How do we search for exoplanets?
With the global warming and sea pollution constantly growing trends, the future of Earth might be at serious risk. In addiction, the overpopulation of some regions might cause a global food crisis in nearly 30 years.
These are just a few reasons why some brilliant minds such as Jeff Bezos and Elon Musk have started to plan a colonization of other planets like Mars, launching several rockets of their futuristic companies Spacex and Blue origin.
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What are exoplanets? How can we reveal their presence? Is it possible to find a place similar to our beautiful Earth? These and other great questions will be discussed in this video. Stick with me and I’ll tell you everything in a moment.
It’s surely interesting to wonder about a possible future destination for everyone, but in order to understand how this can be done we need to take a step back and try to look at our planet: Earth.
We all agree, except for some sceptics, that it has a spheric shape and that it has two main rotating motions: one around the sun, which causes the existence of four different seasons, and another around his axis, which is the source of day and night.
But why we use to call Earth as a planet? What is a planet?
The first revolution around the sun takes more time than the rotation around the axis, but this is not something that Earth shares with other “colleagues” of the solar system: for example, on Venus a year lasts less than a day. So what do all planets have in common?
They all complete a close motion around the Sun and they have a stable shape typical of a certain mathematical equilibrium called hydrostatic equilibrium. Practically speaking, this is the reason why all planets are spherical.
Addictionally, to gain the definition of planet a body must have a clean orbit without rocks or other astronomical detritus. As a matter of fact, in 2006 Pluto was declassified to the rank of dwarf planet because Eris was discovered, a big satellite that had nearly 27% of Pluto’s mass.
Finally, a planet must have less than thirteen times the mass of Jupiter, the biggest one in the solar system.
In parallel, an exoplanet is an astronomical object orbiting around a star different from the sun, but with the same features we already listed.
Is it easy to detect the presence of an exoplanet? Definitely not. They’re not simple to find and only a bit more than four thousand have been discovered after 1992, when the first two planets were seen orbiting around a pulsar. Even if this number seems really big, it’s totally incomparable with the amount of stars discovered, which is almost 500000 only in the milky way.
Stars are way easier to be discovered and catalogued as they shine on their own. On the contrary, planets happen just to radiate some tenuous infrared rays, that are surely not capable of reaching our detectors on earth. As a matter of fact, just less than 30 exoplanets have been detected by this technique called “direct imaging”.
Given the fact that it’s not possible to measure their emission, how can we “see” a planet? Through indirect methods. Physicists love to study little changes in the radiation of the major star that are capable of revealing the presence of one or more planets.
Let’s investigate the main techniques that are commonly used in astronomy for searching exoplanets.
The first one deals with radial velocity. A planet has certainly a consistent amount of mass that weakly attracts the star, which has some slight displacements due to its presence. More precisely, both the star and the exoplanet are orbiting around the center of mass, a virtual point on the line that connects the two bodies, which is located near the heaviest one. This movements of the star can be well detected through a very common technique: redshift. Have you ever heard anything about this?
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