Kepler-186 is a stellar system of five planets with an Earth-size world in the habitable zone.
Simulated comparison of a sunset on Kepler-186f and Earth. On Kepler-186f the star looks dimmer but slightly larger.
All the known potentially habitable exoplanets so far are superterran worlds (aka super-Earths) somewhat larger than Earth. The potential of life of these worlds is difficult to relate to Earth since there are no planets in the Solar System of comparable size and we know very little of them. Now a team of scientists led by Elisa V. Quintana
from the SETI Institute
and NASA Ames
report the discovery of Kepler-186f, the first terran world (Earth-size) in the habitable zone of a star.
Kepler-186f has a similar size to Earth and it is most likely a rocky world. It orbits the M-dwarf star Kepler-186 along with four other inner planets, which are as old as the Solar System (>4 Gyr), in the constellation Cygnus 500 light years away. Kepler-186f receives less stellar flux (~32%) than presently does Mars (~43%). It could have a temperate climate if it has an atmosphere much denser than Earth. Even Earth probably experienced at least one episode of global glaciation
with just a slightly lower stellar flux than today, 650 million years ago. However, early Mars had running surface liquid water with a similar stellar flux as Kepler-186f.
Kepler-186f was added to the Habitable Exoplanets Catalog
with a low Earth Similarity Index
(ESI) of 0.64 due to its potential colder climate. Still, it could be a more Earth-like world if it is experiencing a much higher greenhouse effect than Earth. Nevertheless, Kepler-186f is also the best candidate now of a rocky world in the habitable zone compared to the other known potentially habitable worlds.
Artistic representation of Kepler-186f as a cold world with shallow oceans as compared to Earth. Other possible interpretations of Kepler-186f are as a snowball frozen world
) or a dry cold world (Mars-like
Orbital distribution of planets in the stellar system Kepler-186 (top) compared to Kepler-62 (bottom). Both planets 'f' of Kepler-186 and Kepler-62 receive about the same stellar flux.
Figure 3. Analysis of the orbit of Kepler-186f. Its equilibrium temperature is around 192 K for a similar terrestrial albedo. For comparison, Mars has an equilibrium temperature of 210 K. Kepler-186f also orbits just in the outer stellar zone for tidally locked-planets but its rotational state is uncertain. The diagram does not show the orbits of the other inner planets of Kepler-186. More details about this figure are available in the Exoplanet Orbital Catalog.
Figure 4. The new lineup of up to 21 potentially habitable exoplanets according to the Habitable Exoplanets Catalog. Kepler-186f is the most Earth-size planet now but it also receives one third the energy from its star than Earth. This significantly lowers its observable similarities with Earth as compared with other planets in the catalog.
- The Habitable Exoplanets Catalog uses now a revised ESI that only considers observed properties, either planetary radius or mass, and stellar flux. The original ESI provides a better comparative habitability assessment but it requires planetary radius, mass, and surface temperature.
- The sunset image of Earth was taken in the Playa Puerto Nuevo, Vega Baja, Puerto Rico. Here is a video of the beach, just wait for it.
Four new nearby potentially habitable planet candidates, two of them in the same star system.
An international team of astronomers led by Mikko Tuomi from the University of Hertfordshire
announced the discovery of four nearby potentially habitable super-Earth worlds among eight new planet candidates. They orbit the habitable zone of the nearby stars, Gliese 180, 422, and 682.
These new four planets increase the number of potentially habitable worlds of the Habitable Exoplanets Catalog to twenty, among fifteen stellar systems. Just last week four NASA Kepler planets were also added. The catalog went from twelve to twenty planets in less than a week. Twelve of these are in the Solar Neighborhood, within 50 light years from Earth.
Gliese 180 is 38 light years away and it is the fourth stellar system found with multiple potentially habitable planets, after Gliese 581, Gliese 667, and Kepler-62. The orbital proximity of its two planets is quite remarkable and very rare. The inner planet, Gliese 160 b, has a minimum mass of 8.30 ME and a radius of ~1.8 RE if rocky in composition, just like Earth. Gliese 160 c has a minimum mass of 6.40 ME and a radius of ~1.7 RE if rocky.
Gliese 442 is 41 light years away. Its only planet, Gliese 442 b, has a minimum mass of 9.9 ME and a radius of ~1.9 RE if rocky. This planet could easily be instead a mini-Neptune, rather than a rocky world, due to its large mass, but there is no way to tell at the moment.
Gliese 682 is 17 light years away and the second closest system found with potentially habitable planets, after Tau Ceti. Its habitable zone planet, Gliese 682 b, has a minimum mass of 4.4 ME and a radius of ~1.5 RE if rocky. There is also a second outer and larger super-Earth planet in the Gliese 682 system.
We only know the minimum masses of these new planet candidates but they could be much more massive and therefore non-habitable. The unique orbital architecture of the two particular planets of Gliese 180, if confirmed, better constrain their maximum mass thus improving their chances of being the right size for life. This also improves their chances of being transiting planets and prime targets for atmospheric characterization by future observatories such as the JWST.
Without any information about their size there is no way to tell if these planets are indeed rocky worlds or small gas planets. There is also no guarantee about the habitability of any potentially habitable world as we know very little of them, some even need to be confirmed as true planets. They are only objects of interest for additional observations.
Stellar systems with multiple habitable planets seem to be common. So far, four out of the fifteen (~27%) known stellar systems with potentially habitable planets have more than one. Astronomers have been struggling to determine how common are stellar systems with Earth-like planets in the universe
. Today a new question is emerging about how common are stellar systems with multiple Earth-like planets
Other members of the research team are Hugh R. A. Jones and John R. Barnes from the University of Hertfordshire, Guillem Anglada-Escude ́ from the University of London, and James S. Jenkins from the Universidad de Chile.
Figure 1. Artistic representation of the habitable zone super-Earth planets Gliese 180 b and c, and Gliese 422 b and Gliese 682 b. They are represented here as worlds with thick cloud covers that look pinkish due to the reddish light of the red dwarf stars they orbit. Only their minimum masses are known but they are shown with sizes corresponding to rocky worlds, just like Earth. They could be twice as big, almost like Neptune, if they are instead non-habitable gas worlds. Earth, Mars, Neptune, and Jupiter are shown for size comparison. Credit: PHL @ UPR Arecibo, NASA.
These images show the star fields around the new three stellar systems with four potentially habitable planet candidates discovered by astronomers led by Mikko Tuomi from the University of Hertfordshire. The field of view is about the size of the Full Moon. A small telescope is necessary to see these since they are dim red dwarf stars. Credit: PHL @ UPR Arecibo, CDS/Aladin.
Figure 3. The individual orbits of the four new potentially habitable planets discovered by astronomers led by Mikko Tuomi from the University of Hertfordshire. Two are around the star Gliese 180, and the other two around Gliese 422 and Gliese 682. Note that each frame shows only the orbit of one planet at a time for simplicity. Click the frames to enlarge. Credit: PHL @ UPR Arecibo.
The new lineup of twenty potentially habitable exoplanets according to the Habitable Exoplanet Catalog including four new ones from NASA Kepler and the four new ones discovered by astronomers led by Mikko Tuomi from the University of Hertfordshire. Six out of these twenty planets are still unconfirmed.
Figure 5. Location in the night sky of the now known fifteen stellar systems with potentially habitable worlds. New ones are Gliese 180 in the constellation of Eridanus, Gliese 422 in Carina, and Gliese 682 in Scorpius. Click the image to enlarge. Credit: PHL @ UPR Arecibo, Jim Cornmell.
The milestone of 1,000 confirmed exoplanets was surpassed today after twenty-one years of discoveries. The long-established and well-known Extrasolar Planet Encyclopedia
now lists 1,010 confirmed exoplanets. Not all current exoplanet catalogs list the same numbers as this depends on their particular criteria. For example, the more recent NASA Exoplanet Archive
lists just 919. Nevertheless, over 3,500 exoplanet candidates are waiting for confirmation.
The first confirmed exoplanets were discovered by the Arecibo Observatory in 1992. Two small planets were found around the remnants of a supernova explosion known as a pulsar. They were the surviving cores of former planets or newly formed bodies from the ashes of a dead star. This was followed by the discovery of exoplanets around sun-like stars in 1995 and the beginning of a new era of exoplanet hunting.
Exoplanet discoveries have been full of surprises from the outset. Nobody expected exoplanets around the remnants of a dead star (i.e. PSR 1257+12
), nor Jupiter-size orbiting close to their stars (i.e. 51 Pegasi
). We also know today of stellar systems packed with exoplanets (i.e. Kepler-11
), around binary stars (i.e. Kepler-16
), and with many potentially habitable exoplanets (i.e. Gliese 667C
The discovery of many worlds around others stars is a great achievement of science and technology. The work of scientists and engineers from many countries were necessary to achieve this difficult milestone. However, one thousand exoplanets in two decades is still a small fraction of those expected from the billions of stars in our galaxy. The next big goal is to better understand their properties, while detecting many new ones.
* planet candidate CREDIT: PHL @ UPR AreciboBy Dirk Schulze-Makuch
According to the Exoplanet Catalog
maintained by the Planetary Habitability Laboratory (PHL) of the University of Puerto Rico at Arecibo, the number of confirmed planets outside our own solar system is approaching 1,000, while another 3,500 exoplanets—most of them detected by NASA’s Kepler mission—are yet to be confirmed. We’re not talking only about Jupiter- or Neptune-like gas giants, but also Super-Earths (terrestrial planets several times the mass of Earth) and Earth-size planets.
From this growing list, the PHL, directed by Abel Méndez, has identified the top 12 potentially habitable exoplanets based on an Earth Similarity Index (ESI). Their top choice is Kepler 62e, with an ESI value of 0.83 (an ESI of 1.0 would be a 100 % match with Earth in terms of astronomical parameters). Kepler 62e is a Super-Earth in the Constellation Lyra, with an estimated mass of 3.6 Earth masses and an estimated radius 1.6 times that of Earth. Its surface temperature is estimated at 31°C (88°F) and it is 7 billion years old, significantly older than Earth. It’s also very far away—1,200 light years, meaning that we won’t be visiting it any time soon.
How much like our own world is Kepler 62e, really? We should be careful to distinguish Earth similarity from planetary habitability. In many respects the Moon has very similar astronomical values to Earth, yet we know it’s a dead rock. On the other hand there’s Saturn’s moon Titan, a top candidate for finding primitive extraterrestrial life in our solar system. But Titan couldn’t be more different from Earth—an icy moon with liquid methane/ethane lakes on its surface, a nitrogen-methane atmosphere, and temperatures well below Earth’s arctic regions.
My own favorite candidate for a habitable exoplanet is Gliese 581d. A mere 20 light years from us, it’s #12 on the PHL list. The planet has an estimated mass of about seven Earth masses, with a radius about double Earth’s. Gliese 581d orbits a red dwarf star with an orbital period of 67 days, which is important. Why? A red dwarf has less energy output than our (yellow dwarf) sun, and an orbital period of 67 days would put the planet in a Mars-like orbit in terms of temperature. In our own solar system, Mars is cold and dry today because it was too small to retain a thick atmosphere, internal heating, and a magnetic field. However, if Mars had been a Super-Earth like Gliese 581d, it would surely still be heated from inside, have kept its magnetic field and thick atmosphere, and would likely still have liquid oceans (and perhaps even life!) on its surface.
Gliese 581d’s estimated surface temperature of -37°C (-35°F) should not concern us too much. If aliens were to observe Earth from afar, based just on the amount of incoming solar radiation they would estimate our surface temperature as -18°C (0°F). It’s only due to the greenhouse effect that Earth’s average temperature is actually a benign +15°C (59°F; yes, a limited greenhouse effect can be a good thing!). On a Super-Earth planet such as Gliese 581d, I would expect the effect to be quite a bit stronger than on Earth. And one last thing in this planet’s favor: Gliese 581d is nearly twice as old as Earth, which could have given evolution plenty of time to develop advanced, perhaps even technologically advanced, life forms.
The 'Bright Blue Marble' and the 'Pale Blue Dot' Together
Here are actual satellite images of Earth near the moment and the angle the pictures from Cassini and Messenger were taken from Saturn and Mercury on the Day the Earth Smiled, respectively. High resolution black and white images from the GOES East and Meteosat meteorological satellites were combined with color information from NASA Visible Earth to generate true-color images. Check here for additional details.
Earth taken from orbit and from Saturn on the Day the Earth Smiled (July 19, 2013). Earth from orbit is shown with a little more illuminated area at the moment of the Cassini picture from Saturn. The Moon is also visible to the right of Earth in the image from Saturn. Earth was visible to the naked-eye (+1.9 magnitude) as a dim star at the moment the image was taken from Saturn. This figure makes references to the iconic 'Blue Marble' and 'Pale Blue Dot' images of Earth from space. Credit: PHL @ UPR Arecibo, NASA/JPL-Caltech/Space Science Institute, NERC Satellite Station, Dundee University, Scotland.
Earth taken from orbit and from Mercury on the Day the Earth Smiled (July 19, 2013). Earth from orbit is shown with almost exactly the area and illumination at the moment of the Messenger picture from Mercury. The Moon is also visible to the right of Earth in the image from Mercury. Earth was as bright (-4.8 magnitude) as the maximum brightness of Venus at the moment the image was taken from Mercury. This figure makes references to the iconic 'Blue Marble' and 'Pale Blue Dot' images of Earth from space. Credit: PHL @ UPR Arecibo, NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington, NERC Satellite Station, Dundee University, Scotland.
On July 19, 2013 the NASA Cassini and Messenger spacecrafts took pictures of Earth from Saturn and Mercury, respectively. These photos provide some context as to the approximate appearance of Earth during these pictures as seen from geostationary weather satellites. Click image for larger version. Credit: PHL @ UPR Arecibo, NASA, NERC Satellite Station, Dundee University, Scotland.
Figure 4. Earth from the geostationary weather satellite GOES East on July 19, 2013 at 5 PM EST - 2 PM EDT (21 UTC). Click for high resolution version. Credit: PHL @ UPR Arecibo, NASA, NERC Satellite Station, Dundee University, Scotland.
Figure 5. Earth from the geostationary weather satellite GOES East on July 19, 2013 at 5 PM EST - 2 PM EDT (21 UTC). Click for high resolution version. Credit: PHL @ UPR Arecibo, NASA, NERC Satellite Station, Dundee University, Scotland.
The star Gliese 667C is now the best candidate for harboring habitable worlds.
Our Solar System has only one habitable planet, or maybe two if you count Mars’ past when liquid water was running on its surface. More than one potentially habitable planet per star has been a very rare event in the known stars with planets. The well-known star Gliese 581 might have two and just recently the Kepler Space Telescope discovered two in the star Kepler-62. Now a team of scientists, led by Guillem Anglada of the University of Göttingen, reports the discovery of a star with three potentially habitable worlds.
Gliese 667C is part of a nearby triple system of stars 22 light years away. The team discovered that Gliese 667C has six planets, or even more, with three of them in the habitable zone and not much more massive than Earth. Gliese 667C is now the most interesting object for studying stellar systems with the potential for life.
About one hundred exoplanets, of the 898 detected so far, orbit their star at the right distance to sustain liquid water or the so-called ‘habitable zone’. However, most are big Jupiter-like worlds that are unable anyway to have a surface with liquid water. Only a few probably have the right size to be rocky worlds just like Earth.
Gliese 667C is the fourth known planetary system with at least six confirmed planets (Kepler-11, HD 10180, and HD 40307 also have six planets). Gliese 667C f and e will be added to the Habitable Exoplanets Catalog, now having a dozen objects of interest. Gliese 667C c was already added last year.
Artistic representations of the three potentially habitable planets around the star Gliese 667C as compared with Earth. The planets are shown assuming a rocky composition with surfaces mostly covered by water clouds. Credit:
PHL @ UPR Arecibo.
Figure 2. The Habitable Exoplanets Catalog now list a dozen object of interest as potentially habitable worlds with the addition of two new planets, Gliese 667C e and f (Gliese 667C c was known since early 2012). Credit: PHL @ UPR Arecibo.
Figure 3. Simulated view of the star Gliese 667C from its three orbiting potentially habitable worlds. The Earth image is an unretouched photo of a beach sunset. The size of the star, and the brightness and color of the sky was carefully adjusted in subsequent frames to approximate the same view from each planet. The original photo is from a beach in Puerto Rico. Credit: PHL @ UPR Arecibo.
Figure 4. Gliese 667 is a nearby system of three stars that is easy to locate in the Scorpius constellation. The main two central stars Gliese 667AB are barely visible to the naked eye but easy to spot by binoculars or a small telescope. They are so close together that they appear as a single star. Gliese 667C is far enough from the central stars to be seen as separate star. However, it requires a larger telescope to be seem. Credit: PHL @ UPR Arecibo.
Figure 5. Orbits and approximate relative size of the planets around Gliese 667C (orbits and planets are not to scale with each other). All three potentially habitable planets (c, f, and e) orbit within the 'conservative habitable zone.' Credit: PHL @ UPR Arecibo.
Figure 6. This image shows the relative location of each potentially habitable planet of Gliese 667C with respect to the habitable zone. The location of Earth and Mars are shown for comparison. Note that Earth is not at the center of the habitable zone. Any planet close to the inner edge risk being a super-Venus while a frozen world closer to the outer edge. The star is not to scale with the planets.
Table 1: Planetary properties of the six planets around the star Gliese 667C plus one still unconfirmed (Gliese 667C h). Three of these (e, f, and e) are potentially habitable (highlighted in red). This table includes some estimated values that are not part of the original observations (see table notes below). Table 2 has similar values for the Solar System planets.
Planet Type - according to the PHL's Classification of Exoplanets.
Expected Mass - estimate assuming a probable inclination of 60°.
Expected Radius - estimate from an empirical mass-radius relationship.
Equilibrium Temperature - estimate assuming a bond albedo of 0.3.
Expected Surface Temperature - estimate assuming a scaled Earth-like atmosphere.
Habitable Zone Distance (HZD) - a measure of the orbital location of the planet with respect to the HZ. Planets with HZD values between -1 and +1. are within the HZ.
Earth Similarity Index (ESI) - using the new revised ESI which only considers observed parameters, stellar flux, and radius or mass.
Table 2: Planetary properties of the planets of the Solar System for comparison purposes. Description similar to Table 1.
took radar images of asteroid 1998 QE2 and its moon as the space rock sailed safely past earth. The sequence of images show a dark, cratered asteroid 3.0 kilometers across (1.9 miles) across with a companion moon about 750 meters (2500 feet) in size. Both the asteroid and its moon passed 6 million kilometers (3.8 million miles) from earth. This object has no chance of hitting the Earth, but comes close enough to study with a variety of telescopes, large and small.
Figure 1. Radar images of asteroid 1998 QE2 (bottom) and its satellite (top) on June 6. Each image is a sum of 4, spaced apart by about 10 minutes. Each vertical pixel corresponds to 7.5 meters (25 feet) in range, while horizontal pixels correspond to 0.075 Hz (Doppler shift due to rotation).
Figure 2. Radar image from June 7 (left) and from June 9 (right) showing the satellite moving past the primary. Orbital period is about 32 hours.
Many new potentially habitable worlds waiting to be confirmed
Last week NASA’s Kepler mission added 1,924 new objects of interest
to its list of 2,713 exoplanet candidates. The new data has not been completely analyzed yet and many of these objects might be attributed to non-planetary processes (false-positives). However, this new batch gives a general idea of what new types of planets could be announced in the future.
The Planetary Habitability Laboratory (PHL) did a basic analysis of this new Kepler data compared to the existing exoplanets data. The new data suggests the addition of up to 83 new potentially habitable exoplanet candidates, a big increase from the current 18 listed in the Habitable Exoplanets Catalog
. Only four of these have been confirmed so far: Kepler-22b, Kepler-62e, Kepler-62f, and Kepler-61b.
Two types of potential exoplanets are particularly notable in this new Kepler data. There is a big increase of the number of warm and cold super-Earths. This is somewhat expected since the new data includes objects with longer periods. However, other larger objects did not increase as well but it might be too early to attribute this to the abundance of low mass planets.
The most interesting additions are the first potential Earth-like planets. All currently known potentially habitable exoplanets are quite larger than Earth and therefore not very Earth-like by definition. The new Kepler data suggests six new objects with the right size and distance from their star to be considered Earth-like worlds. Since Kepler is no longer operating, it will be very hard to confirm any of these objects with additional data in the near future.
The recent study by Everett et al. (2013)
suggests that one fourth of the Kepler exoplanets candidates are 35% larger than expected, which could also affect the number of those considered potentially habitable. The new Kepler data is being used by the PHL and other groups to prioritize targets of interest for analyses and future observations.
About the Habitable Exoplanets Catalog
The PHL’s Habitable Exoplanets Catalog (HEC) uses a wide definition for potentially habitable exoplanets that includes planets with 0.1 to 10 Earth masses (or 0.4 to 2.6 Earth radii) orbiting the habitable zone
of their parent star within the Venus-Mars empirical limits. Other research groups use narrower or wider definitions. A much wider definition that includes ‘dry planets’ and ‘hydrogen-rich planets’
will be implemented in the future.
New 1,924 NASA Kepler objects of interest added to the NASA Exoplanet Archive. These are objects that are still being considered for inclusion as exoplanets candidates. Notable additions are many 'warm and cold superterrans' (super-Earths) and six 'warm terrans' (potential Earth-like worlds). Check the Periodic Table of Exoplanets
for confirmed and current Kepler exoplanets candidates for comparison. CREDIT: PHL @ UPR Arecibo
Figure 2. Planetary radius versus habitable zone location for the current 890 confirmed exoplanets. All known potentially habitable exoplanets are superterrans (labeled) and there are no terrans yet. Solar System planets in dark blue. Note that most of these radii are estimates based on mass-radius relationship since only their mass was available. CREDIT: PHL @ UPR Arecibo.
FIgure 3. Planetary radius versus habitable zone location for the current 2,713 NASA Kepler exoplanet candidates. All potentially habitable exoplanet candidates are superterrans and there are no terrans yet. Light blue dots are candidates, red dots confirmed, and Solar System planets in dark blue. CREDIT: PHL @ UPR Arecibo.
FIgure 4. Planetary radius versus habitable zone location for the new 1,924 NASA Kepler objects of interest. All potentially habitable objects include many superterrans and now, for the first time, six terrans. Solar System planets in dark blue. CREDIT: PHL @ UPR Arecibo.
Astronomers led by Sarah Ballard from the University of Washington announced the discovery of Kepler-61b, a superterran exoplanet orbiting near the inner edge of the habitable zone of a small K star. Kepler-61b has a size of 2.15 Earth radii and an orbital period of 60 days. It was previously listed as KOI-1361.01 in the NASA Kepler candidates. Kepler-61b receives about 32% more light from its star than Earth from the Sun. Its surface temperature might be close to 40°C assuming an Earth-like atmosphere. Kepler-61b was added to the Habitable Exoplanet Catalog (HEC) and is now ranked number six based on its Earth Similarity Index. HEC lists now ten objects of interest for the search for life outside our Solar System.
Figure 1: Current list of potentially habitable exoplanets including Kepler-61b. Earth, Mars, Jupiter, and Neptune were added for scale.
Figure 2: Current list of potentially habitable exoplanets including Kepler-61b. Earth and Mars were added for scale.
Orbit of Kepler-61b around its parent K-star Kepler-61. The shaded region corresponds to the size of the narrow habitable zone (darker green) and wider habitable zone (lighter green).
Two new exoplanets discovered by NASA Kepler, Kepler-62e and Kepler-62f, were added to the Habitable Exoplanets Catalog. The two planets are part of a planetary systems of five planets around a star smaller than the Sun 1,200 light years away from Earth. Both are considered potentially habitable because they have a size not much larger than Earth and orbit within the habitable zone of their parent star. Kepler-62e is now the most Earth-like exoplanet discovered so far based on the similarity to some of its properties to Earth. However, the actual habitability of Kepler-62e and Kepler-62f depends on conditions that we can not measure yet. Another interesting planet, Kepler-69c, was also announced today but was not included in the catalog because it barely matches our habitability criteria.
Figure 1. Current potentially habitable exoplanets showing the new Kepler-62e and Kepler-62f. Kepler-62e is now the best candidate for an Earth-like planet based on measured parameters. However, the actual potential for life of any of these worlds depends on their atmospheric properties which are unknown at this time.
Figure 2. Current potentially habitable exoplanets showing the new additions, Kepler-62e and Kepler-62f.
Figure 3. Artistic representations of Kepler-62e and Kepler-62f compared with Earth. Both are shown with a similar terrestrial atmosphere thus making Kepler-62e slightly hotter than Earth and Kepler-62f a cold but still habitable world. Another possibility is that both have dense atmospheres. In that case the temperatures of Kepler-62f might be more suitable for life than on Kepler-62e.
Figure 4. Comparison of the orbit and size of the exoplanets of Kepler-62 with the terrestrial planets of our Solar Systems. The darker green shaded area corresponds to the 'conservative habitable zone' while its lighter borders to its 'optimistic habitable zone' extension. Planet sizes and orbits are not to scale between them.
Table 1: Planetary properties of the planets around the K2V star Kepler-62. Kepler-62e and Kepler-62f are potentially habitable and were added to the Habitable Exoplanets Catalog. This table also includes some estimated values that are not part of the original observations. They are described in the table notes below.
Planet Type - according to the PHL's Classification of Exoplanets.
Mass was estimated for comparison purposes only using a mass-radius relationship for rocky planets.
Equilibrium temperature was estimated assuming a bond albedo of 0.3.
Surface temperature was estimated assuming an Earth-like atmosphere.
The habitable zone distance (HZD) is a measure of the location of the planet with respect to the HZ. Planets with HZD values between -1 and +1. are within the HZ.
This table uses the new revised Earth Similarity Index (ESI) which only considers the observed parameters size of the planet and stellar flux.
Table 2: Planetary properties of the terrestrial planets of the Solar System to be used for comparison with those of the planets of Kepler-62. See Table 1.