Changes

{{Night Sky

{{Night Sky

| image          =

| image          =

| declination    =Star A: +28^o 19′ 51.0″<br/>Star B: +28^o 19′ 59″

| declination    =Star A: +28^o 19′ 51.0″<br/>Star B: +28^o 19′ 59″

| distance        =40.3 ±0.4 ly

| distance        =40.3 ±0.4 ly

| constellation  =[[Cancer_(constellation)|Cancer]]  

| constellation  =[[Cancer (constellation)|Cancer]]  

| type            =[[Binary star]]  

| type            =[[Binary star]]  

| dimensions      =  

| dimensions      =  

}}

}}

'''55 Cancri''', also known as '''Rho Cancri''', is a binary star system located 41 [[light year|light years]] away in the constellation of [[Cancer_(zodiac)|Cancer]] and is best known for having five [[extrasolar planets]] (as of 2007), including possibly one terrestrial, rocky, "super-Earth".  55 Cancri A is visible to the unaided eye only under very dark, clear conditions with an apparent magnitude of 5.95.  The much dimmer 55 Cancri B's apparent magnitude is only 13.15 and is invisible to the unaided eye.

'''55 Cancri''', also known as '''Rho Cancri''', is a binary star system located 41 [[light year]]s away in the constellation of [[Cancer (zodiac)|Cancer]] and is best known for having five [[extrasolar planets]] (as of 2007), including possibly one terrestrial, rocky, "super-Earth".  55 Cancri A is visible to the unaided eye only under very dark, clear conditions with an apparent magnitude of 5.95.  The much dimmer 55 Cancri B's apparent magnitude is only 13.15 and is invisible to the unaided eye.

==The Stars==

==The Stars==

'''55 Cancri b''', sometimes caled '''55 Cancri Ab''' so to distinguish it from the companion star 55 Cancri B, is the first [[extrasolar planet]] discovered orbiting 55 Cancri A in 1996.  It is the fourth extrasolar world discovered overall.

'''55 Cancri b''', sometimes caled '''55 Cancri Ab''' so to distinguish it from the companion star 55 Cancri B, is the first [[extrasolar planet]] discovered orbiting 55 Cancri A in 1996.  It is the fourth extrasolar world discovered overall.

The world has at least 82.4 percent (but probably 103 percent) of Jupiter's mass.  The planet is second in order of distance from its star, orbiting with an average distance of only 0.115 AU (an orbit that would be well within [[Mercury|Mercury's]]), taking only 14.7 days to complete.  The world appears to be a gas giant, and assuming that, its radius would be 1.2 times of [[Jupiter]], classifying the world as a "hot Jupiter".  Because the world was detected indirectly the actual radius, composition, and temperature at this time are still unknown<ref name="exo">http://www.iop.org/EJ/article/1538-4357/474/2/L115/5590.html</ref>.

The world has at least 82.4 percent (but probably 103 percent) of Jupiter's mass.  The planet is second in order of distance from its star, orbiting with an average distance of only 0.115 AU (an orbit that would be well within [[Mercury|Mercury's]]), taking only 14.7 days to complete.  The world appears to be a gas giant, and assuming that, its radius would be 1.2 times of [[Jupiter]], classifying the world as a "hot Jupiter".  Because the world was detected indirectly the actual radius, composition, and temperature at this time are still unknown.<ref name="exo">http://www.iop.org/EJ/article/1538-4357/474/2/L115/5590.html</ref>

===55 Cancri c===

===55 Cancri c===

'''55 Cancri c''' is the second planet to be discovered around its parent star on June 13, 2002, it is the third planet in order of distance from its sun.

'''55 Cancri c''' is the second planet to be discovered around its parent star on June 13, 2002, it is the third planet in order of distance from its sun.

The world itself orbits only some 0.224 AU from the star, well within the orbit of [[Mercury]] from our Sun, which takes 44.3 days to complete.  The planet is estimated to have at least 16.9 percent, but much more likely 21 percent of [[Jupiter|Jupiter's]] mass.  The orbit of the planet is the most eccentric of the five known, where it is 19% further from 55 Cancri A at [[apoastron]] then at [[periastron]].<ref name="exo">http://www.iop.org/EJ/article/1538-4357/474/2/L115/5590.html</ref>

The world itself orbits only some 0.224 AU from the star, well within the orbit of [[Mercury]] from our Sun, which takes 44.3 days to complete.  The planet is estimated to have at least 16.9 percent, but much more likely 21 percent of [[Jupiter|Jupiter's]] mass.  The orbit of the planet is the most eccentric of the five known, where it is 19% further from 55 Cancri A at [[apoastron]] then at [[periastron]].<ref name="exo"/>

===55 Cancri d===

===55 Cancri d===

Like 55 Cancri c and many extrasolar worlds, 55 Cancri d was detected through observing changes in the star's [[radial velocity]] though sensitive measurements of the Doppler shift in 55 Cancri's spectrum.

Like 55 Cancri c and many extrasolar worlds, 55 Cancri d was detected through observing changes in the star's [[radial velocity]] though sensitive measurements of the Doppler shift in 55 Cancri's spectrum.

55 Cancri d's distance is 5.77 AU from its parent [[star]], just outside of the orbit of Jupiter in our solar system, at that distance, the planet takes 14 years to orbit.  Because [[radial velocity]] was used to discover the planet, only the lower limit of its mass can be determined, which is estimated as 3.385 times that of [[Jupiter]], although it may be more massive, most likely a gas giant.  55 Cancri d also has the largest inclination of all the planets in the system, with its orbit at 53 degrees in respect to the plane.<ref name="exo">http://www.iop.org/EJ/article/1538-4357/474/2/L115/5590.html</ref>

55 Cancri d's distance is 5.77 AU from its parent [[star]], just outside of the orbit of Jupiter in our solar system, at that distance, the planet takes 14 years to orbit.  Because [[radial velocity]] was used to discover the planet, only the lower limit of its mass can be determined, which is estimated as 3.385 times that of [[Jupiter]], although it may be more massive, most likely a gas giant.  55 Cancri d also has the largest inclination of all the planets in the system, with its orbit at 53 degrees in respect to the plane.<ref name="exo"/>

===55 Cancri e===

===55 Cancri e===

55 Cancri e is the fourth planet to be discovered in the 55 Cancri system and the closest to its parent star.  Like the other worlds, 55 Cancri e was discovered through [[radial velocity]].  It was discovered on August 30th 2004.

55 Cancri e is the fourth planet to be discovered in the 55 Cancri system and the closest to its parent star.  Like the other worlds, 55 Cancri e was discovered through [[radial velocity]].  It was discovered on August 30, 2004.

'''55 Cancri e''' is only 0.038 AU from its parent star with an orbit of only 2.8 days. Such a close orbit is often known as a "torch orbit".  The minimum mass of the planet is measured to be some 11 times that of Earth or about 60 percent of [[Neptune]].  At this time it is unknown whether the planet is a very small [[gas giant]] or a large terrestrial, rocky world. Another hypothesis is that the world may be a gas giant core that could not accumulate a significantly large gaseous atmosphere.<ref name="exo2">http://arxiv.org/abs/0712.3917</ref>

'''55 Cancri e''' is only 0.038 AU from its parent star with an orbit of only 2.8 days. Such a close orbit is often known as a "torch orbit".  The minimum mass of the planet is measured to be some 11 times that of Earth or about 60 percent of [[Neptune]].  At this time it is unknown whether the planet is a very small [[gas giant]] or a large terrestrial, rocky world. Another hypothesis is that the world may be a gas giant core that could not accumulate a significantly large gaseous atmosphere.<ref name="exo2">http://arxiv.org/abs/0712.3917</ref>

In 2005, the existence of 55 Cancri e was questioned by astronomer Jack Wisdom after reanalyzing the data.  Wisdom claimed that instead there was a [[Neptune]] sized world orbiting 0.78 AU away.  A new analysis was done in 2007 discovering that both worlds existed, the latter now deemed as 55 Cancri f, which was announced on November 6, 2007.

In 2005, the existence of 55 Cancri e was questioned by astronomer Jack Wisdom after reanalyzing the data.  Wisdom claimed that instead there was a [[Neptune]] sized world orbiting 0.78 AU away.  A new analysis was done in 2007 discovering that both worlds existed, the latter now deemed as 55 Cancri f, which was announced on November 6, 2007.

'''55 Cancri f''' is fourth in distance from 55 Cancri A of the known planets and orbits at 0.781 AU, inside the habitable zone of the star.  The planet itself is estimated to be at least 44 Earth masses (possibly 57 Earth masses), meaning it is a smaller Neptune-like gas giant.<ref name="exo2">http://arxiv.org/abs/0712.3917</ref>

'''55 Cancri f''' is fourth in distance from 55 Cancri A of the known planets and orbits at 0.781 AU, inside the habitable zone of the star.  The planet itself is estimated to be at least 44 Earth masses (possibly 57 Earth masses), meaning it is a smaller Neptune-like gas giant.<ref name="exo2"/>

The [[habitable zone]] of 55 Cancri A extends from 0.5 to 2 AU distance, and thus it is very possible there could be an Earth-like rocky world orbiting within that zone.<ref>http://www.jpl.nasa.gov/news/news.cfm?release=2007-128</ref>  At present it would be almost impossible to detect such a world using current methods.  In addition to a possible planet(s) orbiting in that zone, 55 Cancri f itself may have moons that could be habitable to life as we know it.

The [[habitable zone]] of 55 Cancri A extends from 0.5 to 2 AU distance, and thus it is very possible there could be an Earth-like rocky world orbiting within that zone.<ref>http://www.jpl.nasa.gov/news/news.cfm?release=2007-128</ref>  At present it would be almost impossible to detect such a world using current methods.  In addition to a possible planet(s) orbiting in that zone, 55 Cancri f itself may have moons that could be habitable to life as we know it.