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55 Cancri b
Extrasolar planet List of extrasolar planets
Parent star

<tr> <td colspan="2">Star</td> <td>55 Cancri A</td></tr><tr> <td colspan="2">Constellation</td> <td>Cancer</td></tr><tr> <td>Right ascension</td> <td style="text-align: center">(α)</td> <td>08h 52m 35.8s</td></tr><tr> <td>Declination</td> <td style="text-align: center">(δ)</td> <td>+28° 19′ 51″</td></tr><tr> <td>Apparent magnitude</td> <td style="text-align: center">(mV)</td> <td>5.95</td></tr><tr><td colspan="2">Distance</td><td>40.3 ± 0.4 ly
(12.3 ± 0.1 pc)</td></tr><tr><td colspan="2">Spectral type</td> <td>G8V</td></tr><tr> <td>Mass</td> <td style="text-align: center">(m)</td> <td>0.95 ± 0.10 M</td></tr><tr> <td>Radius</td> <td style="text-align: center">(r)</td> <td>1.152 ± 0.035 R</td></tr><tr> <td>Temperature</td> <td style="text-align: center">(T)</td> <td>5373 ± 9.7 K</td></tr><tr> <td>Metallicity</td> <td style="text-align: center">[Fe/H]</td> <td>0.29</td></tr><tr> <td>Age</td> <td style="text-align: center"></td> <td>7.4–8.7 Gyr</td></tr>

Orbital elements

<tr><td>Semimajor axis</td><td style="text-align: center">(a)</td> <td>0.115 ± 0.0000011[1] AU
(17.2 Gm)</td></tr><tr><td> </td> <td style="text-align: center"> </td> <td>9.18 mas</td></tr><tr> <td>Periastron</td> <td style="text-align: center">(q)</td> <td>0.113 AU
(16.9 Gm)</td></tr><tr> <td>Apastron</td> <td style="text-align: center">(Q)</td> <td>0.116 AU
(17.4 Gm)</td></tr><tr> <td>Eccentricity</td> <td style="text-align: center">(e)</td> <td>0.014 ± 0.008[1]</td></tr><tr><td>Orbital period</td><td style="text-align: center">(P)</td> <td>14.65162 ± 0.0007[1] d
(0.04011325 y)</td></tr><tr> <td>Inclination</td> <td style="text-align: center">(i)</td> <td>~85[2][3]°</td></tr><tr> <td>Argument of
</td> <td style="text-align: center">(ω)</td> <td>131.94 ± 30[1]°</td></tr><tr> <td>Time of periastron</td> <td style="text-align: center">(T0)</td> <td>2,450,002.94749 ± 1.2[1] JD</td></tr><tr> <td>Semi-amplitude</td> <td style="text-align: center">(K)</td> <td>71.32 ± 0.41[1] m/s</td></tr>

Physical characteristics

<tr><td>Mass</td><td style="text-align: center">(m)</td><td>0.824 ± 0.007[1][2] MJ</td></tr><tr><td>Stellar flux</td><td style="text-align: center">(F)</td><td>48 </td></tr>

Discovery information

<tr> <td colspan="2">Discovery date</td> <td>April 12, 1996</td></tr><tr> <td colspan="2">Discoverer(s)</td> <td>Butler, Marcy</td></tr><tr> <td colspan="2">Discovery method</td> <td>Radial velocity</td></tr><tr> <td colspan="2">Other detection methods</td> <td>Transit</td></tr><tr> <td colspan="2">Discovery site</td> <td>California, USA</td></tr><tr> <td colspan="2">Discovery status</td> <td>Published</td></tr>

Other designations
55 Cancri Ab, Rho1 Cancri b, HD 75732 b

<tr style="background-color: #A0B0FF;"><td align=center colspan=3>Database references</td></tr><tr valign=baseline><td colspan=2>Extrasolar Planets
</td><td>data</td></tr><tr><td colspan=2>SIMBAD</td><td>data</td></tr>


55 Cancri b (abbreviated 55 Cnc b and occasionally referred to as 55 Cancri Ab in order to distinguish it from the star 55 Cancri B) is an extrasolar planet orbiting the Sun-like star 55 Cancri A every 14.65 days. It is the second planet in order of distance from its star, and is an example of a hot Jupiter, or possibly rather "warm Jupiter".[4] Discovered in 1996 by Geoffrey Marcy and R. Paul Butler, 55 Cancri b was the fourth known extrasolar planet, excluding pulsar planets.


File:55 Cnc b rv.pdf

Like the majority of known extrasolar planets, 55 Cancri b was discovered by detecting variations in its star's radial velocity caused by the planet's gravity. By making sensitive measurements of the Doppler shift of the spectrum of 55 Cancri A, a 15-day periodicity was detected. The planet was announced in 1996, together with the planet of Tau Boötis and the innermost planet of Upsilon Andromedae.[5]

Even when this inner planet, with a mass at least 78% times that of Jupiter was accounted for, the star still showed a drift in its radial velocity. This eventually led to the discovery of the outer planet 55 Cancri d in 2002.

Orbit and massEdit

55 Cancri b is in a short-period orbit, though not so extreme as that of the previously detected hot Jupiter 51 Pegasi b. The orbital period indicates that the planet is located close to a 1:3 mean motion resonance with 55 Cancri c, however investigations of the planetary parameters in a Newtonian simulation indicate that while the orbital periods are close to this ratio, the planets are not actually in the resonance.[1]

In 2012, b's upper atmosphere was observed transiting the star; so its inclination is about 85 degrees, coplanar with e. This helped to constrain the mass of the planet but the inclination was too low to constrain its radius.[2]

The mass is about .85 that of Jupiter.[2]


55 Cancri b is a gas giant with no solid surface. The atmospheric transit has demonstrated hydrogen in the upper atmosphere.[2]

That transit is so tangential, that properties such as its radius, density, and temperature are unknown. Assuming a composition similar to that of Jupiter and that its environment is close to chemical equilibrium, 55 Cancri b's upper atmosphere is predicted to be cloudless with a spectrum dominated by alkali metal absorption.[6]

The atmosphere's transit indicates that it is slowly evaporating under the sun's heat. The evaporation is slower than that for previously studied (hotter) hot Jupiters.[4]

The planet is unlikely to have large moons, since tidal forces would either eject them from orbit or destroy them on short timescales relative to the age of the system.[7]

See alsoEdit

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  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 DA Fischer et al. (March 2008). Five Planets Orbiting 55 Cancri. Astrophysical Journal 675 (675): 790–801.
  2. 2.0 2.1 2.2 2.3 2.4 D. Ehrenreich et al. (October 2, 2012). Hint of a transiting extended atmosphere on 55 Cancri b. Astronomy & Astrophysics.
  3. D. Dragomir, 2012-08-27, referred to in Ehrenreich
  4. 4.0 4.1 Astrophile: First puffy, 'warm Jupiter' spotted - space - 12 October 2012. New Scientist. Retrieved 2012-11-09.
  5. Butler et al. (1997). Three New 51 Pegasi-Type Planets. The Astrophysical Journal 474 (2): L115–L118.
  6. Sudarsky, D. et al. (2003). Theoretical Spectra and Atmospheres of Extrasolar Giant Planets. The Astrophysical Journal 588 (2): 1121–1148.
  7. Barnes, J., O'Brien, D. (2002). Stability of Satellites around Close-in Extrasolar Giant Planets. The Astrophysical Journal 575 (2): 1087–1093.

External linksEdit

Coordinates: Sky map 08h 52m 35.8s, +28° 19′ 51″

Template:55 Cancri

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