Extrasolar Planets - The 55 Cancri System
It is a source of wonder and awe to me, who grew up learning that the planets of other star systems were so far away that we would never learn anything about them until we sent probes, to be able to talk in a more than purely speculative fashion about the planetary system of another star. Thank you, Marcy and Butler, and thank you to the whole human race for daring to reach out a bit further each time.
===
55 Cancri is a binary star in the constellation of Cancer, in the Northern Hemisphere, located about 40.9 LY from the Earth. The primary star, 55 Cancri A is a G8v yellow dwarf, surface temperature 5240 Kelvin, 0.95 solar mass, 1.1 radius, and 0.61 luminosity. It is thus a bit cooler and redder than our Sun. It rotates more slowly than the Sun, about 42 days; and has a metallicity of 186% that of Sol. 55 Cancri (and presumably its whole system) is estimated as having an age of about 5 billion years: a bit older than our own system's 4.5 billion. This means that its planets have had plenty of time to evolve, both geologically and biologically -- and have the heavy elements to facilitate such evolution.
The secondary star, 55 Cancri B, is an M3.5-4 red dwarf, of 0.13 Solar masses, 0.30 radius, and 0.0076 luminosity. It orbits its primary over 1000 AU out, which means that it would not directly affect any planets in or near its primary's habitable zone. However, it would perturb its star's Kuiper Belt and certainly would have a strong effect on its Oort Cloud, if any. Though we know nothing about its planetary system, it almost certainly would have picked up one from such debris.
55 Cancri is believed to have four planets, which means that it probably has considerably more than four: possibly, more than are possessed by our own Sun (since we could detect Jupiter and Saturn at over 40 LY but would have trouble with Uranus and Neptune, and could not detect any of our Sun's four terrestrials).
The known planets are as follows (all figures other than orbits highly speculative):
===
55 Cancri e is a Super Hot Super Terrestrial, closely orbiting 55 Cancri A at a distance of 0.038 AU (a bit over 3.5 million miles), eccentricity 0.174, period 2.81 days, mass 0.045 Jovian, surface temperature 1179 Kelvin. This is almost certainly a rocky world: the main reason why it is probably not a "gas giant" as we normally use the term is that the intense heat from its star would have driven off its primordial hydrogen and helium, leaving other gases to dominate its atmosphere. Rotation would be tidally locked, with a permanent day side, dark side and twilight zone. The planet would be without a moon.
Assuming an Earth-like density, this world would be about 16 thousand kilometers in diameter, with a surface gravity of 2.6 G. The crust would be very thin -- only a few kilometers in places -- and very geologically active, with numerous microplates and frequent earthquakes and eruptions. 55 Cancri e would have formed with a greater percentage of radioactive elements than the Earth, and a mere 500 million years of greater age would not be enough time for them to have advanced much further upon their decay. Tremendous amounts of geothermal energy would have been generated, and with a smaller surface-to-volume ratio than the Earth, less of it released over any given period of time. Adding to this would be the tremendous heat emnating from its sun, only about a dozen times as far from the planet as is our own Moon from the Earth. Gigantic solar tidal forces would squirt lava out of every active crack and volcano each orbit, as the eccentricity caused the planet to approach and recede.
Surface temperatures are estimated at a mean of 1176 Kelvin. All but the most refactory substances, such as metals and silicates, would be in liquid or gasceous form. Due to the frequent tectonic activity coupled with the extreme heat, the surface would be constantly renewed, and there would be long-lasting lakes or even seas of molten lava.
The atmosphere would be crushingly dense and completely dry -- all water on 55 Cancri e would long since have boiled and photo-dissociated. I'm guessing that it would be primarily nitrogen and carbon dioxide, probably with significant sulfur, sodium and noble gas impurities. There would be silicate clouds riding over a dark sodium haze; the surface itself would be glowing red-hot in many places. Greenhouse effects would be considerable, increasing the already Doc-Smithian climate to truly indescribable extremes. The nearby star and huge nickel-iron core would drive a hellacious magnetosphere which would probably produce spectacular aurorae.
As with any super-terrestrial, mountain-building would be common but heights limited: on this world, the highest peaks would be about six kilometers. Most mountains would be active or recently-active volcanoes; intense erosion and occasional crustal melting (during local heat waves) would rapidly wear down any inactive volcano to (at best) shallow-sloped mesas. Much vulcanism would come from cracks rather than volcanoes: these cracks would randomly open and squirt out vast floods of lava.
55 Cancri e would be utterly hostile to any chemically-based life, though the recently-hypothesized living plasma vorticies might find it ideal, as there would be tremendous energy from the nearby star, a nice warm climate, a powerful magnetosphere, and plenty of warm matter around which vortices might coalesce. If we could reach this world, not even our machines could survive for more than a few seconds in its atmosphere.
===
55 Cancri b is a Hot Jovian, orbiting at 0.115 AU, with an eccentricity of 0.0197 and a period of 14.67 days. Its mass is at least 0.784 Jovian and its surface temperature is estimated at around 700 Kelvin. The heat puffs up the atmosphere to give it a radius of about 1.2 Jovian. The planet may rotate slowly, or be tidally locked.
From space it would appear a "nearly-featureless deep blue ball of haze" (Extrasolar Visions). The atmospheric temperature is too cool for silicate but still too warm for water clouds to form. Sulphurous clouds could form by night but would burn off in the heat of day. Gigantic bolts of lightning would be common.
Composition would be as all Jovians: a deep atmosphere of hydrogen and helium, shading into a metallic hydrogen ocean, which in turn would swathe a superterrestrial planetary core. There would be considerable heat production owing to gravitational pressure.
Because the planet is so close to its star it would have only small moons: no bigger than 0.92 the mass of Pluto, and probably smaller. It would have difficulty retaining moons for billions of years, and would instead tend to capture and lose them over time.
===
55 Cancri c is an Eccentric Hot Jovian, orbiting at 0.24 AU with an eccentricity of 0.44 (periastron 0.13 AU and apastron 0.34 AU) and a period of 43.93 days, which appears to be at or close to a 3:1 resonance with planet b, the next in. Mass is at least 0.217 Jovian, which makes it similar to Saturn in size. Surface temperature ranges from around 390 to 626 Kelvin, with a mean average around 469.
As can be seen, the eccentricity of the orbit would create strong seasons. Near periastrion, the atmosphere would be cloudless, as it would be too hot for water or sulfur clouds to form. The planet would appear a deep clear blue, like 55 Cancri b. Near apastrion, however, rotational bands of white sulfurous or even aqueous clouds would develop.
55 Cancri c would have few moons. The most distant stable Lunar orbit would be only half a million kilometers, and the most massive stable moon would be about 0.95 the mass of Ceres.
===
55 Cancri d is a Eccentric Cool Super Jovian, orbiting at 5.27 AU distance (periastron 3.53, apastron 9.97 AU) with a 4514-day period. Mass is 3.92 Jovian. Cloud-top temperature is an average 100 Kelvin; ranging from 122 Kelvin at periastron to 87 at apastron. However, internal heating due to gravitional contraction would add 174 Kelvin to these figures in the upper atmosphere: like all Jovians, temperatures and pressures in the depths would be immense. As a relatively cool Jovian, the extra mass would increase density rather than radius, and hence its radius is only 1.039 Jovian.
From space one sould see white ammonia and water-ice clouds, with the browner stains of various hydrocarbons. Orbiting eccentrically in the Outer System, there well might be large, prominent rings. There might be practically any number of moons of any size, and orbital distances out to 30 million km.
===
Applying Bode's Law
With 4 known planets, Bode's Law is easily applicable to the 55 Cancri system. R=0.04 and B=0.04, which is a much smaller distance than normally the case, which means that many of the orbits generated will be emptied by gravitational interference from objects in other orbits.
Orbit 1 (0.04 AU) is occupied by the Very Hot Superterrestrial planet "e," whose actual distance is 0.038 AU.
Orbit 2 (0.08 AU) is emptied by interference from "e" and "b".
Orbit 3 (0.12 AU) is occupied by the Hot Jovian planet "b," whose actual distance is 0.115 AU.
Orbit 4 (0.20 AU) is occupied by the Eccentric Hot Jovian planet "c," whose actual distance ranges between 0.13 and 0.34 AU (average 0.24).
Orbit 5 (0.36 AU) is emptied by interference from "c."
Orbit 6 (0.68 AU) is available. A planet up to 0.6 Earth mass might orbit here, and it's right in the center of the Habitable Zone!
Orbit 7 (1.32 AU) is available. A small, cool Marslike planet might fit in here, if we follow the model of the Solar System.
Orbit 8 (2.60 AU) is available but threatened by "d," the Eccentric Super Jovian. There might well be an asteroid belt here.
Orbit 9 (5.16 AU) is occupied by the Eccentric Super Jovian "d," whose actual distance ranges between 3.53 and 9.97 AU (average 5.257).
Orbit 10 (10.28 AU) might be emptied by "d," or you might get one or more small worlds in synchronized orbits (like the Plutinos with Neptune).
Orbits 11+, if existing, would be available. In fact the system could extend out to Orbits 15 or so before you run into interference from 55 Cancri B and any planets the red dwarf might possess.
Taking "d" as the outer edge of the planetary system, you do have four planets and could have six planets, of which 1-2 might be habitable. Unfortunately, the 1-2 habitable worlds are the hypotheticals: none of the four known planets could be habitable, though "d" might have a Europoid moon or two.
If I were modelling this system for a story, I'd have
I: Super Hot Super Terrestrial
II: Hot Jovian
III: Eccentric Hot Jovian
IV: Small Earth
V: Big Mars
(asteroid belt)
VI: Eccentric Cool Super Jovian
(a mess of Plutinos)
(a Kuiper Belt)
and then a system for 55 Cancri B, probably a small one.
END
===
55 Cancri is a binary star in the constellation of Cancer, in the Northern Hemisphere, located about 40.9 LY from the Earth. The primary star, 55 Cancri A is a G8v yellow dwarf, surface temperature 5240 Kelvin, 0.95 solar mass, 1.1 radius, and 0.61 luminosity. It is thus a bit cooler and redder than our Sun. It rotates more slowly than the Sun, about 42 days; and has a metallicity of 186% that of Sol. 55 Cancri (and presumably its whole system) is estimated as having an age of about 5 billion years: a bit older than our own system's 4.5 billion. This means that its planets have had plenty of time to evolve, both geologically and biologically -- and have the heavy elements to facilitate such evolution.
The secondary star, 55 Cancri B, is an M3.5-4 red dwarf, of 0.13 Solar masses, 0.30 radius, and 0.0076 luminosity. It orbits its primary over 1000 AU out, which means that it would not directly affect any planets in or near its primary's habitable zone. However, it would perturb its star's Kuiper Belt and certainly would have a strong effect on its Oort Cloud, if any. Though we know nothing about its planetary system, it almost certainly would have picked up one from such debris.
55 Cancri is believed to have four planets, which means that it probably has considerably more than four: possibly, more than are possessed by our own Sun (since we could detect Jupiter and Saturn at over 40 LY but would have trouble with Uranus and Neptune, and could not detect any of our Sun's four terrestrials).
The known planets are as follows (all figures other than orbits highly speculative):
===
55 Cancri e is a Super Hot Super Terrestrial, closely orbiting 55 Cancri A at a distance of 0.038 AU (a bit over 3.5 million miles), eccentricity 0.174, period 2.81 days, mass 0.045 Jovian, surface temperature 1179 Kelvin. This is almost certainly a rocky world: the main reason why it is probably not a "gas giant" as we normally use the term is that the intense heat from its star would have driven off its primordial hydrogen and helium, leaving other gases to dominate its atmosphere. Rotation would be tidally locked, with a permanent day side, dark side and twilight zone. The planet would be without a moon.
Assuming an Earth-like density, this world would be about 16 thousand kilometers in diameter, with a surface gravity of 2.6 G. The crust would be very thin -- only a few kilometers in places -- and very geologically active, with numerous microplates and frequent earthquakes and eruptions. 55 Cancri e would have formed with a greater percentage of radioactive elements than the Earth, and a mere 500 million years of greater age would not be enough time for them to have advanced much further upon their decay. Tremendous amounts of geothermal energy would have been generated, and with a smaller surface-to-volume ratio than the Earth, less of it released over any given period of time. Adding to this would be the tremendous heat emnating from its sun, only about a dozen times as far from the planet as is our own Moon from the Earth. Gigantic solar tidal forces would squirt lava out of every active crack and volcano each orbit, as the eccentricity caused the planet to approach and recede.
Surface temperatures are estimated at a mean of 1176 Kelvin. All but the most refactory substances, such as metals and silicates, would be in liquid or gasceous form. Due to the frequent tectonic activity coupled with the extreme heat, the surface would be constantly renewed, and there would be long-lasting lakes or even seas of molten lava.
The atmosphere would be crushingly dense and completely dry -- all water on 55 Cancri e would long since have boiled and photo-dissociated. I'm guessing that it would be primarily nitrogen and carbon dioxide, probably with significant sulfur, sodium and noble gas impurities. There would be silicate clouds riding over a dark sodium haze; the surface itself would be glowing red-hot in many places. Greenhouse effects would be considerable, increasing the already Doc-Smithian climate to truly indescribable extremes. The nearby star and huge nickel-iron core would drive a hellacious magnetosphere which would probably produce spectacular aurorae.
As with any super-terrestrial, mountain-building would be common but heights limited: on this world, the highest peaks would be about six kilometers. Most mountains would be active or recently-active volcanoes; intense erosion and occasional crustal melting (during local heat waves) would rapidly wear down any inactive volcano to (at best) shallow-sloped mesas. Much vulcanism would come from cracks rather than volcanoes: these cracks would randomly open and squirt out vast floods of lava.
55 Cancri e would be utterly hostile to any chemically-based life, though the recently-hypothesized living plasma vorticies might find it ideal, as there would be tremendous energy from the nearby star, a nice warm climate, a powerful magnetosphere, and plenty of warm matter around which vortices might coalesce. If we could reach this world, not even our machines could survive for more than a few seconds in its atmosphere.
===
55 Cancri b is a Hot Jovian, orbiting at 0.115 AU, with an eccentricity of 0.0197 and a period of 14.67 days. Its mass is at least 0.784 Jovian and its surface temperature is estimated at around 700 Kelvin. The heat puffs up the atmosphere to give it a radius of about 1.2 Jovian. The planet may rotate slowly, or be tidally locked.
From space it would appear a "nearly-featureless deep blue ball of haze" (Extrasolar Visions). The atmospheric temperature is too cool for silicate but still too warm for water clouds to form. Sulphurous clouds could form by night but would burn off in the heat of day. Gigantic bolts of lightning would be common.
Composition would be as all Jovians: a deep atmosphere of hydrogen and helium, shading into a metallic hydrogen ocean, which in turn would swathe a superterrestrial planetary core. There would be considerable heat production owing to gravitational pressure.
Because the planet is so close to its star it would have only small moons: no bigger than 0.92 the mass of Pluto, and probably smaller. It would have difficulty retaining moons for billions of years, and would instead tend to capture and lose them over time.
===
55 Cancri c is an Eccentric Hot Jovian, orbiting at 0.24 AU with an eccentricity of 0.44 (periastron 0.13 AU and apastron 0.34 AU) and a period of 43.93 days, which appears to be at or close to a 3:1 resonance with planet b, the next in. Mass is at least 0.217 Jovian, which makes it similar to Saturn in size. Surface temperature ranges from around 390 to 626 Kelvin, with a mean average around 469.
As can be seen, the eccentricity of the orbit would create strong seasons. Near periastrion, the atmosphere would be cloudless, as it would be too hot for water or sulfur clouds to form. The planet would appear a deep clear blue, like 55 Cancri b. Near apastrion, however, rotational bands of white sulfurous or even aqueous clouds would develop.
55 Cancri c would have few moons. The most distant stable Lunar orbit would be only half a million kilometers, and the most massive stable moon would be about 0.95 the mass of Ceres.
===
55 Cancri d is a Eccentric Cool Super Jovian, orbiting at 5.27 AU distance (periastron 3.53, apastron 9.97 AU) with a 4514-day period. Mass is 3.92 Jovian. Cloud-top temperature is an average 100 Kelvin; ranging from 122 Kelvin at periastron to 87 at apastron. However, internal heating due to gravitional contraction would add 174 Kelvin to these figures in the upper atmosphere: like all Jovians, temperatures and pressures in the depths would be immense. As a relatively cool Jovian, the extra mass would increase density rather than radius, and hence its radius is only 1.039 Jovian.
From space one sould see white ammonia and water-ice clouds, with the browner stains of various hydrocarbons. Orbiting eccentrically in the Outer System, there well might be large, prominent rings. There might be practically any number of moons of any size, and orbital distances out to 30 million km.
===
Applying Bode's Law
With 4 known planets, Bode's Law is easily applicable to the 55 Cancri system. R=0.04 and B=0.04, which is a much smaller distance than normally the case, which means that many of the orbits generated will be emptied by gravitational interference from objects in other orbits.
Orbit 1 (0.04 AU) is occupied by the Very Hot Superterrestrial planet "e," whose actual distance is 0.038 AU.
Orbit 2 (0.08 AU) is emptied by interference from "e" and "b".
Orbit 3 (0.12 AU) is occupied by the Hot Jovian planet "b," whose actual distance is 0.115 AU.
Orbit 4 (0.20 AU) is occupied by the Eccentric Hot Jovian planet "c," whose actual distance ranges between 0.13 and 0.34 AU (average 0.24).
Orbit 5 (0.36 AU) is emptied by interference from "c."
Orbit 6 (0.68 AU) is available. A planet up to 0.6 Earth mass might orbit here, and it's right in the center of the Habitable Zone!
Orbit 7 (1.32 AU) is available. A small, cool Marslike planet might fit in here, if we follow the model of the Solar System.
Orbit 8 (2.60 AU) is available but threatened by "d," the Eccentric Super Jovian. There might well be an asteroid belt here.
Orbit 9 (5.16 AU) is occupied by the Eccentric Super Jovian "d," whose actual distance ranges between 3.53 and 9.97 AU (average 5.257).
Orbit 10 (10.28 AU) might be emptied by "d," or you might get one or more small worlds in synchronized orbits (like the Plutinos with Neptune).
Orbits 11+, if existing, would be available. In fact the system could extend out to Orbits 15 or so before you run into interference from 55 Cancri B and any planets the red dwarf might possess.
Taking "d" as the outer edge of the planetary system, you do have four planets and could have six planets, of which 1-2 might be habitable. Unfortunately, the 1-2 habitable worlds are the hypotheticals: none of the four known planets could be habitable, though "d" might have a Europoid moon or two.
If I were modelling this system for a story, I'd have
I: Super Hot Super Terrestrial
II: Hot Jovian
III: Eccentric Hot Jovian
IV: Small Earth
V: Big Mars
(asteroid belt)
VI: Eccentric Cool Super Jovian
(a mess of Plutinos)
(a Kuiper Belt)
and then a system for 55 Cancri B, probably a small one.
END