Read more "How comets paint swirls on the Moon"
At first glance, the swirls do not appear to be related to large impact craters or any other topography. ‘They simply look as if someone had finger-painted the surface,’ Schultz said. ‘There has been an intense debate about what causes these features.’
In the 1970s, scientists discovered that many of the swirls were associated with anomalies of the moon’s crustal magnetic field. That revelation led to one hypothesis for how the swirls may have formed. Rocks below the surface in those spots might contain remanent magnetism from early in the moon’s history, when its magnetic field was much stronger than it is now. It had been proposed that those strong, locally trapped magnetic fields deflect the onslaught of the solar wind, which was thought to slowly darken the moon’s surface. The swirls would remain brighter than the surrounding soil because of those magnetic shields.
But Schultz had a different idea for how the swirls may form – one that has its roots in watching the lunar modules land on the moon during the Apollo program.
‘You could see that the whole area around the lunar modules was smooth and bright because of the gas from the engines scoured the surface,’ Schultz said. ‘That was part of what got me started thinking comet impacts could cause the swirls.’
Comets carry their own gaseous atmosphere called a coma. Schultz thought that when small comets slam into the moon’s surface – as they occasionally do – the coma may scour away loose soil from the surface, not unlike the gas from the lunar modules. That scouring may produce the bright swirls.
Schultz first published a paper outlining the idea in the journal Nature in 1980. That paper focused on how the scouring of the delicate upper layer of lunar soils could produce brightness consistent with the swirls. The structure of the grains in the upper layer (termed the ‘fairy castle structure’ because of the way grains stick together) scatters the sun’s rays, causing a dimmer and darker appearance. When this structure is stripped away, the remaining smoothed surface would be brighter than unaffected areas, especially when the sun’s rays strike it at certain angles. For Reiner Gamma on the lunar nearside, those areas appear brightest during the crescent moon just before sunrise.
As computer simulations of impact dynamics have gotten better, Schultz and Bruck-Syal decided it might be time to take a second look at whether comet impacts could produce that kind of scouring. Their new simulations showed that the impact of a comet coma plus its icy core would indeed have the effect of blowing away the smallest grains that sit atop the lunar soil. The simulations showed that the scoured area would stretch for perhaps thousands of kilometers from the impact point, consistent with the swirling streaks that extend across the moon’s surface. Eddies and vortices created by the gaseous impact would explain the swirls’ twisty, sinuous appearance.
The comet impact hypothesis could also explain the presence of magnetic anomalies near the swirls. The simulations showed that a comet impact would melt some of the tiny particles near the surface. When small, iron-rich particles are melted and then cooled, they record the presence of any magnetic field that may be present at the time. ‘Comets carry with them a magnetic field created by streaming charged particles that interact with the solar wind,’ Schultz said. ‘As the gas collides with the lunar surface, the cometary magnetic field becomes amplified and recorded in the small particles when they cool.’
Taken together, the results offer a more complete picture of how the swirls form, the researchers say.
A group of scientists, including UC Santa Barbara’s James Kennett, professor emeritus in the Department of Earth Science, posited that a comet collision with Earth played a major role in the extinction. Their hypothesis suggests that a cosmic-impact event precipitated the Younger Dryas period of global cooling close to 12,800 years ago. This cosmic impact caused abrupt environmental stress and degradation that contributed to the extinction of most large animal species then inhabiting the Americas. According to Kennett, the catastrophic impact and the subsequent climate change also led to the disappearance of the prehistoric Clovis culture, known for its big game hunting, and to human population decline.
“We conclusively have identified a thin layer over three continents, particularly in North America and Western Europe, that contain a rich assemblage of nanodiamonds, the production of which can be explained only by cosmic impact,” Kennett said. “We have also found YDB glassy and metallic materials formed at temperatures in excess of 2200 degrees Celsius, which could not have resulted from wildfires, volcanism or meteoritic flux, but only from cosmic impact.”
To date, scientists know of only two layers in which more than one identification of nanodiamonds has been found: the YDB 12,800 years ago and the well-known Cretaceous-Tertiary boundary 65 million years ago, which is marked by the mass extinction of the dinosaurs, ammonites and many other groups.
“The evidence we present settles the debate about the existence of abundant YDB nanodiamonds,” Kennett said. “Our hypothesis challenges some existing paradigms within several disciplines, including impact dynamics, archaeology, paleontology and paleoceanography/paleoclimatology, all affected by this relatively recent cosmic impact.”
The Russian Federal Space Agency (Roscosmos) is planning to launch a space system for countering asteroids, comets and space junk by 2025, according to the draft of the 2016-2025 federal space program sent by the agency to the government for approval.
The document proposes to create “means of ensuring the delivery and interference with objects dangerously approaching the Earth, with the aim to change their orbits to prevent collision with the planet.”
The system should also include space ‘cleaners’ designed to remove from orbit large “space junk” such as spacecraft debris and old satellites.
The orbital segment will be an addition to the ground component of a system that will control and test anti-asteroid and anti-space junk technologies, it said.
Roscosmos has asked for nearly 23 billion rubles for the construction of the orbital and ground components of the system.
The project will build upon the experience gained under other programs as part of efforts to boost safe functioning of spacecraft and ground space infrastructure. The anti-asteroid project will be developed around the automatic space emergency prevention system in the near-earth outer space, operating at the Mission Control Center (in Korolyov, Moscow region).
The comet was actually discovered by my computer here under my desk!
Our human-volunteer TOTAS clickers review all the ‘movers’ found by the software and either confirm or reject them. That task can’t be done by software – but the software can combine the single detections and extract the moving objects.
Just one of the ways we’re forming a team with machines and exploring the cosmos.Read more "Finding a comet: the backstory | Rocket Science"
This artist’s conception illustrates a storm of comets around a star called Eta Corvi. Evidence for this barrage comes from NASA’s Spitzer Space Telescope, whose infrared detectors picked up indications that one or more comets was torn to shreds after colliding with a rocky body.
For years, astronomers have been scanning nearby asteroids, the moon, Mars, and deeper space for evidence of the building blocks of life.
Now, a new study in the Proceedings of the National Academy of Sciences finds that both water and organic material could actually have our planet surrounded, floating around space on ubiquitous interplanetary dust particles that constantly rain down on Earth and the other bodies in our solar system.
“It is a thrilling possibility that this influx of dust has acted as a continuous rainfall of little reaction vessels containing both the water and organics needed for the eventual origin of life on Earth and possibly Mars,” researcher and study co-author Hope Ishii of the Hawaii Institute of Geophysics and Planetology said in a release.
In the case of comets, the icy space rocks import frozen water from beyond the solar system when they come to visit, but the traces of water on interplanetary dust particles are actually a product of the solar wind that blasts them with hydrogen ions, shaking up the atoms of the silicate mineral crystals in the dust particles. This process leaves behind some oxygen to react with hydrogen and create water molecules.
“Perhaps more exciting,” Ishii said, “interplanetary dust, especially dust from primitive asteroids and comets, has long been known to carry organic carbon species that survive entering the Earth’s atmosphere, and we have now demonstrated that it also carries solar-wind-generated water. So we have shown for the first time that water and organics can be delivered together.”Read more
Though NASA’s StarDust mission flew through the tail of comet Wild2 in 2004, no craft has ever orbited one. Rosetta will orbit its target at a leisurely walking pace, searching for a landing spot. Things will get even more exciting in November, when the robotic lander Philae (illustrated) detaches from the mother ship and becomes the first spacecraft to land on a comet.
Philae will anchor itself with a harpoon before starting to dig. An on-board lab will analyse the scoops of rock and beam the results to Earth. Like asteroids, comets are thought to preserve material from the birth of the solar system, 4.6 billion years ago. Comets contain water, so the chemistry of the scoops could reveal whether our oceans, and a bunch of molecules necessary for life, came from comets smashing into early Earth.Read more