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.

European scientists recently used a telescope instrument called the High Accuracy Radial Velocity Planet Searcher (HARPS), to measure the chemical content of 500 stars similar to the Sun, some with known planetary systems and others without. They discovered that all the stars that host planets have a curious characteristic in common with our Sun: low levels of the element lithium. While much more remains to learned about why stars with planets share this trait, researchers are heartened that they could use HARPS and similar instruments to quickly find other planets beyond our Solar System.

View the latest Astro Bulletin on the find below:

To learn about other recent astronomical discoveries, visit the Science Bulletins website.

Late last month, an amateur astronomer in Australia, Anthony Wesley, discovered a new impact "scar" on Jupiter left by a comet or asteroid. This Astro Bulletin highlights the flurry of follow-up telescope images taken of this rare event.

To learn about other recent astronomical discoveries, visit the Science Bulletins website.