Tag Archive for 'Mars'

[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.

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 🙂