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One of the most important reasons we go to space聽 is to know our own planet better.

Today I'm going to tell you about an orbiting facility聽 that literally watches Earth's biosphere breath and grow and die with incredible聽 resolution.

I'll talk about its profound existential and economic importance, and聽 about why it's in danger of being lost.

Hey Everybody before we get started I wanted聽 to let you know that August 8th was the 94th birthday of Sir Roger Penrose.

The work of Sir聽 Roger and his famous Penrose diagram have been an important part of Space Time and to celebrate we聽 have a limited edition Penrose diagram pin.

This pin is based off of our original design of the聽 Penrose diagram that is actually featured in the Planetarium at American Museum of Natural History.聽 The pin will only be available via pre-sale through mid September.

We’re also offering 10% off  for the first 24 hours as well as 5% off all our penrose inspired merch.

There’s links to the merch  store in the description.

Now on to the episode.

Look again at that dot.

That's here.聽 That's home.

That's us.

In 1990, Carl Sagan asked NASA to turn the Voyager I聽 spacecraft around for one last snapshot of its planet of origin before it began its聽 long, cold journey towards interstellar space.

The result was this image, dubbed聽 the Pale Blue Dot, and if you haven’t heard Sagan’s full speech and want existential  shivers, there’s a link in the description.

We normally think of astrophysics聽 as an outward-looking science, but one of the most important reasons to look聽 outwards is to better understand ourselves.

And one of the most important reasons to聽 build telescopes in space is to keep a careful eye on the most precious planet in聽 the universe—our own Earth.

Historically, a lot of this good work has fallen to聽 NASA because no one else has the same level of joint expertise and experience in聽 both rocket science and planetary science.

One of NASA’s Earth-watching programs is the  Orbiting Carbon Observatory; the OCO program, which is dedicated to high-sensitivity, high聽 resolution observations of atmospheric carbon dioxide.

The program stumbled at first; OCO-1聽 never quite made it to orbit after its launch vehicle faring failed to separate.

That was聽 in 2009.

OCO-2 launched successfully in 2014, and with the spare parts from both 1 and 2聽 NASA managed to assemble a third instrument, OCO-3, which now resides on the聽 International Space Station.

In fact, OCO-3 wouldn’t exist if OCO-1  hadn’t failed, so, silver lining?

From now on, if I’m referring to both OCO-2  and 3 I’ll say OCO.

Despite the rocky start, OCO is performing quite a bit聽 better than expected.

In fact, it has a pretty remarkable ability that聽 wasn’t even planned.

I’ll come back to that.

First the specs.

OCO-2 is part of聽 the A-train—a close-flying chain of Earth-observing satellites for cross-checks and聽 combined science.

This satellite constellation flies a near-polar, 100-ish-minute orbit at聽 around 700 km.

The orbit is sun-synchronous, which means the path maintains its orientation聽 relative to the Sun, and that helps with the consistency of OCO-2’s measurements.

OCO-3, being  on the ISS, has lower, faster orbit.

Together, the OCOs produce high-resolution maps聽 of CO2 density across the planet.

https://ocov2.jpl.nasa.gov/galleries/spacecraft/#images-7 So how do they do this?

When sunlight reflects off Earth and passes back through the聽 atmosphere, each type of air molecule absorbs a particular set of wavelengths, revealing聽 absorption lines—a sort of barcode—when that light is broken into a spectrum.

OCO captures聽 the spectrum around two of the infrared CO₂ and around one of the oxygen lines.

The聽 depth of the lines is sensitive to the number of molecules while their width carries聽 information about pressure and temperature.

The oxygen line is useful for things like聽 path length and geometry.

With these data, the OCO pipeline applies sophisticated physics聽 like radiative transfer models to solve an inverse problem: “What CO₂ profile best explains  these spectra given the viewing geometry?” The result is a stunningly precise average density聽 of CO₂ along the column of the observation.

These measurements allow OCO to map CO₂  column density with a spatial resolution of a few kilometers and a sensitivity of聽 around a part per million.

This reveals the sources and sinks of atmospheric carbon聽 down to neighbourhood-level precision.

And it does this frequently enough to see聽 seasonal swings and year-to-year anomalies.

Combined with other atmospheric data,聽 OCO’s observations are used to build highly detailed models of the circulation of聽 CO2 around the globe.

This is important for knowing not just where CO2 is being聽 produced, but also where it ends up.

When OCO-2 launched, it executed its intended聽 functions exactly as planned.

And then it revealed an ability that no one expected.

It聽 could literally see plants breathing—-the faint glow emitted by plants during photosynthesis.聽 When chlorophyll is energized by incoming light, most goes to fueling the plant, but some聽 of that energy is quickly reemitted as infrared light.

Sunlight that is simply聽 reflected off the Earth’s surface retains the dark absorption lines of the incoming聽 sunlight.

But this photosynthetic glow partially fills in those bands, allowing OCO聽 to measure the “solar induced fluorescence”.

In this way we can now measure when and聽 how efficiently plants are breathing.

https://ocov2.jpl.nasa.gov/galleries/videos/#images-5 This has broad and incredibly powerful聽 applications.

Combined with other data, OCO allows us to watch the natural daily and聽 seasonal shifts in plant metabolism across the globe.

It also allows us to monitor the聽 health of critical photosynthesizing systems, from forests to savannas to聽 ocean algae to agriculture.

https://www.youtube.com/watch?v=XiwHUpcOwAk For example, OCO facilitates the prediction聽 and assessment of oncoming droughts in a way that was previously impossible.

A plant’s  photosynthesis efficiency drops very quickly in response to stress, for example due to the聽 heat and dryness that precedes a drought.

And these changes happen before there’s any visible  change in the plantlife.

Because OCO can monitor photosynthesis, it can track how vegetation聽 is responding to harsh conditions.

In fact, it’s the response of vegetation often  worsens and even causes the drought; as temperatures rise before the drought,聽 plants actually become more productive and in the process draw water down into聽 the ground.

When temperatures then spike, soil moisture has become dangerously low,聽 leading to the onset of flash drought in mere days.

SIF monitoring is our best tool for聽 catching this dangerous cycle before it happens.

It’s not just security from catastrophic  failure.

OCO also enables us to perform highly nuanced measurements of plant metabolism,聽 which lets us assess stress, forecast growth, and generally do global vegetation health聽 monitoring.

Arguably the most important application of this is in crop yields.

OCO’s SIF  data has been used to predict US corn-belt crop yields down to the county level.

It can do this聽 with better accuracy than current USDA methods, and much sooner.

It’s hard to  overstate the importance of this.

Besides the obvious fact that we have a聽 lot of people to feed, agriculture is an enormous part of the economy.

In the US,聽 agriculture and its dependent industries represent several hundred billion to 1.5聽 trillion dollars in economic activity, depending on how you count, and employ 10s of聽 millions of people.

More reliable crop yield prediction is ultimately important for聽 everyone, and this benefit is very much weighted to rural communities.

And farmers聽 in particular.

For example, they often rely on futures contracts—payments based on crop yield  predictions—to finance their efforts.

Better yield predictions means better financial security聽 for farmers and food security for everyone.

A primary goal of the OCO program was to track聽 CO₂ for the purpose of climate change modeling and mitigation.

However, the program is way聽 broader than this and would be a no-brainer even without the climate factor.

OCO can pinpoint聽 carbon sources and plant metabolic activity, which can be a powerful strategic tool, both聽 for geopolitical and humanitarian reasons.

For example, it enables us to keep聽 track of carbon-intensive activity like urban or industrial development, whether of聽 friends or rivals, with remarkable resolution.

It could literally see a single new powerplant聽 or large factory, no matter how well hidden.

It can also monitor changes in global crop聽 health, enabling the prediction of crop failure and the potential resulting famines聽 and refugee crises.

Regardless of what you think we should do about such things,聽 it’s always better to know in advance.

And heaven forbid a major conflict breaks out聽 between world powers … but if that happens it seems prudent to retain the ability to sense聽 new industrial buildup, shifts in land use, supply chains, etc; efforts that might聽 otherwise be screened from direct observation.

It’s amazing that we have this capability.

Currently both OCO-2 and 3 are in perfect working order and could run well into the 2030s聽 and further.

They were a big investment to build, at around 750 million, however the聽 ongoing cost is relatively cheap, with a combined budget of 16.4聽 million proposed for this year—a tiny fraction of the potential returns聽 for their benefit to agriculture alone, to say nothing of the much larger risk-cost聽 analysis against existential concerns like environmental and food security, and even defence聽 concerns.

Let me reiterate, no nation other than the US nor private organization has anything聽 approaching the capabilities of the OCO program.

Nonetheless, OCO was zeroed out in the White聽 House’s budget request for NASA this year, 2025.

NASA’s OCO team has been directed to plan  for a mission close-out.

That means switching off OCO-3 and de-orbiting OCO-2—burning it up in the  atmosphere.

This still needs to be approved by Congress, so it’s not a done deal.

But there’s a  fair chance that all of these amazing capabilities you just learned about will literally go up in聽 flames.

It’s not too late, but it will be soon.

Now, it IS possible to build and launch new聽 facilities.

There was a plan to build GeoCarb - a satellite with similar sensitivities to sit in聽 geostationary over the Americas.

It would have been a great complement to OCO because it would聽 increase resolution in NASA’s home continent while OCO continues its global surveillance.聽 The project was canceled due to cost overruns, so currently there are no plans for new聽 OCO-like facilities.

If we ever do replace OCO, we’d be much, much better off replacing  it while it’s still running.

OCO now has a decade-long baseline of global monitoring.聽 Shutting that down means breaking a continuous time series that future satellites聽 will need for cross-calibration and continuity.

From a data analysis perspective,聽 that cross-calibration is incredibly important, to say nothing of the importance of聽 continuity from a security perspective.

Sagan usually said it best.

Our planet is a lonely聽 speck in the great enveloping cosmic dark.

In our obscurity, in all this vastness, there is no hint聽 that help will come from elsewhere to save us from ourselves.

NASA’s oft-stated prime directive  is to explore the unknown in air and space, innovate for the benefit of humanity, and聽 inspire the world through discovery.

The image of the Earth as a lonely blue speck, barely聽 a pixel across, surrounded by the vast emptiness of space certainly does that.

So does OCO’s  exquisitely resolved surveillance of a living, breathing planetary biosphere, our only known聽 refuge in a vast and inhospitable spacetime.

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