LRO Locates Lunokhod 1 Rover and its Laser Retroflector

The first successful robotic lunar rover, Lunokhod 1, landed on 17 November 1970. For the next ten months the rover was driven by operators in the Soviet Union, with the total distance traveled exceeding 10 km. A French-built laser reflector was aboard rover, but after Lunakhod 1 fell silent on September 14, 1971, the location of the rover and retroreflector was unknown.

Laser retroreflectors are used by ground-based telescopes to pulse of laser light to the Moon and back. The time for the return tells the position of the retroreflector to less than a centimeter. This allows scientist to measure the shape or the moon as it bulges due to tides, the wobble of the Moon as it rotates on its axis, and the motion of the of Moon on its orbit to within an accuracy of one millimeter, or about the thickness of a paperclip. Three reflectors are required to lock down the orientation of the moon – the retroreflectors left by the Apollo 11, 14, and 15 missions are still routinely used for these measurements. Additional retroreflectors would allow determination of different lunar parameters and enable grater precision. Occasionally the Soviet Lunokhod 2 reflector has been used for this information, though it is severely degraded relative to the Apollo reflectors.

Ground-based observers had occasionally looked for the Lunokhod 1 reflector over the last two years, but faced tall odds against finding it until recently. The breakthrough came last month when the high-resolution camera on NASA’s Lunar Reconnaissance Orbiter, or LRO, obtained images of the landing site. The camera team, led by Mark Robinson at Arizona State University, identified the rover as a sunlit speck on the image (see below) —miles from where teams had been searching. On April 22, Tom Murphy at UCSD and his team used the 3.5 meter telescope at the Apache Point Observatory in New Mexico to find the long lost Lunokhod 1 reflector and pinpoint its location to 10 meters on the surface and 2 cm distance from the earth. Finding the Lunokhod 1 allows for much better geodynamics and studies of the lunar interior.

Perigee Moon & Mars at Opposition

The last weekend of January 2010 promised two very special "close encounters" with our nearest neighbors. Planetary scientist Barbara Cohen at NASA's Marshall Space Flight Center answered your questions online about Mars at Opposition and the "largest" full moon of the year via a live Web chat on Friday, January 29, 2010 for over 90 minutes. http://www.nasa.gov/connect/chat/marsmoon_chat.html

Here's the transcript. Enjoy!

(Moderator) Brooke: This is a moderated chat. If you haven't seen your question answered yet, please wait a moment as it is in the queue to be answered. Many thanks for your patience.

Barbara: Hi everyone. Tonight is a special night because there's a full moon and Mars is near Opposition.

Omnologos: Given the extraordinary success of Spirit and Opportunity why don't we just build and send more of them to explore more of the Mars surface?

Barbara: Every mission we send builds on the others. We have new science questions even as we learn from Spirit and opportunity. Our next mission Curiosity (Mars Science Laboratory) will have more instruments and be able to roam further.

Erin: Is there science or observations that can be done at an Opposition that can't be done during other times?

Barbara: At opposition, Mars is very bright, so you can see it with your own telescope, so you can observe it. We learn more about the planet's orbit.

TelescopPeMater55: Hello, I tried to look at mars with my telescope and I don't know how much magnification I need to see it can you tell me how much I need?

Barbara: You can see Mars with your naked eye. It's small, reddish-orange, and doesn't twinkle. If you have binoculars, you can see a disk. If you have a larger telescope, you might be able to see bright polar caps and dark dust.

Goody: How often do we have a perigee moon?

Barbara: About once a year. But it doesn't always exactly coincide with a full moon.

Michael_C.: Why doesn’t Mars “twinkle” like Sirius? Thank you.

Barbara: Because the planets are very close relative to stars. The light they give comes from a disk, so the light doesn't "twinkle."

(Moderator) Brooke: We're working on answering your questions right now. If you haven't seen your question answered yet, please wait a moment as it is in the queue to be answered. Many thanks for your patience.

Gabrielle: Is there a way to see it online, since it's very overcast where I live?

Barbara: There will be lot of amateur photos online.

gayle: Hi, I'm a student at an elementary school in Tampa. I was wondering why, if we knew that Mars would be so close to the moon tonight, didn't we schedule a trip to Mars when it wouldn't take so long to get there?

Barbara: Great question! We DO schedule Mars launches so they take advantage of when the Earth and Mars are close to each other. But it takes six months to get to Mars, so we have to launch six months in advance of when they line up together.

omnologos: The Moon is quite close indeed compared to Mars. If Ares is cancelled, can we expect at least some rovers to explore the more interesting bits we have only looked at from orbit?

Barbara: Curiosity (Mars Science Lab) is a rover the size of a VW. We're launching it in 2011, and it will explore more of Mars from the ground.

Erin: What do you learn about a planet's orbit from it coming closer during the Opposition?

Barbara: Planets orbits aren’t exactly circular. They're influenced by many objects: the Sun, its own moons, Jupiter, etc. It doesn't come closer during Opposition, but it's a special time when it's on the opposite side of the Earth as the Sun.

earthvisitor: Where will Mars be located in the sky in relation to the moon?

Barbara: Very near the moon. Looking at the moon with the naked eye, Mars will be within a "fist" of the moon tonight (Friday).

WIstormspotter: With spirit now stationary, is there a plan if while doing stationary exploration that it gets dislodged to start up and move again?

Barbara: No, Spirit is going to remain motionless during Martian winter because there's not enough solar power. In Martian spring, we may try to start moving it again.

Erin: Does the increased brightness of Mars at Opposition help observations from the large, professional observing telescopes?

Barbara: Yes, it does.

dwscott: What's the typical time gap between concept for a probe/rover and the time it lands on Mars? How far into that gap can the instrument(s) be modified to conduct an investigation inspired by results from existing probes/rovers?

Barbara: From concept to landing, it takes many years. :)

goody: How often does the moon and mars both have close encounters with the earth?

Barbara: The moon and Mars are both in elliptical orbits. The moon comes closest at a time called perigee, which happens once a month. For Mars, it gets to its closest point to the sun every two years.

Michael_C.: Is there a website similar to http://spaceflight.nasa.gov/realdata/sightings that provides sighting information for “natural” objects in the sky such as Mars? Thank you.

Barbara: Try Sky and Telescope's Web site.

robertbl22: What kind of binoculars (what power) do you recommend for viewing Mars?

Barbara: Any kind will work.

(Moderator) Brooke: We're working on answering your questions right now. If you haven't seen your question answered yet, please wait a moment as it is in the queue to be answered. Many thanks for your patience.

cosmo36: Hello, Is it possible for any unexplained Observation in 2003, on Earth? For instance perhaps unstable Magorstetic outer core disturbance that cause anything such as car malfunction?

Barbara: Opposition of the planets happens regularly. For Mars, it’s every two years. Mars isn't big enough to cause any disturbance on Earth.

(Moderator) Brooke: To those who want to see tracks of other near Earth objects, visit http://neo.jpl.nasa.gov/

gayle: How much difference in time does it take to get to Mars when the Earth and Mars aren't so close to each other?

Barbara: The fastest we can get there is about six months, but slowest could be years or more.

omnologos: Why not rovers on the Moon too?

Barbara: I wish! Many groups are proposing them, but NASA only has so much money. And we can't do everything. Hopefully, you'll see these in the future.

jjgravity: Will this conjunction happen with an eclipsed moon any time in the next few years?

Barbara: Great question. It's much rarer to happen with a lunar eclipse -- probably many years in between.

Erin: Regarding a question from gayle; might want to mention that (I think) the Curiosity mission was supposed to launch in time to take advantage of this opposition, but was delayed.

Barbara: Yes, that's right. There was a mission delay that caused us to miss the 2009 launch window, so next window is 2011.

Artemis: Are there other options besides the Aries project for space travel if this administration decides to kill the budget? It would be a shame if we couldn't explore the Moon or Mars.

Barbara: I can't speculate about future U.S. spaceflight plans. Right now we're staying focused on our current spacecraft such as LRO, MRO, and of course Spirit and Opportunity,

Ken: What is your opinion on the possibility of life on subsurface Mars, and would surface life be impossible due to radiation and sublimation of any water?

Barbara: We don't currently have any evidence for life on Mars. We think life depends on having liquid water and a benign radiation environment. So our Mars missions are looking for environments such as these where life might be able to live.

gwotty: Hi, Just joined & I'm happy to say after 2 weeks of total cloud, we have a FANTASTIC clear sky for viewing Mars & Moon tonight. I'm looking at it as we chat, out of my window, here in UK......

Barbara: Great -- good luck. If people have telescopes, they can take a look on any magnification. You can use binocular or the naked eye.

nasa: Will this be orange in colour?

Barbara: Yes, Mars is orange because the rocks are oxidized, making them red like rust.

robertbl22: How long will opposition last, or how long will it affect viewing?

Barbara: It's a moment in time, technically, but you can see it in that position for many days. In a year, it will be in its opposite configuration called conjunction, when it goes behind the sun.

One_Witchy_Woman: Can I take a picture of the moon and mars with a regular digital camera and have the halo show? Do I need something special?

Barbara: Yes, but the moon is so much brighter than Mars that it might not show up.

nasa: Will it look like a orange star next to the moon, when viewing with naked eyes?

Barbara: Yes, it will. But it won't twinkle like other stars.

revrosales: Humans have spent more than the six months for a trip to mars in the ISS and Mir already, correct?

Barbara: Oh yes. We learn a lot about how humans will be able to handle long spaceflight from our experience on the ISS. One difference is that the ISS is protected from radiation by Earth's magnetic field.

omnologos: Are the lessons learned from Spirit getting stuck being applied to Curiosity or is it too late?

Barbara: Yes, many lessons learned about the nature of the Martian surface, and the mechanics of roving. But Curiosity is probably not going to the same place, so we'll have more to learn when Curiosity arrives.

cbekiaris: what is your favorite color??!

Barbara: Magenta. :)

(Moderator) Brooke: This is a moderated chat. If you haven't seen your question answered yet, please wait a moment as it is in the queue to be answered. Many thanks for your patience.

Artemis: How long does it take to reach Mars with conventional spacecraft, and how long are the Martian seasons?

Barbara: Six months to arrive with current spacecraft. Martian year is about two years, so each Martian season is about six months.

llama1: Does NASA have any tentative schedule for sending people to Mars?

Barbara: No, not yet.

ZhaneDoe: Explain Perigee.

Barbara: The Moon's orbit around the Earth isn't exactly a circle, but an ellipse or oval. Earth isn't in the center. One end of the oval is far from Earth, one is close. When the moon is at the far end, it's called apogee. Near end is perigee. The orbit is once a month.

nasa: Can we see the pictures of mars as of today's event?

Barbara: There will be images online at various Web sites.

TaviGreiner: Read today that the Full Moon 15% of the Sun's light, compared to just 8% the day before or after - that's a 50% difference for not really much difference in illumination. Are those numbers accurate?

Barbara: I don't know if the exact numbers are accurate, but yes, the combination of the full moon and perigee make this full moon very bright compared to other full moons this year.

greg_p10: Can bacon be cooked in outer space? I need to settle a bet....

Barbara: Yes. If it couldn't, I wouldn't want to go! J

yummynuga: Will I be able to see Mars in the night sky?

Barbara: Yes, very close to the full moon. You must have clear skies.

Artemis: Will Mars be relatively visible to the naked eye this evening?

Barbara: Yes, will look like an orange "star" that doesn't twinkle.

quarkspin: Why use orbiters, landers, and rovers? Are there advantages to each?

Barbara: There are advantages to each kind of mission. Orbiters give you a global view of the planet. Rovers allow you to explore a small area in great detail. Landers allow you to do long-term observations in the same place.

goody: Question is there really a ring around earth made up of space junk??

Barbara: Yes, there is a lot of space junk around the Earth. NASA monitors it locations to make sure our satellites and the ISS have a clear orbital path.

WIstormspotter: Do you guys get a good laugh every time that article gets thrown out on the internet about Mars being so close to the earth it will be as large as a full moon?

Barbara: Yes, we do. :) Mars is not ever going to appear as large as the moon.

ZhaneDoe: How long is Mars away from earth?

Barbara: About 70 million miles.

cbekiaris: But seriously, is there any way to view Mars from Illinois at night? if so what kind of telescope would you recommend? And is there any way to view the moon and Mars at the same time?

Barbara: If it's not cloudy you can see Mars near the full moon tonight. To the naked eye, it will look like a small orange dot. With binoculars or telescope, you can see the disk.

Azorean: Hi all, Portugal here! Without the magnetosphere protection, it's not dangerous to travel between Earth and Mars?

Barbara: Yes. One of the primary risks in traveling between the Earth and Mars will be radiation. Humans and spacecraft will both need to be protected.

Clover: Is there a set date for sending another probe to explore Mars?

Barbara: Yes, Curiosity will launch in 2011.

julieta: Which features/aspects of the moon can viewers see today that can't be seen in another time of the year?

Barbara: It's about the same for each full moon, just brighter tonight.

Erin: Does having the Moon and Mars both being at least a little bit closer to Earth (compared to other times) affect tides?

Barbara: Great question. Yes, the closer the moon, the higher the tides. Perigee moon causes higher than normal tides by a tiny bit (millimeters). Mars has no measurable effect on Earth tides.

ZhaneDoe: Was water really found on the moon?

Barbara: Heck yeah! :) LCROSS kicked up a big cloud that had gallons of water in it.

Michael_C.: It’s cool that this event is taking place on the NASA Day Of Remembrance. A fitting tribute!

Barbara: Yes, all of us at NASA are remembering our lost comrades.

TaviGreiner: Will future human missions to Mars pose the same/similar dust issues that we faced with the Moon?

Barbara: Yes, but no. :) Mars is a dusty place, but Mars dust is very different than moon dust. Mars dust is rounded, moon dust is jagged. Mars dust is oxidized like rust, so it may react with metal. We'll have to deal with Mars dust in a different way.

omnologos: Is there a website with all scheduled and proposed future Mars missions?

Barbara: Yes, visit www.nasa.gov

(Moderator) Brooke: Learn more about past, present, and future Mars missions at http://mars.jpl.nasa.gov/missions/

Mitch: I'm a retired NASA Expert and have heard rumor of a space rover to launch for Jupiter in 2012?

Barbara: Jupiter has no solid surface, so rovers won't work. :) But, NASA is sending a probe called JUNO in a few years.

yummynuga: How big is the moon?

Barbara: About 2,000 miles in diameter.

(Moderator)Brooke: Learn more about NASA's JUNO mission to Jupiter at http://www.nasa.gov/mission_pages/juno/main/index.html

Sunstreaked: What exactly does a planetary scientist do?

Barbara: Web chats! :) Seriously, I study rocks from other planets to learn about their geology. We get the rocks here from missions like Apollo, or delivered to us as meteorites.

(Moderator) Brooke: We're working on answering your questions right now. If you haven't seen your question answered yet, please wait a moment as it is in the queue to be answered. Many thanks for your patience.

Yellowstone: Why is Mars the only red planet (oxidized)?

Barbara: It's not the only red planet. Jupiter is kind of red, and so is Mercury because oxygen has reacted to minerals on those planets as well.

johnpv: Will Curiosity investigate about the methane too, or is that a mission for MAVEN and later?

Barbara: I believe there's a joint ESA/NASA mission called Mars Trace Gas Explorer that will specifically investigate methane and other atmospheric gases.

vca186: Since Mars is closer to Earth than usual, what effect does its gravity have on Earth’s orbit?

Barbara: No measurable effect.

goody: Is there any possibility of another planet that can support life like Earth??

Barbara: Definitely. What we need to support life are air to breathe, water, shelter, and sunlight -- and solid surface. Other planets may not have the natural perfect combination, but we can bring some things with us or create them there.

Mitch: Will the Earth and Mars ever collide? When is that projected to be?

Barbara: No, they won't collide. The orbits are stable even if they're not perfect circles.

guest: Where will Mars be in relation to the Moon tonight?

Barbara: Within about a "fist" of the moon, to the naked eye.

TaviGreiner: For current Mars viewing, is one hemisphere more prominent than the other (N vs. S)?

Barbara: Only very slightly more visible in the northern hemisphere.

Erin: What would your reactions be if life was found on Mars?

Barbara: I think it would be one of the most interesting discoveries of all time.

(Moderator) Brooke: Learn more about the MAVEN mission mentioned earlier at: http://www.nasa.gov/mission_pages/mars/news/maven_20080915.html

Joyce: When is man going to Mars?

Barbara: We don't know yet. NASA doesn't have a current date.

(Moderator) Brooke: This is a moderated chat. If you haven't seen your question answered yet, please wait a moment as it is in the queue to be answered. Many thanks for your patience.

SpaceChimp16: I see the moon, full and clear and a small orange-y star looking thing on the top left from the moon, how big will Mars get? I am 16 and I'm really excited!!

Barbara: Yes! :) Mars looks like small star with the naked eye. It won't be very large.

planewatchers: Should we expect to see a halo with this evening’s event as we did last night?

Barbara: The halo you saw is probably related to your local weather. You might have ice crystals in your local atmosphere.

Erin: What originally got you interested in Planetary Science?

Barbara: I took a class in college about geology and how you can "read" rocks to understand the planet. I thought it would be cool to read the history of a planet that I couldn't step on.

werkbert: Hi. Q? If the moon is moving away from Earth (1 inch a yr), did the moon look any different in the sky 1 bil or 2 bil yrs ago vs. today and by what % bigger?

Barbara: It is moving away from the Earth, so it did appear bigger, but we don't really know where it was 3 billion years ago. Scientists are working on models to understand this.

BEA: When can I see the full moon the best?

Barbara: Tonight is the full moon. It will look nearly full tomorrow night.

(Moderator) Brooke: We're working on answering your questions right now. If you haven't seen your question answered yet, please wait a moment as it is in the queue to be answered. Many thanks for your patience.

Erin: What classes in school or experiences do you feel prepared you for work as a Planetary Scientist?

Barbara: All of them. :) Math, science, writing -- I do a lot of writing. Problem-solving and critical thinking.

TaviGreiner: Why do planets not twinkle, as opposed to the stars that do?

Barbara: Because they're closer to Earth than stars, they aren't perfect point sources of lights. They're disks.

Michael_C.: Are Phobos and/or Deimos ever closer to the Earth than Mars? Thank you.

Barbara: No, very close to Mars.

ve3cxb: Regarding the electron microscope image of the alleged bacterial-like life form found in the Martian meteorite several years ago that caused all the excitement. I'm a professional electron microscopist so as soon as I saw that photo I knew it wasn't a life form. However I never did hear what you folks determined it to be.

Barbara: Yes, they were too small to be life forms as we know life, so probably are minerals.

the11ama: Would a spacecraft sending people to mars contain a rotating section for artificial gravity?

Barbara: We don't know how to solve that problem yet. We use research on ISS to determine long-term effects of microgravity on humans.

guest: Does NASA have any tentative schedule for returning people to the Moon?

Barbara: I can't speculate on the future of U.S. spaceflight plans. However, here at Marshall are working on plans to send robotic missions to the moon for science.

omnologos: What do you think of the proposal of sending people to Mars on one-way tickets? It'd make a great site for a retirement home!

Barbara: NASA isn't in the business of sending humans to places where we can't bring them home safely.

WIstormspotter: Will Mars transit the moon at all tonight or will they basically be moving in sync with each other?

Barbara: The moon occulted -- passed in front of -- Mars during conjunction in 2007 but won't this year.

CollinDue: Will the nearness of MARS cause a shift in the tide, or change the ocean's PULL in any way?

Barbara: No, Mars is too small to have measureable effect on the tides.

guest: Would it be to the left, right, above or below the full Moon tonight?

Barbara: It's to the west, but what you see will depend on where you're observing from tonight. Check the Sky and Telescope Web page.

CollinDue: Does NASA have any regulation/restrictions in regards to leaving Spacecraft debris on MARS?

Barbara: Yes. We have a policy called Planetary Protection that governs our decisions in sending and leaving spacecraft.

Erin: How do you feel about the argument of robotic versus human missions to the Moon and Mars?

Barbara: Good question. Robotic and human missions are complementary to each other. You need both to effectively explore the solar system.

revrosales: Barbara, I recall reading about a training simulation in Russia that involved six months of isolation for the "crew", and that there would be more simulations in the near future. Any idea when further simulations are scheduled to run? –Thanks

Barbara: Sorry, I don't know.

Erin: What are your thoughts on the private companies aiming for landings on the Moon?

Barbara: The Google lunar X-Prize projects are very exciting. I'd love to see a whole fleet of rovers and landers on the moon.

hello: Are you posting the pics on NASA website?

Barbara: No, but many other sites will be.

Erin: Yes, bacon can be cooked in space. Heat works the same way there as here. But remember, there's nothing to hold it to a frying pan! =D

Barbara: Agreed. :) Maybe you could spin the frying pan really quickly.

LuDean: How many rover robots are currently operating on Mars?

Barbara: Two: Spirit and Opportunity. Both are still going after six years.

TaviGreiner: Why does the Full Moon look so much larger against the horizon than in the sky? Is this an illusion created by our atmosphere, the curvature of our Earth, or simply the perspective of foreground objects? I've seen explanations for all three.

Barbara: You're right, an illusion. The perspective of foreground objects is by far the greatest contributor.

Erin: Would you rather see humans first go to the Moon or to Mars?

Barbara: It's a personal opinion, but I'd like to see humans go to the Moon first.

jmorcone: Why is this the fullest moon of the year? What makes it bigger than others... is it the proximity to Earth?

Barbara: Yes, proximity at perigee makes it the biggest full moon of the year.

Richard_Stember: In the announcement that the MER Spirit is now a stationary observatory it was mentioned that it be used to determine if Mars has a solid of liquid core. How will this be done? Measuring wobbles in its orbit?

Barbara: Yes, this technique is very much like the laser ranging arrays on the moon. The position of the spacecraft when stationary tells you how the planet wobbles around its axis, which is related to its internal structure.

CollinDue: Would Mars have a sky if we added more water on the surface?

Barbara: I think you're asking about an atmosphere? Yes, if Mars were warmer and there were liquid water there would be thicker atmosphere and the sky would be bluer.

the11ama: How different would Mars look tonight between someone on the ground and someone on the ISS?

Barbara: Almost no difference because Mars is so far away.

TaviGreiner: Are meteoroids / asteroids of much concern when sending crafts to Mars?

Barbara: Micrometeorites are a great concern. They are everywhere and we have to make spacecraft able to withstand them.

earthvisitor: With the newest announcements of cuts to NASA, will Curiosity still launch as scheduled or is it in danger?

Barbara: Just can't speculate right now. Sorry!

DankNugs: Is the moon made of cheese?

Barbara: No. :) It’s made of rocks like Earth and other planets.

Vladimir: If there’s water on mars does that mean we can live there if we actually go to it?

Barbara: It would certainly help!

cbekiaris: I want to say thank you for answering my question, I’m in my high school astronomy class right now working on a worksheet (you don’t need to answer this or anything) but for someone at NASA to answer my question is really awesome! Also all the silly questions you are getting like the one about bacon in space, they are all from kids in my class so on behalf of Mundelein High School Astronomy class I want to say thank you for amusing us. I hope you have a nice day!

Barbara: My pleasure. Now get back to work! :)

Vladimir: How would it take us to get to Mars if we flew there?

Barbara: Six months at the best.

omnologos: Mars has no effect on Earth...has the Earth any effect on Mars?

Barbara: No, no measurable effect. The biggest effects on Mars are the Sun and Jupiter.

LuDean: Would a manned mission to Mars potentially launch from a base on the Moon?

Barbara: Good question. Some people think it would be helpful to launch from the moon because the moon's gravity is lower than Earth, but at this point we build everything on Earth. So we'd have to launch from Earth to the moon first, which probably negates savings now.

Karl_Hovekamp: Could it be there is liquid water on Mars periodically (in millions of years)?

Barbara: You may have heard that Mars has what we call "chaotic obliquity" which means over many millions of years, the seasons aren't constant and could be warmer. Maybe warm enough to have liquid water. Missions are looking for evidence of that liquid water, even though it's not there now.

(Moderator) Brooke: We've got time to answer just a few more questions.

Erin: Was there any modifications proposed to be made to Curiosity to protect it, when the Martian dust devils were discovered by Spirit and Oppy?

Barbara: We already knew that there's dust in the Martian atmosphere. Curiosity won't rely on solar panel for power like Spirit and Opportunity do.

DankNugs: Are there rocks on other planets that look like some from Earth or the moon?

Barbara: Do you mean meteorites? Spirit and Opportunity have found rocks on Mars that come from the asteroid belt, but so far none that we think came from the Earth or the moon.

WIstormspotter: Now that the LCROSS mission had found that there is water on the moon, Is there anything else that is worth looking for on the moon?

Barbara: Sure. Resources on the moon are things like light, water, and the oxygen found in the rocks.

(Moderator) Brooke: We've only got time for 2 more questions.

TaviGreiner: We've returned dust from a comet - why have we not returned samples from asteroids or Mars? Do on-site investigations with rovers tell us as much as would a sample return?

Barbara: Sample return is an important part of space exploration. We can learn more about the rocks in our labs and do duplicate analysis. Sample return missions are proposed for Mars and the moon and hopefully will happen soon.

adam: Why can liquid water not exist on the surface of Mars for extended periods of time?

Barbara: To have liquid water, you have to have warmth and pressure. Mars is very cold and has a very thin atmosphere, so water isn't stable as a liquid. We've seen it exist as a solid.

Bill_Macfarlane: Several years ago, Mars was at it closest in many thousands of years. What is the difference in distance now compared to back then?

Barbara: presently about twice as far away during this conjunction as during the 2003 conjunction, when it was closest

(Moderator) Brooke: Thanks to all of you for all the great questions, and thanks to our guest scientist, Barbara Cohen! Our Mars Opposition chat is now closed, but you can find more information at http://science.nasa.gov/headlines/y2010/26jan_mars.htm Check back on Monday for a posted transcript of today’s chat. Have a great weekend.