An instrumental advance has made it possible to trace in detail the distribution of Ordinary water and heavy water in the coma of a Halley-type comet. In the case of 12P/Pons-Brooks, the ratio of deuterium to hydrogen (D/H) appears practically identical to that of the water in the Earth's oceans, a result that once again puts the role of these bodies in the history of the planet's water on the table.
The work, led by NASA scientists Martin Cordiner and Stefanie Milam, combined the sensitivity of the Atacama Large Millimeter/submillimeter Array (ALMA) with observations of the NASA Infrared Telescope (IRTF) to nail the isotopic measurement of water. The data set suggests that some comets may have contributed volatiles essential for habitability early Earth.
What has been measured
La The D/H ratio obtained was (1,71 ± 0,44) × 10⁻⁴, a value that is practically indistinguishable from that recorded in ocean water and which, in addition, is situated at the lowest extreme observed in Halley-type comets to date.
To achieve this, the team simultaneously mapped the emission of H2O (ordinary water) and HDO (heavy water) within the coma, the gaseous envelope that surrounds the icy core during its approach to the Sun, obtaining an unprecedented spatial image of both species.
The combination of ALMA and IRTF also provided complementary information on other volatile gases present in the comet's environment, refining the chemical context in which the measurement of D/H is inserted, considered a fundamental chemical fingerprint to trace the origin of the water.
Implications for the origin of water on Earth
This finding, which shows a D/H ratio similar to that of terrestrial water, supports the hypothesis that Some comets may have contributed part of the water inventory of our planet. Although measurements on other comets have been inconsistent, these data represent a important point in favor.
That a Halley-type comet shows a isotopic signature so close to that of ocean water suggests that, at least in certain cases, the water carried by these bodies would have been compatible with that existing on the early Earth, accompanied by potentially prebiotic molecules essential to initiate chemical processes that lead to life.
How the study was carried out
The technical key was in the ALMA's unprecedented sensitivity, capable of detecting the weak signal of heavy water (HDO) in the innermost areas of the coma, a milestone that had not been achieved until now in this type of analysis and which increases the reliability of the measurements.
Infrared observations of the FTIR provided additional support, allowing the spectral lines of water and other compounds to be verified and contextualized. The joint analysis helped determine whether the gases originated from ice sublimated directly from the core or reactions in the gaseous cloud; the data clearly point to origin in the solid core.
What characterizes Halley-type comets?
Halley-type comets are, in essence, icy remnants of the dawn of the Solar System, with orbital periods ranging from approximately 20 to 200 yearsTheir passage through the inner solar system is infrequent, so every observation window is invaluable for improving planetary formation models.
Own 12P/Pons-Brooks It is known for its bursts of gas and dust, phenomena that provide a natural laboratory to follow changes in composition and dynamics of the material it contains. Each approach to the Sun offers new clues about the processes operating in the region where the volatiles are released.
Next steps in research
With such a precise measurement, the next step is compare the D/H signature in a larger sample of comets to understand how common this Earth-like pattern is and what variations there may be in different dynamic families.
It is also important to consider missions that collect core material and analyze it in the laboratory, in order to confirm these measurements and detect organic molecules related. Direct analysis could help clarify how water and other essential compounds were transported to early Earth.
This updated portrait of 12P/Pons-Brooks reinforces the idea that Halley-type comets are relevant candidates to have contributed water and key elements to our planet, supported by a D/H ratio almost identical to the oceanic one and an unprecedented mapping of its coma that opens new avenues for understanding our chemical history.