Another Impact on Jupiter

[xilman]

Originally Posted by Primeinator

Correct assumption on number two, incorrect on number one. For the first statement, I meant to say that the object passing by the planet was not moving with enough kinetic energy (i.e. at or beyond the escape velocity for that planet) with the given radius from the planet the object was passing. If the object passes with a velocity less than the escape velocity, it will be pulled into orbit and eventually will enter the planet's atmosphere and collide.

Consider the approach in the reference frame in which the planet is at rest.

How do you propose that a body falling from infinity in this frame will have a velocity below than the planet's escape velocity.

It is possible, but not within a 2-body point mass scenario.


Paul

[Primeinator]

Originally Posted by xilman

Consider the approach in the reference frame in which the planet is at rest.

How do you propose that a body falling from infinity in this frame will have a velocity below than the planet's escape velocity.

It is possible, but not within a 2-body point mass scenario.


Paul

I don't consider the body to be falling from infinity. Rather, it is passing a distance r from the planet's center of gravity where the influence of the planet's gravity at said distance r is still influential on objects in that region. I realize that once you get past a certain distance, r', then the planet's gravitational influence is negligent.

[cheesehead]

Originally Posted by cheesehead

Support your local search for Near Earth Objects.

"Report: US planetsmash-asteroid scan running years late"

http://www.theregister.co.uk/2009/08/12/us_asteroid_report/

An official study by a heavyweight science and technology panel has said that "there has been relatively little effort by the US government" to tackle the threat to planet Earth from possibly devastating asteroid strikes. Politicians in Washington have directed NASA to make a start on dealing with the issue, but without supplying any funds.

The assertions come with the publication of an interim report by the National Research Council into America's asteroid strategy, titled Near-Earth Object Surveys and Hazard Mitigation Strategies. The document is published today.

Note the links under "Table of Contents" in the middle of page http://www.nap.edu/catalog.php?record_id=12738

In it, a hefty list of US professors and experts - including former astronaut, Vietnam veteran and US Marine general James Bolden, who has become head of NASA since working on the report - offer several major findings.

Firstly, they say that NASA has almost accomplished its original Congressionally-set task of compiling a database holding 90 per cent* of Near Earth Objects (NEOs, space objects whose orbits about the Sun could make them a threat to Earth) bigger than 1km in size. Such massive space rocks, if they hit Earth, would release energies in the hundred-thousand-megaton range - more than a global nuclear war. As the report says, such a strike would be a "great potential hazard to life on Earth".

However, the panel adds that NASA is nowhere near its supplementary mandated task of logging objects sized 140m and up. These would offer potential destruction in the hundred-megaton range, equivalent to a couple of extremely powerful hydrogen bombs going off. The report states that these would be "a very significant threat to life if they strike in or near urban areas".

NASA is supposed to have 90 per cent of these smaller space boulders logged by 2020, but the panel says this can't possibly be done without major additional funding. The analysis offered in the report says that if new groundbased telescopes in Chile and Hawaii come on line as planned, this goal will be reached in 2030, ten years late. If instead the new Large Synoptic Survey Telescope were dedicated entirely to asteroid hunting (rather than having other tasks as well) the job could be done as soon as 2023.

The asteroid logging could be speeded up further still by the deployment of a detection telescope in space. If this were placed relatively economically at the L1 Lagrange point between the Earth and the Sun, the threat database would be done by 2022.

The only way for NASA to complete the >140m threat database on Congress' legal deadline would be to deploy the scanning scope in its own "Venus-like" orbit around the Sun.

As the panel notes, "none of these alternatives is currently fully funded" (their emphasis). If only existing equipment was brought to the task, the threat data might not be compiled until well into the next century - by which time a significant asteroid might have hit us.

. . .

Finally the NRC says that lame as US efforts are in the field of planetbuster asteroid tracking, at least America is making an effort. The report concludes:

the United States is still the most significant actor in this field with few exceptions, if only because other countries have devoted negligible resources to it. If the threat of NEOs and solutions to deal with that threat are to be further explored, additional resources will be required.

The matter of actually doing something about a large NEO on a collision course with Earth (as opposed to just noticing it) will be tackled in a future report. For now, the NRC panel seems to be saying, most of the human race can't be bothered even to keep a lookout - and the one exception, the USA, is doing a pretty half-hearted job of it. ®

*Building a database more comprehensive than this within a reasonable time span is difficult as some unknown objects might be on orbits which only bring them within observing distance on very long timescales.