Astronomy

Why did the distribution of asteroids discovered in 2010 have a radial modulation?

Why did the distribution of asteroids discovered in 2010 have a radial modulation?


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This answer links to one of Scott Manley's excellent asteroid videos Asteroid Discovery - 1970-2015 - 8K resolution. The animation highlights the positions of the meteors at the moment of their discovery, and by watching one can see the technology improve and notice patterns as instruments are pointed in different directions to avoid the light from the Sun and (at least sometimes) the Moon. (there is music, adjust volume accordingly)

There are often fan-shaped patterns showing the directions that more sensitive telescopes with modest fields of view are pointed.

However, I noticed that only during the year 2010, roughly between asteroid numbers500,000and520,000there are radial striations at certain distances from the Sun. I don't see this happen at any other time during the video.

Is this just a rendering artifact, or is it real? If real, what would cause the periodic radial modulation of sensitivity, and only in 2010?

note 1: YouTube allows for playback rates between 25% and 200%, and variable video resolutions. I found 25% and 1080p optimal for my current internet connection and screen.

note 2: For those with GIFs disabled, one image is a GIF.

note 3: 2nd image contains several cropped screenshots highlighting the "periodic radial modulation of sensitivity" in asteroid detection during 2010, for clarification purposes.


I'm pretty sure that the radial pattern found in the data is a result of WISE's approximately 90 minute sampling cadence (dictated by the satellite's orbit), astrometric precision (about 0.2 arcseconds in the stacked images around launch, see Wright et al. 2010), and the number of free parameters in fitting the asteroid orbits based on that data. See, in the actual images the asteroids appear as points of light that shift appreciably between frames. IIRC, they expected 7 to 12 observations per asteroid. So you have 10-ish observations spanning 15 hours or so to fix the asteroid's orbital parameters around the sun. As you can imagine, there will be more parameters than can be perfectly fit with a single pass in this data set alone.

At a guess: it's related to quantization in uncertainty estimates and how that feeds forward into the orbit fitting algorithm.

I don't know the details behind the striping, but I'd bet it's related to the numerical precision used in the early processing of the data. They've either refined the orbits since using observations from passes separated by ~6 months, or modified how they're handling the numerical precision in their astrometric measurements since. More likely the former, but I'm sure if you asked Amy Mainzer (PI of NEOWISE, and head of the asteroid hunting part of the mission), Roc Cutri (head of the database creation and data processing part of the team), or any of the people on Mainzer's team, they could tell you more.

Relevant background: I was Ned Wright's grad student (original PI of WISE), and he had me design and test an asteroid hunting algorithm in the run-up to launch (we ultimately didn't use it - it scaled like $N^2$, IIRC, and existing efforts in the literature scaled like $log(N)$ or $Nlog(N)$). I ended up working with the extragalctic part of the team, hence my uncertainty on the precise details of what the solar system team did. I think I asked them about the striping during a presentation, but I don't recall the answer, so I'm pretty sure the answer was mundane and unavoidable.


Answer based on a misunderstanding of the question, left here because it contains some useful background on WISE.

The pie-shaped patterns starting in 2010 are results of the WISE mission (see the video description). The radial pattern within those pie shapes is not explained by my answer.

NASA's Wide-field Infrared Survey Explorer (WISE) is a space telescope launched in 2009 to map the entire sky in infrared wavelengths.

WISE imaged the entire sky twice before running out of coolant in 2010. It then did a brief mission called NEOWISE, to look at near-Earth objects (NEOs) such as asteroids and comets, for four months before being placed into hibernation in February 2011. Less than three years later, in December 2013, the telescope was revived to continue its NEOWISE mission. That work continues today.

Looking at WISE:

you can see the telescope is perpendicular to the solar panels, so it'll tend to look at objects perpendicular to the Earth-Sun line, which causes the bright bands you see in the video.

https://www.space.com/33659-wise-space-telescope.html


The effect is already visible in the first video released in 2010: https://www.youtube.com/watch?v=S_d-gs0WoUw

For what it's worth, I tried to download the newest astorb.dat and plot it, but couldn't see the effect there. So it might very well be that the 2010 asteroids were based on preliminary WISE data and weren't all that accurate, and the later videos have not updated the old animations.

And indeed, from the comments of the 2010 video:

odysseus9672: @szyzyg I spoke with Prof Wright, the project PI, and he explained that the striping is due to the Minor Planet Center using an approximate fitting technique to the WISE data. The reasoning for this, I think (we've left Ned approved commentary here), is that the WISE data has a relatively short time baseline (~24 to 48 hrs), so the errors on the orbital fits will be quite large anyway, so there's no point in refining it much past what the error bars will support.

Scott Manley: @odysseus9672 Glad to hear an explanation, this pretty much confirms my suspicions and makes me ask how many of the objects are likely to be lost again in the future. Most of the objects discovered in the leading edge scan in January will have passed through opposition with the Earth and most orbits haven't been refined. The second pass of the WISE survey will hopefully start getting longer arcs on some of these, but WISE will run out of coolant before it can observe every asteroid twice.


First Asteroid Companion of Earth Discovered at Last

The first in a long-sought type of asteroid companion to Earth has now been discovered, a space rock that always dances in front of the planet along its orbital path, just beyond its reach.

The asteroid, called 2010 TK7, is nearly 1,000 feet (300 meters) across and currently leading the Earth by about 50 million miles (80 million kilometers).

The asteroid is the first in a category known as Earth's Trojans, a family of space rocks that could potentially be easier to reach than the moon, even though its member asteroids can be dozens of times more distant, researchers said. Such asteroids, which have long been suspected but not confirmed until now, could one day be valuable destinations for missions, especially loaded as they might be with elements rare on Earth's surface, they added. [Photo and orbit of Asteroid 2010 TK7]

To imagine where Trojan asteroids are, picture the sun and Earth as being two points in a triangle whose sides are equal in length. The other point of such a triangle is known as a Trojan point, or a Lagrangian point after the mathematician who discovered them. The sun and Earth have two such points, one leading ahead of Earth, known as its L-4 point, and one trailing behind, its L-5 point.

The sun and other planets have Lagrangian points as well, and asteroids have been seen at those the sun shares with Jupiter, Neptune and Mars. Scientists had long suspected the sun and Earth had Trojans as well, but these companions would dwell mostly in the daytime sky as seen from Earth, making them largely hidden in the sunlight.

Now, with the aid of the Wide-field Infrared Survey Explorer (WISE) satellite launched in 2009, astronomers have discovered Earth's first probable Trojan, a rock that spends its time at the sun-Earth L-4 point.

Earth's first Trojan asteroid

Asteroid 2010 TK7 has a bizarre, chaotic orbit.

Trojan asteroids typically do not orbit right at the Lagrangian points but in tadpole-shaped loops around them, due to the gravitational attraction of other bodies in the solar system. However, 2010 TK7's tadpole orbit is unusually large, at times taking it nearly as far as the opposite side of the sun from the Earth. [Photos: Asteroids in Deep Space]

"This one has behavior much more interesting than I thought we would find," study co-author Martin Connors, an astronomer at Athabasca University in Canada, told SPACE.com. "It seems to do things not seen for Trojans before. Still, it had to have some kind of extreme behavior to move it far enough from its Lagrangian point to get within our view."

Connors and his team began their search for an Earth Trojan using data from WISE's asteroid- and comet-hunting project, called NEOWISE, named after Near-Earth Objects and WISE.

The WISE telescope scanned the whole sky in infrared light from January 2010 to February 2011, a hunt that resulted in two candidates, one of which, 2010 TK7, was confirmed to be an Earth Trojan after follow-up observations at the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii.

The researchers have calculated the asteroid's orbit well enough to understand where it will be over the next 10,000 years — 2010 TK7 will not approach Earth any closer than 12.4 million miles (20 million kilometers), which is more than 50 times the distance from Earth to the moon.

"It's as though the Earth is playing follow the leader," said Amy Mainzer, the principal investigator of NEOWISE at NASA's Jet Propulsion Laboratory, who was not a part of the study. "Earth is always chasing this asteroid around."

The fact that 2010 TK7's behavior is chaotic enough to take it quite far from its rather stable Trojan point suggests it is only marginally trapped there, having perhaps only recently been disturbed from its original position. The researchers will run more computer models of its orbit to find out what happened, Connors said.

Asteroid 2010 TK7 may be the first confirmed Earth Trojan asteroid, but there are several space rocks known to exist in relatively stable orbits in our planet's neighborhoods. They include asteroids Cruithneand 2010 SO16, which have vast horseshoe-shaped orbits, and at least two others. But none of these other asteroids have been conformed to be Earth Trojans.

Still much unknown

So far 2010 TK7 does not have a formal name. "Its orbit needs to be nailed down before a name is considered, so it'll take a couple of years more observations before the WISE team can give it one," Connors said.

No color information of it is at yet available of 2010 TK7 to shed light on its composition. In principle asteroids could have a similar makeup to Earth's, but since they are smaller they would have cooled down faster, meaning that heavier substances would not have had time to sink to their centers as they did on our planet.

As such, elements that are uncommon on Earth's surface might be more accessible on asteroids.

"We could be mining these things one day," Connors said.

Unfortunately, 2010 TK7 is not a good target because it travels above and below the plane of Earth's orbit, which means it would require large amounts of propellant to reach. However, if other Earth Trojans do exist, they could prove more accessible.

Now that the researchers have found one, "it makes you want to wonder if there are any more," Connors said. He noted hopefully the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) array of telescopes and cameras aimed at detecting near-Earth objects could turn more up.

The scientists detailed their findings in the July 28 issue of the journal Nature.


Water Ice Common on Asteroids, Discovery Suggests

Scientists have discovered water ice on an asteroid for the second time, suggesting that it is more common on space rocks in our solar system than previously thought.

Two research teams have found evidence of water ice and organic molecules on the asteroid 65 Cybele, just six months after discovering the same stuff on a different space rock — asteroid 24 Themis — for the first time. The results suggest that asteroids may have delivered much of these essential materials for life to the early Earth, the researchers said.

"This discovery suggests that this region of our solar system contains more water ice than anticipated," said Humberto Campins, of the University of Central Florida, in a statement. "And it supports the theory that asteroids may have hit Earth and brought our planet its water and the building blocks for life to form and evolve here."

The researchers analyzed the sunlight bouncing off 65 Cybele, which has a diameter of about 180 miles (290 kilometers) and circles the sun in the asteroid belt between the orbits of Mars and Jupiter.

The teams used two different NASA instruments: the Infrared Telescope Facility atop Mauna Kea in Hawaii, and the Spitzer Space Telescope. The telescopes picked up the telltale signatures of water ice and complex organic solids on the space rock's surface, researchers said.

They didn't find great sheets of ice — the asteroid's ice layer is probably less than one micron thick, Campins told reporters today (Oct. 8) during the 42nd annual meeting of the American Astronomical Society's Division for Planetary Sciences in Pasadena, Calif.

The ice layer is probably also very unstable, Campins said, so it has probably only coated the space rock for a few thousand years or so. The research team isn't sure where it came from, but one possibility is the asteroid's subsurface.

If the ice did indeed migrate up from 65 Cybele's interior, the water could be primordial, Campins said — leftovers from the early stages of our solar system's formation. But that's just speculation at this point.

"We have a detection, and we're starting to figure out what the physical characteristics and abundance of this ice are," Campins said.

Changing our view of asteroids

The discovery of water ice on 24 Themis — announced in April 2010 by the same two research teams — changed many scientists' perspectives on asteroids. [5 Reasons to Care About Asteroids]

Asteroid 24 Themis resides in the same region of the asteroid belt as 65 Cybele. Many scientists had thought asteroids in this part of the belt were too close to the sun to carry water ice.

These asteroids may have been ice-covered long ago during the solar system's youth, the thinking went, but their surface water should have evaporated by now.

Finding water ice on such space rocks now, 4.6 billion years after the solar system's birth, suggests that asteroids may have delivered much of the water that fills Earth's oceans — and perhaps some of the complex organic molecules that served as the building blocks of life here, scientists have said.

Earth has experienced a violent history, having been bombarded by space rocks throughout much of its life. In particular, a large rock is thought to have crashed into Earth some 4.5 billion years ago, knocking off a giant chunk of material that eventually became our moon.

At that point, the collision would have heated things up so much that any water on Earth would have been vaporized. So, how did the oceans form?

Comets hold a great deal of water ice, but they are not ideal candidates for filling up Earth's early oceans. Comet water tends to be of a different nature — its atoms are in a different configuration — than most of the water on Earth, scientists have said.

The new results strengthen the case for asteroids as water-bearers for the early Earth. In the solar system's early days, asteroids likely slammed into Earth far more frequently than they do today, researchers have said. If many asteroids were even just a little icy, the Earth could have received quite a drenching, they added.

The discovery may also be a boon to NASA's new space exploration program, which is aiming to send astronauts to visit a near-Earth asteroid by 2025.

The research has been accepted for publication in the journal Astronomy and Astrophysics.


Geminid meteor shower 2010: Why is the Phaethon asteroid going to pieces?

Geminid meteor shower 2010 climaxes between midnight Monday and dawn Tuesday. But the spectacle also poses a question: Why is the asteroid that supplies the meteorites breaking apart?

The Geminid meteor shower for 2010 peaks overnight Monday with what promises to be a spectacular show for sky watchers who find themselves under clear, dark skies with an unobstructed view of the horizon.

By some estimates, the Geminid meteor shower – so named because they appear to the observer to be emanating from the constellation Gemini – could yield up to 120 shooting stars an hour for those watching under ideal viewing conditions between midnight and dawn Tuesday.

For astronomy buffs, the Geminids often provide the best meteor-shower show of the year. For some astronomers, however, the display and its source – an asteroid known as 3200 Phaethon – represent something of a mystery: Where did this asteroid come from and why does it appear to be shedding like a golden retriever, something asteroids generally don't do?

"The whole thing is very weird," says David Jewitt, an astronomer at the University of California at Los Angeles who studies comets and asteroids.

Phaethon is a near-Earth asteroid – an object some three miles across whose orbit around the sun each 1.4 years brings it close to Earth's orbit and to within 13 million miles of the sun, well inside Mercury's orbit.

Astronomers discovered Phaethon in 1983 using a space-based infrared telescope known as IRAS. Once researchers had calculated the asteroid's orbit, the late astronomer and comet specialist Fred Whipple noticed that its path matched that of the debris stream that generates the Geminid shower.

That appeared to solve a problem, Dr. Jewitt explains, since until then, no one had identified a source of the material forming the Geminids.

Meteor showers typically stem from dust and rocks that comets shed as they approach the sun. They heat up, the ices they carry flash from ice to gas, and as the gas vents through the comet's surface, it carries dust and debris with it. No one had been able to associate a comet with the Geminid debris stream.

But that raised another question: Why is Phaethon shedding? Asteroids don't tend to do that. Astronomers looked for signs that it might have a small halo of gas around it, similar to a comet's "coma." But none appeared. Indeed, over the years, the object has yielded no evidence of activity that would eject material.

Then last year, Dr. Jewitt and colleague Jing Li received an alert from another colleague that Phaethon had brightened suddenly as it reached its closest approach to the sun.

Jewitt and Dr. Li captured images of Phaethon with NASA's STEREO-A spacecraft – one of a pair of sun-watching probes. They observed the brightening and proposed that Phaethon's flash occurred as it shed rocky material fractured by the heat of its close approach to the sun.

In effect, the researchers say, the object is a "rock comet" rather than an icy "dirty snowball" or "snowy dirt ball" comet. The duo published its results in November in the Astronomical Journal.

As for Phaethon's origins, another team led by Julia Maria de León Cruz at the Institute of Astrophysics of Andalusia in Grenada, Spain, suggests that Phaethon may be a chip off Pallas, a 340-mile-wide asteroid in the main asteroid belt, which circles the sun between Mars and Jupiter.

Although Phaethon and Pallas don't share the same overall color, a first-cut clue as to their surface composition, Phaethon does share more-detailed spectral signatures of nine other, smaller asteroids near Pallas that are associated with it. They posit that Phaethon and its nine siblings constitute debris left over from a collision between Pallas and another object in an event that would have carved a sizable crater into Pallas.

The Grenada team published its study in April in the journal Astronomy and Astrophysics.

It's still unclear if Phaethon is shedding enough material to continually resupply the Geminid meteor stream, Jewitt acknowledges. The stream is about 1,000 years old. Phaethon would have to undergo at least 10 such shedding events each orbit over that time to provide enough material to sustain the Geminid shower that humans observe today. So far, astronomers have observed just one.

More broadly, Phaethon could be opening a window on a little-understood process that marks the end of the line for many asteroids and comets.

"We know small bodies can be destroyed in different ways," Jewitt says. Collisions can break them apart. Comets can run out of gas, their cores becoming dark hulks orbiting the sun. Asteroids and comets can end in fiery plunges into the sun. And comets can get disrupted by planets' gravity and break apart.

With Phaethon however, astronomers may be witnessing that Jewitt calls spontaneous disintegration. "Its a physical decay," he says. "They fall to bits, for reasons which are unclear."

Not a promising future from Phaethon's perspective. But for Earthlings, that slow-mo crumble can put on a good show.


Near Earth Asteroid 2010 GU21 Swoops By Earth On May 5

The Near-Earth Asteroid (NEA) 2010 GU21 was discovered by the Catalina Sky Survey on April 5 2010 (MPEC 2010-G55) and has been designated as a Potentially Hazardous Asteroid (PHA) by the Minor Planet Center. The asteroid will pass within approximately 8 lunar distances on May 05.25 2010 UT… But why wait when we have Joe Brimacombe on our side?

2010 GU21 is photometrically surmised to be a X-type asteroid and very low-albedo… so dim, in fact, that it only manages about a magnitude 18. However, if you give Joe a magnitude 18 blip, he’ll send you back an image! Just watch how fast this crazy little thing travels….

And for heaven’s sake, don’t take the impact seriously! While eight moon distances (roughly two million miles) is darn close in astronomical terms, we’re quite safe when it comes to physical distance. But, with only a couple of million miles separating us, this would be a great time for radar targeting and studying (NEA) 2010 GU21’s rotation period. What’s more, it’s also on the list for the Delta-v for spacecraft rendezvous with all known near-Earth asteroids.

In the meantime, with only two days until 2010 GU21’s closest approach, you’d best keep up your car payments and still plan on keeping those weekend promises. It’s fun to surmise what might what might happen if it were a wee bit closer…

Many thanks to Joe Brimacombe for sharing his awesome video with us!


Answers and Replies

The most prominent features in Fig. 1B are (i) the densely cratered highlands, particularly on the southern nearside and north-central far-side of the Moon, (ii) the interior and surroundings of stratigraphically young impact basins, especially Orientale, and (iii) mare regions, which have the lowest crater densities on the Moon.

I interpret that as showing a significant correlation between highlands and crater density, perhaps because there was no subsequent lava flow to fill the older craters.

Unfortunately that sight and my browser disagree an the images so I can't see them, they show as Zero length .JPG files.

A friend sent me this paper:

"Electrical Phenomena on the Moon and Mars ", which was submitted at the ESA Annual Meeting on Electrostatics 2010, states:

". Measurements during the Apollo missions, together with more recent data from orbital spacecraft, indicate that there are active and dynamic charging processes occurring on and near the lunar surface. One possible consequence of dynamic lunar electrical activity may be the levitation and perhaps large scale transport of lunar dust. .."
http://www.electrostatics.org/images/ESA2010_A1_Delory.pdfc

I was wondering isn't it at least possible that static discharge flash events occur on the moon that may be confused with asteroid impact flashes?

The earth doesn't offer much radial shielding. The distance between the earth and moon is simply too large. The earth spans roughly 2 degrees of sky from the moon - that's roughly .06% of the sky. Hardly enough to make a significant difference in impacts.

If you are only considering the radial direction, then the earth's gravity would bend the path of incoming asteroids so there would be more impacts from that direction than if the earth hadn't been present.

Starting at 18 seconds the video shows several recorded impacts and then discusses the largest, the

5 kiloton TNT equivilant meteor impact of 17 Mar2013 3h 50m 542.7s

Please consider this simple explanton of the central gap and that there were no observatons of impacts at the poles . . . it's an artifact of the observing process (the CCD and telescope system have a limited field of view).

and here's an artist's "cleaned up view"

Actually if you work out the geometry, the earth is not much of a shield. Roughly speaking if the moon were the size of a baseball, the earth would be the size of a soccer ball 22.5 ft away!

Even allowing for gravitational effects, the moon isn't well shielded by the earth.

Indeed, the report spareine referenced explains the central gap and that there are no impacts recorded near the poles . . . they were not looking there.

Here's a collage of screenshots from the NASA video I referenced . . . the Field of View just includes less than half of the Moon.

Actually if you work out the geometry, the earth is not much of a shield. Roughly speaking if the moon were the size of a baseball, the earth would be the size of a soccer ball 22.5 ft away!

Even allowing for gravitational effects, the moon isn't well shielded by the earth.

You have to do the right calculation to get the right answer here and I'm not too sure what's relevant. The soccer ball / base ball model is good to start with. Looking upwards from the Moon, you will see the Earth's disc obscuring about 0.02% of the sky (same hemisphere all the time). I suggest that is the shadowing effect. Seems very low. is that possible? Could that be detected?

Treating the Moon as a disc (as in the pictures) the apparent distribution would not be affected by the curvature. Or did you not mean what I thought you meant?

You have my point correct. A full hemisphere has a solid angle of 2pi steradians (6.2823 Sr). From the moon, the solid angle of the earth is about 0.000957 Sr which is about 0.015% of a hemisphere.

Imagine body armor that only covered 0.015% of your body. That's roughly a 2" disc somewhere on your body.

Indeed, the Earth has a negligible shielding effect concerning impacts on the Moon. Check my earlier post and the post by spareine. No impact were recorded at the central meridian or the poles because they didn't look there.


M-type asteroid

M-type asteroids are asteroids of partially known composition they are moderately bright (albedo 0.1–0.2). Some, but not all, are made of nickel–iron, either pure or mixed with small amounts of stone. These are thought to be pieces of the metallic core of differentiated asteroids that were fragmented by impacts, and are thought to be the source of iron meteorites. M-type asteroids are the third most common asteroid type.

There are also M-types whose composition is uncertain. For example, 22 Kalliope has an accurately known density that is far too low for a solid metallic object or even a metal rubble pile: a rubble pile of iron-nickel metal would need about 70% porosity which is inconsistent with packing considerations. 22 Kalliope and 21 Lutetia have features in their spectra which appear to indicate the presence of hydration minerals [2] and silicates, [3] anomalously low radar albedos inconsistent with a metallic surface, [4] as well as characteristics more in common with C-type asteroids. A variety of other M-type asteroids do not fit well into a metallic body picture.

M-type spectra are flat to reddish and usually devoid of large features, although subtle absorption features longward of 0.75 μm and shortward of 0.55 μm are sometimes present. [5]

16 Psyche is the largest M-type asteroid, and does appear to be metallic. The Psyche spacecraft is slated to visit 16 Psyche. 21 Lutetia, an anomalous, probably non-metallic body, was the first M-type asteroid to be imaged by a spacecraft when the Rosetta space probe visited it on July 10, 2010. Another M-type asteroid, 216 Kleopatra, was imaged by radar by the Arecibo Observatory in Puerto Rico, and has a dog bone-like shape. [6]

M-type was one of three basic asteroid types in early classifications (the others being the S- and C-types), and was thought to indicate a metallic body. [ citation needed ]


The evolution of Saturn’s radiation belts modulated by changes in radial diffusion

Globally magnetized planets, such as the Earth 1 and Saturn 2 , are surrounded by radiation belts of protons and electrons with kinetic energies well into the million electronvolt range. The Earth’s proton belt is supplied locally from galactic cosmic rays interacting with the atmosphere 3 , as well as from slow inward radial transport 4 . Its intensity shows a relationship with the solar cycle 4,5 and abrupt dropouts due to geomagnetic storms 6,7 . Saturn’s proton belts are simpler than the Earth’s because cosmic rays are the principal source of energetic protons 8 with virtually no contribution from inward transport, and these belts can therefore act as a prototype to understand more complex radiation belts. However, the time dependence of Saturn’s proton belts had not been observed over sufficiently long timescales to test the driving mechanisms unambiguously. Here we analyse the evolution of Saturn’s proton belts over a solar cycle using in-situ measurements from the Cassini Saturn orbiter and a numerical model. We find that the intensity in Saturn’s proton radiation belts usually rises over time, interrupted by periods that last over a year for which the intensity is gradually dropping. These observations are inconsistent with predictions based on a modulation in the cosmic-ray source, as could be expected 4,9 based on the evolution of the Earth’s proton belts. We demonstrate that Saturn’s intensity dropouts result instead from losses due to abrupt changes in magnetospheric radial diffusion.

The very low intensities at the moon L-shells indicate that Saturn’s belts are not supplied by inward transport of these particles across the moon orbits. The radiation belt protons are instead produced by the interaction of galactic cosmic rays (GCRs) with matter, as occurs at the Earth: during the cosmic-ray albedo neutron decay (CRAND) process 3,8 , GCRs (mostly GeV protons) that are not deflected by the planet’s magnetic field 12 can directly impact rings and/or the planet’s atmosphere. This impact produces secondary particles (at MeV energies), including neutrons that can decay to protons rapidly and populate the radiation belts.


Four Asteroids Are Buzzing Earth in Flybys Today (But Don't Worry)

Three of them were discovered within the last 24 hours.

At least four potentially hazardous asteroids are making close approaches to Earth today (Oct. 1). Though the space rocks won't be near enough to our planet to cause any harm, three of the asteroids were discovered just hours before whizzing by the Earth-moon system — not much time to prepare for an emergency response had they been in fact on a collision course.

Asteroid 2019 SM8 was discovered by astronomers at the Mount Lemmon Observatory in Arizona on Monday (Sept. 30) and flew by Earth today at approximately 9:56 a.m. EDT (1356 GMT), according to NASA. At its closest, it was about 99,000 miles (159,000 kilometers) from Earth, or slightly less than half the average distance between Earth and the moon. NASA estimated that this asteroid is about 16 feet (4.8 meters) in diameter, about the size of an SUV.

Just over an hour later, another newly discovered asteroid made a close approach to Earth, but this one kept a bit more distance. Asteroid 2019 SE8 was also first discovered at Mount Lemmon just a few hours before it made its closest approach to Earth on Oct. 1 at approximately 11:12 a.m. EDT (1512 GMT). At its closest, the asteroid was about 674,000 miles (1.1 million kilometers) from Earth. That's nearly three times the average Earth-moon distance, so this rock didn't pose much of a threat. Asteroid 019 SE8 is a bit bigger than the last asteroid, and NASA estimates that it's about 47 feet (14 meters) across.

Later tonight, yet another newfound asteroid, 2019 SD8, will pass about 331,000 miles (532,000 km) from Earth at 10:29 p.m. EDT (0229 GMT on Oct. 2). This space rock was found by the Catalina Sky Survey in Tucson, Arizona, also just a day before its close approach to Earth. At about 38 feet (12 m) wide, it's the size of a city bus.

Asteroid 2018 FK5 is the only known asteroid flying by Earth today that NASA already knew about long before its arrival. This rock is also the most distant one: passing more than 3 million miles (5 million km) from Earth tonight at 6:56 p.m. EDT (2256 GMT). Astronomers at Mt. Lemmon discovered this 24-foot-wide (7 m) asteroid just two days before it flew by Earth in March 2018.

Though none of these asteroids had much of a chance of hitting Earth today, NASA still classifies them as "potentially hazardous asteroids" because the rocks could still pose a threat in the future when their orbits intersect with Earth's again. NASA and other institutions around the world are actively scanning the skies for dangerous asteroids, working on ways to stop an asteroid in its tracks, and coming up with an emergency response plan&ndash all to help Earth be more prepared for asteroid threats.


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2017 Wilkins, Ashlee Atmospheric Characterization of Giant Exoplanets in Extreme Environments
2017 McAdam, Margaret Water in the Early Solar System: Mid-Infrared Studies of Alteration on Asteroids
2017 Smith, Krista Optical Time Domain and Radio Imaging Analysis of the Dynamic Hearts of AGN
2017 Avara, Mark Magnetohydrodynamic Simulations of Black Hole Accretion
2017 Toy, Vicki Gamma-Ray Bursts: Lighting Up the High-Redshift Universe
2017 Ballouz, Ronald Numerical Simulations of Granular Physics in the Solar System
2016 Jameson, Katherine Molecular Gas and Star Formation at Low Metallicity in the Magellanic Clouds
2016 Shimizu, Thomas The Star-Forming Properties of an Ultra-Hard X-ray Selected Sample of AGN
2016 Sheets, Holly A Statistical Characterization of the Atmospheres of Sub-Saturn Planet Candidates in the Kepler Archive
2016 Rizzo, Maxime BETTII: A Pathfinder for High Angular Resolution Observations of Star-forming Regions in the Far-infrared
2016 Cohen, Jamie Gamma-Ray Studies of Stellar Graveyards: Fermi-LAT Observations of Supernova Remnants and Spatially Extended Emission
2016 Olmstead, Alice An Assessment of Professional Development for Astronomy and Physics Faculty: Expanding Our Vision of How to Support Faculty's Learning about Teaching
2016 Capone, Jonathan Near-Infrared Instrumentation for Rapid-Response Astronomy
2015 Herrera Camus, Rodrigo Probing the Multiphase Interstellar Medium and Star Formation in Nearby Galaxies through Far-infrared Spectroscopy
2015 Storm, Shaye High-Resolution Imaging of Dense Gas Structure and Kinematics in Nearby Molecular Clouds with the CARMA Large Area Star Formation Survey
2015 McCormick, Alexander Dust and Molecular Gas in the Winds of Nearby Galaxies
2015 Chen, Che-Yu Formation of Magnetized Prestellar Cores in Turbulent Giant Molecular Clouds
2015 Fraine, Jonathan Diagnosing Clouds and Hazes in Exoplanet Atmospheres
2014 Kumar, Sidharth Applications of Advanced Statistical Methods in the Pan-STARRS1 Medium-Deep Survey
2014 Pasham, Dheeraj X-ray Time and Spectral Variability as Probes of Ultraluminous X-ray Sources
2014 Helgason, Kari The Cosmic Near-Infrared Background: From the Dark Ages to the Present
2014 Donaldson, Jessica Characterizing Young Debris Disks through Far-Infrared and Optical Observations
2014 George, Jithin A Comprehensive Study of the Outskirts of Galaxy Clusters Using Suzaku
2014 Lohfink, Anne Probing the Central Regions of AGN
2014 Polisensky, Emil Simulations of Small Mass Structures in the Local Universe to Constrain the Nature of Dark Matter
2013 Gersch, Alan Modeling Optically Thick Molecular Emission Spectra of Comets Using Asymmetric Spherical Coupled Escape Probability
2013 Skinner, Michael Aaron
(Ph.D. in Applied Math)
An efficient method for radiation hydrodynamics in models of feedback-regulated star formation
2013 Schwartz, Steve The Development and Implementation of Numerical Tools for Investigation into the Granular Dynamics of Solid Solar System Bodies
2013 DeCesar, Megan Using Fermi Large Area Telescope Observations to Constrain the Emission and Field Geometries of Young Gamma-Ray Pulsars and to Guide Radio Millisecond Pulsar Searches
2013 Krug, Hannah Neutral Gas Outflows and Inflows in Local AGN & High-z Lyman-alpha Emitters in COSMOS
2013 Gong, Hao Dense Core Formation and Collapse in Giant Molecular Clouds
2012 Jontoff-Hutter, Daniel Magnetic Field Effects on The Motion of Circumplanetary Dust
2012 Park, KwangHo Accretion onto Black Holes from Large Scales Regulated by Radiative Feedback
2011 Sorathia, Kareem
(Ph.D. in Applied Math)
Turbulent Transport In Global Models of Magnetized Accretion Disks
2011 Perrine, Randall N-body Simulations with Cohesion in Dense Planetary Rings
2011 Gill, Mike The Dynamics of Dense Stellar Systems with a Massive Central Black Hole
2011 Koss, Mike The Host Galaxies of Ultra Hard X-ray Selected AGN
2011 Hodges-Kluck, Edmund The Hot Atmospheres of X-shaped Radio Galaxies
2011 Bovill, Mia The Fossils of the First Galaxies in the Local Universe
2011 McDonald, Mike The Origins and Ionization Mechanisms of H-alpha Filaments in the Cool Cores of Galaxy Groups and Clusters
2010 Zauderer, Ashley An Analysis of the Environment and Gas Content of Luminous Infrared Galaxies
2010 Wei, Lisa A Study of Cold Gas and Star Formation in Low-Mass Blue-Sequence E/SOs
2010 Philpott, Catherine M. Three-Body Capture of Jupiter's Irregular Satellites and Resonant History of the Galilean Satellites
2010 Radeva, Yana Infrared Spectroscopy of Parent Volatiles in Comets: Chemical Diversity and a New Fluorescence Model for the Ethane n5 Band
2010 Teng, Stacy H. From Merging Galaxies to Quasars: The Evolution of Nuclear Activity in Luminous and Ultraluminous Infrared Galaxies
2009 LaVigne, Misty A Multi-Wavelength Study of Spiral Arm Substructure
2009 Lauberg, Vanessa Black Hole Dynamics and Gravitational Radiation in Galactic Nuclei
2008 Knight, Matthew Studies of SOHO Comets
2008 Winter, Lisa Extragalactic X-ray surveys of ULXs and AGNs
2008 Vernaleo, John C. Hydrodynamic Models of AGN Feedback in Cooling Core Clusters
2008 Mattson, Barbara J. A Decade of Rossi X-ray Timing Explorer Seyfert Observations: An RXTE Seyfert Spectral Database
2007 Kim, Ji Hoon Star Formation History of Low Surface Brightness Galaxies
2007 Chapman, Nicholas Dust Structure and Composition Within Molecular Clouds and Cores
2007 Shetty, Rahul Gas Kinematics and Dynamics: Spiral Structure and Cloud Formation in Disk Galaxies
2007 Brenneman, Laura W. A Spectral Survey of Black Hole Spin in Active Galactic Nuclei
2007 Kuzio de Naray, Rachel High Resolution Optical Velocity Fields of Low Surface Brightness Galaxies and the Density Profiles of Dark Matter Halos
2007 Zhang, Ke Resonant and Secular Orbital Interactions
2007 Chen, Jian Spatio-Temporal Dynamics of the Magnetosphere During Geospace Storm
2006 Walsh, Kevin Forming Binary Near-Earth Asteroids From Tidal Disruptions
2006 Mazzuca, Lisa Morphology, Star Formation, and Kinematics of Nuclear Rings
2006 Gultekin, Kayhan Growing Intermediate-Mass Black Holes with Gravitational Waves
2006 Pierce, Donna Formation and Destruction of CO in Cometary Comae
2005 Piontek, Robert Thermal and Magnetorotational Instability in the Interstellar Medium
2005 Yang, Yuxuan A Deep X-Ray Survey of the Lockman Hole Northwest
2005 Li, Jianyang Light Scattering Properties of Asteroids and Cometary Nuclei
2005 Fast, Kelly Mars Ozone Abundances From Infrared Heterodyne Spectra and Their Application to the Study of the Study of the Stability of the Martian Atmosphere
2005 Leinhardt, Zoe Planetesimal Evolution and the Formation of Terrestrial Planets
2004 Volgenau, Nikolaus Turbulence in Star Formation: Tracing Velocity Fields of Dense Cores
2004 Marshall, James A Large Survey for Very Low Surface Brightness Galaxies
2004 Rupke, David
(Ph.D. in Physics)
Outflows of Infrared-Luminous Galaxies: Absorption Line Spectroscopy of Starbursts and AGNs
2004 Baumgartner, Wayne Elemental Abundances via X-ray Observations of Galaxy Clusters and the InFOCUS Hard X-Ray Telescope
2003 Berendse, Fred Cosmic Ray Acceleration in Cassiopeia A and Grazing-Incidence Multilayer X-Ray Mirrors
2002 Miller, Scott The Nature and Origin of Diffuse Ionized Gas in Nearby Edge-on Spiral Galaxies
2002 Gibbons, Rachel Deviations of the Fundamental Plane and the Peculiar Velocity of Clusters
2002 Kim, Woong-Tae Giant Cloud Formation in Disk Galaxies
2002 Horner, Donald J. X-Ray Scaling Laws for Galaxy Clusters and Groups
2001 Shao, Xi Investigations of the Earth's Magnetosphere with Global MHD Simulations
2001 Lee, Chin Fei CO Outflows from Young Stars: Observations and Simulations
2001 Sheth, Kartik Molecular Gas Properties of Barred Spirals
2000 Woodney, Laura Chemistry in Comet Hale-Bopp and Hyakutake
2000 Kuntz, Kip Small-Scale Angular Variations in the Soft X-ray Background
2000 Miller, Kristen Numerical Study of Accretion and Accretion Disks
2000 Nagar, Neil Central Engines and Accretion Mechanisms in Low-Luminosity Active Galactic Nuclei
2000 Geier, Sven A Study of Cosmic-Ray Beryllium with the Isotope Magnet Experiment (ISOMAX)
1999 Zhang, Jie A Study of the Sun's Corona Using EUV and Radio Observations
1999 Fernández, Yan Physical Properties of the Nuclei of Comets
1999 Kundu, Arunav Hubble Space Telescope Observations of the Globular Cluster Systems of Early Type Galaxies
1998 Xu, Jianjun The Effect of Cooling on the K-H Instability in Astrophysical Jets
1998 Piner, Glenn Geodetic VLBI Observations of EGRET Blazars
1998 Cavallo, Robert Examining Abundance Anomalies in Globular Cluster Red Giant Stars
1998 Looney, Leslie
(Ph.D. in Physics)
Unveiling the Envelope and Disk: A Sub-Arcsecond Survey of Young Stellar Systems
1997 Colbert, Ed Large Scale Galactic Outflows in Seyfert Galaxies
1997 Thornley, Michele Dynamical Influences in Flocculent Galaxies. An Examination of Structure and Star Formation
1996 Regan, Michael Gas Flow in Barred Spiral Galaxies
1996 Braatz, James H2O Megamaser Emission in Active Galactic Nuclei
1996 Gallimore, Jack The Enigmatic Seyfert Nucleus of NGC 1068 Implications for the Central Engine and Unifying Schemes
1996 Gruendl, Robert Spiral Structure and Global Star Formation Processes in M51
1995 Helfer, Tam The Distribution and Role of Dense Molecular Gas in the Centers of Galaxies
1995 Peng, Yuan A High Resolution Study of the Sagittarius B2 and W33A Massive Star Forming Regions
1995 Rho, J An X-Ray Study of Composite Supernova Remnants
1995 Chan, Kin Wing Spectrophotometric Studies of the Galactic Center
1994 Mulchaey, John Observational Tests of the Unified Model for Seyfert Galaxies
1994 Pound, Marc Proto-Brown Dwarfs
1994 Miyaji, Takemitsu X-Ray Emission as a Tracer of the Large Scale Distribution of Matter
1994 McMullin, Joseph High Resolution Study of the Circumstellar Physical and Chemical Environments of Nearby Young Stellar Objects
1994 Davis, David X-Ray Substructure in a Flux-Limited Catalog of Clusters of Galaxies
1993 Weaver, Kimberly The Complex Broad Band X-Ray Spectra of Seyfert Galaxies
1993 Vasquez, Bernard Nonlinear Wave Packet Evolution in a Dispersive Plasma: Application to Rotational Discontinuities
1993 Phookun, Bikram A Study of One-Armed Spiral Galaxies
1992 Lisse, Carey
(Ph.D. in Physics)
Infrared Observations of Cometary Dust by COBE
1992 Giovanoni, Peter The Effects of Relativistic Neutrons on Nonthermal Models of Active Galactic Nuclei
1992 Christian, Damian Spectral and Temporal Behavior of Low Mass X-Ray Binaries Observed with the Einstein SSS and MPC and the Broad Band X-Ray Telescope
1992 Butler, Paul Pushing the Limit: Precision Radial Velocities, Techniques and Applications
1992 Nath, Biman Energetic Events in the Early Universe
1992 Samarasinha, Nalin Temporal and Spatial Inhomogeneities in Comets
1991 Hewagama, Tilak An Infrared Polarimetric Study of Sunspots
1990 Henning, Patricia A Study of a 21-Cm-Selected Sample of Galaxies
1990 Briley, Mike Carbon and Nitrogen Abundance Variations Among Galactic Globular Cluster Stars
1990 Black, Martin T. Analysis of gravity and topography on Earth and Venus: Comparisons of lithospheric and sublithospheric processes
1989 Armus, Lee An Optical Investigation of Powerful Far-Infrared Galaxies
1989 Hoban, Sue Comet Halley: An Optical Continuum Study
1988 R. J. MacDowall Kilometric Type II Radio Bursts and Interplanetary Transients
1988 T. J. Sodrowski The galactic large-scale far-infrared emission observed by IRAS: Implications for the morphology, physical conditions, and energetics of dust in the interstellar medium
1988 E. P. Smith Multicolor Surface Photometry of Powerful Radio Galaxies
1987 H. Karimabadi The physics of wave-particle interaction with applications to astrophysics
1987 N. Kassim The Galactic Plane at 30.9 MHz
1987 S. A. Baum Extended Optical Emission Line Gas in Powerful Radio Galaxies
1987 R. S. Sopka Mass Loss from Evolved Stars
1986 L. A. Magnani Molecular Clouds at High Latitudes
1987 J. T. Bonnell Spectroscopic determinations of surface gravities of giant stars, and ultraviolet observations of RR Lyrae and X Arietis
1986 R. B. Hindsley An Investigation of Cepheid Variable Stars Using Hydrostatic Model Atmospheres
1986 T. N. LaRosa The Propagation of an Electron Beam through the Solar Corona
1985 J. G. Stacy The Development of the Goddard Compton Gamma-Ray Telescope and Neutral Hydrogen Observations Towards the Puppis Window of the Galaxy
1985 G. H. Kaplan The Earth's Nutational Motion Determined From Radio Interferometry
1985 S. F. Fung Radiation from Nonlinear Coupling of Plasma Waves
1985 M. Bobrowsky Numerical Hydrodynamic Models of Planetary Nebulae
1985 S. B. Kraemer The Effect of Dust in the Emission Line Gas of Seyfert 2 Nuclei
1985 M. J. Henriksen The Physical Characteristics of the X-Ray Emitting Gas in Clusters of Galaxies and Constraints on Dark Matter
1985 S. Ghosh The Onset of Alfvenic Turbulence
1983 D. G. Schleicher The Fluorescence of Cometary OH and CN
1983 J. P. Norris A study of the temporal and spectral characteristics of gamma ray bursts
1982 S. Krishnaswamy Formation of Dust Lanes in Spiral Galaxies by Radiation Pressure
1981 B. A. Williams The Distribution and HI Properties of Spiral Galaxies in the Direction of the Coma/1367 Supercluster
1981 M. H. Moore Studies of Proton Irradiated Cometary-Type-Ice Mixtures
1981 J. S. Ulvestad Radio Emission and the Forbidden Line Region of Seyfert Galaxies.
1981 R. J. Hanisch Radio Halo Sources in Clusters of Galaxies
1980 W. T. Vestrand On the Role of Cosmic Ray Protons in Two Types of Extragalactic Objects
1980 J. D. McKee X-Ray Clusters of Galaxies
1980 J. T. Karpen On the Origin of Multiply-Impulsive Emission from Solar Flares
1980 A. Manduca The Chemical Abundances and Physical Parameters of RR Lyrae Stars.
1980 C. Y. Cheung The Effects of CNO Abundance Variations and Detailed Boundary Conditions on the Evolution of Globular Cluster Red Giants
1980 P. E. Angerhofer A Morphological Study of Two Unusual Galactic Supernova Remnants
1979 R. P. Sinha Kinematics of HI Near the Galactic Center
1979 G. S. Rossano The Morphology of the Monoceros II and Cepheus IV Star Formation Regions
1979 P. A. Marionni Nebular Diagnostics Indicative of the Evolutionary History of Planetary Nebulae
1978 W. S. Gilmore Radio Continuum Interferometry of Dark Clouds. A Search for Newly Formed HII Regions
1977 L. J. Kaluzienski
(Ph.D. in Physics)
Studies of Transient X-ray Sources with the Ariel 5 All-Sky Monitor
1977 R. A. Perley A Study of a Technique of Pencil Beam Synthesis with a Line Aperture and Its Use in Mapping Giant Radio Galaxies
1977 K. R. Nicolas The application of Si III line intensity ratios to determine the solar transition zone density and pressure
1977 R. H. Cornett The Interaction of Supernova Remnants and Interstellar Clouds Containing Carbon Monoxide
1977 J. B. Carlson Radio Interferometric Investigations of Compact Components in Active Spiral and Seyfert Galaxy Nuclei
1977 L. L. Ma-Sung A Study of the Propagation and Intrinsic Characteristic of Flare-Associated Particle Events
1977 D. Lengyel-Frey Titanium Oxide in Cool Stellar Atmospheres
1977 H. V. Frey Crustal Evolution in the Early Earth: Basin-forming Impacts, Crustal Dichotomy, and Plate Tectonics
1977 P. F. Bowers The Galactic Distributions and Kinematics of the Unidentified Type II OH/IR Stars
1977 C. E. Alissandrakis Six Centimeter Wavelength Observations of Solar Active Regions and Bursts with 6 Arc-Seconds Resolution
1976 L. K. Hutton Fine Structure in 3C 120 and 3C 84
1976 B. C. Brown The Orbits of the Galilean Satellites of Jupiter
1976 P. E. Hardee The Generation of Pulsed Emission from Rotating Neutron Stars by Plasma Streaming Instabilities
1976 J. J. Cowan Nucleosynthesis in Red Giant Stars
1976 P. D. Jackson Galactic Structure and Kinematics in the Centaurus Region of the Milky Way
1976 L. A. Dreiling Model Atmospheres for Sirius and Procyon
1975 R. E. Clegg Carbon and Nitrogen Abundances in F and G-Type Stars
1975 G. L. Mader The Relative Positions of the OH and H2O Astrophysical Masers
1975 A. S. Milman Carbon Monoxide Emission from Interstellar Dust Clouds
1975 R. H. Becker High Resolution Radio Observations of Supernova Remnants
1974 A. H. Karp Hydrodynamic Models of a Cepheid Atmosphere
1974 N. R. Vandenberg Meter-Wavelength Observations of Pulsars Using Very-Long-Baseline Interferometry
1974 E. J. Grayzeck Investigation of the Spiral Structure of the Crux-Centaurus Circinus-Norma Region of the Milky Way by Means of Long-Period Cepheids
1974 J. M. Luhmann Balloon observations of low energy electrons and the solar modulation of cosmic rays in interplanetary space
1974 S. L. Knapp A Description of the Cassegrain Amplitude Interferometer and disk Diameter for Five Late-Type Giant Stars
1974 G. L. Hammond The Chemical Composition and Effective Temperatures of Metallic Line White Dwarfs
1974 T. E. Gergely Decameter Storm and Type IV Radiation
1973 M. R. Viner A 26.3 MHz Radio Source Survey with an Absolute Flux Scale
1973 R. A. LeFande Atmospheric Absorption and Emission of Microwave -Radiation
1973 B. M. Krupp A New Analysis of the System of CH and the Carbon Twelve/Carbon Thirteen Ratio in Arcturus
1973 W. L. Upson CNO Abundances in the Sun and Arcturus and the 12C/13C Ratio in Arcturus
1973 T. Velusamy Polarization of Supernova Remnants at Centimeter Wavelengths
1973 T. B. Kuiper An Analysis of Type III Burst Positions
1972 R. K. Riddle A Study of a Region in Monoceros
1972 J. G. Lyon Thermal Stability in Planetary Nebulae
1972 S. Y. Liu Fine Structure of the Solar Chromosphere
1972 J. W. Fowler Line-Blanketed Model Stellar Atmospheres Applied to Sirius
1972 F. J. Ahern A Polarization Fourier Spectrometer: Design, Construction and Astronomical Observations
1972 R. B. Tully The Kinematics and Dynamics of M51
1972 J. R. Fisher Design Tests of the Fully Steerable, Wideband, Decametric Array at the Clark Lake Radio Observatory
1972 G. R. Knapp High Frequency Resolution HI Line Observations of Interstellar Dust Clouds
1972 R. H. Harten A Study of Neutral Hydrogen Gas Motion Within Spiral Arms and in the Local Region
1971 W. T. Sullivan Microwave Radiation of Water Vapor in Galactic Sources
1971 D. M. Gottlieb Abundances in K Giant Stars
1971 A. Sandquist Lunar Occultations of the Galactic Center Region in HI, OH and CH2O Lines
1971 T. Kelsall Multi-Color Photometry of Supergiants and Cepheids
1971 D. Chesters The Dispersion of Gravitational Radiation
1970 D. K. Yeomans Non-gravitational Forces Affecting the Motion of Comet Giacobini-Zinner
1970 J. D. Curtis A Modification of the Brown-Shook Method Based on Lie Series
1970 W. M. Cronyn Radio Scattering in the Interplanetary Medium
1969 E. C. Silverberg Interplanetary Dust Streams. Observation by Satellite and Lidar
1969 D. J. Mullan The Structure of Hydromagnetic Shocks in Regions of Very Low Ionization
1969 D. R. Branch Solar Magnesium Isotopic Abundance Ratios
1968 P. A. Henderson Large Scale Structure of the Neutral Hydrogen in the Galaxy
1968 R. A. Williamson A Study of Radial Velocities in Diffuse Emission Regions Using a Fabry-Perot Interferometer
1968 B. F. Smith Dynamical Relaxation in Galaxy Formation
1968 J. J. Rickard Optical and Radio Evidence of Large-Scale Peculiar Motions in the Cas-Per Arm
1967 T. S. Smith The Lyman Series of Ionized Helium in the Extreme Ultraviolet Solar Spectrum
1966 Riegel, Kurt W. 21-cm Line Observations of Small Diameter Galactic HII Regions

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