The Lunar Reconnaissance Orbiter (LRO) is NASA’s attempt to create a high resolution version of Google Moon, taking high resolution maps of the lunar surface. We’ve blogged before about some of the amazing images that it’s been sending back. Its snaps to date have included the Apollo landers, lost moon buggies and it has even started legal debates about ownership of the lunar surface.
However, while the images sent back so far have been spectacular, one of the non-imaging instruments on the LRO, the Lunar Interior Seismometer (LIS), may end up stealing the show. The LRO-LIS is a prototype moonquake monitoring device which is getting its test run on this project. It uses radio waves to measure the distance to the lunar surface so accurately that extremely tiny vibrations can be detected. This means that unlike in space, where we all know that no-one can hear you scream, the LIS can essentially “hear” sounds on the lunar surface.
Seismographs were amongst the science equipment left on the moon by the Apollo missions, but these were only sensitive to strong quakes (caused by large meteor impacts), due to the technology limitations of the time. Carrying out these measurements from space is a lot more accurate anyway as the instruments don’t become contaminated by the lunar dust, and a much wider area of the moon can be studied.
Now, we don’t generally deal with speculation on this blog (except when we launched a whole Dark Matter Week on the back of a rumour of direct dark matter detection), but it looks like the LIS may be performing way beyond its specifications: rumours being whispered over coffee in academic departments up and down the country say that it’s returning some very strange results indeed. Apparently there is a very clear, intermittent, whistling noise being picked up by the device. These “sounds” seem to be emanating from craters in the Faril Loop region of the moon and are baffling the scientists on the project.
One of the researchers said that he was completely taken aback by the data and thinks it might be the most significant discovery on the moon since we have started looking at it. However the actual interpretation of the results is still ongoing. “We don’t want to drop a clanger here as some of the hypotheses about these observations are a bit woolly,” said Professor Yaffle of Postgate University, “however with a bit of luck they should knit together to form a consistent theory about what we’re hearing from the moon.”
*Note this is raw data and it has not yet been flat fielded or bias subtracted. Due to wordpress’ policy of not allowing free users to host sound files we’ve had to host this on our own Google site.
If we want to build a permanent base on the Moon – and the question of whether we ever will (or even should) remains very open – we need to have some idea of the effect the lunar environmental conditions will have on our equipment. There’s no point going to all the trouble (and expense) of hauling some fancy LunarThingy™ up there only to have it disintegrate within a year because nobody checked to see what it might have to cope with! Well, a paper out today, led by T. Murphy from the University of California, gives some indication of the sort of degradation such a base might encounter by looking at what’s happened to the lunar equipment we already have in place.
As part of the Eclipse Week we had on this blog back in July I talked about the lunar ranging project, which bounces laser light off retroreflecting arrays left on the Moon by the Apollo astronauts to measure the Earth-Moon distance; the picture at the top of this post shows the array left by the Apollo 11 mission. A retroreflector is a clever device that reflects light falling on it back in the direction it came from via – in this case – total internal reflection using three perpendicular mirrors arranged to form a triangular corner (have a look here if that makes no sense!)
By studying nearly 40 years of lunar ranging data Murphy et al. found that the efficiency with which the arrays return the laser light is ten times less now than it was originally and this loss of efficiency is even worse at full moon. This lunar phase dependency surprised them so they double checked that it wasn’t something to do with the overall increased brightness of the Moon at this time of the month interfering with the result. It wasn’t.
Clearly something has happened to the retroreflector arrays to degrade them over the four decades they’ve been up there, but what? The paper puts forward two suggestions – a build up of lunar dust or scratches from micrometeorite impacts. Both of these could alter the way the light is reflected by allowing light from the Sun to slightly heat up the arrays. The effect is strongest at full moon because that is the time when the arrays are exposed to the most solar energy. The authors lean more towards dust as the cause, but point out that laboratory simulations of the lunar conditions would be the best way to understand what’s going on. It’s important to pin this down as dust can be wiped off, but a scratch could permanently damage a piece of equipment and it’s an awfully long way to go to carry out repairs!
T. W. Murphy, Jr., E. G. Adelberger, J. B. R. Battat, C. D. Hoyle, R. J. McMillan, E. L. Michelsen, R. Samad, C. W. Stubbs, & H. E. Swanson (2010). Long-term degradation of optical devices on the moon Icarus arXiv: 1003.0713v1
In honour of Sesame Street’s 40th Anniversary today I thought I’d post some links to videos of space related muppet activities. Finding them has just brightened up what has been a rather cold afternoon (the heating in my office has been broken for a while – I’m huddled up to the computer, wrapped in a scarf at the moment).
Firstly, here’s an important newsflash relating to an imminent bovine lunar mission:
That cow had better be quick though because it looks like the moon’s about to come under attack from something a bit hungrier than the LCROSS impactor:
Finally, this isn’t strictly space-related – it’s more of an Enterprise thing…
Is there water on the Moon, how did it get there and why should we care? The third question is definitely the easiest to answer since if we ever want to build the moon base science fiction has been promising for years, a local water supply will be an essential resource – transporting it from Earth would be both time-consuming and expensive. The second answer is also relatively simple; it’s thought to have accumulated over time from cometary impacts. More information on the first question however will begin to be gathered on Friday when the upper stage of the LCROSS satellite is due to be crashed into the Moon.
The lunar surface is not a very hospitable place for water. Daytime temperatures in the exposed areas can reach up to ~120 degrees Celsius, boiling it off into space. However, ice could survive in the permanently shadowed craters in the polar regions where the Sun’s rays never reach.
Right, now we know where to look for it, finding it should be simple surely? Well yes it would if we wanted to send up some astronauts on a dangerous, costly, mission down into one of these polar craters. A much cheaper option is to send probes and satellites instead.
In 1998 the first tantalizing hints of the presence of lunar ice came from NASA’s Lunar Prospector satellite which detected hydrogen signatures (a possible indicator of water) in polar craters. However, trying to find water from lunar orbit is obviously always going to be harder than finding it from the surface. I’ve already ruled out sending people and a robotic rover (like Spirit and Opportunity on Mars) would also be too inefficient. The simplest and easiest method is to crash a large object into a crater and see what comes out…
This Friday at 4:30 am PDT (12:30 pm in the UK I think) the 2000 kg Centaur upper stage of NASA’s Lunar CRater Observation and Sensing Satellite (LCROSS) will be crashed at 2.5 km/s into the Cabeus crater, the best candidate for finding the signature of water. Four minutes later the remaining part of the spacecraft will then fly through the massive plume of vaporized material thrown up by the impact and analyze what it’s made of. It will then also crash and create a debris plume of its own. Incidentally LCROSS was launched in June along with the Lunar Reconnaissance Orbiter which took the pictures of the Apollo landing sites that Stuart blogged about earlier in the year.
The plume should also be visible from Earth with relatively small telescopes. As a result NASA is encouraging people in America to hold ‘impact parties’ to observe and photograph the crash and then to send them the resulting pictures to help in the data analysis – another example of ‘citizen science’ which I’ve talked about before.
This isn’t the first man-made thing thrown at the moon but I think it’s the biggest so presumably it has the best chance of throwing up enough material to find the water that could be there. It’s just a shame that it’s happening in daytime in the UK so people aren’t going to be able to get their telescopes out and see it here! I’ll be doing the next best thing and watching it live on NASA TV.
(Quick update: you can also watch astronomers observing the impact live at http://mmto.wordpress.com/2009/10/08/watching-lcross-impact/ )
Have you ever considered why the Moon and the Sun appear to be about the same size in the sky? I think it’s one of those things you just accept and never get round to examining how remarkably lucky that is, and what it would mean for eclipses if it wasn’t the case.
It turns out that the Sun is around 400 times bigger than the Moon but also just happens to be around 400 times further away from the Earth – it is this coincidence which causes the two objects to seem to have similar disk sizes. This means that during an eclipse the Moon is able to completely obscure the Sun, giving us a spectacular show in the process.
We do have some experience of what eclipses would be like if the Moon were further away. In an annular eclipse (see Stuart’s post yesterday for an explanation) the small ring of Sun still visible is enough to drown out the beautiful, faint, solar corona. A more extreme example comes from NASA’s STEREO-B solar satellite which is about 4 times further from the Moon than we are. It therefore sees eclipses like this:
As far as we know there’s no physical reason for the Sun/Moon size coincidence. In fact, since the Moon is actually moving away from us by several centimetres per year, in several million years our eclipses will be a lot more boring! Equally the dinosaurs (if any of them wanted to look) would have seen a Moon which appeared larger than the Sun. Basically we’re just lucky to be around at the optimum photograph time.
Interestingly, the reason we know the Moon is moving away is because of the Apollo missions which are being talked about so much at the moment because of the 40th anniversary of the lunar landings. One of the things the astronauts left behind them were reflector arrays (the one left by Apollo 11 is pictured to the right).
Optical telescopes have been sending pulses of laser light at these arrays ever since – timing how long it takes the light to return gives the distance to the Moon at that moment. The initially narrow laser beam is several kilometres wide by the time it reaches its destination but, given that the Moon is over 3000 kilometres in diameter, hitting the correct area is a challenging task!
Well I think that’s all I’ve got to say about eclipses, but don’t worry as there’s lots more to come from everyone else! Tune in tomorrow when Stuart’s back again to talk about what an eclipse would look like from the Moon’s perspective.
Harbingers of death and destruction? A neat way to test how gravity works? A good opportunity to wear silly glasses and crowd around strange looking devices? Yes eclipses are all of these things and more… apart from the harbinger of death thing I just stuck that in there to scare you.
This week India will be treated to a spectacle which will see people flocking from around the world to witness. Taregna a small town in the Indian state of Bihar will be the epicenter for this event seeing the Sun completely covered by the moon. In honor of this event we here at weareallinthegutter have decided to have an eclipse week celebrating all astronomical based shadows.
To start with I want to talk about what eclipses are, how they occur and how we predict when the next one will be. At this point I feel like I have to make a confession: to a professional astronomer there is nothing more terrifying than being asked a question about what actually goes on in the sky. Ask most of us to point a constellation or why planets move the way they do and you will get an answer which will be right eventually, but to get there you will experience a lot of hand waving and muddled sentences. It turns out when you study objects many many times larger than our galaxy which contains all the stuff you normally see in the sky it’s not really that useful to know in depth details of the motion of our little rock and its closest buddies.
With that disclaimer out of the way lets get in to the heart of the matter: an eclipse is the mother of all shadows. When the sun and the moon happen to be located in the same place in the sky the light from the sun is blocked ether in part (a partial eclipse) or fully (a total eclipse) by the moon. To get an eclipse we need to have an alignment of the sun and moon and so their paths have to cross in the sky. The path of the sun across the sky is called the ecliptic: a line which passes through all the signs of the zodiac (and in no way determines how lucky you will be in love or business thank you very much!). So why don’t we get an eclipse every month? Every time there is a new moon the Sun and Moon are very close to each other, so why is it that the vast majority of new Moons dont have an accompanying eclipse? Well it turns out that the moon does not travel along the ecliptic like the Sun does but rather a line which is slightly inclined to the ecliptic by about 5 degrees or so. If they lay along the same line then eclipses would be much more regular but as it stands we get at max about 2 a year. This small inclination means that the Moon is normally a little way above or bellow the Sun. The only time we get an eclipse then is when a new moon happens to occur at the point where the path of the Sun and the Moon also cross. Following me cause I am not sure if I am at this point.
Ok so now things get complicated as the orientation of the tilt in the moons orbit also changes over time. The Sun’s gravity pulls on the moon a little bit in its orbit and the orbit changing its orientation. Its sort of like what a penny does at the end of a good spin. As it slows down it does that little funny dance where the way the face of the penny is pointing moves around. The technical word it precession but that’s not too important, what is important is that it changes the two points at which the moon’s path crosses the ecliptic and so affects when we can have an eclipse.
The third and final effect is that the moon’s orbit is not completely circular but rather elliptical which means that at some points in its orbit the moon is further from the earth than at others and so will appear smaller in the sky. Obviously this has an affect on the type of eclipse we could see. If the moon is just about the right distance from us it fully covers the sun giving a total eclipse but if it is that little further away from us then it leaves a small ring of light around the outside of the Sun which we call an annular eclipse. Simple right? Only the point on its orbit when the moon is the furthest from us also changes with time which we also have to factor into our model.
So for a total eclipse like the one this week we need to have three different cycles all matching up at the same time, we need it to be a new moon, we need that new moon to occur when the paths of the Sun and the Moon are crossing and we need the Moon to be at the right point on its orbit so that its not too far away from us. You begin to understand why events such as this are so rare and attract such large crowds
Given the fact that there are three cycles involved which after different periods of time which eventually repeat, it is interesting to ask if the pattern of eclipses also repeats. Well we have three cycles to consider: the times between new Moons which is roughly every 29.53 days, the time between the moon passing the same point on the ecliptic which happens every 27.21 days and finally the time between the the moon being at the same distance from the earth must be the same which happens every 27.55 days. To get an identical eclipse we have to have a length of time in which a whole number of each of these periods will fit. It turns out that happens only after 18.031 years which is known as a Saros cycle. This basically means that 18.031 years after this weeks eclipse another eclipse will happen which looks pretty much identical in the sky. The only difference will be that it will be visible from a different part of the Earth. In fact it has been estimated that it takes 370 years for an eclipse to occur at the same place on Earth.
As you can imagine this makes the event in Taregna all the more special for its residents as it is truly a once in many lifetimes event which they are witnessing. I for one wish I was there to see it.
Phew ok I think I got through most of that. If any of it is still unclear (which I am sure it is) the best procedure to find out more is to find your local amateur astronomy society, find out which pub they frequent, go there on a Friday night buy a round and casually bring up the topic of eclipses. In no time at all beer glasses, salt shakers and beer mats will be transformed in to a mini solar system to help you visualise what is going on. By the end of the night you will ether be an expert on eclipses or be so drunk that you don’t really care any more so its win win really.
Join us tomorrow when Emma will be talking more about why eclipses look the way they do and why Earth is lucky to have total eclipses at all.
Nasa have just released a series of timely photos taken from their Lunar Reconnaissance Orbiter. This orbiter which is gearing up to map the surface of the moon to identify landing sites for future manned missions took some time to snap some images of the landing sites from the last visit we made to our pale dance partner in space.
The orbiter is still not in its final mapping orbit so we can expect future images of these areas to get 2 to 3 times the resolution but even at this early stage its still really exciting to see the marks we left on the moon still there. While Apollo 11 site wins the historically most important site my personal favorite is the snap of the Apollo 14 landing site:
You can actually see the path that Al Shepard and Edgar Mitchell made as they shuffled from the Lunar Module to some of the scientific instruments. Apollo 14 is also my favorite mission for two reasons: as Al Shepard played some golf on the moon and the astronauts took with them a number of seed which where then germinated back on Earth to make Moon Trees (I am a big old sentimental softy at heart) .
While its exciting to have these photos it does highlight a little how much of a shame it is that this is the first time we have seen the site of what is arguably one of humanities greatest accomplishments in over 38 years.
Forty years ago today Apollo 11 set off on a mission to land on the moon for the first time. To celebrate the anniversary of this historic occasion this website is going to recreate the entire mission in real time! As I write this there’s about 4 hours to go until launch and the crew are reported to be resting…
(Launch photo courtesy of NASA)