55 Cancri e
|Extrasolar planet||List of extrasolar planets|
|Star||55 Cancri A|
|Right ascension||(α)||08h 52m 35.8s|
|Declination||(δ)||+28° 19′ 51″|
|Distance||40.3 ± 0.4 ly
(12.3 ± 0.1 pc)
|Mass||(m)||0.95 ± 0.10 M☉|
|Radius||(r)||1.152 ± 0.035 R☉|
|Temperature||(T)||5373 ± 9.7 K|
|Semimajor axis||(a)||0.01560 ± 0.00011 AU
|Eccentricity||(e)||0.17 ± 0.04|
|Orbital period||(P)||0.7365449 (± 0.000005) d|
|Inclination||(i)||83.4 ± 1.7°|
|(ω)||181 ± 2°|
|Time of periastron||(T0)||2,449,999.83643 ± 0.0001 JD|
|Semi-amplitude||(K)||6.2 ± 0.2 m/s|
|Mass||(m)||8.63 ± 0.35 M⊕|
|Radius||(r)||2.00 ± 0.14 R⊕|
−1.1 g cm-3
|Discovery date||August 30, 2004|
|Discoverer(s)||McArthur et al.|
|Detection method||Radial velocity|
|Discovery site||Texas, USA|
55 Cancri Ae, Rho1 Cancri e, HD 75732 e
55 Cancri e (abbreviated 55 Cnc e) is an extrasolar planet orbiting the Sun-like star 55 Cancri A. Its mass is about 7.8 Earth masses and its diameter is about twice that of Earth's, thus classifying it as the first Super-Earth discovered around a main sequence star, predating Gliese 876 d by a year. It takes less than 18 hours to complete an orbit and is the innermost known planet in its planetary system. 55 Cancri e was discovered on August 30, 2004. However, until the 2010 observations and recalculations, this planet had been thought to take about 2.8 days to orbit the star. In October 2012, it was announced that 55 Cancri e could be a carbon planet.
Like the majority of known extrasolar planets (found previous to the Kepler mission), 55 Cancri e was discovered by detecting variations in its star's radial velocity. This was achieved by making sensitive measurements of the Doppler shift of the spectrum of 55 Cancri A. At the time of its discovery, three other planets were known orbiting the star. After accounting for these planets, a signal at around 2.8 days remained, which could be explained by a planet of at least 14.2 Earth masses in a very close orbit. The same measurements were used to confirm the existence of the uncertain planet 55 Cancri c.
55 Cancri e was one of the first extrasolar planets with a mass comparable to that of Neptune to be discovered. It was announced at the same time as another "hot Neptune" orbiting the red dwarf star Gliese 436 named Gliese 436 b.
Planet challenged 
In 2005 the existence of planet e was questioned by Jack Wisdom in a reanalysis of the data. According to him, instead of the 2.8-day planet there is a planet with a mass similar to that of Neptune in a 261-day orbit around 55 Cancri A. In 2007, Debra Fischer and colleagues at San Francisco State University published a new analysis indicating that both planets existed; the planet in the 260-day orbit was accordingly designated 55 Cancri f.
The planet's transit of its primary was announced on April 27, 2011, based on two weeks of nearly continuous photometric monitoring with the MOST space telescope. The transits occur with the period (0.74 days) and phase that had been predicted by Dawson & Fabrycky. This is one of the few planetary transits to be confirmed around a well-known star, and allowed investigations into the planet's composition.
Orbit and mass 
The radial velocity method used to detect 55 Cancri e obtains the minimum mass of 7.8 times that of Earth, or 48% of the mass of Neptune. The transit shows that its inclination is about 83.4 ± 1.7. So the real mass is close to the minimum. 55 Cancri e is further coplanar with b.
It was initially unknown whether 55 Cancri e was a small gas giant like Neptune or a large rocky terrestrial planet. In 2011, a transit of the planet was confirmed, allowing scientists to calculate its density. At first it was suspected to be a water planet. As initial observations showed no hydrogen in its Lyman-alpha transit signature, Ehrenreich mused that its volatiles might be carbon dioxide instead of water or hydrogen.
An alternative possibility is that 55 Cancri e is a solid planet made of carbon-rich material rather than the oxygen-rich material that makes up the terrestrial planets in our solar system. In this case, roughly a third of the planet's mass would be carbon, much of which may be in the form of diamond as a result of the temperatures and pressures in the planet's interior. Further observations are necessary to confirm the nature of the planet.
See also 
- Dawson et al.; Fabrycky (2010-05-21). "Radial velocity planets de-aliased. A new, short period for Super-Earth 55 Cnc e". The Astrophysical Journal 722: 937–953. arXiv:1005.4050. Bibcode:2010ApJ...722..937D. doi:10.1088/0004-637X/722/1/937.
- Fischer, D. A. et al. (2007-12-23). "Five Planets Orbiting 55 Cancri". Astrophysics 675: 790–801. arXiv:0712.3917. Bibcode:2008ApJ...675..790F. doi:10.1086/525512.
- Winn, J.N et al. (2008). "A Super Earth Transiting a Naked-Eye Star". Astronomy & Astrophysics. arXiv:1104.5230. Bibcode:2011ApJ...737L..18W. doi:10.1088/2041-8205/737/1/L18.
- Staff (20 January 2012). "Oozing Super-Earth: Images of Alien Planet 55 Cancri e". Space.com. Retrieved 2012-01-21.
- Chris Wickham (11 October 2012). "A diamond bigger than Earth?". Reuters. Retrieved 11 October 2012.
- Nikku Madhusudhan, Olivier Mousis, Kanani K. M. Lee (2012). "A Possible Carbon-rich Interior in Super-Earth 55 Cancri e". Astrophysical Journal Letters. arXiv:1210.2720.
- McArthur, B. et al. (2004). "Detection of a NEPTUNE-mass planet in the ρ1 Cnc system using the Hobby-Eberly Telescope". The Astrophysical Journal 614 (1): L81 – L84. arXiv:astro-ph/0408585. Bibcode:2004ApJ...614L..81M. doi:10.1086/425561.
- Wisdom, J. (2005). "Evidence of a Neptune-Sized Planet in the ρ1 Cancri System" (PostScript). The Astrophysical Journal Letters (submitted).
- Minkel, JR (November 6, 2007). "Record Fifth Planet Discovered Around Distant Star". Scientific American.
- Winn, J.N. et al. (2011). "A Super-Earth Transiting a Naked-Eye Star". The Astrophysical Journal Letters 737 (1). doi:10.1088/2041-8205/737/1/L18.
- Lucas, P. W.; Hough, J. H.; Bailey, J. A.; Tamura, M.; Hirst, E.; Harrison, D. (2007). "Planetpol polarimetry of the exoplanet systems 55 Cnc and tau Boo". Monthly Notices of the Royal Astronomical Society 393: 229–244. arXiv:0807.2568. Bibcode:2009MNRAS.393..229L. doi:10.1111/j.1365-2966.2008.14182.x.
- Science@NASA. "NASA Space Telescope Sees the Light from an Alien Super-Earth". NASA. Retrieved 2012-05-10.
- D. Ehrenreich et al. (October 2, 2012). "Hint of a transiting extended atmosphere on 55 Cancri b". Astronomy & Astrophysics. doi:10.1051/0004-6361/201219981.
- Science Daily. 11 October 2012 http://www.sciencedaily.com/releases/2012/10/121011090647.htm
|url=missing title (help). Retrieved 11 October 2012. Text " title Nearby Super-Earth Likely a Diamond Planet " ignored (help)
|Wikimedia Commons has media related to: 55 Cancri e|
- Jean Schneider (2011). "Notes for Planet 55 Cnc e". Extrasolar Planets Encyclopaedia. Retrieved 8 October 2011.
- Extrasolar Visions: 55 Cancri e
- Spitzer Detects a Steaming Super-Earth Eclipsing Its Star (JPL 09.26.11)