Is Pluto Really Bigger Than Eris? New Horizons Settles the Debate.

[CygnusX-1]

New Horizons has found that Pluto is larger than its greatest rival, Eris.

Last year, other observations suggested that Pluto was around 1,471 miles across, which would have meant it was bigger than Eris, whose diameter is 1,445 miles. Link: Pluto Regains Its Title as the Largest Object in Its Neighborhood

Now New Horizons has determined a diameter for Pluto of 1,473 miles. Link: How Big Is Pluto? New Horizons Settles Decades-Long Debate.

The finding means that Pluto is the largest object in the Edgeworth-Kuiper belt, contrary to pronouncements made a decade ago when Eris was discovered.

 

[rootone]

Interesting, but then we haven't got a vehicle on the way to Eris which could corroborate this.

 

[CygnusX-1]

No, Eris is simpler than Pluto because Eris has no atmosphere to complicate the observations. The number for Eris's diameter is 1,445 miles plus or minus 7 miles.

Pluto's diameter was much more uncertain because of the planet's atmosphere.

Still, I do like the idea of a mission to Eris!

 

[rootone]

Not really, the classification has nothing to with the size of a planetary body.
Pluto was reclassified as a minor planet because it has not established an orbit which is free of other larger bodies.
It turns out in fact to be one of the innermost of the Kuiper belt objects, and we know of many more such objects now, since Pluto was originally discovered.
Some of those other objects are in roughly similar orbits are not very different in size to Pluto.

You might compare this reclassification of Pluto with that of Ceres. the largest object in the asteroid belt between Mars and Jupiter.
That has been 'upgraded' from 'Asteroid' to 'Minor Planet'.

I think this reclassification was sensible.
If we grant Pluto the Status of 'Planet', we would also have to classify Ceres and Vesta as planets, plus ten or more other Kuiper belt objects we know about, and there are almost certainly more out there that we don't yet know about.

Instead of hundreds of potential 'planets' we now have just eight, and those are bodies orbiting the Sun in a unique orbit clear of other sizeable bodies.

Other largish bodies which are are not in such unique orbits are now known as the 'Minor planets'
Makes sense to me anyway.

 

[CygnusX-1]

Pluto and Eris are considerably larger than any other known object in the Edgeworth-Kuiper belt. So one can easily call Pluto and Eris planets and the many lesser objects out there nonplanets. Pluto and Eris are more than 50 percent larger than the next largest Edgeworth-Kuiper belt object.