Alien Earths

Searching for Habitable Worlds in Nearby Planetary Systems

where is the closest habitable world?

Does it orbit Proxima Centauri? Barnard’s Star? Or tau Ceti?

Our NASA-funded Alien Earths team integrates research results from fourteen multi-disciplinary projects to advance our understanding of how nearby planetary systems formed and which systems are more likely to harbor habitable worlds. Identifying the closest, likely habitable worlds is a major goal of astrobiology and also a key step in NASA’s search for life in the Universe.

Conditions and Timeline for Planet Formation

To a large extent, planets are what they accrete: The details of the formation and assembly of planets will greatly influence their potential for habitability. The Alien Earths team’s first major task is to advance our understanding of the physical and chemical conditions and timeline for planet formation. Our team combines experts from the observational and theoretical studies of planet-forming disks and their evolution with cosmochemists who specialize on the formation of the solar system, as probed through meteorites and near-pristine materials preserved from 4.56 billon years ago.

Impact of Planet Formation Pathways on Planet Composition

Planet formation and evolution pathways can change the bulk composition, properties, and early evolution of the forming planets. In Module 2, our team explores the interplay and co-evolution of forming giant and rocky planets and the protoplanetary disk. We explore how do large gaps and the transport of pebbles through the planet-forming disks impacts the composition of the forming planets. We also use simulations to identify population-level trends between the details of planet formation and the compositions of planets.

Habitability & Threats

Not all young habitable planets remain hospitable to life: Multiple processes can doom or destroy Earth-like planets.  In our Module 3 we explore known threats to habitable planetary systems and apply the lessons learned to nearby planetary systems to help identify the most promising targets for habitable planet searchers. Threats include the orbital dynamical instability of planetary systems and atmospheric loss processes.

Guiding Exoplanet Missions

In addition to advancing knowledge, the Alien Earths team’s research was defined to best inform current and future NASA exoplanet missions. With multiple missions concepts proposed and under development that aim to find and characterize habitable planets and search these for signatures of life, having the right, comprehensive information on the target planets is essential. Knowing which nearby systems to target, which planets to focus at, how to interpret incomplete information on the planets studied is essential for the success of these missions. Effective target selection can potentially save hundreds of millions of dollars and lower missions risks. Therefore, in our fourth module, our Alien Earths team applies the integrated knowledge from our entire project to nearby planetary systems – the potential targets for biosignature surveys – and uses survey simulations to quantify this information can best guide NASA missions.

Results, TOOLS, and events

The results of our team are published in peer-reviewed journals. The Alien Earths team builds on an extends the research of its pre-cursor project Earths in Other Solar Systems, which was funded by the NASA Astrobiology program between 2015 and 2021. EOS was also led by Daniel Apai and many investigators from the EOS Team continue their work in Alien Earths. EOS has published over 140 refereed papers on the formation and properties of habitable worlds, including multiple high-impact studies. It also built several important tools that are widely used by the community, such as EPOS, DYNAMITE, and the Genesis Database. 

The Alien Earths Team

Assessing the potential of planetary systems to host habitable worlds is a major scientific challenge and requires a closely integrated, highly multi-disciplinary team. Our Alien Earths team includes experts in planet formation, exoplanet detection and characterization, planet formation, planetary atmospheres, astro- and cosmochemistry, meteorite and asteroid sample analysis, planetary interiors and atmospheres, and mathematical biology and ecology. The Alien Earths team built up this broad range of expertise by drawing scientists from eleven institutions based in seven different countries. Our team includes over 30 PhD scientists and, during its 5-year performance period, will support over a dozen graduate students and postdoctoral researchers.

Principal Investigator Daniel Apai

The Alien Earths team is led by Dr Daniel Apai, Associate Professor of Astronomy and Planetary Science at The University of Arizona. Daniel’s research focuses on exploring exoplanets and exoplanetary systems.

Images of a Massive Planetary System in Formation

Protoplanetary disks offer an opportunity to learn about the processes by which planetary systems form and evolve. Images of these young systems also enable us to study, by analogy, the formation of our own Solar System, in which the common orbital plane of the...

Alien Earths Breakfasts are Back!

Due to the COVID19 panedemic, our AE team suspended most in-person interactions for more than a year; and the AE breakfasts for almost two years. In September 2022, we held our first real, in-person AE breakfast in a while. It has been great to meet team members again...

The Genesis Database

The key goal of EOS is to advance our understanding of the formation of habitable planets. As an unusually large and ambitious program, EOS is in a rare position to successfully integrate interdisciplinary knowledge on planet formation – that is, to combine...

The Origins Seminars on YouTube!

The Origins Seminar now has its own YouTube channel and the most recent talks are now available! Origins will continue to operate through most of the Summer and talks will be recorded and available through the Origins Seminar YouTube channel.

Clues to the Processing of Dust Around Stars

Research by University of Arizona Assistant Professor Pierre Haenecour and his team on the effect of ion irradiation on dust grains in circumstellar and interstellar environments, presented by Haenecour at Microscopy and MicroAnalysis 2019, has been...

Unknown Treasure Trove of Planets Found Hiding in Dust

The first unbiased survey of protoplanetary disks surrounding young stars in the Taurus star-forming region turned up a higher-than-expected number of disks with features suggesting nascent planets. Excerpt from UA News-Daniel Stolte, University Communications...

The Search for Planet 9 – TEDx Talk by Renu Malhotra

Renu Malhotra – LPL Professor and EOS Team Member – has recently given an excellent TEDx talk on the Search for Planet 9. The talk is now available online - check it out! https://www.youtube.com/watch?v=MptrypvBTag

The Optical Spectrum of a Sub-Neptune: Or, When Stars Get in the Way

Atmospheric characterization of transiting exoplanets Previous posts on this blog have discussed different methods for detecting exoplanets, including my favorite, the transit method. Transiting exoplanets, which pass directly in front of their host stars as seen from...

Characterizing Exoplanet Atmospheres

There are many ways astronomers have developed to detect exoplanets. Mikayla Mace introduced the most popular methods—radial velocity, transit, and direct imaging—in an earlier post on this blog. Each of these has their own strengths, making them useful for detecting...

Observing Planet Formation from Mauna Kea

I sat down on my third flight of the day, and the last that I would be taking to the big island of Hawaii on my way to the Mauna Kea observatories. The passenger with the seat adjacent to mine followed and sat down. My step-mom was a flight attendant, so flying is...

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