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ToSeek
2004-Nov-11, 04:15 PM
Good News for Pluto: Astronomers Say KBOs May Be Smaller Than Thought (http://www.spaceref.com/news/viewpr.html?pid=15484)


Pluto's status as our solar system's ninth planet may be safe if a recently discovered Kuiper Belt Object is a typical "KBO" and not just an oddball.

Astronomers have new evidence that KBOs (Kuiper Belt Objects) are smaller than previously thought.

George
2004-Nov-11, 04:47 PM
=D> . Nice goin Spitzer.

So, Sedna is a planet. :wink: :)

Last I recall, Sedna was between 1200 and 1800 km in dia. I wonder if their technique would help pin down the size of a warmer body like Sedna?

Glom
2004-Nov-11, 05:09 PM
It is politically sound to call Pluto a KBO and since when has science ever had any bearing on political decisions. :P

Kullat Nunu
2004-Nov-11, 06:31 PM
Pluto's status as our solar system's ninth planet may be safe if a recently discovered Kuiper Belt Object is a typical "KBO" and not just an oddball.

But 2000 AW197 was already known to be bright in color... And perhaps the strangest thing on Pluto is its very high albedo. So after all it is not terribly much brighter than other KBOs. So the press release sounds odd.


Last I recall, Sedna was between 1200 and 1800 km in dia. I wonder if their technique would help pin down the size of a warmer body like Sedna?

Sedna's diameter is probably under 1500 km, which doesn't make it second-largest transneptunian object, because 2004 DW has a diameter of about 1500 km. Sedna is much brighter of the two.

Sedna was observed in spring by Spitzer, but it was too cold to be detected. Hubble detected it, but couldn't resolve it.

pghnative
2004-Nov-11, 07:19 PM
Pluto's status as our solar system's ninth planet may be safe if a recently discovered Kuiper Belt Object is a typical "KBO" and not just an oddball.

But 2000 AW197 was already known to be bright in color... And perhaps the strangest thing on Pluto is its very high albedo. So after all it is not terribly much brighter than other KBOs. So the press release sounds odd.
I think the point is that the 'recently descovered Kuiper Belt Object" is smaller than previously thought. The correction in size is due to discovery of higher than expected albedo. If other KBO's are of similar albedo, then they too are all smaller than previously thought. Therefore Pluto is more of an outlier among KBO's than previously thought. Therefore Pluto is more likely to continue being considered a planet.

sol_g2v
2004-Nov-12, 04:52 AM
Sedna's diameter is probably under 1500 km, which doesn't make it second-largest transneptunian object, because 2004 DW has a diameter of about 1500 km. Sedna is much brighter of the two.


source?

Kullat Nunu
2004-Nov-12, 08:36 AM
source?

* David Jewitt's Kuiper Belt page (http://www.ifa.hawaii.edu/faculty/jewitt/kb/big_kbo.html)
* 2004 DW FAQ (http://www.gps.caltech.edu/~chad/2004dw/)

sol_g2v
2004-Nov-12, 06:01 PM
The sedna web page by the co-discoverer (http://www.gps.caltech.edu/~mbrown/sedna/) says sedna is believed to be close to 1800km in diameter.

Kullat Nunu
2004-Nov-12, 06:28 PM
The sedna web page by the co-discoverer (http://www.gps.caltech.edu/~mbrown/sedna/) says sedna is believed to be close to 1800km in diameter.

Hubble's ACS camera couldn't resolve it, so it must be under 1,000 miles in diameter.

Hubble Observes Planetoid Sedna, Mystery Deepens (http://hubblesite.org/newscenter/newsdesk/archive/releases/2004/14/)

tjm220
2004-Nov-12, 09:07 PM
source?

* David Jewitt's Kuiper Belt page (http://www.ifa.hawaii.edu/faculty/jewitt/kb/big_kbo.html)
* 2004 DW FAQ (http://www.gps.caltech.edu/~chad/2004dw/)

The link for 2004 DW says their best guess for albedo is 9%, which is lower than the new average estimate of 12% (http://www.newscientist.com/news/news.jsp?id=ns99996664). Will this not shrink the size estimate for 2004 DW?

Kullat Nunu
2004-Nov-12, 09:34 PM
source?

* David Jewitt's Kuiper Belt page (http://www.ifa.hawaii.edu/faculty/jewitt/kb/big_kbo.html)
* 2004 DW FAQ (http://www.gps.caltech.edu/~chad/2004dw/)

The link for 2004 DW says their best guess for albedo is 9%, which is lower than the new average estimate of 12% (http://www.newscientist.com/news/news.jsp?id=ns99996664). Will this not shrink the size estimate for 2004 DW?

From the 2004 DW FAQ:


The large KBO, 2004 DW, has an absolute magnitude like that of Quaoar, but no albedo has been measured. If the albedo is like Quaoar's, 0.12, the diameter is near 1500 km. If it is very bright (albedo 0.4, like Charon) it would be near 750 km in diameter. The diameters of all KBOs, other than Pluto-Chiron, remain uncertain at the 10 to 20% level, at best. Most are little more than guesses.

tjm220
2004-Nov-12, 10:44 PM
source?

* David Jewitt's Kuiper Belt page (http://www.ifa.hawaii.edu/faculty/jewitt/kb/big_kbo.html)
* 2004 DW FAQ (http://www.gps.caltech.edu/~chad/2004dw/)

The link for 2004 DW says their best guess for albedo is 9%, which is lower than the new average estimate of 12% (http://www.newscientist.com/news/news.jsp?id=ns99996664). Will this not shrink the size estimate for 2004 DW?

From the 2004 DW FAQ:


The large KBO, 2004 DW, has an absolute magnitude like that of Quaoar, but no albedo has been measured. If the albedo is like Quaoar's, 0.12, the diameter is near 1500 km. If it is very bright (albedo 0.4, like Charon) it would be near 750 km in diameter. The diameters of all KBOs, other than Pluto-Chiron, remain uncertain at the 10 to 20% level, at best. Most are little more than guesses.

That quote isn't in the 2004 DW FAQ link but the other one. My comment was referring to this part:


How big is 2004 DW?

So far, we are not sure. The size has not been accurately measured like the size of Quaoar has. However, we know the object's distance very roughly as well as its brightness. Using this and our best guess at the object's albedo (how light or dark the surface is) of 9%, the object is probably about 1600 km in diameter, larger than the 1250 km Quaoar. If subsequent measurements verify this size estimate, this would make 2004 DW the largest minor planet known, and larger than Pluto's moon Charon, which is about 1300 km in diameter. This still doesn't beat Pluto, which is about 2300 km in diameter.


The one estimates 9%, the other 12% for albedo but both have similar sizes (around 1500-1600 km). How big is the error margin in these estimates?

The Supreme Canuck
2004-Nov-13, 01:18 AM
So, uh, how many planets are going to decide we have here?

Van Rijn
2004-Nov-13, 02:09 AM
Depends on your definiton of "planet." Between our findings with exosolar planets, and what we are finding in our own solar system, I expect we will finally develop a decent classification system. There's one argument that anything with enough mass to be spherical, but not massive enough to be a star should be classified as a planet. There are all sorts of arguments. The one thing certain is that "planet" doesn't currently have a clear definition.

Kullat Nunu
2004-Nov-13, 07:26 AM
That quote isn't in the 2004 DW FAQ link but the other one.

Oops! The pages look too similar... :oops:


The one estimates 9%, the other 12% for albedo but both have similar sizes (around 1500-1600 km). How big is the error margin in these estimates?

Well, we know bright and how distant it is from Earth, so we can infer its absolute magnitude. Only unknown is its albedo.

Let's use this formula:


D = 1329*[10^(-H/5)]/sqrt(pV)

where


D = diameter
H = absolute magnitude
pV = albedo

so albedo = 9 % -> 1600 km
and 12 % -> 1400 km

(hopefully I got them right)