There may be a large number of undetected giant planet-like bodies in the neighborhood of our Sun, according to a Carnegie-led team of astronomers from Canada, the United States and Chile.

An artists conception of a free-floating planet-like object. Image credit: NASA / JPL.

Similarly-aged stars moving through space together in a group are of great interest to astronomers, because they are considered a prime target to hunt for brown dwarfs and free-floating planetary-mass objects.

Recent studies of the TW Hydrae (TWA) group have revealed some of the first known isolated giant planet-sized objects in the solar neighborhood, roughly 100 light-years away. This group contains a few dozen 10-million-year-old stars, all moving together through space.

Two recent discoveries in particular demonstrate the interest of TWA as a laboratory for understanding this isolated planetary-mass population, said Carnegies astronomer Jonathan Gagn and co-authors.

2MASS J11193254-1137466 and 2MASS J11472421-2040204 are both candidate members of TWA with spectral types L7 that display signs of youth, and with estimated masses as low as 5-7 Jupiter masses. Their close distances to the Sun place them at the nearer side of the TWA spatial distribution.

In order to determine whether or not there are more stand-alone planetary mass-sized objects like these in TWA, the astronomers undertook the calculation of an astronomical measurement called the initial mass function.

This function can be used to determine the distribution of mass in the group and to predict the number of undiscovered objects that might exist inside of it.

The initial mass function of TWA had never been published before, Dr. Gagn noted.

In the process of this analysis, the researchers were able to determine that there are probably many more objects 5-7 times the mass of Jupiter in the association that havent been discovered yet.

A tentative overpopulation of isolated planetary-mass members similar to 2MASS J114724212040204 and 2MASS J111932541137466 is identified, they said.

This indicates that there might be as many as 10+13-5 similar members of TWA with hot-start model-dependent masses estimated at 5-7 Jupiter masses, most of which would be too faint to be detected in the Two Micron All Sky Survey (2MASS).

TWA extends out to a distance of 250 light-years, but our instruments arent sensitive enough yet to detect giant planets-like members at this distance, hence many of them might remain to be discovered, Dr. Gagn explained.

The research is published in the Astrophysical Journal Supplement Series (arXiv.org preprint).

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Jonathan Gagn et al. 2017. BANYAN. IX. The Initial Mass Function and Planetary-mass Object Space Density of the TW HYA Association. ApJS 228, 18; doi: 10.3847/1538-4365/228/2/18

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