Star b, represents the fluctuation of slightly more than a meter per second — the effect is almost the speed of the pedestrian, which is easy to take for the activity of the star or instrumental error. It is his consistent expression for twenty years, as shown by the data from many sources suggests that the signal is not due to instrumental noise, and something else.

Barnard’s star may have an advantage, despite the history of hunting on the planet. This is one of the most tranquil of stars, which makes it convenient to calculate the radial acceleration. Ribas and his colleagues also insist that we draw conclusions and learn from past allegations of phantom worlds. Intensive observations further rule out the effects of star spots and other obvious sources that could have been mistaken for the planet and spent millions of simulations to conclude that the chance that the signal is derived from the stellar effects, less than 1%. “I’m 99% sure that the planet is”, says Ribas. “But can’t stop thinking about the story of Peter van de Kamp. If someone will provide a powerful argument against our findings, I shall depart! I would not like to be van de Kamp 21st century.”

Time to take a picture?

Anyway, the certainty on this contentious planetary candidate soon formed. Now the work team ruled out any planet the size of Earth in orbits constituting 40 days or less around Barnard’s Star, also found wiggle until proven hints to another planet, hiding away. (Unfortunately for van de Kamp, this planet still will not match his previous statements).

And though it is unlikely this planet can a chance to stand in an exact line with our perspective from Earth, so that when the transit will be able to throw detectable planetary shadow on our telescopes. But the majority of planets are not so that they can be seen from the Ground, partly because of lying on wide orbits from their stars, like Barnard’s Star b.

However, a relatively wide separation planets and stars offers another interesting option: the prospect to do, to carry out “direct rendering”. The Barnard’s Star b would reveal many unusual things, the true nature of the planet — it will be a frozen super-earths, hydrogen-greenhouse world or something, what the theorists do not even suspect. So the astronomers could make another step closer to solving the mysteries of our crowded loneliness of the universe.

In 2020-ies will appear on the stage a new generation of very large ground-based telescopes. Each of them will be equipped with a mirror to collect starlight with a diameter of 30 meters or more, which will be able to distinguish weak photon emissions of the planet. But the first Observatory will be configured for thermal imaging and it is not very suitable to search for icy worlds. Much more promising would be scheduled to start after the telescope James Webb space Observatory WFIRST.

Unless, of course, the launch will take place. If Barnard’s Star b exists, to identify it with WFIRST can be quite real.

But if it does exist, what will it be? Tell us in our chat in Telegram.

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