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The Gaia Mission

10 Aug 2017 09:30

Hi everyone! Many times in this forum we have talked about gaia without having a proper thread for this. Now we can talk about one of the most important missions of history, Gaia mission (of the European Space Agency). The results are going to make a huge impact in astrophysics and therefore in the future ideas coming to Space Engine.

First of all I'm going to copy and paste a post that Vladimir Romanyuk (Space Engineer) wrote four years ago in the old forum (I think is a very good synthesis of what is coming from GAIA).

Discovering of new objects
  • 1 billion stars down to 20m - coordinates, parallaxes (distances), proper motions, radial velocities and low-resolution spectra
  • 200 million stars - measurement of radial velocities
  • 100 million stars - getting the light curves
  • 200,000 new white dwarfs and 50,000 new brown dwarfs (!)
  • 500,000 small Solar system bodies with photometry and orbits
  • 500,000 quasars with redshifts and photometry
  • Measurement of masses of 10,000 stars with an accuracy of <1%
  • 10,000 - 20,000 exoplanets within 200 pc (!!!)

Stellar Astrophysics
  • Coordinate measurement accuracy (μas = micro arc second = 10-6 seconds of arc)
    - 7 μas up to 10m
    - 10-25 μas up to 15m
    - 300 μas up to 20m
    - HIPPARCOS for comparition: 1000 μas up to 12m
  • Distance with 1% accuracy to about 10 million stars up to 2.5 kpc
  • Distance with 10% accuracy to about 100 million stars up to 25 kpc (the diameter of the galaxy!)
  • Massive numbers of rare types of stars and rapid evolutionary processes
  • Parallax calibration for the distance indicators such as Cepheids and RR Lyrae stars in the LMC / SMC
  • Sharp Hertzsprung-Russell diagram throughout the galaxy
  • The Mass function and the Luminosity function of the solar neighborhood stars
  • - including ~200,000 ~ white dwarfs and 50,000 brown dwarfs
  • The Initial mass function and Luminosity function for the star-forming regions
  • The Luminosity function for the Pre-Main-Sequence stars
  • Detection and collection of data about stars of all spectral types and all types of galactic population
  • Detection and investigation of variability of stars of all spectral types
  • Distribution of distances and velocities of all stellar populations in the Galaxy
  • Spatial and dynamic structure of the disk and halo of the Galaxy
  • Formation history of the Galaxy
  • Huge statistics - a strict basis for the theory of stellar structure and evolution

  • At least 70 measurements of coordinate for 100,000 stars of F, G, K types up to 200 pc
  • Detection of 10,000 - 20,000 exoplanets with astrometric method (~ 10 per day!)
  • Detection of ~5000 exoplanets by transit method (!)
  • Orbits of detected planets for ~5000 systems
  • Detection limits:
    ~ 1 Jupiter mass with a period of <10 years within 200 pc
    ~ 10 Earth masses within 10 pc
  • Complete catalog of all the planets with a period of 2-9 years for all types of stars (!)
  • True masses of the planets, not the lower limit of the mass (M, not M*sin(i))
  • Relative inclinations of the orbits in multiplanetary systems
  • Refinement of parameters of Kepler exoplanets and candidates - thanks to refinement of stellar parameters

  • Deep (up to 20m) and uniform whole sky survey and detection of moving objects
  • 105-106 of new objects (only 340,000 are known for now!)
  • Study of change of taxonomy/mineralogical composition with heliocentric distance
  • Diameters for ~1000 objects, masses for ~100 objects
  • Orbits - 30 times better than present, even after 100 years
  • Trojan asteroids for Mars, Earth and Venus
  • Kuiper Belt Objects: ~ 300 up to 20m (including binaries and Plutinos)
  • Near-Earth objects - Cupids, Apollos and Athenas (currently known - 1775, 2020 and 336 respectively)
  • ~1600 crossing Earth orbit asteroids with diameter > 1 km (currently known - 100)
    Asteroid Gaia-606 (one of the firsts discovered by the mission)


Gaia-606, one of the first asteroids discovered by the mission in his first few months of operations.

Confirmation of the General Relativity
  • Gravitational deflection of light in the gravitational field of the planets
  • Precession of the perihelion of asteroids orbits
  • Astrometric fluctuations of satellites of known stellar black holes
Last edited by FastFourierTransform on 10 Aug 2017 12:38, edited 4 times in total.
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The Gaia Mission

10 Aug 2017 11:33

"Gaia provides the detailed 3D distributions and space motions of all these stars, complete to 20th magnitude. This allows our Galaxy to be mapped, for the first time, in three dimensions. Some 10 million stars will be measured with a distance accuracy of better than 1 percent; some 100 million to better than 10 percent."

Progress of the mission:

Before Gaia (Hipparcos Mission)
The last mission that did something like GAIA was the Hipparcos mission (also from the European Space Agency).
Hipparcos is the source of the Tycho-2 catalogue, that contains 2,539,913 stars with their parallaxes (thus distances), coordinates and proper motions, complete up to 99% for all the stars brighter than magnitude 11 (as seen from Earth).

Gaia Data Release 1 (September 2016)
We are currently here. 14 months after operations began Gaia made hisfirst realease with data from all the sources it could detect but without proper motions and parallaxes (since those have to be gathered comparing their position during several years so at least it can make a meaningful solid measure for each star).
With DR1 we now know that the final catalogue is going to have 1,142,679,769 stars (more than expected). That is the 0,5% of the entire stellar population of the galaxy (suspected).
Since we are all so eager to know the final results, the European Space Agency integrated this DR1 release with data from the previous Tycho-2 catalogue. Comparing the positions of stars between both catalgues and making a bunch of calculations we have been able to create the so called Tycho-Gaia Astrometric Solution (TGAS), a stellar catalogue with all the sources from Tycho-2 but with updated and more precise distances and motions.
In this moment TGAS is the most important reference in astronometry, we have 2,057,050 stars with their motions and 3D coordinates. TGAS is just to give a small taste about what is coming (all the parameters measured for more than a billion stars).


This is not an actual image, it is just a plot of the more than a billion points detected by the DR1 in galactic coordinates

ImageIf you where to zoom in the previous image in the part of the sky where the Triangulum galaxy is you would see this (now you can see the individual dots corresponding to Gaia's detections). As you can see Gaia is going to be capable of detecting also some of the brightest stars in the closest galaxies. In the case of Triangulum it has detected[color=#8e44ad] 40,000 stars (just the 0.0001% of the stars in that galaxy)

Thanks to the Tycho-Gaia Astrometric Solution at least we have the proper motions for 2 million stars. That means we can compute with certain conficence the evolution of the Orion constellation for the next 450,000 years and create an awesome simulation like this

Or why not?the evolution of the entire sky for the next 5 million years! (you just have to be ok with 2 million stars for now)


Gaia Data Release 2 (April 2018)
9 months from now we are going to have a catalogue with 3D coordinates and proper motions for more than a billion stars!

  • Five-parameter astrometric solutions for all sources with acceptable formal standard errors (>109 anticipated), and positions (α, δ) for sources for which parallaxes and proper motions cannot be derived. Wich means that now we have
  • G and integrated GBP and GRP photometric fluxes and magnitudes for all sources.
  • Median radial velocities for sources brighter than GRVS=12 mag.
  • For stars brighter than G=17 mag estimates of the effective temperature and, where possible, line-of-sight extinction will be provided, based on the above photometric data.
  • Photometric data for a sample of variable stars.
  • Epoch astrometry for a pre-selected list of  >10,000 asteroids
Gaia Data Release 3 (late 2020)

  • Improved astrometry and photometry (more measurements for each star means more precision thanks to statistical calculations)
  • Object classification and astrophysical parameters, together with BP/RP spectra and/or RVS spectra they are based on, will be released for spectroscopically and (spectro-)photometrically well-behaved objects.
  • Mean radial velocities will be released for those stars not showing variability and with available atmospheric-parameter estimates. This means more precise 3D motion measurements.
  • Variable-star classifications will be released together with the epoch photometry used for the stars.
  • Solar-system results will be released with preliminary orbital solutions and individual epoch observations.
  • Non-single star catalogues will be released. Yeah, a catalogue of double and multiple stellar systems.
Gaia Catalogue (late 2022)
The catalogue will be consisting of:
  • Full astrometric, photometric, and radial-velocity catalogues. With this we can map a part of the galaxy with high precission and know the past and future evolution for tens of millions of years.
  • All available variable-star and non-single-star solutions.
  • Source classifications (probabilities) plus multiple astrophysical parameters (derived from BP/RP, RVS, and astrometry) for stars, unresolved binaries, galaxies, and quasars. Some parameters may not be available for faint(er) stars.
  • An exo-planet list. As Space Engineer said, it is expected to have 10,000-20,000 exo-planets (5 times more exo-planets than what are currently known).
  • All epoch and transit data for all sources.
Even if 1 billion stars acounts for the 0,5% of all the stars in the galaxy the stars in the GAIA catalogue are going to be from a huge chunk of the galaxy (this means that we are not going to know all the stars inside that chunk but many). The extension of the stars in the final catalogue will reach around the 12% of the volume of the galaxy (so we are going to map entire galactic arms, regions near the core, and structures in the outskirts of the disc).

This map shows the extension of the data on the galaxy from the final release as seen from above. The colors indicate the density of stars that are in the catalogue (as you can see we are going to map nearly every star in the vicinity of the sun). Just by chance there is a hole in the interstellar medium (dust, gas and particles) in the direction to the galactic center so we are going to be capable of seeing through that hole many stars (that's why there is a colored region near the galactic core).

This is a edge-on view of the same simulation performed by the MareNostrum supercomputer. As you can see we are going to map the entire thickness of the disk in our region of the galaxy.
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The Gaia Mission

10 Aug 2017 12:02

Wow thanks for all the beautiful images and info!  So Release 2 in April 2018 is the one to look for here.  I wonder how much computational power will be required to run the whole set at once :-)  But seriously, when this gets incorporated into SE I will do what I do with SNPP, constrain mag to 10 and brighter, and then tighten up the FOV and keep increasing the lim mag.  When I get to a field of view of about 0.5 degrees hopefully I'll be able to increase lim mag to Mag 20.

This will be a real boon to us astrophographers who stack a lot of images and come up with stars on the edge of visibility but can't find them in online planetariums.

Even from my very light polluted location near NYC I've been able to catch stars down to Mag 12 after stacking a bunch of short exposures together (something like 20 images of 13 sec each.)  I can't imagine how great will be to work with this catalog from a lower light pollution location from my second home in the Poconos :-)
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The Gaia Mission

10 Aug 2017 12:33

The implementation in Space Engine so far:
The discussion begun 4 years ago in the old forum. These are quotes from Vladimir Romanyuk (Space Engineer), the developer of Space Engine.

"Currenly SE uses this data per star:
Coordinates (XYZ or RA/Dec/Dist) - 3 floats (12 bytes)
Luminosity or app mag - 1 float (4 bytes)
Spectral class - currently packed to 1 short (2 bytes), but probably must be extended to 1 int (4 bytes).

But don't forget about name or catalog ID. Currently SE uses a csv format where everything is a text, but older versions used a separate file with names, like Celestia. Adding an 32-bit index for the database ID (which is enough to identify 4 billions stars) adds 4 bytes.

Also, future versions of SE will use proper motion data, so stars in SE will have velocities (and maybe it will be possible to observe change in constellation shape, who knows). So add another 3 floats (12 bytes).

So total we'll have 34 bytes per star. Probably some floats may be packed to 16-bit half-precision (2 bytes), so maybe this can be reduced to 32 bytes (computers likes power-of-two)."

So, if the final Gaia Catalogue is about 1,142,679,769 stars then having 34 bytes per star that would mean that the addition of this to Space Engine corresponds to a 36,2 GB addon. Since very few people would download that mountruos addon it is probable that it would be stored on an internet server (when SE reaches this capability) and with your internet connection you would download chunks of the catalogue while flying through the galaxy (more or less like Google Earth where you don't need to download the 3 thousand terabyte database). That's why Vladimir cautiosly said a year ago:

"to handle 1 billion stars (when final data set will be released in 2022), some adaptive loading/rendering algorithm is needed, similar to those used for planet textures. Space must be subdivided in cubes which are streamed from the disk as needed. However, maybe in 2022 one can simply load everything into memory, like SE handles HIPPARCOS catalog now"

Regarding the idea of implementing it without an internet connection he said (for another catalogue: the SDSS galaxies):

"SE can't load more than 4 Gb because it is a 32-bit app. Even if it would be a 64-bit app, I think only few people would have computers capable to load 23 Gb into RAM. Current 0.972 implementation even can't load a single catalog, because of limitation in the std::vector class (it is used in new accelerated script loader). So this great addon should wait implementing of the binary tiled catalog."
"In future I will implement a binary file format for such huge catalogs, with loading of the tiles on-the-fly, like planetary textures (or generation of procedural galaxies). But for now the text catalog should be compressed as more as possible."

He also stated that there are some benefits now that we have the pak compression system since version
"Pak files are zip archives, compression for text files is usually very good, so this catalogs will have a huge benefit from that"

I would like to know more about the feasability of this addon in the future from all of you, specially from Space Engineer and HarbingerDawn
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Joined: 06 Mar 2017

The Gaia Mission

10 Aug 2017 13:24

Wow, so this is the internet connectivity ability that you mentioned would be coming to SE in the future?

With the rapid increase of internet connections and storage space on hard drives, I think we can download 36GB but I see the benefits of a streaming approach also (SNPP7 uses this now too.)

PS can you use a lossless compression algorithm?  SNPP uses something called .DDS

Please keep the 32bit version intact, I use 32bit OS for compatibility reasons.

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