English
Arabic
French
Spanish
Portuguese
Deutsch
Turkish
Dutch
Italiano
Russian
Romaian
Portuguese (Brazil)
Greek
New data confirms: There really is a planet squeezed in between two stars
How'd that get there?
New data confirms: There really is a planet squeezed in between two stars
The planet may have formed from material transferred between the stars.
John Timmer
–
May 22, 2025 2:24 pm
|
5
Credit:
NASA/Goddard Space Flight Center
Credit:
NASA/Goddard Space Flight Center
Story text
Size
Small
Standard
Large
Width
*
Standard
Wide
Links
Standard
Orange
* Subscribers only
Learn more
While our Sun prefers to go solo, many other stars are parts of binary systems, with a pair of stars gravitationally bound to each other. In some cases, the stars are far enough apart that planets can form around each of them. But there are also plenty of tight binary systems, where the stars orbit each other at a radius that would place them both comfortably inside our Solar System. In these systems, exoplanets tend to be found at greater distances, in orbits that have them circling both stars.
On Wednesday, scientists described a system that seems to be neither of the above. It is a tight binary system, with a heavy central star that's orbited by a white dwarf at a distance two to three times larger than Earth's orbit. The lone planet confirmed to be in the system is squeezed in between the two, orbiting at a distance similar to Earth's distance from the Sun. And, as an added bonus, the planet is orbiting backward relative to the white dwarf.
Orbiting ν Octantis
The exosolar system is termed ν Octantis, and its primary star is just a bit heavier than our Sun. It's orbited by a far dimmer companion that's roughly half of our Sun's mass, but which hasn't been characterized in detail until now. The companion's orbit relative to the central star is a bit lopsided, ranging from about two astronomical unitsat its closest approach to roughly three AU at its farthest. And, until yesterday, the exact nature of the companion star was not clear.
The latter question was relatively easy to answer. Detailed imaging of the system in the near infrared should be able to resolve the two stars but was unable to pick up a second object with sufficient brightness. That eliminates any main sequence stars, leaving a white dwarf as the only likely answer. But that's not the only thing that's orbiting the central star of ν Octantis.
Earlier studies of the system had suggested that there was also an exoplanet present in the system. But the properties of its orbit made little sense, in that nobody could seem to figure out a stable orbit that would be consistent with the observations. The only thing that was clear was that the most stable orbits appeared to require that the planet have a retrograde motion, meaning orbiting in the opposite direction to the companion star. ν Octantis definitely fell into the vast category of "more data is needed" questions.
And more data is exactly what a small international team of scientists got, with nearly two years of additional observations using the HARPSinstrument in Chile. The data clearly confirmed the existence of a planet in a retrograde orbit and suggested that the plane of its orbit was 17° off from the plane formed by the orbits of the two stars. Unfortunately, modeling variations on this orbit through time indicated that 98 percent of them were unstable within 50 million years.
So, the researchers tested a range of orbital properties that would keep everything in a single plane. This provided a solution where modeling variations on it led to 75 percent of the orbits being stable out past 50 million years. So, the researchers settle on this as the most likely description of the system.
These orbits do have the planet in ν Octantis in a retrograde orbit, meaning it's moving in the opposite direction from the smaller star in the system. The orbit is roughly one AU, meaning its typical distance to the central star is similar to that of the Earth's distance to the Sun. But the orbit is somewhat squished, with one half of the orbit being significantly closer to the central star than the other.
And, critically, the entire orbit is within the orbit of the smaller companion star. The gravitational forces of a tight binary should prevent any planets from forming within this space early in the system's history. So, how did the planet end up in such an unusual configuration?
A confused past
The fact that one of the stars present in ν Octantis is a white dwarf suggests some possible explanations. White dwarfs are formed by Sun-like stars that have advanced through a late helium-burning period that causes them to swell considerably, leaving the outer surface of the star weakly bound to the rest of its mass. At the distances within ν Octantis, that would allow considerable material to be drawn off the outer companion and pulled onto the surface of what's now the central star. The net result is a considerable mass transfer.
This could have done one of two things to place a planet in the interior of the system. One is that the transferred material isn't likely to make an immediate dive onto the surface of the nearby star. If the process is slow enough, it could have produced a planet-forming disk for a brief period—long enough to produce a planet on the interior of the system.
Alternatively, if there were planets orbiting exterior to both stars, the change in the mass distribution of the system could have potentially destabilized their orbits. That might be enough to cause interactions among the planets to send one of them spiraling inward, where it was eventually captured in the stable retrograde orbit we now find it.
Either case, the authors emphasize, should be pretty rare, meaning we're unlikely to have imaged many other systems like this at this stage of our study of exoplanets. They do point to another tight binary, HD 59686, that appears to have a planet in a retrograde orbit. But, as with ν Octantis, the data isn't clear enough to rule out alternative configurations yet. So, once again, more data is needed.
Nature, 2025. DOI: 10.1038/s41586-025-09006-x .
John Timmer
Senior Science Editor
John Timmer
Senior Science Editor
John is Ars Technica's science editor. He has a Bachelor of Arts in Biochemistry from Columbia University, and a Ph.D. in Molecular and Cell Biology from the University of California, Berkeley. When physically separated from his keyboard, he tends to seek out a bicycle, or a scenic location for communing with his hiking boots.
5 Comments
#new #data #confirms #there #really
New data confirms: There really is a planet squeezed in between two stars
How'd that get there?
New data confirms: There really is a planet squeezed in between two stars
The planet may have formed from material transferred between the stars.
John Timmer
–
May 22, 2025 2:24 pm
|
5
Credit:
NASA/Goddard Space Flight Center
Credit:
NASA/Goddard Space Flight Center
Story text
Size
Small
Standard
Large
Width
*
Standard
Wide
Links
Standard
Orange
* Subscribers only
Learn more
While our Sun prefers to go solo, many other stars are parts of binary systems, with a pair of stars gravitationally bound to each other. In some cases, the stars are far enough apart that planets can form around each of them. But there are also plenty of tight binary systems, where the stars orbit each other at a radius that would place them both comfortably inside our Solar System. In these systems, exoplanets tend to be found at greater distances, in orbits that have them circling both stars.
On Wednesday, scientists described a system that seems to be neither of the above. It is a tight binary system, with a heavy central star that's orbited by a white dwarf at a distance two to three times larger than Earth's orbit. The lone planet confirmed to be in the system is squeezed in between the two, orbiting at a distance similar to Earth's distance from the Sun. And, as an added bonus, the planet is orbiting backward relative to the white dwarf.
Orbiting ν Octantis
The exosolar system is termed ν Octantis, and its primary star is just a bit heavier than our Sun. It's orbited by a far dimmer companion that's roughly half of our Sun's mass, but which hasn't been characterized in detail until now. The companion's orbit relative to the central star is a bit lopsided, ranging from about two astronomical unitsat its closest approach to roughly three AU at its farthest. And, until yesterday, the exact nature of the companion star was not clear.
The latter question was relatively easy to answer. Detailed imaging of the system in the near infrared should be able to resolve the two stars but was unable to pick up a second object with sufficient brightness. That eliminates any main sequence stars, leaving a white dwarf as the only likely answer. But that's not the only thing that's orbiting the central star of ν Octantis.
Earlier studies of the system had suggested that there was also an exoplanet present in the system. But the properties of its orbit made little sense, in that nobody could seem to figure out a stable orbit that would be consistent with the observations. The only thing that was clear was that the most stable orbits appeared to require that the planet have a retrograde motion, meaning orbiting in the opposite direction to the companion star. ν Octantis definitely fell into the vast category of "more data is needed" questions.
And more data is exactly what a small international team of scientists got, with nearly two years of additional observations using the HARPSinstrument in Chile. The data clearly confirmed the existence of a planet in a retrograde orbit and suggested that the plane of its orbit was 17° off from the plane formed by the orbits of the two stars. Unfortunately, modeling variations on this orbit through time indicated that 98 percent of them were unstable within 50 million years.
So, the researchers tested a range of orbital properties that would keep everything in a single plane. This provided a solution where modeling variations on it led to 75 percent of the orbits being stable out past 50 million years. So, the researchers settle on this as the most likely description of the system.
These orbits do have the planet in ν Octantis in a retrograde orbit, meaning it's moving in the opposite direction from the smaller star in the system. The orbit is roughly one AU, meaning its typical distance to the central star is similar to that of the Earth's distance to the Sun. But the orbit is somewhat squished, with one half of the orbit being significantly closer to the central star than the other.
And, critically, the entire orbit is within the orbit of the smaller companion star. The gravitational forces of a tight binary should prevent any planets from forming within this space early in the system's history. So, how did the planet end up in such an unusual configuration?
A confused past
The fact that one of the stars present in ν Octantis is a white dwarf suggests some possible explanations. White dwarfs are formed by Sun-like stars that have advanced through a late helium-burning period that causes them to swell considerably, leaving the outer surface of the star weakly bound to the rest of its mass. At the distances within ν Octantis, that would allow considerable material to be drawn off the outer companion and pulled onto the surface of what's now the central star. The net result is a considerable mass transfer.
This could have done one of two things to place a planet in the interior of the system. One is that the transferred material isn't likely to make an immediate dive onto the surface of the nearby star. If the process is slow enough, it could have produced a planet-forming disk for a brief period—long enough to produce a planet on the interior of the system.
Alternatively, if there were planets orbiting exterior to both stars, the change in the mass distribution of the system could have potentially destabilized their orbits. That might be enough to cause interactions among the planets to send one of them spiraling inward, where it was eventually captured in the stable retrograde orbit we now find it.
Either case, the authors emphasize, should be pretty rare, meaning we're unlikely to have imaged many other systems like this at this stage of our study of exoplanets. They do point to another tight binary, HD 59686, that appears to have a planet in a retrograde orbit. But, as with ν Octantis, the data isn't clear enough to rule out alternative configurations yet. So, once again, more data is needed.
Nature, 2025. DOI: 10.1038/s41586-025-09006-x .
John Timmer
Senior Science Editor
John Timmer
Senior Science Editor
John is Ars Technica's science editor. He has a Bachelor of Arts in Biochemistry from Columbia University, and a Ph.D. in Molecular and Cell Biology from the University of California, Berkeley. When physically separated from his keyboard, he tends to seek out a bicycle, or a scenic location for communing with his hiking boots.
5 Comments
#new #data #confirms #there #really
·86 Ansichten
