Washington (AFP) - Four astronauts entered the International Space Station on Friday after their SpaceX Dragon Crew-6 mission successfully docked, a NASA livestream showed.
The SpaceX Dragon Endeavour spacecraft arrived at the orbiting station at 0640 GMT on Friday, the US space agency said in a statement.
Early results from this first real-world test of our potential planetary defence systems looked promising. However, it’s only now that the first scientific results are being published: five papers in Nature have recreated the impact, and analyzed how it changed the asteroid’s momentum and orbit, while two studies investigate the debris knocked off by the impact.
The conclusion: “kinetic impactor technology is a viable technique to potentially defend Earth if necessary”.
Our Solar System is full of debris, left over from the early days of planet formation. Today, some 31,360 asteroids are known to loiter around Earth’s neighbourhood.
Asteroid statistics and the threats posed by asteroids of different sizes. NASA's DART press brief
Although we have tabs on most of the big, kilometre-sized ones that could wipe out humanity if they hit Earth, most of the smaller ones go undetected.
Just over ten years ago, an 18-meter asteroid exploded in our atmosphere over Chelyabinsk, Russia. The shockwave smashed thousands of windows, wreaking havoc and injuring some 1,500 people.
A 150-metre asteroid like Dimorphos wouldn’t wipe out civilisation, but it could cause mass casualties and regional devastation. However, these smaller space rocks are harder to find: we think we have only spotted around 40% of them so far.
Suppose we did spy an asteroid of this scale on a collision course with Earth. Could we nudge it in a different direction, steering it away from disaster?
Hitting an asteroid with enough force to change its orbit is theoretically possible, but can it actually be done? That’s what the DART mission set out to determine.
Specifically, it tested the “kinetic impactor” technique, which is a fancy way of saying “hitting the asteroid with a fast-moving object”.
The asteroid Dimorphos was a perfect target. It was in orbit around its larger cousin, Didymos, in a loop that took just under 12 hours to complete.
The impact from the DART spacecraft was designed to slightly change this orbit, slowing it down just a little so that the loop would shrink, shaving an estimated seven minutes off its round trip.
For DART to show the kinetic impactor technique is a possible tool for planetary defence, it needed to demonstrate two things:
In the words of Cristina Thomas of Northern Arizona University and colleagues, who analysed the changes to Dimorphos’ orbit as a result of the impact, “DART has successfully done both”.
The DART spacecraft steered itself into the path of Dimorphos with a new system called Small-body Manoeuvring Autonomous Real Time Navigation (SMART Nav), which used the onboard camera to get into a position for maximum impact.
More advanced versions of this system could enable future missions to choose their own landing sites on distant asteroids where we can’t image the rubble-pile terrain well from Earth. This would save the trouble of a scouting trip first!
Dimorphos itself was one such asteroid before DART. A team led by Terik Daly of Johns Hopkins University has used high-resolution images from the mission to make a detailed shape model. This gives a better estimate of its mass, improving our understanding of how these types of asteroids will react to impacts.
The impact itself produced an incredible plume of material. Jian-Yang Li of the Planetary Science Institute and colleagues have described in detail how the ejected material was kicked up by the impact and streamed out into a 1,500km tail of debris that could be seen for almost a month.
The DART impact blasted a vast plume of dust and debris from the surface of the asteroid Dimorphos. CTIO / NOIRLab / SOAR / NSF / AURA / T. Kareta (Lowell Observatory), M. Knight (US Naval Academy)
Streams of material from comets are well known and documented. They are mainly dust and ice, and are seen as harmless meteor showers if they cross paths with Earth.
Asteroids are made of rockier, stronger stuff, so their streams could pose a greater hazard if we encounter them. Recording a real example of the creation and evolution of debris trails in the wake of an asteroid is very exciting. Identifying and monitoring such asteroid streams is a key objective of planetary defence efforts such as the Desert Fireball Network we operate from Curtin University.
So how much did the impact change Dimorphous’ orbit? By much more than the expected amount. Rather than changing by seven minutes, it had become 33 minutes shorter!
This larger-than-expected result shows the change in Dimorphos’ orbit was not just from the impact of the DART spacecraft. The larger part of the change was due to a recoil effect from all the ejected material flying off into space, which Ariel Graykowski of the SETI Institute and colleagues estimated as between 0.3% and 0.5% of the asteroid’s total mass.
The success of NASA’s DART mission is the first demonstration of our ability to protect Earth from the threat of hazardous asteroids.
At this stage, we still need quite a bit of warning to use this kinetic impactor technique. The earlier we intervene in an asteroid’s orbit, the smaller the change we need to make to push it away from hitting Earth. (To see how it all works, you can have a play with NASA’s NEO Deflection app.)
But should we? This is a question that will need answering if we ever do have to redirect a hazardous asteroid. In changing the orbit, we’d have to be sure we weren’t going to push it in a direction that would hit us in future too.
However, we are getting better at detecting asteroids before they reach us. We have seen two in the past few months alone: 2022WJ1, which impacted over Canada in November, and Sar2667, which came in over France in February.
We can expect to detect a lot more in future, with the opening of the Vera Rubin Observatory in Chile at the end of this year.
Eleanor K. Sansom, Research Associate, Curtin University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
In trap-feeding, whales lie at the surface of the water with their mouths open. This allows shelter-seeking prey species such as herring and krill – which do not perceive a stationary object as a threat – to shoal into their open mouths. The whale then heaves its mouth closed, trapping hundreds of prey in a single gulp. This behaviour has been observed in the Gulf of Thailand in Bryde’s or Eden’s whales, and in Canada in humpback whales.
But it appears parallels to this behaviour were also documented in medieval literature, as we describe in a new paper published today in Marine Mammal Science.
There are striking parallels between trap-feeding and the hunting strategy of a monstrous sea creature called the “hafgufa”, described in medieval Scandinavian manuscripts.
The mid-13th-century Old Norse text Konungs Skuggsjá (the King’s Mirror) says of this creature:
‘when it goes to feed, it gives a great belch out of its throat, along with which comes a great deal of food. All sorts of nearby fish gather, both small and large, seeking there to acquire food and good sustenance. But the big fish keeps its mouth open for a time, no more or less wide than a large sound or fjord, and unknowing and unheeding, the fish rush in in their numbers. And when its belly and mouth are full, [the hafgufa] closes its mouth, thus catching and hiding inside it all the prey that had come seeking food‘ (M. Firth, Trans.).
This sea monster from Ortelius’s 1658 map of Iceland is described as having similar behavior as the earlier Norse accounts of a creature called the ‘hafgufa’ - could it be related to a recently observed feeding strategy of whales?
Top: Detail from Ortelius's 1658 map of Iceland - 'H: the greatest of whales which could not chase fish but caught them through cunning. Bottom: digital representation of a trap-feeding humpback. (J. McCarthy, Author provided)
Although this text exaggerates the creature’s size, the other details match trap-feeding surprisingly closely. Even the hafgufa’s belch may correspond to reports of rorqual whales expelling a surplus slurry of water and food particles as they filter and swallow their prey.
Interestingly, the creature is not described as a fantastical monster, but as a fish, a term often used interchangeably with whales in medieval sources.
If these medieval Scandinavian texts really are describing trap-feeding, it demonstrates the technique is much older than previously thought. So, we examined other pre-modern descriptions of sea creatures looking for parallels.
Many of the texts had been adapted or translated directly from earlier texts, so it was impossible to know if the community which produced them had first-hand experience of trap-feeding. However, in some texts new accurate details had been added, suggesting an eye-witness connection.
The earliest of these, an ancient work on natural history called the Physiologus, was compiled in Egypt and dates back nearly two millennia.
Various depictions of known or possible hafgufas/aspidochelones in 13th century medieval bestiaries from Europe. Full details in Marine Mammal Science, 2023. (Author provided)
But if trap-feeding was first recorded 2,000 years ago, why has it not been reported in modern times until 2011?
One possible explanation is that the devastating effect of historical whaling has caused whale numbers to remain much lower than they were in medieval and ancient times. North Atlantic humpback numbers are estimated to be only a fifth of their pre-industrial whaling levels.
Trap-feeding may be a response to higher population density. Just this month, new research on Australian humpbacks showed that whalesongs are becoming less frequent as populations recover from whaling and competition for mating becomes more intense.
The rise in whaling in the 17th and 18th centuries was accompanied by developments in technology and a corresponding prejudice against medieval society, which was increasingly seen as backwards, unscientific, and superstitious.
However, the most fantastical descriptions of the hafgufa are actually from 17th- and 18th-century writers, who conflated the creature with all kinds of other sea monsters, such as the kraken, resulting in a general confusion about the nature of this creature in modern times. One notable recent depiction of the hafgufa in the popular PlayStation game God of War Ragnarök even depicts it as a giant jellyfish!
In conducting our research, we spoke to marine biologists who assumed it would simply be impossible to determine how long whales had been trap-feeding. So, this multidisciplinary research provides evidence from an unexpected quarter, and may highlight new avenues for researching our marine past.
It also shows that although medieval and ancient people did not have modern scientific frameworks to interpret the natural world, their observations can contain unique evidence of natural phenomena and may be more accurate than we realise.
John McCarthy, ARC DECRA Fellow, Flinders University; Erin Sebo, Associate Professor in Medieval Literature and Language, Flinders University, and Matthew Firth, Associate lecturer, Flinders University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
While bacteria that are more sensitive to the antibiotics are killed off, those that are able to survive will continue to reproduce with less competition. This results in increasing abundance of resistant bacteria that can undermine the effectiveness of the antibiotic.
I am a researcher who studies the evolution of antibiotic resistance. During my medical training, I was taught about the importance of hospital hygiene practices like hand-disinfection. It is well established that good hygiene can help prevent transmission of harmful bacteria from other people or from the environment. I came to wonder how hygiene affects the evolution of antibiotic resistance.
Hand-washing is an essential component of hospital hygiene practices. nano/E+ via Getty Images
So I teamed up with my colleagues Magnus Aspenberg, Sara Maad Sasane, Fredrik Nilsson and Sam Brown, experts in mathematics, statistics and microbial evolution, to answer this question.
We built a mathematical model of antibiotic resistance evolution. In this model, resistant and sensitive bacteria compete in the microbial communities living in patients and transmit from one patient to another. We studied the effects of two parameters: hygiene (or use of an alcohol-based hand rub), which limits how much bacteria spreads between patients, and antibiotic use, which selects for resistant bacteria by killing sensitive ones.
We found that hygiene and antibiotic use interact. Antibiotic use had less of an effect on the evolution of antibacterial resistance as hygiene levels increased. This is because evolution toward resistance depends on variation in bacterial sensitivity to antibiotics. By affecting the distribution of resistant and sensitive bacterial strains across patients, hygiene limits the bacterial diversity needed to evolve resistance.
The effectiveness of antibiotics is under threat from bacteria rapidly evolving resistance against them.
Research on the evolution of antimicrobial resistance has focused more on evolutionary selection than hygiene. Most studies investigate, for example, whether a high or a low dose of a drug is better to prevent resistance. Incorporating hygiene and other interventions into research on antibiotic resistance could help build a more comprehensive understanding of how bacteria evolve to become resistant.
The role of good hygiene in preventing illness is already well accepted in practice. Our findings underscore its importance by highlighting the role it plays in the evolutionary process of bacterial resistance.
Kristofer Wollein Waldetoft, Postdoctoral Fellow in Infection Medicine, Georgia Institute of Technology
This article is republished from The Conversation under a Creative Commons license. Read the original article.
