We fly ESA's Gaia mission to map 1 billion stars - Ask us anything!

I imagine that working on a project this large involves a lot of boredom while you organize the data. What are the types of moments that cause the most excitement?

Well, just like any job there are indeed days that are not as exciting as others! But in general I am extremely privileged to work at such a great place on such an interesting mission with a bunch of cool people. For me personally the moment of highest excitement was the launch day – in the first few moments after Gaia was separated from the rocket and we waited for the first signal from space, I could literally feel my heart pounding. The whole first year of operations was generally exciting, when we really got to “know” Gaia and how he/she/it (?!) behaves in her environment. Right now our task is about keeping Gaia operating as well as possible and making sure as much data as possible comes to ground to obtain as good a map as possible – and that in itself is an exciting, interesting and challenging thing to do every day! [PC]

Thanks for your reply! :-)

You're welcome :-D [PC]

Can we expect to see an accurate 3D render of the Milky Way based on information collected by Gaia in a few years?

[JH] Yes indeed we will and will also contain information about the motion of the stars so we can play it forward or backwards in time and see how they are moving. Gaia will reach up to the center of the milky way, further in regions outside the galactic plane which is more dusty.

We've already seen a first PR product! It's a fly-thru based on a combo of initial Gaia data mashed up with earlier Hipparcos data: http://www.esa.int/spaceinvideos/Videos/2016/09/From_the_Solar_System_to_the_Hyades_cluster I can only assume that the full set of Gaia data will enable something better [DS]

What are the biggest challenges you have faced with this mission so far? To me, just the thought of surveying a billion stars is mind boggling! Thanks for doing this AMA.

Hard to pick a biggest. As you can imagine Gaia produces a lot of data and we have to get that efficiently back from L2, 1.5 million kms away. Gaia is the biggest user of the large ESA ground stations (35m diameter) and we have to make sure we use them efficiently (they're shared with other missions). We model in advance which part of the sky Gaia is looking at (some areas are less dense then others and need more or less data). We also model the link budget (how fast we can downlink data based on antenna performance). This means we know how long we need every day and don't waste time. Also since we average 14hrs a day of downlink we automate about 40% of our ground station passes. [DM]

The three ESA 35m deep-space stations are explained here: http://www.esa.int/estrack - look for Cebreros, Malargue and New Norcia [DS]

The critical launch and early orbit phases are always challenging as there is time pressure and you have to get it right. For this reason we have a great team and we rehearse, rehearse and rehearse again before launch. Once the final orbit was achieved the commissioning phase of 6 months was also pretty intense as all the subsystems of this unique machine were switched on and tested for the first time together in space. [DM]

Will Gaia be involved in the search for the Theorized Planet Nine?

Will the exoplanet search involve direct imaging, or will you be looking at star wobbles?

What sort of a network background do you need to work with satellite communications on this level?

[JH] Regarding the Planet Nine I think it would be too dim for Gaia, I think its estimated magnitude would be 24-25 and Gaia "only" reaches up to magnitude 20-21, Gaia's contribution in the Solar System is more relevant in the field of the asteroids as Gaia sees them and sees them moving so it detects new ones and also send alerts for the known ones so that they can be followed up from ground in order to improve the knowledge of their orbit.

Gaia collects data on any point sources passing across the field of view. If planet nine is bright enough Gaia will see it (it would have to be brighter than around 20.5 mag though and it is theorised to be less than this I understand). For exoplanets there is the astrometric 'wobble' technique and also transits may work. [DM].

[GW] I can answer on the network background; There are a number of areas here ground networks, the space links and operations. The ground networks are not terribly different from those used in commerce, just the endpoints are different (operations centres and ground stations). For the space link itself (i.e. communication between the spacecraft and ground station the people involved tend to have physics or electronic engineering backgrounds). For the operations side (i.e. myself) where we control the spacecraft side the background tends towards physics or aerospace engineering. In all cases relevant experience is picked up over the years working in the posts.

[JH] Gaia will detect exoplanets and binary systems in different ways, one of them will indeed be by measuring the star wobbling which will give a lot of information about the orbit and mass of the exoplanet, this will work for jupiter like planets. Other methods like the variation seen in the star luminosity when the planet transits the star or the changes in the spectra of the star will also be exploited by Gaia.

How does the change in the spectra of the star method work? I'm assuming you're referring to something different than Doppler shifts in the spectrum (since I understand that's what the wobble method is)

Gaia also has an spectrometer on board and will use the doppler effect as you said so it will detect spectroscopic binaries, the wobbling I was referring to is not based on the spectroscopy, basically Gaia will measure the change in the position of the star around the center of gravity of the Star-Planet system, a large planet causes the star to move around this center of gravity and Gaia is so precise that can measure that change in the position of the star relative to the center of gravity. [JH]

What turned out to be the problem that caused the AMA to be delayed a few days?

From time to time glitches can occur onboard the spacecraft. Just before our last scheduled AMA Gaia’s Phased Array Antenna (used to downlink high rate data) was switched off by the main computer, which believed it may have a problem. We were able to recover it within the same day and it's working fine. These types of things can happen from time to time. There was no permanent problem. Sometimes units can suddenly switch off due to a radiation hit in a particular component (known as a ‘ Single Event Upset’) but work perfectly fine after being re-activated. [DM]

I imagine GAIA has some pretty cool radiation hardening going on for its software - can you describe some of the techniques used for this? Also, how often do these glitches tend to happen?

Indeed the onboard computer has several of protection for its software against radiation, some are physical such as isolation and electronic design and some in the software level are in the form of Error Detection And Correction (EDAC) techniques which checks for bit changes constantly and corrects them if possible. This happens once-twice a day but most glitches are automatically correctly. [RQ]

Coordinates!? a) What sort of coordinate system do you use for mapping the positions of the objects? --b) Where is the origin of your coord system - Earth? Sun? --c) Given that everything is moving relative to everything else, aren’t the coordinates of everything out of date the minute you record them in your database? --d) Do you compile multiple observations and can you get direction & velocity vectors for everything you locate and record? --e) Do you assume a uniform uncertainty value for each object?

The Gaia archive uses the International Celestial Reference System (ICRS) which has the sun at the origin. It is correct that everything is moving, so it is important to provide a reference time for the data. Each source is observed on average 70 times, so velocity measurements are also made. [ES]

Will the public eventually be able to access the found data? Flying through a realistic simulation of the Milky Way would be awesome.

[JH] Yes the data will be publicly available, the first release was done already and is available to everybody, in the first release there were already positions, distances and proper motions for ~ 2 million stars and indeed there are movies and VRs being made for the general public and there will be many more to come when we release the positions distances and motions for a billion stars.

Yes, you can already access the first data release : https://gea.esac.esa.int/archive/. But you will have to make your own simulation. However, if you go to the web page of our colleagues in Heidelberg you can also get a 3D simulation :https://zah.uni-heidelberg.de/gaia/outreach/gaiasky/. [ES]

What are the challenges you have to face everyday, what can go wrong in this type of missions?

Well with such a unique and complex machine as Gaia, combined with the ground systems needed to contact and control it, and the transfer of large amounts of data every day from space to ground, just keeping that whole chain of systems working efficiently every day is a challenge in itself. On the Flight Control Team side we are responsible 24h per day/365 days per year to make sure things are working and working well. For that reason we each take turns to be “on-call” in a rota system, meaning that for one week a person is always reachable should a problem occur. That can be on-board, with the ground control system software, the communications lines, or anything in between. For me personally that is the biggest challenge, not responding to single events in a specific area, but making sure we keep ourselves trained in all areas to be able to respond quickly when needed (which can also be – and often is - at 3am in the morning!) [PC]

Oh wow, that must be awesome. As a future aerospace systems engineer student, I would love to work in a project as complex as Gaia some day. Thanks for your answer!

Well I look forward to meeting you one day in ESOC! Good luck in your studies :-) [PC]

Gaia is a unique, complex spacecraft with incredible performance. There are 42,000 telemetry parameters to monitor. Many things could go wrong but Gaia is well designed and robust. It has redundancy onboard (there tends to be two of most units - in case one fails or is temporarily out of action we can use the redundant unit). There is software onboard that can be changed to adapt to new situations if needed. [DM]

(Posted by Nathanial Bradford via ESA's Rocket Science blog): Is it possible to see/image Gaia from the earth's surface? What optical setup would be required to do this? Thank you :)) [DS]

Gaia is regularly observed as part of the ground based orbital tracking (GBOT) operations (http://www.cosmos.esa.int/web/gaia/iow_20150219). For the amateur astronomer the good news is that due to the orbit around the second Lagrange point Gaia is in the sky most of the night, every night, although there is some seasonal variation in elevation. The bad news is that Gaia is not very bright, being somewhere less than 20th magnitude. The GBOT uses professional telescopes of 2m aperture which are difficult to get time allocation on, so amateur observers are unlikely to succeed unless they have excellent resources. I found this out the hard way at -6 degreeC last week! [ES]

GAIA is a "big" ESA mission, and I'd expect its team to have a very diverse international composition. In this challenging time for the European ideal, what kind of challenges (if any) and what highlights are coming in sharing the management of such a complex mission between different centres in different European countries?

Gaia is a 'cornerstone' science mission - so large in scale. Like all ESA missions there have been contributions from across Europe in designing, building and flying this mission. These missions show what is possible through European cooperation. [DM]

On the processing side (there are 6 data processing centres in Europe) and 400 people from research institutions and universities, there are the typical challenges from a large scientific project, communication, funding, working practices but overall things are on good shape and usually the motivation to get the best results possible overcomes the difficulties.[JH]

Results from Gaia are being cross-verified with any other source? How are you making sure that the star-mapping is really reliable?

[JH] Yes this is a good question indeed we do comparisons with other catalogues particularly in the first release where there was a big overlap with known sources from Hiparcos for example, in the future there won't be data of a similar quality as to what Gaia will provide so this won't work, at the end some of the validation will be done using the data to understand and improve the models we have about the galaxy and the star formation, evolution,... so by verifying that the scientific results we get from the data are coherent.

I'm really interested in the Gaia mission as a whole. But, since I live in Spain, I must say I'm curious about what has been the role of the ESAC, could you explain it a little bit? Cheers to everyone involved in the project! :D

ESAC takes care of the science operations, we get the science data daily from the Gaia flight control team and process it as it arrives to verify that the quality of the data is good for science. ESAC is also part of the consortium in charge of doing the data processing (the DPAC) acting as the HUB with 5 other processing centres. Some of the scientific processing like the Astrometric Core Solution are executed at ESAC, we are also involved in aspects related to the calibration of the Gaia instruments. [JH]

How much do you know about how the collected data will be used? Who are the most likely end users for a 3D map of the milky way?

[JH] Gaia data will be used in many fields of Astronomy, primarily in Astrophysics, the history and evolution of the Milky Way and how stars evolve and are distributed within our galaxy, the distance to the stars is needed in order to know the true brightness and size of the stars. This distance is also needed in order to calibrate the standard candles like the Cepheids and Variables which are also used in Cosmology to estimate the size and age of the Universe.

(This question posted via twitter) Nicola Willetts @PinkLady2202020 -->@esaoperations @ESAGaia @reddit_AMA will we be able to see any photos taken by Gaia mission craft? Saw Gaia people at science festival in uk?

Gaia doesn't really provide photos, the images that are made onboard are too big to transmit to ground, so the spacecraft has some powerful processors that reduce the data to identify only the point sources and send the information about these sources to ground. This data can be accessed through the Gaia archive (https://gea.esac.esa.int/archive/) and used to representations of the sky, but these are not strictly "photos". A good example of what is possible was created from the star density data that we received here at ESOC : http://www.esa.int/spaceinimages/Images/2016/11/Virtual_Milky_Way [ES]

Can I be awesome like you guys when I grow up?

Yes, you can! Study hard, seize every opportunity to expand your mind and range of experiences, think rationally, find some fun projects on which to work as a trainee and do what you love! [DS]

Just want to say thank you guys for such an amazing mission. The information that comes back from this venture will have benefits that greatly accelerate science. My question is " What has been the most fascinating discovery for the team up to this point?"

The first time that I saw the sunshield heating following a micrometeoroid impact I was amazed. This was a direct detection of an original building block from the solar system, unchanged for 4.6 billion years (until we vapourised it). [ES]

In terms of operating the Gaia mission, it is so precise we see information in the engineering data that other missions would never see. For example, Gaia is so thermally stable that a small temperature change of the sun shield was exactly correlated with a sunspot group transit across the sun (i.e. Gaia never looks at the sun but thermistors on the Gaia spacecraft can ‘notice’ there has been a sunspot since the overall power output of the sun changed – affecting Gaia’s temperature). [DM]

[GW] Not really a discovery, that I will leave to the science team to answer, but what amazed myself with this mission was seeing general relativity in operating the spacecraft; our clocks are accurate enough to see the relativistic effects of the orbit in the timing and we have to correct for this in our ground monitoring. (Over the mission there will be a 1/10th second difference in time between the onboard clocks and the ground clocks).

I think it is still too early to say, the first release was only a small teaser and gave positions and distances for stars which had been quite well known up to now, still there are already tens of papers based on this data, if I had to pick one thing may be the unexpected usage of the first release data in the determination of the Hubble constant related to the age of our universe, still a lot more will come in the next years. [JH]

Did you manage to understand the root cause of the significant erratic variation of the angle between the 2 telescopes (eg dilatation "cracks") and what are the possible consequences for future astrometric space missions ? Eg is it "unavoidable", or should you physically separate satellite in 2 parts (one with the telescopes and CCD, the other one with the computer, the transmission to earth and the sunshield) ? Thanks a lot

There's a couple of links that go into some details on these effects: http://sci.esa.int/gaia/58135-gaia-s-second-anniversary-marked-by-successes-and-challenges/ and their possible impact on the data: http://www.cosmos.esa.int/web/gaia/science-performance Essentially these effects are being dealt with through modelling. Root causes are thought to be tiny thermo-mechanical effects. [DM]

Hello, are there plans for a Gaia successor ? Is it pertinent to envisage a kind of copy of it, with some "simple" improvements (based on the experience accumulated) in order to get an extended period of measure ? Or a completly new and improved satellite, to make even better ?

[GW] There are no plans at the moment. It should be noted that the Gaia implementation is pretty much itself at the limit of present technological capabilities and is a major leap forward. Gaia will keep astronomers busy for decades, however as technological capabilities increase in the future it may be worth doing (also other wavelengths e.g. infra red would allow us to see through the dust clouds).

Gaia tracks stars, is there any hope that a future machine could be able to do the same but with planets instead of stars?

Well actually Gaia basically detects anything that passes across its field of view that is bright enough to be observed (around 20.5 mag is the limit), so in principle it can detect planets that way. Also the technique of measuring the star “wobble” is being exploited by Gaia to observe exoplanets (see the answer from [JH] to the question from stille). This is one example of a “bonus” data set that can be obtained from the Gaia data – by the time the mission is over it is hoped that very many more exoplanets will have been discovered by Gaia than we know about today! [PC]

Hey guys, thanks for doing this AMA. I've been following your project for some time now. It's really ambitious but I'm certain that you can do it.

What is the designation for the stars in the Gaia catalogue? For example, stars in the Hipparcos catalogue has HIP (number).

[JH] We use a long 64-bit number where we encode some information which is useful in the data processing, things like the Data Processing centre that created the source and the healpix (a sort of sky index related to the position of the star) and then a counter within each healpix. With so many sources (>1000,000,000) compared to HIP making sure the stars don't get the same identifier and that the history of their creation and deletion is kept is quite a challenge.

Did you guys see this "Deep Sky Video that you helped make?

Thanks for that! The entire Flight Control Team just watched it together after our weekly planning meeting with the science team. Very interesting :-D [PC]

Nice! We're always interested to see how the science data is being used. Some of our Flight Control Team had physics / astronomy backgrounds before going into space engineering. [DM]

So this is more a question about the ESA in general, but do you guys have any idea if the ESA has or is planning official merchandise?

My girlfriend has recently become obsessed with space and the ESA in particular, and I'm trying to get her some cool presents on this theme but it's been very hard to find anything.

Ahhhhhhh.... yes. This question has come up more and more recently. There is a plan to develop such a shop, but it's ... complex. For now, you can join a site tour at one of the large ESA Establishments (ESTEC, ESOC, ESRIN), they all have space shops to buy stuff in person. You can get Rosetta stuff via http://www.rosettashop.eu/ Info & links to shops for mission patches via http://www.esa.int/About_Us/Welcome_to_ESA/ESA_history/European_manned_spaceflight_patches [DS]

Hello! I am a space studies student and I was hoping you could share some management stuff with me to share with my class.

During on orbit check out, did you use a gantt chart to organize payload initializations or was it mostly handled linearly?

Do you have access to the timeline of develolment?

We are trying to figure out when thermal management systems are developed. Like are they designed after most of the payloaf specs are planned out or is it completely on the bus/host hteam after all the subassemblies are constructed and tested?

Can you share any electrical diagrams with us?

For state of health, how far apart are your data points? Are they different for stored state of health compared to live telemetry? Was this rate chosen to save bandwidth for payload data or does it match the nyquist rate engineers calculated?

What kind of software do you use to monitor state of health?

Thanks.

Good questions, thanks for asking!

1. Indeed we did use a Gantt chart mechanism to plan, track and manage the in-orbit checkout in the first months after launch. Initially there were many inputs of what needed to be checked out by various people, including the spacecraft prime manufacturer (Airbus Defence & Space), the Science Operations Centre engineers at ESAC, and also the many scientists involved in the further processing of Gaia data at centres around the world (collectively termed DPAC). Due to the complexity of handling these inputs, their interactions, dependencies etc. we needed a tool to help us manage them, since running linearly was not an option as it would have taken too much time. Also when things didn’t go to plan (failed tests to be repeated, things took longer than expected etc.), we needed to re-plan efficiently. All of this was handled with daily and weekly meetings in the first months after launch – it was a mammoth task, but an amazingly enjoyable and rewarding one.
2. During the development of any ESA mission, the management of this pre-launch is managed by a dedicated ESA Project team, headed by a Project Manager. This team are often based in ESTEC (ESA’s site in the Netherlands), but travel all over Europe and the world to meet with the spacecraft manufacturer, the sub-contractors, the scientists, the Operations guys at ESOC (i.e. us!), to make sure that the spacecraft development and also the systems needed to operate it and process the data are on-track. The Project manager is the one who manages this complex development timeline during the years before launch. Of course he or she will have their own personal methods of working, and there is often no single definitive timeline showing all the development steps in every detail (it would be huge), but more commonly it is broken up into stages and managed at high level, with detailed planning being done within each stage and at stage boundaries.
3. Thermal management systems can vary in implementation largely from one spacecraft to another depending on the scientific aims, but there are many similarities at a high-level. In a nutshell essentially there may be a need to cool certain parts of a spacecraft (either passively using insulation and thermal decoupling mechanisms or actively with electrical coolers and pumps), and heat other parts (using electrical heaters). On top of that you need to monitor the thermal environment of the entire thing (using thermistors placed at key points). For Gaia, the service module (the part of the spacecraft containing the data management computer, power distribution, attitude control systems etc.) is heated partly by the Sun, and partly actively with a few heaters to maintain units within their operating ranges. The payload module (the part with the telescope and large focal plane) is passively cooled - the telescope is thermally decoupled from the service module and protected by the sunshield. Gaia is special since because of the stability requirements we do not have any heater switching during the normal operations, since even the forces imparted by the tiny electrical switches to control the heaters would be enough to disturb the science observations! For that reason the selection of which heaters remain always on and which remain always off is a balancing act to ensure that each unit and area on-board is maintained at an appropriate temperature. From all of this you can imagine that the thermal management system is an integral part of the spacecraft, and must be developed and iterated throughout the development lifetime of the spacecraft. Of course the specs for each unit and area are the input, but work starts very early in the development phase to try and meet those specs whilst minimising power consumption, weight, number of electrical connections needed etc. etc.
4. I’m sorry but I can’t share any electrical diagrams. Many of these detailed diagrams are protected for proprietary reasons, so I’m unable to share!
5. For the Gaia health telemetry (which we call “housekeeping TM”, to distinguish it from the science TM) there are many parameters to monitor (over 40,000!). Of course some of these we would like to see at a higher rate than others, e.g. gyro rates might be useful at 1 Hz or even higher, voltages maybe every few seconds in a routine case, temperatures maybe a few tens of seconds is enough. Having everything at high rate always would be great for us engineers to analyse, and it would make our job easier, but as you mentioned it is a balancing act against the bandwidth of that generated data and also the amount of memory we have on-board to store it during out-of-ground-contact periods. To make life a little easier to manage we group different parameters into what we call “packets”, with each packet containing TM about a specific unit or area. We then control the acquisition frequency of each of these packets, some higher (e.g. gyro data) and some lower (e.g. thermal data). We are then able to extract more information from this sampled data on-ground by using standard data processing techniques (e.g. moving averages, statistical analysis) in cases where we’d like to look in more detail. We can also adjust these packet acquisition frequencies on-board should we need to for investigation purposes.
6. In ESOC we use a control system on-ground developed in-house called SCOS. This system is capable of processing all the data that arrives from Gaia, displaying it on our screen, plotting it, raising alarms when things are out of expected ranges etc. It also encodes all the commands that we need to send to Gaia to control it, using a database to know which parameters and parameter values to use, and recording all of this in an archive for us to browse the history. On top of the “real-time monitoring” provided by SCOS, we have other ancillary systems that allow us to browse the data over longer periods more quickly, make more detailed analysis etc. It’s a complex setup that requires a whole team of people to develop and manage it – not just the spacecraft is complex, but also the ground monitoring systems!

Very best of luck in your studies, and maybe see you in ESOC one day in the future! [PC]

I looked at the Gaia data available so far, and it seems to be in a series of files. Is there a single file containing all the star locations, or a way to query the data remotely without downloading all of it? Also, what non-location star data is collected about each star?

[JK] We have a website which contains results from our first data release (DR1). This site gives you access to files as well as a way to query the data to find what you need. The data includes dozens of parameters about the star location, motion and type - see for yourself. http://archives.esac.esa.int/gaia/

A few questions. Will this mission be mapping the velocity vectors of celestial objects so we can calculate their path around the galaxy?

Will the Gaia spacecraft have to be kept below a certain temperature? How long will it's coolant last before the craft is no longer usable?

Also, how long do you think the mission will take and how long will it take for the results to be published? What will happen to the Gaia spacecraft after the mission is completed?

Thanks!

1. Yes. The mission 'places' stars on the sky - but sees the same star on average 70 times over the mission, so can plot its track across the 'plane of sky' through time. Additionally, we have a radial velocity spectrometer - which gives through Doppler the line of sight velocity of a subset of stars.
2. Gaia is not actively cooled, so it won't run out of coolant. It is passively cooled (the telescope is thermally decoupled from the service module and protected by the sunshield). The CCDs are around -110C, the telescope mirrors around -140 to -160C.
3. The mission is planned for 5.5 years (until mid 2019). We're hoping to extend it. The first results are already published (Data Release #1) more (and better) releases will come as more data is gathered and processed.
4. We plan to remove it from the L2 orbital area into interplanetary space. This is done to free up the L2 orbit which is popular for Astronomy missions. [DM]

What's behind the often cited 1 billion stars estimate? Is it a mix current galactic understanding and technical limitations?

Secondly do you have an ID for stars in the Gaia catalog and if so how is it that ID assigned?

For the first point it's a design requirement based on the science goals. The first data release has surpassed this with 1.14 billion. [DM]

why not 2 billion? lazy.

Hey! How many did you map? ;-D joking aside, keep an eye out for future data releases. The first release (DR1) made a few months ago has 1.14 billion, so you're getting a few for free already![PC]

Since you are technically the first people to "discover" these stars and place them, do you get to name them all? If so, would you mind naming one after me?

Yes we gave name to the new stars discovered but the name is a 64-bit long number which is useful for the processing (the number encodes information about the centre/pipeline that created the source) as well as the position of the source and a counter. I'm not sure we could do this sort of things with names :-)

How can I get a job there? (Computer scientist student)

Assuming you are an ESA Member state citizen, your first stop is via the ESA website; look in the careers section (http://www.esa.int/About_Us/Careers_at_ESA) - note also the current YGT openings (http://www.esa.int/ygt - over 100 now!). Next, there are multiple contractor positions open to anyone with work permission in the applicable country - search on any of the major job/recruiting websites and there are several that specialise in space jobs. Finally, as mentioned in several answers, flying a mission like Gaia is a collaboration between a number of universities, institutes, &etc. - they, too, offer incredibly interesting jobs working with the data and on the instruments from/for ESA spacecraft. Good luck! [DS]

Why not a billion and one?

Why not indeed - I'm sure we'll squeeze one extra in :-). Joking aside the 1 billion was a design requirement. The first release already had more than this (around 1.14 billion). [DM]

My dad works at Airbus in Stevenage. Did he do a good job?

Yes, he did an excellent job! Gaia is an incredible spacecraft, it is undoubtedly one of the most technologically advanced machines ever made and it works wonderfully "straight out of the box". Say thanks from all of us. [ES]

when you map them...will it be in web Mercator?

The Gaia data is archived using the International Celestial Reference System, the ways that this could be visualised is almost unlimited. Mercator is one possibility : http://www.esa.int/spaceinimages/Images/2016/11/Virtual_Milky_Way [ES]

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Gaia is very specifically designed to work at the second Sun-Earth Lagrange point which is 1.5 million km away from Earth, only 1.01AU from the sun. Solar lensing occurs at a distance of 550 AU and Gaia does not have the fuel to get there. Furthermore, Gaia is entirely solar powered and would not receive enough sunlight to operate at such large distances from the sun. I don't even want to think about how long it would take to get to 550AU, space is very big. [ES]

Would you rather fight ten zombie sized chickens, or ten chicken sized zombies?

We're still trying to sort out which of the 'aliens-on-67P' reports are credible... Now we have to worry about zombies, too? :-) [DS]

I'd say zombie sized chickens would be scary to look at, but peaceful. After all, they're still chickens. [JM]

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Hmmmm... a somewhat off-topic question, so it's hard to know how to answer. If you're referring to music videos, though, we certainly like this one! [DS] http://www.esa.int/spaceinvideos/Videos/2015/09/Ground_station_chillax