Three Small Super-Earths Transiting the nearby star GJ 9827 (1709.01527v2)

Abstract: We report on the discovery of three transiting planets around GJ~9827. The planets have radii of 1.75${-0.12}^{+0.11 }$, 1.36${- 0.09 }^{+ 0.09}$, and 2.10${- 0.15 }^{+ 0.15 }$~R${\oplus}$, and periods of 1.20896, 3.6480, and 6.2014 days, respectively. The detection was made in Campaign 12 observations as part of our K2 survey of nearby stars. GJ~9827 is a $V = 10.39$~mag K6V star at distance of 30.3 parsecs and the nearest star to be found hosting planets by Kepler and K2. The radial velocity follow-up, high resolution imaging, and detection of multiple transiting objects near commensurability drastically reduce the false positive probability. The orbital periods of GJ~9827~b, c and d planets are very close to the 1:3:5 mean motion resonance. Our preliminary analysis shows that GJ~9827 planets are excellent candidates for atmospheric observations. Besides, the planetary radii span both sides of the rocky and gaseous divide, hence the system will be an asset in expanding our understanding of the threshold.

• The paper presents the discovery of three super-Earths transiting GJ 9827, detailing their radii of 1.75, 1.36, and 2.11 Earth radii and orbital periods of 1.209, 3.648, and 6.201 days.
• The paper utilizes precise K2 photometry, advanced detrending, and high-resolution imaging to confirm the planetary signals and reduce false positives.
• The paper identifies these exoplanets as prime candidates for atmospheric studies, offering key insights into the rocky-to-gaseous transition in small planets.

Overview of "Three Super-Earths Transiting the Nearby Star GJ 9827"

The discovery of three super-Earths around the nearby star GJ 9827 provides intriguing insights into exoplanetary systems and offers significant potential for atmospheric characterization. Detailed in this publication, these exoplanets exhibit radii of approximately 1.75, 1.36, and 2.11 Earth radii, with orbital periods of 1.209, 3.648, and 6.201 days, respectively. GJ 9827, a relatively bright K6V type star located 30.3 parsecs away, marks the closest exoplanet-hosting star discovered by the Kepler and K2 missions. The findings emphasize the importance of radial velocity follow-up and high-resolution imaging, reducing the false positive probability substantially, and revealing that the planets' orbits are near a 1:3:5 mean motion resonance.

Detailed Observations and Data Analysis

The detection was part of the K2 survey's Campaign 12, utilizing precise photometric data and a sophisticated pipeline to detrend systematic noise inherent in K2 observations. The analysis reveals that the GJ 9827 planets reside across the critical rocky-to-gaseous threshold, making them excellent candidates for advancing our understanding of this transition zone. The radial velocity measurements, combined with the transit data, indicate no significant RV variation, reinforcing the validity of the detected signals as planetary in origin.

Implications for Theoretical and Applied Astronomy

The system's architecture, featuring planets on both sides of the rocky and gaseous dichotomy, provides a unique opportunity to investigate planetary formation and compositional diversity. The presence of planets in close proximity to resonance aligns with patterns observed in other multi-planetary systems, suggesting possible dynamical interactions and histories of migration and capture.

From a theoretical standpoint, understanding the mass-radius relationship in this system could refine models considering the atmospheric compositions and potential habitability conditions of small, nearby exoplanets. The atmospheric characteristics of these planets are especially pertinent in light of upcoming exoplanetary atmosphere studies with next-generation telescopes such as the JWST.

Prospects for Atmospheric Studies

The planets around GJ 9827 are promising targets for atmospheric studies due to their proximity and the brightness of their host star. The paper notes that all three planets rank highly among super-Earths for favorable atmospheric signal-to-noise ratios, indicating potentially rich datasets for observatories capable of infrared and broad-spectrum analysis. Given their relative brightness, the expectation is that atmospheric observations could yield valuable information on their chemical compositions and climatic conditions.

Conclusions and Future Directions

This paper illustrates the ongoing contributions of the K2 mission in detecting planetary systems conducive to further investigation, particularly regarding composition and atmospheric studies. While the current paper establishes fundamental parameters and proposes possible scenarios for the system's dynamics and structure, future research will likely include detailed RV campaigns and high-precision photometric observations. These efforts aim to elucidate the planetary densities further and explore any potential mystical connections among the planets in the GJ 9827 system.

Overall, this discovery underscores the potential of nearby exoplanetary systems to enrich our understanding of planetary formation and evolution, showcasing the ingenuity of combined observational techniques in fine-tuning our models of planetary systems beyond our own.