Mu Arae d

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**Mu Arae d**
Parent star
Extrasolar planet		List of extrasolar planets
Artist's rendering of Mu Arae e as a "super-earth"
Star		Mu Arae
Constellation		Ara
Right ascension	(α)	17^h 44^m 08.7^s
Declination	(δ)	−51° 50′ 03″
Distance		49.8 ly (15.3 pc)
Spectral type		G3IV–V
Orbital elements
Semimajor axis	(a)	0.0909^[1] AU
Eccentricity	(e)	0.172 ± 0.04
Orbital period	(P)	9.6386 ± 0.0015 d
Inclination	(i)	?°
Angular distance	(θ)	5.882 mas
Longitude of periastron	(ω)	4 ± 2°
Time of periastron	(T₀)	2452991 ± 0.4 JD
Semi-amplitude	(K)	4.1 ± 0.2 m/s
Physical characteristics
Mass	(m)	>0.03321 M_J (>10.56 M_⊕)
Temperature	(T)	~900 K
Discovery information
Discovery date		August 25, 2004
Discoverer(s)		Santos, Bouchy Mayor, Pepe
Detection method		Doppler Spectroscopy
Discovery site		Chile
Discovery status		Published
Other designations
HD 160691 d

Mu Arae d, also known as HD 160691 d, is an extrasolar planet orbiting around Mu Arae. Its discovery was announced on August 25, 2004. At the time, its minimum mass was reported at just 14 times that of Earth, ^[2] although later work established a value of 10.5 Earth masses.^[3] It orbits very close to Mu Arae, completing one revolution every 9.6 days. The discovery was made with the aid of the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph, at the European Southern Observatory's La Silla Observatory in Chile. The data that revealed the presence of this planet was gathered on 8 nights of observations in June 2004.

According to current models of planet formation, ESO scientists believe that μ Arae d is likely to be a rocky planet, not a gas giant; 14 Earth masses is theoretically the maximum size for a terrestrial planet. A rocky planet this size could certainly have formed, since Mu Arae has a higher metallicity than our Sun. If this is the case, Mu Arae d may be the first rocky planet discovered outside our Solar System orbiting a main sequence star. The surface of the planet must be very hot because of its closeness to Mu Arae; it is estimated that the surface temperature would be about 900 K. Its surface would likely be volcanic. The probability of life as we know it existing on this planet is thus extremely small. An alternative possibility is that this planet is a small gas giant similar to Uranus or Neptune.

None of the four planets orbiting Mu Arae are directly visible from Earth using currently available tools. All four were found using the radial velocity method of extrasolar planet detection.

[edit] References

^ HD 160691 page. Geneva Observatory. Retrieved on 2007-08-26.
^ N.C. Santos, F. Bouchy, M. Mayor, F. Pepe, D. Queloz, S. Udry, C. Lovis, M. Bazot, W. Benz, J.-L. Bertaux, G. Lo Curto, X. Delfosse, C. Mordasini, D. Naef, J.-P. Sivan, and S. Vauclair. A 14 Earth-masses exoplanet around μ Arae. arXiv.
^ F. Pepe, A.C.M. Correia, M. Mayor, O. Tamuz, W. Benz, J.-L. Bertaux, F. Bouchy, J. Couetdic, J. Laskar, C. Lovis, D. Naef, D. Queloz, N. C. Santos, J.-P. Sivan, D. Sosnowska, and S. Udry. μ Ara, a system with four planets. arXiv.