Thanks to Einstein, a dead telescope spotted a very familiar exoplanet

Thanks to Einstein, a dead telescope spotted a very familiar exoplanet

Kepler, a retired telescope, has identified a distant twin of Jupiter thanks to the principle of gravitational lensing.

The Kepler telescope retired a few years ago, with impeccable service records and a full array of hundreds of exoplanets. But researchers have not finished hearing about it. During its almost decade of space exploration, it has collected so much data that astronomers continue to discover fascinating things in it. The latest is quite spectacular, since it is an almost exact copy of Jupiter!

Indeed, this gas giant resembles like two drops of water the most imposing celestial body in orbit around the Sun. “It is more or less the identical twin of Jupiter in terms of size, mass, and distance from its star.”, explains Eamonn Kerins, an astronomer at the University of Manchester in a press release.

There are some very interesting details hidden in how this gas giant was spotted. Kepler spent most of his career tracking celestial bodies using the so-called “transit” method. The concept is simple as pie; it consists of measuring the differences in light intensity that occur during the rotation of the planets around a star.

Like our satellite during a lunar eclipse, planets far from the solar system also tend to partially obscure their star at some point in the cycle, as seen in the ESA image below. This generates an extremely subtle difference in light intensity, but nevertheless perceptible by point instruments like those of Kepler.

Using fairly advanced mathematical tools, astronomers can then deduce information such as the size or weight of the celestial body in question. This technique has been proven for decades and works amazingly well.; it has already paved the way for countless major discoveries.

From Einstein’s general relativity to the gravitational lens

But it is however not this concept which made it possible to identify this new gaseous giant. Indeed, the researchers were able to achieve this thanks to the concept of gravitational lensing. This is the same approach that recently enabled Hubble to detect Earendel, the most distant star ever observed (see our article).

This concept derives directly from general relativity conceptualized by Albert Einstein, whose immense solidity has again been demonstrated recently (see our article). It states that objects, especially massive ones, generate a gravitational force large enough to significantly distort the space-time around them.

This has many and varied consequences, but there is one that is particularly useful in this context: the light path precisely follows this curvature. It is therefore possible to liken it to a gigantic lens; this can then be exploited to observe objects located at staggering distances, provided that they are located very precisely on the same axis.

This is already a very interesting technique as normal… but it is even more true in this case, because Kepler is absolutely not designed to exploit this phenomenon. “Kepler was never designed to find planets this way”, enthuses Kerins. “In many ways, it’s quite exceptional that we’ve achieved it this way.”.

If the researcher is so perky, it is above all because the chances of succeeding under these conditions were ridiculously low. “The odds of a star being affected by a passing planet in this way is one in tens or even hundreds of millions.”, explains Kerins. “But there are hundreds of millions of stars towards the center of our Galaxy; Kepler therefore settled there and observed patiently for three months”, he explains.

The phenomenon of gravitational lensing schematized by ESA. The grid represents the curvature of spacetime. © NASA, ESA & L. Calçada

A laboratory to study the history of the solar system

In addition to these technical details, this work could also have very concrete implications in fundamental research. Indeed, it is now accepted that Jupiter is one of the main architects of our solar system. It is so massive that it generates a dantesque gravitational force.

The latter in turn played a determining role in the formation of our cosmic cradle. She not only protected the planets from other celestial bodies on the loose, but also weighed heavily in the overall arrangement of the planets. And, by extension, in the appearance of life as we know it.

The fact of having found a quasi-compliant copy is therefore excellent news. This will allow test different theories that exist on Jupiter to see if they also apply to its twin. It will then be possible to refine these models if everything corresponds… or to start again on sound scientific bases if certain elements were not suitable. But in any case, this discovery represents a small additional stone in the vast edifice which will perhaps allow us, one day, to go back to the origins of life and of the Universe itself.

The research paper is available here.

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