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

From: Jeff Kuyken <info_at_meteoritecentral.com>
Date: Wed, 15 Sep 2010 01:46:58 +1000
Message-ID: <9D1B98DB32874C50A7E80AC6C67DB831_at_JeffPC>

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.
Received on Tue 14 Sep 2010 11:46:58 AM PDT