61 Cygni comprises of two stars, both are K-type considerably smaller, cooler and dimmer than our Sun. The stars have mass of 70% and 63% that of our Sun. The stars orbit the center of mass once every 659 years at an average separation of 84 AU. However, its high eccentricity would cause separation to vary from 44 to 124 AU.
61 Cygni is the first star other than our Sun to have its distance measured using the parallax. In 1838, Friedrich Bessel calculated the distance as 10.4 light-years, close to the modern figure. Due to this, it can alternatively be called "Bessel's Star." It also has high proper motion, also calling this the "Flying Star."
Planetary system Edit
61 Cygni had claims of a planetary system on several occasions. The first such claim was made in 1942 by detecting systematic variations of component stars' orbits. It was later determined that the object masses 8 Jupiters taking 4.8 years to orbit at 2.4 AU. In 1977, Soviet astronomers suggested that this system contains three superjovian planets, two orbiting 61 Cygni A and one orbiting 61 Cygni B. A year later, these claims were found to be spurious as sensitivities at the time can only go down to about 60 Jupiter masses.
|Class||Semimajor axis (AU)||Eccentricity||Orbital period (yr)||Radius||Mass||Density (g/cm3)||Gravity (g)||Rotation period (d)||Surface temp (K)|
There are speculated three planets around 61 Cygni A and four around 61 Cygni B. All three planets orbiting A are gaseous, two are midplanets and one is a low-mass sub-Jupiter. Three of four planets orbiting B are rocky, all are super-Earths, and one is an ice giant midplanet.
These planets have semimajor axes ranging from 0.18 AU to 3.15 AU and have orbital periods from over a month to nearly seven years. Orbital eccentricities are quite high due to planets orbiting in the binary system. An average eccentricity is 0.367, six times the average value of the Solar System's eccentricity.
61 Cygni Ab Edit
61 Cygni Ab orbits at about 0.5 AU (5⁄9 the Earth–Sun distance), and takes half an Earth year to revolve around the star. Its eccentricity is close to the average among all the planets in this binary system. It is a Neptune-mass planet, massing 14.6 Earth masses and has diameter of 57.8 megameters. The planet's density is just 6⁄7 of that of water and under 1⁄6 of that of Earth's, and half the density of Neptune. This density value tell that this planet has a thick hydrogen-helium atmosphere surrounding the oceans of liquid water/ammonia mixture. The surface temperature is −26°F and rotation period is 21⁄7 days. 61 Cyg Ab has 7⁄10 of the Earth's surface gravity, meaning that an average adult person would weigh about 107 pounds when standing on this planet.
61 Cygni Ac Edit
61 Cygni Ac is a planet that takes 98% of an Earth year to orbit the star at a distance of 7⁄8 that of Earth's. With an eccentricity of 0.47, which is the same as orbits of binary stars in this system, the distance varies from 0.46 to 1.29 AU. 61 Cyg Ac is in a 2:1 resonance with 61 Cyg Ab, which can destabilize the planet's orbit due to high eccentricity.
61 Cyg Ac has mass 22 Earth masses and diameter 64.3 megameters, producing the density slightly less than water. The planet's composition and structure is similar to 61 Cyg Ab. The planet's surface gravity is 6⁄7 of that of Earth's. Because this planet orbits farther away from the parent star than 61 Cyg Ab, this planet is colder with the surface temp of −98°F.
61 Cygni Ad Edit
61 Cygni Ad is the outermost of the three planets around 61 Cygni's primary star. 61 Cyg Ad orbits at 2.6 AU (half the distance between Jupiter and Sun) and takes five years to orbit once around the star. It orbits in a 5:1 resonance with 61 Cyg Ac and 10:1 resonance with 61 Cyg Ab, meaning every time when 61 Cyg Ad orbits the star, c orbits five times while b orbits 10 times. Like these other planets, this one has a very eccentric orbit, halfway between the eccentricities of other planets in value.
61 Cyg Ad has more mass than two other planets combined. It masses 39.65 Earth masses or 2⁄5 the mass of Saturn. The diameter of this planet is 69.5 megameters, which is 4⁄7 the size of Jupiter. Its density is similar to two other planets, so do their structural properties. It takes 17 hours to revolve around the axis once and has similar gravitational pull to Earth. It is the coldest planet since the planet orbits farther away from the parent star. The surface temp is −221°F, slightly colder than Saturn.
61 Cygni Bb Edit
61 Cygni Bb is a super-Earth orbiting at 18% of the distance between Earth and Sun. Unlike other planets in this binary system, this one orbits in a circular path with an eccentricity of only 0.005. No others have eccentricities below 0.25. It is due to combined even forces exerted by three planets beyond it and gravity of the nearby star. However, the maximum eccentricity during this long-term cycle is as high as 0.25, reached 260,000 years ago. Due to the planet's closeness of the nearby star, it's rotation is slow due to tidal forces of the star. It takes 26.8 days to rotate once, which is roughly 80% of its year of 331⁄2 days.
The planet has mass 5.4 times that of Earth's, that's why this planet is a super-Earth. This planet is 2.2 times bigger than Earth and volume 102⁄3 times that of Earth. It is a terrestrial planet with a low density, which is half that of Earth's and slightly less dense than our Moon. It is an ocean planet with oceans over 200 miles deep, surrounded by atmosphere of adequate thickness made of hydrogen, oxygen, and water vapor. An average surface temp is 155°F and the planet reflects 28% of the incoming starlight falling onto it.
61 Cygni Bc Edit
61 Cygni Bc is a super-Earth, massing 31⁄4 times more massive than Earth. It has a diameter of 23.55 Mm, which is 85% bigger than Earth. It's density is very similar to 61 Cyg Bb, and this planet has similar structure and composition to that planet, except the surface is not covered in oceans. It is a barren planet, meaning it has a bare, rocky surface. It's surface temp is 180°F and reflects 31% of all light reaching the planet. However, its equilibrium temp is −140°F. This difference is due to planet's powerful greenhouse effect. The planet's atmosphere contains great deal of carbon dioxide, which is an important greenhouse gas. The planet's surface contains few bodies of water in the form of lakes that often steam.
61 Cyg Bc orbits at a semimajor axis of 0.61 AU, which is 3⁄5 of the semimajor axis of Earth. It's year lasts 30 weeks, compared to approximately 52 weeks for Earth. As it is typical of planets in the 61 Cyg system, this one orbits eccentrically, although it has one of the lower eccentricities of all planets. The distance varies from 0.45 to 0.77 AU for an eccentricity of 0.258. The planet takes 3.13 days or 75.2 hours to rotate once on its axis. Its planetary year lasts 67 stellar days.
61 Cygni Bd Edit
61 Cygni Bd is twice as massive as Earth at 2.02 Earth masses, straddling the border between super-Earth and mid-Earth. At a density of 5.64 g/cm3, it is the densest planet of the 61 Cygni system, meaning the planet has similar structure to Earth. 61 Cyg Bd takes overs 38 hours to rotate once on its axis and has 28% stronger gravitational pull than Earth, meaning an average human would weigh about 192 pounds on this planet. The surface temp is −74°F, which is Mars-like. But the surface is not like Mars, it has numerous lakes and rivers of liquid ammonia. The atmosphere is comprised mostly of nitrogen with varying amounts of ammonia. It rains ammonia on this planet, analogous to water on Earth and methane on Titan.
61 Cyg Bd takes 4⁄3 of a year or 493.6 days to revolve once around the star with an extremely high eccentricity of 0.754. It orbits at an average distance of 1.083 AU, but it varies drastically from 0.27 to 1.90 AU. This dramatic variation would cause great deal of seasonal climate changes on this planet. Sometimes, lakes and rivers would be dried up as liquid ammonia boiled away, while at other times, lakes and rivers would be frozen and the surface would be covered in ammonia snow.
61 Cygni Be Edit
61 Cygni Be is a planet orbiting at 3.15 AU, taking 6.7 years to revolve with an eccentricity of 0.305. It is a midplanet massing nearly 20 Earth masses. It has a diameter 57.7 Mm, which is 41⁄2 times the Earth's diameter. It has a density 17% higher than water, meaning that this planet is an ice giant like Uranus and Neptune. The planet's atmosphere composes mostly of hydrogen and helium with trace amounts of methane. The planet would appear green from space surrounded by few rings made of icy particles. 61 Cyg Be takes 25 hours and 50.4 minutes to rotate once on its axis and it rotates on its side at an axial tilt of 711⁄2°.