The search for another
Pluto got a big boost Thursday with a new scientific report detailing how researchers have incorrectly estimated the brightness and size of distant solar system objects.
The study doubles the presumed reflective ability of a giant object in the Kuiper Belt, a vast region of space beyond the orbit of Neptune littered with frozen leftovers of the solar system's formation.
The new estimate allowed researchers to pin down the size of this Kuiper Belt Object, called KBO 20000 Varuna. It is now figured to be 40 percent as large as Pluto, making it the biggest in a string of recently discovered KBOs approaching the size of our solar system's smallest planet.
"The gap is closing," said David Jewitt, a University of Hawaii researcher and lead author of the new study, which appears in the May 24 issue of the journal Nature.
And the reservoir of potential is huge. Because KBOs are so far away, fewer than 400 have been discovered out of hundreds of thousands thought to be the size of Massachusetts and perhaps billions as large as a city. Next to nothing is known about those that have been spotted.
Other researchers who analyzed the new study said it implies that KBOs larger and more distant than Pluto will be found, and they'll be easier to spot because they will be brighter than expected.
Break out the shades
Varuna was discovered last November by astronomers using the Spacewatch telescope in Arizona. The new study of the object estimates how much sunlight Varuna reflects, a figure astronomers call albedo. Dark objects reflect less light and have a lower albedo than light-colored objects.
Until now, researchers have assumed an albedo of 4 percent for all KBOs, a number based on the reflectivity of comet nuclei. Comets, thought to populate the
Kuiper Belt and even more distant regions of space, only become bright when they cruise through the inner solar system, where the Sun burns off ice from the nucleus and creates a highly reflective halo. Otherwise, they are dark as charcoal.
But Varuna turns out to be a real bright spot for KBO researchers.
Jewitt and his colleagues used a technique often employed with asteroids, which are closer. They compared the sunlight reflected from Varuna with its emission of heat, created by the solar energy that Varuna absorbs. The combination allowed them to calculate an albedo of 7 percent.
Varuna is therefore brighter than comet nuclei are thought to be, though still darker than Pluto. Because
Pluto has a faint if not fleeting atmosphere, it is constantly coated and re-coated with bright, fresh ice. Being smaller, Varuna would not have an atmosphere or any fresh ice.
The calculations show Varuna's diameter is 560 miles (900 kilometers). Pluto is 1,490 miles (2,400 kilometers) wide. Charon's diameter is 745 miles (1,200 kilometers).
Path to another Pluto
Alan Boss, a researcher at the Carnegie Institution, was cautiously optimistic about the study and its potential to contribute to the search for even larger objects.
"This does make it more likely that another Pluto could be found," Boss told SPACE.com. "But given that a fair amount of effort has already been put into the search for KBOs, I would not hold the presses or my breath. It may take a while."
Boss called the new study a classic good news-bad news story.
"The good news is that the
larger bodies in the Kuiper Belt are likely to be about twice as bright as was previously assumed to be the case, making these objects twice as easy to detect," he said.
The bad news is that Varuna, originally thought to be perhaps as large as Pluto's moon Charon, is now clearly smaller than Charon. "Close, but no cigar," Boss said. But he added that because Pluto-sized KBOs should now be easier to find, if they are there, institutions might be more inclined to fund searches.
"This is a data-starved field," Boss said, "so more discoveries are the most important factor for future progress."
But Jewitt cautioned that the new reflectivity figure applies to Varuna only.
"We need to measure simultaneous optical and thermal emission for many KBOs so we can determine how large a range of albedos might exist," Jewitt said in an e-mail interview. "Simply using the Varuna albedo on the other KBOs would be no better than assuming a 4-percent albedo for all of them, which is what we did in the past."
Still, Jewitt said astronomers are now on the verge of learning a whole lot more about the outskirts of our solar system, and new surveys "will reveal KBOs by the thousands" in coming years.
Picking on Pluto
If one of these KBOs turns out to be as big or bigger than Pluto, it might further cloud the recent controversy over whether Pluto should ever have been called a planet in the first place. The flap
peaked this past winter when astronomers debated the absence of Pluto from the Hayden Planetarium in New York City.
The controversy centers around three facts: Pluto is dramatically smaller than all the other planets, it has the most distant orbit and its path around the Sun is tilted wildly compared to plane along which the other planets orbit.
But Jewitt doesn't see what all the fuss is about. He said Varuna and its neighbors are definitely Kuiper Belt Objects. "And so is Pluto. Some people want to think of Pluto as a planet as well, to which I say 'fine!'"
Jewitt also suggested another way of thinking of Pluto, Varuna and anything else way out there: "If we call them trans-Neptunians, I think everybody can be happy because that's simply a description of fact, not opinion."
Click here for more news and information about the planets. More about this study is available from the University of Hawaii.
