The industrial contract for the building of the main Comet Interceptor spacecraft and one of its two probes was signed by ESA and OHB last month. Japan will be providing the second small probe for the mission.

The Red Book definitely exists and should be available soon.

Comet Interceptor has been formally adopted by ESA, giving the green light for the implementation phase, i.e. the mission is definitely happening. An industrial consortium to build the main spacecraft and the European small probe will be selected by ESA in the near future; launch will be with the Ariel mission on an Ariane 62, currently scheduled for December 2029.

https://www.gov.uk/government/news/comet-ch...rOwIMSI82ete7R0

and

https://www.esa.int/Science_Exploration/Spa...or_construction

ESA has approved the advancement of Comet Interceptor from Phase 0, involving mission design & initial mission requirements, to Definition Phase A. The agency is now engaging with industry regarding spacecraft final design & build. Some more details here.

The small probes would be attached to the primary spacecraft at L2 and for the cruise to the target. Separation would be around a day to weeks from closest approach, depending on the separation distances needed between the three elements (depends on activity level of the target and desired miss distances).

Separation of the three by diverging Keplerian orbits could be sufficient, but if not, the primary can use its own thrusters to increase rate of separation, rather than the subspacecraft needing to carry their own thrusters.

Mission to a dynamically new comet or an interstellar object selected by ESA:

http://www.esa.int/Our_Activities/Space_Sc...tercept_a_comet

Team website:

http://www.cometinterceptor.space

Comet Interceptor is a mission proposal on a shortlist of six for ESA's F-class mission call. The mission would target a dynamically new comet from the Oort Cloud, or an interstellar object. ESA is expected to select the F-class mission in July 2019. Launch would be with ESA's Ariel exoplanet observatory in 2028.

Comet Interceptor would wait at Sun-Earth L2 until a suitable target is found inbound by survey observatories such as LSST. The primary spacecraft would deploy subspacecraft for the comet encounter, providing multi-point in situ measurements of the environment near the comet, as well as different remote sensing viewpoints of the nucleus and coma.

The mission's website is here, where the team are inviting registration of support for the proposal:
http://www.cometinterceptor.space/

The Twitter handle is @cometintercept

The paper discussed was actually this one - evidence of a plume signature recorded in in-situ Galileo magnetometer and radio wave instrument data.

I was thinking that as the thin crescent as seen from Cassini is fully sunlit, it may be that there are more forward-scattering particles between the sunlit crescent and Cassini that there are relatively near Dione to backscatter sunlight from the daylit side as a whole. Forward scattering around the bright crescent could also explain the apparent enhanced brightness around the 7 o'clock position.

However, your point about the unilluminated portion of Dione being darker than the surrounding glow is a very good one, so yes, the source must be at least partially behind the moon.

Depending on the path between Cassini and Dione through the E ring, maybe this fuzzy halo is due to forward scattering of the light from Dione by E ring grains that were between the moon and spacecraft?

Alternatively, Dione does have a tenuous exosphere which could be considered a potential cause, but I suspect that it'd be surprising for it to be this bright. The falloff in brightness could be compared to the expected scale length of the exosphere. I can't see any hint of a shadow being cast opposite to the narrow sunlit crescent, which I think may be expected if the halo is due to material, either gaseous or particulate, concentrated around Dione itself.

More info here: (and a google hangout in a couple of hours' time)

http://hubblesite.org/newscenter/archive/releases/2015/09

Althought it's most obvious in the latest image, there is a bright point at that same location in all three images; down to just 1-2 pixels though. Maybe it's one of the three airbags, and we're seeing a fold in the material?

Landed successfully, but only partially deployed, in which case the antenna probably wasn't uncovered. So close...

Images now on BBC News website here:

Ah, I see. I haven't looked at the numbers, and I appreciate it's been orbiting Saturn for a very very long time, so small effects could build up (as the YORP effect can be significant on asteroids), but still I'd be extremely surprised if this would make an observable contribution. Would be very happy to be proven wrong though!

By the way, the Hyperion paper is open access, so anyone can read it here.

Given that the charging times are much, much shorter than the rotation/tumbling period, I doubt that the rotation state is likely to have a signficant effect, apart from making it difficult to predict what the potential is going to be across the surface at any one time. The irregular shape and rugged surface make it difficult to simulate too.

oDoug - welcome back! Regarding other bodies... something is in the works; watch this space!

All the inactive/airless bodies build up charge. Sunlight tends to charge things positive, through the photoelectric effect releasing electrons, whilst the flow of plasma in the magnetosphere onto bodies tends to charge them negative. The dust detected by Cassini has been found to be charged. Close to Saturn, it's negatively charged, where the plasma in the magnetosphere is denser, whilst roughly beyond the orbit of Rhea, it tends to charge positive, where the effect of sunlight dominates.

Cassini itself has a potential, which varies depending on where it is and whether it's in shadow, and the potential follows the same general pattern as observed on the dust. That can be a problem for certain observations, when for example very low energy electrons can't reach the spacecraft when it's got a negative potential, so they can't be detected by the plasma instruments.

For the moons, it's a little more complex as you'll have one half continuously exposed to plasma, because they're sitting inside Saturn's magnetosphere, and another, usually overlapping hemisphere exposed to the Sun. You can also get local effects such as shadowed regions, etc. that complicate things quite a bit, and the effects of the plasma depend on its temperature too.

When a moon's surface has a negative potential, it can reflect low energy electrons, and can also accelerate electrons away from its own surface. Hyperion didn't really zap Cassini has it went past - this process of electron reflection and acceleration is going on all the time, and the electrons stream away along Saturn's magnetic field lines that pass through Hyperion. During the encounter in 2005, Cassini happened to be on magnetic field lines connecting the moon to the spacecraft, and the CAPS instrument happened to be looking in the right direction to detect the electrons arriving from the direction of Hyperion. The feature was spotted in the data at the time, but it took a few years to fully understand what was being observed, and it's a neat result!

One definition of a flux tube is the collection of magnetic field lines that thread a moon, so, yes, Cassini did cross Hyperion's flux tube.

Application of a data scrubbing algorithm yields surprising results...

What a fantastic day - many congratulations to all involved! Really impressive and inspiring stuff...

Is there an official (or semi-official) touchdown time? How much did it differ from the pre-landing estimate? I know it's a pretty minor matter in the big scale of things; hope I'm not being too much of an anorak!

A glider's definitely doable, as proven in November with the PARIS flight in Spain.

I can't see that anyone else has reported this: ESA have today announced the four shortlisted mission candidates for the M3 medium-class mission for launch around 2022.

Marco Polo, which narrowly lost out in the competition for consideration for an earlier M1 or M2 mission slot, is through again. Also of planetary science interest is exoplanet-characterization mission EChO. It doesn't look like ESA are going to provide a full list of the 47 submitted proposals, but I understand that there were many planetary proposals submitted.

Snowballs like this have been detected by radar before, e.g. Hyakutake, as reported in this paper in 1997. A trail of these objects were also observed from Earth, including by amateurs, as an anti-sunward "spike"; larger telescopes resolved mini-comae surrounding 1-10m-sized "snowballs", as reported here.

If it does, one good thing is that it won't be a fast flyby; as it'll be moving with the nucleus, the relative speed will be tiny compared to the 12.3 km/s relative speed of EPOXI, so the kinetic energy of each impact will be way lower. Giotto, by the way, endured dust impacts at 68.4 km/s at Halley.

I thought it was a good programme overall, but it was a shame that they didn't include some real images of encountered asteroids rather than not-very-impressive simulations. We have quite a good sample of such images by now, as demonstrated by Emily's growing montage, including lovely rotation movies of Eros from NEAR, Itokawa from Hayabusa, etc. A real puzzle when the material's free of copyright.

Also, why not continue the incredible story of finally finding an asteroid about to hit the Earth with a brief story of its recovery from the African desert? They didn't mention at all that it had been recovered, just implied that it burnt up and left a trail of smoke.

For those able to receive BBC2 and BBC HD, tonight's Horizon at 9pm is entitled "Asteroids: The Good, the Bad, and the Ugly". Should be interesting for UMSFers.

http://www.bbc.co.uk/programmes/b00vv0w8