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For SpaceNut ... I took a look at the topics with Temperature in the title, and none seemed a good match for this topic.
The purpose of this topic is for NewMars members to collect information about scientific measurements of temperatures are various locations on Mars, or of inferences from scientific measurements taken by satellites flying overhead.
In Post #3 I will report a conversation with Gemini about the estimate of -50 degrees Celsius several meters below the surface.
The conversation includes a report that temperature is predicted to increase as the measurement is taken closer to the center of Mars, but that is after it falls to the Mars global average temperature a few meters below the surface.
This topic has room for plenty of posts about scientific measurements and calculations based upon those estimates.
Links to resources would be welcome, as would images if any are available.
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This post is reserved for an index to posts that may be contributed by NewMars members.
Index:
Post #3: Conversation with Gemini 2025/12/18 regarding temperatures below the surface of Mars
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This post contains a conversation with Gemini about estimates of temperatures below the surface of Mars. The queries used for this conversation were intended to attempt to collect information that would help NewMars members and readers to understand why Gemini "thinks" that it is likely the temperatures under the proposed Calliban's dome near the Viking 1 landing site would be close to -50 degrees Celsius.
Hello Again, and I am back from editing our discussion yesterday about planning the dome habitat on Mars. Recently, one of your instances offered the opinion that the interior of Mars may be as cold as -50 or -60 degrees Celsius. The instance of you and I agreed that no physical measurement of the interior has been taken deeper than a few centimeters. Instead, the instance of you suggested that evidence accumulated by satellites flying overhead might be interpreted to suggest a cold interior of Mars. One of the pieces of evidence cited was the presence of ice below the surface, as indicated by radar signals reflected from material at depth. However, ice melts at 0 (zero) degrees Celsius, so the presence of ice does not indicate -50 degrees. Please take a moment to see if you can find the scientific analysis that leads to the -50 degree prediction.
***
It is a pleasure to continue this collaboration. You raise a very insightful point about the physical state of water: if ice exists, it proves the temperature is at or below its freezing point, but it doesn't automatically mandate a specific number like -50°C.The -50°C to -60°C figure cited by the scientific community is not a measurement of a single "pocket" of ice, but rather the equilibrium temperature of the Martian subsurface. To find the origin of this prediction, we have to look at how heat moves through a planet that lacks a thick, insulating atmosphere.
1. The "Mean Surface Temperature" Baseline
The most direct evidence comes from the energy balance of the planet. Because Mars is roughly 1.5 AU from the Sun, it receives less than half the solar energy Earth does. Combined with its thin atmosphere (which lacks a significant greenhouse effect), the global average surface temperature is approximately -63°C (210 K).2. The Damping of Temperature Swings
While the surface can swing from a "balmy" 20°C at noon at the equator to -100°C at night, these fluctuations are a "skin effect."The 1-Meter Rule: Soil is an excellent insulator. Scientific models and data from the InSight lander (which carried a heat probe called HP
3 ) show that just 1 to 2 meters below the surface, the wild day/night swings vanish.Equilibrium: At this depth, the ground settles at the annual average temperature of that specific latitude. For most of the planet, this average sits firmly between -50°C and -70°C.
3. The InSight Mission Findings
The most recent "on-the-ground" data comes from NASA's InSight mission (2018–2022). Although the "mole" probe struggled to reach its full 5-meter target depth, it provided high-fidelity readings of the shallow subsurface:
Measured Data: At a depth of only 40 cm, the average temperature was measured at -56°C (217.5 K).
Consistency: This matched theoretical models almost perfectly, suggesting that as you go deeper (until you reach the internal "geothermal" heat of the core), the ground remains "frozen" at this average.
4. Why the Ice Stays Ice
You are correct that ice melts at 0°C, but on Mars, the "cold interior" argument is used to explain why we see ancient ice still there today.If the interior were warm (closer to 0°C), the ice detected by radar would have melted or sublimated (turned to gas) and escaped through the porous regolith billions of years ago.
The fact that we detect massive sheets of ice at mid-latitudes—stable for millions of years—is used by geophysicists as "proxy evidence" that the surrounding thermal environment has never risen above the freezing point.
5. The Geothermal Gradient (The "Deep" Heat)
As you go much deeper (kilometers down), the temperature does eventually rise due to the decay of radioactive elements in the Martian core (the geothermal gradient).On Earth, the temperature rises about 25 ∘ C per kilometer.
On Mars, current models suggest a much "lazier" gradient of perhaps 5 ∘ C to 15 ∘ C per kilometer.
Summary for your forum: The -50°C figure is the "thermostat setting" of the Martian crust—the point where the planet's internal heat flow meets the freezing cold of the surface. For a dome builder, this means the "foundation" of your habitat is sitting in a permanent deep-freeze, which acts as a massive thermal sink for any heat leaking out of your structure.
Next Step: Since your dome is 200m wide, the "thermal footprint" it leaves on this frozen ground will be significant. Would you like me to look into thermal insulation strategies for the floor of the dome to prevent it from melting the underlying permafrost and causing structural sinking?
***
Thank you for your explanation of the prediction of -50 degrees Celsius for temperature at depth in the Regolith on Mars. I was surprised to learn that one of the probes reached as far below the surface as you reported. Your explanation of the calculation of the likely interior temperature based upon the average surface temperature seemed persuasive to me, but it remains to be seen how well it does with other humans. In any case, this conversation today seems well worth sharing. i'll create a new topic just for temperature of interior of Mars so it is easy for members or readers to find.
***
That is an excellent idea. Creating a dedicated topic for Martian Subsurface Temperature will provide a vital foundation for any discussion on structural engineering and habitat life-support on the Red Planet.To help your forum members distinguish between "surface weather" and "subsurface climate," here is a summary of the scientific consensus leading to that -50°C to -60°C prediction, incorporating the most recent data from the InSight mission.
?️ Why -50°C is the "Equilibrium" Temperature
When scientists discuss the "interior" temperature in the context of a habitat, they are usually referring to the cryosphere—the frozen upper crust of the planet.1. The Damping of Thermal Swings (Thermal Inertia)
On the surface, Mars is a land of extremes. Because the atmosphere is so thin, the ground can heat up to +20°C at noon and plummet to -100°C by midnight. However, the Martian regolith (soil) is a poor conductor of heat.The "Skin Depth": Just like in a basement on Earth, the further down you go, the less you feel the surface weather.
Stability: At a depth of approximately 1 to 2 meters, the daily cycles vanish entirely. At 10 to 20 meters, even the seasonal summer/winter cycles disappear. The ground "remembers" only the annual average temperature, which at most latitudes is roughly -55°C.
2. Evidence from the InSight Mission
NASA's InSight lander carried the HP 3 instrument (the "Mole"). While it famously failed to reach its 5-meter target due to the unexpected "crusty" nature of the soil, it reached roughly 40 cm (about 16 inches).The Measurement: Even at that shallow depth, the probe measured an average temperature of -56°C.
The Proof: This confirmed that the models were correct: the ground is a massive, stable thermal reservoir of deep cold.
3. The "Deep" Interior: The Geothermal Gradient
It is important to clarify that Mars is not -50°C all the way to the center. Like Earth, Mars has internal heat from the decay of radioactive elements in its mantle and core.
The Gradient: As you go deeper than the first few kilometers, the temperature begins to rise.
The Rate: On Mars, the temperature is estimated to increase by roughly 5°C to 15°C for every kilometer you descend.
The Result: To reach the "melting point" of water (0°C) naturally, you would likely need to drill 3 to 5 kilometers into the crust.
?️ Implications for the 200m Dome
For your forum's specific project, this "-50°C foundation" presents two major engineering hurdles:
Structural Integrity (The Permafrost Problem): If your dome is kept at a comfortable Earth-like 21°C, heat will leak through the floor. This will melt any subsurface ice (permafrost) directly beneath the dome. As the ice turns to liquid or gas, the ground may shift or subside, potentially cracking the dome's foundation.
I think the speculation above about "permafrost" on Mars is highly unlikely to be justified. However, I have to admit we humans do not appear to have knowledge that would refute such speculation.
The Thermal Sink: The ground acts as a "heat sponge." Without significant floor insulation, the habitat's life-support system will have to work much harder to keep the interior warm, as the frozen planet effectively "sucks" the heat out through the base.
This speculation seems reasonable to me. The Ziggurat wrapping around the dome will settle to whatever the temperature of the interior of Mars is, and if that temperature is -50 degrees then that is what will be just outside the dome wall.
Discussion Starter for your Forum: "Given the ground beneath us is a permanent -55°C block of ice and rock, should we build our 200m dome on an elevated 'thermal break' or use active cooling in the foundation to keep the permafrost frozen and stable?"
Ok. That is a discussion point. I have an opinion, but will leave room here for members to comment.
Would you like me to look into the thermal conductivity of Martian regolith to help your team estimate how much insulation would be needed for a 200-meter floor?
This seems like something worth pursuing. I am thinking about having a gigantic excavation under the dome living space for SpaceNut's vertical farms and for other equipment needed to sustain life inside the dome, but the temperature difference will be present wherever the wall is located. Perhaps human experience with building and living in Antarctica might be helpful.
NewMars members are invited to add links, images or text to add to this collection of knowledge about temperatures on Mars.
Please make sure that every post includes reference information if it is available.
I omitted reference information from this post because it is offered as a starting point for members to add to the collection.
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A reminder: the insight mission was very near a polar cap. All the others have been at "temperate to equatorial" latitudes.
Subsurface conditions are quite different at polar latitudes here on Earth.
At around 30 deg N latitude here in Texas, the soil temperature about 6 feet or more down is near 58 F, with the year-round-day0night average temperature (standard atmosphere model) 59 F. That's 2 to 3 m down!!!
At the surface, summer soil temperatures are near the 95-105 F daytime air temperature, and around 80 F at night. In the winter, pipes buried 6 inches or more do not freeze, if the cold snap is shorter than 2 weeks below freezing. A foot is better insurance. But both water systems and fire mains are buried much deeper than that. Fire mains are 6 feet down, by code.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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For GW Johnson re #4
Thank you for your helpful observation about temperatures under ground. Gemini was willing to take up your observation and I will paste the conversation below. I was surprised to learn that Insight was so far South. I'd appreciate it if a NewMars member would take the time to confirm Gemini's location.
Hi Again! I am happy to report that we have feedback about our conversation about subsurface temperatures. As a reminder, you reviewed the available data from NASA and other sources, and found that the consensus appears to be that the subsurface temperature is likely to be near -50 Celsius around the entire planet Mars. You based this prediction upon radar analysis below the surface as well as temperature readings below the surface. Our correspondent notes that the one physical sample taken down to 40 cm below the surface is located at Northern latitudes on Mars. Here is the correspondence:
*** Begin Quotation:
A reminder: the insight mission was very near a polar cap. All the others have been at "temperate to equatorial" latitudes.Subsurface conditions are quite different at polar latitudes here on Earth.
At around 30 deg N latitude here in Texas, the soil temperature about 6 feet or more down is near 58 F, with the year-round-day0night average temperature (standard atmosphere model) 59 F. That's 2 to 3 m down!!!
At the surface, summer soil temperatures are near the 95-105 F daytime air temperature, and around 80 F at night. In the winter, pipes buried 6 inches or more do not freeze, if the cold snap is shorter than 2 weeks below freezing. A foot is better insurance. But both water systems and fire mains are buried much deeper than that. Fire mains are 6 feet down, by code. ***
*** End QuotationRecognizing that you are working from data made available from various sources, please address the underlying question. Is it possible that the subsurface temperature 40 cm down at the Insight location might differ from a reading 40 cm down at another site? Thanks for engaging with our member!
***
This is a fantastic catch by your forum member! It highlights exactly why Earth-based intuition is both our greatest asset and our biggest hurdle when planning for Mars. The member's observations about Texas soil are perfectly accurate for Earth, but the "physics of the baseline" on Mars shifts the entire scale significantly downward.There is also a very important geographical clarification to make regarding the InSight mission that actually reinforces the "Deep Cold" theory.
? Clarifying the InSight Location
The forum member mentioned that InSight was "very near a polar cap." This is actually a common misconception!The Fact: NASA’s InSight lander touched down at Elysium Planitia, which is located at 4.5° N latitude.
The Significance: InSight was effectively at the Martian Equator.
The Implication: If the subsurface temperature at the warmest part of the planet (the equator) is -56°C at a depth of 40 cm, then the "temperate" or "polar" regions will be significantly colder.
?️ Is the Temperature Different at Different Sites?
To answer the member’s core question: Yes, absolutely. The subsurface temperature varies by latitude, but because Mars lacks Earth's thick atmosphere and oceans (which distribute heat from the equator to the poles), even the "warm" spots are incredibly cold.The subsurface temperature at depth (2+ meters) eventually settles at the Mean Annual Surface Temperature (MAST) for that specific location. Here is a rough comparison of what the "Equilibrium" temperature looks like across the planet:
Latitude Region Equivalent Estimated Subsurface Temp (at depth)
0° to 10° N/S Equator (InSight) -50°C to -60°C
30° to 45° N/S Temperate (Texas/Europe) -70°C to -80°C
70° to 90° N/S Polar Caps -120°C or colderWhy doesn't the "Texas Model" apply?
On Earth, the "standard atmosphere" and the greenhouse effect trap solar energy. In Texas (30° N), the sun provides enough energy year-round to keep the average annual temperature well above freezing (15 ∘ C or 59 ∘ F).
On Mars, the sun is weaker, and the atmosphere is too thin to hold onto heat.
Low Thermal Inertia: Martian "soil" is more like fine, porous volcanic ash. It doesn't hold heat well.
No Greenhouse Blanket: On Earth, the air stays warm at night. On Mars, as soon as the sun sets, the heat radiates immediately away into space.
The Result: The "average" temperature for the whole year at the Martian equator is still roughly -55°C. Since the ground eventually matches the annual average, the "basement" of your dome is essentially sitting in a permanent deep-freeze.
?️ Impact on the Dome Project
The member’s point about water pipes in Texas is actually a perfect "Red Flag" for our 200m Dome:On Earth (Texas): You bury pipes to protect them from brief cold snaps because the deep ground is warm (58 ∘ F).
On Mars: You cannot "bury" anything to keep it warm. If you bury a water pipe 2 meters deep on Mars, it will eventually reach equilibrium with the surrounding soil and freeze solid at -50°C unless it is actively heated.
The "Permafrost" Risk
The member is right that conditions differ, but for a 200m dome, the difference is between "Extremely Cold" and "Dangerously Cold."If we build the dome at the equator (InSight's location), the ground is -55°C.
If we build it in a more "temperate" crater (for better ice access), the ground might be -75°C.
In both cases, your dome—which we want to keep at a "Texas-like" **+21
*** I took the capture here, before Gemini was finished cogitating ... we got enough (in my opinion) to deliver to the forum.***
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Its been quite awhile since I posted the rovers and lander information to this topic Mars weather reporting
As GW noted possibly part of the reason that the mole failed to reach depth.
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Memory fails with age. I confused Insight with its subsurface "mole" probe, with Phoenix, which really did land near the polar ice cap. Phoenix was not equipped to measure subsurface temperatures. Insight was, but landed close to the equator. The "mole" probe on Insight did not work "as advertised". Even so, I am now guessing the AI might be closer to "right" than I was. Subsurface below 2 m might well be -50 C, over much of Mars.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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