Remember that asteroid everyone was worried about 2 months ago? The JWST just got a clear view of it
For a few weeks in January and February this year, asteroid 2024 YR4 had us all worried.
Shortly after it was discovered, astronomers calculated that the asteroid had a 1-in-83 chance of hitting Earth in 2032 — that's an impact risk of around 1%. Experts urged caution, though noting that the impact odds were likely to fall significantly. Sure enough, by late February, the probability of the asteroid hitting Earth fell to near zero.
This asteroid, however, is still worth analysis in its own right. As such, scientists recently turned the James Webb Space Telescope's (JWST) powerful gaze towards 2024 YR4, capturing the object in both visible and thermal light. The team measured the asteroid to be around 200 feet (60 meters) in diameter. "That's just about the height of a 15-story building," Andy Rivkin of the Johns Hopkins University Applied Physics Laboratory said in a statement.
The JWST also helped scientists study how quickly the space rock heats up and cools down. According to Rivkin, these thermal properties in 2024 YR4 are "not like what we see in larger asteroids," likely due to the fact that it spins very quickly and that its surface is "dominated by rocks that are maybe fist-sized or larger," rather than fine grains of sand.
Rivkin said studying asteroids like 2024 YR4 with the JWST is "invaluable" for helping scientists figure out how our space telescopes might aid planetary defense efforts if another "possible impactor" is found down the line.
"All together, we have a better sense of what this building-sized asteroid is like," Rivkin said.
"This will help us determine the best approach to use during a more urgent observing program should another asteroid pose a potential impact threat in the future."
A study about the JWST's observations of asteroid 2024 YR4 were published in the journal Research Notes of the AAS.
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Scientific American
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On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. But JWST's infrared and ALMA's radio observations have pierced this veil, peering through a gap in the envelope to probe other structures around HOPS-315 in unprecedented detail—most notably a whirling halo of hot gas and dust called a protoplanetary disk. Such disks are wombs for embryonic worlds; in them, clumps of rock called planetesimals coalesce and eventually build up into full-fledged planets. Yet no planetesimals can form without smaller grains of crystalline minerals first condensing within the disk, which occurs as the disk's gas cools. For generations, astronomers have been literally in the dark about this process, as the enveloping clouds that nourish a protostar typically obscure its intimate details. 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HOPS-315 is also burping up an outflowing jet of material as it feeds, however, which the researchers worried might be the source of those signals. Subsequent observations with ALMA in November 2023 helped to confirm the mineral grains were present not in the jet but rather in a region of the protostar's disk that spans twice the distance between the Earth and the sun—and that is located at the equivalent orbit around our star of our solar system's main asteroid belt. The churning of the disk or intense stellar winds from the growing protostar may help the grains accumulate there. Although the JWST and ALMA observations did not directly detect CAIs, the ratios of the detected minerals and their location around HOPS-315 are consistent with many models' predictions of the conditions for the emergence of CAIs at 'time zero' in the very early solar system. 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'It would be extremely important to detect CAIs in protoplanetary disks because it would allow us to connect the evolution of these disks with that of the solar system,' she says. 'But in this paper, the authors clearly state they haven't detected CAIs; they've [instead] detected crystalline grains that could have formed in an environment where CAIs could form, too. It's a very interesting link.' Observations of protostars such as HOPS-315, she adds, can be very difficult to interpret. 'There is the star, the disk, the wind, the jet, the envelope—these are very complex objects,' she says. 'The authors have done a really nice job of teasing out all the information they can from their observations [of HOPS-315], but this is a challenging object, so we definitely need to find and look at more.' One protostar in particular, Pascucci notes, is HOPS-68. Other astronomers observed it with Spitzer in 2011 and found similar features in the lower-resolution data that was available then. At the time, they interpreted those features as part of the protostar's obscuring envelope rather than its inner protoplanetary disk, she says, yet this new result suggests it may be time to revisit that object with JWST for another, deeper look. As for HOPS-315, McClure speculates that the system may still hold surprises. Her team's JWST data, she says, show that the outflow jet that complicated their analysis is conspicuously depleted in silicon—which happens to be the most important element for making the silicates that serve as planetary building blocks. Perhaps, then, instead of feeding the jet, the silicon has been locked away elsewhere—such as in reservoirs of dust or even larger rocky objects that are deeper in the disk. 'Our estimates suggest that something like 98 percent of the silicon we'd expect relative to the carbon we see [in the jet] is missing,' she says. 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Yahoo
4 hours ago
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When you buy through links on our articles, Future and its syndication partners may earn a commission. Three years ago, NASA made history by deliberately smashing a spacecraft into a large asteroid, altering its course and demonstrating humankind's ability to protect our planet from "potentially hazardous" space rocks in the future. But a new analysis hints that the debris from this monumental collision is not behaving as expected, raising doubts about the success of future asteroid-deflecting missions. On Sept. 26, 2022, NASA's Double Asteroid Redirection Test (DART) spacecraft purposefully collided with the asteroid Dimorphos, crashing directly into the middle of the space rock at around 15,000 mph (24,000 km/h). The mission was a smashing success: Not only did DART alter Dimorphos' trajectory — shortening its trip around its partner asteroid Didymos by around 30 minutes — it also completely changed the shape of the asteroid. 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The choice of sperm is 'entirely up to the egg' — so why does the myth of 'racing sperm' persist?
When you buy through links on our articles, Future and its syndication partners may earn a commission. It's a commonly held belief: Sperm cells are like runners in an epic race, competing against each other for access to the coveted egg at the finish line. The egg, in turn, waits patiently for the winning sperm to pierce its outer membrane, triggering fertilization. This narrative of racing sperm and waiting eggs has persisted through time — and yet, it simply isn't accurate. Scientific research has debunked this idea time and time again. In her new book "The Stronger Sex: What Science Tells Us about the Power of the Female Body" (Seal Press/Hachette, 2025), science writer Starre Vartan addresses this and other pervasive myths about the female body, highlighting what science actually tells us about differences in biology between the sexes and where gaps in knowledge still exist, in part, due to a historic lack of research focused on females. Making all your eggs at once, stress-testing and dumping most of them, and having one available at a time for fertilization is a mammalian adaptation. It represents a shift in reproductive strategy, according to Professor Lynnette Sievert, a biological anthropologist at the University of Massachusetts, Amherst. That shift is away from an earlier, or more ancient method of reproduction, which fish, amphibians, and most reptiles still employ today to great success. They both make both eggs and sperm continually, in great quantities, and throughout their lifetimes until they die. Female fish and frogs expel their masses of eggs into the water, and the males shoot, deposit, or generally aim their sperm in the eggs' direction. The eggs that get fertilized then develop — or don't, due to environmental conditions, or get eaten by predators. Sea turtles have sex, but still lay hundreds of fertilized eggs at a time and do so until they are elderly, as do oviparous snakes (viviparous snakes give birth to live young). For all these animals, reproduction is a numbers game. Lots of eggs, lots of sperm, plenty of fertilized eggs and hatchlings, with just a few young surviving to adulthood. In many cases the newly hatched turtles, tadpoles and wee snake-babies are an important food source for other animals who live in their ecosystem, like a biological offering to the greater community. This more-reproductive-stuff-is-better design is still employed by male humans, but not females. Related: Do sperm really race to the egg? "Human males still follow the fish pattern. They're still putting out a million sperm. They're not cleaning the sperm, they're not putting out the best sperm, they're just putting out all the sperm just like a fish," Sievert says. She wonders why then, female mammals made a significant shift away from that model. "Why was there never a selection on male sperm and mammals to be like eggs? Something shifted, that separated the sexes," she says. It's an unanswered biological question, but there is one obvious possible answer: Control. Female mammals house the mechanisms over which eggs (and sperm) are used for reproduction inside their bodies, while amphibians, reptiles, and fish let outside ecological conditions like temperature, predators, salinity and pollutants decide who lives and dies. Both strategies are clearly effective, but why would mammals have shifted away from a successful model? It could be that longer-lived mammals are able to store epigenetic information about local conditions as they grow, which could influence when and which eggs and sperm are chosen. The choices about who lives and who doesn't are made before or during conception, instead of after, resulting in offspring that are best suited to current conditions. Why all this trouble to "turn your body into an eggshell," as Cat Bohannon puts it in her book "Eve: How the Female Body Drove 200 Million Years of Evolution" — when the eggshell, or other reproductive strategies work so well? It could be explained by a combination of energetics and fine-tuning. By bringing fertilization and growing their young inside the female body, mammals can then use their lived experience (not just conditions at the moment of conception) to affect which traits are selected for. They can do this by controlling both which egg and which sperm are preferred. All this energy being used at or before the stage of conception means there are fewer fertilized eggs, and fewer babies. When you only have a baby or two at a time, instead of hundreds, it then becomes logical to invest in ensuring it has the best chances of survival — so an egg battle and a female body that's choosy about sperm makes total sense. As do the years of parenting that follow. That eggs choose sperm is a basic biological fact that has been "discovered" quite a few times over the years. The stubbornness of the "active sperm and waiting egg" story despite the facts highlights how hard it is for humans to accept biological narratives that run counter to our cultural ideas. As Emily Martin detailed in her memorable paper, we know that it was once the narrative that the sperm was the active party in fertilization, with all the speedy, tough sperm out swimming each other and trying to be the first one to attack the egg's outer membrane to gain entry and deposit their DNA packages. Way back in the mid-1980s, it was first discovered that the egg was actually the active decider in fertilization. The egg does this by using its zona pellucida (a thick protein coat that protects the egg cell) to chemically grab onto sperm, test it, and then reject or admit its DNA into the egg. The sperm, wiggling back-and-forth, can't break even a single chemical bond, but the egg can. Research in the 1990s went on to support the idea, and it's widely accepted. Yet, over the last 20 years, scientists continue to "discover" this fact. In 2017, Quanta magazine published an article about a researcher whose work was "challenging this dogma" that "the egg is not the submissive, docile cell that scientists long thought it was" and in 2019, a University of Virginia magazine article stated: "The old notion of the egg as a passive partner for sperm entry is out. Instead, the researchers found, there are molecular players on the surface of the egg that bind with a corresponding substance on the sperm to facilitate the fusion of the two." The writer called this an "unexpected discovery." This "rediscovery" of already known scientific information about the egg and sperm's interaction was covered by a Ms. Magazine article in 2024 about Evelyn Fox Keller, a pioneer in the field of feminist philosophy of science. The passive egg/active sperm idea just wouldn't go away, even in the same journals that published the research that it wasn't true. "One of Fox Keller's key findings was that seemingly neutral assumptions in biology can in fact be gendered. Keller's informed social analysis of the sciences paved the way to approach science as a cultural phenomenon." That researchers and the science press are repeating the same "discoveries" for decades shows just how gendered ideas stick to the culture, and can hold science back. The newest evidence shows that not only does an egg decide which sperm it wants to admit, the egg may be attracting or repelling different sperm even before they make it to the egg. In 2020, scientists at Stockholm University collaborating with colleagues at the University of Manchester found that eggs release a chemical that can attract sperm as it makes its journey. They also found that different eggs attract different varieties of sperm — not all eggs attracted the same sperm. The eggs sometimes attracted sperm that was not their partner's. They figured this out by obtaining reproductive material from couples who gave them permission to at an IVF clinic in Manchester, U.K. "Each experimental block comprised the follicular fluid and sperm samples from a unique set of two couples, exposing sperm from each male to follicular fluid from their partner and a non-partner," the researchers wrote of their methods. RELATED STORIES —1st 'atlas' of human ovaries could lead to fertility breakthrough, scientists say —Sperm don't swim anything like we thought they did, new study finds —Watch 1st-ever video of ovulation occurring in real time Chemosensory communication between eggs and sperm allows "female choice and bias fertilizations toward specific males," the researchers wrote. What are the egg's criteria? It's unknown at this point. It could be selecting higher-quality sperm or sperm that's more genetically compatible in some way. "This shows that interactions between human eggs and sperm depend on the specific identity of the women and men involved," one of the researchers told Labroots. He went on to say that the choice of sperm was entirely up to the egg. The science shows that contrary to some cultural stories, the menstrual cycle is highly sensitive to conserve energy; eggs go to war each month so that only the strongest survive; that winner egg sends out come-hither signals to sperm it likes; and then it chooses which sperm to unite with to make a possible new human being. So much for the inherent weakness of women's bodies and the passive female reproductive system. In interviews with dozens of researchers from biology, anthropology, physiology, and sports science, plus in-depth conversations with runners, swimmers, wrestlers, woodchoppers, thru-hikers, firefighters, and more, "The Stronger Sex" squashes outdated ideas about women's bodies. It's a celebration of female strength that doesn't argue "down with men" but "up with us all."
