An international research team led by Harvard scientists has announced the first-ever detection of an atmosphere on an Earth-like rocky exoplanet, LHS 1140 b, orbiting within its star’s habitable zone, only 48 light-years away.

The researchers behind the historic discovery, which they are calling “a major milestone in the search for life on other planets,” said the detection of an atmosphere on an Earth-like rocky exoplanet offers the strongest evidence to date that worlds with similar compositions and temperatures to Earth that are also capable of supporting life could exist beyond our solar system.

Models Predicted First Earth-like Rocky Habitable Zone Exoplanet Atmosphere

In a statement announcing the detection of an atmosphere around a habitable-zone rocky exoplanet, the discovery was motivated by theoretical predictions suggesting that LHS 1140 b may contain an atmosphere. The planet was even more tantalizing because its orbit around its host red dwarf star allows for liquid water on its surface, a key ingredient for life as we know it.

Although thousands of exoplanets have been confirmed since 1995, including habitable-zone rocky worlds similar in size and composition to Earth, the team notes that determining whether any of these potential Earth analogs maintain an atmosphere. Like water, an atmosphere is considered a likely necessity for life to emerge.

“An atmosphere is essential for a planet to support life as we know it,” explained Collin Cherubim, the lead author of a study detailing the findings, who recently earned his Ph.D. in Earth and Planetary Sciences from Harvard University.

Robin Wordsworth, the Gordon McKay Professor of Environmental Science and Engineering and Professor of Earth and Planetary Sciences at Harvard, said that as recently as twenty years ago, astronomers still didn’t know if other, terrestrial-type planets “even existed.” However, he explained, they quickly found that this type of planet was common, including some orbiting within their star’s habitable zone.

“The next question was whether any of them had managed to keep an atmosphere,” the professor added.

Infrared Observations Confirm Historic First  

Before performing any direct observations, the team used computer models to predict what they might find on LHS 1140 b. As noted, those models predicted an upper atmosphere rich in helium. The models also suggested that the atmospheric helium was slowly escaping into space.

To test the model’s predictions, Cherubim and colleagues gained access to the Warm Infrared Echelle (WINERED) Spectrograph on the Magellan Observatory in Chile. The team noted that this powerful telescope allowed them to observe an alignment of LHS 1140 b and another planet transiting its star “on the same night.”

When analyzing the data, the team found that one of the planets appeared to lack any measurable atmosphere. However, as their models had predicted, helium was actively escaping from LHS 1140 b. The finding confirmed that this rocky exoplanet orbiting within its star’s habitable zone was actively maintaining an atmosphere.

David Charbonneau, the head of the Harvard Department of Astronomy and an astronomer at the Center for Astrophysics | Harvard & Smithsonian, and Cherubim’s co-advisor with Wordsworth, was initially skeptical because the entire concept was based on a mathematical prediction of a phenomenon astronomers had never witnessed directly. However, Professor Charbonneau ended up praising the student’s determination and follow-through, which led to the historic detection.

“Collin analyzed the planets we knew about and predicted that this one would have a helium atmosphere,” Charbonneau said. “Then he organized telescope time, got the data, and the detection was statistically rock solid.”

“Hopefully it’s just the First of Many More Observations to Come”

When discussing the implications of the findings, Cherubim noted that “this is the first time anyone has found an atmosphere on a rocky planet in the habitable zone of another star.” Professor Wordsworth agreed, once again noting that until now, planets in these categories with atmospheres had been purely theoretical.

“Now we know at least one has,” the professor said.

The data also suggest that LHS 1140 b’s atmosphere has likely survived for more than three billion years, roughly three-quarters of Earth’s existence. This durability makes LHS 1140 b an excellent candidate for future exoplanet atmosphere studies.

More broadly, the team said that using ground-based observatories to search for escaping gases, such as the helium detected leaving LHS 1140 b, “may become an important tool for studying atmospheres on rocky exoplanets.” They also note the potential value of atmospheric detection for astrobiologists searching for signs of life in the cosmos.

As for Cherubim, he plans on following up his historic discovery with a more detailed analysis of the planet’s atmospheric composition. He also said he would like to investigate the possible presence of surface oceans or other planetary characteristics typically associated with habitability and life. The entire team also said they would like to use Cherubim’s model to search for similar Earth-like, habitable-zone rocky exoplanets.

“This has been a model validation, and hopefully it’s just the first of many more observations to come,” Cherubim said.

The study, “Helium escaping from the atmosphere of a nearby rocky exoplanet orbiting in a habitable zone,” was published in Science.

Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.

An international team of researchers has demonstrated a new biosignature detection method for distinguishing between abiotic and biotic apatite mineral samples on Mars using instruments already aboard the Perseverance Rover, rather than returning samples to Earth.

The team said their mineral-based biosignature detection approach was successful in identifying samples with nearly 98% accuracy and allows for “deeper time” searches for signs of life, given the longer-lasting nature of minerals compared to biological materials. They also suggest their approach could broaden the capabilities of upcoming rover and life-hunting missions without adding new tools or sensors.

Advantages of a Mineral-Based Approach for Hunting Biosignatures

In a study detailing the team’s technique, Robert M. Hazen from the Carnegie Institution for Science and colleagues explained that searching for life and biosignatures beyond Earth “is a central objective of astrobiology.” They also note that this research is complemented by studies exploring the origin and early evolution of terrestrial life. Still, they add, although identifying biosignatures remains a key challenge, “robust mineral biosignatures remain limited.”

For example, most proposed biosignature missions focus on organic molecules or searching for fossils preserved in sedimentary environments or aquatic environments, including the subsurface oceans of some of the solar system’s moons. However, there are few, if any, proposed missions searching for signs of life preserved in mineral records, which the team notes “can retain records of biological activity over much longer geological timescales”

On Mars, NASA’s Perseverance rover has meticulously collected soil and rock samples deemed most likely to contain biosignatures. However, efforts to send a future sample-return mission to the red planet to retrieve samples are currently stalled and may never be completed.

According to the study authors, there are flight-ready instruments “already deployed on the “Perseverance” rover and planned for deployment on the “Rosalind Franklin” rover capable of searching for signs of life in place rather than returning the samples to labs on Earth. However, they add, “to fully exploit these mission-limited yet information-rich tools, it is essential to efficiently extract as much diagnostic value as possible from the data they generate.”

To search for mineral-based biosignatures, the team focused its research on Raman spectroscopy.

Using Instruments Already Aboard Mars Rovers to Search for Life

“Raman spectroscopy is particularly attractive because it provides bond-specific information on crystal structure and chemical substitution in a nondestructive manner,” they explain.

The team also notes that the Raman spectra acquired by the rover’s instruments “are highly comparable to those obtained under laboratory conditions,” increasing the robustness of any possible life signal.

“This consistency enables direct translation of laboratory reference datasets to planetary environments,” they write.

However, they add, Raman spectra from natural geological samples are often complex, including “overlapping vibrational modes, heterogeneous backgrounds, and chemistry-dependent band shifts.” Until now, this complexity has made interpreting samples based on individual spectral peaks or qualitative inspection inherently challenging.

“Identifying reliable biosignatures that can be detected by flight-ready instruments, such as Raman spectroscopy, remains a central challenge in astrobiology,” the researchers explain. “Developing robust mineralogical indicators of life therefore represents a critical and complementary approach for planetary exploration.”

Approach Distinguishes Abiotic and Biotic Features

To test their approach, the team focused on the mineral apatite. A ubiquitous phosphate, the team notes that apatite can be found “in terrestrial and extraterrestrial environments.” Although apatite is a major component of biological formations such as teeth and bones, it also forms naturally, providing an opportunity to search for biosignatures over much longer timescales if scientists can differentiate the two.

“Here, we integrate Raman spectroscopy with interpretable machine learning to distinguish biotic from abiotic apatite, a ubiquitous phosphate mineral in terrestrial and extraterrestrial environments,” the researchers write.

First, Hazen and colleagues compiled 331 Raman spectra samples. Critically, they included only specimens with known origin attributes: biogenic, abiogenic, or synthetic.

Next, they used this data to extract 21 “band-resolved features.” This was accomplished by training a random forest classifier to identify the “most diagnostic” features of each sample.

“Determining the origin of a sample involves assessing multiple independently varying features of a Raman spectrum, including band positions, widths, and relative intensities, the type of multivariate analysis well suited to machine learning,” the study authors explain.

After some comparative analysis, the team ultimately determined that a sample’s carbonate band and the width of the dominant phosphate band, “reflecting chemical composition and crystal structure, respectively,” were the strongest indicators of biological, natural, or synthetic origin.

After using their method to check the 311 samples, the team said the model successfully  distinguished biotic from abiotic apatite “with classification accuracy exceeding 96%.” In fact, the team reported that their mineral-based biosignature detection method misidentified only one biotic apatite sample as abiotic and one abiotic sample as biological.

“Here, we show that biologically formed apatite can be distinguished from abiotic counterparts using interpretable machine learning applied to Raman spectra,” the study authors write.

Life Detection Across Diverse Planetary Environments

When discussing the potential implications of their new mineral-based biosignature detection approach, the team noted that their findings establish a “broadly applicable and mission-relevant strategy for deep-time archives and future planetary missions.” More broadly, the researchers note that their findings highlight the “growing importance of combining flight-ready analytical instruments with AI” to fully leverage datasets already captured by Mars rovers and other “in situ” planetary missions.

“As planetary exploration increasingly shifts toward autonomous decision-making and target selection, the integration of interpretable AI with mineralogical biosignatures offers a powerful and extensible framework,” they write.

Beyond mineral-based biosignature detection strategies, the research team notes that future life hunting missions will “increasingly rely on the joint interpretation of mineralogical and organic spectroscopic signatures.” These include on-board py-GC-MS measurements, infrared spectroscopy, luminescence, laser-induced breakdown spectroscopy, X-ray fluorescence, and “other analytic methods.”

Future approaches will increasingly rely on AI to analyze these disparate datasets, which the authors note will allow for biologically mediated patterns to be distinguished from natural or synthetic backgrounds “in a physically and chemically consistent manner.”

“In this context, such an integrative and interpretable framework provides a pathway toward autonomous, mechanism-informed life detection across diverse planetary environments, advancing the broader goals of planetary science in understanding habitability, biosignature preservation, and the coevolution of geology and biology,” the authors conclude.

The study “Mineral biosignature identification from Raman spectroscopy using machine learning” was published in PNAS Nexus. 

Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.

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