Evolution and Magnitudes of Candidate Planet Nine (1602.07465v2)

Abstract: The recently renewed interest in a possible additional major body in the outer solar system prompted us to study the thermodynamic evolution of such an object. We assumed that it is a smaller version of Uranus and Neptune. We modeled the temporal evolution of the radius, temperature, intrinsic luminosity, and the blackbody spectrum of distant ice giant planets. The aim is also to provide estimates of the magnitudes in different bands to assess whether the object might be detectable. Simulations of the cooling and contraction were conducted for ice giants with masses of 5, 10, 20, and 50 Mearth that are located at 280, 700, and 1120 AU from the Sun. The core composition, the fraction of H/He, the efficiency of energy transport, and the initial luminosity were varied. The atmospheric opacity was set to 1, 50, and 100 times solar metallicity. We find for a nominal 10 Mearth planet at 700 AU at the current age of the solar system an effective temperature of 47 K, much higher than the equilibrium temperature of about 10 K, a radius of 3.7 Rearth, and an intrinsic luminosity of 0.006 Ljupiter. It has estimated apparent magnitudes of Johnson V, R, I, L, N, Q of 21.7, 21.4, 21.0, 20.1, 19.9, and 10.7, and WISE W1-W4 magnitudes of 20.1, 20.1, 18.6, and 10.2. The Q and W4 band and other observations longward of about 13 microns pick up the intrinsic flux. If candidate Planet 9 has a significant H/He layer and an efficient energy transport in the interior, then its luminosity is dominated by the intrinsic contribution, making it a self-luminous planet. At a likely position on its orbit near aphelion, we estimate for a mass of 5, 10, 20, and 50 Mearth a V magnitude from the reflected light of 24.3, 23.7, 23.3, and 22.6 and a Q magnitude from the intrinsic radiation of 14.6, 11.7, 9.2, and 5.8. The latter would probably have been detected by past surveys.

• The paper models the thermodynamic evolution and observable characteristics of hypothetical Planet Nine across different masses (5-50 M⊕) and distances (280-1120 AU) from the Sun.
• Key findings include predicting that a 10 M⊕ candidate at 700 AU would have an effective temperature of 47 K due to intrinsic luminosity, and would be detectable primarily in mid- and far-infrared bands (e.g., WISE W4 magnitude 10.2).
• The study highlights that intrinsic self-luminosity significantly aids detection, and future telescopes like the Vera C. Rubin Observatory have the potential to discover such a distant object.

Analysis of "Evolution and Magnitudes of Candidate Planet Nine"

The exploration of potential celestial objects in the outer solar system remains a vital endeavor in advancing our understanding of planetary formation and evolution. This paper, authored by Esther F. Linder and Christoph Mordasini, presents an in-depth paper on the hypothesized "Planet Nine," an additional planet possibly existing at a significant distance from the Sun. The researchers focus on modeling the thermodynamic evolution of such a candidate planet by considering it as a smaller analog to the known ice giants, Uranus and Neptune.

Key Findings and Methodologies

The paper employs comprehensive simulation methodologies to evaluate the evolution of a hypothetical planet with masses of 5, 10, 20, and 50 Earth masses (M⊕), located at distances of 280, 700, and 1120 AU from the Sun. These distances correspond to various possible positions on its orbit given its considerable distance from the Sun. The simulations encompass diverse planetary parameters including the radius, effective temperature, intrinsic luminosity, and atmospheric conditions.

The notable result from the nominal 10 M⊕ model at 700 AU suggests an effective temperature of 47 K, distinctly higher than the equilibrium temperature of approximately 10 K, largely due to the significant intrinsic luminosity posed by the planet's internal processes. This is contrasted with observations of Neptune's present-day characteristics. The paper further elaborates on apparent magnitudes across various filters, predicting that the candidate would be perceptible primarily in mid- and far-infrared bands. For instance, at 700 AU, it would showcase apparent magnitudes of 21.7 in the Johnson V band and brighter values in specific infrared bands, as seen with a magnitude of 10.2 in the WISE W4 band.

Implications and Theoretical Underpinnings

The findings have profound implications for the detection potential of hypothetical distant objects. Importantly, with efficient energy transport in its interior, the planet could be self-luminous – a characteristic that greatly aids in detection by virtue of prominent intrinsic radiation, predominantly in infrared. Such self-luminosity might reflect the retention of significant heat from its formation stages, impacting theoretical models related to planetary ejection and evolution in the context of the solar system's dynamics.

Future Prospects and Speculations

The paper underscores the potential for detection of such a body despite its current evasion from surveys, depending on the composition and heat transport efficiency within its atmosphere and interior. Considerations of a potential Neptune-like, or alternatively a Uranus-like interior, delineate a pathway for future observational campaigns aimed at confirming or refuting the presence of candidate Planet 9. Upcoming telescopic capabilities, notably those of the Large Synoptic Survey Telescope (now known as the Vera C. Rubin Observatory) with its advanced sensitivity, harbor prospects for a breakthrough in detecting such outer solar system objects.

In conclusion, Linder and Mordasini's work provides a robust framework for future explorations of the hypothesized Planet Nine, contributing valuable insights into the observable characteristics that could one day reveal such an enigmatic presence in our solar system. The exploration of these extreme conditions not only aids direct discovery efforts but also enriches our understanding of the potential diversity and evolution mechanisms of planetary bodies far from their host stars.