The phrase "visiting planet Proxima Centauri b" here, of course, connotative meaning, only a form of imagination. Because to realize it with the technology controlled by mankind today is really unimaginable ever. Because the distance between Earth and Proxima Centauri b is 4.22 light years, while the light year is equivalent to the distance of 9.46 trillion kilometers. So when we use commercial rockets orbiting satellites into Earth orbit (whose top speed is an average of 7.7 km/sec), it takes at least 165,000 years since leaving from Earth until it arrives at Proxima Centauri b. The 165,000-year time is almost similar to the time it takes for the ancestors of mankind to migrate from the land of East Africa to the whole of the world to form a civilization as it is today.
Suppose we use the fastest man-made space (spacecraft) space, Juno (top speed 40 km/sec) that has just arrived in the gigantic Jupiter gas planet, the time it takes is still almost 29,000 years. Even if the Breakthrough Starshot project which is being initiated can embrace success, which weighing a few grams will arrive at Proxima Centauri b after 20 years despite sped as fast as one fifth the speed of light.
Proxima Centauri b is a name which is horrendous to the astronomical universe in these last days. Especially since August 24, 2016. The culprit is the ESO (European Southern Observatory), research institute interstate Europe and also the owner of the latest giant telescope on Earth. They launched an exciting find: there are Earth-sized planets found orbiting the star of Proxima Centauri. It's the closest star to our Earth after the Sun, but so dim so it is impossible to see with ordinary eyes (without the aid of a telescope). First indicated in 2013, the ESO then launched an ambitious campaign titled Pale Red Dot to drag the planet out of its hiding comforter.
Unmitigated, ESO deployed a giant reflector telescope with a 3.6 meter diameter objective mirror at the La Silla Observatory (Chile). The great telescope was paired with a superb HARPS spectrograph (High Accuracy Radial velocity Planet Searcher). Not only that, the ESO also deploy another giant telescope of its flagship, the VLT reflector telescope (Very Large Telescope) with a 8 meter diameter mirror based in the Atacama Desert (also in Chile). The VLT telescope is assembled with another spectrograph that is not less great, the UVES (Ultraviolet and Visual Echelle Spectrograph). With these two sophisticated (instrumental) instruments ESO hunts down the existence of the nearest Exoplanet to our Earth via the Doppler method.
The hunt culminates with the discovery of the planet, which is temporarily named the planet Proxima Centauri b. Although up to now mankind has found no less than 3,200 Exoplanet counted since 1995, Proxima Centauri b remains exciting. For in addition to being closest to our Earth, it also has the same size as the blue planet in which we live. In addition, he is thought to be warm enough to keep the water in liquid form. Water in liquid form becomes an important component in life.
Main Star
Planet Proxima Centauri b is a planet orbiting the star of Proxima Centauri, the closest star to our Earth after the Sun. But the star of Proxima Centauri is quite dim. So that he can only be witnessed by using a telescope with a lens/mirror objectively diameter at least 8 cm. It is therefore not surprising that the nearest star but dim is only realized by humankind in the last century alone. Robert Innes, a Scottish-born astronomer who heads the Union Observatory in Johannesburg (South Africa), is aware of an unusual star around the Alpha Centauri star system. The star has a proper motion (self-motion) equivalent to the Alpha Centauri star system, but very dim and far apart (elongation 2.2 °). The meticulous parallax measurements by Harold Alden in 1928 showed that the star, known as Proxima Centauri, was closer to Earth than the alpha Centauri double star system.
Because it has an equivalent self-motion, this star is also considered as part of the system of Alpha Centauri stars. Then alpha Centauri is a triple star system consisting of Alpha Centauri A, Alpha Centauri B and Centauri C alpha star (Proxima Centauri). All three circulate around a common center point of the mass. But there is something odd in this triple star system. The average distance of alpha Centauri A to Alpha Centauri B is only 11 AU (astronomical unit), or the equivalent distance from the Sun to the orbit of Uranus. Thus both Alpha Centauri A and Alpha Centauri B only takes 80 years to complete motion around the center of the mass along one round. But not so with Proxima Centauri. The distance is enormous, ie 13,000 AU or equivalent to a quarter of a light year from that point. So Proxima Centauri took 500,000 years to circle the center of mass together once round.
Another peculiarity, if the Alpha Centauri A and Alpha Centauri B stars are relatively bright stars with an apparent magnitude of +0.01 and +1,33, then the star of Proxima Centauri is very dim (the apparent magnitude +11.02). The next peculiarity, when the Alpha Centauri A and Alpha Centauri B stars are members of the main sequence stars (each class G and K), the star of Proxima Centauri is actually a member of a red dwarf. These peculiarities prompted some astronomers to question whether the star of Proxima Centauri is really part of the Centauri alpha star system. Because it is open the possibility that the star Proxima Centauri is a star that just happened to be passing near the system of stars alpha Centauri and unbound (with gravity) with the star system.
As the closest star to Earth after our Sun, much information about Proxima Centauri has been revealed. In many ways, these dim stars are outnumbered by the Sun. For example, the mass of Proxima Centauri is only 12% of the Sun's mass. While the radius is only 14.1% of the radius of the Sun. So the star Proxima Centauri is only slightly larger than Jupiter. Furthermore, the luminosity, ie the amount of energy released per unit time, is also very small. The bolometric luminosity is 0.15% of the Sun's luminosity. While in the visible (visual) light spectrum, its luminosity is even much smaller that is only 0.005% of the Sun's luminosity. For 85% of Proxima Centauri energy is delivered in the infrared spectrum. The temperature of the photosphere (surface) is also low at only 3,050 Kelvin, while in the Sun it reaches 5,800 Kelvin. Like the Sun, Proxima Centauri also has its own activity cycle with peak activity marked by events like the storm of the Sun. However, Proxima Centauri's activity cycle period is much shorter, ie 'only' 442 days. While at the Sun period reached 11 years.
But on the other hand, many of the more dominant characters of Proxima Centauri. For example, in terms of density (mass type) is much larger, ie 40 times from the Sun. Stars with large densities are common in exotic stars that have undergone further evolution, including dwarf stars. Also, it's magnetic field. As a star with a low mass, heat transfer in the interior of Proxima Centauri is entirely in the form of convection. One consequence is the resurrection and retention of a strong magnetic field of stars, 600 times stronger than the Sun. Another consequence, 88% of the photosphere of Proxima Centauri is active, a much larger proportion than the Sun. The impact Corona Proxima Centauri also experienced a higher warming so that the temperature of 3.5 million Kelvin. While the temperature of the sun's corona 'only' 2 million Kelvin.
Proxima Centauri is known as a flare star or star that often spewing storm stars. This fact was known in 1951 by astronomer Harlow Shapley after analyzing photographic plates related to this star since 1915. He found that the star Proxima Centauri has a tendency to grow brighter to 8% brighter than before, then dimmer again. This increase and decrease in brightness take place periodically with an average period of 442 days. The source of this increase in brightness is the storm of stars. Unlike the Sun storm, the much stronger Proxima Centauri magnetic field causes almost all of its photosphere to be a storm area. So that storm star Proxima Centauri often sized up to its star itself. When a storm occurs, the star's temperature jumps to 27 million Kelvins, which allows it to emit X-rays. This makes Proxima Centauri X-ray luminosity equivalent to the Sun. Even in the peak of the storm, Proxima Centauri's X-ray luminosity can be 100 times larger than the Sun.
Planet
Planet Proxima Centauri b, or call it Proxima b, is found by the Doppler method or the radial velocity method. This is an indirect method of discovering exoplanets by detecting a shift in the emission spectral lines of its parent star. This method as well as we detect the presence or absence of ambulances that are moving away or closer to the soft sound of a siren. It's just that this case is not the voice that became the focus of attention, but the spectrum of star emissions. Although, both in the case of ambulances and stars, the key lies in frequency. Namely the sound frequency (for ambulance cars) and the frequency of light (for stars).
Basically, every star moves relative to our Earth at a certain speed called radial velocity. When the star has a planet, the planet's gravitational impairment will cause a periodic change in the radial velocity of the star. Let's see our solar system as an example. Although Jupiter remains faithful around the Sun in its orbit, Jupiter's gravitational impairment also makes the radial velocity of the Sun change periodically. Although the amplitude of the change is very small, ie only 12.4 meters/sec with a period of 12 years (the same as the period of Jupiter revolution). If a similar thing is applied to our Earth, whose mass is much smaller than Jupiter, the amplitude of the radial velocity change of the Sun is much smaller. Namely only 0.1 meters / second with a period of 1 year. Attempts to detect radial star velocity changes can be made through highly accurate high-precision spectrometry specially crafted for it.
Radas HARPS has the ability to detect radial star velocity changes of up to 0.3 m / sec. When HARPS is directed to Proxima Centauri star in relatively long observation range, there is a radial velocity change with an amplitude of 1.76 meters/sec with a period of 11.19 days. The same change with the same period is also detected by UVES radicals although the amplitude is slightly different, ie 1.69 meters/sec. The change in radial velocity on the star Proxima Centauri b becomes an indication that the star is surrounded by at least a planetary candidate.
Further analysis showed the planet, Proxima Centauri b, circulating at an average distance of 0.049 AU or 7.33 million kilometers from the star Proxima Centauri. The slope of its orbit (eccentricity) is known to be less than 0.35. If the Elips value is precisely 0.35 then Proxima Centauri b circulates around its parent star in an oval orbit having the periastron (the nearest point to the star) of 0.032 AU or 4.79 million kilometers and the apastron (the furthest point to the star) of 0.066 AU or 9.87 million kilometers. The period of Proxima Centauri b revolution is 11.19 days so that the year there is equal to 11.19 days. The mass, precisely the minimum mass is 1.27 times the mass of the Earth so that the planet Proxima Centauri b may be a terrestrial planet (rock planet). While the exposure to light it receives is 65% exposure to sunlight on Earth or the equivalent of 889 watts / meter2.
What is interesting about this planet is its average temperature and the environment it is in. If considered to have no atmosphere, the average temperature of Proxima Centauri b is minus 39 ° Celsius (234 Kelvin). Conversely, if the planet Proxima Centauri b has an atmosphere, the average paras temperature becomes greater at 30 ° Celsius (303 Kelvin). But this estimate is relatively rough because it only takes into account the distance of the planet to its parent star and the intensity of the irradiation. In digging this issue further, the Laboratoire de Météorologie Dynamique's Planetary Global Climate Model simulated with two assumptions based on Proxima Centauri b orbit proximity to its parent star. The first assumption, planet Proxima Centauri b has 3:2 resonance. This means that every time Proxima Centauri b exactly twice surrounds the parent star, it also exactly three times rotates (spins on its axis). So in this assumption, the rotation period of Proxima Centauri b is 7.46 days. While the second assumption is the planet Proxima Centauri b is bound in the tidal style with its parent star or undergoes synchronous rotation. Under this condition, the rotation period of Proxima Centauri b will be exactly the same as its revolutionary period, ie 11.19 days. So the Proxima Centauri b hemisphere facing the star of Proxima Centauri is always the same.
The possibility of the presence of water in liquid form becomes the most interesting part of the discovery story of this planet Proxima Centauri b. For its orbit, the planet is practically located within the Goldilocks zone or the zone of density, which is a region of 0.0423 AU (6.33 million kilometers) to 0.0816 AU (12.21 million kilometers) from the star of Proxima Centauri. Inside the Goldilocks zone, when there is water then it may be in the form of a liquid. Water in liquid form becomes one of the factors that support life, both with living beings harvesting energy from the rays of their host stars and with living creatures that are powered by the planet's internal heating. When water is available in large quantities, the water cycle may be able to walk and contribute to the rocky landscape of the planet.
Some Notes
OK. So when we come to Planet Proxima Centauri b, somehow, we will most likely encounter a rocky landscape of rocks like Earth and also a vast ocean. The planet is odd, because a year there is equivalent to 11.19 Earth days while one day may be equivalent to two-thirds of the year or even a year. The most important question, is there life there? Or can the planet Proxima Centauri b be inhabited by a life like Earth?
The answer to that question makes astronomers polarized into two different poles of opinion. The first pole of opinion says it is impossible, either to inhabited or to live. There are four reasons: Proxima Centauri b may have a synchronous rotation, the star Proxima Centauri has a very strong magnetic field (600 times the magnetic field of the Sun), the star Proxima Centauri often spewing storms and Proxima Centauri b exposed to X-rays and ultraviolet rays which is very high (its X-ray exposure may be 400 times stronger than Earth). With synchronous rotation, the Proxima Centauri b hemisphere facing its parent star will be overheated. While the hemisphere behind her shivered in freezing cold. And in synchronized rotation conditions, the Proxima Centauri b (when present) atmosphere will be eroded by the storms and the magnitude of the Proxima Centauri magnetic field. And finally, with extremely powerful X-rays and ultraviolet rays, which are also capable of eroding and eroding the atmosphere of Proxima Centauri b up. In short, for the poles of this first opinion the planet Proxima Centauri b is a dangerous planet.
Instead, the poles of the second opinion say differently. So Proxima Centauri b may be inhabited and seed the seed of life. The reason is also four. Despite its synchronous rotation, the planet Proxima Centauri b can have an average paras temperature balance between the star-facing hemispheres and the ones behind them when there is a stable atmosphere capable of distributing heat through the global atmospheric circulation. The planet is indeed dealing with star magnetic fields and strong storm stars. However, some studies show that if Proxima Centauri b has a sufficient magnetic field (like the Earth's magnetic field), it will be able to defend its atmosphere from the onslaught of magnetic fields and storm stars. The amount of eroded atmospheric material will be quite small. So he can avoid the unfortunate fate like Martian life. Similar research also reveals that the magnetic field Proxima Centauri b can also make it defend its atmosphere from the onslaught of X-rays and ultraviolet rays. In short, for this pole the planet Proxima Centauri b does live in a dangerous environment. But he can survive if he has a sufficient magnetic field.
What is clear is that both poles of opinion agree that the planet Proxima Centauri b is in a warm environment, which is able to retain water in liquid form. Need further observation to ascertain whether this planet is so. Observations, especially by other independent research teams, will confirm whether there really is a planet in question at the star of Proxima Centauri. Because in 2012 ago we have experienced uncomfortable incident related to alpha centauri star system. At that time, a team of European astronomers, also armed with HARPS radicals, announced it had identified the existence of a terrestrial planet orbiting alpha Centauri B. But three years later another research team based on the same HARPS data concluded the planet did not exist. What was originally suspected as a planet in the alpha star Centauri B turned out to be just a defect of mathematical calculations.
Further observation will also be able to determine the mass of Proxima Centauri b better. Currently, the information we know is only the minimum mass. Depending on the angle of its inclination, the mass of Proxima Centauri b may range from as little as 2.6 times the mass of Earth to 70 times the mass of the Earth. If the mass is too large, then it is not a terrestrial planet.
Reference :
- http://adsabs.harvard.edu/abs/2016Natur.536..437A
- https://en.wikipedia.org/wiki/Proxima_Centauri_b
- https://www.space.com/33844-proxima-b-exoplanet-interstellar-mission.html
- https://www.theverge.com/2017/11/15/16655236/new-planet-discovery-ross-128-b-red-dwarf
- http://www.eso.org/public/news/eso1629/
- https://www.newscientist.com/article/mg23130884-100-proxima-b-closest-earth-like-planet-discovered-right-next-door/
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