Echoes of Jezero, with Joel Hurowitz
Reverberations from the discovery of [what seems to be] ancient life on Mars.
“The thing that sets Mars apart is that it is the one planet that is enough like Earth that you can imagine life possibly once having taken hold there.”
- Carl Sagan
Jezero Crater doesn't drop as low in elevation compared to most other calderas on Mars’ surface, but it’s the landing spot for what could be one of our biggest cosmic revelations made to date.
The 28 mile wide crater is accentuated with veins of channels that would have surely carried water into it, signifying that it had once been a lake.
In a wetter and denser Mars of 3.5 billion years past, sunlight would glint across its open water, 250 meters deep in some places, rippled with shallow deltas and winding inlets carrying rich sediment down into the basin.
Likely caused by a mile-wide meteor that drifted in from the asteroid belt between Mars and Jupiter, the crater shows off its excavated rock and melted crust as a cosmic battle scar from the 3.9 billion year old impact.
At the height of its activity, Cheyava Falls would have been a roaring cascade where one of these rivers descended into the crater—scientists named it after the Cheyava waterfall in Arizona’s Grand Canyon, which resembles the imagined Martian cataract.
The lake itself pulsated with activity through the variable eons of the Martian planet. At the most energetic of times, waters carrying sandy muds and rocks gushed through the inlets to fill the crater; at calmer periods, the inlets were backed up amidst a low energetic aqueous environment, allowing for the deposition of sediments.
The Crater would have hosted the lake for millions of years before drying out for millions more, becoming idle and thus existentially meaningless until a rover named Perserverance would land in 2021 (human time) to spur it back into any kind of relevance.
NASA has finally confirmed an idea that was increasingly lurking about in the collective patchwork of assumption (which exists only one step below the collective understanding): that Mars once supported ancient biology.
While pointing at the screen of the living room TV to a low-res image of boring speckled rock, I tried to explain to my daughter what the awkward NASA scientists were trying to tell us: that the sands and rocks on Mars seem to show signs of… “POOP” she guessed, probably just to say poop.
But she was right.
“These minerals are often the byproduct of microbial metabolisms that are consuming organic matter and making these minerals as a result of those reactions.”
- Joel Hurowitz
But this is about more than ancient Martian microbial poop.
This is about how life has finally landed on Mars, only not in the literal way that we had been anticipating.
It’s about how something materializes out of the realm of the idealistic and roots itself into our observable and measurable reality - into our sphere of working truth.
For the first time in the entirety of the human epoch, life exists on Mars because it has now entered the domain of our collective understanding; we now know that Mars once supported some level of ancient existence.
And that changes things, maybe even more so than actually landing on the planet itself.
It wasn't long ago that we had watched the existence of Martian water slowly step out from the warm smoke of ephemeral wonder and into the cold light of scientific scrutiny.
And, cosmically speaking, it wasn’t long at all since we humbly realized that the universe isn’t orbiting around us.
But now, we’re able to overlay our understanding of biochemical compositions onto other planets and do what we do so well: pattern the environment around us.
Our discernment of the universe fractals outwards through space; life now exists on two planets that orbit one star in a humble solar system corkscrewing through a small habitable bit of space situated within a greater interstellar system travelling even faster through yet deeper space - also in a habitable cosmic void within a greater network of galactic assemblies that increasingly look just like the veins that once pulsated aqueous life into the Jezero Crater.
The reverberant meaning from all of this is just as significant as the biochemical signatures.
Below is an interview with the lead author of the paper that curated one of the most potent extra-terrestrial discoveries that we’ve ever made, Joel Hurowitz.
What evidence supports the idea that Jezero’s delta was fed by long-lived inflow, and how do you distinguish between brief floods versus sustained river systems?
Jezero's western and northern deltas are fed by inlet valleys (Neretva and Sava vallis, respectively), and there's an outflow valley as well (Pliva Vallis). This inflow-outflow relationship suggests that there was a period of time where water was entering and leaving the crater at the same rate, filling it to a steady-state level.
How long was this period of "lake full" conditions? I don't think we know. I'm sure there are estimates, but I suspect that they have significant uncertainty. We also know that there were periods of time when water was only transiently present.
For example, there are large boulder deposits atop the delta that appear to have been emplaced by short lived, energetic "bursts" of water entering the crater.
So, I think we can confidently say that Jezero was a dynamic environment, with periods of stable water fill in the crater, and periods where water was present more intermittently. But how long each of those intervals lasted is really hard to tell.
The lake itself is said to have existed for perhaps hundreds of thousands of years—a blink compared to Earth’s oceans. How does that brevity shape your sense of the fragility or resilience of habitable environments?
That's a really cool question. I think that IF the material in the Bright Angel turns out to be more than a potential biosignature, then this tells us that life is incredibly resilient and can get started under (and survive) a wider range of dynamic (and possibly hostile) conditions than we would have imagined before.
What do the textures and layering revealed in Perseverance’s imaging suggest about seasonal or climatic variability during Jezero’s lake phase?
There's some really interesting information on this topic contained in the analyses we've conducted and the samples we've collected. There's a lot of detailed work left to be done on this front, but one interesting thing is that the visible contrasts in the "rustiness" of differing layers of sedimentary rock in Jezero seem to suggest that the ability of the atmosphere to cause the oxidation reactions that cause iron to turn to rust was variable in time.
If Perseverance were to confirm unambiguous signs of biosignatures, what next steps—analytical or exploratory—would be most critical in confirming life’s past presence on Mars?
I think it is important to say that this really is about as far as the rover's scientific payload was designed to get us - to the point of finding compelling potential biosignatures, and collecting samples of the rocks that contain them so that we can pass them off to a Mars Sample Return mission.
For this specific detection described in our Nature paper, additional laboratory experiments on Earth and field work in analogous depositional settings on Earth are likely to provide us with important lessons for how to distinguish between biological and non-biological hypotheses.
The lessons we learn could be applied to the analysis of the sample we collected from the Bright Angel formation if it were returned to Earth. It is the return of this sample (and its companions) that is critical to the ultimate determination.
I suspect that among the first measurements we would make on this sample would be isotopic analyses of the iron, sulfur and carbon in the rock to determine whether the isotopic compositions showed any signal of the influence of biological activity.
You get to choose the next landing spot for the next probe - where are you landing and why?
That's an easy one - right back in Jezero crater with a Sample Retrieval Lander!
What does this all mean for you, personally - on either an existential or philosophical or maybe even just intellectual level?
For me, this feels like a real fulfillment - I have been working on Mars rover missions since 2004 when I was a grad student on the Spirit and Opportunity missions, "Following the Water" on Mars. Then I got to work on the Curiosity rover mission when I was at JPL, "Exploring Habitable Environments" with that mission. And now, as a member of the Perseverance team, I get to play a role taking the final step leading up to Mars Sample Return by "Seeking the Signs of Life" on Mars.
It has been such a privilege to be part of this successful, multi-decade strategy to improve our knowledge of Mars and understand whether or not it could have hosted life.
With Mars Sample Return, we may get all the way to answering that question, and it is an honor to have been able to play a part in it.
