Saturday, June 25

Finding an exoplanet is extremely difficult, and astronomers have already found more than 4,800: this is how they are making the almost impossible possible

4827. This is the exact number of extrasolar planets that, according to NASA, have already been rigorously identified by astronomers so far. However, despite the enormous difficulty involved in identifying objects that do not emit light and that are located at almost unimaginable distances from us, this figure keeps increasing.

The success that astrophysicists are reaping in the field of the search for exoplanets is the consequence of an indefatigable determination, a very remarkable scientific development in which artificial intelligence plays an essential role, and, above all, of an overflowing wit.

Finding a planet outside our solar system is like finding a needle in a haystack, but cosmologists have devised five extraordinarily clever strategies that are allowing you to find them.

Cosmologists have devised five extraordinarily ingenious strategies that are allowing them to find exoplanets. There are already more than 4800

In this article we propose to investigate them in the most didactic way possible, although before doing so it is important that we review that an extrasolar planet, or an exoplanet (they are two slightly different ways of identifying the same type of objects), is nothing more than a planet that is situated outside our solar system. That’s it.

Of course, scientists believe that most of them do not meet the appropriate conditions so that they can be inhabited by the human being. Still, finding just one of them is a scientific feat, and, above all, a surprising display of ingenuity, as we are about to see.

1st strategy: radial velocity

Stars tend to accumulate more mass than the planets that orbit them, but this does not make them immune to gravitational interaction with other objects. During their movement around a star the planets usually cause it to wobble in a more or less pronounced way, depending, as we can guess, on the mass of both objects and the distance that separates them.

The funny thing is that astronomers have devised a very ingenious method that allows them to identify the gravitational interaction between a star and a planet candidate even if the latter is not visible using other procedures. When the star vibrates, even minimally, due to gravitational interaction with the planet, the wavelength of the light it emits change subtly.

What scientists do is identify these variations in the light that their instruments collect to confirm that, indeed, one or more planets are orbiting that star. To date this method has allowed researchers to identify 899 exoplanets.

Radial velocity

2nd strategy: the transit period

When a planet comes between us and a star masks a part of its light. During its journey around the star there will be times when it will hide a certain amount of light (just when it comes between the star and the observer), and times when it will not because it will be circling the section of the orbit. in which it does not get in the way.

If the light we receive from a star varies periodically, it is possible that a planet is orbiting around it

What astronomers do to identify that one or more planets are orbiting the star they are observing is measure the amount of light they receive. If this number varies periodically and in a predictable way, it is likely that a planet is coming between us and the star.

This method is even useful for estimating the volume of the planet. However, it is not always possible to apply it; when the plane that describes the orbit of the planet is approximately perpendicular to the plane from which we observe the star from Earth it is not possible to identify the light it masks. In this case it is necessary to use another method of observation. Even so, this procedure is very fruitful; in fact, so far it has allowed astronomers to identify 3752 extrasolar planets.


3rd strategy: taking direct images

Sometimes, although it is rare, astronomers are able to directly capture an image of a planet. What this exoplanet identification procedure proposes is to expressly mask most of the light that the star emits directly towards us in order to prevent its brightness from dazzling us, preventing us from seeing the planet.

What this procedure proposes is to expressly mask most of the light that the star emits directly towards us to prevent its brightness from dazzling us

In doing so, it is possible that we can perceive a part of the star’s light reflected by the planet. When these circumstances occur, it is possible to see this last object directly, although for the moment the researchers have only identified 55 extrasolar planets using this method.


4th strategy: gravitational microlenses

“Spacetime tells matter how to move, and matter tells spacetime how to bend.” This phrase by the American theoretical physicist John Archibald Wheeler clearly reflects how the interaction manifests between the space-time continuum and matter. The latter acts on it by bending it, so that not even light can remain unscathed from this deformation of the continuum through which it travels.

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If a planet is periodically interposed between us and a distant star, there will be periods in which we will directly receive the light emitted by the star without it having undergone any type of alteration, and moments in which the warping of space-time introduced by the planet alter the path that the light follows.

This astronomical phenomenon is known as gravitational microlens, and astrophysicists are able to identify it because when it occurs they receive a slightly distorted image of the star, giving them the feeling that it occupies two different positions in space. To date this procedure has allowed researchers to identify 120 exoplanets.

Microlens gravity

5th strategy: astrometry

The latest strategy astronomers are using to identify exoplanets is based on the same principle used by the first method that we have explored in this article: gravitational interaction that occurs between the stars and the planets that orbit them.

Sometimes the gravitational interaction with a nearby planet causes the distance between the star under observation and its neighbors to vary very slightly on a periodic basis.

The difference between the first and the fifth strategy is that in the latter, astrophysicists resort to astrometric techniques to measure relative distance that exists between the star you are observing and the stars in your neighborhood.

Sometimes the gravitational interaction with a nearby planet causes the distance between the star under observation and its neighbors to vary very slightly periodically, so that this phenomenon can betray the presence of an object that has been captured by its gravitational field.

This procedure requires carrying out very precise measurements that are only possible by carrying out very complex calculations, so for the moment it has only allowed researchers to locate an extrasolar planet.


Cover image | Miriam Space

More information | NASA

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