Possible satellite detected around the Trans-Neptunian object Varuna

Astronomers have detected hints of a satellite orbiting Varuna, an object located beyond Neptune, after observing it for nearly 15 years, in particular from Calar Alto.

Beyond Neptune, the eighth and last planet in the Solar System, orbit many Trans-Neptunian objects (TNOs). Lying at large distances (more than 30 times the one of the Earth to the Sun), TNOs preserve fossil records of the nebula that gave birth to the Solar System. To date, about 2,500 TNOs have been discovered; among them, Varuna, a large TNO of nearly 1000 km in its longest (elongated) shape.

After collecting images of Varuna from various Spanish observatories for nearly 15 years, in particular from Calar Alto, Estela Fernández-Valenzuela, a Postdoctoral Research Associate at University of Central Florida (UCF) Space Institute, has lead a research, together with a team at the Instituto de Astrofísica de Andalucía, in which they have detected hints of a satellite orbiting the TNO.

“It is the first time that the existence of a satellite in this kind of object has been suggested using analysis of rotational light-curves techniques,” she said. “It’s quite exciting, additionally because this is a very peculiar object.” The team analyzed the data looking at how the rotational light curves (the brightness variation of the object due to the rotation on its main-inertial axis) of this TNO differed from what was expected from a single object.

varuna es

They found that, beside the periodicity due the rotation of the body, there was a second periodicity indicating there was likely a satellite orbiting Varuna once every 12 hours (in the CAHA 1.2 and 2.2-m light curves, the shaded areas show these deviations).

“Up to date, satellites in the trans-Neptunian region have only been detected using direct imaging, which means there may be many satellites we are not able to differentiate from the main body as they are very close to each other,” Fernández-Valenzuela said. “Adding this technique, which has been used for asteroids (much closer than TNOs, and therefore much brighter) should help us detect more satellites that are too close to its host which should in turn improve our theoretical models about the formation of systems with satellites and also about the different physical processes that take place in the outer solar system.”

 REFERENCE: Fernández-Valenzuela, E., Ortiz, J. L., Morales, N. et al. Astrophysical Journal Letters. 


Calar Alto Observatory is one of the infrastructures that belong to the national map of Unique Scientific and Technical Infrastructures (Spanish acronym: ICTS), approved on November 6th, 2018, by the Science, Technology and Innovation Policy Council

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