Carl Sagan Institute

Someday soon, we may be able to say that out of 70 habitable zone planets, out of 6000 found, out of hundreds of billions that surely exist in the Milky Way… there is one more corner of the universe that knows itself.

Recent papers from Carl Sagan Institute researchers and exoplanet scientists worldwide (such as studies of TRAPPIST-1 e!) have brought us one step closer to detecting an atmosphere around an Earth-like, potentially habitable world.

Around 70 exoplanets with rocky surfaces in the habitable zone (with artist's depiction of TRAPPIST-1 planets, four of which orbit within the broadest zone that may allow for liquid water on their surface) *** Stats from the NASA Exoplanet Archive and from under-review habitable zone paper from CSI researchers.

The star will have to treat its planet kindly, lest it strip away the planet’s atmosphere, or heat the planet so intensely it becomes a “lava world.” Even if the planet avoids these extremes and organisms manage to thrive, the world those organisms call home may look quite different from ours.

87 exoplanets discovered through direct imaging (with real image of b Centauri b, which has 10x the mass of Jupiter but appears small with current imaging technology) *** Stats from the NASA Exoplanet Archive.

Some of these planets—the more sedate, less extreme ones—have a chance at hosting life. They’ll need to be not too far, not too close, but just the right distance from their host star: in the “Goldilocks” or “habitable” zone where liquid water could exist on a planet's surface.

1171 exoplanets with masses likely larger than Jupiter (with artist's depiction of Kepler-7 b, a hot Jupiter—named for size rather than visual similarity, as it is far too hot to have many bands of clouds) *** Stats from the NASA Exoplanet Archive.

There is a planet that takes 49 minutes to orbit its pulsar, in a pirouette too tight to ever allow for life; there are red-hot planets where gems may fall from clouds of metal and deep blue dots where glass may rain sideways.

552 exoplanets with more than one sun in their skies (with artist's impression of Proxima Centauri b, closest planet to Earth, and in a triple-star system). *** Stats from the NASA Exoplanet Archive. Note: 552 exoplanets are in multiple-star systems—though some likely orbit very far from their stars, so the “suns” in their skies wouldn’t be very large!

There are exoplanets that see two Suns in their skies, even three Suns; there are “rogue planets,” likely ejected from the disks of young stars, that shoot through an endless night; there is a planet that takes one million years to orbit its star;

600 exoplanets. The strange worlds we've found so far—and what we still don't know. ***Artist's depiction by Pablo Carlo Budassi (Celestialobjects)

6000 exoplanets. 🔭

We’ve found worlds orbiting all sorts of stars, from tiny, slow-burning reds to fast-living blue-whites to middle-of-the-road, prime-of-their-life yellows like our own...

Just over five hours until Cornell's Alpha CubeSat launches on its way to the International Space Station! Learn more about the satellite, its lightsail, and its holograms at alphacubesat.cornell.edu, and tune into the livestream of the rocket launch there!

Congratulations to project lead/CSI engineer Josh Umanksy-Castro, project advisor/CSI fellow Mason Peck, and to all the Cornell students who poured their heart into this mission!

The NG-23 ISS commercial resupply mission launch is scheduled for Sunday 9/14 at 6:11pm EST with a backup opportunity on Monday 9/15 at 5:49pm. Alpha will ride to the International Space Station, then patiently wait for its turn to launch off the station and into space in mid-November.

A large group of Cornell students, alumni, family and friends are traveling to Cape Canaveral this weekend to view the launch! We invite you to join us by tuning into the livestream, linked at alphacubesat.cornell.edu.

After 9 years and over 100 students, Cornell's Alpha CubeSat mission is launching to space TOMORROW! This small cube-shaped satellite will test the deployment of the first-ever free-flying light sail in low Earth orbit, a stepping stone towards laser sailing to the stars. 🔭

alphacubesat.cornell.edu

From NASA / Joseph Olmsted: "The Earth-size exoplanet TRAPPIST-1 e, depicted at the lower right, is silhouetted as it passes in front of its flaring host star in this artist’s concept of the TRAPPIST-1 system."

For now, CSI researchers will construct better and better models for TRAPPIST-1 e's busy host star, until the day we can fully disentangle little planets from jumpy starlight!

Read more: carlsaganinstitute.cornell.edu/news/there-w...
(Papers also linked in article)!

From the second of the two research papers (linked at end of thread): nitrogen-rich (like Earth) atmospheric models, and possible signatures of gases like CH4 (methane).

But even noisy data lets us rule out a few possibilities—models that would cause much larger dips than the ones in the graph. TRAPPIST-1 e is unlikely to have a huge hydrogen atmosphere, nor a huge carbon dioxide atmosphere like Venus, which traps enough heat to melt lead.

Graph of host star size and light different planets receive. TRAPPIST-1 e orbits a tiny, very active red dwarf star, and receives less light than Earth.

Artist's impression of a planet and its moon orbiting an active red dwarf star. Credit: David A. Aguilar / NASA

TRAPPIST-1 e orbits a small red dwarf star, which tend to have a lot more stellar activity than our own Sun. The activity of the star might be interfering with what we see.

TRAPPIST-1 e: bare rock or cloudy world? The data on the graph could conceivably fit an "airless" scenario or an "Earth-like atmosphere" scenario.

As is typical for tiny planets, noise makes our measurements uncertain, so the white error bars overlap with two models: a possibly Earth-like atmosphere in blue and a bare, airless world in orange. CSI researchers Nikole Lewis, Elijah Mullens, and Ryan Challener say it could go either way.

TRAPPIST-1 e: bare rock or cloudy world? The data on the graph could conceivably fit an "airless" scenario or an "Earth-like atmosphere" scenario.

What do you see in the light from planet TRAPPIST-1 e?

Signs of alien life? Not yet...

Take a look for yourself at real data in the James Webb Space Telescope graph, and read more about it below! 🔭

Beebe Lake on Cornell's campus, surrounded by deep green trees.

Of course, higher levels of oxygen will also make it easier to detect! For this reason, among many others… it’s helpful not to deforest your planet.

(Stay tuned for more CSI research spotlights!)

If oxygen and combustion are requirements for life, then we know the limits: oxygen needs to comprise 16% of the atmosphere in order for fires to start, but must stay beneath 35%, or else fires would burn uncontrollably. Beyond that, it’s hard to say what level of oxygen an alien planet might have.

We think it might be common, since the first organisms on a planet would likely be single-celled photosynthesizers, getting their energy from the environment before a full food chain evolved. Photosynthesis would produce lots of byproduct oxygen as these organisms spread across a planet.

It’s completely possible that alien life could follow different paths than ours. Is having a high amount of oxygen at some point in your planet’s past a requirement?

🦕 🦕 🦕 So those are the methods, and we know the results: we might have a shot at detecting oxygen and other gases, depending on the planet and using very powerful telescopes. But how helpful is this spectra for “alien dinosaurs,” anyway?

Payne & Kaltenegger's work can be used by future observers to answer whether oxygen, methane, and other biosignatures (signs of life) are detectable on a certain planet or with a certain telescope. This is represented visually by the silhouette of a green triceratops gazing through a blue telescope at the star Vega, in the constellation Lyra. The telescope is a trace of Fuertes Observatory's 102-year-old telescope, Irv, on Cornell's campus!

Payne & Kaltenegger don’t explore this final step with the “alien dinosaur” spectra, since their paper is meant to aid future observers who may have a certain planet or telescope in mind. The wavelengths you choose (and the noise levels you curse at) depend on the planet and the telescope.

Whenever we model spectra, it’s idealized: the perfect theoretical observation, without any noise to interfere with the data. The next step is to feed these “perfect spectra” into an algorithm that simulates noise for whichever telescope you want to use.

Scientists have developed software to simulate light from dozens of gases at once. The software combines all these emissions and absorptions into a single “spectrum” (plural “spectra”), showing the intensity of the signal at each and every wavelength of color our telescopes can detect.

A closer look at oxygen's "spectrum," or the intensity of light we'd receive in our telescope at different wavelengths. The left graph slightly differs from the right graph due to using a different input model (slightly different levels of oxygen over time). However, these models are still largely consistent with one another. Individual signals of oxygen and other gases are then combined into one complex model (the full "spectra").

The second step is to translate the amounts of gases (percentage of oxygen in the lower atmosphere, in the upper atmosphere, etc.) into the actual intensities of light that we’d receive in our telescope. Each gas has its own signal, since different elements emit or absorb different colors of light.

Graph of different models for CO2 and oxygen over time, with the birth of dinosaurs marked by a happy dinosaur drawing and their extinction by... a sad dinosaur and meteor. The different models vary, since estimates of the abundances of gases can be hard to determine. Payne & Kaltenegger used multiple models as inputs.

Here are the in-depth methods (or skip to 🦕 for unanswered questions)!

It takes a few steps to determine the how detectable oxygen is on ”alien dinosaur” planets. First, you need to choose a model for the levels of gases in the atmosphere over time. Billions of years of history are hard to predict!

Payne & Kaltenegger find that oxygen, ozone, and methane would be prominent in light from a dinosaur-era world. That makes these gases detectable—either to aliens, or to humans searching for ”alien dinosaurs”—but just how detectable they are depends on the quality of your telescope.

The types of life have changed over time, as have levels of oxygen, methane, and other molecules in the atmosphere. CSI researchers Payne & Kaltenegger chose to simulate the light of Earth’s atmosphere (its “spectra”) at a time when oxygen was higher than modern day: the age of the dinosaurs!

Life beyond Earth may look very different from us, flashing different colors or breathing different molecules. But Earth is the only example we can base our search on so far. The best way to gather more data, then, is to expand beyond our modern view—into Earth’s past.