- 3386 - PLANETS - free floating planets? Astronomers have discovered at least 70 new free-floating planets (FFPs), planets that wander through space without a parent star to orbit, in the Upper Scorpius OB stellar association, which is the nearest region of star formation to our Sun.
--------------------- 3386 - PLANETS - free floating planets?
- This is the largest sample of such planets found in a single group and it nearly doubles the number known over the entire sky. Identifying FFPs within a star cluster is a major challenge, like trying to find a needle in a haystack.
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- First, one needs eyes sensitive enough to detect the “needles”. While stars are relatively bright and easy to spot, planetary-mass members are several thousand times fainter and can only be detected with large aperture telescopes and sensitive detectors.
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- Second, one must identify the rare planetary-mass members (the “needles”, typically a few hundreds) within the overwhelming multitude of field stars and background galaxies (the “haystack").
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- To solve this challenge, the astronomers combined proper motions ( motion across the plane of the sky) with multi-wavelength photometry. Proper motions are an extremely effective method to identify members of an association since all the members were born from the same molecular cloud complex and have similar motions to the parent cloud.
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- Unrelated field stars have almost random proper motions, and background galaxies have no measurable proper motions. Photometric luminosities and colors are useful to refine the selection and reject the few remaining interlopers.
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- The astronomers also combined the vast number of images available in public astronomical archives with the new deep wide-field observations obtained with the best infrared and optical telescopes on the ground and in space.
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- Using over 80,000 wide-field images adding up to around 100 terabytes and spanning 20 years, they identified at least 70, and up to as many as 170 of these Jupiter-sized planets, as members of the Upper Scorpius association among the background stars and galaxies. This is by far the largest sample of FFPs in a single association, and almost doubles the number of FFPs known to date over the entire sky.
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- The nature and origin of FFPs remains unknown: do they form like stars through the gravitational collapse of small clouds of gas? Or, do they form like planets around stars and are then dynamically ejected or stripped off?
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- The number of FFPs discovered in the Upper Scorpius association exceeds the number of FFPs expected if they only form like stars from the collapse of a small molecular cloud, indicating that other mechanisms must be at play.
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- These observations suggest that giant-planet systems must form and become dynamically unstable within the observed lifetime (3-10 million years) of the region to contribute to the population of FFPs. Current studies suggest that dynamical instability among the giant planets in our Solar System may also have occurred at early times, although it was much less violent than the instability needed to eject planets as massive as the ones we have found.
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- FFPs, lurking far away from any star illuminating them, would normally be impossible to image. However, the astronomers took advantage of the fact that, in the few million years after their formation, these planets are still hot enough to glow, making them directly detectable by sensitive cameras on large telescopes.
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- The FFPs will be essential to study planetary atmospheres in the absence of a blinding host star, making the observation far easier and more detailed. The comparison with atmospheres of planets orbiting stars will provide key details about their formation and properties. Studying the presence of gas and dust around these objects, what we call 'circumplanetary discs’, will shed more light on their formation process.
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- There could be several billions of Jupiters roaming the Milky Way without a host star. This number would be even greater for Earth-mass planets since they are known to be more common than massive planets.
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- Using observations and archival data from several of NSF's NOIRLab's observatories, together with observations from telescopes around the world and in orbit, astronomers have discovered at least 70 new free-floating planets, planets that wander through space without a parent star, in a nearby region of the Milky Way.
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- Aastronomers, used observations and archival data from a number of large observatories, including facilities from NSF's NOIRLab, telescopes of the European Southern Observatory, the Canada-France-Hawaii Telescope, and the Subaru Telescope, amounting to 80,000 wide-field images over 20 years of observations.
The data include 247 images from the NEWFIRM extremely wide-field infrared imager at Kitt Peak National Observatory (KPNO) in Arizona.
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- 1348 images from the same NEWFIRM instrument after it was relocated to the Cerro Tololo Inter-American Observatory (CTIO) in Chile.
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- 2214 images from the Infrared Side Port Imager that was previously operating on the Víctor M. Blanco 4-meter Telescope at CTIO.
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- 3744 images from the Dark Energy Camera.
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- The free-floating planets lie in the Upper Scorpius OB association, which is 420 light-years away from Earth. This region contains a number of the most famous nebulae, including the Rho Ophiuchi cloud, the Pipe Nebula, Barnard 68, and the Coalsack.
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- Free-floating planets have mostly been discovered via microlensing surveys, in which astronomers watch for a brief chance alignment between an exoplanet and a background star. However, microlensing events only happen once, meaning follow-up observations are impossible.
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- These new planets were discovered using a different method. These planets, lurking far away from any star illuminating them, would normally be impossible to image. However, in the few million years after their formation, these planets are still hot enough to glow, making them directly detectable by sensitive cameras on large telescopes.
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- The team used the 80,000 observations to measure the light of all the members of the association across a wide range of optical and near-infrared wavelengths and combined them with measurements of how they appear to move across the sky.
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- They measured the tiny motions, the colors and luminosities of tens of millions of sources in a large area of the sky, allowing astronomers to securely identify the faintest objects in this region.
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- This discovery also sheds light on the origin of free-floating planets. Some scientists believe these planets can form from the collapse of a gas cloud that is too small to lead to the formation of a star, or that they could have been kicked out from their parent system.
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- The ejection model suggests that there could be even greater numbers of free-floating planets that are Earth-sized. The free-floating Jupiter-mass planets are the most difficult to eject, meaning that there might even be more free-floating Earth-mass planets.
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- The range in the number of free-floating planets occurs because the mass of the objects is not measured directly in this study. Objects larger than 13 Jupiter masses are not likely to be planets.
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- An upper limit on the mass of the objects was inferred from their brightness, which is dependent on their age. Since the age of the stellar association in which these planets reside is only known to a given certainty, the exact number of planets is also uncertain.
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- December 29, 2021 PLANETS - free floating planets? 3386
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