How can it be known that Venus does not have plate tectonics?

How can it be known that Venus does not have plate tectonics?

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This answer provides some insight into Venus' surface geology:

Water may be necessary as a lubricant for plate tectonics. Whether or not this is the case, Venus does not have plate tectonics. It instead has a stagnant lid geology, punctured occasionally by extreme vulcanism (Siberian traps level vulcanism, and then some).

What are the observations that lead to this conclusion? The existence of plate tectonics on Earth was first determined by putting a lot of pieces of the first-hand observational puzzle together. There's much less data available from Venus.

There's much less data available from Venus.

Some data exists. As mentioned in HDE 226868's answer, maps of Venus's surface exist. Like Earth's atmosphere, Venus's atmosphere is transparent to some low frequency electromagnetic radiation such as those used by radar. These observations are consistent with a planet that has stagnant lid tectonics and inconsistent with a planet that has active plate tectonics; more on this below.

In addition to these remote observations, the Soviet Union successfully sent several spacecraft into Venus's atmosphere, some of which landed and briefly operated on the surface of Venus. The initial attempts failed because nobody thought the surface conditions on Venus would be as brutal as they are. To make landing successful, the Soviet Union had to significantly downsize the parachutes and they had to use materials and avionics that could withstand very high temperatures.

Every piece of evidence gathered to date regarding Venus is inconsistent with a planet with active plate tectonics:

  • Venus surface temperature and pressure are well above water's critical point. Venus cannot have any liquid water on its surface. Water is widely (but not universally) thought to be critical as a lubricant that enables plate tectonics to occur.
  • The radar observations show a planet with a nearly universal surface age, about half a billion years old. This is inconsistent with a planet with active plate tectonics but consistent with a planet with stagnant lid tectonics.
  • Venus's atmosphere is very thick, much thicker than the Earth's atmosphere, and is dominated by carbon dioxide. Plate tectonics recycles carbon dioxide at subduction zones. Stagnant lid tectonics does not. A planet with plate tectonics will see a gradual reduction in the amount of carbon dioxide in its atmosphere over geologically long periods of time. A planet with intermittently active stagnant lid tectonics will instead see a gradual increase in the amount of carbon dioxide in its atmosphere over geologically long periods of time.
  • Multiple physics-based models of a planet with very high surface temperatures suggest that such planets will have rather thin and rather ductile crusts that can readily repair themselves against damage caused by subsurface tensions.

Note very well: The stagnant lid tectonics of hot terrestrial planets such as Venus and possibly Titan (Titan is "hot" because its geology is ice-based rather than rock-based) is rather different from the stagnant lid tectonics of cold terrestrial planets such as the Moon and Mars. The surfaces of the Moon and Mars are very old. The surface of Venus is much younger in comparison. Venus has undergone at least one somewhat recent nearly global resurfacing event. This has not happened on the Moon or Mars. Plate tectonics appears to require a planet whose surface is neither too cold nor too hot, and that has a good amount of liquid water on the surface.

Some references:

  • David Bercovici and Yanick Ricard, "Plate tectonics, damage and inheritance," Nature 508.7497 (2014): 513.
    DOI: 10.1038/nature13072.
  • A. Davaille, S. E. Smrekar, and S. Tomlinson, "Experimental and observational evidence for plume-induced subduction on Venus," Nature Geoscience 10.5 (2017): 349.
    DOI: 10.1038/NGEO2928.
  • James F. Kasting and David Catling, "Evolution of a habitable planet," Annual Review of Astronomy and Astrophysics 41.1 (2003): 429-463.
    DOI: 10.1146/annurev.astro.41.071601.170049.
  • Mikhail A. Kreslavsky, Mikhail A. Ivanov, and James W. Head, "The resurfacing history of Venus: Constraints from buffered crater densities," Icarus 250 (2015): 438-450.
    DOI: 10.1016/j.icarus.2014.12.024

  • Ignasi Ribas et al., "Evolution of the solar activity over time and effects on planetary atmospheres. I. High-energy irradiances (1-1700 Å)," The Astrophysical Journal 622.1 (2005): 680.
    DOI: 10.1017/S0074180900182427.
    Accessible pdf:

Essentially, it boils down to the question of uniformity.

Magellan reached Venus in the early 1990s, and was able to greatly improve on previous mapping attempts. The spacecraft was able to map essentially all of the surface, including the distribution of craters. By measuring the crater density, scientists found that the surface was fairly uniform; given our knowledge of cratering on other inner Solar System bodies (e.g. the Moon), they were able to say that the surface is roughly 500 million years old.

What's more, that's a uniform figure - while there are variations across the planet, it's believed that they're due to local resurfacing events from volcanism. One possible explanation for the planet's particular age is that it underwent a period of global volcanic activity about 500 million years ago, and the entire crust was essentially reformed.

You would have severely reduced crust eccentricity and no tides. You would still have volcanoes, but no earthquakes. Water would spread out more, meaning that you would need to have a lot less water for there to be liveable land.

Consider the following simplified diagram (I made it, feel free to share with credit). The vertical axis represents global mantle heat flow, though there are other factors like the presence of water that influence where the red and blue lines are. The horizontal axis represents the mantel's potential temperature.

Tectonic plates can exist between the red and the blue line, there are essentially two forms without tectonic plates:

How Hot is Venus?

You might be surprised to know that Venus is the hottest planet in the Solar System. The temperature across the entire planet is 735 Kelvin, or 462 degrees Celsius.

That makes it hotter than Mercury, which can dip down to -220 degrees Celsius and get up to 420 degrees C. Venus is nearly twice as far away from the Sun as Mercury, and receives 25% of it’s sunlight.

The temperature on the surface of Venus is the same across the entire planet. It doesn’t matter if it’s day or night, at the poles or at the equator – the temperature is always the same 462 degrees.

[/caption]So why is Venus so hot? Billions of years ago, the atmosphere of Venus was probably very similar to the Earth’s, with liquid water lasting on the surface. But a runaway greenhouse effect evaporated all the water, leaving a thick atmosphere of carbon dioxide. The light from the Sun is trapped by the carbon dioxide atmosphere and keeps the planet so warm.

It’s also believed that Venus once had plate tectonics like we have on Earth. Here on Earth, the plate tectonics help regulate the amount of carbon dioxide in the atmosphere by trapping excess carbon dioxide underneath the surface of the Earth. When the plate tectonics stopped, the carbon cycle stopped as well, and carbon dioxide was able to accumulate in the atmosphere of Venus.

Want to learn about other planets in the Solar System? Here’s how hot Mercury can get, and here’s an article about the hottest place on Earth.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.

Venus Lacks Plate Tectonics. However It Has One thing A lot Extra Quirky.

Inside the subsequent decade or so, Venus shall be visited by a fleet of spacecraft. This grand tour of the second planet, the likes of which hasn’t been seen for the reason that Chilly Struggle, is being pushed by the search to resolve a profound planetary puzzle. Earth and Venus are the identical measurement, are proper subsequent to one another and are manufactured from the identical star stuff. However Earth grew to become an oasis whereas Venus grew to become an acid-flecked inferno. Why?

To derive a solution, each side of Venus requires examination. That features the way in which its face has metamorphosed over time. Earth has plate tectonics, the gradual migration of continent-size geologic jigsaw items on its floor — a game-changing sculptor that crafts an exuberance of numerous volcanoes, big mountain ranges and huge ocean basins.

Venus doesn’t have plate tectonics. However in accordance with a examine printed Monday within the Proceedings of the Nationwide Academy of Sciences, it could possess a unusual variation of that course of: Elements of its floor appear to be made up of blocks which have shifted and twisted about, contorting their environment as they went.

These boogying blocks, skinny and flat slices of rock known as campi (Latin for “fields”), will be as small as Eire or as expansive as Alaska. They have been discovered utilizing knowledge from NASA’s Magellan orbiter mission, the company’s final foray to Venus. Within the early Nineties, it used radar to look by means of the planet’s obfuscating ambiance and map your complete floor. Taking one other take a look at these maps, scientists discovered 58 campi scattered all through the planet’s lava-covered lowlands.

These campi are bordered by strains of small mountain ranges and grooves, options which have additionally been warped and scarred over time. What made them? In keeping with Paul Byrne, a planetary scientist at North Carolina State College and the examine’s lead creator, there is just one affordable clarification: Primarily dragged round by the flowing mantle under, the campi “have been shimmying across the place, similar to pack ice.” Campi shifting towards motionless land would trigger the bottom to crumple up, forming mountains. One shifting away would have stretched the land, opening grooves. And alongside these boundaries, campi shifting side-to-side would have left pressure marks and etchings.

That this deformation came about within the lowlands of Venus is important: The lava smothering them is anyplace between 750 and 150 million years outdated, making these landscapes a few of the planet’s youngest. Which means the tectonic two-step of those campi occurred comparatively just lately within the photo voltaic system’s historical past. However is that this dance nonetheless taking place at present?

NASA’s VERITAS and Europe’s EnVision missions will discover out. Geared up with their very own superior radar techniques, these orbiters will study these campi in high-resolution, permitting scientists to establish if any have shimmied about for the reason that days of Magellan. If they’ve, then it is going to additional proof a long-harbored notion: Venus is tectonically lively, if not as hyperactive or as dynamic as Earth.

Way back, Venus had an ocean’s value of water, for probably billions of years. This might have made plate tectonics doable, as liquid water permits plates to interrupt, bend and movement. This course of additionally regulates the local weather by burying and erupting carbon, stopping worlds from present process runaway world warming that may render them uninhabitable.

However one in all a number of doable apocalypses — maybe a number of volcanic cataclysms — turned Venus into an arid hellscape, and its plate tectonics would have shut down. Consequently, for the previous billion years or so, your complete planet’s floor was a solitary, stagnant and largely static plate.

However that doesn’t imply the planet has turn out to be quaver-free. Due to missions like Magellan, scientists have beforehand noticed fault networks, rift zones and mountain ridges — the scar tissue left by each historic and considerably extra modern motion. If this new examine is right, and full swaths of Venus have been just lately jiggling about, then the planet’s floor “is extra cell than folks have conventionally assumed,” stated Joseph O’Rourke, a planetary scientist at Arizona State College who wasn’t concerned with the work.

Explaining why Venus has this stunning tectonic tempo would have hefty implications. There are numerous Earth- and Venus-size worlds within the cosmos, and their tectonic exercise can even decide their fates. However “we are able to’t declare to know any rocky world within the photo voltaic system or past if we are able to’t perceive Earth and its nearest neighbor,” Dr. O’Rourke stated.

The Volcano Planet LHS 3844b

Like the volcano planet Mustafar from Star Wars, half of the exoplanet 3844b could be covered in active volcanoes. This planet, discovered in 2019, could be the first world we know, outside the solar system, to have plate tectonics, which guides much of geology on our own world.

On Earth, plate tectonics drives earthquakes and builds mighty mountains, and it ferries materials from beneath the surface of the Earth, expelling material to the crust and atmosphere. This movement of the crustal plates of Earth also plays a crucial role in the return of these materials back underground, completing the geological process.

This tectonic cycle, essential to driving climatic conditions on Earth, has never been observed on a world outside our solar system — until now.

Running Hot and Cold

Located just 45 light years from Earth, LHS 3844b is thought to not have an atmosphere. This makes it slightly easier for astronomers to see tectonic processes taking place on this distant world. Even under the best of conditions, these measurements are right at the edge of technology.

“The first mission to Mars did not expect to find craters and river valleys, and yet they did. The first mission to Jupiter didn’t expect to find ocean worlds and volcano worlds, but they did.” — Alan Stern

This volcano planet, composed mostly of rock like our own world, is slightly larger than Earth.

This world orbits so close to its star that it is tidally locked — eternally facing one side toward its stellar parent, as the face on the Moon always points to Earth. Because of this, one side of LHS 3844b is constantly heated, while the other side remains perpetually frozen. While the sun-facing side of this world burns at temperatures of 800 degrees Celsius (1470 Fahrenheit), temperatures on the nightside drop to -250 C. (-420 F).

A diagram showing how material could flow through throughout LHS 3844b. Image credit: University of Bern / Thibaut Roger

Researchers suspected this extreme difference in temperatures might drive geological flows within this volcano planet.

An international team led by Tobias Meier from the Center for Space and Habitability (CSH) at the University of Bern developed computer models to test the theory.

The models showed geology within LHS 3844b would likely result in mantle material flowing from one side of the exoplanet to the other. Logically, one might think that hotter material on the “day side” of the world would be lighter, making it more likely to rise on that side. However, some of the simulations showed just the opposite pattern, resulting in a nightside filled with volcanoes.

“This initially counter-intuitive result is due to the change in viscosity with temperature: cold material is stiffer and therefore doesn’t want to bend, break or subduct into the interior. Warm material, however, is less viscous — so even solid rock becomes more mobile when heated — and can readily flow towards the planet’s interior,” Dan Bower at the University of Bern explains.

Upswelling of material on one side of the planet could lead to active vulcanism across that hemisphere, researchers determined. This would be similar to processes which drive the highly-volcanic regions of Hawaii and Iceland. Such conditions could lead to the development of a volcano world, with one side covered in volcanoes, while the other half remains nearly barren of the features.

It’s Like Pompeii Without the Tourist Food…

Evidence for recent vulcanism has been spotted on Venus and Io. This new finding shows how tectonic activity on another world can be significantly different than geological activity on Earth.

“Earth is the only known planet with active plate tectonics, but observations of exoplanets may deliver insights into the diversity of tectonic regimes beyond the solar system,” researchers describe in an article published in The Astrophysical Journal Letters .

An interview with Dr. Laurent Montesi, geologist at the University of Maryland, who discovered evidence for recent volcanic activity on Venus. Video credit: The Cosmic Companion.

Volcanoes play essential roles in the development and evolution of life on Earth, and these occasionally-explosive centers can alter our climate, even today, under the right conditions.

“When Mount Pinatubo erupted in the Philippines June 15, 1991, an estimated 20 million tons of sulfur dioxide and ash particles blasted more than 12 miles (20 km) high into the atmosphere. The eruption caused widespread destruction and loss of human life. Gases and solids injected into the stratosphere circled the globe for three weeks,” NASA reports.

Volcanoes would, similarly, likely be a guiding factor in the development of life on other worlds. Although LHS 3844b is the first exoplanet known to show plate tectonics, other such volcano planets may soon be discovered by astronomers searching the vast prairie of the open sky.

James Maynard

James Maynard is the founder and publisher of The Cosmic Companion. He is a New England native turned desert rat in Tucson, where he lives with his lovely wife, Nicole, and Max the Cat.

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How can it be known that Venus does not have plate tectonics? - Astronomy

"That we can now think of no mechanism for astrology is relevant but unconvincing. No mechanism was known, for example, for continental drift when it was proposed by Wegener [2] . Nevertheless, we see that Wegener was right, and those who objected on the grounds of unavailable mechanism were wrong." [3]

Carl Sagan, astronomer, astrophysicist, author, cosmologist, broadcaster and sceptical of astrology.

    Gravitational Resonance: Many critics of astrology have repeated the story that the gravity of the midwife has more effect on the newborn baby than the planets. However, astrologers do not claim that gravity is the basis for natal astrology.

Tidal Forces: It is universally accepted that gravity and orbital resonance of the Sun and the Moon affects the Earth's oceanic tides and the Earth tide (body tide). The tidal force is part of what some astrologers call natural astrology which also includes the study of the coincidence of seismic activity with celestial positions, harvests and weather. The most popular ancient book on astrology Tetrabiblos by polymath, Ptolemy, contains the first records of a tidal connection with the Moon - a theory he derived from ancient observation. Centuries later, Galileo and Kepler, both astronomers and astrologers disagreed on this. Kepler supported Ptolemy's theory and identified the role of the 18.6-year nodal cycle: the precession of the lunar nodes even though he did not know the mechanism. (Kepler's nodal cycle affects the tides, harvests and climate). Galileo however, incorrectly believed that the tidal effect was caused by the Earth's orbit of the Sun. It was Newton who accepted natural astrology (but there is no evidence he practiced judicial astrology) who applied his theory of universal gravitation to the role of the Sun and the Moon and the tides.

Studies have proposed that the tidal forces also affect the Earth's plate tectonics (Continental drift). (Moore 1973) (Scoppola 2006) The tidal force is part of what some astrologers call natural astrology which also includes the study of the coincidence of seismic activity with celestial positions, harvests and weather.

I believe it is premature to set limits on the effect of gravity and orbital resonance on Earth as there is much we don't understand. For example, gravity is the one known force that does not yet fit into a Unified Field Theory. Also, the effects of gravity can be amplified by circumstances such as tidal resonance resulting in 16m tides in the Bay of Fundy (Canada).

  • Chin Cheh Hung Apparent Relations Between Solar Activity & Solar Tides caused by Planetary Activity [2007 NASA]
  • Glyn Wainright Jupiter's Influence [2004 New Scientist]
  • Ian Wilson Planetary Tidal Forces [University of Southern Queensland, Aus 2008] that attempt to account for this planetary/sunspot correlation.

Frontiers of Science. As stated above, it is unwise and premature to use the current model of the four fundamental interactions (previously known as fundamental forces) as a basis to rule out possibilities for several reasons. First, within this model, quantum mechanics and gravity are not yet reconciled. Scientists are still struggling to develop a theory of Quantum Gravity and as a result a Grand Unified Field Theory. In addition, several discoveries within quantum physics suggests that this could in the future become a fertile area for research into a possible mechanism.

Niels Bohr, (like Wolfgang Pauli) a leading pioneer in Quantum Mechanics.

Theory of Thermal Convection

In 1929, Arthur Holmes, a British geologist, introduced a theory of thermal convection to explain the movement of the Earth's continents. He said that as a substance is heated its density decreases and it rises until it cools sufficiently to sink again. According to Holmes it was this heating and cooling cycle of the Earth's mantle that caused the continents to move. This idea gained very little attention at the time.

By the 1960s, Holmes' idea began to gain more credibility as scientists increased their understanding of the ocean floor via mapping, discovered its mid-ocean ridges and learned more about its age. In 1961 and 1962, scientists proposed the process of seafloor spreading caused by mantle convection to explain the movement of the Earth's continents and plate tectonics.

I don't like the new ice worlds.

Maybe I've just been looking at the wrong ones then.


Koma Pahu

Deleted member 121570


Deleted member 121570

Koma Pahu


Pretty much. Olympus Mons is vertically huge, but it's laterally much huger, so it's not very prominent. You can also get some cool mountainy features from beating the crap out of a body with lots of overlapping impact craters though.

From what we know of Earth, Mars, and Venus, plate tectonics is kind of finicky and I wouldn't expect most planets, let alone moons, to have it. And then you need some erosion to carve the lifted terrain into mountains. And if you have both those features, hey guess what you're probably a planet with >0.1 atmospheres of surface pressure because you've got lots of volcanism spewing out gases that probably won't be blown away because you also have a hot juicy core that's giving you a magnetic field as a bonus.

Edit: They're probably very rare in-game if they exist at all yet, but a dead no-atmo ex-earthlike world would be amazing.


if this is the extent of the new planetary tech, we are in for along run bois.

it looks like an old man s.c.r.o.t.u.m

Agrar Therenus

It makes me wonder if the game is truly 1:1 scale. As an approximately 6ft human is 1km really 1km? (mixing measurements I know but the game forces metrics on us) It can of course be measured properly but I don't really know or honestly have the patience to work it out.

The lighting is deceptive because the haze makes those mountains in the very far distance look extremely high compared to the background surfaces. When you fly up to them it's just baffling "Is this those mountains?"

So it seems the game can render relatively sharp peaks, but I've yet to see interesting patterns on the sides or stratigraphy of any kind (I suppose that requires weather and climate changes, but things like lava events should be in there). I've not seen any proper canyons or rifts, or valleys as 'extreme' as in Snowdonia or something, rather those low-level bumpy canyon systems like my images show.

5 Answers 5

Josh - burn the world and let out some sulphur and you'll have your effect here.

Venus is a good example of run away warming. for the most case the 'global warming' term here is a direct relation towards our CO2 emissions, but sulphur and other gasses are extremely more effective at causing run away warming effects. And yes, it can last for extremely long periods. but some concerns to address

Due to the amount of water on earth, it is quite difficult to get extreme heat changes going. For every gram of water that is increased by 1 degree, you could raise the temperature of the same mass of air by 15 degrees or more. Removing waer (and ice) from the globe as part of your war would be quite useful in getting your intended result here.

Microbes can resist almost anything (atleast you will be able to fiund a few strains that have resistances to anything you can think of). Self DNA repairing Microbes exist that can readily resist radiation for example.

Earth plate tectonics do not readily make for a good setup with 'lava plains'. however a simple background of a large energy device could cause the Yellowstone super volcano to create a north american sized lava plain.

To get the desert (and warm) effect, go for 2 large events. 1. release every bit of carbon on the surface into the air as CO2. Burn every forest, cause underground oil reserves to burn, and bring the CO2 levels of this planet back up to where it was early in the earths formation. 2. Add sulphur to the equation. 'Sour' gas is gas with a high sulphur content, having gas and oil reserves burn is one way of doing this.

(an unintended effect here is the air pressure on the planet should increase with all this weight of new airborne matter. makes the planet that much more inhospitable. and sulphur stinks, your wasteland would suck to breathe).`

The effects of above should be - without plant life, erosion will run away. soil will 'flatten' as it rapidly erodes and shift towards dust and sand. The Sahara is expanding already, this should aplify the expansion. - Between sulphur and high amounts of carbon, you should have the necessary ingredients to initiate extreme warming without the unintended nuclear winter effect.

Still struggling to do something with all the earths water for you. without resorting to some form of weapon that removed it all, I'm not quite sure. - An explosion large enough to evaporate and eject water into space - An underground event that causes the majority of earths water to drain into the underground. This would be interesting as the water would still have a heat insulating effect, but not as much at the surface.

Lets give this blowing the water off Earth scenario a go. The process I'm relying on here is Thermolysis. basically the degradation of molecules due to heat. At around 2000 degrees Celcius, water begins separating into it's base components at about a ratio of 3:100. At around 3000 degrees, this becomes closer to 50/50. Ok, the energy I'm talking here to achieve these temperatures is kinda silly, but plutonium and iridium work as catalysts in this reaction, bringing down the 3% line to around 1300 degrees. Pretty theoriectical and estimated, but 2000 degrees with a iridium and platinum catalyst should reduce 50% of water to hydrogen and oxygen to be released out into space (at that temps, I'd assume there is enough momentum to break free of earths gravity?).

Ya, that seems a bit far fetched, and the temperatures involved would likely ignite close to anything nearby, maybe even the atmosphere. Let me see what else I can come up with. Heh, is a blackhole generated at the bottom of the ocean that collpases the water into it center doable?

A Volcanic View of the Habitable Zone

Our understanding of habitable zones is a work in progress, but the detection of multiple planets with potentially water-bearing surfaces around TRAPPIST-1 is heartening. Today we examine the prospect of extending the habitable zone further out from the host star than previously thought possible. The idea is found in new work by Ramses Ramirez and Lisa Kaltenegger (both at the Carl Sagan Institute at Cornell University). Volcanism is the key, allowing interactive effects that pump up greenhouse warming and sustain habitability.

Go back for a moment to the habitable zone limits that Andrew LePage looked at yesterday in his analysis of TRAPPIST-1. The classical habitable zone — allowing liquid water to exist on the surface — has an inner edge at which surface temperatures become high enough to lead to a runaway greenhouse and the rapid loss of water. The outer edge is defined by the distance beyond which CO2 can no longer produce the needed greenhouse effect to keep the surface warm.

Image: Ramses Ramirez, research associate at Cornell’s Carl Sagan Institute, left, and Lisa Kaltenegger, professor of astronomy and director of the Sagan Institute. Credit: Carl Sagan Institute.

But consider, say Ramirez and Kaltenegger, the effect of additional greenhouse gases on these worlds at the outer edge of the HZ. Here’s some context: The warming effect of hydrogen atmospheres has already been considered on young planets, allowing a primordial super-Earth to stay above freezing at the surface out to distances in the range of 10 AU. The paper explains that this greenhouse effect comes from what is known as collision-induced absorption, the result of so-called ‘self-broadening’ when H2 molecules collide.

The problem: Primordial hydrogen in the large amounts needed isn’t sustainable over geological timescales, meaning a super-Earth without a renewable hydrogen source would lose hydrogen to space. But volcanism can be the renewable source needed. The authors point out that climate studies of the early Earth and Mars both show that volcanism could have outpaced the escape of H2. Hydrogen here is not a major atmospheric constituent but is continually replenished by volcanism that offsets H2 loss.

Now we are in a situation where any atmospheric CO2 can interact with hydrogen to increase the greenhouse warming potential for the planet over long time periods. The effect could extend a habitable zone by between 30 and 60 percent. Says Ramirez:

“On frozen planets, any potential life would be buried under layers of ice, which would make it really hard to spot with telescopes. But if the surface is warm enough – thanks to volcanic hydrogen and atmospheric warming – you could have life on the surface, generating a slew of detectable signatures.”

Image: The eruption of the Tavurvur volcano in Papua New Guinea, part of the Rabaul Caldera on New Britain. Can similar eruptions produce the factors needed for habitability at the outer edge of the habitable zone? Credit: Taro Taylor edit by Richard Bartz – originally posted to Flickr as End Of Days, CC BY 2.0.

In terms of our own Solar System, the researchers point out that the addition of 30% H2 can extend the habitable zone to 2.4 AU, putting its outer edge in the main asteroid belt (the habitable zone around Sol is normally considered to extend to 1.67 AU, just beyond the orbit of Mars). Because we’ll be looking for atmospheric biosignatures with upcoming instruments like the James Webb Space Telescope and the European Extremely Large Telescope, we’ll want to factor this extended habitable zone into our list of search candidates.

In their paper, which appears in The Astrophysical Journal Letters, the researchers use climate models to compute the boundaries of what they are calling the ‘volcanic hydrogen habitable zone’ for concentrations of hydrogen between 1% and 50% — finding that at a hydrogen concentration at the upper end of that range, the effective stellar flux needed to support the outer edge of the habitable zone decreases by

35% to 60%, with the corresponding orbital distances to remain habitable increasing by 30% to 60%. The effective temperatures (TEFF of the stars examined range from 2,600K to 10,000K — the stellar classes range from M dwarfs to A-type main sequence stars.

Given these prospects, how do we go about searching for life signatures on outer planets with sizeable amounts of atmospheric hydrogen? It’s a vexing question:

Certain atmospheric spectral features, including N2O and NH3, which can, but do not have to be produced biotically, could be detected in H2 -dominated atmospheres (Seager et al., 2013 Baines et al., 2014). Such volcanic-hydrogen atmospheres may also be able to evolve methane-based photosynthesis (Bains et al., 2014). Distinguishing biosignatures from abiotic sources in such atmospheres will be challenging.

Note the possibilities that must be distinguished here:

NH3 can be formed abiotically through reaction of N2 and H2 in hydrothermal vents on planets with reducing mantles (Kasting et al., 2014). N2O can be formed a number of ways including through atmospheric shock from meteoritic fall-in, lightning, UV radiation (e.g. Ramirez, 2016) and through solar flare interactions with the magnetosphere (Airapetian et al., 2016). Thus, future biosignature studies should focus on modeling biotic and abiotic sources for these gases in thin volcanic-hydrogen atmospheres.

Clearly there is plenty of work ahead, but a combined greenhouse effect from hydrogen, water and CO2 could be the key to expand stellar habitable zones and widen our observational window. As Kaltenegger puts it, “Where we thought you would only find icy wastelands, planets can be nice and warm – as long as volcanoes are in view.” And warming hydrogen, all too easily lost into space, can be renewed by the same kind of volcanic hydrogen that puffs up planetary atmospheres, making that much stronger a signal for the detection of biomarkers.

Does TRAPPIST-1, then, have the capacity for yet another planet in the habitable zone? Kaltenegger isn’t ready to go that far, saying “…uncertainties with the orbit of the outermost Trappist-1 planet ‘h’ mean that we’ll have to wait and see on that one,”

The paper is Ramirez and Kaltenegger, “A Volcanic Hydrogen Habitable Zone,” The Astrophysical Journal Letters 837, No. 1 (2017). Abstract available.

Comments on this entry are closed.

Where there is hydrogen and carbon dioxide plus lightning there will be other hydrocarbons forming which also are greenhouse gases provided they do not form smog to block light coming in.

There has already been a search (with negative results) for a hydrogen dominated atmosphere for the inner 2 Trappist-1 planets using transmission spectroscopy during a mutual transit. I don’t think we will have to wait for Webb to resolve this particular issue, at least for the Trappist-1 system.

Interesting point Marshall. However, the atmospheres in our new study are not hydrogen-dominated (most contain well under 50% hydrogen) although they are hydrogen-rich. What we are proposing are mostly CO2-dominated atmospheres (near the outer edge) with some amount of hydrogen. Towards the inner edge, these atmospheres may be N2- or H2o-dominated. So these atmospheres will still be considerably denser and less “puffed up” than a pure- or hydrogen-dominated atmosphere.

If we have hydrogen and carbon bearing matetials methane can be formed which is a powerful greenhouse gas. If we look at Neptune for instance it has 1.5 % methane which would have a substantial warming effect.

Venus is also volcanically active. Not much life there that we’ve detected.

Not in the sense described here. It requires volcanoes that require plate tectonics and this requires water as a lubricant . Provided via plate subduction at continental / ocean margins ( think Pacific ” Ring of Fire ” on Earth .

Venus has long lost its water so has lost its tectonics ( via a runaway greenhouse effect that independently rendered it uninhabitable ) . It’s crust is a ” stagnant lid “. This is theorised to vent internal heat build up in its outer mantle by essentially melting en masse every few hundred million years.

Where there is energy and there is a lot of it at Venus’s orbital distance
together with heavy elemental chemicals, less of them in Venus’s atmosphere, it could potentially support primitive life in Venus’s clouds.

Do HZ calculations (liquid water at surface) take into account that water can be liquid at higher temperatures at higher pressure…up to 374 C/705 F at 218 atm.?

Fascinating if such a greenhouse cocktail could be confirmed as the brew that warmed Early Mars – and Earth. So long as we’re discussing “Hydrogen Earths” several researchers have shown that planets with trapped primordial H2 atmospheres can retain liquid water even out in interstellar space. The outer limit of the Photosynthetic Habitable Zone is somewhat more restrictive, being about

0.01 Earth’s insolation levels. A hydrogen-rich ‘moon’ could orbit Saturn and have open water oceans with exotic plants.

An intriguing question is whether H2/O2 can exist in sufficient disequilibrium to make such outer worlds habitable by humans. If the total pressure was

10 bar and O2 was less than 5%, but still at a breathable partial pressure, then there’s no chance of igniting the atmosphere. Hydrox is a deep-diving breathing mix which pigs have tolerated to 70 bar pressure.

Alternatively future explorers of H2/CH4 greenhouse worlds could wear simple O2 masks. Eventually we might figure out how to replace our O2 utilizing mitochondria with H2 using alternatives and do away with the masks.

Tom, thanks for your question. Yes, our HZ calculations do take into account that water stays liquid up to the critical point of water that you mentioned. On a planet with an Earth-like amount of surface water, beyond that critical point, no liquid water can exist on the surface. It instead becomes a steam atmosphere and a full-blown runaway greenhouse ensues.

The argument assumes that early rocky worlds have reducing mantles that can outgas H2. Over time this loss results in an oxidized mantle which prevents further H2 emissions.

The source of the hydrogen is from water, or some other compound? The paper argues that Mars may have released hydrogen for a billion years, while earth for only 100 m. This appears to be an empirical observation, but what is the underlying chemistry model that would support this?

An interesting idea that should be testable soon.

Yes, where is all of this volcanic H2 supposed to have come from? Sure, it’s the most common molecule in space, but in the interiors of rocky planets that have experienced meltdowns during formation how common can it be?
Also, light gases like H2 would be the easiest for stars to strip away during a star’s very active youth.

Alex, more details are in works like Wade and Wood (2005). Essentially, Mars is too small to generate the pressures necessary to lead to mantle oxidation, favoring volcanic outgassing of hydrogen-rich products. Earth, being larger, is more likely to generate the processes that result in an oxidized mantle, leading to the eruption of more hydrogen-poor gases. Such results are predicted from lab experiments exposed to different pressures/conditions.

I’m interested in what sort of effect H2S would have as a greenhouse gas. It is produced volcanically in large quantities.

Dave, I’ve played around with H2S a bit in trying to warm early Mars. My experience is that it has some greenhouse effect, but it isn’t particularly strong. SO2 is the stronger sulfur species out of the two.

Could the inner two planets be as active as Io? There would seem to be a good chance that the other planets would also have an active lithosphere because of the tides caused by the nearby planets. The two inner planets could also be elongated bacuase of the interaction between the red dwarf and its high magnetic field and the planets cores causing them to stay in a molten state. What about meathane on the outer planets, could some type of lifeforms use it and what forms could it take under different tempatures and pressures?

A New Window on Alien Atmospheres

The James Webb Space Telescope, originally intended for scanning the outer reaches of the cosmos, is now expected to break new ground exploring exoplanets.

One of the most exciting potential uses of the James Webb Space Telescope (JWST), which is scheduled to launch in 2018, is to hunt for habitable exoplanets—something that was beyond imagining at its inception. In the 1970s, no one even knew whether exoplanets existed. In the 1990s, when JWST was conceived as the successor to the Hubble and Spitzer space telescopes, the notion that the atmospheres of alien worlds could be studied seemed faintly ludicrous. Part of the early motivation was to build a telescope that would be powerful enough to detect the earliest stars and galaxies. Because the universe is expanding, which reddens light as it travels across space, this new eye on the cosmos would need to be built for the infrared spectrum. Fast forward to 2017, and the measurement of atmospheric properties of exoplanets is now fairly routine. Humanity’s most expensive telescope, originally intended for scanning the outer reaches of the cosmos, is turning out to be a decisive instrument for exploring alien worlds and—if we are lucky—will find ones that are habitable.

When JWST was conceived, studying the atmospheres of exoplanets was not on the minds of its developers. Then in 2005, photons from the atmosphere of an exoplanet were detected for the first time using the Spitzer Space Telescope. Later, astronomers learned how to record signals from these atmospheres at different colors and interpret them to identify the presence of atoms and molecules, using both space- and ground-based telescopes.

To date, water, carbon monoxide, hydrogen, magnesium, methane, sodium, and potassium have been robustly detected. Nowadays, the Hubble Space Telescope is routinely used to check whether an exoatmosphere contains water. Astronomers have also made crude temperature maps of these atmospheres. Exoatmospheric science tells us about the general climate conditions of an exoplanet, including chemistry and temperature. As technology has advanced, enabling us to probe cooler (and fainter) exoatmospheres, these discoveries have opened a potential window into studying an exoplanet’s habitability.

These recent advances are prompting changes to JWST—both in terms of tweaks to the hardware and the telescope’s operation—while it undergoes testing in preparation for its scheduled launch in October of 2018. Given the limited lifetime of JWST, which may be as short as 5.5 years, astronomers and astrophysicists are focusing on the best targets for advancing our understanding of exoplanetary atmospheres: gas and ice giants first, and a selected sample of smaller exoplanets second.

Interesting and unsurprising research results given what we know about our own system of planets and Moons.

I have often despaired at the statements of researches that claim this, that and the other based only on anecdotal evidence or assumptions.

Venus is a cauldron by Earth standards and we understand that as the young Sun increased in energy and brightness the atmosphere of the young Venus was modified. However, there are two key differences between Earth and Venus.

Earth is effectively a double planet and the gravitational tug of war clearly assists with volcanism and plate tectonics on Earth and is , in my opinion, the main reason for Earth having a powerful and global magnetic field.

This magnetic field is an important difference for our planet, will this be the case with other worlds? Well Venus lacks a decent global field that would have protected the upper atmosphere from the ravages of the early Sun’s energetic solar wind.

When calculating the alleged “habitable zones” around stars I am curious as to whether a global magnetic field, or lack of, is taken into account because clearly it is a major influence.

Lastly, without a global greenhouse effect by Water Vapour in the atmosphere Earth would actually be a frozen wasteland so as far as I see Earth validates this research.

James, you are certainly right that a magnetic field plays an important role in habitability for the Earth although some studies have suggested that magnetic fields could be *bad* for habitability in some cases.

In the case of Venus, your comments suggest that it never had one. However, Venus could have very well had a substantial early magnetic field although this is not currently known. Even with such an early magnetic field, I am not so sure that it would have been able enough to protect Venus from the ravages of an early Sun.

In my view, the potentially biggest issue with Venus is that it receives nearly twice as much solar energy as our planet does given its close proximity to the Sun. As I show in our paper (discussed here on Centauri Dreams as well :, “The Habitable Zones of Pre-Main-Sequence Stars”, Venus was close enough to the young Sun that it could have been in a runaway greenhouse state for at least several million years, removing whatever water it may have had very early on. If that happened, the issue here does not have as much to do with the strength of the magnetic field, but with the resultant high surface temperatures, which could have lead to vaporization of the entire surface water inventory and total planetary desiccation.

Ramses, the proximity of Venus to the Sun does not make as large a difference as is often thought. Venus receives about 1.7x the solar flux that Earth does, however several studies have shown that with a different atmospheric composition so it was more ain to Earth the global mean temperature would be about 22°C, up from Earth’s approx 14°C.

As far as I am aware Earth’s vulcanism is predominantly if not totally driven by plate tectonics and subduction with the whole process lubricated by water (something Venus has lost along with similar vulcanism replaced by a ” stagnant lid” crust that melts every few hundred million years) . This in turn is driven by convection in the mantle .

The whole process could operate in the absence of any moon which for Earth raises significant tides in the oceans but unlike Io, is not nearly enough to do so in the crust or mantle . Io’s crust has been shown to shift hundreds of feet thanks to its substantial tidal interactions with proximal ( and massive ) Jupiter and its neighbouring moons that so heat its mantle . It’s vulcanism has a total different aetiology .

Venus is now most likely tidally locked given its slow rotation which is unlikely to produce much in the way of a Dynamo effect in its liquid outer core . Ironically extended vulcanism has been mooted as a mechanism of protecting against atmospheric erosion even in the absence of a magnetic field .

Kite et al looked at this for Super Earth’s orbiting red dwarfs the hypothesis / simulations looking at the volcanic production of secondary atmospheric gases to replenish those lost to the hostile stellar flux of early and pre main sequence red dwarfs . As long as the internal pressure in the mantle didn’t become high enough to shut down convection ( and there were enough volatiles to lubricate tectonics) as might happen with too large a terrestrial planet, they found that vulcanism on such planets could be sustained for tens of billions of years.

James, I’d like to see what study you are referring to because it contradicts not only my calculations, but all of the recent modeling on the subject.

The flux Venus receives today is over 1.9 times that received at Earth (1/(0.718^2))

1.94, a ratio of the inverse square law of their distances to the Sun.

At Earth’s distance from the Sun, newer studies (e.g. Leconte et al. 2013) obtain that a flux level only

1.1 times that received by Earth today would trigger a runaway greenhouse. And Venus receives much more energy than this.

A magnetic field has little to do with this here. This is solely the fact that if water gets too hot, it will evaporate.

Did Venus have a long enough temperate environment to at least evolve simple lifeforms? Could they have descendants in the planet’s upper atmosphere or under the surface?

Today’s news that terrestrial microbial fossils dating back over four billion years lend some support to the idea of life evolving even in harsh conditions given enough of the right materials and climate. And we already know how life on this planet can survive in what was once considered very inhospitable conditions.

ljk, it is possible that Venus could have supported life in the past if the climate was more temperate. Some studies argue (e.g., Yang et al., 20132014 Way et al., 2016) that if Venus had been rotating slowly enough, a larger than normal amount of clouds could have formed on the Sun-lit side, reflecting much of the extra energy back out to space. Such conditions may have helped moderate surface temperatures on Venus even though it is closer to the Sun (maybe for a couple of billion of years or so) before it eventually lost its water to a runaway.

Thank you, Ramses. Do you think it is possible that some substantial sources of water might still survive deep under the surface of Venus?

Venus although has a degassed significantly still has very small amounts of water vapour, even less of which come from the ground.

ljk…Another good question. This is unknown. One of my colleagues thinks that Venus’ mantle may be wet although its surface is dry. This is something that will require future missions to answer. My take is that if water is needed to lubricate plates for plate tectonics to function (that is one hypothesis), then if there is much water deep in Venus, it is somehow not being accessed to lubricate them.

James, thank you, this is another argument for the Rare Earth theory.

That all depends on whst you are looking for. Like people all planets are unique, thus the Earth is rare regardless of how you look at it.

Two things stand out about this. ONE: Is THIS what kept Earth warm when the Sun was only two thirds as warm as it is today(Ramses and Lisa any thoughts. A future paper on this possibility would be fascinating)? TWO: The PRIME BENEFICIARIES of this NEW “greenhouse effect among the existing CONFIRMED planets are TRAPPIST-1g and Kepler 186f. Already IN the habitable zone but EXTREMELY COLD, BOTH of these planets COULD have much more moderate climates than previously invisioned.

Harry, we actually do not know for sure what had kept Earth warm early on (aka “the faint young sun paradox). There have been several proposed solutions to this paradox, including a similar volcanic hydrogen solution that we had used here for the habitable zone and in my 2014 early Mars paper. This volcanic hydrogen solution for early Earth had assumed a N2-H2 greenhouse combination, though, instead of CO2-H2.

To my understanding, the earth’s atmosphere used to be much thicker, which explains a number of things about our prehistoric past. A thick atmosphere distributes heat efficiently and has a larger greenhouse effect, which explains the global tropical climate of the mesozoic. The thicker air was also able to support larger terrestrial megafauna such as apatosaurus/brontosaurus and the ability of dactyls to fly.

I’m sure volcanism played a significant role in this, although there could have been other factors.

There is a NEW paper out regarding Proxima b, but with POSSIBLE IMPLICATIONS for TRAPPIST-1d on ArXiv today. ArXiv: 1702.08463. Exploring the Climate of Proxima B with the Met Office Unified Model, by Ian A. Boutle, Nathan J. Moyne, Benjamin Drummond, James Manners, Jayesh Goyal, F Hugo Lambert, David M Acreman, Paul D Earnshaw. The pertinent sentence is …”However, we find interesting differences from previous simulations, such as cooler mean temperatures for the tidally-locked case”… Rameses and Lisa. This paper is WAY OVER MY HEAD. Any comments on it would be greatly appreciated.

Harry, yes I have recently seen this paper as well. You touch on a major area of research right now that involves understanding how heat is transferred between the atmospheres and oceans on a potentially habitable tidally-locked planet. Currently, we do not understand this too well. For that matter, neither do we understand too well how clouds form/vary nor how water vapor is transferred throughout the atmosphere. All of this is necessary in order to understand atmospheric-ocean heat transport, including for tidally-locked planets. Different models make different assumptions regarding all of these aspects, and unsurprisingly, yield different answers.

I would guess that the complex and substantial interplanetary and stellar gravitational interactions would raise potent tides and currents in any putative oceans on TRAPPIST-1 planets . ( as well as Io like vulcanism ?) This apart from being impressive would certainly help transfer of heat on a tidally locked planet , even under ice ( assuming those self same tides and IR stellar flux haven’t help melted it ) and even without considering similarly heat transferring winds in any atmosphere.