by Rex Parker, PhD
director@princetonastronomy.org

May 13 2025 Meeting of AAAP.   Our meeting in Peyton Hall on May 13 will be the final monthly  session on campus until September. The June 10 meeting will convene at the State Planetarium in Trenton, then our schedule takes a summer hiatus until September.  The guest speaker on May 13 will be James Stone, renowned Professor of Astrophysical Sciences at Princeton.  He’ll illuminate the deep mysteries of the physics of black holes.  For more on the speaker please see program chair Victor’s article below.  I hope to see you in person at Peyton Hall May 13, though Zoom will also be available (thanks to Dave and Ira).

Observatory Status.  This summer should offer many opportunities to gather for hands-on astronomy at the AAAP Observatory in Washington Crossing State Park. The electrical problem discussed at the meeting last month is being rectified, although state permitting can be slow. An electric repair company has been selected and a quote for the job has been accepted by the Board. Until the wiring repair is completed, for Friday night public observing sessions (when weather permits) a portable AC generator will be on site to power the observatory and enable the FiOS wifi system. 

Election of Officers May 13.  It is important that you, as a member of AAAP, attend the May 13 meeting to help us get the quorum needed for the annual election of officers.  I would like to thank Daniel Opdyke for agreeing to serve as the nominations chair.  According to the Constitution and By-laws, the Nominating Committee will identify a slate of candidates for the 7 Board positions of director, assistant director, secretary, treasurer, program chair, observatory chair, and outreach chair.  “Officers shall be elected at the Annual Meeting of AAAP in May.  Subject to the quorum requirement of Section 5, Subsection C, a simple majority of votes cast shall be sufficient for election.  Newly elected officers shall assume office at the end of the Annual Meeting.”  So this year we are pleased that 6 of the 7 incumbents indicated willingness to serve again.  Michael Mitrano has decided to step down as Treasurer, and we are indebted to him for a decade and a half of excellent service to the club.  And I am happy to inform you that Ira Polans has put his name up as Treasurer candidate.

Board of Trustees candidates for May 13 election:
Director, Rex Parker
Assistant Director, Bob Vanderbei
Secretary, Gene Allen
Treasurer, Ira Polans
Program Chair, Victor Davis
Observatory Chair, David Skitt and Jennifer Skitt assistant chair
Outreach Chair, Bill Murray

Biosignature on an Exoplanet!  In mid-April a major announcement splashed across the news media – an astronomy research group at Cambridge Univ. in England had detected a sign of life on an exoplanet.  The big news centered on planet candidate K2-18, orbiting a red dwarf star in Leo.  It was first discovered by the Kepler space telescope about 10 years ago. In the 10 years since, much attention has been drawn to sub-Neptune type planets, which can have environments potentially harboring life outside our solar system. The sub-Neptune “hycean worlds” (hydrogen ocean worlds) feature vast water oceans, but very unlike earth have atmospheres that are rich in molecular hydrogen (H2).  This recognition has markedly increased the number of planet candidates which might have life-habitable environments.  It’s important to recognize that the large size of Hycean worlds makes them much more accessible to atmospheric spectroscopy study with JWST compared to rocky earth-like planets.  Here is the publication that created the current news media stir:  Madhusudhan et al., ApJ Lett, Vol 983, No. 2, April 17 2025.

K2-18b is a hycean world situated in the habitable zone of its star.  The new findings build on  previous JWST near-IR (0.8 to 5 μm ) observations which showed CH4 and CO2 in its atmosphere consistent with predictions for hycean conditions. Those observations also provided a tentative hint of dimethyl sulfide (DMS), a possible biosignature gas, but the previous data reached only low statistical significance. The new report analyzed the mid-infrared transmission spectrum (6 to 12 μm) of K2-18 b using the JWST MIRI LRS instrument. They found that among the molecules predicted for K2-18b’s atmosphere, the data best fit the biosignature gases DMS and dimethyl disulfide (DMDS) with high statistical significance.

The excitement about dimethyl sulfide (DMS) in the atmosphere of an exoplanet comes from understanding it’s biological origin on earth.  It is unstable and doesn’t persist for long, although its half-life depends on conditions as for most chemical substances. Its detection on K2-18b therefore implies continual formation, which on earth is essentially 100% biological.  On earth DMS is the product of bacterial breakdown of an important organo-sulfur biochemical (dimethylsulfoniopropionate) produced in marine algae and phytoplankton.  This precursor has an important role in regulating internal pressure and ability of plankton to float in the ocean. The DMS product is volatile and diffuses from seawater into the atmosphere on earth, where it further oxidizes to form sulfate aerosols.  These aerosols are a main  source of cloud-condensation nuclei over the oceans, which ultimately control the earth’s radiation budget through cloud reflectance.  The DMS levels on K2-18b based on the newer JWST data (>10 ppm) are higher than in the bulk atmosphere on earth.  If the data can be further verified, this represents the strongest biosignature on an exoplanet ever detected to date.

Life beyond Earth, a Continuing Discussion in AAAP.  NASA first developed a major program to search for life on other planets and moons in the mid-1990’s.  In 1996, NASA chief Dan Goldin expanded on the intense public interest stirred by the report of putative fossil microbes in a Martian meteorite and the recent discovery of exoplanets.  The subsequent advances made by NASA planetary probes defined the most likely places in the solar system to harbor life.  Today, with hundreds of exoplanet candidates discovered by the Kepler and TESS orbiting telescopes and Mars rovers continuing to explore, extraterrestrial life seems less sci-fi and more like impending reality. 

A few years ago, it was proposed that the science community establish a framework for how to present evidence for life beyond Earth (Green et al., Nature vol 598, p 575, Oct 28 2021).  At the time of that paper, the interstellar visitor Oumuamua had recently sailed through the solar system and provoked a lot of interest, including the Amazon best-selling book, Extraterrestrial by Avi Loeb (who was a AAAP guest speaker the next year).  In the Nature article, former NASA chief of Planetary Sciences James Green stated, “Our generation could realistically be the one to discover evidence of life beyond Earth.”  Responsibility comes with this privilege because of the deep implications and impact that such a discovery would have on humanity.  Findings presented in the public media may take on more weight than the data actually support or the principals intend.  There are challenges of perception and communication, as evidence likely would be revealed in stages, for example from one set of JWST spectroscopy data to the next.  Our society has a tendency to turn scientific findings into binary, all-or-nothing propositions, placing unrealistic expectations on initial stages. The paper lays out a conceptual framework for how to proceed with a dialogue among scientists, technologists, and the media, to agree on objective standards of evidence for life and best practices for communicating it.  If indeed we are on the verge of making the most significant scientific and philosophical discovery ever in human history, this is an essential step to prepare society for acceptance.

An Owl in the Deep Sky.  Messier 97 (NGC 3587) in Ursa Major is known as the Owl Nebula, one of the most colorful planetary nebulae in the northern sky in spring.  The image below was taken over the last few nights in April by Rex Parker in New Jersey.  Final image is the mean of  81 x 6 min subframes, with Antlia RGB Tri-Band filter, ASI2400MC camera at gain 140 (unity), and 12.5” Cassegrain reflector on a Paramount MX mount.