A Dream of Discovering Alien Life Finds New Hope

A decade ago at an astronomy conference, Lisa Kaltenegger had a dream that woke her up a bit. She was holding a terrible cup of coffee because she had waited in line and it was warm in her hands. Bill Borucki moved towards her.

She prepared to tell him not to drink coffee. Borucki, the head of NASA's mission to find planets around other stars, had something else to talk about. The first two Earth-size exoplanets had a good chance of having liquid water. The strange new worlds that everyone at the conference had imagined at least once were these. Kaltenegger would confirm that the planets might be wet.

Kaltenegger began running new climate models before the conference was over, incorporating basic facts like the planets' diameter and the star's glow. Her final answer was a yes. It's possible that the planets are suitable for life and even for liquid water, encased in endless oceans without a single rocky outcrop poking above the waves. She needed more advanced observations to be certain.

Kaltenegger is the world's leading computer modeler. She was called on to play the role of Cosmic Home Inspector when NASA's TESS discovered its first rocky, temperate worlds. She was contacted by the survey to help understand a planet that is close to its star. The analysis uploaded as a preprint in September shows that the water could be in the process of steaming away like sauna vapor, as any seas of Venus did long ago and as Earth's own oceans will begin to do in the near future. Telescope observations should be able to tell within a few years if that is happening, which will help reveal our own planet's future.

Kaltenegger uses the strange life and geology found on Earth to create a more systematic set of expectations about what might be possible elsewhere. She told me during a recent visit to Cornell University that she was trying to do the basics.

The search for alien life is entering a new phase. Most of the time, the best chance of finding life in the universe is to detect biosignature gases in the atmosphere of planets. The kind of measurement needed to make that kind of detection has strained the capabilities of the most advanced observatories. With the first few months of observations, a discovery has become possible.

The new SPECULOOS-2c is one of a few rocky worlds that the space telescope will scrutinize over the next few years in order to see if they are suitable for life. Some of these planets may be dripping with liquid water, and at least one of them should have atmospheres. If biospheres bloom easily from Earth-like worlds, the telescope can detect odd ratios of carbon dioxide, oxygen and methane. Astronomers might be tempted to attribute the mix to the presence of an alien environment.

A small group of Kaltenegger's peers will need to find biosignatures. She and her colleagues must model a planet's possible interplay of starlight, rock and air accurately to be sure that nothing else could explain the presence of a particular atmospheric gas. The analysis must navigate between a Scylla and Charybdis to avoid both false negatives and false positives.

The consequences of getting it wrong are serious. Unlike most scientific endeavors, the search for signs of extraterrestrial life happens under an unavoidable spotlight, and in an information environment where any scientist crying "life!" warps the fabric of funding, attention and public trust. Kaltenegger had a seat in the front row.

She faces another pressure, one I intended to pose delicately but ended up blurting out just an hour after meeting her. At the beginning of the era of exoplanets, she and her colleagues started their careers. They are racing to find life on one before they die.

Planetary Dreamers

After the 1995 discovery of the first exoplanet, the search for biosignatures began. Planet-hunting quickly became a race for attention. Senior astronomer doubted that the subfield could deliver much more than a single measurement of a few unique planets. Sara Seager is an astronomer at the Massachusetts Institute of Technology. enclaves of like minded researchers began gathering at workshops to explore open sky's worth of new questions Seager was a graduate student at the time.

When the first giant exoplanets were announced, Kaltenegger was a freshman. She grew up in a small town in Austria with her parents who supported her interests in math, physics and languages, and the town librarians knew her so well they would give her the new books they hadn't yet categorized. She said that everything was possible when she was a child. She was drawn to the quest for a new world. Seager, who met Kaltenegger at a summer school program in 1997, now praises the boldness that led an undergrad to join a subfield that was still fringe. It wasn't just a coincidence that Seager was there at the beginning. Kaltenegger invited herself to an observatory on the Canary Islands after securing funding from the European Union.

The space agencies were involved. In 1996, a NASA administrator, Dan Goldin, publicized a plan that would have sprinted straight from the discovery of the first gas giant exoplanets. His plan called for massive space-based observatories, dubbed Terrestrial Planet Finders, that could take detailed spectroscopic measures of alien Earths, breaking their light into its component colors to understand their chemical makeup.

Goldin wanted pictures of planets. Our world was reduced to a pale blue dot in 1990 because of a photo taken by the NASA probe. What if there was a blue dot in the dark?

The European Space Agency's version of a Earth twin-scouting, life- finding mission was called Darwin. Kaltenegger got the job after applying. She asked if she could help if she lived in a time when she could figure out if we were alone in the universe. I would like to have done that in the past. She was tasked with considering the mission's design tradeoffs and drafting a list of stars that Darwin's fleet of telescopes should look for.

The visions of grand alien-hunting telescopes on both sides of the Atlantic fell away in the 2000s. In 2007, Darwin studies didn't go well. The sagging development schedule was one of the reasons. Astronomers had no idea how many stars have rocky planets with the possibility of a stable climate.

The fraction was revealed by the Kepler space telescope, which went on to find thousands of exoplanets. There are a lot of places to point out a Terrestrial Planet Finder mission.

Astrobiologists have scaled back their ambitions since the launch of Kepler. A rocky planet next to a brighter star is a challenge compared to taking a picture of a firefly. There is a cheaper way to go.

The alternative method was dreamed up in 2000 by Seager and the Harvard astronomer. The diminution in the starlight is caused by planets that transit in front of their star as seen from Earth. There is a lot of information in these transits. Some of the starlight shines through the ring of atmosphere around the planet and some of the light is absorbed by the atmosphere. The high-altitude chemistry is revealed by artful analysis. The Hubble Space Telescope was the first to use this technique, and it has since used it on dozens of targets.

The universe needs to give up some Earth-like worlds to look at.

There were lots of overcooked Jupiters and undersize Neptunes around other stars, but rocky planets with the potential for liquid water were hard to find. The mid-2010s saw the emergence of Earth-size worlds, like the pair Kaltenegger and Borucki. It was too far away for a follow-up study to be done. Astronomers discovered in 2016 that the nearest star to Earth has a potentially Earth-size planet. That planet doesn't have a transit system.

A qualification was added by Kaltenegger in 2009, when she was at Harvard and shaping the field. They wondered what it would take for an alien civilization to detect biosignature gases on Earth, a planet with a relatively tight blanket of atmosphere. Astronomers needed to observe hundreds or even thousands of transits in order to get any statistical certainty, because a telescope like the JWST would only see tiny signals from atmospheric gases. Astronomers began to look for Earths in close proximity of dimmer red dwarf stars, where atmospheric signals will be less drowned out by starlight.

The universe made its way through. Astronomers discovered seven rocky planets around a red dwarf star. The backup system was the SPECULOOS-2. The stars are not far away. They're not bright and not red. There are multiple rocky planets that are transiting. The JWST is up and running better than anticipated. The next five years will be spent looking at these messy globes of rock and chemicals. For theoreticians like Kaltenegger who went from dreaming of alternate Earths to making predictions about their atmospheric chemistry, decades of anticipation have passed.

Glowing Alien Lady

Kaltenegger's office was frozen in time for over two years. The first came the flu and then a break. She was back in August and she was working on a list of ideas that would make sense in a Star Trek series. Gata and SETI. The ocean is dark. The air is ozone. There is land The oceans are shallow. Are you talking about iron? She struck through the topics of the papers she has published.

Kaltenegger ran her first lab while she was in Germany and became the founding director of the Carl Sagan Institute. The head of the astronomy department at Cornell sent her an email asking if she wanted to talk about important opportunities. It is an event for women in science. You get too many of those invites. Lunine was trying to find a new professor. Kaltenegger said she would prefer to work at an institute focused on Astrobiology. He said to lead one here.

A few days ago, we sat in a garden near the institute, surrounded by flowers. A little bird hopped up a tree trunk, a cicada buzzed, and the lawn mower moved closer and closer as the sun set. It was obvious that this was a world of people.

Astronomers trust Kaltenegger's imagination when planning a $10 billion space telescope, and the more poetic kind when it comes to stirring public audiences. This scene looked like it to her.

She looked at something. Most of the organisms that perform photosynthesis are green. They were able to take advantage of the yellow sun's visible-light radiation by using pigments that snatch up blue and red light. Plants that are greedy for light might take on darker colors. She said that if she wanted to, she would have to sit under a red sun. The leaves are purple.

Kaltenegger has had a nagging doubt about her work on the Darwin mission since the early 2000s.

The goal was to compare the spectrum from rocky planets to what the Earth would look like from far away. Kaltenegger objected to the idea that Earth had no oxygen for the first 2 billion years. Oxygen took a billion years to build up. The highest concentration of this biosignature was in the late Cretaceous Period, when birds chased giant insects through the sky.

Kaltenegger feared that the big planet-finding missions could miss a living world if they didn't have a theoretical model for how Earth's own spectrum has changed. She needed to imagine that Earth would evolve through time. One of the first global climate models was adapted by her to include references to the 1970s magnetic tape era. Kaltenegger developed this code into a tool that can analyze not only Earth through time but also alien scenarios.

On the day after our conversation in the garden, I sat in the office next to Kaltenegger's and looked over the shoulder of Rebecca Payne as we looked at the text on a black background. She wants to fall out of her head if she doesn't go with a black color scheme.

Payne and her colleagues give their software basic facts about a planet, such as its distance from the sun and type of star. They run their models to see how the atmosphere would change over time. They were able to see virtual chemicals being bathed in virtual starlight rise, fall and destroy each other through simulations. The software popped out a table after the atmosphere settled into an equilibrium. Payne gestured towards the screen. She showed her guess at the new planet's temperature and chemistry by flicking her mouse over the rows. She and her colleagues were able to identify compounds that could be seen by the JWST.

Many of Kaltenegger's papers follow a similar pattern. She wants to gather up what we know of Earth's richness in her theoretical palm, then spin it like a basketball. We could rewound it in time. Imagine if an alien Earth had different geology. There is a different atmosphere. Is it an all- ocean surface? It could be a red sun or a white dwarf.

If a volcanic eruption like the 1991 Mount Pinatubo eruption occurs on an exoplanet, the then-upcoming JWST should be able to infer the presence of gases. It could identify worlds ruled by sulfur released by volcanoes and then broken down by starlight, rather than by the cycling of carbon between the surface and atmosphere. Climate cycles matter because they are part of the larger physics of planets. There is a lot of cake to eat and biosignatures are just sitting there as the cherry on top of the cake.

Over the last decade, Kaltenegger has scoured the Earth to assemble a public database of strange spectrum. Her database could provide the key to figuring out what the wiggle is.

Kaltenegger was enamored with the multicolored slicks on the surface of hot ponds during his visit to the park. She and her colleagues cultivated 137 different types ofbacteria in petri dishes and published their results. Lynn Rothschild, a synthetic Biologist at NASA's Ames Research Center, said that there is probably not a color in the rainbow that you can't find on Earth. Kaltenegger's group isolated 80 cold-loving microbes similar to what might evolve on an ice planet and published a reference database of these data this March.

It's possible that other worlds are biofluorescent. Corals protect themselves from the harmful rays of the sun by absorbing them and emitting them as visible light. Kaltenegger believes that alien life could evolve in red dwarf star systems because they are bathed in ultraviolet radiation. She has been called that glowing alien lady. A colleague and a new graduate student will soon start melting rocks.

Kaltenegger has experienced both opportunities andignities as her publication list has grown. When she was filming an IMAX short in Hawaii on the search for life, producers decided to dress her in shorts to match their idea of a scientist, so she had to cover her mosquito bites.

She is an ebullient, warming presence within a tight-knit field. She makes her fingers move through the air as she talks. Rothschild said that she signed every text to him. There are no other colleagues who do that.

First Dots on the Map

The first biosignatures will be small and ambiguous. Some claims have been made.

In the fall of 2020, there was a case study that was very important. A team including Seager announced that they had spotted an unusual compound called phosphine in the upper atmosphere of Venus. phosphine is produced by organisms. The analysis suggested that the abiotic processes that can make the compound weren't likely to happen on Venus. Tiny floating Venusian organisms were seen as a plausible explanation. The New York Times had a question about life on Venus.

Groups formed opposing camps outside. VictoriaMeadows, an exoplanet atmosphere modeler at the University of Washington who uses a similar approach to Kaltenegger's, reanalyzed the Venus data and found that the phosphine signal was not real. Lunine argued that even if phosphine is present, it could come from geological sources.

Kaltenegger believes in the validity of the critiques. She thinks that the phosphine saga shows a feedback loop between science and funding. NASA was in the final stages of choosing between four small solar system missions, two of which were Venus bound. Two people were chosen by NASA to fly. Kaltenegger said that the phosphine study was a good way to get missions approved to Venus. The sarcastic take was taken. The timing of the paper was a coincidence, according to the lead author of the phosphine study.

The next phase in the hunt for exoplanet biosignatures depends on what is revealed about the TRAPPIST-1 planets. It's unlikely that they'll see biosignatures in their skies. The Earth- and Venus-based models predict the ratios of carbon dioxide and water. It would be confirmed that modelers have a good handle on which cycles matter in the universe. Researchers would be helped by seeing something more unexpected.

There is a chance that these planets don't have atmospheres at all. TRAPPIST-1 is a red dwarf star that emits solar flares. Kaltenegger believes that the planets should replenish their skies.

By the second half of this decade, data from multiple planet transits will have piled up, enough for astronomer to look for chemistry on these worlds, as well as examine how given molecule wax and wane from season to season. By that time, the data could be added. The largest telescope in the world, the Extremely Large Telescope in Chile, is going to open basin-size mirrors in 2027. They should be able to study planets outside of transit, because they will be sensitive to different wavelength of light.

One of those giant space-based Terrestrial Planet Finders is what biosignature hunters want. When the National Academy of Sciences released the decadal survey, which summarizes the astronomy community's ideas of what NASA should prioritize, they effectively deferred a major push on the issue to the 2030s.

I have been pondering if it is us or not. Kaltenegger made a statement. If it isn't our generation, what should we do? She thinks that the most likely person to lead such a mission is a graduate student.

She said that her group of early exoplanet scientists have always been dreamer. Science has been an intergenerational activity for a long time.

She sat in her office and drew a scene. A far-future voyager walks up the bridge of a departing spaceship to reach a new world. Kaltenegger is certain she won't be on the ship herself, but she sees them on the old star chart. Candidate living planets would be marked on the antique map. It was brought along for sentimental reasons. I would like to be the one who put the first dots on the map.