G 139-21 / GJ 1214

On March 11, 2011, a team of astronomers using older observational data from NASA's infrared Spitzer space telescope with newer data that they collected through the MEarth Project submitted a paper confirming that the "warm" super-Earth GJ 1214 b does not have an atmosphere composed of an outer gas layer hydrogen and helium like Uranus or Neptune, with high statistical confidence (over 99.99 percent). The team was also able to provide better support for their earlier conclusion that the planet's atmosphere is likely to be "dominated" by elements heavier than hydrogen and helium with a water mass fraction of over 10 percent water vapor (with over 99.7 percent confidence), but possibly over 50 percent (68 percent confidence). On the other hand, they also estimated that the planet's equilibrium temperature to be around 282° Celsius or 539° Fahrenheit (555 kelvin). Using data from two consecutive transits of planet b across its host star, moreover, the team failed to detect the presence of other planets in the GJ 1214 system through their gravitational influence on planet b's orbit through (Desert et al, 2011; and Jon Voisey, Universe Today, March 15, 2011).

Luis Calçada, ESO



Large and jumbo animation slides.



The planet, GJ 1214 b, has
an atmosphere that is either
dominated by steam or covered
by thick clouds or hazes (more).

On December 1, 2010, a team of astronomers announced the results of the first analysis of the atmosphere of a super-Earth planet, GJ 1214 b, using the European Southern Observatory's Very Large Telescope. The planet's atmosphere was analyzed when it passed in front of its host star as some of its infrared light passed through the planet’s atmosphere. Based on the available data, the astronomers concluded that the planet's atmosphere is either a thin but dense layer rich in water steam or a thick layer of high clouds or hazes, similar to those seen in the atmospheres of Venus and Titan in the Solar System. A puffy hydrogen-helium gas envelope like that of Uranus or Neptune is ruled out, unless it's covered by a high cloud layer of noxious hydrocarbons (ESO press release; NASA/JPL news release; and Bean et al, 2010).

Digitized Sky Survey 2,
ESO






Large and jumbo
animation slides.






Field image around GJ 1214,
a very dim, red dwarf star
not visible with the naked
eye (more).

The high proper motion of this star was detected during the Lowell Proper Motion Survey of the Northern Hemisphere begun in 1957 by Henry Lee Giclas (1910-2007), Robert Burnham, Jr. (1931-93), and Norman G. Thomas at Lowell Observatory and designated as G 139-021 in the Giclas catalogues of faint proper motion stars (Giclas et al, 1971). It was also included in the 1979 Luyten Half-Second Catalogue as LHS 3275 by Willem Jacob Luyten (1899-1994). The star was added to the 1979 update of the Gliese Catalogue of Nearby Stars (CNS, now ARICNS database) by Wilhelm Gliese (1915-93) and Hartmut Jahreiss (Gliese and Jahreiss, 1979) as GJ 1214.

Luis Calçada, ESO



Large and jumbo animation slides.



A likely hot "steam planet,"
with around 6.6 Earth-masses
and some 2.6 times Earth's
diameter, has a "torch" orbit
around GJ 1214 (more).

On December 16, 2009, a team of astronomers announced the discovery of a super-Earth in an inner orbit using the "transit method" of planetary detection using "a fleet of ground-based telescopes no larger than those many amateur astronomers have in their backyards" as part of the MEarth Project (CfA news release). With a (revised) diameter of 2.63 ± 0.11 times that of Earth, the planet was estimated to have around 6.6 Earth-masses based radial-velocity measurements using the ESO 3.6-meter telescope and its HARPS spectrograph) (ESO press release; Bean et al, 2010; Charbonneau et al 2009; Geoffrey Marcy, 2009; Rogers and Seager, 2009; Dennis Overbye, New York Times, December 16, 2009; and Ivan Seminuik, New Scientist, December 16, 2009 -- more below).

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	Orbital Distance (a=AUs)	Orbital Period (P=years)	Orbital Eccentricity (e)	Orbital Inclination (i=degrees)	Mass (Earths)	Diameter (Earths)	Density (Earths)	Surface Gravity (Earths)	Metallicity (Solar)
GJ 1214	0.0	...	...	...	52,000	23	...	...	...
Planet "b"	0.014	0.0043	<0.27	88.6	~6.6	~2.6	...	...	...
Inner H.Z. Edge?	0.057	0.034	0.0	...	...	...	...	...	...
Outer HZ Edge?	0.110	0.092	0.0	...	...	...	...	...	...

The Star

GJ 1214 is a cool and dim, main sequence red dwarf of spectral and luminosity type M4.5 V (NASA Star and Exoplanet Database, based on Hawley et al, 1996). The star has 15.7 ± 1.9 percent of Sol's mass, 21.1 (± 0.97 percent of its diameter, and under 0.02 percent of its visual and over 0.328 percent of its bolometric luminosity (Rogers and Seager, 2009). GJ 1214 is around six billion years old. Some other useful star catalogue designations include: GJ 1214, G 139-21, LHS 3275, USNO 256, and 2MASS J17151894+0457496.

David Aguilar, CfA







Large and jumbo illustrations.







GJ 1214 is a red dwarf star with
one known planet in a hot inner
orbit, beyond even the inner edge
of the star's close-in habitable
zone, as imagined by Aguilar with
two hypothetical moons (more).

Habitable Zone

With a spectral type of M4, Ross 128 can be used as a rough proxy for GJ 1214 (M 4.5). According to calculations performed for the NASA Star and Exoplanet Database, the distance from Ross 128 where an Earth-type rocky planet may have liquid water on its surface has been estimated to be between 0.06 and 0.11 AU -- well within the orbital distance of Mercury in the Solar System. In that distance range from the star, such a planet would have a "year" of only 13 to 34 days.

Planet "b"

On December 16, 2009, a team of astronomers (including David Charbonneau, Zachory K. Berta, Jonathan Irwin, Christopher J. Burke, Philip Nutzman, Lars A. Buchhave, Christophe Lovis, Xavier Bonfils, David W. Latham, Stéphane Udry, Ruth A. Murray-Clay, Matthew J. Holman, Emilio E. Falco, Joshua N. Winn, Didier Queloz, Francesco Pepe, Michel Mayor, Xavier Delfosse, and Thierry Forveille) announced the discovery of a planet "b" of 6.55 ± 0.98 Earth-masses in a tight inner orbit using the "transit method" of planetary detection using "a fleet of ground-based telescopes no larger than those many amateur astronomers have in their backyards" as part of the MEarth Project (CfA news release). With a (revised) diameter of 2.63 ± 0.11 times that of Earth, the mass of the planet was derived from radial-velocity measurements using the ESO 3.6-meter telescope and its HARPS spectrograph) (ESO press release; Bean et al, 2010; Charbonneau et al 2009; Geoffrey Marcy, 2009; Rogers and Seager, 2009; Dennis Overbye, New York Times, December 16, 2009; and Ivan Seminuik, New Scientist, December 16, 2009). It revolves around GJ 1214 at an average distance of 0.014 AU, in a roughly circular orbit (e<0.27) which it completes in 1.6 days (38 hours), and so the planet must have a very hot equilibrium temperature -- updated in 2011 to around 555 kelvin, 539° Fahrenheit, or 282° Celsius (Desert et al, 2011, page 6). With respect to Earth's line of sight, the planet's orbit is inclined at 88.6 degrees.

Luis Calçada, ESO



Large and jumbo animation slides.



A likely hot "steam planet,"
with around 6.6 Earth-masses
and some 2.6 times Earth's
diameter, has a "torch" orbit
around GJ 1214 (more).

The planet's mass and diameter are consistent with the hypothesis that it has a low average density due to an inferred composition of three-fourths water (possibly 47 percent) and other ices (that have subliminated into a "supercritical fluid" above an "electronically conductive," dense fluid plasma below a steamy atmosphere) and one-fourth rock and iron in the core. If the planet formed early in the star's development, moreover, then it may have accreted an atmosphere of hydrogen and helium that may be around 200 kilometers (124 miles) thick. At the planet's orbital distance of only 0.014 AU from its host star, however, the surface temperature has been estimated to be around 400° Fahrenheit (200° Celsius), which is way too hot for liquid water. Totalling no more than one percent of the planet's mass, the planet's atmosphere "is probably escaping hydrodynamically" into space, suggesting that the planet has lost most of its primordial atmosphere since formation. An interesting possibility is that GJ 1214 b is a hot "steam planet," with a "steam atmosphere that transitions continuously to a super-fluid without passing through the liquid phase" (Charbonneau et al 2009; Geoffrey Marcy, 2009; Rogers and Seager, 2009).

David A. Aguilar, CfA




Large and jumbo illustrations.




Planet "b" may have a dense
wet atmosphere above layers
of "supercritical fluid" and
plasma, created when water
and other ices subliminated
as the planet migrated closer
to its parent star, around a
rocky core (more).

Theoretical modelling indicate that a hot steam planet could form if it formed in a colder orbit farther from GJ 1214, where lower temperatures would have created an ice-rock composition similar to Jupiter's moon Ganymede, and the planet should have formed too late to accrete a large hydrogen-helium gas envelope. Over time, the planet could have migrated inward into a closer orbit and melted into a water world that vaporized into a steamy atmosphere. Alternative explanations include a small rocky planet with an implausibly large atmosphere that could be replenished by volcanic activity and a mini-Neptune with a much less massive gas atmosphere than Neptune or Uranus in the Solar System (Rogers and Seager, 2009). Based on its visual luminosity, a planet may be able to hold water on its surface around 0.057 AU of GJ 1214, with an orbital period slightly over 12.6 days. (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)

On December 1, 2010, a team of astronomers announced the results of the first analysis of the atmosphere of a super-Earth planet, GJ 1214 b, using the European Southern Observatory's Very Large Telescope. The planet's atmosphere was analyzed when it passed in front of its host star as some of its infrared light passed through the planet’s atmosphere. Based on the available data, the astronomers concluded that the planet's atmosphere is either a thin but dense layer rich in water steam or a thick layer of high clouds or hazes, similar to those seen in the atmospheres of Venus and Titan in the Solar System. A puffy hydrogen-helium gas envelope like that of Uranus or Neptune is ruled out, unless it's covered by a high cloud layer of noxious hydrocarbons (ESO press release; NASA/JPL news release; and Bean et al, 2010).

Luis Calçada, ESO



Large and jumbo animation slides.



The planet, GJ 1214 b, has
an atmosphere that is either
dominated by steam or covered
by thick clouds or hazes (more).

On March 11, 2011, a team of astronomers using older observational data from NASA's infrared Spitzer space telescope with newer data that they collected through the MEarth Project submitted a paper confirming that the "warm" super-Earth GJ 1214 b does not have an atmosphere composed of an outer gas layer hydrogen and helium like Uranus or Neptune, with high statistical confidence (over 99.99 percent). The team was also able to provide better support for their earlier conclusion that the planet's atmosphere is likely to be "dominated" by elements heavier than hydrogen and helium with a water mass fraction of over 10 percent water vapor (with over 99.7 percent confidence), but possibly over 50 percent (68 percent confidence). On the other hand, they also estimated that the planet's equilibrium temperature to be around 282° Celsius or 539° Fahrenheit (555 kelvin). Using data from two consecutive transits of planet b across its host star, moreover, the team failed to detect the presence of other planets in the GJ 1214 system through their gravitational influence on planet b's orbit through (Desert et al, 2011; and Jon Voisey, Universe Today, March 15, 2011).

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