Artist’s impression of a view from the HD 7924 planetary system looking back toward our sun, which would be easily visible to the naked eye. Since HD 7924 is in our northern sky, an observer looking back at the sun would see objects like the Southern Cross and the Magellanic Clouds close to our sun in their sky.
The following are data quoted, with little modification, from the paper that describes the discovery:
The Eta-Earth Survey at Keck Observatory played a important role in the discovery that super-Earths are abundant. Using the HIRES spectrometer, our team searched for planets in a volume-limited sample of 166 nearby G and K dwarf stars. Our search yielded new planets and detection limits for each star.
The first low-mass planet discovered in the Eta-Earth Survey was HD 7924b, a super-Earth with a mass of 8.7 M⊕ and an orbital period of 5.4 days.
HD 7924, also known as HIP 6379 or GJ 56.5, is a nearby (16.82 pc) and bright K0.5V dwarf star. It is slightly metal poor relative to the Sun. It is relatively inactive, but we do detect some low-level chromospheric activity nonetheless. We computed the stellar mass and radius from Teff, log g, and [Fe/H] and found 0.81 ± 0.02 M⊙ and 0.75 ± 0.03 R⊙.
The two new planets have minimum masses of Mc sin ic = 7.8 M⊕ and Md sin id = 6.3 M⊕, and orbit HD 7924 with semi-major axis of ac = 0.113 AU and ad = 0.155 AU. Their orbital periods are of 15.3 and 24.5 days. Both planets receive far too much radiation from HD 7924 to be within the habitable zone with incident stellar irradiation values 114, 28, and 15 times that received from the Sun by Earth for planets b, c, and d respectively. Assuming that these planets have bond albebos similar to the mean total albedos of super-Earths (At = 0.32) their equilibrium temperatures are 826, 584, and 499 K.
