A Tour of the Star Systems within 13.0 light years of Earth.
As a media design teacher at Mountainland Applied Technology College from 2000-2009, I created an activity to teach layout design and desktop publishing software with students creating their own version of newsletters. They had to arrange articles I had written about the nearby stars. I used the same articles for many years, but when I dusted them off for our Ad Astra Per Educare magazine 4th edition on the nearby stars, I found that these articles are quite obsolete. Much has changed. It was time to revise the articles.
In my 2020 astrobiology class, my students took on the challenge. Each student chose two star systems to research and report on. For those stars not chosen or written about, I filled in the gaps and also provided additional details on the stars the students wrote about.
It is surprising how much new information has been found about these stars just in the past year since these articles were written. For example, a new candidate exoplanet in the habitable zone around Alpha Centauri A was reported just this last February. Back when I started researching the nearby stars in the early 1990s, this was a somewhat moribund subject without much interest in the astronomy community since no exoplanets had yet been discovered. Now, everyone seems to be getting in on the planet hunting craze and new discoveries are occurring almost weekly.
In addition to describing the star systems themselves, the students wrote sidebar articles on star characteristics such as coordinate systems, classification, naming systems, how we find the distances to them, and other topics. I will post these as our next post.
The Alpha Centauri System: by Hannah T.
The Alpha Centauri triple star system is the closest star system to us, around 4.37 light years away in the far southern constellation of the Centaur. Alpha Centauri A and B are a pair, also known as AB, that orbit close to each other. Proxima Centauri orbits AB and is the closest known star to earth. The declination of Proxima is –62.68, its apparent magnitude is 11.09 and its absolute magnitude is 15.53.
Proxima Centauri is a small red dwarf star of spectral class M5.5V. It is exactly 4.244 light years away and the right ascension is 14h 29m 43s. This star was discovered by Robert T. A. Innes in 1915. Recently in 2016 an exoplanet was located in the habitable zone of Proxima Centauri using the radial velocity method. It is about the size of Earth but would be most likely tidally locked. Because Proxima is a flare star (V465 Centauri), it is unlikely for life to exist there. Proxima now has two confirmed planets, Proxima Cent c is a super-Earth or sub-Neptune planet 7 times more massive than Earth and about 1.49 AU from Proxima. It is therefore too far away to be habitable. There may be a third, sub-Earth sized planet that has not yet been confirmed.
Alpha Centauri A, also known as Rigil Kentaurus (“the Foot of the Centaur”) is the largest and brightest star of this triple star system. It is a spectral type G2V and is just larger and slightly brighter than the sun, with an apparent magnitude of .01 and an absolute magnitude of 4.38 (compared with 4.85 for the Sun). This is the third brightest star visible in the night sky and is 4.365 light years away. Alpha Centauri A has a right ascension of 14h 39m 36.5s and a declination of –60.83. The corona of a star is the aura of plasma surrounding it; Alpha Centauri A shows coronal variability because of star spots. A recent Feb. 2021 paper from the Breakthrough Watch Initiative used a direct imaging technique and found evidence for one planet orbiting around Rigel Kentaurus with a distance of about 1.1 astronomical units (AU or the Sun-Earth distance), putting the planet in the middle of the habitable zone. Called Candidate 1, its mass would be slightly larger than Neptune, so it would be a gas giant. It could have habitable moons. The observation was made using only 100 hours of observing time, so further observations are needed to confirm that this is a true planet and not a dust disk or observational artifact.
Alpha Centauri B, sometimes known as Toliman (“the ostrich”), is an orange dwarf star of spectral class K1V with a mass of .907 that of Sol. This star’s apparent magnitude is 1.34, and its absolute magnitude is 5.71. A planet was proposed using radial velocity in 2012 but it has since been refuted as an artifact of data analysis; another candidate planet (Alpha Centauri Bc) was proposed in 2013 using transit data but has yet to be confirmed. It would be slightly smaller than Earth with a 20 day orbit, so not in the habitable zone.
As the closest star system to Earth, Alpha Centauri has figured prominently in science fiction. It was to be the destination of the Robinson family in the Lost in Space series and movie. The character Zephram Cochran, inventor of the warp drive in the Star Trek franchise, lived for a time in the Alpha Centauri system before going missing (“Metamorphosis”). Other episodes throughout the Star Trek universe mention Alpha Centauri. In Babylon 5, an Earth colony is mentioned in the Proxima system and it is the site of a battle between Babylon 5 forces and Earth during the civil war story arc. The planet Polyphemus in the Avatar movie series, orbited by the moon Pandora where the fictional mineral unobtanium is being mined, is located in the Alpha Centauri system. In literature, Alpha Centauri figures prominently in many science fiction novels including The Songs of Distant Earth by Arthur C. Clarke, Foundation and Earth by Isaac Asimov, Footfall by Larry Niven and Jerry Pournelle, Neuromancer by William Gibson, and The Three-Body Problem by Liu CiXin.
The second closest star system to our sun was discovered by E. E. Barnard in 1916 as part of his proper motion studies. It has the fastest known proper motion of any star, at 10.3 arcseconds per year relative to our sun, making it a very close star. Using parallax with refinements by the Hipparcos and Gaia satellites, its distance has been measured at 5.96 light years. It is a small red dwarf with a mass 0.144 times the mass of our sun and a spectral type of M4.0V. It is located in the constellation Ophiucus at 17h 57m 48.5s right ascension and +04° 41m 36.2s declination. It can only be seen with a powerful telescope and has an apparent magnitude of 9.511.
For many years, Peter van de Kamp argued that Barnard’s Star had at least one planet based on his astrometry measurements, which involved measuring the changes in the positions of stars on photographic plates as small as one micron. These arguments were largely refuted in the 1970s when it was shown that the perturbations seen in the plates corresponded to maintenance upgrades of the telescope’s lens. However, in 2018 a candidate super-Earth was announced from the Red Dots project using highly precise measurements of radial velocity with data from the ESO HARPS (High Accuracy Radial velocity Planet Searcher) spectrograph and other instruments over a 20 year period. It is believed to have a minimum of 3.2 Earth masses and to orbit at 0.4 astronomical units and a period of 233 days, putting it beyond the habitable zone. This planet is also disputed, since star spots might produce a similar radial velocity shift. Barnard’s Star is a flare star, as are most red dwarfs, making life on such a planet unlikely.
Based on its slow rotational speed and low metallicity, Barnard’s Star is estimated to be between 7-12 billion years old, making it much older than the sun. A surprisingly large solar flare was detected in 1998, very unusual for such an old star. Smaller ultraviolet and x-ray flares were detected in 2019.
In the Hitchhiker’s Guide to the Galaxy series by Douglas Adams, Barnard’s Star is said to be the location of an interstellar roundabout used by the Vogon Constructor Fleet. It is also a major part of the novels The Garden of Rama by Arthur C. Clarke and Gentry Lee and Hyperion by Dan Simmons.
Luhman 16 A and B: by Navah D.
Luhman 16 is a binary star system with both stars being brown dwarfs orbiting each other at about 3.5 astronomical units (the Earth-Sun distance) and an orbital period of 27 years. The system is actually located in the southern hemisphere in the constellation Vela and is approximately 6.503 light years away from the sun. This very unique star system is also known as WISE 1049-5319 because the stars can only be seen in infrared using data from the WISE telescope. Kevin Luhman, an astronomer with Pennsylvania State University, discovered the stars in 2013. Because they lie close to the galactic plane, where stars are crowded, they eluded discovery until then. They are the nearest known brown dwarfs to the solar system, and the closest system discovered since Barnard’s star in 1916. These stars have not been around for a very long time; they are fairly young for stars at about 600-800 million years old.
For Luhman 16 A, the largest of the pair, is classified as an L8 star with .032 times the mass of our sun and 33.5 times the mass of Jupiter. It has a surface temperature of about 1400 K. Luhman 16 B is a T1 star with a mass of .027 Sols or 28.6 Jupiters. Both stars are located at RA 10h 49m 15.57s and declination of -53° 19m 06s. Luhman 16A is suspected of having a planet, Luhman 16Ab, measured through astrometry with the Hubble Space Telescope in 2013. That planet is now considered unlikely based on further measurements of the system.
A sub-brown dwarf of classification Y4 in the constellation of Hydra, this smallest of all stars yet known was discovered by Kevin Luhman using data from the WISE infrared telescope in 2013. It is right at the border between planet and star, and would have only fused deuterium for a short time before starting to cool down. Its surface temperature is 225-260 K, making it about the same temperature as Mars and therefore the coldest known star, but also much too warm for it to be a rogue planet; it must have had an internal heat source suggestive of previous deuterium fusion. Yet it only has a mass of 3-10 times the mass of Jupiter, putting it into the planetary mass range. It is 7.43 light years away and has a high proper motion. There is some evidence from the Magellan Baade Telescope that it may have water clouds. If seen up close, it would have a purple to deep magenta color.
This small red dwarf is located exactly on the ecliptic in the southern part of Leo not far from the star Regulus. It is 7.9 light years away and has a classification of M6.5V and an apparent magnitude of 13.54; it can only be seen with a large telescope. It is far too dim to be seen with the unaided eye. Its surface or photosphere has a temperature of only 2800 K, about half the temperature of our sun. At this temperature, chemical compounds such as titanium (II) oxide and even water can exist in gaseous form. It has a stronger magnetic field than our sun due to the complete circulation of materials inside because of convection currents; as a result of this magnetic field, strong X-ray and gamma ray flares can sometimes be observed. It is less than a billion years old and hasn’t had time for these flares to die out as its rotation slows. It is just barely large enough to sustain proton-proton fusion and be considered a red dwarf instead of a brown dwarf, having only 8% of the sun’s mass. Because it is able to convect all of its material, it can sustain fusion for eight trillion years. It is just getting started.
Wolf 359 was the 359th star listed by German astronomer Max Wolf in his 1919 catalog. He was cataloguing stars with high proper motion, knowing they were nearby stars. It is known to have at least two planets. Wolf 350c is a super-Earth with 3.8 Earth masses and near the star, with an orbital period of 2.7 days. It receives three times the energy that Earth does. Wolf 359b (the first to be discovered) is a Neptune-class planet 44 times the mass of Earth with an orbital period of about 3000 days even though it is only about 2 astronomical units from the star. The low mass of the star allows the planet to have such a slow orbit.
Because of its proximity to Earth, Wolf 359 has been the subject of several important science fiction works. Most notably, it was the site for a major battle between Federation forces and a Borg cube on its way to Sector 001 (Earth) to assimilate humanity. 40 starships engaged the Borg, but because Captain Picard had been assimilated, they knew all of his tactical knowledge and easily defeated the Federation. Someone in the Star Trek writers group did their homework and found that Wolf 359 was close to Earth and a likely site for such a battle. However, the Borg are supposed to originate from the Delta Quadrant on the opposite side of the galaxy from our position. Wolf 359 is in Leo, putting it further out from the galactic center than Earth; the Borg would have had to take a very roundabout route to come at Earth from Leo. “Wolf 359” is also the title of an Outer Limits episode where a scientist creates a simulation of Dundee’s Planet in the Wolf 359 system only to see a dangerous life form evolve. In the novel Chindi by Jack McDevitt, a lost spaceship is found in the Wolf 359 system.
Lalande 21185: by Sarah S.
Another red dwarf located in the southern corner of Ursa Major, this star is 8.31 light years from Earth. With an apparent magnitude of 7.5, it is somewhat brighter and hotter than Wolf 359 and may be as old as 10 billion years. It is also known as BD +36 2147, Gliese 411, and HD 95735. It was first listed in 1801 by Joseph-Jerome de Lalande and its proper motion was first measured by Friedrich Wilhelm Argelander for the Bonner Durchmusterung (BD) or Bonn Star Catalog. It has 38% the mass of Sol and a photospheric temperature of 3828 K. Although listed as a flare star, it is rather quiet as far as red dwarfs go.
Peter van de Kamp claimed in 1951 that Lalande 21185 had a planet based on astrometric measurements using the same photographic plates as for his Barnard’s Star planet claim, but those plates were shown to be flawed. George Gatewood made his own astrometric measurements and claimed that there were multiple planets in the system, although his data remains unconfirmed. Using sensitive radial velocity measurements in the 1980s, Geoff Marcy could not find any planets in the system. However, recent measurements by the HIRES system at Keck Observatory supported there being at least one close in planet with a mass of at least 3.8 Earths and a period of 10 days. Further measurements with the SOPHIE echelle spectrograph showed this planet to have a period of 12.95 days and 2.99 Earth masses, which has been confirmed by other measurements. One other planet orbiting at 2806 days and with 14 Earth masses has also been confirmed, with a third planet suspected between them. Thus, van de Kamp and Gatewood’s claims have been somewhat vindicated even if these are not the planets they claimed to have found.
In fiction Lalande 21185 is the star of the planet Ormazd in Rogue Queen by L. Sprague de Camp (1951) and is one of many nearby stars mentioned by Gregory Benford in Across the Sea of Suns (1983), where it is renamed Ra. In the Revelation Space stories by Alastair Reynolds, the planet Zion orbits Lalande 21185.
Sirius: by Katie T.
Sirius is the brightest star in the sky seen from earth. The name comes from the Greek word meaning glowing/ scorching. Sirius is part of the Canis Majoris constellation, which is also called “The Greater Dog,” and can therefore also be called Alpha Canis Majoris. The star lives up to its name; in ancient Greek times a myth was created. Sirius the star was so hot men would feel weaker, plants would fail to grow, and women would become very aroused. Whenever Sirius first made an appearance, it was known as the “Dog Days” to the Egyptians and signaled the beginning of the inundation of the Nile, the beginning of the their calendar year.
A German astronomer, Friedrich Wilhelm Bessel, predicted Sirius B in 1844. The star is part of a binary star system consisting of two stars orbiting each other, with Sirius B as the closest white dwarf to Earth. Bessel made the assumption there was another star, after observing the motion of Sirius A. Following the information provided by Bessel, an astronomer in 1862 discovered Sirius B (the Pup). Alvan Graham Clark was testing the aperture of the largest telescope in America and came across a smaller star orbiting around Sirius A.
You may not think it, but Sirius is even bigger and hotter than our sun. If you observe the sky on a clear day, you may even be able to catch a sighting of the brightest star, using just the naked eye.
Coordinates: RA: 6h 45m 9s, Dec: -16° 42’ 58”, Distance: 8.6 light years
Apparent Magnitude: -1.46
Stellar Type: A1V
In fiction, Sirius Black is the name of the godfather of Harry Potter in the series of books by J. K. Rowling, first introduced in the third book, The Prisoner of Azkaban (although mentioned in the first book as the owner of the motorcycle being used by Hagrid in the first book). He is able to transform into a dog, of course, and he is killed by his cousin, Bellatrix LaStrange, who is also named after a star (meaning “Warrior Woman”). Sirius’ brother is named Regulus Arcturus Black, a double star reference. In Homer’s The Iliad, Achilles is compared with the brilliance of Sirius. Voltaire’s Micromegas describes an alien from a planet orbiting Sirius. In the Foundation series and the novel Pebble in the Sky by Isaac Asimov, Earth is considered to be somewhere in the “Sirius Sector.” Much of the technology mentioned in Douglas Adam’s Hitchhiker’s Guide to the Galaxy series is made by the Sirius Cybernetics Cooperation.
A binary red dwarf system in the constellation Cetus, it is also known as UV Ceti or Gliese 65. They are 8.7 light years away and considered as prototypes of UV flare stars. They were discovered by Willem Jacob Luyten in 1948, have almost equal brightness and orbit each other every 26.5 years. They may be part of the Hyades open star cluster.
Another small red dwarf single star located in Sagittarius, it was discovered by Frank Elmore Ross in 1925 as part of his lists of new variable stars and stars with high proper motion. It is a UV Ceti type flare star, with a variable star designation of V1216 Sagittarii and average time between ultraviolet flares of about two days. Using highly precise data from the HARPS spectrograph during the Red Dots campaign, Ross 154 is shown to have a rapid rotation of 2.87 days, which corresponds to a young age of less than one billion years. This was the third star, including Proxima Centauri and Barnard’s Star, that was studied in the 2017 Red Dots study. It is of spectral type M3.5Ve and is 9.7 light years distant. It is not known to have any planets, but detecting planets is a challenge because of its rapid rotation and active surface, which produce a great deal of noise in the radial velocity data. In fiction, it is the site of Glory Station in C. J. Cherryh’s Downbelow Station.
Another unremarkable red dwarf flare star discovered by Frank Ross. It is also known as HH Andromedae or Gliese 905 and is 10.3 light years away, with Right Ascension: 23h 41m 54.7s and Declination: +44.18 °.
Also known as Ran (based on a 2015 naming contest by the International Astronomical Union, won by 14-year old James Ott), this is an orange dwarf star slightly smaller and cooler than our sun. It is 10.5 light years away with RA: 3h 32m 55.84s and Dec: -09° 27′ 29.73” and spectral class K2V. It has 82% of the sun’s mass and is a fairly young star, less than one billion years old and perhaps as young as only 200 million years and still gives off appreciable amounts of ultraviolet radiation.
As a close sun-like star, E. Eridani has been intensely studied for planets. This was another star thought to have had planets by Peter van de Kamp but his measurements were later shown to be caused by defective photographic plates. Measurements by the IRAS infrared satellite showed that it still retains at least two dusty rings containing asteroids, one that is about 4 AU from the star and one at about 20 AU. It also has a Kuiper belt analog or cometary cloud about 30 AU out. Clumping in the dust rings was considered evidence that it may have planets, and at least one large exoplanet perhaps 1.2 times the mass of Jupiter is considered to be confirmed now that the Hubble Space Telescope has shown perturbations in the path of Epsilon Eridani using astrometry. This planet has been given the name Ægir by the IAU and orbits the star every 7.4 years at about 3.4 AU, or just outside the inner asteroid belt. Computer simulations of the clumping of dust particles in the rings suggests their may be a second planet in an eccentric resonance orbit. E. Eridani has slightly less metal than our sun, but enough for rocky planets to exist closer to the star.
Because of its nearness and similarity to our sun, E. Eridani was one of the two stars first chosen for listening for alien signals by Project Ozma in 1961 by Frank Drake. No signals were detected. Project Daedalus of the British Interplanetary Society has suggested E. Eridani as one of the possible targets for an interstellar space probe. It has been the subject of many science fiction works, including Babylon 5. In the series, the station orbits at the L5 point of Epsilon Eridani III and its moon. The planet is also the site of the Great Machine that figures prominently in several episodes. In Star Trek, Epsilon Eridani is the system of the planet Axanar, where a famous space battle occurred between the Federation and the Klingon Empire prior to the events of the original series and where Garth of Issus became famous for his battle tactics. It is also mentioned in Space: Above and Beyond, The Orville, and Space Precinct as well as many novels, short stories, and games.
Ross 128: by Julia W.
Ross 128 is a red dwarf star, found in the equatorial zodiac constellation Virgo at RA: 11h 47m 44.4s and Dec: +00° 48′ 16.4”, not far from the star Beta Virginis as seen from Earth. It is a fairly old and quiet star, as red dwarfs go, not exhibiting as many flares a seen in other red dwarfs, although a strong flare was noted in 1972 in the UV band. It is 11.13 light years from Earth with a spectral class of M4V and a mass of 15% that of the sun. It was first cataloged in 1926 by Frank Elmore Ross. It is considered to be an old disk star, and recent measurements by the APOGEE instrument indicate is has nearly the same metallicity as Sol. It does not have the infrared excess that would indicate a dust ring. It is a slow rotator, spinning only once every 165.1 days, because of it old age and the gradual slowing or rotation due to magnetic braking.
A great deal of excitement and speculation occurred when an exoplanet, Ross 128 b, was announced orbiting the star in its habitable zone. This planet is slightly larger than Earth at 1.8 Earth masses with about 1.4 times as much energy reaching it than Earth. Although hotter than Earth, its orbit and the quietness of the Ross 128 make this one of the best candidates for life of any exoplanet discovered so far and the second closest habitable zone planet after Proxima b. Ross 128 b orbits every 9.9 days and is close enough to be tidally locked, which, if it has oceans, would make it a candidate as an “eyeball” planet and an Earth-like analog. It is most likely a rocky planet based on its size, orbit, and the parent star’s metallicity.
Radio signals were detected in 2017 by the Aricebo observatory that appeared to be coming from the vicinity of Ross 128, but the Allen Array was able to show that these signals were actually from geosynchronous satellites orbiting the Earth; Ross 128 orbits near the celestial equator near the orbits of many communication satellites.
Gregory Benford, in his 1984 novel Across the Sea of Suns, describes an amphibious alien race living below the ice of a Ganymeda-type exomoon orbiting a planet in the Ross 128 system. They are hiding from extinction caused by a Berserker killing machine called a Watcher orbiting the moon. In the TV series War of the Worlds (2019) Earth is attacked from Ross 128 after picking up a signal.
EZ Aquarii by Lily M.
EZ Aquarii is in the constellation Aquarius and is a triple star system about 11.3 light years away from the Sun and is also known as Luten 789-6 and Glieses 866. Its Right Ascension is 22h 38m 33.4s and its Decl. (deg.) is –15.3. For EZ Aquarii A the stellar type is M5.0V, the other two stars are about the same or slightly smaller. Its magnitude is 12.87. EZ Aquarii may have been found by All of the EZ Aquarii stars A, B, and C are M-typed red dwarf stars and are too faint to be seen by our eyes without help. An interesting fact about EZ Aquarii is that both A and C form a spectroscopic binary that orbit at 3.8 days, with B having an orbit of 823 days. A and B are both flare stars, and the system has no known planets as yet. Its nearest neighbor at this time is Lacaille 9352, which is about 4.1 light years away, making this system rather isolated.
This binary system southeast of Deneb in the summer sky has bright enough stars that they were included in John Flamsteed’s star maps and therefore have a Flamsteed designation from his 1712 Historia Coelestis Britannica. Both stars are old K-type orange dwarf stars (K5V and K7V respectively) and can be seen with the naked eye under clear, dark skies or with binoculars in areas of high light pollution. They orbit each other every 659 years at about 44 AU, having a wide separation. In clear skies, the pair of stars can be resolved with a 10x power pair of binoculars. The proper motion of 61 Cygni was measured in 1804 by Giuseppe Piazzi; this is the only visible eye star system that has a high proper motion and was therefore called “Piazzi’s Flying Star.” In 1834 Friedrich Bessel measured its distance as 10.4 light years using stellar parallax, the first star to ever be measured in this way. Its actual distance is 11.4 light years. There have been claims of a massive planet orbiting one of the two stars which have been controversial. The 2018 data release from the Gaia spacecraft indicates that there are anomalies in the orbits of the stars around each other showing that they are not quite orbiting around their center of mass and that 61 Cygni B is moving too slowly for its mass. This may indicate the presence of an as yet unconfirmed planet around 61 Cygni B. Measurements of the infrared signature of the system show a possible infrared excess suggesting a possible circumstellar dust disc.
Procyon by Cate L.
Procyon A is the brightest star in the constellation of Canis Minor, which means “smaller dog” in Latin, the eighth brightest star in our sky, and is a binary star, which indicates that another star orbits around Procyon. The distance of Procyon A and B from our planet Earth is 11.46 light years away. The right ascension for both stars is 7 h 39 m 18.1 s, and the declination of both stars is 5°13 m 30 s. Their stellar types are F5 IV-V, and DQZ. The first one is yellowish-whiteish and the second one is a white dwarf. The temperature for A is 6,530 K, whereas B is 7,740 K. As a white dwarf, B is the core of a star much like our sun that threw off its outer layers leaving a white hot companion to the slightly cooler and more yellowish A star. The two stars orbit a common center of gravity every 40.84 years in moderately eccentric or elliptical orbits.
Procyon was known to the ancients and to all cultures, being one of the brightest stars in the sky. In Greek, its name means “before the dog” referring to it rising before Sirius, the dog star. In other non-Greek cultures, it has been known as Nangar, the Carpenter to the Babylonians. The Latin version of Procyon is Antecanis and Arabic names are Al Shira or Elgomaisa and Turkish Rumeysa, the Bleary-Eyed Woman. To the Hawaians, it was Puana, the Blossom and to the Chinese, Nan He San, the Third Star of South River.
The A star is a late main sequence class F star, and will reach the end of hydrogen fusion in its core within the next 10-100 million years, after which it will swell 80-150 times it current diameter and become a red giant.
Procyon B was first proposed by Friedrich Bessel based on astrometric measurements and it was visually confirmed in 1896 by John Martin Schaeberle at Lick Observatory. It was originally a B-type star about 2.59 times the mass of our sun, which came to an end about 1.19 billion years ago after a main sequence lifetime of about 680 million years, making its remnant an old white dwarf.
A binary red dwarf system in the constellation of Draco, these stars were first included in the double star catalog of Friedrich Georg Wilhelm von Struve as system 2398. Also known as Gliese 725, the Greek letter sigma is sometimes used to designate Struve catalog stars. Both stars in the system are x-ray flare stars, as are most red dwarfs, and orbit each other with a period of 295 years. They are 11.6 light years away. The B star in the system has two planets, both of about Neptune’s size. One has an orbital period of 91.29 days and the other 192.4 days.
Located in the constellation Andromeda, this pair of binary red dwarf flare stars is ll.618 light years away and was first listed in A Catalogue of Circumpolar Stars by Stephen Groombridge, published posthumously in 1838. They orbit around a common center of gravity in almost circular orbits every 2600 years at about 147 AU. Using radial velocity measurements, two planets have been inferred orbiting around Groombridge 34 A, one a super-earth with 3.03 Earth masses and the other a larger Neptune-class planet with 36 Earth masses.
This dim M6.5V red dwarf flare star is in the constellation Cancer and is 11.8 light years away. It is small for a red dwarf, with only 9% of the Sun’s mass and a temperature of 2840 K. It is proposed to be part of a group of stars called the Castor moving group that all had a common origin about 200 million years ago in an open cluster and are moving together as a group while gradually spreading apart. It is not known to have planets.
Tau Ceti by Ruby R.:
This is one of the most important stars near us in that it is a G8V star only slightly smaller and cooler than Sol, with 78% of the sun’s mass. It has a lower percentage of metals than the sun, and is 11.91 light years away in the constellation of Cetus, the whale. It does not have a Greek common name, and was first listed in western catalogs in 1603 by Johann Bayer in his Uranometria. The Calendarium of Al Achsasi al Mouakket of 1650 lists this star as Thalith al Na’amat, the Third Ostrich. It is the Fifth Star of the Square Celestial Granary in Chinese. Estimates of Tau Ceti’s age, based on its metallicity and models of stellar evolution, put it at about one billion years older than our Sun. It is a very stable star, with few if any sunspots and a weak magnetic field.
Because it is the closest single G-type star, it is a Solar analog and has been continually studied for SETI and exoplanet research. It was one of Frank Drake’s original stars for Project Ozma in 1961. Four planets are confirmed to orbit Tau Ceti, designated g, h, e, and f. They are all super-Earths. Planet e orbits every 163 days, putting it at the inner edge of Tau Ceti’s habitable zone with a radiative flux slightly less than Venus, and Planet f orbits at 636 days, putting it at the outer edge with a solar flux comparable to Mars, but with a thick enough atmosphere could sustain liquid water on the surface. Four other planets are suspected to be in the system but are not yet confirmed, although statistical modeling agrees with the detected radial velocities of Planets b, c, and d. With the possibility of 8 or 9 planets, the Tau Ceti system is similar to our own and one of the best candidates to search for life.
Infrared measurements show that Tau Ceti has a thick debris disc similar to our asteroid belt but ten times more dense, and orbiting roughly in the same area as our Kuiper Belt, which would make collisions with any potentially habitable planets more frequent. If there is a large gas giant, as some have proposed (unconfirmed Planet i) then it might have a similar role to Jupiter in deflecting potential impactors. As dense as this dust disc is, it is only 1/20 as dense as the one around Epsilon Eridani. Such dust discs may be common around sun-like stars and may play a role in planet formation; our solar system may be an exceptionally dustless system that had many of its comets and asteroids cleared out early on by a passing star.
In science fiction, Tau Ceti is the system of the planet Aurora in Isaac Asimov’s robot novels as the first settled of the spacer worlds and is the setting of the novel The Robots of Dawn. It is the home world of the roboticist Dr. Han Fastolfe. It is the destination of the torchship Lewis and Clark in Heinlien’s novel Time for the Stars. The planets of Tau Ceti are the setting of Ursula LeGuin’s The Dispossessed. The Downbelow Sation of C. J. Cherryh’s novel of the same name is located on planet Downbelow orbiting Tau Ceti. The Legacy of Heorot by Niven, Pournelle, and Barnes takes place on the planet Avalon (Tau Ceti IV). 100 colonists, sent by sleeper ship, find that ice crystals have built up in their brains while in suspended animation and arrive on Avalon with reduced mental abilities only to be forced to counter the threat of ferocious grendel monsters. In Rama Revealed by Arthur C. Clarke, a group of colonists travel on the Rama II to a node in the Tau Ceti system. In Leviathan Wakes in the Expanse series of novels and TV show by James S. A. Corey, the Mormon generation ship S. S. Nauvoo is traveling to the Tau Ceti system before being commandeered to crash into Eros.
This is an unusual trinary system with an orange K-type dwarf star in the far southern constellation Indus orbited by two T-type brown dwarfs that are orbiting each other and designated Epsilon Indi Ba and Bb. The A star has at least one planet called Epsilon Indi Ab and it has a mass of about 3.25 Jupiters, making it the closest Jovian planet to us. It has an orbital period of 45 years compared to about 12 years for Jupiter, putting this planet much further out. Since Epsilon Indi is an orange dwarf star cooler than the sun, this planet is far outside the habitable zone. The two brown dwarfs are about 1460 AU from the main star or over 37 times the distance between our sun and Pluto (which is 39 AU away from Sol). They orbit each other at about 2.1 AU every 15 years. They have the masses of about 47 and 28 times the mass of Jupiter. The complexity of this system makes it a good candidate for studying the evolution of stellar systems. The size and distance of Epsilon Indi Ab make it a good candidate for direct observation by the James Webb Space Telescope.
Located 11.98 light years from Earth in the constellation Horologium, this small red dwarf was first discovered by Wilhelm Gliese in 1974 when its proper motion was measured, but it was assumed to be much further away at 25 light years. The RECONS satellite was able to measure its parallax much more accurately in 1997 and provide a better estimate of its distance. It is at the lower limit of a red dwarf star at only 11.3% the size of Sol and 0.2% as luminous. Any smaller and it would be a brown dwarf.
In 2019 the Red Dots program announced that the star has three exoplanets: b, c, and d with periods of 3.2, 6.69, and 13.03 days respectively. They are all super-earths with similar masses of 1.38, 1.75, and 1.68 Earth masses. Because of the small size of Gliese 1061, the second planet (Gliese 1061 c) actually orbits just within the inner edge of the star’s habitable zone but would have an equilibrium temperature of 307 °K or 93 °F assuming a similar atmosphere to Earth. It receives 34% more radiative flux than Earth but is so close to its parent star that is likely to be tidally locked with one side constantly facing the star. The third planet, Gliese 1061 d, is also possibly in the habitable zone but on the cool side with 40% less stellar flux than Earth, making it more like Mars. Although its close proximity to the star would indicate tidal locking but it has a fairly eccentric orbit at 0.54, which would tend to destabilize the tidal locking and allow for a day-night cycle. This eccentricity would be a challenge for life.
At 12.11 light years from Earth, this red dwarf flare star in the constellation Cetus is unusually close to Tau Ceti at only 1.6 light years and is about 13% of the size of Sol. The YZ designation indicates that this is a variable star with periodic changes in brightness caused by starspots or chromospheric variation as the star rotates every 68.3 days. It also gives off frequent ultraviolet flares.
In 2017 three planets were announced with a possible fourth that still needs confirmation. All three confirmed planets are too close to the star to be inside the habitable zone. Planets b and c are smaller than Earth (0.75 and 0.98 Earth masses) and planet d slightly larger at 1.14 Earth masses.
Also known as BD+05°1668 from the Bonn Star Catalog (Bonner Durchmusterung) or GJ 273, this star is located in Canis Minor at a distance of 12.36 light years. Its proper motion and distance were first measured by Willem Jacob Luyten and Edwin G. Ebbighausen. It is about 35% of Sol’s mass and rotates slowly once every 116 days according to variations in surface activity and has a surface temperature of 3150 °K. It is only 1.2 light years from Procyon.
In 2017 two planets were confirmed. GJ 273 b is a super-earth with 2.89 Earth masses at the inner edge of the habitable zone with a radiative flux of 106% that of Earth and a mean equilibrium temperature of 206 to 293 °K depending on the atmosphere’s composition, if an atmosphere exists. It is therefore one of the best potential candidates for being similar to Earth and therefore possibly to have life. The inner planet, GJ 273 c, is only 1.18 Earth masses and orbits much closer to the star. In 2019 two more planets were detected using radial velocity but still need confirmation.
Because GJ273 b is one of the closest potentially habitable exoplanets, it was the target for a project in 2019 called Sónar Calling GJ273b, where a series of radio signals containing 33 musical compositions and a decoding tutorial were sent from the Ramfjordmoen radar antenna in Norway toward GJ273b, with more transmitted in 2018. If anyone hears us, we could expect a response no sooner than 2042.
Located in Ares, this small red dwarf is 12.578 light years distant and was only discovered in 2003 using near-earth asteroid tracking (NEAT) data and is named after the discovery team’s leader, Bonnard J. Teegarden. This discovery helps to confirm a hypothesis that many small mass stars have yet to be discovered within 20 light years of Earth. Their low luminosity makes them very difficult to find.
Two planets, both inside the habitable zone, have been confirmed. One orbits at a distance that would put it between Earth and Venus in temperature and the other is cooler, similar to Mars. Both are only slightly larger than Earth at 1.05 and 1.11 Earth masses for Teegarden b and c, respectively. Different studies disagree as to whether these planets could have retained a dense atmosphere.
Another small red dwarf lies in the southern constellation of Pictor at 12.83 light years distance. It is a bit larger and brighter than some red dwarfs, with a stellar class of M1 instead of usual M3.5-6 of a typical red dwarf. This star may have had an unusual origin, as its motion and elemental abundances indicates it may have been a part of the Omega Centauri globular cluster, a small irregular dwarf galaxy that was absorbed by the Milky Way and produced a stellar stream of which Kapteyn’s Star may be a part. Jacobus Cornelius Kapteyn first announced the closeness of the star in 1898. It was listed in the Cape Photographic Durchmusterung as CPD -44° 612 and he noted that it had moved considerably (15 arcseconds) from its originally charted position in 1873. This makes it one of the fastest moving stars in terms of proper motion (sideways motion through the sky). It has fluctuations in its brightness due to starspot activity or chromospheric variation. Because of its high metallicity (14% of Sol) it is considered to be a relatively old star at about 11 billion years.
Two planets were announced in 2014 but their existence has been controversial due to one planet’s orbit being a resonance frequency of the star’s variation and the other almost identical to the star’s rotation, so possibly the planetary induced stellar radial velocity is not due to actual stellar motion but luminosity variations of the surface. If the planets do exist, they would be among the oldest known. Kapteyn b could be potentially habitable, but its atmosphere is likely to have been stripped away over time due to stellar flares and age if it exists at all. In 2014 science fiction author Alastair Reynolds wrote a short story about the proposed planets called “Sad Kapteyn.”
As the last star on this list (but not in our model, which went out to 15.0 light years), this red dwarf is in the southern constellation Microscopium and is 12.9 light years away. It is the brightest of the red dwarf stars in our night sky, and may be seen under ideal conditions under very dark and clear skies by the unaided human eye, the only red dwarf to be visible with binoculars or a telescope. It was first listed in 1763 in a posthumous catalog by the Abbé Nicolas Louis de Lacaille and was discovered by him while he worked at an observatory at the Cape of Good Hope. It is a flare star and erupts about once per day. It has 60% of Sol’s mass and has been classified anywhere between a K7 to an M2 dwarf star. It is slightly older than Sol at five billion years and rotates only once every 40 days, with a photospheric temperature of 3800 ° K. It is estimated that this star will last about 75 billion years. No planets have been detected around this star.
This is the list of stars within 13.0 light years of Earth. As we go further out, the spherical volume becomes ever larger and a greater number of stars are located within the radial distance. There are 14 more star systems located between 13.0 and 15.0 light years. From our 3D model, it is apparent that the stars are not evenly distributed in our stellar neighborhood. The Alpha Centauri system is located in a region where it is the only star system for many light years in all directions – our solar system is the closest star to it and beyond it there is largely a void with few stars. In other areas the stars are packed more closely, but are still separated by at least a light year. Sol is at the edge of the Orion Branch of the Sagittarius Arm of the Milky Way, so that as we travel beyond the edge of the branch we reach a large gap without stars between the spiral arms.
A quick count of the number of different classes of stars show that red dwarfs far outnumber all other types of stars. It is obvious that small mass stars are like rabbits: they may be dim, but there are a lot of them. Of the 28 star systems within 13 light years (including Sol) there are 21 planetary systems (assuming all the unconfirmed planets are real). That statistic certainly increases the odds of there being life somewhere out there beyond our solar system; quite a few of these planets are within the habitable zone of their stars, but most of these stars are flare stars. This both increases and decreases the odds of life existing on these worlds. We are constraining many of the variables in the Drake Equation and estimates run to as many as 40 billion Earth-like planets in our Milky Way galaxy.
Surely we are not a special case; if life could get started here and chemistry is the same everywhere in the universe, then the factors that led to life here (whatever they were) are likely to occur elsewhere. Life could be abundant in the universe. That isn’t to say that intelligent life is abundant; on Earth, conditions may have been just right for us to evolve intelligence (more on this in our next edition). But once life gets started on a planet, according to how tenacious life has been here through six major extinctions, it is likely to hold on; perhaps even in our own solar system, on Mars, or Enceladus, or Europa. If we can get remote instruments out to these 21 star systems, we may very well find life.
I for one hope that some day a form of faster-than-light travel can be realized, perhaps even something like a warp drive in Star Trek. I hope life is as common as science fiction hypothesizes. It would be a wasted universe if we are the only ones out here.