Archive for ESA

Rendezvous Rosetta!

Posted in The Universe and Stuff with tags , , on August 6, 2014 by telescoper

Just a quick post to remind you (as if you needed it) that, in about 5 minutes’ time at 10am BST, the ESA spacecraft Rosetta will begin its encounter with a comet (actually Comet 67P/Churyumov-Gerasimenko).

As it approached its target, Rosetta took this picture that revealed the comet to be a rather peculiar beast, rather like a rubber duck:

Comet

Here’s a more recent, closer, view:

Comet_close

Rosetta’s journey began on 2 March 2004 when Rosetta was launched on an Ariane 5 from Europe’s Spaceport in Kourou, French Guyana. Since then, the spacecraft has orbited around the Sun five times, picking up speed through three gravitational “slingshots” at Earth and one at Mars, to enter an orbit similar to that of its target, said comet 67P/Churyumov–Gerasimenko, which is in an elliptical 6.5-year solar orbit that takes it from beyond the orbit of Jupiter at its furthest point, and between the orbits of Mars and Earth at its closest to the Sun.

To perform its rendezvous Rosetta has to match the pace of the comet – currently about 55 000 km/h – and travel alongside it to within just 1 m/s between them. This has required a complex and delicate series of manoeuvres:

The spacecraft will then travel alongside the comet as it approaches the Sun. In November 2014 the Philae probe will be deployed and will land on the comet surface. Rosetta will follow the comet to its closest distance to the Sun on 13 August 2015 and as it moves back towards the outer Solar System. The nominal mission end is December 2015.

I bet there’s quite a lot of stress in the ESA control centre in Darmstad, Germany, as the probe’s epic journey nears its end, not least because telemetry is lost while the burn happens. Those ten years in space will count for little if something goes wrong now. Good luck everyone involved!

You can watch a live feed of the encounter here.

UPDATE: after an agonizing wait – it takes 23 minutes for telemetry to reach Earth from Rosetta – the spacecraft has entered orbit correctly. Well done everyone!

UPDATE: click here for an amazing collection of images of the comet.

UPDATE: Relief at ESA HQ as The Clangers finally emerge to greet the Rosetta Spacecraft:

BuW-AFJIEAA6L3k

Top Ten Gaia Facts

Posted in Astrohype, The Universe and Stuff with tags , , , on December 20, 2013 by telescoper
Gaia looks nothing like the Herschel Space Observatory shown here.

Gaia looks nothing like the Herschel Space Observatory shown here.

Since yesterday’s successful launch of the European Space Agency’s Gaia mission I have been inundated with requests for more information about this impressive satellite and the science behind it. As a service to the community, and for the edification of the public at large, I therefore thought I’d share my list of top ten Gaia facts via the medium of this blog:

  1. The correct pronunciation of GAIA is as in “gayer”. Please bear this in mind when reading any press articles about the mission.
  2. The GAIA spacecraft will orbit the Sun at the Second Lagrange Point, the only place in the Solar System where the  effects of cuts in the UK science budget can not be felt.
  3. The data processing challenges posed by GAIA are immense; the billions of astrometric measurements resulting from the mission will be analysed using the world’s biggest Excel Spreadsheet.
  4. To provide secure backup storage of the complete GAIA data set, the European Space Agency has commandeered the world’s entire stock of 3½ inch floppy disks.
  5. As well as measuring billions of star positions and velocities, GAIA is expected to discover thousands of new asteroids and the hiding place of Lord Lucan.
  6. GAIA can measure star positions to an accuracy of a few microarcseconds. That’s the angle subtended by a single pubic hair at a distance of 1000km.
  7. The precursor to GAIA was a satellite called Hipparcos, which is not how you spell Hipparchus.
  8. The BBC will be shortly be broadcasting a new 26-part TV series about GAIA. Entitled WOW! Gaia! That’s Soo Amaazing… it will be presented by Britain’s leading expert on astrometry, Professor Brian Cox.
  9. Er…
  10. That’s it.

Planck (but only in name?)

Posted in Science Politics, The Universe and Stuff with tags , , , , , , on March 3, 2013 by telescoper

First, a serious announcement. It appears that the announcement of results from the Planck Mission will be streamed live from ESA HQ on 21st March from 10.00 to 12.00 CET (whatever that is). The UK will remain on GMT until 31st March so the  ESA web server will probably crash at 9am British time on 21st March.

There’s a short press release making this announcement here. It says:

On Thursday 21 March 2013, the main scientific findings from the European Space Agency’s Planck spacecraft will be announced at a press briefing to be held at ESA’s Headquarter in Paris. Simultaneously with this event, data products and scientific papers based on the “nominal” operations period will be made public through the Planck Legacy Archive.

I was interested in the appearance of the word “nominal” in quotes in there so I searched for its meaning in the One True Chambers Dictionary, where I found:

nominal, adj relating to or of the nature of a name or noun; of names; by name; only in name; so-called, but not in reality; inconsiderable, small, minor, in comparison with the real value, hardly more than a matter of form…

Interesting. It seems that the “nominal” could mean, on the one hand, that ESA are being unusually modest about the importance of the forthcoming Planck results or, on the other, that there will now be a host of conspiracy theorists suggesting that the Planck results aren’t real….

That reminds me that years and years ago I had an idea for a crime novel with a plot that revolves around the murder of a prominent cosmologist just as some important scientific discovery is about to be announced. Suspicion gathers that the whole thing is an enormous hoax and the discovery bogus. But the experiment is shrouded in secrecy, and so expensive that it can’t easily be repeated, so  who can tell, and how?

It’s very difficult to know for sure whether any scientific discoveries are genuine or not, even if the data and analysis procedures are made public. There’s always the possibility that everything might have been fabricated simulated, but in most cases the experiment can be repeated at a later date and the fraud eventually exposed, such as in the Schön Scandal.  In Big Science, this may not be practicable. However, Big Science requires big teams of people and the chances are someone would blow the whistle, or try to…

Anyway, I know that there are people out there who take everything I write on this blog absurdly literally so I’ll spell it out that I am in no way suggesting that the Planck mission is a fraud. Or predicting that there’ll be a murder just before the announcements on March 21st. Any similarity purely coincidental and all that. And I’ve never had time to write the book anyway – perhaps a publisher might read this and offer me an advance as an incentive?

Moreover, going back to the Chambers Dictionary, I note the final definition omitted above

…according to plan (space flight)

So that’s that. Nothing sinister. I’m not sure how “nominal” acquired that meaning, mind you, but that’s another story…

The case for JUICE

Posted in Science Politics, The Universe and Stuff with tags , , , on May 8, 2012 by telescoper

telescoper:

Here’s a nice blog peace giving the case for JUICE (The Jupiter Icy Moon Explorer recently selected by the European Space Agency for its next L-class mission).

Originally posted on Well-Bred Insolence:

There’s been a lot of chatter in astronomy circles about the negative consequences of ESA’s latest L-class (i.e. large) space mission selection.  JUICE (The JUpiter Icy moon Explorer) was selected over two rival missions – the New Gravitational wave Observatory (NGO), and the Advanced Telescope for High ENergy Astrophysics (ATHENA).  In the current age of global austerity, one group’s win is several groups’ losses, and understandably the X-Ray and gravitational wave communities are upset at the choice.  Indeed, reading the comments section on astro blogs might make planetary scientists go a little pale. Not least the fact that ATHENA supporters have already delivered a 1450 signature petition demanding a rethink.  The fact that the decision making process has been somewhat cloudy doesn’t help matters.

It does indeed suck that this is a zero-sum game (in fact, probably…

View original 813 more words

It’s JUICE!

Posted in Science Politics, The Universe and Stuff with tags , , on May 3, 2012 by telescoper

Not unexpectedly, the European Space Agency announced yesterday that it’s next large mission will be the Jupiter Icy Moon Explorer (aka JUICE). There’s a piece in Physics World about the selection – and rejection of the other two contenders, NGO and ATHENA. Andy Lawrence has commented already on his own blog and is also quoted extensively in the Physics World article.

A lot of allegations are flying around about how the selection process was conducted, specifically relating to conflicts of interest. I don’t know any details, so I won’t comment on whether this is justified outrage or simply sour grapes.

Anyway, for what it’s worth, I think I agree with what Andy Lawrence says in the Physics World story in that the final decision was pretty inevitable after NASA’s decisions in the areas of gravitational waves and X-ray astronomy pulled the rug out from under the other contenders. I’ll also add that, although it’s far from my own specialism, I think JUICE looks like a very exciting mission. I wish it every success.

It just remains to be seen how long the recriminations will rumble on.

Controversy brewing at ESA?

Posted in Science Politics with tags , , , , on April 23, 2012 by telescoper

telescoper:

Interesting stuff over at the e-astronomer relating to ESA’s handling of the process of selecting its next L-class mission. The plot thickens.

Originally posted on The e-Astronomer:

So the Athena folk are somewhat miffed at being pipped by Juice. (This metaphor doesn’t seem quite right ? Ed.) But what about Horse Number Three ? Aren’t the NGO folk doing a Grand Petition ? Nope. It seems their tactic is a semi-formal complaint about inadeqacies in the process : an email letter direct to Gimenez. I am not sure how widely it has been circulated, but I understand it is stern stuff, bringing up issues of inappropriate revisions of costings and risk factors, and inadequately resolved conflicts of interest. Feel free to comment if you have clear knowledge, but please (a) do not leak things that are confidential, and (b) keep coments about process and not about individuals.

Its not really clear what competition means when a very small number of items is under consideration, and moreoever each item represents one community-segment, each of which ESA wishes to…

View original 356 more words

On the Dearth of Dark Matter in the Solar Neighbourhood

Posted in Astrohype, The Universe and Stuff with tags , , , , , , , , on April 22, 2012 by telescoper

I’m a bit late getting onto the topic of dark matter in the Solar Neighbourhood, but it has been generating quite a lot of news, blogposts and other discussion recently so I thought I’d have a bash this morning. The result in question is a paper on the arXiv by Moni Bidin et al. which has the following abstract:

We measured the surface mass density of the Galactic disk at the solar position, up to 4 kpc from the plane, by means of the kinematics of ~400 thick disk stars. The results match the expectations for the visible mass only, and no dark matter is detected in the volume under analysis. The current models of dark matter halo are excluded with a significance higher than 5sigma, unless a highly prolate halo is assumed, very atypical in cold dark matter simulations. The resulting lack of dark matter at the solar position challenges the current models.

As far as I’m aware, Oort (1932, 1960) was the first to perform an analysis of the vertical equilibrium of the stellar distribution in the solar neighbourhood. He argued that there is more mass in the galactic disk than can be accounted for by star counts. A reanalysis of this problem by Bahcall (1984) argued for the presence of a dark “disk” of a scale height of about 700 pc. This was called into question by Bienaymé et al. (1987), and by Kuijken & Gilmore in 1989. In a later analysis based on a sample of stars with HIPPARCOS distances and Coravel radial velocities, within 125 pc of the Sun. Crézé et al. (1998) found that there is no evidence for dark matter in the disk of the Milky Way, claiming that all the matter is accounted for by adding up the contributions of gas, young stars and old stars.

The lack of evidence for dark matter in the Solar Neighbourhood is not therefore a particularly new finding; there’s never been any strong evidence that it is present in significant quantities out in the suburbs of the Milky Way where we reside. Indeed, I remember a big bust-up about this at a Royal Society meeting I attended in 1985 as a fledgling graduate student. Interesting that it’s still so controversial 27 years later.

Of course the result doesn’t mean that the dark matter isn’t there. It just means that its effect is too small compared to that of the luminous matter, i.e. stars, for it to be detected. We know that the luminous matter has to be concentrated more centrally than the dark matter, so it’s possible that the dark component is there, but does not have a significant effect on stellar motions near the Sun.

The latest, and probably most accurate, study has again found no evidence for dark matter in the vicinity of the Sun. If true, this may mean that attempts to detect dark matter particles using experiments on Earth are unlikely to be successful.

The team in question used the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory, along with other telescopes, to map the positions and motions of more than 400 stars with distances up to 13000 light-years from the Sun. From these new data they have estimated the mass of material in a volume four times larger than ever considered before but found that everything is well explained by the gravitational effects of stars, dust and gas with no need for a dark matter component.

The reason for postulating the existence of large quantities of dark matter in spiral galaxies like the Milky Way is the motion of material in the outer parts, far from the Solar Neighbourhood (which is a mere 30,000 light years from Galactic Centre). These measurements are clearly inconsistent with the distribution of visible matter if our understanding of gravity is correct. So either there’s some invisible matter that gravitates or we need to reconsider our theories of gravitation. The dark matter explanation also fits with circumstantial evidence from other contexts (e.g. galaxy clusters), so is favoured by most astronomers. In the standard theory the Milky Way is surrounded by am extended halo of dark matter which is much less concentrated than the luminous material by virtue of it not being able to dissipate energy because it consists of particles that only interact weakly and can’t radiate. Luminous matter therefore outweighs dark matter in the cores of galaxies, but the situation is reversed in the outskirts. In between there should be some contribution from dark matter, but since it could be relatively modest it is difficult to estimate.

The study by Moni Bidin et al. makes a number of questionable assumptions about the shape of the Milky Way halo – they take it to be smooth and spherical – and the distribution of velocities within it is taken to have a very simple form. These may well turn out to be untrue. In any case the measurements they needed are extremely difficult to make, so they’ll need to be checked by other teams. It’s quite possible that this controversy won’t be actually resolved until the European Space Agency’s forthcoming GAIA mission.

So my take on this is that it’s a very interesting challenge to the orthodox theory, but the dark matter interpretation is far from dead because it’s not obvious to me that these observations would have uncovered it even if it is there. Moreover, there are alternative analyses (e.g. this one) which find a significant amount of dark matter using an alternative modelling method which seems to be more robust. (I’m grateful to Andrew Pontzen for pointing that out to me.)

Anyway, this all just goes to show that absence of evidence is not necessarily evidence of absence…

Follow

Get every new post delivered to your Inbox.

Join 3,701 other followers