Weird Planet Is Orbiting Backwards Between Two Stars (newscientist.com)
(Friday May 23, 2025 @03:00AM (BeauHD)
from the how'd-that-get-there dept.)
- Reference: 0177696853
- News link: https://science.slashdot.org/story/25/05/23/006244/weird-planet-is-orbiting-backwards-between-two-stars
- Source link: https://www.newscientist.com/article/2480992-weird-planet-is-orbiting-backwards-between-two-stars/
Astronomers have confirmed the existence of a bizarre planet in the Nu Octantis binary star system that [1]orbits in reverse between two stars -- one of which is now a white dwarf. This retrograde orbit, once thought impossible, defies traditional planetary formation models and may have resulted from dramatic shifts in the system's history. New Scientist reports:
> The key observation was that the Nu Octantis planet is retrograde -- the planet and one star both orbit the second star, but they do so in opposite directions, with the planet having the tighter orbit around the second star. [Man Hoi Lee at the University of Hong Kong] says this is unusual but makes the system's configuration stable -- even though it means that the planet repeatedly moves through the narrow space between the two stars. His team was able to determine this with lots of certainty thanks to improved measuring devices, such as the HARPS spectrograph at the European Southern Observatory's 3.6-metre telescope in Chile. The fact that the planet's signal persisted through years of observation helped too. "We are pretty sure [the planet] is real, because if it was something like stellar activity, it shouldn't be so consistent in years of data," says Lee.
>
> But this backwards-moving planet isn't the only exotic feature of Nu Octantis. The researchers used the European Southern Observatory's Very Large Telescope, also in Chile, to determine that one of its stars is a white dwarf, which means that it has reached the end of its life cycle, becoming denser and smaller. Lee says this complicates the Nu Octantis threesome's history because mathematical models of its past show that the planet's current orbit was impossible when this star was younger, bigger and brighter. So, the planet either used to orbit both stars at once, but then radically shifted trajectory when one of the two stars became a white dwarf, or it was formed from the mass that the star ejected as it transformed into a white dwarf. Future observations, and a lot more mathematical modelling, may be able to pinpoint which of these scenarios is more likely to have occurred, but both are rather novel, says Lee.
The research has been [2]published in the journal Nature .
[1] https://www.newscientist.com/article/2480992-weird-planet-is-orbiting-backwards-between-two-stars/
[2] https://www.nature.com/articles/s41586-025-09006-x
> The key observation was that the Nu Octantis planet is retrograde -- the planet and one star both orbit the second star, but they do so in opposite directions, with the planet having the tighter orbit around the second star. [Man Hoi Lee at the University of Hong Kong] says this is unusual but makes the system's configuration stable -- even though it means that the planet repeatedly moves through the narrow space between the two stars. His team was able to determine this with lots of certainty thanks to improved measuring devices, such as the HARPS spectrograph at the European Southern Observatory's 3.6-metre telescope in Chile. The fact that the planet's signal persisted through years of observation helped too. "We are pretty sure [the planet] is real, because if it was something like stellar activity, it shouldn't be so consistent in years of data," says Lee.
>
> But this backwards-moving planet isn't the only exotic feature of Nu Octantis. The researchers used the European Southern Observatory's Very Large Telescope, also in Chile, to determine that one of its stars is a white dwarf, which means that it has reached the end of its life cycle, becoming denser and smaller. Lee says this complicates the Nu Octantis threesome's history because mathematical models of its past show that the planet's current orbit was impossible when this star was younger, bigger and brighter. So, the planet either used to orbit both stars at once, but then radically shifted trajectory when one of the two stars became a white dwarf, or it was formed from the mass that the star ejected as it transformed into a white dwarf. Future observations, and a lot more mathematical modelling, may be able to pinpoint which of these scenarios is more likely to have occurred, but both are rather novel, says Lee.
The research has been [2]published in the journal Nature .
[1] https://www.newscientist.com/article/2480992-weird-planet-is-orbiting-backwards-between-two-stars/
[2] https://www.nature.com/articles/s41586-025-09006-x
Larry Niven's universe (Score:2)
by chthon ( 580889 )
There is short story from Larry Niven that seems to be this situation. "The Soft Weapon".
Nomenclature out the window... (Score:2)
by The123king ( 2395060 )
Most people understand a star as being the center of a solar system. And again, most people can understand a binary star as having 2 stars at the center, with planets orbiting around both.
This system however throws that out of the window. Sure, the stars are a binary system, but to the planet, the White dwarf orbits like a planet. So whilst it is a binary star system, from the planet's perspective, it's not. The white dwarf is just a big glowing planet orbiting a star.
On another note, it would be a
YT Link (Score:5, Informative)
> The key observation was that the Nu Octantis planet is retrograde -- the planet and one star both orbit the second star, but they do so in opposite directions, with the planet having the tighter orbit around the second star.
This (old) vid should help if you're having trouble visualizing the orbits:
[1]https://www.youtube.com/watch?... [youtube.com]
[1] https://www.youtube.com/watch?v=EpMMXz4AtlI