2018-01-12 13:00:00
Our vision of our place in the Universe has changed a lot in the last 30 years. If, in the early 1990s, we considered Earth one of the only nine known planets (only 8 since Pluto was demoted in 2006), it currently occupies an indefinite place in a long list of more than 3,500 planets whose existence has been confirmed by science, all of them, excepting the primitive ones, revolve around stars other than the Sun.
The curious thing about the case is that the instruments that offer us the current vision of the cosmos have not changed much since then. If we focus our best telescopes on a star, we’ll barely see a distant point of dimensionless light, and of course we’ll still be unable to see any planets orbiting it, at least any planets like those that revolve around the Sun, unable to see them. to generate their own light How, then, do astrophysicists manage to detect those distant extrasolar worlds? How, in addition to detecting its presence, do they manage to calculate its size, period of translation, temperature and composition of its atmosphere?
Our guest is one of those observant scientists capable of capturing what, by all accounts, seems unobservable, at least directly. William Torresan Argentine by origin and researcher at the Harvard Smithsonian Center of Astrophysics, explains today from Cambridge, Massachusetts, the United States, the different observation techniques that have allowed the miracle of placing the Earth in its place, that is, as one more among the huge number of planets that inhabit the Milky Way.
Guillermo Torres says that scientists are convinced that every star in our galaxy, and probably in all galaxies, has at least one planet on average. That “at least” is a cautious way of saying things because, despite the limitations of technology, many of them, more than 600, have already been discovered to have planetary systems with up to 8 planets in some cases.
The diversity of discovered planets has no limitations neither in terms of the type of star to which they belong, nor in terms of their shape and size.
The evident sample that practically any type of star can have its planetary system was offered to us by the first extrasolar system discovered in the history of humanity. It happened in 1992, in that year, Aleksander Wolszczan, using the Arecibo radio telescope, discovered the presence of two planets (later a third would be discovered) around a pulsar, that is, the dying remains of a huge star. This discovery took place three years before the detection of 51 Pegasi B, the first extrasolar planet to orbit a solar-type star.
The planets discovered so far are of all kinds: rocky planets like Earth or Mars, gaseous planets like Jupiter or Saturn, and an intermediate range between the two has also been discovered, which has been called “super-Earths.”
Guillermo Torres explains during the interview how observers manage to extract information about a planet from the light that reaches us from its parent star. There are two main detection methods: the Doppler or radial velocity method and the transit method.
The Doppler method is based on the detection of changes in the speed of the star when, due to the effect of the gravitational attraction of a planet, it rotates around the center of mass of both bodies. It is easy to understand by looking at the couple formed by the Earth and the Moon. Both bodies revolve around a common center located 4668 km from the center of the Earth, on the line that separates both bodies. If the Moon were not visible, it would be enough to observe that eccentric rotation of the Earth to detect it, this would allow the relative mass of the Moon with respect to the Earth and its period of translation around it. This is how extrasolar planets are detected around distant stars. If the planet is large enough, the parent star will revolve around the center of mass of both bodies and as a consequence, in some moments it will move away from us and in others it will come closer, periodically changing its speed. This change in speed is reflected in its light and observers like Guillermo Torres can discover and calculate specific data about the planet even if it is not visible. This is how 51 Pegasi B (now named Dimidio) were detected in 1995 by Michel Mayor and Didier Queloz.
The second most widely used method is known as the transit method. Basically it is about the detection of the light variation of the star when a planet passes in front of its stellar disk, that is to say when an eclipse occurs. The decrease in light can be very small, if the planet is the size of Jupiter and the star is like the Sun, the decrease will be 1%; if the planet were like Earth, it would barely decrease by 0.01%. Such subtle variations are very difficult to detect from the Earth’s surface due to the disturbing effect of the atmosphere. Instead, space probes specifically built for observing large areas of the sky have provided a clean view that has allowed multiple discoveries. Space observatories like COROT, KEPLER and soon, TESS They have tracked, or will track, patches of sky populated by hundreds of thousands of stars and systematically image them to detect the subtle changes in light that occur as planets pass in front of them.
William Torres He talks about the difficulties that the investigation of extrasolar planets has and the methods that allow extracting information hidden in the light of their stars. Some investigations that, without a doubt, will contribute to understanding the Universe and will allow, in the future, to find other Earths, capable of harboring life and, why not think about it, intelligence.
I invite you to listen to Guillermo Torres, observational astrophysicist, researcher at the Harvard Smithsonian Center of Astrophysics, in Cambridge, Massachusetts, USA, and Member of the International Astronomical Union.
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