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).