Archive for the 'Science' Category

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[Science] A natural nuclear reactor on Mars? Not likely…

A nuclear explosion on Mars? Not likely...

A nuclear explosion on Mars? Not likely…

An article by SF writer Charles Stross has been doing the rounds over the past week, describing an LPSC abstract which mentions “evidence” for a possible ancient nuclear explosion on Mars, caused by a “natural nuclear reactor” going critical. A lot of folks seem to be getting a bit excited by this because (not unreasonably) they think that since it’s published it must be scientifically valid, and I feel obliged to put on my party pooper hat and point out that it probably isn’t.

So first things first – here’s the LPSC abstract.

Now, you may be surprised to know that there IS actually such a thing as a “natural nuclear reactor”. We have evidence that at least one existed on Earth – at Oklo in Ghana – and you can read all about it on its wikipedia page. Essentially, you can get circumstances occurring in nature that are similar to those that occur in a nuclear fission reactor, if you have the right combination of geology, radioactive ore bodies and groundwater acting as a moderator. (you’ll note that the Mars “reactor” got a mention on the wikipedia page – that’s likely to be disappearing soon, given the scrutiny the abstract is now receiving).

So, why should we be skeptical of this LPSC abstract?

Peer review

Peer-review is a pretty important part of scientific methodology – it’s the process by which ideas are discussed and scrutinised and criticised and accepted (or rejected) by the scientific community. For a paper to be accepted for publication it must pass the peer-review process, which means that experts in the field have looked at the science, examined the evidence, and possibly duplicated any described experiments themselves and verified that the conclusions reached are valid. If they don’t then the paper is rejected, and the authors must either do more work to demonstrate their hypothesis or just start again and try another approach (or move on to something else). However, the article being discussed here is not a paper, it’s a conference abstract.

Conference Abstracts are not the same as papers. Conference abstracts are normally short summaries of work in progress – especially for teams working on ongoing missions – or interesting hypotheses that could be considered, and they may or may not be developed into papers later on (LPSC, DPS, and AGU are three of the big planetary conferences where abstracts are presented). Some are presented at the conference as posters or talks where they can be discussed further. Some of them get shot down, some pass scrutiny – that’s how science works. I’ve submitted and presented a few LPSC abstracts myself while I was at university – some worked out, some didn’t. The important thing though is that they are not peer-reviewed at all.

At this point I would like to strenuously and enthusiastially point out that the vast majority of abstracts submitted to LPSC are perfectly good science written by scientists and students of science. However, because (as far as I’m aware) the abstracts are not checked or vetted after they’re submitted, a handful of abstracts about… well, I’ll be charitable and call them “less likely scenarios” do slip through. For example, I remember reading one abstract a few years back suggesting that the sun had accreted around a neutron star – which makes no sense in terms of stellar formation/evolution at all. It probably got a few chuckles from those who noticed it, but otherwise it passed by unnoticed at the conference itself because its authors didn’t show up to elaborate on it (granted, a lot of authors aren’t able to turn up to LPSC for many reasons – but if you have a controversial idea then it helps if you show up to defend it!).

So – the important thing to be aware of here is that this is an LPSC abstract that has not been peer-reviewed, which means that its conclusions should be viewed with quite a bit of skepticism.

What about the science though?

There are questions to be raised about the author’s credibility – it doesn’t help that he previously authored an article suggesting that the so-called “Face on Mars” was created by an ancient martian civilisation (even if there ever was any doubt about its origins – not that I think there was – we now have plenty of evidence to show that it’s a completely natural feature). But be that as it may, the proper way to proceed is to analyse the science. Unfortunately, it seems to me that the science in the paper is not very good. Here are a few issues I found:

a) he says that the “reactor” was “tamped” by the overlying rock but doesn’t provide any calculations to support this (and for all I know he forgot that Mars has lower gravity than Earth, so pressure is lower at a given depth). That’s a fairly critical part of the scenario that we just have to take his word for.

b) He also doesn’t provide a satisfactory explanation of how the radioactive ore body forms and how it’s concentrated on Mars in the first place (radioactive ores are not usually concentrated by asteroid impacts).

c) He doesn’t provide any evidence for this supposed explosion beyond “it looks like the radioactive stuff was concentrated around a depression” which could have been caused by a number of other means (e.g. it could have been an depression caused by an ancient asteroid impact). Occam’s Razor seems sorely lacking.

d) I didn’t see a source mentioned for the maps of K and Th distribution presented in the abstract.

e) We know of precisely one natural nuclear reactor on Earth, which implies that they’re somewhat unlikely to form… and it didn’t blow up. And yet there was supposedly one on Mars that did? Seems like a lot of unlikely coincidences would have to line up to make that happen on the next planet over from us.

f) And he spends a lot of time telling us his interpretation of the data, and not a lot of time just objectively describing the data and saying what other options could explain it.

g) if this happened so long ago, why would there be evidence left on the surface after a billion years of deposition and erosion (and redeposition) by the winds that scour the surface of Mars? Surely that would have redistributed the material (if not hidden it)?

And this is before I even get to the nuclear physics side of it… I’ll leave that for others more knowledgeable about the subject. Either way, while some discussion and dissection of the evidence is happening now on various internet fora (now that it’s got some attention), so far the verdict is that the evidence to support the hypothesis is lacking.

So in the end I’d say that the “evidence for a nuclear reactor on Mars” – particularly one that exploded and blasted radioactive material across the planet – seems to be rather unconvincing! It’s an interesting idea to examine and dissect (that’s pretty much why it’s there, after all), but this does show that we need to always critically assess what we see on the internet so that we don’t mistake unreviewed conference abstracts for peer-reviewed science!

Addendum: And funnily enough, this LPSC abstract even gets a mention in this rather excellent video (around the 2:47 mark) explaining how the popular media often doesn’t really understand the science it reports.

[Boardgames] High Frontier – first session report!

HFcover
High Frontier is a realistic “science-adventure boardgame” where you play the role of space agencies who research technologies, launch them on rockets into the solar system to exploit the resources out there, and build extraterrestrial factories that in turn can build new fancier technologies. These give you victory points, and once you’ve built a certain number of factories, the game ends and you count up the VPs. It’s a little intimidating at first, but between a good walkthrough and the High Frontier yahoo group I managed to figure it out enough to give it a shot. The game itself does have a lot of science in it (the map does look a bit terrifying, but it’s actually very realistic in terms of energy requirements), but once you look at the actual gameplay it’s actually not that hard to understand what’s going on.

If you don’t know about the High Frontier board game then its BoardGameGeek page has lots of info. It’s available from most board game stores or directly from Sierra Madre Games – there’s one expansion out already that covers the outer solar system (the rules for the expansion are already in the base game), and there’s a new High Frontier: Colonization expansion coming out soon that extends the map further into the outer Kuiper belt and adds new rules for colonies (you can preorder that from SMG too).

So here’s a little session report that I wrote of our first attempt at playing it over the weekend. We do plan to play again so hopefully I’ll be able to take some pictures of the action next time, and I’ll write up a proper review of the game after a few more playthroughs. Meanwhile, enjoy the action :).

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I finally managed to play High Frontier for the first time last night after spending all week poring over the rules… AND IT WAS AWESOME! :).

I played with two gaming buddies – I picked ESA, one picked NASA, and the third picked China. We played using only the basic rules and we started off with just the basic map, but we brought in the expanded map (out to Saturn) later on for more targets. We had a spot of bother straight away because the first thruster that was picked was a 1-0 solar sail and we were trying to figure out how it worked, but we solved that and got going.

NASA was first into LEO and decided to head off to asteroid Phaeton on its solar sail and with an ISRU 4 robonaut just so we could get a rocket going somewhere to see how that all worked. They took a few turns to get there, landed, and (unsurprisingly) failed the prospect roll. Then they decomissioned the rocket, started up a new one at LEO and headed off to the main belt.

China was in the air next with the other robonaut/solar sail combo, headed off to asteroid Khufu and actually managed to prospect there successfully to get a claim! But they didn’t have a refinery with them so they decommissioned and sent up another rocket there with a robonaut/refinery combo so they could set up a factory later.

ESA (that’s me!) took its sweet time building its rocket (everything in ESA is built by committee, you know). However, we were ambitious from the start and went for a full three-stage (robonaut-refinery-thruster) rocket setup for our first launch – we weren’t having any of this namby-pamby hippy solar sail crap! 🙂 We built a MAN’S rocket – a Ponderomotive VASIMR! But that meant we had a rocket that was about twice as heavy as the others to launch (mass 9 vs mass 4 and 5) so we had to spend more time building up fuel. Eventually ESA got into LEO though, to much cheering from mission control :), and decided its mission target was asteroid Minerva in the Gefion family.

Unfortunately by this time the pesky Americans had managed to launch their new rocket from LEO with a better thruster, and had beaten ESA to the asteroid belt, where they started their nefarious goal of blackening the asteroid belt by zapping as many of them as possible from orbit! There was much wailing and gnashing of teeth at ESA as we watched Minerva and the other small rocks of the Gefion family being mercilessly blackened by NASA’s rayguns – particularly as the ESA rocket was already enroute just past the Sun-Earth L2 Lagrange. NASA at least managed to prospect Ceres successfully but only because they couldn’t really fail that!

So Plan B was hastily assembled at ESA mission control, and we decided to try our luck at asteroid Hertha in the Nysa family, where our ISRU 2 raygun would be useful too. [I was going for size 3 worlds because I could land/take off from them without needing lander fuel – I had thrust 3, -1 for wet mass, +1 for beamed power, and I could use the afterburner to get another +1 for a total of 4 thrust. Also, size 3 is a 50:50 chance of actually getting a claim, which is better than 1 in 6 or 1 in 3].

Naturally, the universe continued to mock ESA as we also managed to completely blacken the Nysa family once we got there :(. But at least we could refuel on Hertha, and Plan C was formulated after all the players agreed to use the Expanded Map to find more targets (otherwise I was kinda screwed, since there aren’t any other size 3 hydrated bodies on the basic map). With new vistas of space open to us, ESA decided to head off to asteroid Lutetia to see if we could stake a claim there.

Meanwhile, the Chinese had managed to get their factory set up at Khufu, and managed to develop the Zubrin thruster there (uh-oh…), and promptly decided to use that to conquer the solar system by sending it back to Earth and loading up another robot/refinery package on it to build another factory elsewhere. Since the Zubrin drive basically allows them to go anywhere in one turn (15 thrust – 1/3 fuel/burn), they promptly set up shop on Jupiter’s outermost Galilean satellite Callisto.

While this was happening, NASA had been happily turning the Koronis cluster in the asteroid belt into a blackened wasteland, and had moved on to the Vesta cluster where they finally managed to get claims on Vesta, Unitas and Eichsfeldia. They built a factory on Eichsfeldia, refuelled there, launched again to plunder more asteroids, and promptly turned themselves into a new crater on asteroid Ida [they failed the ‘rapid rotation” crash hazard roll], thus ending their asteroid-killing spree. Fortunately their new factory was nearby so they sent up a freighter with a new instance of their black (robonaut?) card to pick that up with an earthbound rocket later (they didn’t really get a chance to do much after that).

ESA’s mission to Lutetia was also a disaster (the dice really hated me!), but at least we managed to refuel on its now scorched, blackened surface. ESA obviously had the utmost trust in their equipment by having so many backup plans, but at this point we were getting a bit desperate. That said, I guess it was testimony to our spacecraft that it had survived for so long and visited so many targets (there really should be some kind of VP reward for doing that with a single ship…). So, while the Chinese were busy zipping around the solar system and setting up their new base in Asgard’s ice spires on Callisto, we made a last-ditch effort to stake a claim on asteroid Hygiea.

Hygiea’s ‘siblings’ Badenia and Friederike turned out to be a bust, but FINALLY ESA got lucky on Hygiea itself and managed to stake a claim and build a factory there (we landed on fumes!)! Cue much raucous celebration at ESA Mission Control!!

ESA didn’t have much of a plan after that, but we noticed that we could actually get to Ganymede and at least claim that. Armed with our newly-minted Nanobot robonaut (black, ISRU 1, buggy) the refuelled ESA rocket managed to land on Memphis Facula and claim both Ganymede locations (no factory though since I didn’t have a refinery)! [this was particularly cool moment for me, since I’d spent a good chunk of my PhD studying Ganymede, so it was only fair that I claim it! :)]. ESA and China now both had claims in the Galileans and were eyeing eachother warily over the gap – fortunately the Chinese didn’t try to jump ESA’s Ganymede claims though.

Having accomplished ESA’s main mission – and being quite tired by this point since it was now the wee hours of the morning – I wasn’t actually sure what to do next so I ended up turning my rocket into an outpost on Ganymede and attempted to start a new rocket at LEO to find a new target. China had meanwhile turned its greedy eyes on NASA’s Vesta claim, claim jumped it and built a factory on it for good measure. I’d just managed to boost my rocket into orbit and was considering a trip to Mars, but the Chinese managed to get Space Tourism (Space Venture) and then paid the 5 WT to end the game since they had three ET factories (Khufu, Callisto, and Vesta).

So the Chinese won by miles (I think they ended up with 24 VP, and ESA and NASA both had 9 VP), but despite the length of the game and our initial trouble we all agreed that it’d be fun to try it again now that we had some idea what we were doing, so I consider that mission accomplished! 🙂

I think we did everything correctly, but being our first game I’m sure we probably slipped up in a few places (and we’re still not sure what the general strategy should be). But I’ll ask questions on the HF Yahoo Group and hopefully get those sorted out by the next time we play! (and next time, I’ll take photos 😉 ).

Curiosity Sol 2 & 3 Image Roundup!

Curiosity is still doing very well on the surface of Mars, and some full resolution images have arrived back here on Earth over the past couple of days!

First there’s this overview of Curiosity and all its associated landing paraphernalia, taken by Mars Reconnaissance Orbiter’s HIRISE camera in orbit around the red planet – the heatshield, skycrane, parachute and backshell are all accounted for, as is Curiosity itself (labelled as “MSL” – Mars Science Laboratory). The dark patch around Curiosity itself was caused by the backblast if the skycrane’s rocket motors as it was being lowered to the ground – brighter dust was blown away, leaving darker material behind. To get a sense of scale, the skycrane is located at a distance of 650 metres from Curiosity. There are no plans to go and visit any of the wreckage, however.

Curiosity landing site (image credits: NASA/JPL/MSSS)

Curiosity’s Cameras

Before I go on, I should explain the cameras that Curiosity uses to take pictures – there are 17 of them in total, so it can be difficult to keep track of them all! The sensor mast (Curiosity’s Wall-E like “head”) containing the cameras was successfully raised on Sol 2 and seems to be working fine.

The cameras on Curiosity’s sensor mast
(image credits: NASA/JPL/Constantine Thomas (labels))

The CHEMCAM (not used yet) is the round opening at the top. This shoots a laser at distant rocks (!) – CHEMCAM’s spectrometers and telescope can then determine the composition of the rock by analysing the puff of material blown off by the laser (which is pretty darn clever, really).

The NAVCAMs are the two little cylindrical things on the left and right of the “head”, below the CHEMCAM. There are two on each side, but only one left/right pair is used at a time – the other is a backup. This allows Curiosity to take stereo images, which can be used to make 3D anaglyph images.

The MASTCAMs are the two trumpet-like things mounted below the CHEMCAM. The one with the wider opening directly below CHEMCAM is the wide angle camera, and the one on its right is the telephoto camera. These won’t be able to take stereo images because they aren’t the same kind of camera, but they’ll be taking the bulk of the high resolution images of the landscape.

There are also the front and rear HAZCAMs (there are actually eight of these, mounted on all four corners of the rover), which take low resolution images of what’s immediately in front of and behind the rover in order to avoid obstacles – we’ve already seen pictures from those that were taken shortly after Curiosity landed. MARDI is the MARs Descent Imager, which is on the bottom of Curiosity and was used to take the Descent video. Last I heard on one of the press conferences, the team were hoping to get some further use out of this camera by taking pictures of the ground directly under the rover, since some light can still get through underneath the rover. And then there’s MAHLI (MArs Hand Lens Imager), which is the hand-lens imager mounted on a robotic arm that will be used to take closeup shots of the rocks that Curiosity examines (and can also apparently be used to image more distant objects too).

If you want a more complete roundup of what these instruments (and others) do, wikipedia explains all!

OK. Now you know what’s taking all the pictures, let’s go back to the images!

Next up is the first view from the NAVCAMs. While these can be used to take 3D stereo images if they are taken in pairs (you’ll need red-blue glasses to view them – apparently comic shops may be a good place to find these!), they can of course also be viewed as individual images too – this is the first high resolution scene returned from Curiosity through the left NAVCAM, and the scenery looks pretty astounding. I love the hazy mountains of the crater rim in the distance, and the detail in all the rocks and pebbles in the foreground!:

The view from Curiosity (left NAVCAM) – Image credits: NASA/JPL-Caltech

The NAVCAMs managed to get a good look around the whole rover, and the images were stitched together to make this amazing 360° view of the rover’s surroundings. Mount Sharp (the central peak of Gale crater) is at the bottom/left of the image (the rover’s pointing in its general direction), the crater rim is visible to the right, and I think the sun’s washing out the horizon at the top of the image. I love how you can actually see the rover here (I would have expected some distortion because of the 360° view, but it looks nicely rover-shaped!) – also note the bits of gravel on the top surface of Curiosity, which were kicked up by the skycrane’s rockets as it was landing!

360 degree view around Curiosity – Image credits: NASA/JPL-Caltech/James Sorenson

Finally, the MASTCAM was fired up and returned this very nice colour panorama looking towards Mount Sharp. The dark streaks at the base of the mountain are sand dunes – from what I gathered from the press conferences, Curiosity is going to be heading towards them (skirting the left side in this view) once it starts moving in a couple of weeks. There are several very cool things to note here – first, this panorama is actually made up of 130 thumbnail images with a resolution of 144×144 pixels – these aren’t even full resolution images (which are 1200×1200 pixels), so the full resolution panorama will be absolutely enormous and ridiculously detailed! We’ll have to wait a few days for that to come back down though, since updating the rover’s software is a higher priority in the coming days. Second, the grey circular patches on the left and right are where the skycrane’s rockets blew away some of the dust during the landing, which means that bedrock might be exposed there! Third, that line of holes in the treads of the wheels apparently spell out “JPL” in morse code… so Curiosity will be leaving JPL’s name in its tracks in the martian dust as it travels!

Curiosity MASTCAM colour panorama (Image Credits: NASA/JPL-Caltech/MSSS)

As always, if you want more info, check out Emily Lakdawalla’s Planetary Society blog!

More images from Curiosity!

There was another press conference at 4pm PDT this afternoon where the MSL team showed off some more awesome images!

This one is from the front HAZCAM, and by good fortune it looks like Curiosity is pointing towards Mt. Sharp, the mountain at the centre of Gale crater that it’s going to be climbing throughout the mission! The dark line in the foreground is actually a field of sand dunes between the rover and the mountain!

Front HAZCAM view, showing Curiosity’s shadow, and Mount Sharp looming in the distance. (Image credits: JPL/NASA/UA)

Another VERY cool thing they released was a low resolution video showing the descent of Curiosity, taken from the MARDI camera (MARs Dscent Imager) – they took 220 frames and stitched them together to make the video. They’ll be sending back higher resolution images over the next few weeks, so this is going to look even more spectacular soon. But meanwhile, feast your eyes on this:

MARDI video of Curiosity’s descent (that’s the heat shield dropping away in the first few frames!) (image credits: NASA/JPL/MSSS)

Again, Emily Lakdawalla has more details so I’ll point you to her article for those rather than repeat it all here :).

Curiosity is on Mars!

Curiosity (more formally known as the Mars Science Laboratory) has landed successfully on Mars! A very complex landing system (The so-called Seven Minutes of Terror) was required to get such a massive (one ton!) rover safely on the ground, but it seems to have worked flawlessly – it landed with a vertical velocity of 0.75 metres per second, and a horizontal velocity of only 4 centimetres per second, and well within its estimated landing ellipse – well done to everyone involved!

Curiosity’s shadow on the surface of Mars! (Image credits: NASA/JPL/UA)

There’s a news conference at 9am PDT today, apparently they’ll be showing images from Mars Reconnaissance Orbiter’s HiRISE camera of Curiosity on its way in to landing on Mars! There’ll be another at 4pm PDT possibly with MARDI (Mars Descenmt Imager) images too – You’ll be able to watch a livestream of the news conference (and future ones) here: http://www.nasa.gov/externalflash/mars/curiosity_news3.html.

Meanwhile, here’s a very nice summary of what we have so far from Emily Lakdawalla at the Planetary Society.

And if you want to see the scenes at mission control during the “Seven Minutes of Terror” as Curiosity landed, you can watch them here – it’s pretty tense!

This is going to be an awesome mission. Curiosity has enough power for 2 years of roving, but it’s undoubtedly going to last longer than that (the only real limitation is the life of the mechanisms and motors, but they’ve apparently been tested to at least three times the mission duration). Stay tuned for some amazing images over the coming weeks, months and years!

EDIT: And here’s the MRO picture! The orbiter was almost directly overhead, about 340 km away – even from this distance you can see a lot of detail on the parachute and the backplate (you can read more about it from Emily here).

Curiosity parachuting in, viewed from the HiRISE camera! (Image courtesy: NASA/JPL/UA)

They’ll be spending Sol 1 (a Sol is a day on Mars) checking out the equipment and should be getting the High Gain Antenna up and running later this afternoon – that’ll allow the rover to communicate directly with Earth. Over the next few Sols they’ll be raising the Mastcams, taking some higher resolution pictures, and getting the onboard equipment up and running, and then hopefully in a couple of weeks once they’ve made sure everything is working properly they’ll take Curiosity on her first drive. There’s no rush though 🙂

[Stellar Mapping] Brown Dwarf dataset added, plus some major updates!

I’ve added a new Brown Dwarf dataset to the Stellar Mapping page (thanks to LiNeNoiSe for pointing this out to me)! This should hopefully be the last major update to the stellar datasets for a while – the next project on the list is to figure out what the reworked Arms for 2300AD might look like based on the realistic data.

The new catalogue is the LDwarf dataset – this is a list of brown dwarfs taken from the IPAC Brown Dwarf Archives (this dataset was last updated on 14 Feb 2011). It is not a complete list of all known brown dwarfs – these are the only the ones for which parallax data is provided there.

L Dwarf dataset, looking Corewards

While some of the distances presented in this dataset are derived from trigonometric parallaxes, others are derived instead from (spectro)photometric parallaxes. Trigonometric parallaxes are derived by measuring the angular shift of a star relative to the background stars as the earth moves around the sun on its orbit (the stellar distances in the HIPX, RECONS and other datasets here are derived using this method) – these are generally more accurate than photometric parallaxes. “Photometric parallaxes” are techically not really “parallaxes” at all – instead the spectral type of the object is checked against luminosity models to get an estimate of its luminosity, which is used along with the observed visual/IR magnitude to calculate the distance to the object. Unfortunately this method is not very precise, and some of the photometric parallaxes for these objects in the LDwarf dataset have very large error bars – but this is the best data that is currently available.

One of these systems – SDSS J141-134 – is listed in the original data as having a (photometric) parallax of 127 +/- 27 mas. This places it almost in the right location to allow a 7.7 ly link between Xi Bootis and CE Bootis, which would be very useful in the 2300AD setting. I have changed its parallax to 122 mas on this list (which is comfortably within its error bars, and allows it to connect those two stars and link to the stars around Arcturus). The original (127 mas) data for this system is listed in the text file in the LDwarf.zip file if it’s needed.

It should also be noted that two Brown Dwarfs (UGPS J072227.51-054031.2 and DENIS J081730.0-615520) are located within the RECONS sphere. These are not listed in the RECONS data, but are retained here since their parallaxes indicate that they are within 22.8 lightyears of Sol (even given their large error bars). They do not make a significant difference to the 2300AD route distribution.

Some of the Brown Dwarfs in this list are members of multiple systems that are listed in other datasets presented on this site. These are listed as complete multiple star systems on this list (the other components are duplicated here using the original data) – the datasets should merge seamlessly when combined (the ID numbers are preserved in both lists) but some components may be duplicated – this should not create problems since they will have the same name and position.

Other Updates

I’ve also made several other updates to the datasets, so you’ll need to download them again to get the latest versions!

  • The Pleiades Corridor has been updated to use Extended Hipparcos data.
  • The Yale and Gliese 3 Historical Datasets have been moved into a blog article to separate them from the more accurate datasets on the Stellar Mapping page.
  • The Extended Hipparcos and CTIOPI datasets have been updated to include Multiple Systems. A and B components of some of the multiple stars in the original data were separated by several lightyears due to parallax inconsistencies – these were listed separately, but now they have been combined nto Multiple star systems that are located at the XYZ co-ordinates of the original A component.
  • The Further Stars list is still using New Reduction Hipparcos (and other) data. I will be updating it to HIPX at a later date, but it does contain duplicate stars in different positions and should be considered to be less accurate than the other datasets!
  • [Stellar Mapping] Historical Datasets (Yale & Gliese3)

    As part of this weekend’s update to my Stellar Mapping page (more details about that will be in the next post), I’ve decided to move the Historical datasets (Yale and Gliese3) onto a blog post since they’re no longer accurate and probably aren’t being used much anyway (there’s a link from the Stellar Mapping page to this blog post). So, here they are!

    Historical Datasets

    Historical databases should not be considered “accurate” by modern standards, and have been largely superseded by the ones listed in the “Accurate Datasets” section. The full Yale and Gliese catalogues have been clipped at 300 ly from Sol.

    Yale Trigonometric Parallaxes, Fourth Edition: The Yale catalogue (a.k.a the General Catalogue of Trigonometric Parallaxes, or GCTP) is a historical dataset that was one of the most accurate near star catalogues before Hipparcos, with parallax measurements taken from the ground-based observations. It includes many fainter stars that are not in the Hipparcos catalogue, but the distance accuracy is much lower. It also include many stars that are in the Hipparcos catalogue, but because of the lower accuracy they are somewhat shifted from their Hipparcos-derived positions – the difference increases with distance from Sol. However, the Yale catalogue does include Spectral data for most stars. As such, the Yale and Hipparcos catalogues should NOT be combined.

    Source: http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=I/238A/picat.
    Number of star systems: 6,051
    Distance range: 22.8 – 300 lightyears from Sol.
    Accuracy: Positional data are less accurate than Hipparcos, but spectral data is included. Physical data are not accurate. All stars are listed as single stars.

     

    Gliese Nearby Stars, Preliminary 3rd Version: The Gliese catalogue is one of the “classic” historical star catalogues – it was updated in 1991, and includes all stars known at the time within 25 pc of Sol, and a few that are further out. It has low accuracy, but again includes some of the dimmer stars that Hipparcos does not include. The 2300AD star map is apparently based on the 2nd version of this catalogue.

    Source: http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=V/70A.
    Number of star systems: 3,667
    Distance range: 22.8 – 300 lightyears from Sol.
    Accuracy: Positional data are less accurate than Hipparcos, but spectral data is included. Physical data are not accurate. All stars are listed as single stars.

    [Stellar Mapping] Extended Hipparcos dataset added!

    I’ve now replaced the New Reduction Hipparcos data with the new Extended Hipparcos (HIPX) dataset published in 2012 by Anderson & Francis (see this paper for all the details). The HIPX dataset expands the original dataset to include luminosities, spectral types and much more useful astronomical data from a variety of sources, making this the definitive source of information about these stars! The searchable online HIPX catalogue is located at http://vizier.u-strasbg.fr/viz-bin/VizieR-3?-source=+V/137A/XHIP.

    The HIPX data replaces the New Reduction Hipparcos data on this website – Astrosynthesis and Galactic XYZ data have both been updated! In most cases the HIPX XYZ data is identical to the New Reduction Hipparcos XYZs, but issues with the parallaxes for some of the multiple systems in the New Reduction data led to significant inaccuracies there – in those cases, the parallaxes were reverted back to the original Hipparcos parallax data (again, refer to the XHIP paper for further explanation).

    The XHIP data includes more star names (including common/arabic names), which are also presented here. However, note that Gliese numbers higher than 3000 have been removed for ease of reference. Technically these numbers aren’t “Gliese numbers”, they’re “NN” or “Wo(oley)” numbers. Because this could cause confusion, I decided to remove them instead of editing them all, but this isn’t a huge loss since the stars can still be tracked using their HIP numbers or other names.

    If you’ve been using the New Reduction data, then be sure to head over to my Stellar Mapping page to download the new Extended Hipparcos dataset!

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    In other news, my Stellar Mapping page now has the Atomic Rockets Seal of Approval! This is Winchell Chung’s way of saying that he likes my work, and I’m very happy about that because I’ve been a fan of his Atomic Rockets website pretty much since it first appeared online (it’s a great resource for any SF fan)! His 3D Starmaps site is also one of the main inspirations for my own stellar mapping efforts! Thanks, Winchell! 🙂

    [Stellar Mapping] CTIOPI dataset added, Stellar Mapping page reorganised!

    I have now added the CTIOPI (Cerro Tololo Interamerican Observatory Parallax Investigation) dataset to my Stellar Mapping page! CTIOPI is another dataset from the RECONS group, aimed at locating red, white, and brown dwarfs that are within 25pc of Sol – it adds 164 stars that are mostly contained within 300 ly of Sol. However, it only covers (roughly) the southern sky as viewed from Earth, so only about half of the volume around Sol contains stars from this dataset – that said, the distribution of CTIOPI stars could be used as a guideline for adding fictional stars in the rest of the volume.

    CTIOPI dataset, looking corewards.

    I have also edited the DENSE dataset to remove all the stars that were duplicated in CTIOPI and HIPPARCOS datasets – the most accurate data has been retained (the original DENSE dataset is no longer available here, though I may make it available again in a later blog update). The CTIOPI dataset has also been edited somewhat to remove duplicates (none of the CTIOPI stars have HIP numbers though, though it does include one star – HIP 3856 – that is missing from the Hipparcos dataset). All CTIOPI entries within 22.7 lightyears have also been removed to avoid overlap with RECONS.

    This means that there should now be no duplicated stars at all if the RECONS, DENSE, CTIOPI and HIPPARCOS datasets are used together, so the combined dataset is now about as accurate as it can be. Full details of these edits can be found in the “CTIOPI-DENSE merging details” section in the Astrosynthesis.txt and Galactic.txt files contained in the new RECONS-DENSE-CTIOPI.zip file available from Section 2 of the Stellar Mapping page.

    I’ve also updated and reorganised the Stellar Mapping page to (hopefully) make it easier to decide which datasets to use. If you have already downloaded the DENSE dataset then you should download it again to make sure you have the latest version!

    [Stellar Mapping] The 2300AD Near Star Map

    The 2300AD Near Star Map

    The 2300AD RPG – originally published by Game Designer’s Workshop in 1988 – presented an excellent gritty, realistic near-future hard sci-fi setting with lots of exploration, mystery, and interesting aliens. It’s also about to be republished by Mongoose Publishing as a setting for their version of the Traveller RPG!

    One of 2300AD’s most interesting features is that the setting is built around a realistic (for the 1980s) Near Star List based on the Gliese Catalogue (2nd Version). FTL travel in 2300AD has a maximum range of 7.7 lightyears, resulting in the creation of “Arms” that extend from Sol to connect only the stars that are within this range of eachother (this limit can potentially be extended to 11.55 ly using Stutterwarp tugs, but this is expensive and uncommon).

    There are three of these Arms, each colonised by a different political power in the setting – the French Arm, the Chinese Arm, and the American Arm. The French Arm stretches “upwards” from Sol towards Galactic North, ending at the orange giant star Arcturus. The American and Chinese Arms share the same beginning, but split off so that the American Arm heads Coreward/Spinward while the Chinese Arm sprawls around the (galactic) southern part of the solar neighbourhood.

    Unfortunately the Near Star List (NSL) has not been updated for the new version of 2300AD. A lot of stars have been discovered in the solar neighbourhood since the late 1980s (as shown on my Stellar Mapping page), and the locations and distances of existing stars have been greatly refined since then too – so how does the updated stellar data affect the Arms?
    Continue reading ‘[Stellar Mapping] The 2300AD Near Star Map’