Archive for Saturn

Countdown to Cassini’s Grand Finale

Posted in The Universe and Stuff with tags , , , , on September 12, 2017 by telescoper

In case you didn’t realise, this week sees the end of the superbly successful NASA mission Cassini, which has been exploring Saturn, its ring systems and its many satellites since it arrived there in 2004, including sending the Huygens probe into the largest moon Titan. Its final act will be to plunge into Saturn itself, which it will do on Friday 15th September, taking measurements all the way until it is destroyed. It has already started the final manoeuvre that will end when it enters the planet’s atmosphere. Radio contact with the spacecraft is expected to be lost  just before 1pm GMT.  For further information about this final act, see here.

Cassini was launched in on October 15 1997, so its mission will have lasted  one month shy of twenty years (although there were many years of preparation before that). Although I don’t work on Solar System studies, I have followed the progress of Cassini with great interest over the years primarily because there was a group (led by Carl Murray) working on Cassini (specifically on its imaging system) at Queen Mary when I was there during the 1990s.  I was there in 1997 when the spacecraft was launched, but at that time the rendezvous date with Saturn of 2004 seemed in the unimagineably distant future. Seven years seems a very long time when you’re young!

Anyway, I’m sure Carl (along with all the other scientists working on the Cassini mission) will feel sadness when it all finally comes to an end, but the consolation will be that the mission  has been such a spectacular scientific triumph. Here’s a video about the end of Cassini, showing some of the highlights of the mission and some of the thoughts of the scientists that have been working in it for so long.

 

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Another Day at the ArXiv..

Posted in Cosmic Anomalies, The Universe and Stuff with tags , , , , , , , on October 8, 2009 by telescoper

Every now and again I remember that this is supposed to be some sort of science blog. This happened again this morning after three hours of meetings with my undergraduate project students. Dealing with questions about simulating the cosmic microwave background, measuring the bending of light during an eclipse, and how to do QCD calculations on a lattice reminded me that I’m supposed to know something about stuff like that.

Anyway, looking for something to post about while I eat my lunchtime sandwich, I turned to the estimable arXiv and turned to the section marked astro-ph, and to the new submissions category, for inspiration.

I’m one of the old-fashioned types who still gets an email every day of the new submissions. In the old days there were only a few, but today’s new submissions were 77 in number, only about half-a-dozen of which seemed directly relevant to things I’m interested in. It’s always a bit of a struggle keeping up and I often miss important things. There’s no way I can read as widely around my own field as I would like to, or as I used to in the past, but that’s the information revolution for you…

Anyway, the thing that leapt out at me first was an interesting paper by Dikarev et al (accepted for publication in the Astrophysical Journal) that speculates about the possibility that dust grains in the solar system might be producing emission that messes up measurements of the cosmic microwave background, thus possibly causing the curious cosmic anomalies seen by WMAP I’ve blogged about on more than one previous occasion.

Their abstract reads:

Analyses of the cosmic microwave background (CMB) radiation maps made by the Wilkinson Microwave Anisotropy Probe (WMAP) have revealed anomalies not predicted by the standard inflationary cosmology. In particular, the power of the quadrupole moment of the CMB fluctuations is remarkably low, and the quadrupole and octopole moments are aligned mutually and with the geometry of the Solar system. It has been suggested in the literature that microwave sky pollution by an unidentified dust cloud in the vicinity of the Solar system may be the cause for these anomalies. In this paper, we simulate the thermal emission by clouds of spherical homogeneous particles of several materials. Spectral constraints from the WMAP multi-wavelength data and earlier infrared observations on the hypothetical dust cloud are used to determine the dust cloud’s physical characteristics. In order for its emissivity to demonstrate a flat, CMB-like wavelength dependence over the WMAP wavelengths (3 through 14 mm), and to be invisible in the infrared light, its particles must be macroscopic. Silicate spheres from several millimetres in size and carbonaceous particles an order of magnitude smaller will suffice. According to our estimates of the abundance of such particles in the Zodiacal cloud and trans-neptunian belt, yielding the optical depths of the order of 1E-7 for each cloud, the Solar-system dust can well contribute 10 microKelvin (within an order of magnitude) in the microwaves. This is not only intriguingly close to the magnitude of the anomalies (about 30 microKelvin), but also alarmingly above the presently believed magnitude of systematic biases of the WMAP results (below 5 microKelvin) and, to an even greater degree, of the future missions with higher sensitivities, e.g. PLANCK.

I haven’t read the paper in detail yet, but will definitely do so. In the meantime I’d be interested to hear the reaction to this claim from dusty experts!

Of course we know there is dust in the solar system, and were reminded of this in spectacular style earlier this week by the discovery (by the Spitzer telescope) of an enormous new ring around Saturn.

That tenuous link gives me an excuse to include a gratuitous pretty picture:

It may look impressive, but I hope things like that are not messing up the CMB. Has anyone got a vacuum cleaner?