Scientists estimate that every few hundred thousand years an asteroid capable of causing global catastrophe careens dangerously close to Earth. Science-fiction writers and movie directors have capitalized on this statistic so much that many people connote “asteroid” with apocalypse. Yet asteroids are, in fact, incredibly useful objects by which to study the very beginnings of the Solar System.

Asteroids are astronomical leftovers—ancient rubble that failed to accrete into planets as the Solar System formed more than four billion years ago. Many asteroids retain chemical components that are virtually unchanged from this formative period, whereas on the planets, the Moon, and some large asteroids, these components have melted and undergone other geologic alterations. Asteroids range in size from about one-third the size of the Moon to little more than gravel. Astronomers estimate that there are billions of asteroids in the Solar System, and most of them reside in the asteroid belt between the orbits of Mars and Jupiter.

Scientists from around the world are currently experimenting with new ways to study these treasure troves of data, including three missions designed to collect asteroid images, samples, and other data.

Japan’s Hayabusa spacecraft, which launched on May 9, 2003, was the first mission specifically designed to return asteroid samples to Earth. Hayabusa began orbiting the near-Earth asteroid Itokawa in September 2005. After remotely collecting data about the asteroid’s composition, density, topography, and more, the spacecraft made a successful landing on Itokawa in November of that year. Unfortunately, the sampling equipment malfunctioned. While Hayabusa’s capsule successfully returned to Earth on June 13, 2010, the technical glitches may mean that very little useful material from the asteroid was captured. Scientists are now investigating the few particles discovered in the capsule to know for certain.

The Rosetta robotic spacecraft, which was launched by the European Space Agency (ESA) on March 2, 2004, is currently en route to reach comet 67P/Churyumov-Gerasimenko in 2014. Along the way, it aims to fly by a handful of main-belt asteroids for data collection. The first fly-by, of asteroid 21 Lutetia, was successfully completed on July 10, 2010, yielding some of the most detailed asteroid images ever collected.

Another asteroid-bound spacecraft, NASA’s Dawn, will reach 4 Vesta, the first of two large main-belt asteroids it will visit, by autumn 2011. After nearly a year in orbit around Vesta, Dawn will depart for its three-year trip to the most massive known asteroid, 1 Ceres. Dawn is not only the first spacecraft to visit either of these space rocks, but also is taking the first attempt to orbit a space body and then proceed to orbit a second target.

For more recent space news, visit the Science Bulletins website.

Swift is a NASA satellite designed to spot gamma-ray bursts, the most powerful explosions in the Universe. They are named for the extremely energetic gamma rays they emit. Swift can also detect high-energy, or "hard" X-rays, which have nearly the energy of gamma rays. Swift’s ongoing survey of hard X-rays in space is revealing details about the kinds of dynamic cosmic activity can release such high-energy wavelengths of light. What kinds? Find out in the latest Astro Bulletin:

Swift’s views reveal only a spot of bright light at the source of the X-rays. By comparing Swift’s X-ray sources to visible-light views of the same regions, scientists found that many of the high-energy X-ray emissions are positioned at the centers of colliding galaxies. Since supermassive black holes typically occupy galaxy centers, the research supports theories that the merger of matter in the galaxy centers can fuel black holes to spawn extraordinary flares of high-energy light, much more energy than is typically observed from the center of a single, non-colliding galaxy. The find has meaning for the future of the black hole at the center of our own Milky Way galaxy, which is destined to collide with the nearby Andromeda galaxy in approximately three billion years. The collision simulation in this Astro Bulletin was developed by AMNH astrophysicists and featured in the Space Show Cosmic Collisions.

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What’s the difference between a comet and an asteroid? The distinction is hazy at best. Thanks to the recent discovery of ice on an asteroid in the main belt, the lines have been further blurred.

Comets are typically thought to be small masses of rock and ice. They originate in the outer Solar System and are characterized by vapor tails that stream out as the comet ventures close to the Sun. Most asteroids, on the other hand, are relatively large and waterless rocks that typically orbit in the inner Solar System. They have no observable tails. Astronomers admit that these are loose definitions, and in recent years scientists have uncovered exceptions to both.

In 2006, astronomers observed tails of vapor and dust coming from a few small objects in the main asteroid belt. Never before had they seen this type of comet-like behavior from objects that were thought to have formed so near to the Sun. In April 2010, two independent research teams reported in the scientific journal Nature that the asteroid 24 Themis is completely covered by a thin layer of ice.

The discovery of ice on 24 Themis does more than muddle the lines between comet and asteroid. The astronomers responsible for the discovery say that it’s now conceivable that an icy asteroid similar to 24 Themis may be responsible for delivering water to our planet. The researchers don’t yet know how water ice found its way to 24 Themis, but they believe it has been there for at least four billion years. At that time, asteroids were regularly bombarding the young Earth—and perhaps, making a lasting impression that characterizes our blue planet today.

For other recent discoveries in astronomy, check out the Science Bulletins website.