Scientists now predict thousands of objects from alien star systems are trapped in the outer reaches of our solar system.
Interstellar visitors caught in the solar wind
Three interstellar objects have been spotted streaking through our solar system over the past decade.
It is likely that dozens more of these interlopers will be discovered in the coming years.
These objects travel so fast that they can escape the gravitational clutches of the Sun. This is why they are only visible for weeks before hurtling back out to speed-run the galaxy.
But while some interstellar objects leave in a hurry, others may be here to stay. They lurk in the outermost reaches of the solar system, known as the Oort cloud. This is the conclusion of a new study.
Over the course of its 4.6-billion year lifespan, the Sun has wandered close enough to other stars to collect thousands of non-native objects from the fringes of those passing systems. It may have also sent off many of its homegrown objects to join alien star systems during these encounters.
“The Solar System has long been suspected to contain captured, non-native material,” said researchers led by Sean Raymond of the Bordeaux Astrophysics Laboratory. “The recent ISO discoveries have now confirmed directly that extraterrestrial material regularly passes through the Solar System.”
Drawing on these discoveries, Raymond and his colleagues ran models to predict how many ISOs might be exchanged between stars during close encounters, called stellar flybys. The Sun is estimated to have had at least one or two of these meetups during its life so far. This could be responsible for a large fraction of the captured ISOs currently residing in the Solar System.
“Given that flybys are unavoidable in the Galactic field, most stars should host sparse Oort clouds populated with ISOs captured during stellar flybys,” the team said.
The Oort cloud — composed of frozen comet-like objects — extends for about three light years away from the Sun. It is not currently possible to send a spacecraft to go out to sift for ISOs in these distant wilds. Still, it is neat to know there are so many interstellar hitchhikers riding in the Sun’s backseat.
Trapped air in lunar glass
A memory of an ancient ephemeral sky on the Moon may be locked inside glass beads scattered across the lunar surface, according to a new study.
The Moon is airless, but there is evidence that it was surrounded by a transient atmosphere billions of years ago. This atmosphere was fed by volcanic eruptions in its early history. Rocks crashing into the surface may have also vaporized material and created brief, gassy skies over time.
Scientists have now examined glass beads that were scooped up from the far side of the Moon by China’s Chang’e 6 sample-return mission. The mission delivered the samples back to Earth in the summer of 2024.
The lunar glass was forged by rocks crashing into the surface. It captured the chemical signatures of the vapor plume created by those impacts. This preserves a whiff of a long-lost transient atmosphere.
“Chang’e 6 (CE6) mission has returned the first lunar samples from the farside of the Moon,” said researchers led by Ziyan Han of Nanjing University. “The returned CE6 lunar regolith contains impact glass beads that could have recorded impact-induced vaporization on the Moon’s farside and may serve as barometers, providing critical constraints on the global distribution of the Moon’s transient atmosphere.”
The team noted that these fleeting impact-induced atmospheres might exist on other airless bodies in the solar system, and beyond it. For this reason, the researchers warned that atmospheres detected around exoplanets may not always solely represent stable, long-lived atmospheres. This could complicate the interpretation of atmospheric data as evidence of long-term planetary habitability on the rocky exoplanets.
Fossil fuel subsidies are a policy failure
How bad does an energy policy have to be for experts to declare it the worst in the world?
In an editorial published in Science this week, a pair of researchers lament the widespread rollout of consumer fossil fuel subsidies. This response came to the spike in gas and oil prices caused by the U.S.-Israel war with Iran.
While it is understandable for governments to want to ease financial hardships, the team stressed that these subsidies are a major setback to confronting the climate crisis. They also fumble the chance to present the Iran war as a clear example of why we need to reduce global reliance on fossil fuels.
“Consumer fuel subsidies are the worst kind of energy policy: they boost the most polluting kind of energy—fossil fuels—with a policy that is wasteful and deceptively hard to reverse,” said authors Paasha Mahdavi of the University of California, Santa Barbara and Michael L. Ross of the University of California, Los Angeles.
“The Iran war represents a once-in-a-generation opportunity to accelerate the transition away from fossil fuels,” the team continued. “But short-term measures that governments are taking—to help their citizens cope with unaffordable gasoline and diesel prices—will have long-term effects. Making fossil fuels cheaper now will have catastrophic consequences in the future.”
Cacao found in Georgia
Humans have been consuming the delectable fruits of the cacao tree for many thousands of years in Central and South America. The plant made its way into parts of North America, such as the American Southwest.
Now, archaeologists have discovered cacao was also consumed as far east as the Etowah Site in Georgia. This is an ancient city built by the Mississippian culture. It reveals the unexpected spread of the delicacy deep into the Southeast.
“There is very little material evidence of connections between people living in Mississippian places like Etowah and those living in Central America,” said researchers led by Adam King of the University of South Carolina. “As a result, the possibility that the Mississippian world had access to cacao has always seemed remote.”
When the team analyzed ancient DNA sequences of residue found on Etowah pottery, they detected notes of cacao.
“Despite the fact that Etowah is separated from potential sources of cacao by great distances, ancient DNA confirms the site’s inhabitants consumed cacao,” the team said.
The researchers speculated that Etowah may have sourced its cacao from trade routes to Mexico or the American Southwest. They noted that no direct connections to Mexico nor the American Southwest are supported by archaeological evidence for now.
“These results ask us to reopen lines of research long closed, especially regarding contacts between the impressive civilizations of Central and South America and the great Mississippian civilization of the Eastern Woodlands,” King and his colleagues said in the study.
The study suggested that at Etowah and possibly across the Mississippian world, cacao consumption played a role in world renewal rites of intensification.
