The Second Earth Has Already Been Narrowed Down to Candidates: The Identity of the "Top 45 Planets" Chosen by Astronomers

The term "second Earth" strongly stimulates human imagination. However, actual astronomy is not a world driven solely by romance. Researchers are now transitioning from the stage of "vaguely searching for stars that might resemble Earth" to the stage of "precisely narrowing down where to focus observational resources." The core of the topic introduced by scinexx on March 23, 2026, lies precisely there. Out of over 6,000 known exoplanets, they have selected 45 rocky planets as priority candidates for life exploration.

The interesting aspect of this research is that it doesn't end with "counting planets in the habitable zone." The research team used data from Gaia DR3 and the NASA Exoplanet Archive to compare factors such as distance from the star, received radiation energy, and orbital eccentricity to organize which planets have a stronger potential to retain liquid water on their surface. Furthermore, they reselected candidates under more conservative conditions in the "3D habitable zone," indicating 24 additional candidates when viewed more stringently, in addition to the 45 promising ones. Thus, the outcome of this research is not a report of "discovering a star with life," but rather a roadmap of observational strategy saying "if you're going to look for signs of life, start here."

The lineup of candidates includes names familiar to space enthusiasts. For example, Proxima Centauri b, Kepler-186 f, Kepler-442 b, and several planets in the TRAPPIST-1 system. Among them, researchers are particularly interested in the four planets TRAPPIST-1 d, e, f, g, and LHS 1140 b. The TRAPPIST-1 system is about 40 light-years from Earth, and LHS 1140 b is about 48 light-years away, both meeting the conditions of being "rocky planets," "in the habitable zone," and "relatively easy to observe." In a field where the expression "second Earth candidate" tends to take on a life of its own, the fact that researchers themselves have identified these as a "group with high observational value" is significant.

Even more intriguing is that the research team is also focusing on planets that receive a similar amount of light as Earth. According to introductions by RAS and Cornell, notable examples include TRAPPIST-1 e, TOI-715 b, Kepler-1652 b, Kepler-442 b, Kepler-1544 b, and the non-transit planets Proxima Centauri b, GJ 1061 d, GJ 1002 b, and Wolf 1069 b. Among these, TRAPPIST-1 e and TOI-715 b are particularly promising for future detailed observations. Having a solar environment similar to Earth's means that at least the starting point for considering surface environments is close to Earth's.

However, calmness is necessary here. Being in the habitable zone is neither proof of the existence of life nor proof of being exactly like Earth. What is needed are not just temperature conditions, but multiple conditions such as the ability to retain an atmosphere, withstand stellar flares, actually have liquid water on the surface, and geological activity. As NASA explains about TOI-715 b, even if it is in the "conservative habitable zone," the presence of surface water requires other factors like an atmosphere to be in place. In other words, the 45 planets this time are not a "definitive list of habitable stars," but a "list of prime candidates worth investigating in detail."

TRAPPIST-1 e symbolizes this caution. This planet has been particularly noted among the seven Earth-sized planets in the TRAPPIST-1 system, but observations by the JWST show both expectations and uncertainties. According to NASA, while TRAPPIST-1 e is at a distance where water could exist on its surface, it is highly likely that its original light primary atmosphere has been lost due to stellar radiation. The possibility of a secondary atmosphere remains, but it is not yet confirmed. While a thick atmosphere dominated by carbon dioxide is unlikely, there is room for an atmosphere that maintains a certain greenhouse effect or local seas. There is hope. However, it is still too early to make definitive statements. This is the intriguing yet challenging aspect of this field.

Therefore, this research should be seen as a steady but important "update of target setting" rather than a flashy discovery. Next-generation observational instruments, such as the James Webb Space Telescope, the Nancy Grace Roman Space Telescope scheduled for launch in 2027, the Extremely Large Telescope expected to have its first light in 2029, and future Habitable Worlds Observatory, have limited time. Clarifying which stars should be observed first will greatly influence the overall efficiency of life exploration. The 45 celestial bodies this time are essentially a list that organizes the "observation queue for astrobiology."

The reaction this news received on social media was also quite symbolic. The most noticeable aspect is the pure excitement. Official announcements likened this research to "Project Hail Mary" by Cornell and RAS, and this context spread on X and Threads. Many people are thrilled that what seemed like a distant future sci-fi "destination candidate" is beginning to line up as a real observation catalog. When space topics are widely shared, science often reaches people first as a story, not just numbers or graphs. In that sense, this research successfully connects academic value with popular imagination.

On the other hand, the science-loving crowd on social media quickly poured "cold water" on the excitement. On Reddit, practical questions and criticisms followed from those who saw the charts, such as "Where would Mars be placed on the same chart?" "Is it okay to be so optimistic about planets around red dwarfs?" and "How should we interpret the relationship between the conservative habitable zone and the optimistic habitable zone?" In another comment, Mars was compared in the context of receiving about 43-44% of the solar radiation Earth does, with additional notes like "lacking gravity, magnetic field, and atmosphere." Observing the reactions on social media, it is clear that while people are drawn to headlines suggesting "life might exist," they simultaneously understand that "that's not enough."

Interestingly, such cautious opinions actually reinforce the value of this research. The habitable zone theory has long faced criticism for being "too simplistic." However, this catalog, aware of its limitations, intentionally extracts "stars near the boundary," "stars with high eccentricity," and "stars with radiation environments similar to Earth." In other words, it presents falsifiable observational targets to test "how far the surface environment can be maintained." The cautious views on social media and the research's design philosophy are not actually opposing. They are, in fact, aligned. It is not just about raising expectations but about breaking them down into verifiable questions. This is the maturity of modern exoplanet research.

A "second Earth" might be found today or tomorrow, or it might remain "quite close but not definitive" for decades. However, at least this time, the search has become much more concrete. We are no longer just vaguely gazing at the cosmos. Whether it's TRAPPIST-1 e, TOI-715 b, or another less-noticed candidate, the direction in which to point our telescopes is now much clearer than before. The era of romance has not ended. Rather, romance has begun to transform into the reality of observation plans.

Source URL Summary

・scinexx
https://www.scinexx.de/news/kosmos/diese-planeten-koennten-eine-zweite-erde-sein/

・Peer-reviewed paper of the original research (Published in MNRAS. The primary source for the selection of 45 rocky planets, 24 stricter candidates, and the selection criteria itself)
https://doi.org/10.1093/mnras/stag028

・Introduction article by Cornell University (A summary from the research team's side. Useful for understanding why this list was created and which observational instruments it benefits)
https://news.cornell.edu/stories/2026/03/where-find-other-earths-new-list-narrows-down-targets

・Explanation article by the Royal Astronomical Society (Useful for organizing the list of candidate planets and notable targets like TRAPPIST-1 e and TOI-715 b)
https://ras.ac.uk/news-and-press/research-highlights/best-places-look-alien-life-scientists-identify-45-earth-worlds

・NASA's explanation of TOI-715 b (Notes on "being in the habitable zone ≠ immediately habitable" and for checking basic information on TOI-715 b)
https://science.nasa.gov/universe/exoplanets/discovery-alert-a-super-earth-in-the-habitable-zone/

・NASA's explanation of TRAPPIST-1 e (For checking the current status of atmosphere presence and uncertainties based on JWST observations)
https://science.nasa.gov/missions/webb/nasa-webb-looks-at-earth-sized-habitable-zone-exoplanet-trappist-1-e/

・Reference 1 for SNS reactions (Reddit. For checking practical reactions like chart reading and "where would Mars be placed" or "how about planets around red dwarfs")
https://www.reddit.com/r/spaceporn/comments/1rztgjj/the_best_places_to_look_for_alien_life_scientists/

・Reference 2 for SNS reactions (Reddit. A thread for checking readers' candid impressions of the article and interest in the chart itself)
https://www.reddit.com/r/space/comments/1ryjvzy/astronomers_create_catalogue_of_habitablezone/