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A Radioactive Metal May Be Vital For Building Water Worlds

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water world exoplanet formation

Planets that form in regions with high levels of aluminum may be left with dry materials leading to Earth-like planets, while those in aluminum-light environments may stay wet and form ocean worlds. (Credit: Roger Thibaut)

While we tend to think that Earth’s oceans make it a watery planet, it’s actually only a tiny fraction of a percent of water by mass. Looking out into the universe, it’s clear water is more common than our own planet implies. Some exoplanets can have half their mass as water. So, what causes some planetary systems to stay wet, while others dry out? The answer might be aluminum.

Tim Lichtenberg is the lead author of a new study published Feb. 11, in Nature Astronomy. He says that large amounts of Al-26, a radioactive form of aluminum, can heat up and dry out the large boulders, some 5 to 50 miles across (called planetesimals), that collide to form planets. As a result, the amount of aluminum a young system has could be a predictor of what types of planets will evolve there.

Location and Size Matter

All stars tend to heat and dry out material – from pebbles to planetesimal – that orbits closer than what’s called the snow line. Beyond the snow line, ice sticks around and gets incorporated into planets, which can then keep that ice and eventually turn it into water, even if they later migrate closer to the sun. For instance, our own Earth keeps water trapped under its atmosphere, while Mars, farther out, lost its water. Both are now inside the snow line, but probably formed farther out.

Aluminum heating only matters to planetesimals of a certain size. Small pebbles don’t have enough Al-26 to cause any heating. Full-size planets may be able to hang onto their water through other methods – like having an atmosphere. But aluminum heating would affect all planetesimals in the unlucky size range, no matter how close or far they are from their sun.

Missing Water

A good example of this effect in action might be the TRAPPIST-1 exoplanet system. TRAPPIST-1 has seven rocky planets circling a dim red dwarf star. Three are in the habitable zone, and all are thought to be temperate enough to host water. Researchers still don’t know all the details of the system, and Lichtenberg cautions that uncertainties are still high for many of the TRAPPIST-1 planets. But it seems that only about one percent of their mass is made of water, which is surprising to most planetary scientists. Red dwarfs are cool stars compared to the sun, meaning their snow line should be quite close, allowing lots of icy material for planets to sop up as water. So if this water is missing, it’s worth asking why.

TRAPPIST-1 is strange in another way. In any system, planets circling farther from the star, traveling larger orbits, should have more chances to pick up icy material – they literally travel a bigger circuit through space. But that’s not what observers see in the TRAPPIST-1 system. Lichtenberg says, “This speaks to a system-wide mechanism, which is exactly what our Al-26 method is.”

Lichtenberg points out there’s no proof that aluminum heating caused our solar system or TRAPPIST-1’s relative dryness. “This is not the only method,” he says, that can dry out systems. “But it is a powerful one.”



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Ecology

Japan’s Hayabusa2 Is Going to Shoot an Asteroid Tonight

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Did Huge Volcanic Eruptions Help Kill Off The Dinosaurs?

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A large series of volcanic eruptions created India’s Deccan Plateau right around the same time dinosaurs were going extinct. (Planet Labs, Inc/Wikimedia Commons)

Nearly 66 million years ago, most living things on Earth died. Most researchers agree that the prime culprit was an asteroid that struck Mexico’s Yucatan Peninsula, leading to the mass extinction that took out most of the dinosaurs. But in a new research published Thursday, two independent research groups are making the case that enormous volcanic eruptions in India likely contributed to the demise of life, too.

The findings shed light on not only one of the most famous events in Earth’s history, but also the potential consequences of current environmental change, the researchers say.

“Understanding past extinction events — their causes, and eventual climatic and biotic recoveries — is crucial … when trying to wrap our heads around the many possible outcomes of our current trajectory towards disastrous climate change, ecosystem destruction and potential mass extinction,” Blair Schoene, a geologist at Princeton University in New Jersey, who led one of two new studies, said in a statement.

Death Debate

Geologic evidence uncovered in the ’80s and ’90s led researchers to conclude that a giant asteroid’s collision with Earth caused the extinction event. That setoff a worldwide hunt for the impact site. Amd geologists announced they’d finally discovered the Chicxulub crater in 1991.

“Despite this evidence, the impactor hypothesis has met with some skepticism because many extinction events roughly coincide with the [explosion] of enormous volumes of volcanic rock onto and into Earth’s crust,” explains Seth Burgess, a volcanologist with the U.S. Geological Survey in Menlo Park, California, who was not involved in the research, in a related perspective piece.

That lingering debate has led other scientists to study India’s Deccan plateau, an enormous landmass extending east and south of Mumbai, to create a precise timeline of the volcanic eruptions. For the latest analysis, Schoene and a research team studied uranium and lead isotopes — commonly used to date rocks — that they found in zircon mineral crystals buried beneath the lava flows. It revealed four high-volume eruptions that happened between 66.4 and 65.6 million years ago. The data show that the second of these eruptions likely began tens of thousands of years before the mass extinction event, the researchers report in the journal Science.

Unending Eruption

In a second study also out Thursday in Science, another team used a different technique to corroborate the finding. Here, the researchers assessed argon isotopes to date the eruption of lavas in the area. Their analysis also showed the eruptions began thousands of years before the mass extinction. However, the investigation revealed a more or less continuous eruption that lasted for about a million years. Although the finding contrasts with the punctuated eruptions Schoene and team discovered, both studies agree the Deccan eruptions likely played a role in the mass extinction event.

Given the timing of the eruption events and the meteor impact, it’s possible the two triggers delivered a double-whammy deathblow.

“Both of our datasets suggest a coincidence between the onset of Deccan eruptions and Late Cretaceous climate change, which has been attributed to the weakening of Late Cretaceous ecosystems, possibly making them more susceptible to the effects from the meteor impact,” Courtney Sprain, a geoscientist who led the second study while at the University of California Berkeley, said in a statement.



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A New Species of Tiny Tyrannosaur Helps Explain the Rise of T. rex

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moros intrepidus the tyrannosaur

Moros intrepidus, a new species of tyrannosaur whose name means “harbinger of doom,” weighed just 200 pounds as a fully grown adult. (Credit: Jorge Gonzalez, Copyright: Lindsay Zanno)

Scientists have discovered a new species of tiny tyrannosaur that lived some 95 million years ago in what’s now Utah. The find helps fill a frustrating gap in the fossil record at a critical time when tyrannosaurs were evolving from small, speedy hunters, into the bone-crushing apex predators we know so well.

The new dinosaur has been dubbed Moros intrepidus, and its name means “harbinger of doom.” The creature, known only from a leg bone and some various teeth, weighed under 200 pounds as a fully-grown adult. It was a specialist predator and scientists say it was fast enough to easily run down prey while avoiding other meat-eaters.

Their discovery was published Thursday in the journal Nature Communications Biology.

The Tiniest Tyrant

Tyrannosaurus rex was one of the most terrifying creatures to ever live. Few larger predators have walked the Earth. But tyrannosaurs – a group including T. rex and dozens of relatives and ancestors – weren’t always so awe-inspiring.

Tyrannosaurs roamed the planet for more than 100 million years. And for much of that time, the two-legged predators were bit players in Earth’s ecosystems. The earliest of their kind stood shorter than a human. They were fleet-footed and relied on their brains and strong senses to hunt down prey.

Meanwhile, during that same time in the Jurassic period, another kind of dinosaur, the allosaurs, which look like T. rex to the untrained eye, grew as big as a school bus and hunted giant, long-necked sauropods. But a big change was coming. A period of intense volcanic eruptions rocked the end of the Jurassic 145 million years ago. The allosaurs and other large dinosaurs started dying out.

Then, over a relatively short period, tyrannosaurs in North America evolved into the beasts we now imagine. And by the time an asteroid killed off the non-avian dinosaurs 66 million years ago, a full-grown T. rex weighed in at some nine tons and spanned a whopping 40 feet from snout to tail. How that happened is one of the biggest unanswered questions for dinosaur experts like Lindsay Zanno, a paleontologist at North Carolina State University.

That’s why Zanno and her team have spent more than a decade systematically searching North America’s rocks for fossils from this era. As she puts it, she wants to know how tyrannosaurs went from “wall flowers to prom kings.”

In particular, they’ve been combing the deserts of Utah near a giant 1,000-foot-tall rock formation the team calls the Cliffs of Insanity. The name sprung from the realization that one day they’d have to climb them looking for fossils.

“We have this data desert in between these small-bodied tyrannosaurs that lived in North American during the Jurassic and the sudden appearance of these large bodied, bone crushing tyrannosaurs that lived here in the Late Cretaceous,” she says. “And there’s no record of how we made this transition.”

Scientists already have some ideas about what may have happened. But there’s scant fossil evidence to confirm or refute their theories. It may be that amid the mini-mass extinction, dinosaurs and other animals migrated across a land bridge from Asia into North America, like our own ancestors eventually would. The small, ancient tyrannosaurs might have simply been following their prey: relatives of triceratops, which were also much smaller at the time.

“We know that there’s this ecological transition happening in this time when a lot of dinosaurs living in North America disappear and go extinct, and a lot of other animals suddenly appear that have their closest relatives in Asia,” says Zanno. “They become established here in North America and then they go on to evolve into these iconic species that we know and love like Tyrannosaurus rex and Triceratops.”

Mind the Gap

One of the major hang-ups in deciphering what happened has been a 70-million-year gap in North American tyrannosaur fossils during the time when this evolution was taking place. The new tiny tyrannosaur, Moros, narrows that gap by 15 million years.

And the team’s analysis of the new animal and its relatives hints that tyrannosaurs evolved into giants in no more than 16 million years. Though it could have happened much faster.

Tyrannosaurs were opportunistic in their rise to power,” Zanno says. “Moros tells us that the T . rex lineage moved here from Asia and remained small until they were able to take over ecosystems.”

Still, this doesn’t answer the question of why exactly all this change took place. Zanno says finding that answer is part of a decade-long project still in the works.



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