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Ask an Expert: Why Study Comets, Meteors and Asteroids?
Comet Hartley 2, captured by the NASA EPOXI mission between Nov. 3 and 4, 2010 Comet Hartley 2, captured by the NASA EPOXI mission between Nov. 3 and 4, 2010. (NASA)
Comet Hartley 2, seen on Oct. 20, 2010 Comet Hartley 2, seen on Oct. 20, 2010. (NASA/MSFC/B. Cooke)
Fireball observed on Oct. 16, 2010. Fireball with "Hartley-esque" orbit, observed on Oct. 16, 2010. (NASA/MSFC/B. Cooke)

More Information
Gallery: EPOXI Views Hartley 2
NASA Worldbook: Meteors
NASA Worldbook: Comets
Wikipedia: Comet Hartley 2
Link: NASA's Lunar Impact Monitoring
Link: NASA's EPOXI Mission
Small but active Comet Hartley 2 just made one of the closest approaches to Earth of any comet in centuries. Recently backyard stargazers with a telescope and binoculars on a clear night have observed a good show, and on Nov. 4, NASA's EPOXI mission approaches within 700 kilometers (435 miles) of Hartley 2. the sequel to the recent show could come in the form of a meteor shower.

Dr. Bill Cooke of NASA's Meteor Environment Office at the Marshall Space Flight Center is watching the sky, especially on Nov. 2-3. That's when a potential Hartley-id meteor shower would be most intense -- according to calculations by meteor experts. On Friday, Nov. 5, Dr. Cooke answered your questions via live chat.

More About Chat Expert Bill Cooke

The head of NASA's Meteoroid Environment Office, Dr. Bill Cooke specializes in the meteoroid environment and its effects on space vehicles of all sorts. While a graduate student at the University of Florida, he worked on instruments flying onboard balloons, the Space Shuttle, Giotto (European mission to Halley's Comet), and the Long Duration Exposure Facility.

After obtaining his PhD, he came to work at Marshall Space Flight Center as a member of the Space Environments Team. When not occupied with meteor observations and shower forecasts, he dabbles as a free- lance author for magazines and is a mentor for the Team America Rocketry Challenge and NASA's Student Launch Initiative rocketry programs.

Chat Transcript

Bill: Hi everyone, thanks for joining us. We'll get the chat underway in about five minutes at the top of the hour. Looking forward to your questions!

(Moderator Jason): Welcome to today’s Web chat with NASA scientist Dr. Bill Cooke. Our topic today is why we study comets, meteors, and asteroids; will there be a new meteor shower surrounding Hartley 2; and what did NASA’s EPOXI spacecraft observe on its close approach yesterday? Please remember to stay on topic! This is a moderated chat. It may take a few moments for the queue to catch up to your question, so please don’t leave if you don’t see your question right away.

r2d2: Why did EPOXI choose comet Hartley as the mission target?

Bill: The first choice was comet Boethin, but it "disappeared" and possibly broke apart. Hartley 2 was 2nd choice and a good one. It's a very active comet, which you can see from the jets on the EPOXI images.

Eli: In what way is the study of asteroids, meteors and comets, related to astrobiology?

Bill: Meteoroids and meteors are thought to be vehicles for panspermia which is the notion that life can be transported from planet to planet. We know that Earth and Mars have been swapping meteors since the origin of the solar system, Some astronomers argue that bacteria and viruses can survive within meteorites during the time it takes to make the journey between the two planets, so life here could have originated on Mars, or life on Mars could have originated here, if it ever existed. Some people think comets also carry bacteria or viruses, though this is highly unlikely.

Akarsh_Valsan: Where do comets come from?

Bill: Most start out in the Oort Cloud, which is a halo of dirty snowballs about 1 light year from the sun. Gravitational tugs or "perturbations" from nearby stars will sometimes throw one of these dirty snowballs into the solar system, and that's the origin for the comets we see today. Jupiter's gravity can alter the orbit so it only takes a few years instead of many thousands of years to go around the sun once. For example, Hartley 2 now just takes over six years to orbit the sun.

Akarsh_Valsan: Did comets help create Earth's seas?

Bill: Comets contains lots of water and many astronomers think they delivered a large percentage of water to the early Earth -- so there are at least some who support this idea.

Brad_Sheaks: Where do comets originate from? Supernovas?

Bill: Comets don't come from supernovas, but from the Oort Cloud which is a bunch of "dirty snowballs" orbiting the sun one light year away.

Vani: Is there any studay or research undergoing to the possiblity of landing the spacecraft on comet surface and study, rather than close up approach?

Bill: Landing on a comet presents numerous challenges, especially if the comet is active. You have to worry about getting hit by pieces coming off the comet. I don't know of any plans for a comet lander, though I expect we'll certainly see mission proposals to do so within the next decade.

r2d2: It seems like many intense meteor showers happen when the comet returns to perihelion. But usually those showers are attributed to dust ejected long ago and not dust being ejected right now. Why does the return to perihelion matter so much to the intensity of the shower if all the dust spreads out and does its own thing? I'd think the comet coming back to perihelion wouldn't matter.

Bill: In some cases, such as Leonids, the return to perihelion does matter in the sense that the meteoroids ejected by the comet while in a slightly different orbit have essentially the same period as the comet. Given this, it's not surprising that meteor outbursts or storms would happen near the perihelion of the comet.

Eli: Is spectroscopy a common used method in this area of study?

Bill: They are taken and do give insights into composition. As a matter of fact, early use of spectroscopes in the 1910 apparition of Comet Halley revealed the presence of cyanogen gas in the coma, which caused a panic among Earth dwellers at that time. Even though the amount was ridiculously small, doomsayers suggested that the atmosphere might become contaminated from poisonous gas. Gas mask vendors did a BOOMING business in 1910, as well as those selling comet pills, supposed to protect users from the poisonous cyanogen.

r2d2: Did anyone observe Hartley-id meteors this year?

Bill: There are no confirmed observations. Many people saw fireballs, but they were Taurid meteors and the South Taurid meteor shower peaks today.

(Moderator Jason): We're working to answer your great questions. Keep them coming! To submit your own questions, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

Brad_Sheaks: What does the shape indicate to you? Its failry smooth and curved in the middle, the edges look "grainy"...

Bill: To me, Hartley 2 resembled the asteroid Itowaka in both shape and the smooth feature around the middle, or narrowest part. Of course, Hartley 2 is an active comet, so has jets, whereas Itowaka doesn't.

Curious: Why do Hartley2 and asteroid Itakawa look so similar?

Bill: Good question. The smooth feature around the narrow part of both objects is an area of high gravity, so dust tends to collect in that area. So since both are shaped somewhat like peanuts, we expect smooth areas around the narrow part of the peanut. That explains one similarity, but for others, we'll have to wait for the science team to figure it out. :)

RattUT: Do we know the chemical composition of comet Hartley 2's jets?

Bill: Suspect they're water vapor, carbon dioxide gas, mixed with dust -- but don't know for sure. We'll have to wait for science team results.

Curious: Was EPOXI hit by any dust from the comet during the flyby?

Bill: Not as far as we know. Its trajectory was chosen so that there would be less than a 1% change it would take a hit.

Chris_L: Simple question, can you use the chemical content of a comet (et cetera) to alter its path. For example, could you develop a carbon dioxide bomb.

Bill: I would think if you're going to use a bomb, you'd use something with a little more "oomph" than carbon dioxide. :)

JohnDoe: Since Earth has it's own gravity and has a moon orbiting it -- do we also have other celestial objects orbiting the earth??

Bill: No natural objects, other than the moon have been detected orbiting Earth -- but of course, a ton of man-made items.

r2d2: Why does comet Hartley appear green in the images taken from earth?

Bill: The green color is due to excited oxygen gas.

JohnDoe: Why do we discover asteroids pasing close to the earth so late? Like 24 hours before they pass? Don't we have better early detection systems?

Bill: Our network called SpaceGuard is designed to detect 1 km and larger asteroids, not the small stuff. We can detect 1 km asteroids very far out, but most stuff you recently read in the news is only like 10 yards across -- very hard to see these, especially when you consider they're the color of a pencil lead.

r2d2: The text on the chat page mentions that a meteor shower from comet Hartley would be something new. If the comet is periodic, wouldn't we have seen Hartley-id meteors in the past?

Bill: Not necessarily. A close encounter with Jupiter in the 80s altered the comet's orbit so it now passes near that of the Earth. The question was, would "stuff" ejected into this new orbit produce a meteor shower.

r2d2: Followup Q about the green Hartley images -- So there is oxygen around the comet in space? Or are we seeing oxygen in the atmosphere?

Bill: You're seeing oxygen coming from the comet being excited by sunlight out in space. There's not very much, so please don't go to Hartley and expect to breathe!

JohnDoe: Pencil lead? Isn't that lighter than the deep blackness of space? Plus doesn't the sun's light reflect/illuminate these objects?

Bill: Yes, but the amount of light reflected falls off as the square of the distance from the object -- so it gets increasingly dimmer the farther away it is. That's why we can only see small objects when they're very close. Hopefully, new telescopes such as PANSTARRS will enable us to see these smaller objects farther out.

BlackJack: Is Apophis (99942, 2004NM4) a real threat?

Bill: No, recent data has virtually eliminated the chance of a collision.

Curious: Where does EPOXI go next? Does it have a new target to explore?

Bill: Not as far as I know -- I think Hartley 2 was the last object they were planning to visit. But, you never know. Those JPL guys are pretty clever.

Curious: Do most meteors come from comets or asteroids?

Bill: Most come from comets, some astronomers think as much as 90% of meteors come from comets. The rest come from asteroids, and a TINY fraction can come from the moon or Mars.

Akarsh_Valsan: What can be the speed of a comet?

Bill: A comet's speed varies with distance from the sun, but at Earth, the fastest a comet can move and still be in orbit around the sun is 26 miles per second (mps), relative to the sun, or 44 mps relative to the Earth.

Akarsh_Valsan: Why are asteroids called minor planets?

Bill: Because they're not very big.

r2d2: Did you personally expect there to be any Hartley-id meteors this year? Was it in your shower forecast?

Bill: No, I didn't really expect them this year, but I wanted people to look just in case. :)

sclanham: You said comet Hartley 2 "has jets". How does that work? What provides, for lack of a better term, propulsion?

Bill: The jets you can think of a geysers of gas and dust, caused when sunlight vaporizes ice on the surface, causing areas of high pressure underneath. This pushes the gas and dust away from the comet and it appears to look like a jet when illuminated by the sun.

BlackJack: If Apophis is not a threat, what about 2007 VK184? It's at Torino Scale 1.

Bill: I don't worry much about Torino Scale 1 objects because they're QUITE likely to become Torino Scale 0 objects.

qiub: Hi Dr Cooke, some questions about the comet itself, thanks! By looking at the size of the comet, it seems its mass is quite limited, assuming ejecting jets will reduce its mass, then how can it keep ejecting jets for years?

Bill(A) You're correct in that a comet loses mass each time it goes around the sun. Eventually all active comets will lose their ice and other volatiles and will no longer show activity. An astronomer looking at such dead comets may very well classify them as asteroids.

sclanham: So do the jets provide rpopulsion, or is that from another factor, such as gravity?

Bill: The jets do provide enough propulsion to alter the orbit of the comet slightly, and they must be taken into account. We do this by adding in a non-gravitational term in the equations of motion.

(Moderator Jason): Really good questions so far. Keep them coming! To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

Curious: Do the jets change the orbits of the comets?

Bill: They do, slightly, but we need to take these changes into account to accurately predict a comet's position.

ZacharyTroxell: Are all comets we know of made of the same components? What are these comets composed of?

Bill: Pretty much the same: dirty snowballs would be a good first-order description.

PaulAFelty: You said Jupiter affects the orbit of comets, asteroids, and other space debry in orbit, is there any chance at seeing Hale-Bopp again in under 2000 years? I remember seeing that as a kid in 1995 and it was spectacular to see so close to the earth! Any chance at another comet comming that close again?

Bill: We see long period comets, such as Hale-Bopp, all the time. I'm sure there will be another like it visible over the next decade.

qiub: Thanks! A related question, when you mention "ice", are they from water or something else?

Bill: Both water and carbon dioxide ice (dry ice).

Akarsh_Valsan: Do Solar Eclipses or any other eclipses cause any problems to comets,meteors or asteroids?

Bill: No effect.

BlackJack: On September 1st I took a picture of the sky and I saw an object mooving very fast (it left a track of about 2.5° in 60 seconds). What could it be?

Bill: Could have been a bright satellite or a pass of the International Space Station.

Vani(Q) Follow up question of qiub, once the comet is dead, how can we differentiate the dead comet from any asteriod, because now the dead comet doesn't have the 'jet'? Is that the reason we call them as asteriod?

Bill: We can't. That's why many astronomers suspect we have classified some inactive comets as asteroids. if you look at Hartley 2 and remove the jets, some people may classify it as an asteroid like Itowaka.

ZacharyTroxell: How cold are comets? (In degrees F)

Bill: Typical temps experienced by a comet are -260C to 100C.

Akarsh_Valsan: Have any asteroid or any comets ever coillided with sun?

Bill: The SOHO spacecraft sees comets Kamikaze-ing into the sun all the time.

Curious: From the shape I would call Hartley 2 a dirty snowman.

Bill: Looks like a peanut to me. :)

RattUT: How many periodical comets (long- or short-period) are we aware of in the solar system?

Bill: Our periodic catalog now has well over 200.

ZacharyTroxell: Do we really know that comets are made of snow/ice or is this just a theory? If it's a fact... how do we know?

Bill: Spectroscopic observations indicate that strong presence of water ice and we know because comets produce meteor showers that they produce a large amount of dust.

qiub: By watching the video "EPOXI Mission Captures Jets in Action", it seems the trajectory of the comet is not straight, is it because the ejected jets change the direction of the flight? Is that change kind of random? Does the comet rotate?

Bill: The comet rotates in a period of approximately 18 hours, as best we can tell. The jets change the orbit very slowly with time, and all data indicates the comet is following a normal trajectory around the sun.

(Moderator Brooke): Thanks for the great questions! It may take a few moments for the queue to catch up to your question, so please don’t leave if you don’t see your question right away.

Chris_L: What colors are comets, asteroids, and meteors. How many are bright in color and how many are not bright in color.

Bill: Comets would be brighter due to the "dirty snowball" effect because they have trails. Asteroids and meteors aren't as visible because they're basically a "rock in space."

Akarsh_Valsan: What does the holes depict on Comet Hartley 2?

Bill: If by holes you mean the bright spots, it might be boulders, or it could be a hole on the surface exposing ices. But that's more of our opinion at this point, rather than a confirmed fact.

Akarsh_Valsan: Why does the Comet gets its name Hartley 2?

Bill: It's the last name of its discoverer, Malcolm Hartley.

Nick_Howes: Dr A'Hearn mentioned that if the comet "spins up" (i.e the jets increase the rotation rate), there is a possbility of it fragmenting (like C/2007 Q3). Will ground based scopes or the spacecraft continue to track 103P and for how long to see if this increase in spin rate occurs?

Bill: If the comet is loosely held together, a spin-up will result in fragmentation. You can bet ground-based telescopes will continue to track 103P for the next several months, if not for another year.

qiub: I understand that for a time scale of several years, the perturbation from the ejection of jets should be small to the orbit of the comet, however, for the time scale of several minutes as for the impact with Hartley 2, the "perturbation" from the jets to the comet trajectory should be significant. Then how can you calibrate the trajectory of the spacecraft to make close contact? Thanks! Do you apply some on-the-fly control? If yes, how is the communication delay between NASA center and the spacecraft due to limited speed of light taken care of ? thanks!

Bill: You continuously monitor the comet with telescopes and radar -- when close -- and make a course correction if needed to bring the spacecraft to the desired encounter distance. The communication delay is easily calculated because we know the spacecraft distance from Earth, and this is accounted for in the command uplinks.

sclanham: If a comet fragments, does it become several comets or does the fragmentation result in its demise?

Bill: Either. Comet 73P has fragmented back in the 90s and then again a few years ago. Each of the large fragments became a mini-comet and exhibited activity like their bigger "parent." But back in the late 1800s comet Biela broke apart and all we saw was a spectacular, short-lived meteor shower called the Andromedids.

Nick_Howes: Why didn't Deep Impact, if there was a possbility of an Earth orbit flyby, have a sample return portion (like stardust) for comparison analysis of the cometary material? With the sample retunr capsule "thrown" back to Earth at an applicable point? Was it purely budgetary or design constraint/mass issue, or didn't it seem appropriate for this mission?

Bill: The simple reason is that Deep Impact was never designed for a sample return. Sample return missions are very difficult and present significant technical challenges. Deep Impact was never intended for sample return -- we wanted to see what comets were made of.

qiub: Sorry to ask again, it seems I sumbitted this question but get skipped. Follow up question of Akarsh_Valsan, if the comet is dead, it will not lose any more mass through vaporation of ice etc, then it should not lose energy when traveling. The question is how can it change its orbit then fall into the sun?

Bill: A dead comet will not fall into the sun unless the gravity of a planet such as Jupiter perturbs the orbit into a sun -grazing trajectory.

PaulAFelty: If a Hartley-2 sized object made up of the same composition, hit the earth at it's given velocity, what kind of crater are we talking about here?

Bill: A 1 km object would leave a crater roughly 6 miles in diameter.

Nick_Howes: Why did the HRI images need deconvolution, was a different focusing model used for the MRI and HRI or was it another constraint (CCD ype/exposure length etc)

Bill: I have no idea -- you'd have to talk to the EPOXI people on that one. :)

Kaloyan: Do you have an explanation for the smooth area in the center of the Hartely 2 comet?

Bill: Some astronomers think that area looks smooth because it has trapped dust coming off the surface of the comet as it's an area of high gravity, compared to other parts of the comet's surface.

Chris_L: Have comets been discovered in other galaxies.

Bill: No, but they're almost certainly there.

ZacharyTroxell: How often will Hartley2 orbit for viewing?

Bill: Hartley 2 will make its next close approach to Earth on April 20, 2017, but it will be over 95 million miles away, and you'll need a telescope to see it.

Mooseman: What are the differences between meteors and asteroids?

Bill: Asteroids are much bigger but there's no hard separation between the two. Some people would say an object 10 yards across is an asteroid, whereas others would call it a big meteor. Everone agrees that something as big as a football field should be called an asteroid.

Akarsh_Valsan: What are dustless asteroids?

Bill: To my knowledge, there's no such thing. Asteroids can be depleted in ice, but they're all dusty.

Chris_L: My assumption is that your "light falling off" equation was just an estimate. What would a more accurate equation consist of. How accurate is the estimate.

Bill: Light from a point source falls of as the inverse square of the distance. This isn't an estimate -- this is the equation.

srda: Why do you make the distinction between meteors and asteroids? Why can't they all be meteors?

Bill: Because people like classifying things into categories and one wants to distinguish big rocks from little rocks somehow. :)

(Moderator Jason): We're working to answer your great questions. Keep them coming! To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

flowinert: What exactly shapes a comet ? for example Hartley2's middle section appears smooth, almost like a handle.

Bill: Comets can get their shapes through a variety of means, like more ice may vaporize from one part than another, which would cause a depression to occur. Some peanut-shaped comets may look that way because they're really two comets that have collided and stuck together. You can think of lots of ways that comets can get unusual shapes.

(Moderator Brooke): Thanks for the great questions! It may take a few moments for the queue to catch up to your question, so please don’t leave if you don’t see your question right away.

Mooseman: What is the trail of a comet made out of?

Bill: The tail is made of gas that's been pushed out by light pressure from the sun. Sometimes comets sport a second tail of dust.

Akarsh_Valsan: Is meteors the reason for extinction of dinosaurs?

Bill: It's currently accepted that an asteroid caused the demise of the dinosaurs 65 million years ago.

ZacharyTroxell: Prior to April 20, 2017, can we expect to hear any more about comet Hartley2?

Bill: i would expect that you'll hear a great deal over the next couple of years as data from EPOXI is analyzed and results are reported.

Chris_L: Has the dinosaur killing meteor been given a name?

Bill: No name.

ZacharyTroxell: What's the most interesting thing we've learned about Hartley2 & comets from our recent view of Hartley2?

Bill: I was surprised by the resemblance to Itowaka, but I'm sure the science team has a lot of interestings things they can tell.

Chris_L: Where did the dinosaur killing meteor hit the Earth?

Bill: Yucatan Peninsula.

Mooseman: What is the expected lifespan of recieving data from EPOXI?

Bill: I'm not sure about that.

Chris_L: What colors do comets come in. Does the frequency of the various color change in different galaxies. For example, are there more red comets in the Milky Way than in other galaxies.

Bill: Comets look gray. I have yet to see a comet with a significant red or blue color -- they're kind of drab, color-wise. I'd expect comets in other galaxies to be similar to those in our galaxy.

sclanham: How many comets pass by Earth in a given year?

Bill: It varies from year-to-year, no specific number.

qiub: So what are the composition of the dust? Is it similar to that of earth dust?

Bill: Yes, the dust consists of minerals similar to those found here on Earth: olivine, etc.

solarsystem1970: How has the population of comets in the solar system changed over time?

Bill: In the early days of the solar system right after formation, there were a great many more comets. However, the migration of the giant planets created what we called the "Late Heavy Bombardment" over 4 billion years ago, which sent most of these comets crashing into the surfaces of the planets and the moon -- which still shows the scars from this event. The remaining comets in the solar system have either collided with other bodies or the sun. But, there are lots of comets still out in the Oort Cloud, 1 light year away.

qiub: Did EPOXI collect things other than photos and videos? I understand it's not designed for sample collection, but any radiation signatures, etc.? You mentioned "we wanted to see what comets were made of", is that done just by looking at the photos it took? Thanks!

Bill: EPOXI had a suite of instruments but there were no samples taken from the comet. We don't just look at photos -- there are infrared spectroscopes and ground-based observations with various instruments that can look at material coming from the comet.

Nick_Howes: On the colour question, whilst the albedo is very low, has any minerology/spectroscopy been done to determine if the comet composition is even (analogy with things like Moon minerology mapping)

Bill: I don't know on this one -- you'd have to talk to a comet composition person. EPOXI wil take infrared spectral maps of gases in the innermost coma and of the jets.

Mooseman: How much data from EPLOXI will be published?

Bill: All of the results will be published as well as the data analysis. Hard to fit many megabytes of data into a journal. :)

Chris_L: Why isn't there a well known telescope on the International Space Station.

Bill: The International Space Station is well-suited for many types of science, but telescopic observation isn't one of them.

Mooseman: Have valuable metals been found in meteors/asteroids?

Bill: No gold and silver, but a Mars meteorite will sell for thousands of dollars per ounce to a collector. This is not because of any precious metal, but because rocks from Mars are so rare.

Mooseman: Is there any proof of a dinosaur-killing meteor, or is this a hypothosis?

Bill: There's a worldwide layer of iridium -- an element which is commonly found in meteorites, but rare here on Earth -- dated to 65 million years ago. Geological observations by oil companies have located the crater in the Yucatan, also dated at 65 million years and ejecta layers contained shocked quartz have been found in North America and other locations. So, there's quite a lot of evidence supporting a major impact 65 million years ago.

phyicsfan: How was the asteroïd belt formed?

Bill: The asteroid belt are debris left from the origin of the solar system. Jupiter's gravity prevented a planet from forming in this area, so all we have are these asteroid-sized pieces of rock.

(Moderator Brooke): Thanks for the great questions! It may take a few moments for the queue to catch up to your question, so please don’t leave if you don’t see your question right away.

qiub: By the way, did we collect comet samples before? If you look at the materials coming from the comet or look at the spectra of reflected light, you'd get a good idea of what's on the surface. But, how can you tell what its core is made of?

Bill: Yes, the Stardust spacecraft flew by a comet Wild 2 and collected samples of dust in its vicinity. it brought these samples back to Earth for analysis. Studying stuff beneath the surface is one reason we sent the Deep Impact mission to comet Tempel 1. By hitting that comet with a "copper brick," we kicked up material from beneath the surface which we could then analyze, spectroscopically and by other means.

qiub: How can you tell a comet is from inner solar system as the "leftover building blocks" but not from the outside?

Bill: The orbit. If it's a Jupiter-family or Halley-family comet, that means it has been around long enough for Jupiter or one of the other planets to significantly perturb it from its original path.

Brad_Sheaks: Do any comets or asteroids effect solar activity such as storms/flares?

Bill: No, no effect.

ZacharyTroxell: Why does it take scientists years to properly analyze the data? What type of data are we talking about?

Bill: The data we're talking about are images, spectroscopic measurements and so forth. It takes years to analyze the data because one, we want to get it right, and two, a lot of scientists are at universities where they have classes to teach, and three, sometimes it takes us awhile to figure out what's going on.

Chris_L: Can you explain why telescopic observation is not well suited for the ISS. They take a lot of pictures on the station.

Bill: Yes, they take a lot of photos of Earth, but the ISS houses humans and humans produce a lot of junk. A telescope on ISS would have its optics coated by water dumps and other things that are flushed overboard from the ISS. Not a good place for a telescope!

Mooseman: Are there any known metals on Mars other than iron?

Bill: Pretty much the same stuff you find here on Earth.

Nick_Howes: Based on the spectral signatures, can the teams determine any similarities between the long period comets and the shorter period ones visited, and are there any major differences?

Bill: Long-period comets appear to be more active, probably because they haven't gone around the sun many times. Short-period comets have been "cooked" more often, but we don't see much difference between the two spectroscopically -- except that long-period comets are more rich in volatiles, such as water vapor.

solarsystem1970: If the rotation of Hartley 2 speeds up and it breaks apart, could that produce a "Hartleyids" meteor shower?

Bill: Possibly, depends in the severity of the fragmentation and the orbits of the fragments.

qiub: A follow up question, have you ever looked at the composition of a comet from the outside of solar system?

Bill: We haven't detected any comets outside the solar system.

sclanham: If telescopes are not suitable for the ISS, what do they use for observations?

Bill: If you're referring to the Earth, they use cameras similar to what you would use. Not much astronomy done from the space station.

qiub: So the waste and dumps are flushed out of the ISS and then allowed to orbit around the earth? I thought they'd be put into containers and brought back and dealt with on earth...

Bill: Water and other volatiles are flushed, but solid waste IS brought back to Earth.

Mooseman: Has there ever been any record of comets colliding?

Bill: No, no record that we have.

ZacharyTroxell: Are asteroids similar in size to the astroid that hit the Yucatan Peninsula a threat to humanity?

Bill: Obviously yes, but there's no such object currently tracked by any of our telescopes. I don't go to sleep worrying about this. :)

Nick_Howes: Interestingly on the Iridium layer front, has MER considered looking for similar layers in any of the craters on Mars, and potentially dating an event which may have caused the catastrophic loss in atmosphere/water which is now being theorised?

Bill: I'm not sure the MER rovers are capable of spotting an iridium layer on Mars -- but you'd have to check with the MER science team.

Mooseman: What exactly happens to the water being no air and no resistance? Will it disapate as it nears the sun?

Bill: Water sublimates to gas, and the gas disperses into space.

qiub: What'd happen to the EPOXI spacecraft? Is it moving on to next mission or is its glorious journey coming to an end? How much longer can it function?

Bill: I'm sure NASA will post further information about EPOXI. I'm not on the spacecraft science team, so I'm not sure what the future plans are, if any.

Nick_Howes: Has this mission, along with the previous 5 encounter missions given us any further insights into how/if we should improve the NEO monitoring and our possible response to a potential Earth impacting object?

Bill(A) Actually, we can track big stuff approaching Earth fairly well. These missions underscore the importance of first sending an unmanned spacecraft to study any potentially hazardous asteroid or comet, as this data will help determine how we are going to avert a collision.

Mooseman: I have heard that water on the ISS is purified and reused. Is this still done?

Bill: There is a system called ECLSS that purifies water aboard ISS for reuse, and it's still operational.

michal: Why is the comet so long active?

Bill: Comets are active only while close to the sun. Hartley 2 like many others will exhibit several months of activity before it gets so far from the sun that it goes dormant.

PaulAFelty: Are you or anyone of your other colleagues part of the Curiosity or Jovian missions comming up next year?

Bill: No, not part of those.

qiub: What's the vaporation rate of the ice on comet surface? By looking at the temperature range you mentioned, it seems ice can be easily gasified, and for the size of Hartley 2, how long it will take before it loses all its ice? Just a rough time scale, a few years, hundreds of years, etc. Thanks!

Bill: It varies with the comet. A Halley-type comet (Hartley 2 is a Jupiter family comet) requires several hundred to a few thousand orbits of the sun before its ices are exhausted.

solarsystem1970: Do you think it would be a good idea if people installed fish-eye lens video cameras at home aimed at the sky to detect fireballs at night? Wouldn't that help in trying to find fresh meteorites for study?

Bill: Of course! :) We're planning to deploy 15 of these systems.

Mooseman: Is there a prediction of when there will be a comet sighting without a telescope? If yes, when?

Bill: No prediction at this time.

(Moderator Brooke): Thanks for all the great questions! It may take a few moments for the queue to catch up to your question, so please don’t leave if you don’t see your question right away.

Chris_L: Has any meteor that hit the space station been captured and recovered?

Bill: No, but we have brought pieces of Hubble Space Telescope back to Earth and studied the debris left behind in the craters on the surfaces. Unfortunately, it appears that most of these holes were caused by man-made debris.

Mooseman: What are the "in case of emergancy" ways that could avert a collision with a asteroid or comet?

Bill: It's kind of hard to answer this question, as a method to avoid a collision will depend on the nature and orbit of the object that would pose a threat to Earth. You can't come up with a "one size fits all" planetary defense.

PaulAFelty: So what is next for you then? Is it studying these pictures and data for then next few years or something else?

Bill: I will continue my studies of meteors and leave Hartley 2 to the EPOXI science team. I look forward to hearing their results!

ZacharyTroxell: Dr. Bill Cooke & Nasa: Thank you so much for your time!! :D

Bill: You're very welcome -- thank you for coming!

Nick_Howes: So will NASA be sending something to 99942 Apophis as this currently is the highest threat NEO?

Bill: There's nothing planned at this time. The Russians are considering it.

Chris_L: How many meteors have hit the ISS. How safe are they. Can they take further precautions to protect theirselves.

Bill: We don't know how many have hit ISS, as the ones that have are very, very small. You have to remember that ISS is armored against orbital debris, which also provides extremely good protection against meteoroids. It's the "tank" of Earth orbit.

Paulty: I appreciate you taking the time to answer my questions, I tune in every day I work and look forward to the next thing from NASA! =)

Bill: Thank you for being here, and keep tuning in. :)

Mooseman: Thanks for having having this, Dr. Bill Cooke!

Bill: My pleasure. :)

Mooseman: What metals protect the exterior of the ISS?

Bill: Google something called a "Whipple shield." ISS armor consists of Whipple shields, stuffed with Nextel/Kevlar -- the stuff used in bulletproof vests.

Mooseman: Thank you for your time Dr. Bill Cooke, very informative!

Bill: Very welcome!

Brad_Sheaks: Just wondering, Do you have the ablility to study or find "comets and such" in other galaxy's close to ours?

Bill: No, other galaxies are too far away.

Curious: Have there been any meteors from Hartley 2?

Bill: We haven't observed any confirmed meteors, I'm sad to say.

Vani: Since we dicovered that living organisms can survive in hydro thermal vent, no need the sunlight for survining, is there a possible that these comet has any life forms?

Bill: I sincerely doubt it. The space environment is very harsh, even for extremophiles.

Chris_L: What are the chances of finding new elements in comets.

Bill: Almost nil. Superman is safe from Kryptonite. :)

Bill: Thanks for the great questions everyone -- this has been a great chat! To learn more about the EPOXI mission, visit

(Moderator Brooke): Thanks to all of you for the great questions, and thanks to our guest scientist, Dr. Bill Cooke. Check back in the next day or two for a posted transcript of today’s chat. Have a great day.

Janet Anderson, 256-544-0034
Marshall Space Flight Center, Huntsville, Ala.