A cosmic tango: this distant planet's very strange orbit points to a violent and chaotic past

There are a number of reports on this exoplanet system.

Reference paper, HD 83443c: A highly eccentric giant planet on a 22-year orbit, https://arxiv.org/abs/2204.05711, 12-April-2022. "We report the discovery of a highly eccentric long-period Jovian planet orbiting the hot-Jupiter host HD 83443. By combining radial velocity data from four instruments (AAT/UCLES, Keck/HIRES, HARPS, Minerva-Australis) spanning more than two decades, we find evidence for a planet with m~sin~i=1.35+0.07/−0.06 mj, moving on an orbit with a=8.0±0.8 au and eccentricity e=0.76±0.05. We combine our radial velocity analysis with \textit{Gaia} eDR3 /\textit{Hipparcos} proper motion anomalies and derive a dynamical mass of 1.5+0.5−0.2MJup. We perform a detailed dynamical simulation that reveals locations of stability within the system that may harbor additional planets, including stable regions within the habitable zone of the host star. HD 83443 is a rare example of a system hosting a hot Jupiter and an exterior planetary companion. The high eccentricity of HD 83443c suggests that a scattering event may have sent the hot Jupiter to its close orbit while leaving the outer planet on a wide and eccentric path."

My observation, modeling the *scattering event* to explain these two exoplanets looks challenging :) Details for both exoplanets with properties can be seen in the exoplanet sites.

The Extrasolar Planet Encyclopaedia — HD 83443 b (exoplanet.eu)
The Extrasolar Planet Encyclopaedia — HD 83443 c (exoplanet.eu)

NASA Exoplanet Archive (caltech.edu)

HD 83443 c shows a semi-major axis of 8 au, b a = 0.0406 au.
Some more notes here on this interesting exoplanet report. Another report was published last month, A cosmic tango: This distant planet's strange orbit points to a violent and chaotic past, https://phys.org/news/2022-07-cosmic-tango-distant-planet-strange.html

My observation. Presently HD 83443 b semi-major axis = 0.0406 au, e = 0.012. HD 83443c semi-major axis = 8.0 au, e = 0.76. Currently the semi-major axis is some 197x larger for HD 83443 c than HD 83443 b. Given the properties for HD 83443 c with e = 0.76, the periastron ~ 1.92 au, apoastron (apastron) ~ 14 au. The initial birthplace for both exoplanets in HD 83443 system and effect(s) of a near miss or near collision requires some serious modeling to account for the two-exoplanet system using migrating planets in a large disc to explain their present orbits. Using properties shown for HD 83443 b, I calculate P = 3.1491E+00 days, listed P = 2.985628-day orbital period. In 1 Gyr this exoplanet could complete 1.1599E+11 revolutions or about 116 billion if in a stable orbit. No disc is reported at HD 83443 system with age published as 2.94 Gyr old. Using the 1 solar mass MMSN and applying to the host star 0.9 solar mass size, a postulated protoplanetary disc may contain 2.996635E+03 or nearly 3,000 earth masses, total gas and dust. As the phys.org report stated about this two-exoplanet system, “The newly-discovered world, HD83443c, might be the reason its sibling ended up on its current hellish orbit."

I note some unobserved objects (UOs) in the report.

1. Primordial protoplanetary disc around HD 83443
2. The two exoplanets initial birth locations in the disc
3. Planet-planet near miss when the system was young (e.g., Planet–
planet scattering in the upsilon Andromedae system, https://www.nature.com/articles/nature03427,
4. Migrations of the two planets to their present orbits.

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