This artist's conception shows how families
of asteroids are created. Over the history of our solar system,
catastrophic collisions between asteroids located in the belt between
Mars and Jupiter have formed families of objects on similar orbits
around the sun. Image credit: NASA/JPL-Caltech. This artist's conception shows how families
of asteroids are created. Over the history of our solar system,
catastrophic collisions between asteroids located in the belt between
Mars and Jupiter have formed families of objects on similar orbits
around the sun. Image credit: NASA/JPL-Caltech. › Full image and caption
PASADENA, Calif. -- Data from NASA's Wide-field Infrared Survey
Explorer (WISE) have led to a new and improved family tree for asteroids
in the main belt between Mars and Jupiter.
Astronomers used millions of infrared snapshots from the
asteroid-hunting portion of the WISE all-sky survey, called NEOWISE, to
identify 28 new asteroid families. The snapshots also helped place
thousands of previously hidden and uncategorized asteroids into families
for the first time. The findings are a critical step in understanding
the origins of asteroid families, and the collisions thought to have
created these rocky clans.
"NEOWISE has given us the data for a much more detailed look at the
evolution of asteroids throughout the solar system," said Lindley
Johnson, the program executive for the Near-Earth Object Observation
Program at NASA Headquarters in Washington. "This will help us trace the
NEOs back to their sources and understand how some of them have
migrated to orbits hazardous to the Earth."
The main asteroid belt is a major source of near-Earth objects (NEOs),
which are those asteroids and comets that come within 28 million miles
(45 million kilometers) of Earth's path around the sun. Some near-Earth
objects start out in stable orbits in the main asteroid belt, until a
collision or gravitational disturbance flings them inward like flippers
in a game of pinball.
The NEOWISE team looked at about 120,000 main belt asteroids out of the
approximately 600,000 known. They found that about 38,000 of these
objects, roughly one third of the observed population, could be assigned
to 76 families, 28 of which are new. In addition, some asteroids
thought to belong to a particular family were reclassified.
An asteroid family is formed when a collision breaks apart a large
parent body into fragments of various sizes. Some collisions leave giant
craters. For example, the asteroid Vesta's southern hemisphere was
excavated by two large impacts. Other smash-ups are catastrophic,
shattering an object into numerous fragments, as was the case with the
Eos asteroid family. The cast-off pieces move together in packs,
traveling on the same path around the sun, but over time the pieces
become more and more spread out.
Previous knowledge of asteroid family lineages comes from observations
of their orbits. NEOWISE also looked at the asteroids' reflectivity to
identify family members.
Asteroids in the same family generally have similar mineral composition
and reflect similar amounts of light. Some families consist of
darker-colored, or duller, asteroids, while others are made up of
lighter-colored, or shinier, rocks. It is difficult to distinguish
between dark and light asteroids in visible light. A large, dull
asteroid can appear the same as a small, shiny one. The dark asteroid
reflects less light but has more total surface area, so it appears
brighter.
NEOWISE could distinguish between the dark and light asteroids because
it could detct infrared light, which reveals the heat of an object. The
larger the object, the more heat it gives off. When the size of an
asteroid can be measured, its true reflective properties can be
determined, and a group of asteroids once thought to belong to a single
family circling the sun in a similar orbit can be sorted into distinct
families.
"We're separating zebras from the gazelles," said Joseph Masiero of
NASA's Jet Propulsion Laboratory in Pasadena, Calif., who is lead author
of a report on the new study that appears in the Astrophysical Journal.
"Before, family members were harder to tell apart because they were
traveling in nearby packs. But now we have a better idea of which
asteroid belongs to which family."
The next step for the team is to learn more about the original parent bodies that spawned the families.
"It's as if you have shards from a broken vase, and you want to put it
back together to find out what happened," said Amy Mainzer, the NEOWISE
principal investigator at JPL. "Why did the asteroid belt form in the
first place and fail to become a planet? We are piecing together our
asteroids' history."
JPL, a division of the California Institute of Technology in Pasadena,
managed and operated WISE for NASA's Science Mission Directorate. The
spacecraft was put into hibernation mode in 2011, after completing its
main objectives of scanning the entire sky twice.
More information about the mission is online at: http://www.nasa.gov/wise .
Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov
J.D. Harrington 202-358-5241
NASA Headquarters, Washington
j.d.harrington@nasa.gov
