Moons vs. comets:  A NASA news release today, in announcing the Cassini mission's discovery of two small moons (3 and 4 km. wide, 2 to 2.5 miles) in orbits between two of Saturn's major satellites, includes this commentary:

“ The fact that these moons exist where they do might provide limits on the number of small comets in the outer solar system, a quantity essential for understanding the Kuiper Belt of comets beyond Neptune and the cratering histories of the moons of the giant planets. . .  “If small, house-sized comets are common, these moons should have been blown apart many times by cometary impacts during the history of the solar system.” ”

NEO missions:  The Other ESA NEO Activities page has a link to the July report (1.46Mb PDF) of the ESA Near-Earth Object Mission Advisory Panel that was charged with suggesting to ESA “cost-effective options” for an NEO space mission from among six proposals made last year (see July 14th and 19th news).

Three of the NEO proposals were for space-based telescopes. The committee said the advantages in survey completeness offered by these proposals would be essentially matched by coming improved ground-based surveys that should be operational before the missions could fly. Of the three, EUNEOS is preferred, and “The case for a space-based NEO observatory should be reconsidered in 10-15 years time, after the residual hazard from NEOs not accessible to the ground-based surveys has become better defined.”

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Today's issue status: done

• News briefs – moons vs. comets, NEO missions & mission technology
• Risk monitoring – no news

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Of three rendezvous proposals, the committee concluded that the Don Quixote impactor proposal is “the only mission that could provide a vital link in the chain from threat identification to threat mitigation,” for which “little has been done” to date.

Even for non-technical readers, this is a good read about what is known today on the NEO threat, about progress in NEO surveys, and about some ideas of what could be done next with limited budgets.

Mission technology:  A report at the Planetary Society from 13 August tells that the ESA SMART-1 spacecraft will be captured from Earth orbit into lunar orbit in mid-November instead of January, following launch late last September. See the mission status report today for current details. This low-cost strategy of using ion propulsion to gradually extend an Earth orbit to reach lunar gravitational influence could be used to sling a spacecraft past the Moon and toward an asteroid or comet. Project scientist Bernard Foing says in the article that they had considered, but decided against, sending SMART-1 on to an asteroid or other destination after completing its lunar mission.

Risk monitoring 16 August

No observations of objects with impact solutions were reported in the Monday Daily Orbit Update MPEC (DOU), and JPL hasn't updated its 2004 PU42 risk assessment with the observations reported in the Saturday and Sunday DOUs.