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The Value of an Exo-Venus

Looking back at science fiction’s treatment of Venus, you can see a complete reversal by the 1960s, at which time we had learned enough about the planet to render earlier depictions invalid, and even quaint. Think back to the inundated surface of Venus in Bradbury’s “Death by Rain” (1950) or Henry Kuttner and C. L. Moore’s Clash by Night (1943), where humans live under water and the land surfaces are carpeted with jungle. Heinlein’s Space Cadet is another example of a fecund Venus much like an Earthly rain forest.

But by 1965, Larry Niven would be writing “Becalmed in Hell,” about a nightmare Venus based on our insights into its intolerable surface. I should also mention a prescient tale by a writer who is a personal favorite of mine, James Gunn. It’s “The Naked Sky” (1955), which shows us a desert Venus with hydrochloric acid clouds and huge atmospheric pressure, a land Gunn described as “embalmed at birth.” As far as I know, this was the first SF tale that began to get Venus accurately, though at the time Gunn wrote, spacecraft had yet to confirm the hypothesis.

By 1962, we would have Mariner 2 readings of surface temperatures on Venus, while Soviet Venera probes would begin their work in 1967 with the first landing of a man-made object (Venera 4) on another planet. The program would continue for 16 launches, with 10 successful landings on the planet. Venera found a surface hot enough to melt lead, and survival times were short, with even the final iterations lasting no longer than about two hours.


Image: An image from the Soviet Venera 13 spacecraft. This was the first of the Venera missions to include a color TV camera and the first to succeed in obtaining pictures since Venera 10. Venera 13 lander touched down on 3 March 1982.

Now we’re finding planets much like Venus — or with the potential of being so — around other stars. With all the current interest in identifying an Earth 2.0, why be interested in Venus analogues? Elisa Quintana (NASA GSFC/SETI Institute), who works with the Kepler team, is one of the discoverers of such a world, Kepler 1649b. And here’s her take:

“Many people are hung up on finding other Earths. But Venus analogs are just as important. Since new telescopes coming down the pike will allow us to probe atmospheres, focusing on both Earth and Venus analogs may help decipher why, in our Solar System, one planet allows life to thrive, and one does not, despite having similar masses, comparable densities, etc.”

It’s a telling point, because the reason we got all those science fiction tales about a jungle Venus is that in so many ways it seemed to be a twin of the Earth, albeit one that was 40 percent closer to the Sun. It was easy to transfer tropical traits to the place, as if a journey there were somewhat like heading into unexplored equatorial terrain on our own planet.

Although Kepler 1649b circles a red dwarf star about 220 light years away, it receives about 2.3 times the stellar flux that the Earth does. The number for Venus is 1.9 times the terrestrial value. Looking into what makes Venus the nightmare it is can help us understand habitable zone boundaries around M-dwarfs that much better as we examine the tidal effects and stellar activity through flares and stellar wind that distinguish red dwarf planets from the Sun’s.

Follow-up spectroscopy and imaging of Kepler 1649 indicated to lead author Isabel Angelo (SETI Institute) and team that the parameters of the star had to be adjusted. It turned out to be considerably hotter and larger than had been thought, the adjusted figures affecting the planet observed in transit. We now know that Kepler 1649b is just slightly larger than Earth. This is another case where Kepler planets have been re-characterized because of revisions to the properties of the host star, and a reminder of the importance of such follow-ups.

We learn from all this that the planet is on a 9-day orbit, but it is too small to produce solid radial velocity data that would help determine its mass, leading the authors to make no conclusions about mass or composition. The likelihood, though, considering that Kepler 1649b is 1.08 times the radius of the Earth, is that we are dealing with a rocky world. The paper compares the planet to Kepler-186f, an Earth-sized exoplanet thought to orbit in the habitable zone of another M-dwarf. Flares and coronal mass ejections are factors around such stars, while tidal locking and heating could affect the geological activity on both. The authors consider the two to be good candidates for Earth- and Venus-analog studies.

From the paper:

The discovery of Kepler-1649b is part of a larger movement toward confirmation and characterization of a variety of Earth-sized exoplanets, with the ultimate goal of understanding what factors place constraints on habitability. Most of these planets have orbital periods measured to high precision, allowing us to calculate the flux received by the planet from its host star. As a result, determining the correlation between incident flux and atmospheric compositions would be highly useful in assessing the habitability of known exoplanets. More specifically, determining the compositions and atmospheres of planets like Kepler-1649b and Kepler-186f, two planets that together span a wide range of distances within the habitable zones of M-dwarfs, will be useful in understanding the nature of habitable zone boundaries for such star types. Future missions like K2, TESS, and JWST… will make these studies possible and therefore lend themselves to a better understanding of conditions required for exoplanet habitability.

Confirming what surface conditions are actually like on either world will demand spectroscopic analysis of their atmospheres, and when it comes to Venus analogues, this is a tricky proposition because of their opacity. But the paper adds that there are distinguishing features in the high clouds of Venus like carbon dioxide absorption and an upper haze layer with sulfuric acid, that could make detection possible. The thick atmosphere dominated by clouds also produces scattering and reflection effects that lead to high albedo, which the authors see as another piece of evidence that could link an atmosphere to a runaway greenhouse.

All such studies rely upon our confidence in the properties of the planets we find, and that means accurate information about their host stars. Missions like Gaia are designed to measure the distances to nearby exoplanet systems like Kepler-1649 through the most precise parallax measurements ever obtained, which should further tighten the parameters on systems like this one. We need to know more about the factors that can take two worlds of similar mass and density in our system and render one habitable while turning the other into a furnace.

The paper is Angelo et al., “Kepler-1649b: An Exo-Venus in the Solar Neighborhood,” Astronomical Journal Vol. 153, No. 4, published online 17 March 2017 (abstract and full text).


Comments on this entry are closed.

  • Andrew LePage April 10, 2017, 13:33

    Nice piece highlighting the value of characterizing not only potentially habitable exoplanets, but the “near misses” as well in order to probe the true limits of planetary habitability. Putting on my space historian’s cap for a moment, I do have one little nit:

    > Soviet Venera probes would begin their work in 1967 with the first landing of a man-made object (Venera 4) on another planet.

    Actually, Venera 4 never reached the surface of Venus intact. While it managed to return the first in situ measurements of the atmosphere of Venus during descent, it was crushed well above the surface because Soviet engineers had underestimated the surface pressure of Venus by about a factor of five (in all fairness, the true value was anyone’s guess at the time). Venera 4 wasn’t even the first man made object to enter Venus’ atmosphere. That honor goes to Venera 3 which entered the atmosphere of Venus on March 1, 1966 (although it had fallen silent two weeks earlier):


    > The program would continue for 16 launches, with 10 successful landings on the planet.

    In addition to the Venera landers, there was also NASA’s Pioneer-Venus Multiprobe mission where one of the “small” probes, the Day Probe, survived impact after its long descent through the Venusian atmosphere and managed to continue transmitting from the surface for just over 67 minutes before its batteries gave out.


  • Gary Wilson April 10, 2017, 14:03

    It will be very interesting to see what proportion of earth sized planets with high stellar fluxes end up being Venus-like in their surface properties. Would a water world with a high stellar flux like Venus always end up losing its surface water? At what stellar flux will this happen as a general rule? I hope to see many more of these planets characterized.

  • Harry R Ray April 10, 2017, 15:46

    DON’T FORGET! TRAPPIST-1c is a VIRTUAL CLONE of Kepler 1649b, and we already have some VERY BASIC information about ITS atmosphere due to the double transit(with TRAPPIST-1b)observed by HST on May 4, although not nearly as DETAILED INFORMATION as we have now for Gliese 1132. Some claim the TRAPPIST-bc detection to be the REAL first detection of the atmosphere of an earth-sized planet, albeit with an asterisk(due to the inability to DIFFERENTIATE BETWEEN the atmospheres of the two planets observed)due to the ELIMINATION of even the POSSIBILITY of puffed-up Hydrogen envelopes around EITHER OF THEM! On the subject of HST. It has apparently made EVEN MORE OBSERVATIONS of Europa’s geysers, which will be revealed in a NASA press conference Thursday afternoon. STAY TUNED!

    • john walker April 10, 2017, 18:33

      Thanks for the heads up on that press conference. Both Chris Glein and Hunter Waite will attend so fingers crossed they’ll have good news on the Enceladus H2 question.

  • Mauro Cavalcanti April 10, 2017, 16:14

    Nice article, as usual in Centauri Dreams.

    Since the article begins by evoking the sci-fi literature comparing the óld’ and ‘new’ visions of the real Venus, let me add a question ( which may be as valid as the next one in the context of the truly fascinating research on exoplanets): what if instead of looking just for ‘new’ Venus-like exoplanets, future searches also do not look for planets like the ‘old’ Venus not only imagined by sci-fi authors but also considered serioulsy by scientists until around the end of the 1950’s (when microwave observations already suggested a hellish environment there)?

    I suppose this cannot be achieved using currently available instruments, but is there anything fundamentally wrong with the concept of an exo-Venus covered by a lush jungle or oceans of carbonated waters (as the ‘old’ Venus was supposed to be)?

    • Joe April 10, 2017, 18:17

      But wouldn’t an exo-Venus with a lush jungle really be an exo-Earth with a warmer climate or closer orbit to its sun?

      • Mauro Cavalcanti April 11, 2017, 7:16

        Fair enough. But should the orbit of such an exo-Earth be closer to its sun (assuming it is a G-type star)?

  • DCM April 10, 2017, 16:29

    If we often find similar planets in other systems what will that tell us….

    • Paul Gilster April 10, 2017, 21:58

      The authors are arguing that finding and characterizing planets in a Venus-like position in various solar systems will help us learn about the different outcomes that can move a planet closer or further away from habitability. That should also help us tighten up the parameters of habitable zones.

      • DCM April 11, 2017, 3:43

        If there are common types of planets it would suggest that there are other life bearing worlds.

      • Harry R Ray April 11, 2017, 9:34

        There also appears to be a previously unknown “intermediate” class of planet BETWEEN Venus and EARTH: Hot Super Mars. If you take the first four planets in the TRAPPIST-1 system and compare them to Mercury, Venus, Earth, and Mars, the first two planets match up rather nicely(although you would have to call TRAPPIST-1b a SUPER Mercury), but then everything breaks down. My theory is that TRAPPIST-1d USED TO BE about the same mass and radius as TRAPPIST-1e, but has since lost ALL OF ITS VOLITILES due to a closer proximity to TRAPPIST-1 AND an INITIAL tidal heat flux approaching IO’S! In fact, I believe that the ONLY REASON that the TRAPPIST-1 system is stable TODAY is DUE to the mass-loss from TRAPPIST-1d! However, once the mass WAS lost, the final STABILIZING of the entire system would GREATLY REDUCE TRAPPIST-1d’s tidal heat flux, leaving it with an atmosphere SIMILAR to Mars’s, and render it inhabitable due to that, and NOT a runaway greenhouse atmosphere.

        • DCM April 11, 2017, 11:06

          We may get a classification of possible life bearing worlds even before we can ever get to other systems. Alas, none of us will ever know how accurate it is.

        • Michael April 11, 2017, 15:50

          You would have to make a planets surface seriously hot to blow it off into space, Io loses mass to space due to its low mass.

  • John Davies April 10, 2017, 17:58

    An early 50s SF Venus envisaged a Flame Belt between two mutually hostile halves of a hot planet (en.wikipedia.org/wiki/Dan_Dare) one ruled by a bulging-brained tyrant (en.wikipedia.org/wiki/The_Mekon) and the other by peaceful Therons (www.dandare.org/dan/aliens/venus.htm)

    • ljk April 11, 2017, 15:45

      Astronomers also used to think that Mercury had a livable zone back when they thought the planet kept the same hemisphere always facing Sol with the planet’s day matching its year, or 88 Earth days.

      We found out with radar in 1965 that Mercury rotates on its axis once every 59 Earth days, thus removing the pre-Rod Serling “Twilight Zone” girdling the day-night terminator, where it was thought and hoped that temperatures in that narrow region would be just Goldilocks enough to support some kind of life.

  • Michael April 11, 2017, 5:33

    These Aridia worlds may form when Red dwarfs go through their long term contraction phases leaving behind liquid oceans of CO2, not sure how long they will have these oceans though.

  • kzb April 11, 2017, 7:33

    Notice that here we have another planet in close orbit around an M-dwarf, and the atmosphere has NOT been stripped.

  • FrankH April 11, 2017, 15:23

    “Farewell Fantastic Venus” (edited by Brian Aldiss and Harry Harrison) is an anthology of pre-space age stories and essays about Venus. It’s a good read.

    • Mauro Cavalcanti April 12, 2017, 9:11

      Also the more recent collection “Old Venus”, edited by George Martin and Gardner Dozois.

  • David Grinspoon April 11, 2017, 17:01

    It is also quite possible that Venus was a habitable planet, conventionally defined, for billions of years. (see, for example, http://onlinelibrary.wiley.com/doi/10.1002/2016GL069790/full) It may be that for much of its history our solar system had two neighboring terrestrial planets with oceans. This “meta stable” habitability condition may be common on the inner edge of habitable zones. Another reason why such a discovery is very important. Also illustrates the absurdity of the fact that we have not been putting much resources into exploring Venus when it is so close at hand (certainly compared to Venus-like exoplanets) when there is so much to learn about habitability, and its loss, from understanding the divergence of Venus and Earth.

  • Ricardo L. Garcia April 11, 2017, 20:12

    Back in 1953, Pohl’s and Kornbluth’s novel THE SPACE MERCHANTS featured a Venus like we today know it to be–hot and hellish and barren. I wonder how they knew?

    • ljk April 12, 2017, 13:50

      Not everyone in the pre-Mariner 2 days thought Venus was a steamy jungle full of exotic plants and dinosaur-like creatures or covered in a global ocean of water/oil/seltzer.

      There were a few early Twentieth Century astronomers who, unable to detect any serous amounts of water vapor in the thick Venusian atmosphere, assumed the planet was bone dry and that the clouds were composed of dust blown up from the surface by high winds. They were not entirely on target but they were much closer than the alternatives.

      Did you know the early Soviet Venera landers were designed to float in an ocean of liquid water? Yes, this was after the Mariner 2 mission in 1962.

      See here:


  • andy April 14, 2017, 14:13

    Exo-Venus planets, particularly ones close enough to their stars to have been rapidly tidally-locked would make interesting test cases for the Yang et al. (2014) result that slowly-rotating planets with Venus-like levels of insolation can maintain habitable conditions. (If correct, this suggests that Venus would likely have undergone the runaway greenhouse when it was rotating faster than its current state.)

    Kepler-1649b may be spinning slowly enough to build up enough reflective clouds at the substellar point to avoid a runaway greenhouse, while TRAPPIST-1c is likely in the fast-rotating regime where the clouds get smeared around the planet, resulting in lower albedo and a runaway greenhouse transition further from the star.

  • ljk April 24, 2017, 13:30

    Mysteries of Crown-like Structures on Venus’ Surface Unveiled in New Study

    By Charles Q. Choi, Space.com Contributor | April 24, 2017 06:44 am ET

    On Venus, plumes of superheated rock from near the planet’s core may rise up intermittently, destroy patches of the planet’s surface and create unique crown-shaped geologic features called coronae, a new study finds.

    The new study suggests that the surface of Venus is more active than scientists previously thought, and the findings could shed light on how the early Earth evolved, the researchers said.

    Full article here:


    To quote:

    “Understanding how these twin planets diverged down different paths is essential for understanding how rocky planets evolve,” said Anne Davaille, a physicist at the University of Paris-Saclay and lead author of the paper describing the new research.

    Another way Venus differs from Earth is that Earth has long experienced a phenomenon called plate tectonics, in which surface plates constantly shift over the underlying mantle layer. This activity is responsible for the changing position of Earth’s continents over time, and it is the major driver of earthquakes and volcanoes on the planet’s surface.

    In contrast, previous research suggested that the surface of Venus has largely remained stagnant for the past 300 million to 600 million years. Prior work suggested that Venus does not experience plate tectonics because its surface is hotter, and therefore softer, than Earth’s, thus preventing it from becoming rigid enough to break up into plates.


    “What we see on Venus today may be very similar to an earlier phase on Earth,” Davaille said. “Studying these processes on Venus sheds light on the conditions needed for planets to develop plate tectonics, and may shed light on our origins.”

    Davaille said she and her colleagues are now proposing a new mission to NASA to better investigate Venus and learn more about its geology.

    The scientists detailed their findings online April 10 in the journal Nature Geoscience.

  • ljk August 2, 2017, 13:08

    Did Venus once have oceans?


    What does this mean for exo-Venuses?