Asteroids Archives

November 10, 2008December 24, 2015 by Nancy Atkinson

Impressive Craters on Earth

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Ever since our recent encounter with asteroid 2008 TC3 — the first asteroid that was correctly predicted to hit our planet — I’ve had impact craters on the brain. Earth has about 175 known impact craters, but surely our planet has endured more bashing than that in its history. All the other terrestrial planets and moons in our solar system are covered by impact craters. Just look at our Moon through a telescope or binoculars, or check out the recent images of Mercury sent back by the MESSENGER spacecraft, or pictures of Mars from the armada of spacecraft orbiting the Red Planet, and you’ll see that impact craters are the most common landforms in our solar system.

But since two-thirds of Earth is covered by water, any asteroid impacts occurring in the oceans are difficult to find. And even though Earth’s atmosphere protects us from smaller asteroids, just like in the case of 2008 TC3, which broke up high in the atmosphere, weathering, erosion and the tectonic cycling of Earth’s crust have erased much of the evidence of Earth’s early bombardment by asteroids and comets. Most of Earth’s impact craters have been discovered since the dawn of the space age, from satellite imaging. In fact, a geologist recently discovered an impact crater using Google Earth!

Here’s my list of Earth’s Ten Most Impressive Impact Craters, starting with #1. the largest and oldest known impact crater, Vredefort Crater, shown above, located in South Africa. It is approximately 250 kilometers in diameter and is thought to to be about two billion years old. The Vredefort Dome can be seen in this satellite image as a roughly circular pattern. What an impact that must have been!

2. Manicouagan Crater: fifth largest known impact crater. This crater is located in Quebec, Canada. It was created about 212 million years ago. Now, it is an ice-covered lake about 70 km across. This image, taken by space shuttle astronauts, shows an outer ring of rock. Close up, the rock reveals clear signs of having been melted and altered by a violent collision. The original rim of the crater, though now eroded away, is thought to have had a diameter of about 100 km.

3. Chicxulub Crater, third largest and possible dinosaur killer. The third largest impact crater lies mostly underwater and buried underneath the Yucatán Peninsula in Mexico. At 170km (105 miles) in diameter, the impact is believed to have occurred roughly 65 million years ago when a comet or asteroid the size of a small city crashed, unleashing the equivalent to 100 teratons of TNT. Likely, it caused destructive tsunamis, earthquakes and volcanic eruptions around the world, and is widely believed to have led to the extinction of dinosaurs, because the impact probably created a global firestorm and/or a widespread greenhouse effect that caused long-term environmental changes.

4. Aorounga Crater: possible triple crater. The main Aorounga Crater in Chad, Africa, visible in this radar image from space, shows a concentric ring structure that is about 17 kilometers wide. But, this crater might have been formed as the result of a multiple impact event. A second crater, similar in size to the main crater, appears as a circular trough in the center of the image. And a third structure, also about the same size, is seen as a dark, partial circular trough on the right side of the image. The proposed crater “chain” could have formed when a 1 km to 2 km (0.5 mile to 1 mile) diameter object broke apart before impact. Ouch!

5. Clearwater Craters: two for the price of one. Twin, lake-filled impact craters in Quebec, Canada were probably formed simultaneously, about 290 million years ago, by two separate but probably related meteorite impacts. The larger crater, Clearwater Lake West has a diameter of 32 km, and Clearwater Lake East is 22 km wide.

6. Barringer Crater: well preserved. While this crater isn’t all that big, what’s most impressive about Barringer Crater in Arizona (USA) is how well preserved it is. Measuring 1.2 km across and 175 m deep, Barringer Crater was formed about 50,000 years ago by the impact of an iron meteorite, probably about 50 m across and weighing several hundred thousand tons. Most of the meteorite was vaporized or melted, leaving only numerous, mostly small fragments with in the crater and scattered up to 7 km from the impact site. Only about 30 tons, including a 693-kg sample, are known to have been recovered.

7. Wolfe Creek Crater, well preserved, too. Another relatively well-preserved meteorite crater is found in the desert plains of north-central Australia. Wolfe Creek crater is thought to be about 300,000 years old and is 880 meters across and and about 60 meters deep. It’s partially buried under the wind-blown sand of the region, and although the unusual landform was well-known to the locals, scientists didn’t find the crater until 1947.

8. Deep Bay Crater: deep and cold. Deep Bay crater is located in Saskatchewan, Canada. The bay is a strikingly circular 13 km wide impact crater and is also very deep (220 m). It is part of an otherwise irregular and shallow lake. The age of the crater is estimated to be 99 million years old.

9. Kara-Kul Crater: high altitude crater. This crater was formed about 10 million years ago, and is located in Tajikistan, near the Afghan border. In total, the crater is about 45 km in diameter and is partially filled with a 25 km-wide lake. This might be the “highest” impact crater, almost 6,000 m above sea-level in the Pamir Mountain Range. It was found only recently from satellite images.

10. Bosumtwi Crater: built of bedrock. The last crater on our tour of impressive impact craters is this located in Ghana, Africa. It is about 10.5 km in diameter and about 1.3 million years old. The crater is filled almost entirely by water, creating Lake Bosumtwi. The lakebed is made of crystalline bedrocks.

Source:
Wikipedia: Impact Craters

November 8, 2008December 24, 2015 by Ian O'Neill

First Images of Asteroid 2008 TC3 Impact Aftermath

The long-lasting persistent train after the impact of 2008 TC3 over the Sudanese skies (NASA)

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A month after asteroid 2008 TC3 hit the Earth’s atmosphere, the first ground-based image of the event has surfaced on the Internet. Admittedly, it’s not the fireball everyone has been waiting to see, but it is visual evidence that something hit us above Sudan on October 7th. The image above was taken from a frame of video that was being recorded by Mr. Mohamed Elhassan Abdelatif Mahir in the dawn following the asteroid impact with the atmosphere. The smoky feature is the remnant of the fireball as the 3 meter-wide asteroid blasted through the upper atmosphere, eventually exploding. The long-lasting persistent train is seen hanging in the air, high altitude winds causing it to twist in the morning sunlight.

We may not have a dazzling fireball re-entry video of 2008 TC3, but this striking image provides the first ground-based evidence of the direct hit, and may help refine the search for any meteorites from the disintegrated asteroid…

Although details are sketchy, it would appear that a person on the ground observed the skies of Sudan shortly after 2008 TC3 exploded in the upper atmosphere. It is unclear whether the observer was part of a meteorite-hunting team, or a Sudanese resident videoing the scene, but it is very fortunate he captured this footage. Dr. Muawia H. Shaddad of the University of Karthoum communicated this single frame, and the picture is being showcased as the November 8th NASA Astronomy Picture of the Day.

It is currently the only ground-based evidence that something hit the Earth at the right time and right location as predicted by scientists using the Mount Lemmon telescope in Arizona as part of the NASA-funded Catalina Sky Survey for near-Earth objects. However, as Nancy reported on October 13th, indirect support for an atmospheric fireball came from a webcam on a beach in Egypt. Also, at 02:43 UTC on that Tuesday morning, an infrasound array in Kenya detected an explosion in the atmosphere (with an energy equivalent of 1.1–2.1 kT of TNT). These observations were backed up by the European weather satellite METEOSAT-8, capturing the fireball from orbit. The pilot of a KLM airliner also witnessed a bright flash, 750 miles from the impact location.

This was the first time that an asteroid has been discovered before it hit the Earth, thereby proving an early-warning system for future asteroid impacts is possible. Although there are 5-10 space rock collision events per year, this is the first time we knew something about it before it happened. This is an amazing achievement as 2008 TC3 was only 3 meters in diameter.

To aid the search for any 2008 TC3 debris, SpaceWeather.com is hoping this image of the aftermath of the October 7th impact will jog any potential witness memories of the African skies a month ago:

Readers, were you in Sudan on Oct. 7th? Send your fireball reports and photos to meteor expert Peter Jenniskens of the SETI Institute. Your data could improve the chances of recovering meteorites.

Sources: SpaceWeather.com, Astroengine.com, NASA APOD

October 24, 2008December 24, 2015 by Ian O'Neill

Could Strange Mars Craters be from a Fallen Third Moon?

[/caption]Was there a third Martian moon orbiting the planet? Did Phobos and Deimos have a triplet sibling? According to the discovery of two elliptical impact craters, there might just have been another moon, but it ploughed into the Red Planet’s surface a long time ago. The moonlet would have been approximately 1.5 km wide (0.9 miles), and it will have succumbed to the Mars gravity, entering the atmosphere at a shallow angle. As it tumbled through the atmosphere it broke in two, hitting the surface and creating two elongated impact craters, near-perfectly aligned.

It is thought that the “third moon” of Mars dropped from orbit a billion years ago and the same will happen with Phobos in a few million years. However, there might be another explanation, with no third moonlet in sight…

Observations of the Martian surface, just north of Olympus Mons, show two oval-shaped craters (pictured top). Usually impact craters are approximately circular, so the elongated craters indicate the impactor(s) entered the atmosphere at a very shallow angle. This isn’t the only strange characteristic of these two craters. They lie 12.5 km (7.8 miles) apart and they are almost exactly aligned from east to west (they are off-alignment by only 3.48°). The larger crater is 10 km (6.2 miles) wide at its longest point, and the smaller crater is 3km (1.9 miles) wide.

There are two possible answers to this puzzle, but researchers are having a hard time in agreeing on which one. In a recent publication, John Chappelow and Rob Herrick of the University of Alaska, Fairbanks, have calculated that the impact craters were caused by a small moon that entered the atmosphere, broke into two (due to atmospheric drag) and then struck the surface at an oblique angle of 10° or less. The moonlet would have been 1.5 km (0.9 miles) in diameter. This sounds feasible, after all for both craters to be aligned, one would think they came from the same mass, right?

NASAs Lunar Orbiter spacecraft imaged the Messier A (right) and B craters on the Moon. Messier A is about 11 km long (NASA) — The lunar Messier craters (NASA)

This moon-impact theory has a few drawbacks however. The first problem is that the impact craters are located at 40° latitude in Mars’ northern hemisphere. One would expect natural satellites to orbit around the equatorial plane if their orbits are stable (hovering around 0° latitude). “Any close natural satellite must, like Phobos, orbit in Mars’s equatorial plane,” said Jay Melosh, a crater expert at the University of Arizona in Tucson, who is highly sceptical of Chappelow and Herrick’s findings.

However, Herrick believes that the moonlet may not have established a stable orbit, above the equator. “We don’t know the details of the [moonlet’s] capture mechanism, so I don’t know that we can definitively say that the object must have moved to an equatorial orbit before spiralling in,” countered Herrick.

Artist impression of binary asteroid 90 Antiope (ESO)

Melosh argues that the craters may have been caused by a binary asteroid (or “double asteroids”) entering the Martian atmosphere at a very shallow angle. After all, there is a confirmed example of a binary asteroid impact on the Moon (a.k.a. the Messier craters on the Moon, pictured above). Chappelow however disputed this claim saying, “In such a case, the craters should be oriented randomly.” After all, wouldn’t the binary asteroid have a randomly oriented orbital plane?

Apparently not. It appears that over hundreds of thousands of years of asteroid evolution, the effect of sunlight has a huge role to play in the dynamics of binary asteroid formation. A process known as the “Yarkovsky-O’Keefe-Radzievskii-Paddack Effect,” or the YORP Effect, causes the uneven heating of an asteroid. Carrying a tiny jolt of momentum, photons are emitted from the surface in jets, eventually causing the asteroid to spin. Eventually a piece of rock breaks loose, forming the binary asteroid. It would appear there is an observed trend for the majority of binary asteroids to orbit in the same plane as the rest of the Solar System.

So it seems possible that a binary asteroid could create the two elongated and aligned impact craters after all.

Regardless, whether a third moon or binary asteroid hit Mars, it will be of little comfort to Phobos. The moon (with a mean radius of 11 km) is slowly dropping in altitude due to tidal forces. In about 11 million years it will either crash into Mars or be ripped apart through gravitational shear. Either way, Phobos is a doomed moon.

Original Source: Space.com

October 13, 2008April 26, 2016 by Nancy Atkinson

Where Are the Images from Asteroid 2008 TC3?

Asteroid-2008-tc3. From Kite Power El Gouna web cam.

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One of the big news items last week was the prediction that an asteroid was on a collision course with Earth. Although it was a small space rock – estimates ranged from 1-5 meters (3-15 feet), scientists were excited because this was the first time an asteroid was discovered with an imminent known impact. Granted, we’d all probably feel a little safer if we knew about this asteroid, named 2008 TC3, days or months ahead of time instead of only 19 hours, but it’s a step in the right direction. Astronomers even predicted correctly the asteroid would come through the atmosphere over Africa. So with this prediction, many were hoping someone with a camera would be watching the skies of Sudan. But the flight path of the object was over a remote area and so far the only ground-based image that has surfaced is the one shown here, taken by a webcam from a beach in Egypt. (The words on the image indicate the objects on the beach — which were illuminated by the fairly distant explosion low on the horizon. ~~try to find the tiny bright spot in the center of the image — that’s the asteroid~~.) But we do have satellites constantly monitoring Earth’s atmosphere and a few of them captured images and data about 2008 TC3. However, it’s not known if any parts of the meteoroid hit the ground.

The explosion was recorded directly by the cameras of a European weather satellite called METEOSAT-8. This was taken in infrared, and the temperature scale on the right is in Kelvin.

Asteroid 2008 TC3 seen from space in infrared. Credit: EUMETSAT

Data from this satellite helped determine the asteroid entered Earth’s atmosphere at a velocity of 12.8 kilometers per second. “As it entered the Earth’s atmosphere, it compressed the air in front of it. The compression heated the air, which in turn heated the object to create a spectacular fireball, releasing huge amounts of energy as it disintegrated and exploded in the atmosphere, dozens of kilometers above ground,” the Eumetsat website explains. Meteostat also took a visible image:

Also, according JPL’s Near Earth Object Program, an undisclosed U.S. system has monitored the airburst and yielded a precise time (02:45:45 UTC) and explosive energy equivalent (0.9 to 1.0 kT of TNT). The NEO office also said, “Tthe follow-up astrometric observations from professional and sophisticated amateur astronomers alike were rather extraordinary, with 570 observations from 26 observatories being reported between the time of discovery by the Catalina Sky Survey to just before the object entered Earth’s shadow (57 minutes prior to impact).” These observations revealed a tumbling, rotating object. The CAST astronomical observatory created a “movie” of their observations of the asteroid before it entered into Earth’s shadow.

CAST astronomical obervatory in Italy created this 2008tc3 animation.

Here’s links to a few other ground based observatories and their pre-impact sightings: from Eric Allen of Observatoire du Cegep de Trois-Rivieres, Champlain, Quabec; from Ernesto Guido et al. of Remanzacco Observatory, Italy; from S.Korotkiy and T.Kryachko of Kazan State University Astrotel observatory, Russia

Also, SpaceWeather.com reported the crew of an airplane saw a flash in the sky which may have been from this object. But beyond that, sadly, there’s not many images available related to this extraordinary event. If any surface, we’ll be sure to post them.

Sources: SpaceWeather.com, Cosmos4U, Planetary Society Blog, JPL NEO Program

October 6, 2008April 26, 2016 by Nancy Atkinson

Asteroid To Enter Earth’s Atmosphere Tonight (Oct. 6)

Looking for a little excitement tonight? An asteroid between 1-5 meters (3-15 feet) was discovered just hours ago at an Arizona observatory, and might provide a spectacular light show as it comes through Earth’s atmosphere. But don’t be alarmed – scientists predict it will be harmless and burn up before it reaches the ground. It is expected to be visible over eastern Africa, at approximately 2:46 a.m. Greenwich Mean Time (10:46 p.m. Eastern time ). There is no danger to people or property since the asteroid will not reach the ground. It will burn up in the upper atmosphere, well above aircraft heights. A brilliant fireball will be visible as a result. “We want to stress that this object is not a threat,” said Dr. Timothy Spahr, director of the International Astronomical Union’s Minor Planet Center. “We’re excited since this is the first time we have issued a prediction that an object will enter Earth’s atmosphere,” Spahr added. Odds are between 99.8 and 100 percent that the object will encounter Earth, according to calculations provided by Andrea Milani of the University of Pisa.

When a meteoroid (small asteroid) enters the atmosphere, it compresses the air in front of it. That compression heats the air, which in turn heats the object, causing it to glow and vaporize. Once it starts to glow, the object is called a meteor.

“A typical meteor comes from an object the size of a grain of sand,” explained Gareth Williams of the Minor Planet Center. “This meteor will be a real humdinger in comparison!”

The meteor is expected to be visible from eastern Africa as an extremely bright fireball traveling rapidly across the sky from northeast to southwest. The object is expected to enter the atmosphere over northern Sudan at a shallow angle.

“We’re eager for observations from astronomers near the asteroid’s approach path. We really hope that someone will manage to photograph it,” said Williams

Source: Center for Astrophysics Minor Planet Center

Image source

September 22, 2008December 24, 2015 by Nancy Atkinson

Earth’s Precious Metals Could Be From Meteorites and Asteroids

Artist impression of the Asteroid Kleopatra. Credit: NASA

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Meteorites and asteroids from the inner solar system could be responsible for Earth’s store of precious metals such as platinum and iridium, brought to our nascent planet during the period of Late Heavy Bombardment, about 4,000 million years ago. Dr. Gerhard Schmidt from the University of Mainz, Germany, has calculated that about 160 metallic asteroids of about 20 kilometers in diameter would be sufficient to provide the concentrations of these metals, known as Highly Siderophile Elements (HSE), found in the Earth’s crust. “A key issue for understanding the origin of planets is the knowledge of the abundances of HSE in the crust and mantle of the Earth, Mars and the Moon. We have found remarkably uniform abundance distributions of HSE in our samples of the Earth’s upper crust. A comparison of these HSE values with meteorites strongly suggests that they have a cosmo-chemical source,” said Schmidt.

Schmidt and his colleagues have spent the last 12 years analyzing the concentrations of HSE at meteorite impact sites around the world, as well as in the samples from the Earth’s mantle and crust. In addition, he has compared the data from the Earth with data from impact breccias from the Moon brought by the Apollo missions and Martian meteorites, believed to be samples from the mantle and crust on Mars.

As the Earth formed, the heavy elements, including HSE that were present, sank to form the iron and nickel-rich metallic core. HSE were added again later by meteorite impacts, creating a veneer of material over the Earth’s surface after the core had formed, about 20-30 million years after the planet’s accretion. This could have been by the collision with a Mars-sized impactor that led to the formation of the Moon.

However, Schmidt believes that the meteorites responsible for the HSE elements on Earth are iron or stony-iron meteorites that match up with theoretical predications of asteroids formed in the Mercury-Venus region of our solar system.

Different classes of meteorites have characteristic elemental ratios of HSE that give indications where in the Solar System they formed. Chondrites are stony meteorites that represent the pristine material from the early Solar System, and iron or stony-iron meteorites, which are fragments of larger asteroids that had enough internal heat in the past to form a molten metal core. These most likely would have formed in the inner solar system.

The ratios of HSE found in Earth’s crust bear a much closer resemblance to iron or stony-iron meteorites, and Schmidt believes these meteorites came from the inner solar system.

There’s a problem, however. Of the 175 known impact craters on Earth, remains of the projectiles have been found for about 40, and none of these meteorites have been identified as being formed in the region between Mercury and Venus.

Intriguingly, some of the Martian meteorites found in Antarctica, which are probably represent samples of the Martian crust also have HSE values that resemble groups of iron meteorites and stony irons, suggesting that a similar process took place on Mars.

Rock on Mars found by Opportunity rover, believed to be a meteorite. Credit: NASA/JPL

Also, the first meteorite found on Mars by the Opportunity Mars Exploration Rover in 2005 was an iron
meteorite.

Dr. Schmidt presented his findings at the European Planetary Science Congress in Muenster on Monday, 22nd September.

Source: European Planetary Science Conference Press Release

September 10, 2008January 24, 2021 by Fraser Cain

Announcing Asteroid 158092 Frasercain

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Well, I’ve just been accepted into an elite club of people with astronomical objects named after them. And no, my Mom didn’t name a star after me. The asteroid hunting team of David Healy and Jeff Medkeff have collectively discovered 487 asteroids, and designated 62 of them. You might already recognize some of asteroid names: Philplait, Paulmyers, Rebeccawatson, and Derekcolanduno.

At the end of August I received an email from David Healy notifying me that I was a new member of the asteroid club.

Asteroid 158092 Frasercain was officially designated on August 21, 2008. You can see the full list of named asteroids here – scroll down to see Frasercain. And you can see its current position in the Solar System here.

Those of you who know Jeff Medkeff will know the sad part of this story. Jeff, aka “The Blue Collar Scientist”, passed away on August 3rd from complications with liver cancer – he was 39. I’ve got to be honest and tell you that I didn’t know Jeff. We clearly ran in similar circles, but it wasn’t until Phil, Pamela and other people in the space blogging community informed me of his death that I found and read through his blog; I really wish I’d found it earlier.

If you haven’t already, please visit the Blue Collar Scientist blog. And you can read a very moving blog entry fulfilling Jeff’s last request.

So to Jeff and David, thank you very much for this incredible honour – I promise this won’t go to my head… much.

September 6, 2008December 24, 2015 by Nancy Atkinson

Rosetta Flies By ‘Diamond in the Sky’ Steins

Mosaic of images from Rosetta's fly by. Credit: ESA

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ESA’s Rosetta spacecraft successfully flew by the asteroid 2867 Steins, coming within 800 km (500 miles) and gathering images and data on the irregularly shaped rock in space. “Steins looks like a diamond in the sky,” said Uwe Keller, Principal Investigator for the OSIRIS imaging system on board the spacecraft. Watch a movie of the flyby here. Visible in the images are several small craters on the asteroid, and two huge ones. While the wide-angle camera worked perfectly during the flyby, the narrower and higher resolution camera switched itself off and into safe mode a few minutes before closest approach, but switched back on after a few hours. “The software switched off automatically,” said Gerhard Schwehm, Rosetta mission manager. “The camera has some software limits and we’ll analyze why this happened later.”

Rita Schulz, Rosetta Project Scientist, said, “In the images is a chain of impact craters, which must have formed from recurring impact as the asteroid rotated. The impact may have been caused by a meteoroid stream, or fragments from a shattered small body.”

The chain is composed of about 7 craters. To determine the age of the asteroid, a count of the craters on the asteroidâ€™s surface has been started (the more the number of craters, the older the asteroid). So far, 23 craters have been spotted.

From the images, scientists will try and understand why the asteroid is unusually bright, and how fine grains of the surface regolith are. This will tell them more about how the asteroid formed. Images from the narrow angle camera are yet to be retrieved, and will help add to the knowledge of the surface composition and mineralogy.

“It looks like a typical asteroid, but it is really fascinating how much we can learn from just the images,” said Schwehm. “This is our first science highlight; we certainly have a lot of promising science ahead of us. Iâ€™m already looking forward to encountering our next diamond in the sky, the much bigger Lutetia.” Rosetta will meet up with asteroid (21) Lutetia on June 10, 2010.

What’s next for Rosetta? It will reach the maximum distance from the Sun on its current orbit on the 17th of December (2.26 AU) to head back to Earth for the next and last swing-by on the Nov. 13, 2009. After it flies by Lutetia, its final destination is going into orbit around Comet 67P/Churyumov-Gerasimenko in 2014.

Source: ESA

September 3, 2008December 24, 2015 by Nancy Atkinson

Asteroid Imposters

Are some asteroid masked of their true identity?

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A frequent plot device in the old “Mission: Impossible” television show was the special masks the IMF team used so they could impersonate anyone. Viewers were often surprised to find out who ended up being an imposter. Similarly, astronomers and planetary scientists are considering that a fair amount of Near Earth Objects (NEOs) aren’t what they appear: they could be comets impersonating asteroids. Paul Abell, from the Planetary Science Institute says between five and ten percent of NEOs could be comets that are being mistaken for asteroids, and Abell is working on ways to make unmasking them a mission that’s possible.

Some NEOs could be dying comets, those that have lost most of the volatile materials that create their characteristic tails. Others could be dormant and might again display comet-like features after colliding with another object, said Abell. He is using NASA’s Infrared Telescope Facility at the Mauna Kea Observatories in Hawaii and the MMT telescope on Mount Hopkins, south of Tucson, Ariz., to uncover observational signatures that separate extinct/dormant comets from near-Earth asteroids.

This is important for a couple of reasons. First, dormant comets in near-Earth space could become supply depots to support future exploration activities with water and other materials. Second, like other NEOs, they could pose a threat to Earth if they are on a collision course with our planet. Third, they can provide data on the composition and early evolution of the solar system because they are thought to contain unmodified remnants of the primordial materials that formed the solar system.

Unlike rocky asteroids that blast out craters when they slam into Earth, comets are structurally weak and likely to break up as they enter the atmosphere, leading to a heat and shockwave blast that would be much more devastating than the impact from an asteroid of the same size.

Low-activity, near-earth comets flashed onto the planetary-science radar screen in 2001, when NEO 2001 OG108 was discovered by the Lowell Observatory Near Earth Asteroid Search telescope. It had an orbit similar to comets coming in from the Oort Cloud, but had no cometary tail. But in early 2002 when it came closer to the sun, the heat vaporized some of the comet’s ice to create the clouds of dust and gas that make up the comet’s coma and tail. It was then reclassified as a comet.

“That’s what started me on this line of reasoning and scientific investigation,” Abell said.
By combining orbital data with spectra and the albedos (brightness) of these objects, Abell hopes to identify which are low-activity comets and where they are coming from.
“Are all these comets made of the same type of material or are they different?” Abell asked. “If they’re composed of different materials, they may have different spectral signatures, and our preliminary work on Jupiter-family comets and Halley-type comets shows that this may be true. Why is that? Is it something to do with the initial conditions of their formation regions? Or is it due to the different environments in which they spend most of their time?”

“All this is important to understanding their internal makeup, which will give us data on the material composition and evolution of the early solar system,” he added.

Source: PSI Press Release

September 2, 2008April 26, 2016 by Nancy Atkinson

Countdown to Asteroid Flyby

Artist impression of Rosetta and Asteroid 2867 Steins. Credit: ESA

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Time critical is approaching for the Rosetta spacecraft and it’s flyby of the asteroid 2867 Steins. Closest approach is expected on September 5, at 20:58 CEST, (Central European Summer Time), 2:58 pm EDT (US Eastern Daylight Time). To help the public follow the flyby, the Rosetta team now has a blog available, and a timeline has also been posted. At the time of closest approach, Rosetta is planned to be 800 km from the asteroid, passing by at a speed of 8.6 km/s relative to Steins. Both Rosetta and Steins will be illuminated by the Sun, providing an excellent opportunity for science observations.

Although most scientific observations will take place in the few hours around closest approach, several instruments will be switched on for a longer time around the event.

Between 40 and 20 minutes before closest approach, Rosetta will be flipped and the spacecraft will switch to a specially designed asteroid fly-by mode, an optimal configuration that supports the intensive observation and tracking activity of the on-board instruments. The first images and results will be available for presentation to the media during a press conference on Saturday, September 6 at 12:00 CEST.

The timeline is as follows (more details are available in the Rosetta Blog — all times CEST (Central European Summer Time):

1 September
02:20 Instruments switched on (except OSIRIS which was already on for the navigation campaign)

4 September
07:20-11:20 Slot for possible trajectory correction manoeuvre (36 hours before closest approach)
13:20-18:20 Last opportunity to acquire images for optical navigation campaign

5 September
07:20-10:20 Slot for possible trajectory correction manoeuvre (12 hours before closest approach)
10:20 Navigation cameras switch to tracking mode – initially both used, then use CAM ‘A’ only (to be decided)
11:00 Uplink fly-by commands for asteroid fly-by mode (AFM)
Includes an update to the command profile already on board & the final updated AFM commands (only if 1 CAM at least is tracking)
20:18-20:38 Spacecraft flip over
20:39 Spacecraft switches automatically to asteroid fly-by mode
20:56 Sun illuminates Rosetta from the back and the asteroid fully
20:58 Closest approach, at a planned distance of 800 km from the asteroid
22:27 First post-fly-by acquisition of signal (AOS) – telemetry received via NASA’s Goldstone ground station
22:30 Start of science data download via Goldstone

6 September
12:00 Live streaming of Rosetta Steins fly-by press conference from the European Space Operations Centre begins
13:00 Images from fly-by published on ESA web
15:00 End of press conference streaming
16:01 End of reception of first set of science data

News Source: ESA