NASA’s Perseverance rover found those pale rocks in Jezero crater. They are now changing what scientists thought they knew about the weather on Mars a long time ago and the water that used to be there. NASA’s Perseverance rover
A tropical Mars hidden in white rock
For years, the standard image of early Mars showed a cold world with short-lived lakes and streams, but it wasn’t often warm. New information from the Jezero crater shows that there was something more like a tropical episode in the distant past. standard image of
Perseverance has found rocks on the floor of the crater that are scattered and have an unusual light colour. Kaolinite, a white clay mineral that forms on Earth in hot, rainy areas where water deeply leaches soils, is a big part of their makeup. white clay mineral
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Kaolinite on Mars suggests that there was a lot of rain and a thick, active water cycle more than three billion years ago. thick active water
Kaolinite can be found on Earth in places like old tropical soils and volcanic areas that have been weathered down a lot. It takes a lot of water to make it, and it has to flow through rock for a long time. Finding the same mineral in Jezero suggests that Mars used to have a climate that was not only wetter, but also consistently warm and humid. old tropical soils
What Perseverance really measured
Since 2021, Perseverance has been roaming Jezero, looking at rocks in what used to be a 45-kilometer-wide lake. The pale pieces it found, which are sometimes called “float rocks,” don’t seem to be firmly attached to the bedrock below them. This suggests that they may have been moved from where they came from. pale pieces it
The rover’s tools, like SuperCam and Mastcam-Z, looked closely at the bright pieces. Their infrared spectra match the signature of kaolinite, which includes absorption bands that show how hydroxyl groups bond with aluminium. Chemical tests show that there is a lot of aluminium and titanium and very little iron. This is a pattern that geologists who study very weathered tropical soils on Earth are used to seeing. infrared spectra match
The Martian rock called “Chignik” has up to 1.4% titanium dioxide and very little iron. This is a sign that rainwater has been washing it away. Martian rock called
Titanium doesn’t move much in water on Earth, so it tends to build up in soils that have been washed by heavy rain for thousands of years. The fact that the Martian samples have very little iron in them suggests that dissolved iron was washed away when the samples were wet and dry again and again, leaving behind pale, bleached material. heavy rain for
Hints from Earth’s distant past
The research team looked at the Martian rocks and compared them to old soils on Earth to make sense of the Jezero data. They looked at: research team looked
- A paleosol from the Eocene era, 55 million years old, near San Diego, California; a paleosol from the Hekpoort area in South Africa, 2.2 billion years old;
Even though the Mars samples were from a different time and place, they were very similar to these old tropical and subtropical soils in terms of infrared spectra and bulk chemistry. That similarity backs up the idea that Mars used to have a lot of weathering on its surface, not just short, underground bursts of fluid flow. old tropical and
What kind of weather can make kaolinite on Mars?
Kaolinite doesn’t form in a storm that lasts a weekend. It keeps track of conditions over time. The chemistry in Jezero suggests that some parts of ancient Mars may have gotten more than 1,000 millimetres of rain each year, which is similar to what we see in temperate or subtropical areas on Earth today. storm that lasts
That means there is a strong water cycle, with water evaporating from lakes or seas, condensing in the air, and then falling back to the ground as rain. Temperatures had to be warm enough for liquid water to stay on the surface for long periods of time, at least during certain times of the year. strong water cycle
Mars probably had a lot more greenhouse gases in its atmosphere at one point, which would have kept heat trapped and water flowing. more greenhouse gases
Older models of Mars showed it as mostly frozen, with only short periods of melting caused by impacts or volcanic eruptions. This scenario doesn’t fit with those models. It is possible that the planet actually went through a “tropical” phase, but only in certain latitudes and for a short time in its history. Older models of
How did the white rocks make it to Jezero?
We now know what the rocks are like, but we still don’t know how they got there. Perseverance has not yet found any large, intact kaolinite outcrop in Jezero itself. The white pieces, on the other hand, look like they were scattered, like rubble left behind by something that happened a long time ago. white pieces on
Two main possibilities for where they came from
| Scenario | Mechanism | Evidence that supports |
|---|---|---|
| Transport by river | Old rivers brought kaolinite-rich sediments into Jezero Lake. | Orbital data show clay signatures along fossil river channels like Neretva Vallis. |
| Ejecta from the impact | A meteor hit the area and sent kaolinite-bearing rocks from nearby highlands into the crater. | Clusters of light breccia blocks and clay-rich areas far away may be where the source zones are. |
The CRISM instrument on the Mars Reconnaissance Orbiter has found a number of kaolinite-rich areas near the southwestern edge of Jezero, some of which are only a few kilometres from Perseverance’s path. There are other good targets farther away in Nili Planum, where magnesium-rich clays are on top of aluminum-rich clays. The layered sequences suggest that the Martian crust has changed a lot over a long period of time. Mars Reconnaissance Orbiter
What this means for the water that Mars is missing
Kaolinite not only keeps track of water that has already fallen, but it can also keep that water safe. The mineral structure has hydroxyl groups and tightly bound water that doesn’t leave until the temperature rises above about 450°C. Some Jezero samples still have a strong hydration band, which means they never got hotter than that point. strong hydration band
Molecules of ancient Martian water may be stored inside clays that have not been disturbed for billions of years. ancient Martian water
If kaolinite-rich areas are common on Mars, then a significant amount of the planet’s early atmospheric and surface water could still be in these quiet mineral reservoirs. Mars doesn’t have active plate tectonics like Earth does, so those clays can’t be recycled back into the mantle and the water can’t be released again. A lot of that water stays trapped once it is. quiet mineral reservoirs
This process may have had a quiet but important effect on the planet’s drying out. Solar radiation may have taken away some of the atmosphere from above, while chemical weathering and clay formation may have taken away water from the climate system from below. planet’s drying out
Habitability during Mars’s “tropical” period
The conditions that help kaolinite form—mildly acidic water, dissolved oxygen, and steady rainfall—are also good for microbes. Lakes that filled Jezero and the areas around it would have made stable, long-lasting homes with chemical gradients that living things could use for energy. mildly acidic water
These kinds of places make people hopeful that evidence of ancient life, if it ever existed on Mars, might be found in or around these bright clay-rich rocks. Organic molecules, microfossil textures, or isotopic patterns may be concealed at microscopic scales, awaiting accurate testing by laboratory instruments on Earth. evidence of ancient
Next, why sample return is important
Remote instruments can find minerals and guess their makeup, but they aren’t as sensitive as labs on Earth. There are many reasons why future missions to bring Perseverance’s samples back home will be very important: future missions to
- finding out exactly how much water and hydrogen isotopes are in the clays
- looking for weak organic compounds or complicated carbon structures
- determining exact ages of rock formation and alteration; testing models of early Martian climate with tangible, physical materials
These kinds of measurements would help us figure out if the “tropical” climate phase was a short, intense pulse or a long, slow chapter in Martian history. They would also show us how quickly the planet changed from a wet, thick-atmosphere planet to the dry, thin-atmosphere planet we see today. tropical climate phase
Important words and ideas that explain the results
If you don’t know much about planetary geology, a few ideas can help you understand these results. A “paleosol” is just an old soil that has turned into rock. Paleosols on Earth keep records of past climates, like how much rain and how hot it was. When rocks on Mars look like paleosols on Earth, it means that the weathering processes and, by extension, the environmental conditions are probably the same. old soil that
The “hydrological cycle” is another important term. This is the constant movement of water between the surface, the subsurface, and the atmosphere. There would be a strong cycle on early Mars that included evaporation from lakes, clouds forming, snow or rain falling, runoff into rivers and lakes, and infiltration into the ground. Kaolinite and other clay minerals are part of the long-term memory of that cycle, which shows how strong and long-lasting it used to be. constant movement of
Climate models of early Mars now have to meet stricter standards. They have to copy not only valley networks and old shorelines, but also the exact chemistry of deeply weathered clays. The Jezero data is making scientists rethink simulations that include thicker atmospheres with a lot of carbon dioxide, which may have been helped by hydrogen or methane. Scientists are looking into how long these warm spells could last and how quickly they would end as the atmosphere got thinner. Climate models of
These white rocks, which are sitting quietly in a dusty crater, are making scientists imagine a very different Mars: one with thick clouds, heavy rain, and soils that slowly turn white. This planet may have been much more like Earth’s moods than its frozen surface suggests today. thick clouds heavy
