Forum Topic

What next - a comet collision?

Massive 200k ton container ship, like a horizontal skyscraper, blown by the desert wind blocks the Suez Canal, and resists being shifted.This year, perhaps we should have stayed in bed?

David Ainsworth ● 1834d21 Comments

Meant to add: its not about size or shape 🙂

Michael Ixer ● 1831d

Its the Plutonian's own fault for being lazy. They should have got their shovels out and cleared Pluto's orbit of the other plutoids (similar bodies to Pluto). 

Michael Ixer ● 1831d

Dwarf planet? They should sue someone for heightist (or maybe sizeist) discrimination. Are they just too small to be a “normal” planet or is it their slightly eccentric orbit that is the problem?  Blimey, they’ve even got their own moons!  What more do they need to do to win promotion?

Jonathan Callaway ● 1832d

Ha ha, Jonathan.  No, the Plutonians didn't have a good enough lawyer so they're still relegated to dwarf planet status 🙂Not all earthlings astronomers are happy with it either but I don't think the IAU decision will change ...https://www.iau.org/public/themes/pluto/

Michael Ixer ● 1832d

I thought Pluto had appealed to a higher court and got its planet status back?  The Plutonians felt they had been discriminated against because the Universal Declaration of Human Rights didn't cover them.

Jonathan Callaway ● 1832d

Not sure if they link can be copied https://upload.wikimedia.org/wikipedia/commons/f/fc/Euler_diagram_of_solar_system_bodies.svg

Michael Ixer ● 1832d

Correction: small solar system bodies, not objects!https://commons.wikimedia.org/wiki/File:Euler_diagram_of_solar_system_bodies.svg

Michael Ixer ● 1832d

Good question, Jonathan. It's probably important it has a mixture of rock and ice, and it would usually have an eccentric orbit. If it was in a less eccentric orbit then either it would be close enough to the Sun so that its tail was permanently dispersing so it would disappear, or it would be far enough away so its gases did not form a tail - in both cases it would probably be classed as an asteroid! There doesn't seem to be an IAU definition of as comet (or a BAA one) just a description in the naming convention section: "a body made if rock and ice, typicallya few kilometres in size which orbits the Sun ... A comet's tail is formed when the Sun heats its coma or nucleus releasing vapour into space ". The IAU only defines planets and dwarf planets lumping everything else, apart from natural satellites, together as small solar system objects; interestingly, some groups of asteroids can straddle the sets of dwarf planets and small solar system objects.I think we're looking at general descriptions developed over centuries that some are now attempting to group in a taxonomy as we gain more knowledge (and more questions?) - remember when Pluto was a planet? 🙂 

Michael Ixer ● 1832d

"Or does it have to be part ice part gravel and have a tail?"That sounds like a politician for whom I would vote!

David Ainsworth ● 1832d

Mike, how eccentric does an asteroid have to be before it’s classified as a comet?  Or does it have to be part ice part gravel and have a tail?

Jonathan Callaway ● 1832d

Don't worry, David. NASA is working on a test to develop defences against asteroids. Not sure if it's still on schedule ...https://www.nasa.gov/planetarydefense/dart

Michael Ixer ● 1832d

Guardian today:-"Much-feared asteroid Apophis won't hit Earth for at least 100 years, Nasa says""Nasa has given Earth the all clear on the chances of an asteroid called Apophis hitting our planet any time in the next century, having worried space scientists for over 15 years.The 340-metre (1,100ft) chunk of space rock hit the headlines in 2004 after its discovery led to some worrying forecasts about its orbit. It became a “poster child for hazardous asteroids”, according to one Nasa expert.It was supposed to come frighteningly close in 2029 and again in 2036. Nasa ruled out any chance of a strike during those two close approaches a while ago, but a potential 2068 collision still loomed.But new telescope observations mean that collision has been ruled out and Apophis has been officially taken off the US space agency’s asteroid “risk list”."Good to have one to cross off.

David Ainsworth ● 1832d

No, because the Earth meets the IAU definition of a planes. Many asteroids are considered to be the left over remnants of the materials involved in the original construction of planets during the formation/evolution of the solar system. The asteroid belt  is considered by some to be the remains of another planet that failed to get completed because of the gravitational forces of the neighbouring planet, Jupiter.

Michael Ixer ● 1834d

My goodness, does this mean that Earth is an asteroid???

Ivonne Holliday ● 1834d

This is quite a good definition of these solar system objects. Only thing I'd add is that asteroids usually have orbits similar to planets (such as those in the asteroid belt between Mars and Jupiter) whereas comets have highly eccentric orbits from the outer regions of the solar system at one end and the very close to the sun at the other (sometimes close enough to the Sun to be destroyed by the ice in them melting so they disintegrate). https://www.mercurynews.com/2013m/03/10/comet-meteor-asteroid-heres-how-to-tell-the-difference/

Michael Ixer ● 1834d

When does a comet become an asteroid?  Or a meteor or even a meteorite?

Jonathan Callaway ● 1834d

After the bang surely that's a distinction without a difference?

David Ainsworth ● 1834d

Aren't we waiting for an asteroid rather than a comet?

Michael Ixer ● 1834d

I've been expecting better for many years, but, since the late 60s ...

David Ainsworth ● 1834d

Bit soon to do that!  Things will be so much better any year now.

Jonathan Callaway ● 1834d

Perhaps we should just write this decade off?

Matt Palmer ● 1834d