At least 70 ‘wandering’ planets discovered in our galaxy

Let’s start with a definition: Migrating planets are unusual cosmic objects whose mass is comparable to the planets in our solar system, but which do not orbit a star and move freely as they would », Explains the European Southern Observatory (ESO).

In a study published in Nature Astronomy, astronomers discovered dozens of them: ” We did not know how many wandering planets we could expect and we are glad we found so many », Declares Núria Miret-Roig from Bordeaux Astrophysics Laboratory and first author of the publication.

Unlike the (exo) planets orbiting a star, those orbiting as lost souls hide yourself far from any star shining on them ” and is therefore ” usually impossible to photograph You can also not use the transit method.

“Shiny” wandering planets

Núria Miret-Roig and her team therefore used a different technique: ” within a few million years of their formation, these planets are still warm enough to glow, making them directly detectable by the sensitive cameras of large telescopes “.

This research has paid off: They found at least 70 new orbiting planets with Jupiter-like masses in a star-forming region near our sun, in the constellations Upper Scorpius and Serpentarius. “.

Jupiter is the largest planet in the solar system. Its average diameter is 142,984 km, its volume is 1,317 times larger than Earth’s. She is so impressive that she plays the role of protector of the eight “kingdoms”.

Between 70 and 170 wandering planets … where does this inaccuracy come from?

Let us return for a moment to a detail that is important: ESO talks about “aat least 70 new wandering planets “. Why such inaccuracy, if they have been discovered? In fact, a crucial piece of data is missing to refine this estimate: the mass of objects that observations cannot measure.

Jupiter is already a monster in the case of our solar system: its mass is 318 times that of our planet and ” more than double all the other planets in the solar system , ”Recalled the European Space Agency. While there are probably even more massive exoplanets, ” objects with a mass greater than about 13 times the mass of Jupiter are most likely not planets “, explains ESO.

So what can be done without having the mass of identified objects? The team ” had to rely on the study of the brightness of the planets “. The basic postulate is simple: the older a planet is, the more it has cooled, and the more it has lost its brightness. The brightness is therefore directly related to the age of the planet.

From there, ESO explains its rationale: If the studied area is old, the brightest objects in the sample are likely to have a mass greater than 13 Jupiters and lower if the area is younger. “. We must also take into account uncertainty about the age of the region studied “.

Astronomers then arrive at a series of traveling planets ” between 70 and 170 For the sake of safety, they are therefore talking about at least 70 wandering planets “.

Location of wandering planets discovered
Migrating planets are in red circles. Credit: ESO / N. Risinger (

20 years of measurements, on earth and in space

Do not think it’s easy to see 70 wandering planets. The data used have been collected over a period of approximately 20 years. They come from several telescopes on earth and in space.

We measured the small movements, colors and brightnesses of tens of thousands of springs in a large area of ​​the sky […] These measurements enabled us to reliably identify the weakest objects in this region, the wandering planets Details Núria Miret-Roig.

Several observatory telescopes were used – the Very Large Telescope (VLT), the Visible and Infrared Survey Telescope for Astronomy (VISTA), the VLT Survey Telescope (VST) and the MPG – as well as the European Space Agency’s Gaia satellite.

The vast majority of our data comes from the ESO observatories, which were absolutely crucial to this study. Their wide field of vision and unique sensitivity have been the key to our success », Says Hervé Bouy, astronomer at Bordeaux Astrophysics Laboratory and project manager for this research.

Total, ” tens of thousands of wide-field images […] equivalent to hundreds of hours of observations and literally tens of thousands of terabytes of data was taken into use. These observations suggest that there may be many more wandering planets in our galaxy: There could be billions of these giant planets floating freely in the Milky Way without a host star “, According to Hervé Bouy.

Where do wandering planets come from?

These orbiting planets could help to understand how they are formed. Two tracks are on the carpet: from the collapse of a gas cloud too small to form a star “, or they have” could be thrown out of their mother system “Researchers still do not know which mechanism is most likely “.

The successor, we suppose, will come with the new instruments. The future Extremely Large Telescope to begin with, which ” will be absolutely crucial in gathering more information about most of the wandering planets we found “. It will not be the only thing the James Webb Space Telescope and others of its kind will certainly be put to use.

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