Thus a planet was born

Still surprised by the planetary system HR 8799?  A study, published in Science, reconstructs the stages of formation of one of the four worlds that populate it. All thanks to high-resolution spectral analysis of its atmosphere. There is an unusual ferment around the star HR 8799. Just recently, researchers became aware of an unusual chemical composition of the four planets that orbit the planetary system HR 8799.



The output almost simultaneously of these results is itself an indication of the importance of the planets around HR 8799 – about 158 ​​light years is its distance from us – for astronomers who deal with extrasolar planetary systems. Their peculiarity lies primarily in the possibility of being directly observed, a rare opportunity for such remote worlds. Even more interesting, the two studies, one of the American team in recent days and that of today’s Canadian team (the latter led by a postdoc researcher at the University of Toronto, Quinn Konopacky), were conducted with completely different means therefore completely independent. Different suite of tools: a cutting-edge equipment called Project 1640 for the American team, the OSIRIS integral field spectrograph for the Canadian.

Although different teams and different instruments, similar results have been discovered. Americans Project 1640 showed, on HR 8799c, the absence of carbon dioxide and methane. The Canadian group, however, focuses its analysis on the spectral lines of water and carbon monoxide. “While there has been a considerable amount of water vapors in the atmosphere of HR 8799c, in reality there’s a little ‘ less than what we would have expected if the planet had the same composition of its star,” says Quinn Konopacky. “This means that the planet has a slightly higher amount of carbon than oxygen.” But the relationship between carbon and oxygen, in exoplanets, is in turn an indicator of their formation mechanism. In particular, explain the authors of the study in Science, the ice grains of water must have been condensed into the planetary disk surrounding HR 8799, consuming oxygen.



“These ice grains are gradually agglomerated into larger blocks, in the order of kilometers. Blocks that continuing to collide gave rise to the solid core of the planet”, tries to reconstruct Konopacky. “The atmosphere was added at a later time, the gas that the planet has attracted once grew enough. At that point, however, a part of the grains of ice had already disappeared; therefore there was no more gas in plenty of water. ”

The story of HR 8799c would be the story of a gas giant (beautifully rugged, among other things: its mass is equal to about 7 times the size of Jupiter) which was developed from growth of the nucleus. It has grown in later stages and not through the simultaneous formation of the core and atmosphere provided by models based on the instability of the protoplanetary disk. A process of growth, therefore, similar to what has shaped the Solar System, with the gas giants farther i.e. rocky planets closest to the Sun “And since the planetary system around HR 8799 looks like a scaled down version of our system solar, ” the researchers write, ” it would not be a surprise to find in its inner planets similar to Earth.”


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