During early investigations of the Lafayette Meteorite, scientists discovered that it had interacted with liquid water while on Mars. Scientists have long wondered when that interaction with liquid water took place. An international collaboration of scientists including two from Purdue University’s College of Science have recently determined the age of the minerals in the Lafayette Meteorite that formed when there was liquid water. The team has published its findings in Geochemical Perspective Letters.

Marissa Tremblay, assistant professor with the Department of Earth, Atmospheric, and Planetary Sciences (EAPS) at Purdue University, is the lead author of this publication. She uses noble gases like helium, neon and argon, to study the physical and chemical processes shaping the surfaces of Earth and other planets. She explains that some meteorites from Mars contain minerals that formed through interaction with liquid water while still on Mars.

“Dating these minerals can therefore tell us when there was liquid water at or near the surface of Mars in the planet’s geologic past,” she says. “We dated these minerals in the Martian meteorite Lafayette and found that they formed 742 million years ago. We do not think there was abundant liquid water on the surface of Mars at this time. Instead, we think the water came from the melting of nearby subsurface ice called permafrost, and that the permafrost melting was caused by magmatic activity that still occurs periodically on Mars to the present day.”

In this publication, her team demonstrated that the age obtained for the timing of water-rock interaction on Mars was robust and that the chronometer used was not affected by things that happened to Lafayette after it was altered in the presence of water.

“The age could have been affected by the impact that ejected the Lafayette Meteorite from Mars, the heating Lafayette experienced during the 11 million years it was floating out in space, or the heating Lafayette experienced when it fell to Earth and burned up a little bit in Earth’s atmosphere,” she says. “But we were able to demonstrate that none of these things affected the age of aqueous alteration in Lafayette.”

Ryan Ickert, senior research scientist with Purdue EAPS, is a co-author of the paper. He uses heavy radioactive and stable isotopes to study the timescales of geological processes. He demonstrated that other isotope data (previously used to estimate the timing of water-rock interaction on Mars) were problematic and had likely been affected by other processes.

“This meteorite uniquely has evidence that it has reacted with water. The exact date of this was controversial, and our publication dates when water was present,” he says.

Found in a drawer

Thanks to research, quite a bit is known about the Lafayette Meteorite’s origin story. It was ejected from the surface of Mars about 11 million years ago by an impact event.

“We know this because once it was ejected from Mars, the meteorite experienced bombardment by cosmic ray particles in outer space, that caused certain isotopes to be produced in Lafayette,” Tremblay says. “Many meteoroids are produced by impacts on Mars and other planetary bodies, but only a handful will eventually fall to Earth.”

But once Lafayette hit Earth, the story gets a little muddy. It is known for certain that the meteorite was found in a drawer at Purdue University in 1931. But how it got there is still a mystery. Tremblay and others made strides in explaining the history of the post-Earth timeline in a recent publication.

“We used organic contaminants from Earth found on Lafayette (specifically, crop diseases) that were particularly prevalent in certain years to narrow down when it might have fallen, and whether the meteorite fall may have been witnessed by someone,” Tremblay says.

Meteorites: time capsules of the universe

Meteorites are solid time capsules from planets and celestial bodies from our universe. They carry with them bits of data that can be unlocked by geochronologists. They set themselves apart from rocks that may be found on Earth by a crust that forms from its descent through our atmosphere and often form a fiery entrance visible in the night’s sky.

“We can identify meteorites by studying what minerals are present in them and the relationships between these minerals inside the meteorite,” says Tremblay. “Meteorites are often denser than Earth rocks, contain metal, and are magnetic. We can also look for things like a fusion crust that forms during entry into Earth’s atmosphere. Finally, we can use the chemistry of meteorites (specifically their oxygen isotope composition) to fingerprint which planetary body they came from or which type of meteorite it belongs to.”

An international collab

The team involved with this publication included an international collaboration of scientists. The team also includes Darren F. Mark, Dan N. Barfod, Benjamin E. Cohen, Martin R. Lee, Tim Tomkinson and Caroline L. Smith representing the Scottish Universities Environmental Research Centre (SUERC), the Department of Earth and Environmental Science at the University of St Andrews, the School of Geographical and Earth Sciences at the University of Glasgow, the School of Earth Sciences at the University of Bristol, and the Science Group at The Natural History Museum in London.

“Before moving to Purdue, Ryan and I were both based at the Scottish Universities Environmental Research Centre, where the argon-argon isotopic analyses of the alteration minerals in Lafayette took place” Tremblay says. “Our collaborators at SUERC, the University of Glasgow, and the Natural History Museum have previously done a lot of work studying the history of Lafayette.”

Dating the alteration minerals in Lafayette and, more generally, in this class of meteorites from Mars called nakhlites, has been a long-term objective in planetary science because scientists know that the alteration happened in the presence of liquid water on Mars. However, these materials are especially difficult to date, and previous attempts at dating them had either been very uncertain and/or likely affected by processes other than aqueous alteration.

“We have demonstrated a robust way to date alteration minerals in meteorites that can be applied to other meteorites and planetary bodies to understand when liquid water might have been present,” Tremblay says.

Because of the Stahura Undergraduate Meteorite Fund, Tremblay and Ickert will be able to continue studying the geochemistry and histories of meteorites and undergraduates at Purdue EAPS will be able to assist in this research.

With the demand for donor organs far outstripping the supply, calls for changes in public policy are growing. An opt-out (‘presumed consent’) default policy is often seen as a promising approach. This policy stipulates that all adults are automatically considered potential organ donors after their death, unless they explicitly withdraw their consent during their lifetime. In contrast, the opt-in (‘explicit consent’) system requires potential donors to actively consent to donate their organs after they die. The discussion around implementing an opt-out policy has recently gained traction again in Germany, raising the question of whether such a change in policy would actually lead to an increase in the number of deceased organ donors.

A recent analysis of all member countries of the Organisation for Economic Co-operation and Development (OECD) found no significant difference in deceased donor rates between opt-in and opt-out countries, but significantly fewer living donors — individuals who voluntarily donate organs, like a kidney, while alive — in opt-out countries. However, such cross-sectional analyses cannot control for all country-specific factors like health infrastructure, culture, and religious issues — all of which can influence donation rates.

To address the limitations of prior research, the current study used a longitudinal approach, analyzing changes in deceased donor rates over time in five countries — Argentina, Chile, Sweden, Uruguay, and Wales — that had switched from an opt-in to an opt-out default policy. This method provided a more reliable assessment of the impact of opt-out policies by controlling for long-term trends and country-specific factors.

Data was collected from international databases, including the International Registry in Organ Donation and Transplantation (IRODaT) and the Global Observatory on Donation and Transplantation (GODT). Of the 39 countries that had changed from explicit to presumed consent by December 2019, only five could be included in the analysis due to a lack of historical data for changes made before the IRODaT database was launched in 1996 and because presumed consent practices often existed informally prior to formal legislation.

Consistent with previous cross-sectional analyses, the study found that switching the default from opt-in to opt-out did not lead to any increase in organ donation rates in the five countries considered. Moreover, the results indicated that the opt-out default did not cause even a slight upward curve in organ donations: the long-term trend remained the same, showing no change in the rate following the switch. As expected, the results did show a reduction in deceased donations with the onset of the COVID-19 pandemic, with only a slow recovery observed by 2022.

“Simply switching to an opt-out system does not automatically lead to more organ donations,” states author Mattea Dallacker, who led the project at the Center for Adaptive Rationality at the Max Planck Institute for Human Development. “Without accompanying measures, such as investments in the healthcare system and public awareness campaigns, a shift to an opt-out default is unlikely to increase organ donations. There is no easy solution to the complex challenge of boosting organ donation rates,” she continues.

The study also underscores the crucial role of relatives in organ donation decisions. Even in presumed consent systems, where individuals are considered donors unless they opt out, families are often consulted and can override the presumed consent. Since many people do not talk about their donation wishes with loved ones, presumed consent can lead to uncertainty and hesitation among families, potentially resulting in refusals.

“A possible alternative to the opt-out system is a mandatory choice system,” says Ralph Hertwig, Director at the Center for Adaptive Rationality at the Max Planck Institute for Human Development. “This would allow citizens to explicitly register their consent or objection to organ donation, when applying for a driver’s license or ID card, for example. This active choice system could prompt people to make an informed decision, which would eliminate the perceived ambiguity about their preference that appears to lead to higher family refusal rates. Good and accessible information about organ donation is essential for informed choice,” Hertwig continues.

“It’s a very weird event, called AT 2021hdr, that keeps recurring every few months,” said Lorena Hernández-García, an astrophysicist at the Millennium Institute of Astrophysics, the Millennium Nucleus on Transversal Research and Technology to Explore Supermassive Black Holes, and University of Valparaíso in Chile. “We think that a gas cloud engulfed the black holes. As they orbit each other, the black holes interact with the cloud, perturbing and consuming its gas. This produces an oscillating pattern in the light from the system.”

A paper about AT 2021hdr, led by Hernández-García, was published Nov. 13 in the journal Astronomy and Astrophysics.

The dual black holes are in the center of a galaxy called 2MASX J21240027+3409114, located 1 billion light-years away in the northern constellation Cygnus. The pair are about 16 billion miles (26 billion kilometers) apart, close enough that light only takes a day to travel between them. Together they contain 40 million times the Sun’s mass.

Scientists estimate the black holes complete an orbit every 130 days and will collide and merge in approximately 70,000 years.

AT 2021hdr was first spotted in March 2021 by the Caltech-led ZTF (Zwicky Transient Facility) at the Palomar Observatory in California. It was flagged as a potentially interesting source by ALeRCE (Automatic Learning for the Rapid Classification of Events). This multidisciplinary team combines artificial intelligence tools with human expertise to report events in the night sky to the astronomical community using the mountains of data collected by survey programs like ZTF.

“Although this flare was originally thought to be a supernova, outbursts in 2022 made us think of other explanations,” said co-author Alejandra Muñoz-Arancibia, an ALeRCE team member and astrophysicist at the Millennium Institute of Astrophysics and the Center for Mathematical Modeling at the University of Chile. “Each subsequent event has helped us refine our model of what’s going on in the system.”

Since the first flare, ZTF has detected outbursts from AT 2021hdr every 60 to 90 days.

Hernández-García and her team have been observing the source with Swift since November 2022. Swift helped them determine that the binary produces oscillations in ultraviolet and X-ray light on the same time scales as ZTF sees them in the visible range.

The researchers conducted a Goldilocks-type elimination of different models to explain what they saw in the data.

Initially, they thought the signal could be the byproduct of normal activity in the galactic center. Then they considered whether a tidal disruption event — the destruction of a star that wandered too close to one of the black holes — could be the cause.

Finally, they settled on another possibility, the tidal disruption of a gas cloud, one that was bigger than the binary itself. When the cloud encountered the black holes, gravity ripped it apart, forming filaments around the pair, and friction started to heat it. The gas got particularly dense and hot close to the black holes. As the binary orbits, the complex interplay of forces ejects some of the gas from the system on each rotation. These interactions produce the fluctuating light Swift and ZTF observe.

Hernández-García and her team plan to continue observations of AT 2021hdr to better understand the system and improve their models. They’re also interested in studying its home galaxy, which is currently merging with another one nearby — an event first reported in their paper.

“As Swift approaches its 20th anniversary, it’s incredible to see all the new science it’s still helping the community accomplish,” said S. Bradley Cenko, Swift’s principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “There’s still so much it has left to teach us about our ever-changing cosmos.”