How the first planet to revolve around a star other than the Sun was discovered

The discovery of planets similar to ours outside the solar system has changed the concept of exploring the universe.

The discovery of planets similar to ours outside the solar system has changed the concept of exploring the universe.


Our star, the Sun, is accompanied by a procession of planets.

We are in one of them, the Earth, and from its surface we can observe the other planets of the solar system in the sky.

The night sky is also filled with thousands of stars, whose fixed positions relative to each other form constellations.

From our observations of the sky, we understood that the Earth and the other planets were cold spheres orbiting the much larger and hotter Sun.

We also understood that the Sun was a star similar to the others; it is simply its closer proximity that makes it appear very bright to us compared to other stars that are considerably further away and therefore appear much less luminous.

Let’s get out of the solar system

Since the Sun is a star like the others, a question naturally arises: do the other stars also have planets in their orbit?

And if they exist, do these exoplanets or extrasolar planets have characteristics similar to those of the planets in the solar system, or are they very different?

Are these possible extrasolar planets very abundant, or are they rare, with only a few stars harboring them?

And finally, if some exoplanets are similar to Earth, have they experienced the appearance and development of life forms on their surfaces?

As we can see, these questions are far-reaching, from a scientific, philosophical and social point of view.

Asking them and trying to answer them is also a source of many emotions.

The problem of the uniqueness of our universe or of the plurality of worlds has been approached regularly, since Antiquity and throughout history.

From the Copernican revolution of heliocentrism in the 16th century, it was understood that the planets of the solar system were stars similar to Earth and, therefore, capable of constituting new worlds.

Didier Queloz and Michel Mayor

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Didier Queloz and Michel Mayor (left and center) received the Nobel Prize in Physics for the discovery of exoplanets.

Giordano Bruno even affirmed the existence of exoplanets around other stars, which were also inhabited.

In XVII century, especially with Johannes Kepler and Isaac Newton, the knowledge was ripe for a truly scientific approach to the question of exoplanets: if they really exist, we now know more or less what their motion around their host stars should be.

In fact, few astronomers have doubted its existence since then; Since the Sun is accompanied by a planetary system, it seems reasonable to assume that many, if not all, of the other stars are as well.

The exoplanets would end up being detected.

Observation of planets around other stars

But such observation is arduous and challenging, and was out of reach of telescopes for centuries. Since possible exoplanets are smaller and much less massive than their host stars, their effects on them are tenuous.

And getting a direct image of an exoplanet next to its star would be like successfully photographing a seabird flying around a lighthouse several thousand kilometers away.

With the improvement of astronomical instruments, it was not until the end of the 20th century that programs were launched that had the potential to detect them, but these were not successful for a long time due to the difficulty of the task.

The first exoplanet was detected in the mid-1990s by Swiss astronomers Michel Mayor and Didier Queloz at the Haute-Provence Observatory (France).

Using and perfecting the so-called radial velocity method, they obtained this result by measuring with great precision the motion of a star and interpreting its slight periodic variations as caused by the presence of a planet.

Exoplanets

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Planet 51 Pegasi b was the first exoplanet to be discovered by man.

After checking your analysis several times, presented with great emotion the discovery of planet 51 Pegasi b at a conference in Florence on October 6, 1995. Their results were published the following month in the magazine Nature.

This announcement caused a commotion and an emotion shared by the entire scientific community: if the existence of extrasolar planets was little discussed, their discovery made it a reality, finally gave the answer to this century-old question and opened the way to many other detections.

Observation programs and theoretical studies of exoplanets will multiply.

Exoplanetology will develop considerably after 1995, and hundreds of astronomers around the world are now dedicating their research to it.

The Nobel Prize in Physics that Michel Mayor and Didier Queloz received in 2019 for this discovery underscores the revolution it brought for astrophysics and, more generally, for human knowledge.

The ubiquity and great diversity of planetary systems

Since then, thousands of exoplanets have been detected, characterized and studied.

By comparing its properties with the predictions of the theoretical models, we better understand how planetary systems form and evolve. These detections also show the ubiquity of planets in our galaxy – most stars appear to harbor them – and reveal a great diversity of planets.

In fact, while some are similar to those in the solar system, many others have very different and sometimes surprising properties.

An example is the hot Jupiters, that is, planets as big and massive as our Jupiter, but located so close to their star that they surround it in just a few days. 51 Pegasi b belongs to this category. Heated by their star, the atmospheres of these planets have temperatures above 1000 ° C.

Haute-Provence Observatory.

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The discovery of the first exoplanet was made at the Haute Provence observatory in France.

There are also super-earths or mini-neptunes, about two or three times bigger than our planet.

Depending on their internal structure, they can be large telluric planets or small gaseous planets. Although they are totally absent around the Sun, they are very abundant around other stars.

We can also study the atmospheres of certain exoplanets, for example, by measuring its thickness or its temperature, identifying chemical species and detecting movements.

Also, while some exoplanets appear to be alone in orbit around their star, many others are found in systems with multiple planets revolving around the same star, sometimes in very close orbits.

Some orbits are especially eccentric or inclined, which is not the case with the planets of the solar system. These different configurations are probably the signature of various types of dynamic evolution.

Towards other lands?

Finally, exoplanets with properties similar to Earth are beginning to be detected, such as size, mass or distance from their star.

exoplanet in space

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Will there be other Earth-like planets outside the solar system?

New instruments are being developed to try to detect a greater number of them and study them with greater precision, improving the techniques currently used.

Methods are beginning to be designed to detect possible life in these objects, including the study of their atmospheres, and they should be put into practice for decades to come.

We are living, therefore, a privileged, unprecedented and especially exciting period. After centuries of waiting, we begin to have very concrete evidence to compare the Earth and the solar system with other planetary systems, and to know why they are unique … or very common.

These questions are directly related to the place that the Earth and we occupy in the universe. Their answers have great implications from a scientific point of view, but they go much further.

* Guillaume Hébrard is director of research at the CNRS. He has carried out his research at the Institute of Astrophysics in Paris and at the Observatoire de Haute-Provence. After studying the interstellar medium and the abundance of elements, he is now primarily engaged in the research and characterization of extrasolar planets.


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