A planetary system consisting of 4 giant planets has been
detected around HD 141399, a nearby, slightly evolved, K-type star. This
discovery was made by Vogt et al. (2014) using precise radial velocity data
from the HIRES (High Resolution Echelle Spectrometer) instrument on the Keck-I
telescope and the Levy spectrometer on Lick Observatory’s Automated Planet
Finder (APF). 91 observations spread over 10.5 years indicate the presence of 4
planets with orbital periods of 94.35, 202.08, 1070.35 and 3717.35 days, and
minimum masses of 0.46, 1.36, 1.22 and 0.69 Jupiter-mass. In order of
increasing distance from the host star, the 4 planets are dubbed HD 141399 b,
c, d and e.
Figure 1: Artist’s impression of a ringed giant planet with
a moon in the foreground. Image credit: Nick Stevens.
Figure 2: Artist’s impression of a giant planet.
Compared to the Sun, HD 141399 has 1.59 ± 0.39 times its
luminosity, 1.46 ± 0.15 times its radius and 1.14 ± 0.08 times its mass. HD
141399 is a rare example of a star with a planetary system consisting of
multiple giant planets. Other examples of such planetary systems include Upsilon
Andromedae - a system of 4 giant planets, and 55 Cancri A - a system with one close-in
super-Earth and 4 giant planets. An unusual aspect of HD 141399 is that its inner
3 giant planets lie at distances normally associated with the terrestrial
planets (i.e. Mercury, Venus, Earth and Mars) in our Solar System. The fourth planet,
labelled HD 141399 e, is a Jupiter-like planet with a Jupiter-like orbital
period of roughly a decade.
The two inner planets - HD 141399 b and c, have estimated
equilibrium temperatures of 500 K and 390 K, respectively. At these
temperatures, the atmospheres of both planets are expected to be dominated by
water clouds and complex chemistry. Transits by HD 141399 b or c, if they do
occur, would be of great scientific value since it would allow their
atmospheres to be studied via transmission spectroscopy by the Hubble Space
Telescope (HST) or James Webb Space Telescope (JWST). HD 141399 b and c lie in
a relatively unexplored temperature regime between the well-studied
hot-Jupiters at one extreme and the giant planets (i.e. Jupiter and Saturn) in our
Solar System. Nevertheless, the odds that HD 141399 b or c can be observed in
transit are 1.3 and 0.8 percent, respectively.
Reference:
Vogt et al. (2014), “A 4-Planet System Orbiting the K0V Star
HD 141399”, arXiv:1404.7462 [astro-ph.EP]