[QUOTE=xilman;454644]
Al the above concerns only exo-planets. Personally I believe that Sedna, Pluto and Ceres should also be classified as planets but we seem to have lost that argument for the time being. Assuming Planet-X exists, it will be difficult to claim that it's not a planet, despite having ~10 Earth masses, because it hasn't yet cleared its orbit --- a hypothesis I think is quite likely.[/QUOTE]
Poor Pluto :cry:
[quote]in the Solar System, a planet is a celestial body which:

1. is in orbit around the Sun,
2. has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
3. has "cleared the neighborhood" around its orbit.
[/quote]If Planet-X is found I hope the IAU change the 3rd requirement to something like:
"
- has a radius of at least 1000km
and
- has a mass of at least 10x10[sup]21[/sup]kg
"
This definition would include Pluto (1,186km, 13x10[sup]21[/sup]kg) and Eris (1,163km, 16.7x10[sup]21[/sup]kg) as planets and would be less vague than 'clearing its neighborhood' .
The same requirements would still be 'high' enough to not make every body orbiting the sun a planet. Ceres and Sedna wouldn't make it to planet status.

For size/mass comparison (some are natural satelites):
Mercury 2,439km radius, 330x10[sup]21[/sup]kg
Moon 1,737km radius, 73.5x10[sup]21[/sup]kg
Europa 1,560km radius, 48x10[sup]21[/sup]kg
Charon 606km radius, 1.5x10[sup]21[/sup]kg
Ceres 473km radius, 0.9x10[sup]21[/sup]kg
[URL]https://en.wikipedia.org/wiki/List_of_Solar_System_objects_by_size[/URL]

[QUOTE=chalsall;454621]Fingers crossed...

SpaceX plans to launch an [URL="http://www.space.com/36005-spacex-test-fires-rocket-for-march-14-launch.html"]EchoStar 23 satellite on a "flight proven" (read: pre-flown) rocket[/URL] very early Tuesday morning.[/QUOTE]

That is incorrect. I'm not sure where you read that, but the first reused booster will launch SES-10 in "late March", the launch immediately following EchoStar 23. ES 23 is both a new booster and expendable (sadly).

[QUOTE=chalsall;454636][URL="https://en.wikipedia.org/wiki/The_Mote_in_God's_Eye"]The Mote in God's Eye[/URL] anyone?

We're already considering using this kind of technology to send exploratory robots ourselves in the near future. Why wouldn't others? Very interesting times.[/QUOTE]
Indeed. I do take issue with reference to a planet-based laser array.
[QUOTE]Artist's illustration of a light sail powered by a radio beam (red) generated on the surface of a planet.[/QUOTE]
Unless this "planet" were airless it would not be a good place to run a googley-google watt laser.
However, it has been suggested, by Niven I think, that banks of robotic laser cannons on Mercury would have lots of solar power, and could drive intra-system vessels even pretty far into trans-Jovian space.

He also portrayed their conspiratorial use to burn alien spacecraft sniffing around the edges of the system. But don't worry. They were really bad threatening aliens with much better tech than ours.

Niven also included the [URL="https://en.wikipedia.org/wiki/Bussard_ramjet"]Bussard Ram Jet[/URL] in a number of books.Fascinating concept, but as presented they require [URL="https://en.wikipedia.org/wiki/Magnetic_monopole"]magnetic monopoles. [/URL]These are currently pretty scarce. :smile:

[QUOTE=Dubslow;454665]That is incorrect.[/QUOTE]

Whoops! My bad. Got things muddled up....

[QUOTE=VictordeHolland;454651]Poor Pluto :cry:
If Planet-X is found I hope the IAU change the 3rd requirement to something like:
"
- has a radius of at least 1000km
and
- has a mass of at least 10x10[sup]21[/sup]kg
"
This definition would include Pluto (1,186km, 13x10[sup]21[/sup]kg) and Eris (1,163km, 16.7x10[sup]21[/sup]kg) as planets and would be less vague than 'clearing its neighborhood' .
The same requirements would still be 'high' enough to not make every body orbiting the sun a planet. Ceres and Sedna wouldn't make it to planet status.

For size/mass comparison (some are natural satelites):
Mercury 2,439km radius, 330x10[sup]21[/sup]kg
Moon 1,737km radius, 73.5x10[sup]21[/sup]kg
Europa 1,560km radius, 48x10[sup]21[/sup]kg
Charon 606km radius, 1.5x10[sup]21[/sup]kg
Ceres 473km radius, 0.9x10[sup]21[/sup]kg
[URL]https://en.wikipedia.org/wiki/List_of_Solar_System_objects_by_size[/URL][/QUOTE]I could make the case, as have many others, that the Moon is a co-orbiting planet. The main argument in favour is that the lunar orbit is everywhere concave to the Sun. AFAIK no other body, including Charon, meets this criterion.

[QUOTE=xilman;454695]I could make the case, as have many others, that the Moon is a co-orbiting planet. The main argument in favour is that the lunar orbit is everywhere concave to the Sun. AFAIK no other body, including Charon, meets this criterion.[/QUOTE]
True, but the barycenter of Earth-Moon system lies inside the Earth, which speaks in favour of a planet + natural satellite. Pluto-Charon on the other hand could be better described as a binary system, since their barycenter lies between them. I personally think it was premature to demote Pluto to dwarf planet status, before a consensus on the definition of a planet was made. But science should be self correcting, so hopefully as we get a better understanding of other star-systems and their planets the professional astronomers can come up with a better definition.

[URL="http://www.planetary.org/blogs/jason-davis/2017/20170306-trumps-first-nasa-budget.html"]Asteroid redirection mission redirected.[/URL] :sad:

[QUOTE=xilman;454991][URL="http://www.planetary.org/blogs/jason-davis/2017/20170306-trumps-first-nasa-budget.html"]Asteroid redirection mission redirected.[/URL] :sad:[/QUOTE]
Grrr....

[QUOTE=xilman;454991][URL="http://www.planetary.org/blogs/jason-davis/2017/20170306-trumps-first-nasa-budget.html"]Asteroid redirection mission redirected.[/URL] :sad:[/QUOTE]

Tis only a proposal, any budgets must be approved by Congress.

Almost certainly that budget isn't passed as described, but... I wouldn't put too much stock in this Congress either.

[QUOTE=VictordeHolland;454651]Poor Pluto :cry:[/QUOTE][YOUTUBE]5nqT7XrYRPc[/YOUTUBE]

[QUOTE=Xyzzy;455033][YOUTUBE]5nqT7XrYRPc[/YOUTUBE][/QUOTE]
Haha, Who is this guy? I love him. :w00t: