[meteorite-list] NASA's Hubble Harvests Distant Solar System Objects

[Jeff Kuyken]

http://www.cfa.harvard.edu/news/2010/pr201015.html

NASA's Hubble Harvests Distant Solar System Objects

Cambridge, MA - Beyond the orbit of Neptune reside countless icy rocks known 
as trans-Neptunian objects (TNOs). One of the biggest, Pluto, is classified 
as a dwarf planet. The region also supplies us with comets such as famous 
Comet Halley. Most TNOs are small and receive little sunlight, making them 
faint and difficult to spot.
Now, astronomers using clever techniques to cull the data archives of NASA's 
Hubble Space Telescope have added 14 new TNOs to the catalog. Their method 
promises to turn up hundreds more.

"Trans-Neptunian objects interest us because they are building blocks left 
over from the formation of the solar system," explained lead author Cesar 
Fuentes, formerly with the Harvard-Smithsonian Center for Astrophysics and 
now at Northern Arizona University.

As TNOs slowly orbit the sun, they move against the starry background, 
appearing as streaks of light in time exposure photographs. The team 
developed software to analyze hundreds of Hubble images hunting for such 
streaks. After promising candidates were flagged, the images were visually 
examined to confirm or refute each discovery.

Most TNOs are located near the ecliptic -- a line in the sky marking the 
plane of the solar system (since the solar system formed from a disk of 
material). Therefore, the team searched within 5 degrees of the ecliptic to 
increase their chance of success.

They found 14 objects, including one binary (two TNOs orbiting each other 
like a miniature Pluto-Charon system). All were very faint, with most 
measuring magnitude 25-27 (more than 100 million times fainter than objects 
visible to the unaided eye).

By measuring their motion across the sky, astronomers calculated an orbit 
and distance for each object. Combining the distance and brightness (plus an 
assumed albedo or reflectivity), they then estimated the size. The newfound 
TNOs range from 25 to 60 miles (40-100 km) across.

Unlike planets, which tend to have very flat orbits (known as low 
inclination), some TNOs have orbits significantly tilted from the ecliptic 
(high inclination). The team examined the size distribution of TNOs with 
low- versus high-inclination orbits to gain clues about how the population 
has evolved over the past 4.5 billion years.

Generally, smaller trans-Neptunian objects are the shattered remains of 
bigger TNOs. Over billions of years, these objects smack together, grinding 
each other down. The team found that the size distribution of TNOs with low- 
versus high-inclination orbits is about the same as objects get fainter and 
smaller. Therefore, both populations (low and high inclination) have similar 
collisional histories.

This initial study examined only one-third of a square degree of the sky, 
meaning that there is much more area to survey. Hundreds of additional TNOs 
may lurk in the Hubble archives at higher ecliptic latitudes. Fuentes and 
his colleagues intend to continue their search.

"We have proven our ability to detect and characterize TNOs even with data 
intended for completely different purposes," Fuentes said.