The four-planet system had been hiding out in the M-shaped, northern hemisphere constellation Cassiopeia, 'just' 21 light years from Earth, a team reported in the journal Astronomy & Astrophysics.
It comprises four planets -- one giant and three super-Earths orbiting a star dubbed HD219134. Super-Earths have a mass higher than Earth's but are lighter than gas giants like Neptune, Saturn or Jupiter. They can be made of gas, rock, or both.
The planet with the shortest orbit, HD219134b, zips around every three days, and has now been observed transiting across the face of its star as seen from the vantage point of Earth.
Measurements from the ground and with NASA's Spitzer space telescope showed its mass was 4.5 times higher than Earth's, and that it was 1.6 times larger.
"Its mean density is close to the density of Earth, suggesting a possibly similar composition as well," said a press statement from the University of Geneva, whose astronomers took part in the research.
"It's very close to the star. The temperature is about 700 degrees" Kelvin (427 Celsius, 800 Fahrenheit), study co-author Stephane Udry said. It was not in the so-called "habitable zone" of its star, and would not have liquid water necessary for life.



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