Astronomers Stunned To Find 70 Mysterious ‘Rogue’ Planets In The 13th Constellation

Jamie Carter

Senior Contributor

This artist’s impression shows an example of a rogue planet detected in the Rho Ophiuchi region where ESO observations have recently helped uncover at least 70 of these objects. Rogue planets have masses comparable to those of the planets in our Solar System but do not orbit a star, instead roaming freely on their own.

 ESO/M. KORNMESSER

A team of astronomers have discovered at least 70 new “rogue” planets in our Milky Way galaxy. It’s the largest group of these “galactic nomads” found so far and could teach astronomers how these mysterious cosmic oddities came to be.

Rogue planets are planets that move through space without orbiting a star. Often described as free-floating, they’re isolated bodies that are planet-like, having possibly been ejected from a star system. Another theory is that rogue planets can form from the collapse of a gas cloud that is too small to lead to the formation of a star.

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“We did not know how many to expect and are excited to have found so many,” said Núria Miret-Roig, an astronomer at the Laboratoire d’Astrophysique de Bordeaux, France and the University of Vienna, Austria, and the first author of the new study published today in Nature Astronomy.

This image shows a small region of the sky in the direction of the Upper Scorpius constellation. It zooms in on a recently discovered rogue planet, meaning a planet that does not orbit a star but instead roams freely on its own. The rogue planet is the tiny, bright red dot at the very centre of the image. The image was created by combining data from the OmegaCam instrument on VLT Survey Telescope (VST) and from the VIRCAM instrument on the Visible and Infrared Survey Telescope for Astronomy (VISTA), both located at ESO’s Paranal Observatory in Chile. Observations with these and other instruments helped the scientists tell the planets apart from stars, brown dwarfs and other objects in this region of the sky. Lurking far away from any star illuminating them, rogue planets would normally be impossible to image, but shortly after formation they emit a faint glow that can be detected by sensitive cameras on powerful telescopes.

 ESO/MIRET-ROIG ET AL.

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So how did they find them? Though dark and cold—and therefore impossible to find—Miret-Roig and her team used the fact that rogue planets are still hot enough to glow in the few million years after their formation. So they can be detected by sensitive cameras on large telescopes. “We measured the tiny motions, the colours and luminosities of tens of millions of sources in a large area of the sky,” said Miret-Roig. “These measurements allowed us to securely identify the faintest objects in this region, the rogue planets.”

All 70 new rogue planets have masses comparable to Jupiter’s in a star-forming region in the Upper Scorpius and Ophiuchus constellations. Ophiuchus is known as the 13th constellation because despite being a large constellation on the ecliptic—so therefore hosting the Sun just like Leo, Taurus and all the others—it was the victim of ancient Babylonians hatred of the number 13.

To find the rogue planets the team used data from 20 years and from a range of telescopes, including the European Southern Observatory’s Very Large Telescope (VLT), the Visible and Infrared Survey Telescope for Astronomy (VISTA), the VLT Survey Telescope (VST) and the MPG/ESO 2.2-metre telescope in Chile.

This image shows the locations of 115 potential rogue planets recently discovered by a team of astronomers in the direction of the Upper Scorpius and Ophiuchus constellations, highlighted with red circles. Rogue planets have masses comparable to those of the planets in our Solar System, but do not orbit a star and instead roam freely on their own. The exact number of rogue planets found by the team is between 70 and 170, depending on the age assumed for the study region. This image was created assuming an intermediate age, resulting in a number of planet candidates in between the two extremes of the study.

 ESO/N. RISINGER (SKYSURVEY.ORG)

“We used tens of thousands of wide-field images from ESO facilities, corresponding to hundreds of hours of observations, and literally tens of terabytes of data,” said Hervé Bouy, an astronomer at the Laboratoire d’Astrophysique de Bordeaux, France, and project leader of the new research. The team also used data from the European Space Agency’s Gaia satellite.

Could there be more rogue planets? “There could be several billions of these free-floating giant planets roaming freely in the Milky Way without a host star,” said Bouy. However, to find more scientists will require a bigger, even more sensitive telescope. Cue the ESO’s forthcoming Extremely Large Telescope (ELT), which is currently under construction in Chile. “These objects are extremely faint and little can be done to study them with current facilities,” said Bouy. “The ELT will be absolutely crucial to gathering more information about most of the rogue planets we have found.”

Wishing you clear skies and wide eyes.

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Jamie Carter

I'm an experienced science, technology and travel journalist and stargazer writing about exploring the night sky, solar and lunar eclipses, moon-gazing, astro-travel, astronomy and space exploration. I'm the editor of WhenIsTheNextEclipse.com and the author of "A Stargazing Program for Beginners: A Pocket Field Guide" (Springer, 2015), as well as many eclipse-chasing guides.