Tracking Evolution in the Asteroid Belt

Asteroids don’t just slam into planets like Jupiter or Earth, they also collide with each other. Astronomers using Hubble witnessed one such impact in the asteroid belt, an area between Mars and Jupiter that holds the rubble leftover from the construction of our solar system. Hubble observations showed a bizarre, X-shaped pattern of filamentary structures near the point-like core of an object with trailing streamers of dust. This complex structure suggested the small body was the product of a head-on collision between two asteroids traveling five times faster than a rifle bullet. This observation helped support the idea that the asteroid belt is slowly eroding through collisions.

Hubble observations of possible asteroid collision remnants

An odd, X-shaped debris field trailing dusty streamers is believed to be the remnants of an asteroid collision. Scientists think that a small, fast-moving asteroid blasted into a larger and slower-moving one.

NASA, ESA and D. Jewitt (UCLA)

Asteroid or Comet?

Another Hubble observation of the asteroid belt revealed an unusual object: an asteroid with six comet-like tails of dust radiating from it like spokes on a wheel. Unlike all other known asteroids, which appear simply as tiny points of light, this asteroid resembles a rotating lawn sprinkler. Computer models of the object suggest the tails may have formed through a series of dust-ejection events.

Images of asteroid P/2013 P5 revealed its unique dust trails radiating in multiple directions and changing in appearance with time.

NASA, ESA, and D. Jewitt (UCLA)

A Binary Asteroid

Hubble also observed the first known binary asteroid that also looks like a comet. The pair orbits each other and has a tail of dust like a comet. The asteroid, called 300163 (2006 VW139), likely broke into two pieces some 5,000 years ago due to its fast rotation.

The asteroid was discovered by Spacewatch in November 2006. Then Pan-STARRS observed its comet like activity in November 2011. Both Spacewatch and Pan-STARRS are asteroid survey projects of NASA’s Near Earth Object Observations Program. After the Pan-STARRS observations it was also given a comet designation of 288P. This makes the object the first known binary asteroid that is also classified as a main-belt comet.

animation of a comet with a shifting tail

This time-lapse video, assembled from a set of Hubble Space Telescope photos, reveals two asteroids orbiting each other that have comet-like features. The asteroid pair, called 2006 VW139/288P, was observed in September 2016, just before the asteroid made its closest approach to the Sun. The photos revealed ongoing activity in the binary system. The apparent movement of the tail is a projection effect due to the relative alignment between the Sun, Earth, and 2006 VW139/288P changing between observations. The tail orientation is also affected by a change in the particle size. Initially, the tail was pointing towards the direction where comparatively large (about 1 millimeter in size) dust particles were emitted in late July. However, from Sept. 20 on, the tail began to point in the opposite direction from the Sun as the pressure of sunlight affects smaller (10 microns in size) dust particles where they are blown away from the nucleus by radiation pressure.

NASA, ESA, and J. DePasquale and Z. Levay (STScI)

A Fragmented Asteroid

Hubble also watched the slow breakup of asteroid P/2013 R3 into ten smaller pieces. The Hubble data showed that the fragments are drifting away from each other at a leisurely one mile per hour – slower than the speed of a strolling human, which suggest the breakup is not the result of a collision.

This video, assembled from a series of Hubble images, reveals the breakup of asteroid P/2013 R3 over a period of several months starting in late 2013. The largest fragments are up to 180 meters (200 yards) in radius, each with "tails" caused by dust lifted from their surfaces and pushed back by the pressure of sunlight. The ten pieces of the asteroid drift apart slowly and show a range of breakup times, suggesting that the disintegration cannot be explained by a collision with another asteroid. One idea for the breakup is that the asteroid was accelerated by sunlight to spin at a fast enough rate to fly apart by centrifugal force. The images were taken in visible light with Hubble's Wide Field Camera 3.

Asteroid Vesta and Dwarf Planet Ceres

Astronomers used Hubble to capture images of the two most massive objects in the Asteroid Belt, Ceres and Vesta, to help them better plan the Dawn spacecraft's visit to these two worlds. Combined, Ceres and Vesta account for roughly 40 percent of the mass of the asteroid belt.

Hubble's observations of Ceres revealed bright and dark regions on the asteroid's surface that could be topographic features, such as craters, and/or areas containing different surface material. Large impacts may have caused some of these features and potentially added new material to the landscape.

Ceres' round shape suggests that its interior is layered like those of terrestrial planets such as Earth. The asteroid may have a rocky inner core, an icy mantle, and a thin, dusty outer crust. The asteroid may even have water locked beneath its surface. It is approximately 590 miles (950 kilometers) across and was the first asteroid discovered in 1801 by the Italian Catholic priest, mathematician, and astronomer, Giuseppe Piazzi.

The Hubble observations of Ceres were made in visible and ultraviolet light between December 2003 and January 2004 with the Advanced Camera for Surveys. The color variations in the image show either a difference in texture or composition on Ceres' surface.

Left: mottled spheroid in colors of white, grey, and tan. Left: mottled spheroid mainly bluish-grey and white with a slight some tan areas.

Hubble made observations of Ceres and Vesta to help astronomers prepare for the NASA DAWN mission.

Vesta image: NASA; ESA; L. McFadden and J.Y. Li (University of Maryland, College Park); M. Mutchler and Z. Levay (Space Telescope Science Institute, Baltimore); P. Thomas (Cornell University); J. Parker and E.F. Young (Southwest Research Institute); and C.T. Russell and B. Schmidt (University of California, Los Angeles);
Ceres image: NASA; ESA; J. Parker (Southwest Research Institute); P. Thomas (Cornell University); L. McFadden (University of Maryland, College Park); and M. Mutchler and Z. Levay (Space Telescope Science Institute)

Astronomers used Hubble's Wide Field Planetary Camera 2 to snap images of Vesta on May 14 and 16, 2007. Using Hubble, they mapped Vesta's southern hemisphere, a region dominated by a giant impact basin formed billions of years ago. Hubble discovered the basin through observations made in 1997. Dawn later confirmed that the basin is actually two colossal impact craters—the 310 mile (500 km) wide Rheasilvia basin, and the older 250 mi (400 km) wide Veneneia crater. Rheasilvia’s width is 95% of the mean diameter of Vesta and about 12 miles deep. Its central peak, which Hubble first detected in its 1997 observations, rises 12-16 miles and is more than 100 miles wide. If Earth had a crater of proportional size, it would fill the Pacific Ocean basin.

The impact broke off chunks of Vesta, propelling about one-percent of the asteroid into space. This produced more than 50 smaller asteroids that astronomers have nicknamed "vestoids," along with many more smaller fragments in the asteroid belt and ejected into the solar system. Roughly 6 percent of all meteorites we find on Earth are likely the result of this ancient impact in deep space.

Hubble's sharp "eye" saw features as small as about 37 miles (60 kilometers) across on Vesta. The image above shows the difference in brightness and color on the asteroid's surface.

Hubble's view also revealed global features stretching from the northern to the southern hemisphere. The image above shows widespread differences in brightness in the east and west, which probably reflects a difference in composition. The size of these different regions varies. Some are hundreds of miles across.

Upper left: a mottled grey and white spheroid. Center: Vesta's crater is revealed in colors of red, yellow, green, blue, and white. Right: a mottled spheroid, darker than the one at left, in grey, white, and black.

Left: This Hubble image of the asteroid Vesta was taken in May 1996 when the asteroid was 110 million miles from Earth. The asymmetry of the asteroid and "nub" and the south pole is suggested a large impact event that NASA's Dawn spacecraft later confirmed. The image was digitally restored to yield an effective scale of six miles per pixel (picture element). Center: A color-encoded elevation map of Vesta clearly shows the giant 285- mile diameter impact basin and "bull's-eye" central peak. The map was constructed from 78 Wide Field Planetary Camera 2 pictures. Surface topography was estimated by noting irregularities along the limb and at the terminator (day/night boundary) where shadows are enhanced by the low Sun angle. Right: A 3-D computer model of Vesta synthesized from Hubble topographic data. The crater's central peak is clearly visible near the pole. The surface texture on the model is artificial, and is not representative of the true brightness variations on the asteroid. Elevation features have not been exaggerated.

NASA, Ben Zellner (Georgia Southern University), Peter Thomas (Cornell University), and NASA

Learn More

Comet or Asteroid? Hubble Discovers that a Unique Object is a Binary
Hubble helped an international team of astronomers find that an unusual object in the asteroid belt is actually two asteroids orbiting each other that have comet-like features.
Suspected Asteroid Collision Leaves Odd X-Pattern of Trailing Debris
Hubble imaged a mysterious X-shaped debris pattern and trailing streamers of dust that suggest a head-on collision between two asteroids.
Hubble Sees Asteroid Spout Six Comet-like Tails
Astronomers using Hubble identified what they can only describe as a never-before-seen "weird and freakish object" in the asteroid belt that looks like a rotating lawn sprinkler.
Hubble Witnesses an Asteroid Mysteriously Disintegrating
Hubble photographed the never-before-seen breakup of an asteroid into as many as 10 smaller pieces.
Hubble Images of Asteroids Help Prepare
for Spacecraft Visit
Hubble images of Vesta and Ceres, two of the most massive asteroids in the asteroid belt, help astronomers plan for NASA's Dawn spacecraft's tour.
Hubble Reveals Huge Crater on the Surface of the Asteroid Vesta
Astronomers have used Hubble to discover a giant impact crater on the asteroid Vesta. The crater is a link in a chain of events thought responsible for forming a distinctive class of tiny asteroids as well as some meteorites that reached Earth.